Next Article in Journal
Advances in Pseudostellaria heterophylla Research: Current Status and Future Directions
Previous Article in Journal
Polymorph Selection and Derivatization in Enantiomerically Pure Medicarpin: Crystallographic and Computational Insights
 
 
Search for Articles:
Title / Keyword
Author / Affiliation / Email
Journal
Article Type
 
 
Advanced Search
 
Section
Special Issue
Volume
Issue
Number
Page
 
Journals
Molecules
Volume 30
Issue 17
10.3390/molecules30173655
molecules-logo
Submit to this Journal Review for this Journal Propose a Special Issue
► Article Menu

Article Menu

share Share announcement Help format_quote Cite question_answer Discuss in SciProfiles
first_page
settings
Order Article Reprints
Font Type:
Arial Georgia Verdana
Font Size:
Aa Aa Aa
Line Spacing:
Column Width:
Background:
Review

The Use of Crude Glycerol as a Co-Substrate for Anaerobic Digestion

by
Wirginia Tomczak
1,*,
Sławomir Żak
1,
Anna Kujawska
2 and
Maciej Szwast
3
1
Faculty of Chemical Technology and Engineering, Bydgoszcz University of Science and Technology, 85-326 Bydgoszcz, Poland
2
Faculty of Chemistry, Nicolaus Copernicus University in Toruń, 87-100 Toruń, Poland
3
Faculty of Chemical and Process Engineering, Warsaw University of Technology, 00-645 Warsaw, Poland
*
Author to whom correspondence should be addressed.
Molecules 2025, 30(17), 3655; https://doi.org/10.3390/molecules30173655
Submission received: 12 August 2025 / Revised: 1 September 2025 / Accepted: 2 September 2025 / Published: 8 September 2025
Browse Figures
Versions Notes

Abstract

One of the most interesting applications of crude glycerol (CG) is its use for biogas production via the anaerobic co-digestion (AcoD) process. The main aim of the current study was to provide a comprehensive review on the performance of the AcoD of CG mixed with various substrates. For this purpose, analyses were performed for studies available in the literature wherein one-stage experiments were conducted. To the best of the authors’ knowledge, the present study is the first one which demonstrates an analysis of the main parameters of CG and substrates (e.g., animal manure, sewage sludge, cattle manure and food waste) used for AcoD. Moreover, a detailed analysis of the impact of selected parameters on AcoD performance was carried out. It is demonstrated that the values of key parameters characterizing the CG used for AcoD were within wide ranges. This can be explained by the fact that the composition of CG depends on many factors; for instance, these include the source of oil used for biodiesel production, processing technology, the ratio of reactants, the type of catalyst and the procedure applied. Moreover, performing a literature review allowed us to demonstrate that adding CG to feedstock caused the enhancement of process performance compared to results obtained for mono-digestion. Additionally, it was shown that, in general, increasing the concentration of CG in feedstock led to improvement of the biogas yield; however, a potential inhibitory effect should be considered. Analysis of data available in the literature allowed us to indicate that for most of the experiments performed, a methane (CH4) content in biogas higher than 60% was obtained for CG content in feedstock up to 8% v/v. In addition, it is demonstrated that in order to evaluate the performance of AcoD performed under thermophilic conditions, more studies are required. Finally, it should be pointed out that the present study provides considerable insight into the management of CG.

1. Introduction

Glycerol (propane-1,2,3-triol, C3H8O3) is a colorless, viscous and nontoxic alcohol with a high boiling point. It has a molecular weight (MW) equal to 92.09 g/mol and a density of 1.261 g/cm3. It is a by-product generated during biodiesel production via the transesterification process that uses feedstock such as vegetable oils or animal fat (Figure 1). About one kilogram of crude glycerol (CG) is generated per 10 kg of biodiesel produced [1,2,3,4].
The global market value of CG is growing. Indeed, it was estimated at USD 3.29 billion in 2023 and is expected to reach up to USD 5.6 billion by 2032 [8] (Figure 2). Glycerol has several applications, for instance in the food, cosmetics and pharmaceutical industries [9,10] and polymer technology [7,11]. However, most of them require its purification [12,13,14] since, in general, it contains many impurities and other chemicals that may affect its biological, chemical and physical properties. Among the most common pollutants are methanol, water, heavy metals, salts, soap, free fatty acids, mono-, di- and tri-glycerides as well as methyl esters [15,16,17]. For this reason, untreated CG cannot be discarded into the environment [2]. Importantly, as indicated in a recently published review paper [18], the purification of CG is expensive and often economically unprofitable for both small and medium-sized biodiesel plants. Therefore, it is obvious that the possibilities of using raw glycerol should be expanded.
As recognized in the literature, CG can be used for conversion into value-added products, for instance 1,3-propanediol [19,20,21], 1,2-propanediol [22,23,24], hydrogen [25,26,27] as well as acrylic acid [28,29,30] and lactic acid [31,32,33]. Figure 3 shows the correlation between different keywords used in publications focused on CG (VOSviewer analysis). The map shows five distinct clusters, each ordered by the frequency of terms in the analyzed works. It can be clearly seen that, recently, there has been a particular research focus on the use of CG as a co-substrate for anaerobic digestion (AD) (Figure 3, green cluster). AD, a biological waste management technology [34,35,36,37], is defined as a series of conversion processes of organic compounds to biogas by various synergistically acting facultative or obligatory anaerobic microbial species [38]. In turn, anaerobic co-digestion (AcoD) is the simultaneous anaerobic digestion of a mixture of at least two substrates [39]. It is one of the most economically attractive methods for revalorizing abundant glycerol streams into a biogas that is predominantly methane (CH4, 50–75% by volume), carbon dioxide (CO2, 25–50% by volume) and minor amounts of other gases, for instance oxygen (O2), hydrogen (H2), hydrogen sulfide (H2S) and water vapor (H2O) (g) [38]. It has been widely reported in the literature that the use of CG as a co-substrate for biogas production is attractive due to the improvement in the process yield. This can be explained by the fact that glycerol is a source of additional carbon which can be consumed by specific microorganisms and converted to methane [40]. In addition to increased efficiency leading to improved economic viability of biogas plants, the AcoD process has other advantages compared to mono-digestion, such as the following [41]:
(i)
Dilution of toxic substances;
(ii)
Increased organic loading rate;
(iii)
Nutrient balance;
(iv)
Synergistic effects on microorganisms;
(v)
Adjustment of the pH and moisture content.
In addition, it offers several environmental benefits, including a reduction in waste disposal and greenhouse gas emission as well as the possibility of nutrient (mainly nitrogen (N) and phosphorus (P)) recovery [42,43,44].
The performance of AcoD of various types of waste has been thoroughly discussed in several recently published review papers [45,46,47,48,49,50,51]. However, to the best of our knowledge, so far, no review article has been published on the use of CG as a co-substrate for AcoD.
Molecules 30 03655 g003
Figure 3. A bibliometric analysis of keywords in papers on crude glycerol published in 2015–2024. VOSViewer software (version 1.6.20).
Figure 3. A bibliometric analysis of keywords in papers on crude glycerol published in 2015–2024. VOSViewer software (version 1.6.20).
Molecules 30 03655 g003
Therefore, the main aim of this study was to provide a comprehensive review on the performance of anaerobic co-digestion process of CG mixed with various substrates. For this purpose, an analysis has been performed for studies wherein one-stage experiments have been conducted. It is related to the fact that, as has been thoroughly discussed in our previous paper [52], single-stage AD provides several significant advantages, such as low costs, higher sludge stabilization compared to few-stage systems, as well as low requirements for advanced control and monitoring. To the best of the authors’ knowledge, this paper is the first one to demonstrate a detailed analysis of the reported characteristics of:
(i)
Crude glycerol;
(ii)
Substrates; used for anaerobic co-digestion, as well as:
(iii)
The impact of selected factors (CG content, C/N ratio, temperature and pH) on the AcoD performance with the use of crude glycerol.
Hence, it should be clearly pointed out that our study provides considerable insight into the management of CG by its utilization for biogas production via AcoD.

2. Characteristics of Feedstocks

2.1. Crude Glycerol

It is well known that crude glycerol is an ideal co-substrate in the AcoD process. Indeed, it is characterized by several advantages, including:
(i)
High anaerobic biodegradability [40,53,54,55];
(ii)
High organic matter content [56];
(iii)
Being a highly concentrated waste [40,54];
(iv)
Easily biodegradable character [55];
(v)
Ease of long-term storage [53].
Despite this, up to now, the characteristics of CG used as a co-substrate for AcoD have not been dealt with in depth. Therefore, in the present study, the main parameters of CG reported in the literature have been thoroughly investigated (Table 1). It has been found that the glycerol concentration in CG used for AcoD was from 46.5% [17] to 80% [57]. CG characterized by the lowest pH value (5.0 ± 0.1) was obtained from a biodiesel production company that produces biodiesel mainly from the following substrates: soybean oil, sunflower oil as well rapeseed oil [53,58]. In turn, the CG with the highest pH (13.28) came from a biodiesel-making company which transforms used cooking oils into biodiesel fuel [59]. It has been determined that the average pH of CG used for AcoD was equal to 8.51, while the median was 8.80 (Figure 4a). These values are significantly higher than that of pure glycerol, which is equal to around 7. Obviously, the noted difference is related to the fact that, as has been indicated in Section 1, CG contains several various impurities, including for instance soap, glycerides and methyl esters. On the other hand, the reported values of CG density (between 1.052 ± 0.1 kg/L and 1.26 kg/L) were similar to that of pure glycerol (1.261 kg/L) [60].
A closer look at CG characteristics brings to light that both total solids (TS) and volatile solids (VS) values had wide ranges. The average values of the above-mentioned parameters were equal to 678.4 g/L (median: 718.0 g/L) and 671.4 g/L (median: 844.0 g/L), respectively (Figure 4b). The lowest values of TS (146 g/L) and VS (29 g/L) have been reported for CG that came from biodiesel industry, wherein soybean oil and animal fat transesterification is performed [61]. In turn, the highest values of TS (1000.8 g/L) and VS (1100 g/L) were noted for CG collected from industry, wherein biodiesel is generated mainly from animal fat and vegetable soy oil [40,62]. Finally, performing the literature review allowed us to demonstrate the values of chemical oxygen demand (COD) which provides the amount of oxygen required for the organic matter to be oxidized by oxidizing agents [63,64]. In the present study, it has been found that the average and median values of COD for CG used for AcoD were equal to 1.38 kg/L and 1.43 kg/L, respectively (Figure 4b). The lowest and highest values of COD were equal to 0.019 kg/L [65] and 2.925 kg/L [66]. It is worth noting that, in general, the CG used in the analyzed studies was characterized by high content of total nitrogen (TN), from 100 mg/L [67] to 1700 mg/L [68].
To sum up, it should be pointed out that the values of key parameters characterizing the CG used for the AcoD were within wide ranges. It can be explained by the fact that the composition of raw glycerol depends on several factors, such as the source of oil used for the biodiesel production, processing technology as well as ratio of reactants, type and concentration of catalyst and procedure applied [69,70,71].
Table 1. Main characteristics of crude glycerol used for anaerobic co-digestion reported in the literature.
Table 1. Main characteristics of crude glycerol used for anaerobic co-digestion reported in the literature.
Glycerol [g/L] or [%]pHTS
[g/L] or [%] or [(g/kg)]		VS
[g/L] or [%] or [(g/kg)]		Density [kg/L]Ash
[g/kg] or [%] or [(g/L])		COD
[kg/L]		TN
[mg/L] or [%]		TP
[mg/L] or [g/kg]		C [%]Na [mg/L] or [mg/kg]Methanol [g/L] or [%]C/N
[–]		Ref.
-8.39 ± 0.02488 ± 3.64488 ± 3.64--1.83000 ± 0.02121------[3]
46.510.478.2495.03-------5.05-[17]
706.35 ± 0.091000.8947.8; 94.8-4.81.023------[40]
-5.0 ± 0.1--1.25 ± 0.12.8 ± 0.1-372 ± 219.6 ± 1.3----[53]
660 ± 19-933 ± 27844 ± 24--0.660 ± 0.019----1.2 ± 0.1-[54]
808–9----1.140---16,939--[58]
-5.0 ± 0.1--1.25 ± 0.12.8 ± 0.1-372 ± 219.6 ± 1.3----[59]
41.6713.2880.9875.23---------[61]
-6.414629--1.0286------[62]
---1100--1.43------[65]
-9.787.47-1.29-0.019361.47-18.88--12.84[66]
-8.86 ± 0.01279.53 ± 3.34254.96 ± 2.94--2.925 ± 0.0071.76 ± 0.01-720.03 ± 0.27--409 ± 0.03[67]
-9.5 ± 0.1662 ± 28623 ± 27--2.409 ± 0.454100-----[68]
-8.8969910--1.761700----949[72]
-10.3 ± 0.3717.99 ± 4.1649.12 ± 2.1--1.82312 ± 0.0063------[73]
-8.8969910--1.761700----949[74]
3948.5986940--1.85------[75]
--80.9875.23---------[76]
--95---1.532------[77]
--81.7772.93---------[78]
-6.3-----------[79]
706.351000.8947.8; 94.8--1.023------[80]
-9.0 ± 0.1277 ± 12240.2 ± 9.51.10 ± 0.1-1.631 ± 0.025------[80]
-10.2 ± 0.1275 ± 12236.0 ± 9.01.10 ± 0.1-1.486 ± 0.021------[81]
-6.8324.4454.42---------[82]
49.4 ± 0.37.6 ± 0.2---4.8 ± 0.5----16760 ± 00535.6 ± 0.8-[83]
--(787.6 ± 8.2)(761.4 ± 9.2)---<0.06 ± 0.1-35.6 ± 0.249.3 ± 7.5--[84]
47 ± 8.6-79.572.11.02-1.477 ± 0.235------[57]
748.0--1.26-1.119----0.019-[85]
50.610.7----1.000----7.1-[86]
-10.02 ± 0.01(62.69 ± 9.00)(56.61 ± 9.29)-6.08 ± 0.330.16850 ± 0.00495<0.01-55.90 ± 0.10---[87]
-8.8969910--1.760167071500---949[88]
-7.0(850.5)(850.3)1.3--------[89]
-10.1 ± 0.1--1.052 ± 0.17.2 ± 0.40.262 ± 0.009--59.4 ± 0.1---[90]
-10.30 ± 0.10870.34 ± 0.10870.10 ± 0.10--1.9740 ± 0.0031<0.05-88.04 ± 0.05---[91]
--992.2 ± 4.2952.6 ± 4.5---------[92]
75----5-----<1-[93]
TS—total solids; VS—volatile solids; COD— chemical oxygen demand; TN—total nitrogen; TP—total phosphorus; C—carbon; C/N—carbon to nitrogen ratio; -—not available.

