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Article

Quantitative Carbon Changes of Selected Organic Fractions during the Aerobic Biological Recycling of Biodegradable Municipal Solid Waste (MSW) as a Potential Soil Environment Improving Amendment—A Case Study

by
Jakub Bekier
,
Elżbieta Jamroz
*,
Magdalena Dębicka
,
Irmina Ćwieląg-Piasecka
and
Andrzej Kocowicz
Institute of Soil Sciences, Plant Nutrition and Environmental Protection, Wrocław University of Environmental and Life Sciences, Grunwaldzka 53, 50-357 Wrocław, Poland
*
Author to whom correspondence should be addressed.
Agriculture 2022, 12(12), 2058; https://doi.org/10.3390/agriculture12122058
Submission received: 26 October 2022 / Revised: 25 November 2022 / Accepted: 29 November 2022 / Published: 30 November 2022
(This article belongs to the Special Issue Sustainable Remediation and Management of Agricultural Soil and Water Resources)
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Versions Notes

Abstract

:
The aim of the investigation was to determine the quantitative changes of selected organic compounds during composting of municipal solid wastes (MSWs). The object of the study was a differently matured compost produced according the to open pile/windrow semi-dynamic technology from selectively collected biodegradable municipal solid waste. During the experiment, the temperature and moisture of the composted wastes were monitored. In the collected samples—taken from differently matured compost—the total organic carbon (TOC) and total nitrogen (TN) were determined. The organic matter fractionation method described by Stevenson and Adani et al. was adopted, which allows to determine the carbon content of the following groups of organic compounds: hydrophobic (HSC), hydrophilic (WEOC), acidophilic (CAC), cellulose (CCEL), core-HA (ligno-humic, CALK) and residual carbon (non-hydrolysing, CR). The TOC and TN content, as well as the origin and quality of the starting materials, allow the product tested to be classified for fertiliser purposes. The most intense changes were observed during the thermophilic composting phase. In spite of the optimal technological conditions of the process, the predominance of the CR and CCEL fraction was observed, and the share of humic compounds did not exceed 30% TOC. The investigated compost met legal, ecological and economic criteria for products of biological recycling, thus can be used as a good organic amendment to improve the soil organic matter balance, stimulate the soil biodiversity and carbon sequestration.