2.2. Substrates

It is important to take into consideration the fact that CG is characterized by a lack of nutrients which are essential for the AD process. To solve this problem, it may be co-digested with several various substrates. Performing the literature review allowed us to demonstrate that the most commonly used substrates include animal manure, sewage sludge and domestic sludge, cattle manure, leachate, distillery wastewaters as well as food waste (Table 2).
Animal manure is defined as by-products generated by animals grown to produce for instance meat, milk and eggs. Roughly speaking, it is a source of nutrients for crops and grasslands [94]; however, its composition varies between animal species and manure types [95]. According to the literature, the main limitation of the use of animal manure as a substrate for AD is the low carbon-to-nitrogen (C/N) ratio, which decreases the microorganism activity [89]. Furthermore, mono-digestion of animal manure may be limited by high nitrogen concentration, which may inhibit methanogens [96]. In the present study, it has been determined that the animal manure used as a substrate for AcoD was characterized by TN in the range between 0.84% [65] and 4.08 ± 0.05% [91]. In addition, it has been found that the substrate was characterized by TS and VS from 20.7 ± 0.1 g/L [90] to 255.97 ± 1.2 g/L [72] and from 13.6 ± 0.2 g/L [90] to 211.43 ± 2.7 g/L [72], respectively. Other parameters, such as pH and COD, also varied significantly. Indeed, values of pH were in the range from 6.51 ± 0.54 [72] to 7.7 ± 0.1 [78], while values of COD were between 27.5 ± 0.4 g/L [90] and 171.26 ± 3.4 g/L [72]. The use of animal manure for AcoD with CG has several advantages. For instance, since animal manure is characterized by high alkalinity, it ensures a buffering capacity for the accumulation of volatile fatty acids (VFAs) produced during digestion. In addition, macro- and micro-nutrients occurring in this substrate have the positive effect on the bacterial growth [87]. In recent years, many researchers have presented a review of studies on the anaerobic digestion of animal manure [47,97,98,99,100].
Sewage sludge is the solid component generated during wastewater treatment [101]. It is mainly composed of the solid portion of the sewage and the microbial cells [102]. Moreover, as indicated in [96], it is characterized by low organic loads. The application of sewage sludge as a substrate for the AD process has been highlighted by an important body of research [103,104,105,106]. Results obtained in the current study documented that the values of the main properties of sewage sludge, such as pH, TS, VS, COD and TN, varied significantly. With regards to pH, the reported values were in the range from 5.65 ± 0.11 [107] to 7.1 [86] and the pH average and median were 6.71 and 6.9, respectively. Values of TS (average: 35.1 g/L, median: 38.25 g/L) and VS (average: 20.11 g/L, median 21 g/L) were from 25.6 g/L [85] to 41.1 ± 3.6 g/L [54] and from 19.6 g/L [86] to 34.3 ± 3.1 g/L [54], respectively. In turn, values of COD (average: 36.89 g/L, median: 38.7 g/L) were from 21.98 g/L [77] to 51.9 ± 6.4 [54], while concentration of TN (average: 731.58 mg/L, median: 791 mg/L) was between 15.2 ± 0.1 g/L [40] and 1200 ± 600 [67].
Cattle manure, a by-product of cattle farming, is a rich source of carbon and nitrogen [108]. Unfortunately, the main characteristics of cattle manure used as a co-substrate for biogas production have been presented only in a few studies [76,82,87,109]. In the above-mentioned investigations, the pH values of cattle manure were in the range from 7.16 ± 0.06 [87] to 7.5 ± 0.5 [82]. In turn, the total COD was from 8.000 ± 0.354 g/L [87] to 293 g/L [76]. In the literature, there are available review studies focused on the methods of cattle manure treatment [110,111], control of bacteria in cattle manure [112], as well as the impact of co-substrate on biogas production with the use of cattle manure [113].
Leachate is a by-product derived from municipal solid wastes formed in several places, for instance landfills, composting plants, and transfer stations [114]. In general, its quality depends on many factors, such as the waste composition and biological, chemical, and physical conditions in a landfill body as well as location, landfill time and seasons [114,115]. According to [61], due to high water content, leachate can be a solvent for CG and can provide specific macro- and micronutrients for growth of bacteria during the AcoD process. Sources, nature, composition and treatment methods of landfill leachate have been thoroughly discussed in [116,117,118,119]. Leachate used as a co-substrate for biogas production via AcoD has been described in [61]. It has been characterized by pH of 7.3 as well as of TS, VS, and COD of 10.79 g/L, 5.53 and 4.04 g/L, respectively. Moreover, concentration of phosphorus (TP), alkalinity and ammonium (NH4+-N) concentration were 18.51 mg/L, 4160 mg/L and 0.67328 g/L, respectively.
Distillery wastewater is the aqueous waste generated during ethanol production. According to [120] it may pose a significant environmental issue since it may contaminate water sources in several ways. In general, it contains various salt and heavy metals and is characterized by high COD [121]. However, its characteristics depend on the feed stock used [122]. As a matter of fact, in the present study, it has been noted that the studies focused on the use of distillery wastewater for AcoD with the CG are very limited [66]. In the above-mentioned study, distillery wastewater was characterized by pH of 3.52 ± 0.02, TS and VS of 44.08 ± 0.60 g/L and 40.67 ± 0.58 g/L, respectively, as well as VFA of 2.21426 ± 0.00001 g/L and COD of 57.00 ± 0.71 g/L. It is worth noting that a detailed overview on the management of distillery wastewater can be found, for example, in [121,123,124].
Food waste refers to uneaten food and material discarded due to color or appearance [125]. According to [126], in the European Union, about 90 million tonnes of food is lost every year. In recent years, it has attracted great attention due to its important resource, environmental and social impacts [127]. Roughly speaking, food waste is a source of fat, starch, protein and cellulose [128]. In the present study, it has been documented that the characteristics of food waste used for AcoD with crude glycerol are very limited. Food waste used as a substrate for biogas production was characterized by TS, VS and VFA equal to 41.90%, 40.43% and 41.25 g/L, respectively [77] (Table 2). The possibilities of food waste management have been discussed in [129,130,131,132]. Moreover, its application in biogas production has been presented in our recently published review paper [52] and others [133,134,135,136,137].
Table 2. Main characteristics of substrates used for anaerobic co-digestion with crude glycerol reported in the literature.
Table 2. Main characteristics of substrates used for anaerobic co-digestion with crude glycerol reported in the literature.
SubstratepHTS
[g/L] or [%] or [(g/kg)]		VS
[g/L] or [%] or [(g/kg)]		VFA
[g/L]		Total COD [g/L] or [g/kg]TN
[mg/L] or [%]		TP
[mg/L] or [%] or [(g/kg)]		C
[%]		Alkalinity [mg/L]NH4+-N [g/L] or [g/kg]C/N
[–]		Ref.
animal manure-64.647.53.343.8---13600--[62]
animal manure7.125.074.76--0.84-15.39--18.32[65]
animal manure6.92 ± 0.2255.97 ± 1.2211.43 ± 2.7-171.26 ± 3.4------[72]
animal manure7.7 ± 0.130.7 ± 1.521.2 ± 1.02.0 ± 0.533.0 ± 3.2---7400 ± 4000.46 ± 0.01-[78]
animal manure-----2.3 ± 0.1-44.9 ± 0.2---[83]
animal manure7.5--------4.416.4[89]
animal manure-20.7 ± 0.113.6 ± 0.2 -27.5 ± 0.4----4.4-[90]
animal manure-46.2 ± 0.232.1 ± 0.2-58.7 ± 0.4----4.4-[90]
animal manure6.51 ± 0.54199.86 ± 0.10167.55 ± 0.10-137.83 ± 1.344.08 ± 0.05-49.62 ± 0.05---[91]
animal manure-71.0 ± 0.648.0 ± 0.8--------[92]
animal manure7.5 ± 0.123.34 ± 0.2415.49 ± 0.43--------[93]
sewage sludge6.52 ± 0.0941.1 ± 1.022.3 ± 0.6; 54.2-38.7 ± 0.115.2 ± 0.1-29.8960-17[40]
sewage sludge6.8 ± 0.235.4 ± 3.126.1 ± 2.8-35.2 ± 2.41042 ± 157845 ± 58----[53]
sewage sludge6.8 ± 0.541.1 ± 3.634.3 ± 3.10.2 ± 0.151.9 ± 6.4----0.8 ± 0.3-[54]
sewage sludge7.3---401200300-1600--[67]
sewage sludge7.1 ± 0.426.3 ± 4.519.7 ± 5.6-38.8 ± 14.21200 ± 600-----[77]
sewage sludge-2.030.833.4899621.98333------[79]
sewage sludge6.5241.1 ± 1.022.3 ± 0.6; 54.2-38.7 ± 0.1392.315.2 ± 0.129.89600.0837 ± 0.000417[84]
sewage sludge----17.4 ±3.6540---0.0998-[57]
sewage sludge7.14.8561.69--------[57]
sewage sludge7.025.615.8--5.43.434.7---[85]
sewage sludge7.12-19.6--------[86]
sewage sludge5.65 ± 0.11---49.41 ± 5.53------[107]
cattle manure-1983-293------[76]
cattle manure7.5 ± 0.5----------[82]
cattle manure7.16 ± 0.06--1.691 ± 0.0128.000 ± 0.3542.75 ± 0.39-36.05 ± 1.33-0.1661 ± 0.0004-[87]
cattle manure7.4 ± 0.02(84.10 ± 0.26)(40.31 ± 0.55)-(48.11 ± 0.27)------[109]
leachate7.310.795.53-4.04-18.51-41600.67328-[61]
distillery wastewater3.52 ± 0.0244.08 ± 0.6040.67 ± 0.582.21426 ± 0.0000157.00 ± 0.711.88 ± 0.02-47.06 ± 0.546.67 ± 0.02-25.03 ± 0.07[66]
food waste-41.9040.4341.26332-------[77]
dairy wastewater-12.5011--------[75]
dairy wastewater7.860.5577.84--------[81]
milk wastewater-4.423.5921.5652354.650------[77]
seafood wastewater6.39.377.762.23010.487053.6-2560-11[88]
agro-industrial waste4.80 ± 0.2015.00 ± 2.2313.00 ± 1.98-99.00 ± 8.772200 ± 11502500 ± 3760----[138]
sardine wastewater6.88.56.4-12.01500----11[68]
sardine wastewater6.88.56.4-14.4870----11[73]
meat and bone meal-98.4668.47--10.524.0744.09--4.19[59]
meat and bone meal-98.4668.47--------[75]
domestic sewage7.0 ± 0.30.183 ± 0.073---------[56]
municipal solid waste4.3 ± 0.540.8 ± 14.430.5 ± 10.9-27.6 ± 2.9480 ± 2964 ± 12--0.014. ± 0.0025-[58]
palm oil mill final4.766.2044.1213.7088.80---940--[74]
TS—total solids; VS—volatile solids; COD—chemical oxygen demand; TN—total nitrogen; TP—total phosphorus; C—carbon; C/N—carbon to nitrogen ratio; -—not available.

3. Performance of Anaerobic Co-Digestion Process

Table 3 shows the performance of the AcoD process with the use of CG as a co-substrate. In the present study, the analysis has been performed for continuous experiments with two and three substrates. The AcoD performance was evaluated in terms of biogas and CH4 production rate, biogas and CH4 yield and CH4 content in biogas.
It can be seen that most of the studies have been performed at a laboratory scale. Indeed, only a few studies [3,57,67,84,86,109,138] provided results obtained for a pilot-scale AcoD. For instance, in [57] the AcoD process of CG and sewage sludge has been investigated with the use of a pilot system consisting of a single-stage 50 L continuously stirred tank reactor (CSTR). In turn, in [138] biogas production was conducted via AcoD of CG and agro-industrial waste in a 300 L pilot plant. To sum up, it can be indicated that further studies with the use of a pilot-scale installation are required. Ormaechea et al. [109] studied the AcoD of CG and cattle manure in a pilot-scale Induced Bed Reactor (IBR) plant with a volume equal to 1250 L.
As can be seen in Figure 5, among the most commonly reported factors influencing the AcoD performance with the use of CG performance are glycerol content, C/N ratio, temperature, pH, substrate-to-inoculum (S/I) ratio, as well as organic loading rate (OLR) and hydraulic retention time (HRT).
In the present study, the analysis has been performed for the following parameters: CG content and C/N (Section 3.1), as well as temperature and pH (Section 3.2).
Table 3. Performance of anaerobic co-digestion process with the use of crude glycerol as a co-substrate: literature data.
Table 3. Performance of anaerobic co-digestion process with the use of crude glycerol as a co-substrate: literature data.
FeedstockScaleS/I RatioGlycerol Content [%v/v] or [g/L]C/NAcoD ConditionsAcoD Performance with the CG AdditionAD Performance Without CGRef.
T [°C]pHHRT [d] or [h]OLR [kgCODred/m3/d] or [kgVSred/m3/d] or [(gVSred/L)]Biogas
[mL/gVSred] or [mL/gCODred] or (L/L/d)		Methane
[mLCH4/gVS] or [mLCH4/gCODred] or [(mL/d)]		Biogas [mL/gVSred/d] or [mL/gCODred/d] or [(L/d)]Methane
[mLCH4/gVSred/d] or [molCH4/m3/d] or [(L/L/d)]		CH4 [%]
CG + animal manurelaboratory-13.8-35------79-Methane: 36 mL/gVS/d[62]
CG + animal manurelaboratory-27.5-35------57-[62]
CG + animal manurelaboratory-55.0-35------3-[62]
CG + animal manurelaboratory-110.0-35------0-[62]
CG + animal manurelaboratory-5-25.4–28.8initial: 8.2, final: 5.4--235---14.9Biogas: 230 mL/gVS[65]
CG + animal manurelaboratory-10-25.4–28.8initial: 8.8, final: 5.4--380---3.5[65]
CG + animal manurelaboratory-15-25.4–28.8initial: 9.2, final: 6.4--00000[65]
CG + animal manurelaboratory1.1629.08-initial: 8.18 ± 0.18, final: 7.38 ± 0.12 ---340.01 ± 5.52--52.04–72.16-[72]
CG + animal manurelaboratory1.7617.82-initial: 8.13 ± 0.19, final: 7.29 ± 0.19 ---330.33 ± 8.05--61.90[72]
CG + animal manurelaboratory2.31553.89-initial: 8.56 ± 0.15, final: 6.33 ± 0.11---172.75 ± 4.82--59.31[72]
CG + animal manurelaboratory2.91526.28-initial: 8.52 ± 0.11, final: 7.50---344.13 ± 12.31--55.43[72]
CG + animal manurelaboratory1.13.7517.47-initial: 7.95 ± 0.23, final: 7.26 ± 0.03---328.62 ± 8.56--52.04[72]
CG + animal manurelaboratory2.816.8635.85-initial: 8.60 ± 0.04, final: 7.00 ± 0.19---199.48 ± 8.69--61.33[72]
CG + animal manurelaboratory1.510.561.82-initial: 8.43 ± 0.06, final: 7.52 ± 0.14---287.13 ± 6.45--60.68[72]
CG + animal manurelaboratory2.410.520.86-initial: 8.31 ± 0.03, final: 7.45 ± 0.05---264.38 ± 12.45--71.94[72]
CG + animal manurelaboratory2.010.526.98-initial: 8.27 ± 0.03, final: 7.56---226.75 ± 16.38--69.95[72]
CG + animal manurelaboratory-327557.7 ± 0.1-2.6 ± 0.1470----Biogas: 170 ± 0.01 mL/gVS[78]
CG + animal manurelaboratory-2-34 ± 1.07.61 ± 0.15302.2-336 ± 53(28.6 ± 1.5)-71.3 ± 1.5-[83]
CG + animal manurelaboratory-4-34 ± 1.07.72 ± 0.08302.5-340 ± 62(30.8 ± 1.4)-68.2 ± 3.0[83]
CG + animal manurelaboratory-6-34 ± 1.07.85 ± 0.09302.9-423 ± 41(43.6 ± 2.7)-69.8 ± 1.9[83]
CG + animal manurelaboratory-8-34 ± 1.07.85 ± 0.10303.7-380 ± 59(51.1 ± 7.1)-68.7 ± 0.8[83]
CG + animal manurelaboratory3:420-35----249.6---Methane: 187.9 mLCH4/gVS[89]
CG + animal manurelaboratory3:440-35----134.1---[89]
CG + animal manurelaboratory3:460-35----92.9---[89]
CG + animal manurelaboratory3:480-35----73.3---[89]
CG + animal manurelaboratory-2-34 ± 18.5 ± 0.130- a-100 ± 20(2.13 ± 0.2)-62.6 ± 2.4-[90]
CG + animal manurelaboratory-5-34 ± 18.4 ± 0.130- b-140 ± 30(3.84 ± 0.3)-62.4 ± 2.1[90]
CG + animal manurelaboratory-8-34 ± 18.3 ± 0.230- c-170 ± 30(5.37 ± 0.3)-62.4 ± 2.1[90]
CG + animal manurelaboratory0.86–2.27-17.88–63.6330 ± 1.07.2–7.6--458.38–834.57; 278.19–521.46-8.64–14.75---[91]
CG + animal manurelaboratory1:24-34 ± 1-30--349.0 ± 27.0---Methane: 202.0 ± 14.2 mLCH4/gVS [92]
CG + animal manurelaboratory1:28-34 ± 1-30--413.2 ± 28.8---[92]
CG + animal manurelaboratory1:212-34 ± 1-30--408.6 ± 25.3---[92]
CG + animal manurelaboratory1:216-34 ± 1-30--467.5 ± 26.0---[92]
CG + animal manurelaboratory-1-378.3 ± 0.117 1.17 ± 0.07(0.81 ± 0.06)480 ± 40---Biogas: 0.46 ± 0.02 L/L/d; 0.41 ± 0.02 L/L/d
Methane: 330 ± 80 mL/gVS; 350 ± 70 mL/gVS		[93]
CG + animal manurelaboratory-1-378.3 ± 0.1220.91 ± 0.09(0.60 ± 0.04)470 ± 40---[93]
CG + animal manurelaboratory-3-378.217 1.91 ± 0.13(1.48 ± 0.13)480 ± 40 ---[93]
CG + animal manurelaboratory-3-378.2 ± 0.1221.42 ± 0.08(1.01 ± 0.07)470 ± 20---[93]
CG + sewage sludgelaboratory---377.29 ± 0.2532---920--Biogas: 350 mL/gVS/d[17]
CG + sewage sludgelaboratory1:2114.1-initial: 7.55, final: 7.16--269.2223.830.621.4-Biogas: 161 mL/gVS, Methane: 138.2 mL/gVS[40]
CG + sewage sludgelaboratory1:2317.3-initial: 7.48, final: 7.02--484.7368.856.8--[40]
CG + sewage sludgelaboratory-1-356.8-7.4---(2353 ± 94)(1.253 ± 0.163)---[53]
CG + sewage sludgelaboratory-0.5-37-170.4---(0.799 ± 0.069)-Methane: 0.522 ± 0.048 L/L/d[54]
CG + sewage sludgelaboratory-0.5-37-170.4---(0.941 ± 0.112)-[54]
CG + sewage sludgelaboratory-2-37-171.5---(1.248 ± 0.058)-[54]
CG + sewage sludgelaboratory-0.5-37-170.4---(0.780 ± 0.053)-[54]
CG + sewage sludgepilot---35--1.2-358----[57]
CG + sewage sludgepilot-3-35.0 ± 0.1-20-- e---59.4; 59.7[57]
CG + sewage sludgelaboratory-10-38initial: 7.90, final: 7.9356--428 ± 1--57 gMethane: 85 ± 1 mL/gVS[77]
CG + sewage sludgelaboratory-5--initial: 7.3, final: 4.9---0--0.4Methane: 79.0 ± 0.5%[85]
CG + sewage sludgelaboratory-10--initial: 7.2, final: 6.7---0--0.2[85]
CG + sewage sludgelaboratory-15--initial: 7.2, final: 5.5---0--0.2[85]
CG + sewage sludgelaboratory-20--initial: 7.3, final: 5.2---0--0.1[85]
CG + sewage sludgepilot-2-376.8–7.212.31.0–1.7--(114 ± 1.7)--Biogas: 30 ± 2.1 L/d[86]
CG + sewage sludgepilot-2-376.8–7.214.01.0–1.7--(100 ± 8.0)--[86]
CG + sewage sludgepilot-2-376.8–7.216.41.0–1.7--(90 ± 2.8)--[86]
CG + sewage sludgepilot-2-376.8–7.219.71.0–1.7--(80 ± 2.6)--[86]
CG + sewage sludgepilot-2-376.8–7.212.31.0–1.7--(139 ± 7.4)--[86]
CG + sewage sludgepilot-2-376.8–7.214.01.0–1.7--(130 ± 5.0)--[86]
CG + sewage sludgepilot-2-376.8–7.216.41.0–1.7--(105 ± 5.5)--[86]
CG + sewage sludgepilot-3-376.8–7.219.71.0–1.7-- (86.5 ± 3.8)--[86]
CG + sewage sludgepilot-4-376.8–7.219.71.0–1.7--0--[86]
CG + sewage sludgelaboratory-1-35-5–201.03–4.05---(0.6–0.9)--[107]
CG + cattle manurelaboratory-5--initial: 8.0, final: 7.8--360 mLCH4/gVSad270 mLCH4/gVSad--74Biogas: 250 mL/gVSad, Methane: 240 mL/gVSad,
Methane: 68.1%		[76]
CG + cattle manurelaboratory-10--initial: 8.0, final: 7.7--350 mLCH4/gVSad260 mLCH4/gVSad--73[76]
CG + cattle manurelaboratory-15--initial: 8.0, final: 7.6--330 mLCH4/gVSad210 mLCH4/gVSad--71[76]
CG + cattle manurelaboratory-20--initial: 8.0, final: 7.3--230 mLCH4/gVSad160 mLCH4/gVSad--67[76]
CG + cattle manurelaboratory-6-55 ± 0.1initial: 7.2 ± 0.1, final: 6.7 ± 0.3 186.01; 3.24-600--67-[82]
CG + cattle manurelaboratory-6-55 ± 0.1initial: 7.2 ± 0.1, final: 6.7 ± 0.5205.41; 2.91-0--0[82]
CG + cattle manurelaboratory-6-55 ± 0.1initial: 7.1 ± 0.2, final: 6.8 ± 0.1 224.65; 2.35-0--0[82]
CG + cattle manurelaboratory---397.53302.3-0.4 g-(0.8) g69-[87]
CG + cattle manurepilot-628.0 ± 0.5055 ± 1initial: 7.82 ± 0.01, final: 7.35 ± 0.07205.8----64.48 ± 0.17-[109]
CG + cattle manurelaboratory-5-35–37---825.3---9.5Biogas: 268.6 mL/gVS[139]
CG + cattle manurelaboratory-10-35–37---825.7---14.3[139]
CG + cattle manurelaboratory-15-35–37---387.9---14.6[139]
CG + leachatelaboratory-5-30 ± 1final: 8.02 ± 0.28 -2-110 ± 60; (360 ± 170)-(0.12 ± 0.35)--[61]
CG + leachatelaboratory-5-30 ± 1final: 8.67 ± 0.20-3.5-180 ± 90; (3290 ± 1500)-(0.86 ± 0.43)-[61]
CG + leachatelaboratory-5-30 ± 1final: 8.01 ± 0.5535.27.1-180 ± 76; (4970 ± 1840)-(1.51 ± 0.66)-[61]
CG + leachatelaboratory-5-30 ± 1final: 7.97 ± 0.4132.311.6-80 ± 30; (3770 ± 1440) -(1.27 ± 0.45)-[61]
CG + distillery wastewaterlaboratory-527.02- f7.8520–35--339--27.02Methane: 265 mL/gCOD[66]
CG + distillery wastewaterlaboratory-125.40- f7.7320–35--289--25.40[66]
CG + distillery wastewaterlaboratory-225.78- f7.7520–35--277--25.78[66]
CG + distillery wastewaterlaboratory-326.18- f7.8020–35--271--26.18[66]
CG + distillery wastewaterlaboratory-425.60- f7.8120–35--270--25.60[66]
CG + food wastelaboratory-10-38initial: 8.16, final: 7.9456-882442 ± 15--60.5 gMethane: 316 ± 7 mL/gVS[77]
CG + milk sludgelaboratory-10-38initial: 7.88, final: 8.0456-858496 ± 12--61.58Methane: 263 ± 1 mL/gVS[77]
CG + milk sludge
+ food waste		laboratory-10-38initial: 7.89, final: 7.4056--409 ± 10--58 g-[77]
CG + sewage sludge
+ food waste		laboratory-10-38initial: 8.37, final: 7.3256--338 ± 3--56 g-[77]
CG + sewage sludge
+ food waste		laboratory1:2118.3-initial: 7.48, final: 7.07--432.4343.355.136.2--[79]
CG + sewage sludge
+ food waste		laboratory1:2338.4-initial: 7.13, final: 7.05--692.6525.779.9--[79]
CG + seafood wastewaterlaboratory-1–10--6.9–8.313–5122–577----CH4: 278 mL/gVS[88]
CG + agro-industrial wastepilot-2.5-387.1–7.528.9 ± 0.5---(480 ± 230) ---[138]
CG + agro-industrial wastepilot-2.5-387.1–7.586.8 ± 0.2---(144 ± 35)--[138]
CG + agro-industrial wastepilot-2.5-387.1-7.543.4 ± 0.3 ---(360 ± 103)--[138]
CG + agro-industrial wastepilot-2.5-387.1-7.533.3 ± 0.4--681 ± 98(576 ± 84)-60–70[138]
CG + sardine wastewaterlaboratory1:1-2737final: 7.28---244.85--73.15Methane: 62.15% [68]
CG + sardine wastewaterlaboratory2:1-4350final: 7.52---255.21--68.48Methane: 37.28%[68]
CG + sardine wastewaterlaboratory1:1127377---244.85 --73.15 Methane:
68.21 mL/gCOD		[73]
CG + sardine wastewaterlaboratory1:1243377---78.42 --60.81 [73]
CG + sardine wastewaterlaboratory1:1351377---67.45 --64.12 [73]
CG + sardine wastewaterlaboratory1:1463377---27.38 --63.71 [73]
CG + sardine wastewaterlaboratory1:1573377---21.92 --60.25 [73]
CG + sardine wastewaterlaboratory1:1127507---210.5 --70.57 Methane:
16.29 mL/gCOD		[73]
CG + sardine wastewaterlaboratory1:1243507---255.21--68.48[73]
CG + sardine wastewaterlaboratory1:1351507---36.79--51.40 [73]
CG + sardine wastewaterlaboratory1:1463507---18.03--33.78[73]
CG + sardine wastewaterlaboratory1:1573507---10.28--26.39[73]
CG + meat and bone meal laboratory1:1--38initial: 7.57, final: 7.80-(27)-320--66.39 -[59]
CG + meat and bone meal laboratory1:1--38initial: 7.60, final: 7.79-(27)-350--66.33[59]
CG + meat and bone meal laboratory1:1--38initial: 7.64, final: 7.77-(27)-400--58.67[59]
CG + dairy wastewaterlaboratory-2-- f7.21 ± 0.05--722.0 ± 20.6---74.99 ± 13.52Biogas: 414.9 ± 57.0 mL/gVS, Methane: 70.40 ± 17.06%[81]
CG + dairy wastewaterlaboratory-4-- f7.13 ± 0.04--1310.0 ± 144.4---73.97 ± 18.44[81]
CG + dairy wastewaterlaboratory-8-- f7.07 ± 0.03--2307.2 ± 312.8---73.10 ± 24.03[81]
CG + dairy wastewater
+ meat and bone meal 		laboratory-131338initial: 6.77, final: 7.67302.651390 ± 10900 ± 10----[75]
CG + municipal wastewater sludgepilot---36 ± 1final: 7.25 ± 0.07-2.34 ± 0.08;
1.03 ± 0.01		(1.45)--(0.93)64.00 ± 1.17Methane: 60.00 ± 0.84%; 60.00 ± 0.74%; 60.00 ± 0.63%[3]
CG + municipal wastewater sludgepilot-1.1-36 ± 1final: 7.18 ± 0.05-2.38 ± 0.06;
1.04 ± 0.04		----66.50 ± 2.02[3]
CG + municipal wastewater sludgepilot-1.8-36 ± 1final: 7.09 ± 0.05-2.88 ± 0.11;
1.18 ± 0.04		----56 ± 1.68[3]
CG + municipal wastewater sludgelaboratory-1.25-377.45 ± 0.03-4.82--(12.2 ± 0.2)--Biogas: 8.2 ± 0.1 L/d; 4.5 ± 0.1 L/d [80]
CG + municipal wastewater sludgelaboratory-1.35-377.30 ± 0.03-3.02--(9.0 ± 0.1)--[80]
CG + municipal wastewater sludgelaboratory-2.72-376.20 ± 0.10-4.01--(4.8 ± 0.1)--[80]
CG + municipal solid wastelaboratory1:1--356.8-7.0---(2094 ± 92)---Metane: 1400 ± 305 mL/d[58]
CG + palm oil mill finallaboratory-1-37initial: 6.89, final: 7.35 ---553.46, 276.73, (45.66)---Methane: 278.64 mL/gVS; 73.34 mL/d [74]
CG + palm oil mill finallaboratory-2-37initial: 6.92, final: 5.34---98.24, 49.12, (26.51)---[74]
CG + palm oil mill finallaboratory-3-37initial: 6.99, final: 5.35---77.48, 38.74, (11.97)---[74]
CG + palm oil mill finallaboratory-4-37initial: 7.08, final: 5.30---62.36, 31.18, (10.09)---[74]
CG + palm oil mill finallaboratory-5-37initial: 7.15, final: 5.30---55.47, 27.87, (8.95)---[74]
CG + sugarcane stillagelaboratory-1.53-30initial: 7.9 ± 0.2, final: 7.7 ± 0.2-5---60.2381.9 ± 0.2Methane: 83.2 ± 0.5%[140]
CG + sugarcane stillagelaboratory-1.53-30initial: 7.55 ± 0.04, final: 7.5 ± 0.1-5---59.6183 ± 1[140]
CG + sugarcane stillagelaboratory-1.53-30initial: 7.4 ± 0.3, final: 7.7 ± 0.2-5---58.5783.5 ± 0.3[140]
CG + sugarcane stillagelaboratory-1.53-30initial: 7.6 ± 0.1, final: 8.2 ± 0.3-5---65.3980.5 ± 0.1[140]
CG + sugarcane stillagelaboratory-1.53-30initial: 7.40 ± 0.09, final: 7.3 ± 0.2-5---68.5784.0 ± 0.6[140]
CG + sugarcane stillagelaboratory-1.53-30initial: 7.5 ± 0.1, final: 7.4 ± 0.3-5---52.1086.0 ± 0.4[140]
CG + sugarcane stillagelaboratory-1.53-30initial: 7.5 ± 0.1, final: 7.6 ± 0.1-7.5---95.0782.6 ± 0.2[140]
CG + sugarcane stillagelaboratory-1.53-30initial: 7.4 ± 0.1, final: 7.7 ± 0.3-10---139.3283.1 ± 0.1[140]
CG + sugarcane stillagelaboratory-1.53-35initial: 7.5 ± 0.2, final: 8.2 ± 0.2-10---122.9983.2 ± 0.7[140]
CG + olive mill wastewater + slaughterhouse wastewaterlaboratory1:1--356.9–7.6---(1210 ± 205)---Methane: 479 mL/d[58]
CG—crude glycerol; S/I—substrate to inoculum ratio; C/N—carbon to nitrogen ratio; T—temperature; HRT—hydraulic retention time; OLR—organic loading rate; a 13.0 ± 0.4 g/d; b 17.5 ± 0.6 g/d; c 19.5 ± 0.5 g/d; e 0.65 m3/L of glycerol; f mesophilic conditions; g data from the graph.