1. Introduction

Soil management and utilization should result in maintaining the soil quality, fertility and productivity, especially as stocks of soil organic carbon have declined in many agricultural systems all over the world. In the last decades there has been a growing interest in the use of alternative fertilizers, such as brown coal, biochar, composts produced from segregated biodegradable waste or biomass, as well as other organic amendments, in agricultural and horticultural production. Soil organic amendments are a good source of stable organic carbon and, due to the presence of good-quality nutrients, can be efficiently used to improve the balance of organic matter, enhance carbon sequestration and stimulate the activity of soil biodiversity [1,2,3]. Moreover, the increasing amount of waste requires a reasonable strategy in its management. It focuses mainly on: quantity and toxicity reduction, recycling and reuse, and energy recovery [1,2,4]. Urban waste management and processing is currently a priority in the environmental policy of many countries. As a consequence of increasing the pro-ecological awareness of citizens and governing elites, the development of those fields of science and technology, which allow a reasonable waste management, has been observed [3,4]. One proposal may be the production of compost, based on the organic part of municipal wastes, physico-chemically appropriate and environmentally friendly. Compost produced from agricultural residues or municipal organic wastes is rich in active humic substances, for which quality and quantity depend on the composted material as well as the conditions of the process. Based on many studies [3,4,5,6], the most important factors determining the waste usefulness for the production of compost were defined and characterised: qualitative composition (morphology), chemical, physico-chemical and biological properties, collection method (selective or non-selective collection), legal and economic aspects [7]. Furthermore, many studies indicate that the average chemical composition of municipal waste, and especially the content of individual groups of organic compounds, is difficult to determine and the results of the previous studies do not exhaust the subject of their transformation during the composting process [8]. The quantity of organic compounds ranges within a very wide limits and depends on many factors [9,10]. It is assumed that on average, in the biodegradable, organic part of municipal waste, carbohydrates and lignin constitute 40–80%, proteins 1–15%, and fats and hydrophobic substances 5–30% of the dry mass [4,5].
Carbohydrates are considered to predominate in the biodegradable compounds of composted waste [11,12,13]. The most important is cellulose, the proportion of which can achieve above 50% of the organic matter of the composted mass [13,14,15]. Since the intensity of the cellulose transformation depends on the microbial activity of the composting microorganisms, it is most often considered as an organic carbon and energy store [13,14]. According to the current understanding, lignin is decomposed into phenolic monomers under the action of hydroxyl radicals, which are then converted by oxidation to quinone monomers. The resulting monomers combine with other compounds to form supramolecular polymers which can be transformed into humic substances (HS) by the biochemical changes [15,16,17,18,19]. Moreover, due to its strong polymerization, lignin is very resistant to biotransformation processes. During composting, its transformations depend on the intensity of the extracellular enzymatic processes initiated by fungi and actinomycetes. In its active form, lignin is a component of the lignin-humic complex which, due to its properties, can bind or unbind important compounds for humification processes, such as biphenyls, phenylcoumarins, diarylpropane, ether and glycerol [12,13,15,20].
Among all of the hydrophobic substances present in composted waste, of the nature of lipids, waxes, tars and resins [7,8,9,21,22], the biotransformation of fats was best identified and described [22,23,24]. An important aspect of municipal waste composting is the quality control system for the substrates used, the composting technology and the quality of the final products obtained [1,3,25,26,27]. One of the most advanced documents regulating these issues internationally is the recently accepted European Union (EU) Circular Economy Package [28]. The formal and legal solutions proposed therein, in conjunction with other studies [5,6,27], aim to regulate the production of fertilisers from municipal waste (UWC), standardise their quality standards (certification) and provide direction for the development of future legislation on the UWC management.
Regardless of the applicable law in different countries, when assessing the usefulness of products resulting from the mechanical-biological treatment (MBT) of waste, both origin and quantitative changes in specific physical, chemical and biological properties should be taken into consideration.
Therefore, the aim of this study was to investigate the quantitative changes in selected organic compounds, together with the humification progress during the composting of municipal solid waste (MSW) under defined technological conditions, to assess the usefulness of the MSW compost as a potential soil environment improving amendment. The scientific hypothesis was adopted that during the proper composting of municipal solid wastes the highest share of organic carbon in the end-product is incorporated in the residual and core-HS fractions.

2. Materials and Methods

The subject of the study was differently matured compost produced from selectively collected biodegradable substances present in municipal waste from the Zabrze agglomeration (Upper Silesia, Southern Poland, population: 173.5 × 103 inhabitants). Composting was carried out according to the open pile/windrow semi-dynamic technology [27] at the facility of the Regional Municipal Waste Treatment Installation in Silesia (Zabrze, Poland).

2.1. Design of the Working Experiment

The total duration of the experiment was 15 weeks. The collected biodegradable municipal waste contained approximately 50% (by mass) urban green waste (UGW) and 50% domestic kitchen waste (DKW). The waste was mechanically mixed to increase the homogenisation and the prepared material was shaped into piles (dimensions L × W × H = 18.0 m × 2.0 m × 1.5 m). Samples for analysis were taken from fresh mixed material and from the pile after 14, 28, 45, 56, 70, 90 and 107 days of composting. Samples were taken from three different locations regardless of the compost maturity stage, and the total number of samples was 24. The collected materials were air-dried, ground and sieved through a 2.0 mm diameter. The temperature of the composted waste was monitored daily, while the moisture content was monitored every five days. The measurements were conducted at three locations at a depth of approximately 30 cm using a Vaisala HUMICAP HM42 (Vaisala GmbH, Hamburg, Germany) mobile device. Based on the moisture measurements, the water deficiencies in the composted material were replenished (after 1, 4, 6 and 8 weeks of the experiment) to an optimal level of 40–60% H2O [7,9]. The pile was mechanically turned every 5 days for the first 8 weeks and every 10 days between the 9th and 15th week of the experiment.