3.1. Crude Glycerol Content and C/N Ratio

The anaerobic digestion of organic waste is a complex biological process that involves a series of metabolic methods, such as hydrolysis, acidogenesis, acetogenesis and methanogenesis. Mono-digestion is limited by several factors, for instance [141,142]:
(i)
Low methane production of methane;
(ii)
Long retention time of digestion process;
(iii)
Low efficiency of volatile solids reduction.
By contrast, the use of CG as a co-substrate for the biogas production via AcoD provides a great improvement of the process yield. This finding has been widely confirmed in the literature for results obtained for AcoD conducted under both mesophilic and thermophilic conditions with the use of various substrates.
With regard to digestion of sewage sludge under mesophilic conditions, Alves et al. [79] demonstrated that the addition of raw glycerol led to the increase in the biogas and methane yield by 67% and 62%, respectively. These results are in agreement with those obtained by Fountoulaki et al. [53], who found that the addition of CG enhanced CH4 production by about 1247 mL/d. In turn, in [67] it has been documented that this type of co-digestion improved biogas production by 4.5 times.
Likewise, in [87] it has been noted that the addition of glycerine phase to cattle manure allowed the generation of 3.1 times more biogas and a 10% higher CH4 content compared to the those obtained for the AD of only cattle manure. In another study [89], it has been indicated that the mixture of crude glycerol and animal manure provided higher methane production by 125% compared to that noted for mono-digestion. Other authors [93] concluded that supplementation of feedstock with CG led to a 222% increase in biogas productivity compared to manure mono-digestion. Furthermore, it has been documented that adding raw glycerol to distillery wastewater allowed the improvement of the methane yield by 29%. It should be pointed out that similar observations have been noted for the process performed with the use of three substrates. Indeed, in [58] it has been found that the addition of raw glycerol to olive mill wastewater and slaughterhouse wastewater allowed an increase in the CH4 production by about 731 mL/d.
It is necessary to mention that with regards to AcoD performed under thermophilic conditions, in [78] it has been demonstrated that the addition of glycerol resulted in a higher specific biogas production by 0.30 L/gVS compared to that obtained for the mono-digestion of animal manure. In addition, Srimachai et al. [68] have demonstrated that the use of CG as a co-substrate for thermophilic AcoD led to the increase in the methane production by 40.76 compared to the mono-digestion of canned sardine wastewater.
Performing the literature review allowed us to show that CG was used as a co-substrate for AcoD in a wide range of concentrations (Table 3). Indeed, its content in the feedstocks was in the range from 0.5% v/v [54] to 20% v/v [85]. It is important to point out that the CG content may have a significant impact on the AcoD process performance. This phenomenon has been investigated in several papers wherein experiments with the use of two [40,62,65,73,81,83,90,93] and three [79] substrates have been conducted. Alves et al. [40] have investigated the impact of CG concentration on the AcoD performance under mesophilic conditions with the use of sewage sludge (Table 2) as a substrate. The above-mentioned authors have noted that higher CG concentration provided higher values of performance. For feedstock containing 1% v/v (C/N of 14.1) and 3% v/v (C/N of 17.3) of CG, the methane yield was equal to 0.2338 mLCH4/gVS and 0.3688 mLCH4/gVS, respectively (Table 3). This observation is in accordance with the relative findings reported in [93], wherein AcoD of CG and animal manure (Table 2) was studied. It has been reported that CG content has a great impact on the process. More specifically, it has been recognized that under HRT of 17 and 22 days, the increase in the CG concentration from 1% v/v to 3% v/v led to an improvement in the biogas productivity from 0.81 ± 0.06 L/L/day to 1.48 ± 0.13 L/L/day and from 0.60 ± 0.04 L/L/day to 1.01 ± 0.07 L/L/day, respectively (Table 3). A higher range of CG content co-digested with animal manure (Table 2) has been applied in [90], wherein it has been found that for CG concentration of 2% v/v, 5% v/v and 8% v/v, biogas production was 2.13 ± 0.2 L/day, 3.84 ± 0.3 L/day and 5.37 ± 0.3 L/day, respectively (Table 3). It is important to note that the increase in the amount of CG ensured high quality of the biogas produced. Indeed, for all applied CG concentrations, the CH4 content in biogas was equal to around 63%. A similar finding has been presented for AcoD of feedstock containing three substrates: CG, food waste and sewage sludge (Table 2) [79]. Indeed, it has been documented that increasing CG content from 1% v/v to 3% v/v allowed an enhancement of the methane and biogas yield from 343.3 mLCH4/gVS to 525.7 mLCH4/gVS and from 432.4 mL/gVS to 692.6 mL/gVS, respectively (Table 3). Therefore, it can be indicated that with a few exceptions, the increase in the CG content led to an increase in the biogas yield.
Although several studies focusing on the impact of CG on the AcoD performance have been performed, there are still some significant issues related to this correlation. It is important to note that adding CG to the system may lead to an inhibitory effect. Indeed, this phenomenon has been reported in the literature for co-digestion of CG with various substrates such as animal manure [72,83,92], sewage sludge [86], cattle manure [76,139] and municipal wastewater sludge [80]. For instance, in [76] it has been found that for AcoD of CG and cattle manure (Table 2), a concentration of CG greater than 6% led to a decrease in the process performance (Table 3). Indeed, in the above-mentioned paper, it has been indicated that this phenomenon could be a result of overload of organic material in digestion, which in turn was associated with the low quality of the CG. More precisely, the used CG was characterized by a high content of lipids (78%), which may have a negative effect on methanogenic archaea in the case of high loading rates. These findings are similar to those reported by Athanasoulia et al. [86], who indicated that adding 4% of CG to sewage sludge (Table 2) led to the failure of the AcoD system due to overloading (Table 3). In [92] the failure of the AcoD process of animal manure (Table 2) and CG was noted for CG content equal to 8% (Table 3). It has been explained by the high evolution of H2S in produced biogas and accumulation of VFA. In turn, Razaviarani et al. [80] demonstrated that adding CG to municipal wastewater sludge at the content of 2.72% v/v led to the significant decrease in the biogas production and methane yield (Table 3). Likewise, in [139] it has been found that increasing the CG concentration used for AcoD with cattle slurry led to a decrease in the process performance. The biogas yield for the CG concentration of 5%, 10% and 15% was equal to 825.3 mL/gVSred, 825.7 mL/gVSred and 387.9 mL/gVSred, respectively (Table 3). The authors have pointed out that this observation could be caused by the inhibition of the AcoD process due to higher concentrations of methanol and KOH present in the substrate resulting from the increase in glycerol content.
It should therefore be clearly emphasized that in the case of AcoD using CG as co-substrate, its suitable concentration should be carefully analyzed. Figure 6 demonstrates the impact of CG content in the feed on the CH4 content in the biogas produced during the AcoD of CG mixed with various substrates performed under mesophilic and thermophilic conditions, based on the data presented in the literature. It has been found that for most of the experiments performed, CH4 content in the biogas higher than 60% has been obtained under CG content up to 8% v/v. This finding may be key in determining the most suitable concentration of raw glycerol used for biogas production via AcoD.
At the same time, it should be noted that generally, the addition of CG leads to an increase in the C/N ratio. During anaerobic digestion, carbon is used as the energy source, while nitrogen is a source of nutrition used by microorganisms to form the body cells. Hence, it is one of the key factors determining the AcoD performance. In short, with regards to AD, in has been indicated that the optimum C/N value is between 16:1 and 33:1 [96]. Nevertheless, according to [143], determining the optimum value of C/N ratio for AcoD is a great challenge since it can be influenced by several parameters, including:
(i)
Type of substrate;
(ii)
Content of trace elements;
(iii)
Chemical components present in the feedstock;
(iv)
Biodegradability.
The analysis performed in the current study has shown that AcoD with CG used as a substrate has been performed under a wide range of C/N (Table 3). Indeed, C/N was applied in the range from 14.1 [40] to 73 [73]. It is worth noting that, in [91], it has been shown that it may have a significant impact on the abundance of the bacterial classes involved in the feedstock treatment and thus, on the AcoD performance (Table 3). However, in order to determine the most suitable range of C/N values, more studies are required.

3.2. Temperature and pH

As mentioned previously, temperature is one of the most important factors influencing the AD performance. Overall, the process can be operated under the following temperature regimes: psychrophilic (10–20 °C), mesophilic (30–40 °C) and thermophilic (50–60 °C). Despite a growing number of studies, little is known about the performance of thermophilic AcoD. Indeed, in the present study, it has been found that most of the studies focusing on the AcoD of CG and various substrates have been performed under mesophilic conditions (Table 3). Indeed, thermophilic conditions have been applied only in a few investigations [68,73,82,109]. This can probably be explained by the fact that thermophilic anaerobic digestion is more energy-intensive and is characterized by lower stability [144]. However, it is important to note that in general, thermophilic digestion has several advantages. For instance, it has the potential to ensure higher CH4 yield since thermophilic microorganisms are characterized by a higher growth rate and thus provide a higher reaction rate [145]. This finding has been confirmed by results obtained by Srimachai et al. [68], who investigated the AcoD of raw glycerol mixed with sardine wastewater (Table 2) under mesophilic and thermophilic conditions. The above-mentioned authors noted higher methane yield performed at a temperature equal to 55 °C (255.21 mLCH4/gCODred) compared to that obtained at 35 °C (244.85 mL CH4/gCODred) (Table 3). What becomes apparent from the discussed studies is that an increase in the process temperature above 50 °C may significantly improve the AcoD performance.
It is widely assumed that another important factor when considering the performance of AcoD is the pH feedstock. Obviously, pH affects the microorganisms’ growth and activity. It is worth mentioning that the analysis performed in the present study revealed that pH values of feedstock used for AcoD were in the range from 6.20 ± 0.10 [80] to 8.5 [90] (Table 3). It is in line with the optimum pH value (from 6.8 to 8.0) widely reported in the literature [146,147,148,149]. Finally, it should be pointed out that co-digestion of CG with selected substrates may decrease the cost of chemicals used for pH adjustment during the process. As has been demonstrated by Phuket et al. [66], the use of CG as a co-substrates for AcoD of distillery wastewater (Table 2) led to the increase in the initial pH. Indeed, it was in the range between 7.73 and 7.85 (Table 3), while during mono-digestion it was equal to 3.52.

4. Conclusions and Perspectives

In recent years, the global size of the CG market has been growing, primarily due to increasing demand for biodiesel. For this reason, appropriate management of this by-product is required. One of the most interesting applications of raw glycerol is its use for biogas production via the AcoD process.
To the best of the authors’ knowledge, the current study is the first one to demonstrate an analysis of the reported characteristics of crude glycerol and substrates used for AcoD as well as the impact of selected factors on the process performance. Detailed analysis allowed us to show that:
(i)
Values of key parameters characterizing the CG (glycerol concentration, pH, TS and VS content as well as COD) used for the AcoD were within wide ranges. It can be attributed to the fact that the CG composition depends mainly on the source of oil used for the biodiesel production, processing technology, ratio of reactants, type of catalyst and procedure applied.
(ii)
Adding CG to the feedstock caused a significant enhancement of CH4 and biogas yield compared to results obtained for the mono-digestion process of various substrates. Indeed, raw glycerol is a source of additional carbon, which can be consumed by specific microorganisms and converted to CH4.
(iii)
The increase in the CG concentration in the feedstock leads to an enhancement of the AcoD performance; nevertheless, the substrate inhibition effect should be considered.
(iv)
For most of the experiments presented in the literature, CH4 content in the biogas higher than 60% has been obtained under CG content up to 8% v/v. A higher concentration may cause a reduction in the biogas yield due to the overload of organic material in digestion.
(v)
Most of studies focusing on the AcoD performance with the use of CG have been carried out by applying laboratory-scale installations; hence, further experimental investigations with the use of pilot-scale systems are recommended.
(vi)
In order to evaluate the performance of AcoD with the use of CG under thermophilic conditions, more studies are required.
Finally, this work has highlighted that CG can be successfully used as a co-substrate for biogas production via the AcoD process. Undoubtedly, the present analysis may have important implications for raw glycerol management.

Author Contributions

Conceptualization, W.T. and M.S.; methodology, W.T. and A.K.; validation, W.T. and S.Ż.; formal analysis, W.T.; investigation, W.T.; data curation, W.T.; writing—original draft preparation, W.T.; writing—review and editing, W.T., A.K., M.S. and S.Ż.; visualization, W.T.; supervision, W.T. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

The data presented in this study are available on request from the corresponding author. The data are not publicly available due to the institutional repository being under construction.

Conflicts of Interest

The authors declare no conflicts of interest.

Abbreviations

ADAnaerobic digestion
AcoDAnaerobic co-digestion
CCarbon
CGCrude glycerol
CODChemical oxygen demand
CSTRContinuously stirred tank reactor
C/NCarbon to nitrogen ratio
HRTHydraulic retention time
IBRInduced bed reactor
MWMolecular weight
NNitrogen
OLROrganic loading rate
S/ISubstrate to inoculum
TNTotal nitrogen
TPTotal phosphorus
TSTotal solids
VSVolatile solids

References

  1. Zhang, J.; Wang, Y.; Muldoon, V.L.; Deng, S. Crude Glycerol and Glycerol as Fuels and Fuel Additives in Combustion Applications. Renew. Sustain. Energy Rev. 2022, 159, 112206. [Google Scholar] [CrossRef]
  2. Almeida, E.L.; Olivo, J.E.; Andrade, C.M.G. Production of Biofuels from Glycerol from the Biodiesel Production Process—A Brief Review. Fermentation 2023, 9, 869. [Google Scholar] [CrossRef]
  3. Razaviarani, V.; Buchanan, I.D.; Malik, S.; Katalambula, H. Pilot Scale Anaerobic Co-Digestion of Municipal Wastewater Sludge with Biodiesel Waste Glycerin. Bioresour. Technol. 2013, 133, 206–212. [Google Scholar] [CrossRef]
  4. Chilakamarry, C.R.; Sakinah, A.M.M.; Zularisam, A.W.; Pandey, A. Glycerol Waste to Value Added Products and Its Potential Applications. Syst. Microbiol. Biomanuf. 2021, 1, 378–396. [Google Scholar] [CrossRef] [PubMed]
  5. He, Q. (Sophia); McNutt, J.; Yang, J. Utilization of the Residual Glycerol from Biodiesel Production for Renewable Energy Generation. Renew. Sustain. Energy Rev. 2017, 71, 63–76. [Google Scholar] [CrossRef]
  6. Andriamanohiarisoamanana, F.J.; Yamashiro, T.; Ihara, I.; Iwasaki, M.; Nishida, T.; Umetsu, K. Farm-Scale Thermophilic Co-Digestion of Dairy Manure with a Biodiesel Byproduct in Cold Regions. Energy Convers. Manag. 2016, 128, 273–280. [Google Scholar] [CrossRef]
  7. Ben, Z.Y.; Samsudin, H.; Yhaya, M.F. Glycerol: Its Properties, Polymer Synthesis, and Applications in Starch Based Films. Eur. Polym. J. 2022, 175, 111377. [Google Scholar] [CrossRef]
  8. Available online: https://www.Wiseguyreports.Com/Reports/Crude-Glycerol-Market (accessed on 1 July 2025).
  9. Lima, P.J.M.; Da Silva, R.M.; Neto, C.A.C.G.; Gomes, E.; Silva, N.C.; Souza, J.E.D.S.; Nunes, Y.L.; Sousa Dos Santos, J.C. An Overview on the Conversion of Glycerol to Value-added Industrial Products via Chemical and Biochemical Routes. Biotech. App. Biochem. 2022, 69, 2794–2818. [Google Scholar] [CrossRef]
  10. Hambali, E.; Fitria, R.; Sari, V.I. Glycerol and Derivatives. In Biorefinery of Oil Producing Plants for Value-Added Products; Abd-Aziz, S., Gozan, M., Ibrahim, M.F., Phang, L., Eds.; Wiley: Hoboken, NJ, USA, 2022; pp. 469–491. ISBN 978-3-527-34876-3. [Google Scholar]
  11. Hejna, A.; Kosmela, P.; Formela, K.; Piszczyk, Ł.; Haponiuk, J.T. Potential Applications of Crude Glycerol in Polymer Technology–Current State and Perspectives. Renew. Sustain. Energy Rev. 2016, 66, 449–475. [Google Scholar] [CrossRef]
  12. Schwingel, A.W.; Orrico, A.C.A.; De Lucas Junior, J.; Orrico Junior, M.A.P.; Aspilcueta Borquis, R.R.; Fava, A.F. Laying Hen Manure in Anaerobic Co-Digestion with Glycerin Containing Different Glycerol and Impurity Levels. J. Clean. Prod. 2019, 215, 1437–1444. [Google Scholar] [CrossRef]
  13. Kurahashi, K.; Kimura, C.; Fujimoto, Y.; Tokumoto, H. Value-Adding Conversion and Volume Reduction of Sewage Sludge by Anaerobic Co-Digestion with Crude Glycerol. Bioresour. Technol. 2017, 232, 119–125. [Google Scholar] [CrossRef] [PubMed]
  14. Kaur, G.; Johnravindar, D.; Wong, J.W.C. Enhanced Volatile Fatty Acid Degradation and Methane Production Efficiency by Biochar Addition in Food Waste-Sludge Co-Digestion: A Step towards Increased Organic Loading Efficiency in Co-Digestion. Bioresour. Technol. 2020, 308, 123250. [Google Scholar] [CrossRef] [PubMed]
  15. Bhukya, G.; Pilli, S.; Chinthala, S.; Tyagi, R.D. Pre-Treated Crude Glycerol a Valuable Green Energy Source in the Era of Circular Bioeconomy—A Review. Circ. Econ. Sust. 2024, 4, 877–904. [Google Scholar] [CrossRef]
  16. Anitha, M.; Kamarudin, S.K.; Kofli, N.T. The Potential of Glycerol as a Value-Added Commodity. Chem. Eng. J. 2016, 295, 119–130. [Google Scholar] [CrossRef]
  17. Nartker, S.; Ammerman, M.; Aurandt, J.; Stogsdil, M.; Hayden, O.; Antle, C. Increasing Biogas Production from Sewage Sludge Anaerobic Co-Digestion Process by Adding Crude Glycerol from Biodiesel Industry. Waste Manag. 2014, 34, 2567–2571. [Google Scholar] [CrossRef]
  18. Attarbachi, T.; Kingsley, M.D.; Spallina, V. New Trends on Crude Glycerol Purification: A Review. Fuel 2023, 340, 127485. [Google Scholar] [CrossRef]
  19. Da Silva Ruy, A.D.; Carvalho, A.; Santos, A.; Lima, D.L.S.D.; Pessôa, L.C.; Alves, R.M.B.; Pontes, L.A.M. A Novel Chemical Route for 1,3-Propanediol Production from Crude Glycerol: Process Simulation and Environmental Assessment. J. Environ. Chem. Eng. 2024, 13, 116864. [Google Scholar] [CrossRef]
  20. Agrawal, D.; Budakoti, M.; Kumar, V. Strategies and Tools for the Biotechnological Valorization of Glycerol to 1, 3-Propanediol: Challenges, Recent Advancements and Future Outlook. Biotechnol. Adv. 2023, 66, 108177. [Google Scholar] [CrossRef]
  21. Fokum, E.; Zabed, H.M.; Yun, J.; Zhang, G.; Qi, X. Recent Technological and Strategical Developments in the Biomanufacturing of 1,3-Propanediol from Glycerol. Int. J. Environ. Sci. Technol. 2021, 18, 2467–2490. [Google Scholar] [CrossRef]
  22. Restrepo, J.B.; Paternina-Arboleda, C.D.; Bula, A.J. 1,2—Propanediol Production from Glycerol Derived from Biodiesel’s Production: Technical and Economic Study. Energies 2021, 14, 5081. [Google Scholar] [CrossRef]
  23. Główka, M.; Krawczyk, T. New Trends and Perspectives in Production of 1,2-Propanediol. ACS Sustain. Chem. Eng. 2023, 11, 7274–7287. [Google Scholar] [CrossRef]
  24. Sun, S.; Shu, L.; Lu, X.; Wang, Q.; Tišma, M.; Zhu, C.; Shi, J.; Baganz, F.; Lye, G.J.; Hao, J. 1,2-Propanediol Production from Glycerol via an Endogenous Pathway of Klebsiella Pneumoniae. Appl. Microbiol. Biotechnol. 2021, 105, 9003–9016. [Google Scholar] [CrossRef] [PubMed]
  25. Gujar, J.P.; Verma, A.; Modhera, B. Optimizing Glycerol Conversion to Hydrogen: A Critical Review of Catalytic Reforming Processes and Catalyst Design Strategies. Int. J. Hydrogen Energy 2025, 109, 823–850. [Google Scholar] [CrossRef]
  26. Qureshi, F.; Yusuf, M.; Pasha, A.A.; Khan, H.W.; Imteyaz, B.; Irshad, K. Sustainable and Energy Efficient Hydrogen Production via Glycerol Reforming Techniques: A Review. Int. J. Hydrogen Energy 2022, 47, 41397–41420. [Google Scholar] [CrossRef]
  27. Macedo, M.S.; Soria, M.A.; Madeira, L.M. Process Intensification for Hydrogen Production through Glycerol Steam Reforming. Renew. Sustain. Energy Rev. 2021, 146, 111151. [Google Scholar] [CrossRef]
  28. Abubakar, U.C.; Bansod, Y.; Forster, L.; Spallina, V.; D’Agostino, C. Conversion of Glycerol to Acrylic Acid: A Review of Strategies, Recent Developments and Prospects. React. Chem. Eng. 2023, 8, 1819–1838. [Google Scholar] [CrossRef]
  29. Ahmad, N.N.R.; Ang, W.L.; Teow, Y.H.; Mohammad, A.W.; Hilal, N. Nanofiltration Membrane Processes for Water Recycling, Reuse and Product Recovery within Various Industries: A Review. J. Water Process Eng. 2022, 45, 102478. [Google Scholar] [CrossRef]
  30. Jin, C.; Sun, S.; Yang, D.; Sheng, W.; Ma, Y.; He, W.; Li, G. Anaerobic Digestion: An Alternative Resource Treatment Option for Food Waste in China. Sci. Total Environ. 2021, 779, 146397. [Google Scholar] [CrossRef]
  31. Wang, Z.; Zhang, Y.; Wang, Y.; Li, J.; Jia, X.; Wu, Z. Recent Progress in Glycerol Oxidation to Lactic Acid and Pyruvic Acid with Heterogeneous Metal Catalysts. Carbon Resour. Convers. 2025, 8, 100250. [Google Scholar] [CrossRef]
  32. Akbulut, D.; Özkar, S. A Review of the Catalytic Conversion of Glycerol to Lactic Acid in the Presence of Aqueous Base. RSC Adv. 2022, 12, 18864–18883. [Google Scholar] [CrossRef]
  33. Wang, K.; Yang, Z.; Ma, Y.; Zhao, W.; Sun, J.; Lu, T.; He, H. Recent Advances in the Utilization of Glycerol for the Production of Lactic Acid by Catalysis. Biofuels Bioprod. Bioref. 2022, 16, 1428–1454. [Google Scholar] [CrossRef]
  34. Gebreegziabher, B.W.; Dubale, A.A.; Adaramola, M.S.; Morken, J. Advancing Anaerobic Digestion of Biodiesel Byproducts: A Comprehensive Review. Bioenerg. Res. 2025, 18, 15. [Google Scholar] [CrossRef]
  35. Li, H.; Gilbert, R.G.; Gidley, M.J. Molecular-Structure Evolution during in Vitro Fermentation of Granular High-Amylose Wheat Starch Is Different to in Vitro Digestion. Food Chem. 2021, 362, 130188. [Google Scholar] [CrossRef] [PubMed]
  36. Zhao, J.; Wang, Y.; Li, B.; Zhang, J.; Guan, D.; Hu, Y.; Fan, H.; Sun, Y.; Wang, H.; Guo, L. New Insights into Microplastics Inhibiting Kitchen Waste Dry Digestion: Digestion Efficiency, Microbial Communities and Microplastic Aging Mechanisms. Chem. Eng. J. 2025, 508, 160907. [Google Scholar] [CrossRef]
  37. Kegl, T. Consideration of Biological and Inorganic Additives in Upgraded Anaerobic Digestion BioModel. Bioresour. Technol. 2022, 355, 127252. [Google Scholar] [CrossRef]
  38. Tomczak, W.; Gryta, M.; Grubecki, I.; Miłek, J. Biogas Production in AnMBRs via Treatment of Municipal and Domestic Wastewater: Opportunities and Fouling Mitigation Strategies. Appl. Sci. 2023, 13, 6466. [Google Scholar] [CrossRef]
  39. Kegl, T.; Torres Jiménez, E.; Kegl, B.; Kovač Kralj, A.; Kegl, M. Modeling and Optimization of Anaerobic Digestion Technology: Current Status and Future Outlook. Prog. Energy Combust. Sci. 2025, 106, 101199. [Google Scholar] [CrossRef]
  40. Alves, I.R.F.S.; Mahler, C.F.; Oliveira, L.B.; Reis, M.M.; Bassin, J.P. Assessing the Use of Crude Glycerol from Biodiesel Production as an Alternative to Boost Methane Generation by Anaerobic Co-Digestion of Sewage Sludge. Biomass Bioenergy 2020, 143, 105831. [Google Scholar] [CrossRef]
  41. Esposito, G.; Frunzo, L.; Giordano, A.; Liotta, F.; Panico, A.; Pirozzi, F. Anaerobic Co-Digestion of Organic Wastes. Rev. Env. Sci. Biotechnol. 2012, 11, 325–341. [Google Scholar] [CrossRef]
  42. Guo, Q.; Dai, X. Analysis on Carbon Dioxide Emission Reduction during the Anaerobic Synergetic Digestion Technology of Sludge and Kitchen Waste: Taking Kitchen Waste Synergetic Digestion Project in Zhenjiang as an Example. Waste Manag. 2017, 69, 360–364. [Google Scholar] [CrossRef]
  43. Romero Güiza, M.S.; Mata Alvarez, J.; Chimenos Rivera, J.M.; Astals Garcia, S. Nutrient Recovery Technologies for Anaerobic Digestion Systems: An Overview. Rev. ION 2016, 29, 7–26. [Google Scholar] [CrossRef]
  44. Vasco-Correa, J.; Khanal, S.; Manandhar, A.; Shah, A. Anaerobic Digestion for Bioenergy Production: Global Status, Environmental and Techno-Economic Implications, and Government Policies. Bioresour. Technol. 2018, 247, 1015–1026. [Google Scholar] [CrossRef] [PubMed]
  45. Chow, W.; Chong, S.; Lim, J.; Chan, Y.; Chong, M.; Tiong, T.; Chin, J.; Pan, G.-T. Anaerobic Co-Digestion of Wastewater Sludge: A Review of Potential Co-Substrates and Operating Factors for Improved Methane Yield. Processes 2020, 8, 39. [Google Scholar] [CrossRef]
  46. Praveen, P.; Chatterjee, B.; Mazumder, D. A Review on Biodegradation of Plastics with Organic Fraction of Municipal Solid Wastes by Anaerobic Co-Digestion. Water Air Soil. Pollut. 2025, 236, 177. [Google Scholar] [CrossRef]
  47. Jasińska, A.; Grosser, A.; Meers, E. Possibilities and Limitations of Anaerobic Co-Digestion of Animal Manure—A Critical Review. Energies 2023, 16, 3885. [Google Scholar] [CrossRef]
  48. Pramanik, S.K. Anaerobic Co-Digestion of Municipal Organic Solid Waste: Achievements and Perspective. Bioresour. Technol. Rep. 2022, 20, 101284. [Google Scholar] [CrossRef]
  49. Liu, K.; Lv, L.; Li, W.; Ren, Z.; Wang, P.; Liu, X.; Gao, W.; Sun, L.; Zhang, G. A Comprehensive Review on Food Waste Anaerobic Co-Digestion: Research Progress and Tendencies. Sci. Total Environ. 2023, 878, 163155. [Google Scholar] [CrossRef]
  50. González, R.; Peña, D.C.; Gómez, X. Anaerobic Co-Digestion of Wastes: Reviewing Current Status and Approaches for Enhancing Biogas Production. Appl. Sci. 2022, 12, 8884. [Google Scholar] [CrossRef]
  51. Ferdeș, M.; Zăbavă, B.Ș.; Paraschiv, G.; Ionescu, M.; Dincă, M.N.; Moiceanu, G. Food Waste Management for Biogas Production in the Context of Sustainable Development. Energies 2022, 15, 6268. [Google Scholar] [CrossRef]
  52. Tomczak, W.; Daniluk, M.; Kujawska, A. Food Waste as Feedstock for Anaerobic Mono-Digestion Process. Appl. Sci. 2024, 14, 10593. [Google Scholar] [CrossRef]
  53. Fountoulakis, M.S.; Petousi, I.; Manios, T. Co-Digestion of Sewage Sludge with Glycerol to Boost Biogas Production. Waste Manag. 2010, 30, 1849–1853. [Google Scholar] [CrossRef]
  54. Jensen, P.D.; Astals, S.; Lu, Y.; Devadas, M.; Batstone, D.J. Anaerobic Codigestion of Sewage Sludge and Glycerol, Focusing on Process Kinetics, Microbial Dynamics and Sludge Dewaterability. Water Res. 2014, 67, 355–366. [Google Scholar] [CrossRef] [PubMed]
  55. Yang, Q.; Wu, B.; Yao, F.; He, L.; Chen, F.; Ma, Y.; Shu, X.; Hou, K.; Wang, D.; Li, X. Biogas Production from Anaerobic Co-Digestion of Waste Activated Sludge: Co-Substrates and Influencing Parameters. Rev. Env. Sci. Biotechnol. 2019, 18, 771–793. [Google Scholar] [CrossRef]
  56. Adames, L.V.; Pires, L.O.; Maintinguer, S.I. Continuous Long-Term Anaerobic Co-Digestion of Crude Glycerol and Domestic Sewage: Plug-Flow In-Series Reactor Performance and Microbiota Acclimatization. Bioenerg. Res. 2023, 16, 1876–1888. [Google Scholar] [CrossRef]
  57. Nghiem, L.D.; Nguyen, T.T.; Manassa, P.; Fitzgerald, S.K.; Dawson, M.; Vierboom, S. Co-Digestion of Sewage Sludge and Crude Glycerol for on-Demand Biogas Production. Int. Biodeterior. Biodegrad. 2014, 95, 160–166. [Google Scholar] [CrossRef]
  58. Fountoulakis, M.S.; Manios, T. Enhanced Methane and Hydrogen Production from Municipal Solid Waste and Agro-Industrial by-Products Co-Digested with Crude Glycerol. Bioresour. Technol. 2009, 100, 3043–3047. [Google Scholar] [CrossRef]
  59. Andriamanohiarisoamanana, F.J.; Saikawa, A.; Tarukawa, K.; Qi, G.; Pan, Z.; Yamashiro, T.; Iwasaki, M.; Ihara, I.; Nishida, T.; Umetsu, K. Anaerobic Co-Digestion of Dairy Manure, Meat and Bone Meal, and Crude Glycerol under Mesophilic Conditions: Synergistic Effect and Kinetic Studies. Energy Sustain. Dev. 2017, 40, 11–18. [Google Scholar] [CrossRef]
  60. Tan, H.W.; Abdul Aziz, A.R.; Aroua, M.K. Glycerol Production and Its Applications as a Raw Material: A Review. Renew. Sustain. Energy Rev. 2013, 27, 118–127. [Google Scholar] [CrossRef]
  61. De Castro, T.M.; Arantes, E.J.; De Mendonça Costa, M.S.S.; Gotardo, J.T.; Passig, F.H.; De Carvalho, K.Q.; Gomes, S.D. Anaerobic Co-Digestion of Industrial Waste Landfill Leachate and Glycerin in a Continuous Anaerobic Bioreactor with a Fixed-Structured Bed (ABFSB): Effects of Volumetric Organic Loading Rate and Alkaline Supplementation. Renew. Energy 2021, 164, 1436–1446. [Google Scholar] [CrossRef]
  62. Kim, S.-H.; Sung, S. Co-Digestion of Waste Glycerol with Swine Manure. J. Korea Org. Resour. Recycl. Assoc. 2010, 18, 71–75. [Google Scholar]
  63. Bendicho, C.; Lavilla, I. Sewage. In Reference Module in Chemistry, Molecular Sciences and Chemical Engineering; Elsevier: Amsterdam, The Netherlands, 2017; p. B9780124095472115197. ISBN 978-0-12-409547-2. [Google Scholar]
  64. Meegoda, J.N.; Li, B.; Patel, K.; Wang, L.B. A Review of the Processes, Parameters, and Optimization of Anaerobic Digestion. IJERPH 2018, 15, 2224. [Google Scholar] [CrossRef] [PubMed]
  65. Goembira, F.; Yuliarningsih, R.; Silvia, S.; Rahmadani, F. The Effects of Crude Glycerol Addition on Biogas Production. IOP Conf. Ser. Earth Environ. Sci. 2024, 1306, 012041. [Google Scholar] [CrossRef]
  66. Phuket, K.R.N.; Srimachai, T.; Luanunkarb, S.; O-Thong, S. Enhanced Efficiency for Biogas Production from Distillery Wastewater as Mixed with Molasses and Glycerol Waste in the Anaerobic Co-Digestion. Sci. Technol. Indones. 2024, 9, 120–128. [Google Scholar] [CrossRef]
  67. Maragkaki, A.E.; Fountoulakis, M.; Gypakis, A.; Kyriakou, A.; Lasaridi, K.; Manios, T. Pilot-Scale Anaerobic Co-Digestion of Sewage Sludge with Agro-Industrial by-Products for Increased Biogas Production of Existing Digesters at Wastewater Treatment Plants. Waste Manag. 2017, 59, 362–370. [Google Scholar] [CrossRef]
  68. Srimachai, T.; Imai, T.; Rattanadilok Na Phuket, K. Biogas and Biohythane Production from Anaerobic Co-Digestion of Canned Sardine Wastewater with Glycerol Waste. ASEAN Sci. Tech. Rept. 2024, 27, 1–13. [Google Scholar] [CrossRef]
  69. Hutňan, M.; Kolesárová, N.; Bodík, I.; Czölderová, M. Long-Term Monodigestion of Crude Glycerol in a UASB Reactor. Bioresour. Technol. 2013, 130, 88–96. [Google Scholar] [CrossRef]
  70. Dhabhai, R.; Koranian, P.; Huang, Q.; Scheibelhoffer, D.S.B.; Dalai, A.K. Purification of Glycerol and Its Conversion to Value-Added Chemicals: A Review. Sep. Sci. Technol. 2023, 58, 1383–1402. [Google Scholar] [CrossRef]
  71. Kumar, L.R.; Yellapu, S.K.; Tyagi, R.D.; Zhang, X. A Review on Variation in Crude Glycerol Composition, Bio-Valorization of Crude and Purified Glycerol as Carbon Source for Lipid Production. Bioresour. Technol. 2019, 293, 122155. [Google Scholar] [CrossRef]
  72. Aguilar-Aguilar, F.; Adaya, L.; Godoy-Lozano, E.E.; Pantoja, L.A.; Dos Santos, A.S.; Eapen, D.; Sebastian, P.J. Anaerobic Co-Digestion of Raw Glycerol and Swine Manure: Microbial Communities. Biomass Conv. Bioref. 2023, 13, 7127–7138. [Google Scholar] [CrossRef]
  73. Panpong, K.; Srimachai, T.; Nuithitikul, K.; Kongjan, P.; O-Thong, S.; Imai, T.; Kaewthong, N. Anaerobic Co-Digestion between Canned Sardine Wastewater and Glycerol Waste for Biogas Production: Effect of Different Operating Processes. Energy Procedia 2017, 138, 260–266. [Google Scholar] [CrossRef]
  74. Prasertsan, P.; Leamdum, C.; Chantong, S.; Mamimin, C.; Kongjan, P.; O-Thong, S. Enhanced Biogas Production by Co-Digestion of Crude Glycerol and Ethanol with Palm Oil Mill Effluent and Microbial Community Analysis. Biomass Bioenergy 2021, 148, 106037. [Google Scholar] [CrossRef]
  75. Andriamanohiarisoamanana, F.J.; Saikawa, A.; Kan, T.; Qi, G.; Pan, Z.; Yamashiro, T.; Iwasaki, M.; Ihara, I.; Nishida, T.; Umetsu, K. Semi-Continuous Anaerobic Co-Digestion of Dairy Manure, Meat and Bone Meal and Crude Glycerol: Process Performance and Digestate Valorization. Renew. Energy 2018, 128, 1–8. [Google Scholar] [CrossRef]
  76. Simm, S.; Orrico, A.C.A.; Orrico Junior, M.A.P.; Sunada, N.D.S.; Schwingel, A.W.; Mendonça Costa, M.S.S.D. Crude Glycerin in Anaerobic Co-Digestion of Dairy Cattle Manure Increases Methane Production. Sci. Agric. (Piracicaba Braz.) 2017, 74, 175–179. [Google Scholar] [CrossRef]
  77. Farghali, M.; Mohamed, I.M.A.; Hassan, D.; Iwasaki, M.; Yoshida, G.; Umetsu, K.; Ihara, I. Kinetic Modeling of Anaerobic Co-Digestion with Glycerol: Implications for Process Stability and Organic Overloads. Biochem. Eng. J. 2023, 199, 109061. [Google Scholar] [CrossRef]
  78. Astals, S.; Nolla-Ardèvol, V.; Mata-Alvarez, J. Thermophilic Co-Digestion of Pig Manure and Crude Glycerol: Process Performance and Digestate Stability. J. Biotechnol. 2013, 166, 97–104. [Google Scholar] [CrossRef]
  79. Alves, I.R.F.S.; Mahler, C.F.; Oliveira, L.B.; Reis, M.M.; Bassin, J.P. Investigating the Effect of Crude Glycerol from Biodiesel Industry on the Anaerobic Co-Digestion of Sewage Sludge and Food Waste in Ternary Mixtures. Energy 2022, 241, 122818. [Google Scholar] [CrossRef]
  80. Razaviarani, V.; Buchanan, I.D. Anaerobic Co-Digestion of Biodiesel Waste Glycerin with Municipal Wastewater Sludge: Microbial Community Structure Dynamics and Reactor Performance. Bioresour. Technol. 2015, 182, 8–17. [Google Scholar] [CrossRef]
  81. Chou, Y.-C.; Su, J.-J. Biogas Production by Anaerobic Co-Digestion of Dairy Wastewater with the Crude Glycerol from Slaughterhouse Sludge Cake Transesterification. Animals 2019, 9, 618. [Google Scholar] [CrossRef]
  82. Castrillón, L.; Fernández-Nava, Y.; Ormaechea, P.; Marañón, E. Methane Production from Cattle Manure Supplemented with Crude Glycerin from the Biodiesel Industry in CSTR and IBR. Bioresour. Technol. 2013, 127, 312–317. [Google Scholar] [CrossRef]
  83. Fierro, J.; Martinez, E.J.; Rosas, J.G.; Fernández, R.A.; López, R.; Gomez, X. Co-Digestion of Swine Manure and Crude Glycerine: Increasing Glycerine Ratio Results in Preferential Degradation of Labile Compounds. Water Air Soil. Pollut. 2016, 227, 78. [Google Scholar] [CrossRef]
  84. Baba, Y.; Tada, C.; Watanabe, R.; Fukuda, Y.; Chida, N.; Nakai, Y. Anaerobic Digestion of Crude Glycerol from Biodiesel Manufacturing Using a Large-Scale Pilot Plant: Methane Production and Application of Digested Sludge as Fertilizer. Bioresour. Technol. 2013, 140, 342–348. [Google Scholar] [CrossRef]
  85. Dos Santos Ferreira, J.; Volschan, I.; Cammarota, M.C. Co-Digestion of Sewage Sludge with Crude or Pretreated Glycerol to Increase Biogas Production. Env. Sci. Pollut. Res. 2018, 25, 21811–21821. [Google Scholar] [CrossRef] [PubMed]
  86. Athanasoulia, E.; Melidis, P.; Aivasidis, A. Co-Digestion of Sewage Sludge and Crude Glycerol from Biodiesel Production. Renew. Energy 2014, 62, 73–78. [Google Scholar] [CrossRef]
  87. Bułkowska, K.; Mikucka, W.; Pokój, T. Enhancement of Biogas Production from Cattle Manure Using Glycerine Phase as a Co-Substrate in Anaerobic Digestion. Fuel 2022, 317, 123456. [Google Scholar] [CrossRef]
  88. Panpong, K.; Srisuwan, G.; O-Thong, S.; Kongjan, P. Anaerobic Co-Digestion of Canned Seafood Wastewater with Glycerol Waste for Enhanced Biogas Production. Energy Procedia 2014, 52, 328–336. [Google Scholar] [CrossRef]
  89. Astals, S.; Ariso, M.; Galí, A.; Mata-Alvarez, J. Co-Digestion of Pig Manure and Glycerine: Experimental and Modelling Study. J. Environ. Manag. 2011, 92, 1091–1096. [Google Scholar] [CrossRef]
  90. Lobato, A.; Cuetos, M.; Gómez, X.; Morán, A. Improvement of Biogas Production by Co-Digestion of Swine Manure and Residual Glycerine. Biofuels 2010, 1, 59–68. [Google Scholar] [CrossRef]
  91. Aguilar Aguilar, F.A.; Lee Nelson, D.; De Araújo Pantoja, L.; Soares Dos Santos, A. Study of Anaerobic Co-Digestion of Crude Glycerol and Swine Manure for the Production of Biogas. Rev. Virtual Quim. 2017, 9, 2383–2403. [Google Scholar] [CrossRef]
  92. González, R.; Smith, R.; Blanco, D.; Fierro, J.; Gómez, X. Application of Thermal Analysis for Evaluating the Effect of Glycerine Addition on the Digestion of Swine Manure. J. Therm. Anal. Calorim. 2019, 135, 2277–2286. [Google Scholar] [CrossRef]
  93. Lymperatou, A.; Skiadas, I.V.; Gavala, H.N. Anaerobic Co-Digestion of Swine Manure and Crude Glycerol Derived from Animal Fat—Effect of Hydraulic Retention Time. AIMS Environ. Sci. 2018, 5, 105–116. [Google Scholar] [CrossRef]
  94. Shober, A.L.; Maguire, R.O. Manure Management. In Reference Module in Earth Systems and Environmental Sciences; Elsevier: Berlin, Germany, 2018; ISBN 978-0-12-409548-9. [Google Scholar]
  95. Sommer, S.G.; Hutchings, N.J. Ammonia Emission from Field Applied Manure and Its Reduction—Invited Paper. Eur. J. Agron. 2001, 15, 1–15. [Google Scholar] [CrossRef]
  96. Mata-Alvarez, J.; Dosta, J.; Romero-Güiza, M.S.; Fonoll, X.; Peces, M.; Astals, S. A Critical Review on Anaerobic Co-Digestion Achievements between 2010 and 2013. Renew. Sustain. Energy Rev. 2014, 36, 412–427. [Google Scholar] [CrossRef]
  97. Song, Y.; Qiao, W.; Westerholm, M.; Huang, G.; Taherzadeh, M.J.; Dong, R. Microbiological and Technological Insights on Anaerobic Digestion of Animal Manure: A Review. Fermentation 2023, 9, 436. [Google Scholar] [CrossRef]
  98. Samoraj, M.; Mironiuk, M.; Izydorczyk, G.; Witek-Krowiak, A.; Szopa, D.; Moustakas, K.; Chojnacka, K. The Challenges and Perspectives for Anaerobic Digestion of Animal Waste and Fertilizer Application of the Digestate. Chemosphere 2022, 295, 133799. [Google Scholar] [CrossRef]
  99. Ankathi, S.K.; Chaudhari, U.S.; Handler, R.M.; Shonnard, D.R. Sustainability of Biogas Production from Anaerobic Digestion of Food Waste and Animal Manure. Appl. Microbiol. 2024, 4, 418–438. [Google Scholar] [CrossRef]
  100. Gyadi, T.; Bharti, A.; Basack, S.; Kumar, P.; Lucchi, E. Influential Factors in Anaerobic Digestion of Rice-Derived Food Waste and Animal Manure: A Comprehensive Review. Bioresour. Technol. 2024, 413, 131398. [Google Scholar] [CrossRef]
  101. Nuamah, A.; Malmgren, A.; Riley, G.; Lester, E. Biomass Co-Firing. In Comprehensive Renewable Energy; Elsevier: Berlin, Germany, 2012; pp. 55–73. ISBN 978-0-08-087873-7. [Google Scholar]
  102. Okopi, S.; Li, Y.; Xu, F. Biomass Digestion. In Encyclopedia of Sustainable Technologies; Elsevier: Berlin, Germany, 2024; pp. 236–251. ISBN 978-0-443-22287-0. [Google Scholar]
  103. Khawer, M.U.B.; Naqvi, S.R.; Ali, I.; Arshad, M.; Juchelková, D.; Anjum, M.W.; Naqvi, M. Anaerobic Digestion of Sewage Sludge for Biogas & Biohydrogen Production: State-of-the-Art Trends and Prospects. Fuel 2022, 329, 125416. [Google Scholar] [CrossRef]
  104. Yuan, H.; Zhu, N. Progress in Inhibition Mechanisms and Process Control of Intermediates and By-Products in Sewage Sludge Anaerobic Digestion. Renew. Sustain. Energy Rev. 2016, 58, 429–438. [Google Scholar] [CrossRef]
  105. Liew, C.S.; Yunus, N.M.; Chidi, B.S.; Lam, M.K.; Goh, P.S.; Mohamad, M.; Sin, J.C.; Lam, S.M.; Lim, J.W.; Lam, S.S. A Review on Recent Disposal of Hazardous Sewage Sludge via Anaerobic Digestion and Novel Composting. J. Hazard. Mater. 2022, 423, 126995. [Google Scholar] [CrossRef]
  106. Damian, C.S.; Devarajan, Y.; Thandavamoorthy, R. Sewage Sludge as a Sustainable Feedstock for Biodiesel: Advances in Conversion Technologies and Catalytic Applications. Results Eng. 2025, 25, 104000. [Google Scholar] [CrossRef]
  107. Zahedi, S.; Rivero, M.; Solera, R.; Perez, M. Mesophilic Anaerobic Co-Digestion of Sewage Sludge with Glycerine: Effect of Solids Retention Time. Fuel 2018, 215, 285–289. [Google Scholar] [CrossRef]
  108. ElMekawy, A.; Srikanth, S.; Bajracharya, S.; Hegab, H.M.; Nigam, P.S.; Singh, A.; Mohan, S.V.; Pant, D. Food and Agricultural Wastes as Substrates for Bioelectrochemical System (BES): The Synchronized Recovery of Sustainable Energy and Waste Treatment. Food Res. Int. 2015, 73, 213–225. [Google Scholar] [CrossRef]
  109. Ormaechea, P.; Castrillón, L.; Suárez-Peña, B.; Megido, L.; Fernández-Nava, Y.; Negral, L.; Marañón, E.; Rodríguez-Iglesias, J. Enhancement of Biogas Production from Cattle Manure Pretreated and/or Co-Digested at Pilot-Plant Scale. Characterization by SEM. Renew. Energy 2018, 126, 897–904. [Google Scholar] [CrossRef]
  110. Font-Palma, C. Methods for the Treatment of Cattle Manure—A Review. C 2019, 5, 27. [Google Scholar] [CrossRef]
  111. Rico, C.; García, H.; Rico, J.L. Physical–Anaerobic–Chemical Process for Treatment of Dairy Cattle Manure. Bioresour. Technol. 2011, 102, 2143–2150. [Google Scholar] [CrossRef] [PubMed]
  112. Manyi-Loh, C.; Mamphweli, S.; Meyer, E.; Makaka, G.; Simon, M.; Okoh, A. An Overview of the Control of Bacterial Pathogens in Cattle Manure. IJERPH 2016, 13, 843. [Google Scholar] [CrossRef]
  113. Tufaner, F.; Avşar, Y. Effects of Co-Substrate on Biogas Production from Cattle Manure: A Review. Int. J. Environ. Sci. Technol. 2016, 13, 2303–2312. [Google Scholar] [CrossRef]
  114. Youcai, Z. Summary. In Pollution Control Technology for Leachate from Municipal Solid Waste; Elsevier: Berlin, Germany, 2018; ISBN 978-0-12-815813-5. [Google Scholar]
  115. Ehrig, H.-J.; Stegmann, R. Leachate Quality. In Solid Waste Landfilling; Elsevier: Berlin, Germany, 2018; pp. 511–539. ISBN 978-0-12-818336-6. [Google Scholar]
  116. Abdel-Shafy, H.I.; Ibrahim, A.M.; Al-Sulaiman, A.M.; Okasha, R.A. Landfill Leachate: Sources, Nature, Organic Composition, and Treatment: An Environmental Overview. Ain Shams Eng. J. 2024, 15, 102293. [Google Scholar] [CrossRef]
  117. Mojiri, A.; Zhou, J.L.; Ratnaweera, H.; Ohashi, A.; Ozaki, N.; Kindaichi, T.; Asakura, H. Treatment of Landfill Leachate with Different Techniques: An Overview. J. Water Reuse Desalination 2021, 11, 66–96. [Google Scholar] [CrossRef]
  118. Renou, S.; Givaudan, J.G.; Poulain, S.; Dirassouyan, F.; Moulin, P. Landfill Leachate Treatment: Review and Opportunity. J. Hazard. Mater. 2008, 150, 468–493. [Google Scholar] [CrossRef]
  119. Babaei, S.; Sabour, M.R.; Moftakhari Anasori Movahed, S. Combined Landfill Leachate Treatment Methods: An Overview. Env. Sci. Pollut. Res. 2021, 28, 59594–59607. [Google Scholar] [CrossRef]
  120. Mikucka, W.; Zielińska, M. Distillery Stillage: Characteristics, Treatment, and Valorization. Appl. Biochem. Biotechnol. 2020, 192, 770–793. [Google Scholar] [CrossRef]
  121. Ratna, S.; Rastogi, S.; Kumar, R. Current Trends for Distillery Wastewater Management and Its Emerging Applications for Sustainable Environment. J. Environ. Manag. 2021, 290, 112544. [Google Scholar] [CrossRef] [PubMed]
  122. Bezuneh, T.T. The Role of Microorganisms in Distillery Wastewater Treatment: A Review. J. Bioremediat. Biodegrad. 2016, 7, 1000375. [Google Scholar] [CrossRef]
  123. Kumar, V.; Chowdhary, P.; Shah, M.P. Recent Advances in Distillery Waste Management for Environmental Safety; CRC Press: Boca Raton, FL, USA, 2021; ISBN 978-1-00-302988-5. [Google Scholar]
  124. Tripathi, S.; Sharma, P.; Purchase, D.; Chandra, R. Distillery Wastewater Detoxification and Management through Phytoremediation Employing Ricinus communis L. Bioresour. Technol. 2021, 333, 125192. [Google Scholar] [CrossRef]
  125. Kohli, K.; Prajapati, R.; Shah, R.; Das, M.; Sharma, B.K. Food Waste: Environmental Impact and Possible Solutions. Sustain. Food Technol. 2024, 2, 70–80. [Google Scholar] [CrossRef]
  126. Ilakovac, B.; Voca, N.; Pezo, L.; Cerjak, M. Quantification and Determination of Household Food Waste and Its Relation to Sociodemographic Characteristics in Croatia. Waste Manag. 2020, 102, 231–240. [Google Scholar] [CrossRef]
  127. Li, Y.; Wang, L.; Liu, G.; Cheng, S. Rural Household Food Waste Characteristics and Driving Factors in China. Resour. Conserv. Recycl. 2021, 164, 105209. [Google Scholar] [CrossRef]
  128. Wang, P.; Wang, H.; Qiu, Y.; Ren, L.; Jiang, B. Microbial Characteristics in Anaerobic Digestion Process of Food Waste for Methane Production–A Review. Bioresour. Technol. 2018, 248, 29–36. [Google Scholar] [CrossRef]
  129. Paritosh, K.; Kushwaha, S.K.; Yadav, M.; Pareek, N.; Chawade, A.; Vivekanand, V. Food Waste to Energy: An Overview of Sustainable Approaches for Food Waste Management and Nutrient Recycling. BioMed Res. Int. 2017, 2017, 1–19. [Google Scholar] [CrossRef]
  130. Al-Obadi, M.; Ayad, H.; Pokharel, S.; Ayari, M.A. Perspectives on Food Waste Management: Prevention and Social Innovations. Sustain. Prod. Consum. 2022, 31, 190–208. [Google Scholar] [CrossRef]
  131. Thi, N.B.D.; Kumar, G.; Lin, C.-Y. An Overview of Food Waste Management in Developing Countries: Current Status and Future Perspective. J. Environ. Manag. 2015, 157, 220–229. [Google Scholar] [CrossRef]
  132. Ananno, A.A.; Masud, M.H.; Chowdhury, S.A.; Dabnichki, P.; Ahmed, N.; Arefin, A.M.E. Sustainable Food Waste Management Model for Bangladesh. Sustain. Prod. Consum. 2021, 27, 35–51. [Google Scholar] [CrossRef]
  133. Zhang, C.; Su, H.; Baeyens, J.; Tan, T. Reviewing the Anaerobic Digestion of Food Waste for Biogas Production. Renew. Sustain. Energy Rev. 2014, 38, 383–392. [Google Scholar] [CrossRef]
  134. Mirmohamadsadeghi, S.; Karimi, K.; Tabatabaei, M.; Aghbashlo, M. Biogas Production from Food Wastes: A Review on Recent Developments and Future Perspectives. Bioresour. Technol. Rep. 2019, 7, 100202. [Google Scholar] [CrossRef]
  135. Bong, C.P.C.; Lim, L.Y.; Lee, C.T.; Klemeš, J.J.; Ho, C.S.; Ho, W.S. The Characterisation and Treatment of Food Waste for Improvement of Biogas Production during Anaerobic Digestion—A Review. J. Clean. Prod. 2018, 172, 1545–1558. [Google Scholar] [CrossRef]
  136. Leung, D.Y.C.; Wang, J. An Overview on Biogas Generation from Anaerobic Digestion of Food Waste. Int. J. Green Energy 2016, 13, 119–131. [Google Scholar] [CrossRef]
  137. Chew, K.R.; Leong, H.Y.; Khoo, K.S.; Vo, D.-V.N.; Anjum, H.; Chang, C.-K.; Show, P.L. Effects of Anaerobic Digestion of Food Waste on Biogas Production and Environmental Impacts: A Review. Environ. Chem. Lett. 2021, 19, 2921–2939. [Google Scholar] [CrossRef]
  138. Muñoz-Martínez, S.; Salmerón-Alcocer, A.M.; Rodríguez-Casasola, F.N.; Ahuatzi-Chacón, D. Biogas Production by Anaerobic Co-Digestion of Agro-Industrial Waste and Crude Glycerol. Agrociencia 2025, 59, 1–15. [Google Scholar] [CrossRef]
  139. Robra, S.; Serpa Da Cruz, R.; De Oliveira, A.M.; Neto, J.A.A.; Santos, J.V. Generation of Biogas Using Crude Glycerin from Biodiesel Production as a Supplement to Cattle Slurry. Biomass Bioenergy 2010, 34, 1330–1335. [Google Scholar] [CrossRef]
  140. Lovato, G.; Batista, L.P.P.; Preite, M.B.; Yamashiro, J.N.; Becker, A.L.S.; Vidal, M.F.G.; Pezini, N.; Albanez, R.; Ratusznei, S.M.; Rodrigues, J.A.D. Viability of Using Glycerin as a Co-Substrate in Anaerobic Digestion of Sugarcane Stillage (Vinasse): Effect of Diversified Operational Strategies. Appl. Biochem. Biotechnol. 2019, 188, 720–740. [Google Scholar] [CrossRef]
  141. Madondo, N.I.; Chetty, M. Anaerobic Co-Digestion of Sewage Sludge and Bio-Based Glycerol: Optimisation of Process Variables Using One-Factor-at-a-Time (OFAT) and Box-Behnken Design (BBD) Techniques. S. Afr. J. Chem. Eng. 2022, 40, 87–99. [Google Scholar] [CrossRef]
  142. Li, P.; Zhao, H.; Cheng, C.; Hou, T.; Shen, D.; Jiao, Y. A Review on Anaerobic Co-Digestion of Sewage Sludge with Other Organic Wastes for Methane Production: Mechanism, Process, Improvement and Industrial Application. Biomass Bioenergy 2024, 185, 107241. [Google Scholar] [CrossRef]
  143. Ibro, M.K.; Ancha, V.R.; Lemma, D.B. Impacts of Anaerobic Co-Digestion on Different Influencing Parameters: A Critical Review. Sustainability 2022, 14, 9387. [Google Scholar] [CrossRef]
  144. Ryue, J.; Lin, L.; Kakar, F.L.; Elbeshbishy, E.; Al-Mamun, A.; Dhar, B.R. A Critical Review of Conventional and Emerging Methods for Improving Process Stability in Thermophilic Anaerobic Digestion. Energy Sustain. Dev. 2020, 54, 72–84. [Google Scholar] [CrossRef]
  145. Suryawanshi, P.C.; Chaudhari, A.B.; Kothari, R.M. Thermophilic Anaerobic Digestion: The Best Option for Waste Treatment. Crit. Rev. Biotechnol. 2010, 30, 31–40. [Google Scholar] [CrossRef]
  146. Rawoof, S.A.A.; Kumar, P.S.; Vo, D.-V.N.; Subramanian, S. Sequential Production of Hydrogen and Methane by Anaerobic Digestion of Organic Wastes: A Review. Environ. Chem. Lett. 2021, 19, 1043–1063. [Google Scholar] [CrossRef]
  147. Gonde, L.; Wickham, T.; Brink, H.G.; Nicol, W. pH-Based Control of Anaerobic Digestion to Maximise Ammonium Production in Liquid Digestate. Water 2023, 15, 417. [Google Scholar] [CrossRef]
  148. Hossain, M.S.; Karim, T.U.; Onik, M.H.; Kumar, D.; Rahman, M.A.; Yousuf, A.; Uddin, M.R. Impact of Temperature, Inoculum Flow Pattern, Inoculum Type, and Their Ratio on Dry Anaerobic Digestion for Biogas Production. Sci. Rep. 2022, 12, 6162. [Google Scholar] [CrossRef] [PubMed]
  149. Cioabla, A.E.; Ionel, I.; Dumitrel, G.-A.; Popescu, F. Comparative Study on Factors Affecting Anaerobic Digestion of Agricultural Vegetal Residues. Biotechnol. Biofuels 2012, 5, 39. [Google Scholar] [CrossRef]
Molecules 30 03655 g001
Figure 1. Lipid transesterification. Based on [2,4,5,6,7].
Figure 1. Lipid transesterification. Based on [2,4,5,6,7].
Molecules 30 03655 g001
Molecules 30 03655 g002
Figure 2. Market value of crude glycerol. Based on [8].
Figure 2. Market value of crude glycerol. Based on [8].
Molecules 30 03655 g002
Molecules 30 03655 g004
Figure 4. Characteristics of crude glycerol used as a co-substrate for anaerobic co-digestion process reported in the literature: (a) pH; (b) TS, VS and COD.
Figure 4. Characteristics of crude glycerol used as a co-substrate for anaerobic co-digestion process reported in the literature: (a) pH; (b) TS, VS and COD.
Molecules 30 03655 g004
Molecules 30 03655 g005
Figure 5. The factors affecting the performance of anaerobic co-digestion process.
Figure 5. The factors affecting the performance of anaerobic co-digestion process.
Molecules 30 03655 g005
Molecules 30 03655 g006
Figure 6. The impact of crude glycerol content on the methane content in biogas produced during the AcoD of crude glycerol mixed with various substrates performed under mesophilic and thermophilic conditions. Literature data.
Figure 6. The impact of crude glycerol content on the methane content in biogas produced during the AcoD of crude glycerol mixed with various substrates performed under mesophilic and thermophilic conditions. Literature data.
Molecules 30 03655 g006
Disclaimer/Publisher’s Note: The statements, opinions and data contained in all publications are solely those of the individual author(s) and contributor(s) and not of MDPI and/or the editor(s). MDPI and/or the editor(s) disclaim responsibility for any injury to people or property resulting from any ideas, methods, instructions or products referred to in the content.

Share and Cite

MDPI and ACS Style

Tomczak, W.; Żak, S.; Kujawska, A.; Szwast, M. The Use of Crude Glycerol as a Co-Substrate for Anaerobic Digestion. Molecules 2025, 30, 3655. https://doi.org/10.3390/molecules30173655

AMA Style

Tomczak W, Żak S, Kujawska A, Szwast M. The Use of Crude Glycerol as a Co-Substrate for Anaerobic Digestion. Molecules. 2025; 30(17):3655. https://doi.org/10.3390/molecules30173655

Chicago/Turabian Style

Tomczak, Wirginia, Sławomir Żak, Anna Kujawska, and Maciej Szwast. 2025. "The Use of Crude Glycerol as a Co-Substrate for Anaerobic Digestion" Molecules 30, no. 17: 3655. https://doi.org/10.3390/molecules30173655

APA Style

Tomczak, W., Żak, S., Kujawska, A., & Szwast, M. (2025). The Use of Crude Glycerol as a Co-Substrate for Anaerobic Digestion. Molecules, 30(17), 3655. https://doi.org/10.3390/molecules30173655

Article Metrics

Back to TopTop