2.2. Basic Chemical Analyses

In the collected materials, the following determinations were performed: content of the total organic carbon (TOC) and total nitrogen (TN) using a Vario Macro Cube CN analyser (Elementar Analysensysteme GmbH, 63505 Langenselbold, Germany). The device has been calibrated for the determination of organic carbon and the total nitrogen, according to 2,5-Bis(5-tert-butyl-2-benzo-oxazol-2-yl) thiophene organic analytical (BBOT-OAS) No. B2044 (Elemental Microanalysis Ltd., Okehampton, Devon, UK), certificate No. 314878 [29]. Inorganic carbonate carbon (IC) was eliminated by acidifying the solid samples with hydrochloric acid (Cp = 3%), according to the procedure recommended by the instrument manufacturer [S1]. The determined organic carbon and total nitrogen contents were compared with the standards for the chemical parameters for the product qualification and compost quality assessment in the EU [26,30].

2.3. Detailed Chemical Analyses

The organic matter fractionation method described by Stevenson [17] and Adani et al. [31,32] was adopted, which allows different groups of organic matter to be extracted from solid samples by appropriately selected reagents (Figure 1).
Based on the applied procedure, the quantitative changes of the organic carbon of the following groups of compounds were determined:
  • Carbon of hydrophobic substances (HSCs): extracted by means of an ethanol and benzene mixture (1:2 v/v) using the Soxhlet extractor (extraction time: 4 h). Following the extraction, the samples were dried in a controlled condition at 40 °C temperature for 24 h to evaporate the extractant. The HSC was calculated as the difference in the organic carbon before and after the extraction [22];
  • Water-extractable organic carbon (WEOC): determined in a centrifuged aqueous solution 5 g ÷ 50 mL (1 ÷ 10 m ÷ v) after the dynamic [33] extraction (three repetitions, intensity: 40 rpm, extraction time: 4 h per repetition, centrifugation: 4000 rpm 10 min−1);
  • Carbon extracted with 5% H2SO4 (CAC): determined in a centrifuged acid solution 5 g ÷ 50 mL (1 ÷ 10 m ÷ v) after the dynamic extraction (three repetitions, intensity: 40 rpm, extraction time: 4 h per repetition, centrifugation: 4000 rpm 10 min−1);
  • Cellulose carbon extracted with 72% H2SO4 (CCEL): two-stage extraction: the acid stage 5 g ÷ 50 mL (1 ÷ 10 m ÷ v)—three repetitions in acid, intensity: 40 rpm, extraction time: 4 h per repetition, centrifugation: 4000 rpm 10 min−1 and the neutralisation stage with water 5 g ÷ 50 mL (1 ÷ 10 m ÷ v)—three repetitions, intensity: 40 rpm, extraction time: 1 h per repetition, centrifugation: 4000 rpm 10 min−1. CCEL content determined the summed solutions of both stages.
  • Carbon of the ligno-humic complex extracted with 0,1 M NaoH dm−3 (CALK): determined in centrifuged alkaline solution 5 g ÷ 50 mL (1 ÷ 10 m ÷ v) after the dynamic extraction (three repetitions, intensity: 40 rpm, extraction time: 4 h per repetition, centrifugation: 4000 rpm 10 min−1);
  • Residual carbon (CR): non-hydrolysing organic carbon and humin fractions [34] remaining in the sample, calculated according to the formula: CR = TOC − (HSC + WEOC + CAC + CCEL + CALK).
The organic carbon content of the mentioned extracts was determined with a Vario Macro Cube CN analyser (Elementar Analysensysteme GmbH, 63505 Langenselbold, Germany) with the hardware attachment for the solutions.

2.4. Statistical Analyses

Most of the results presented in this paper are averaged values (arithmetic mean), based on the results from all replicates obtained during the chemical analyses. The results obtained from the chemical analyses (three repetitions for each parameter at each time) were statistically processed using the ANOVA package of Statistica 13 software. The correlation matrices for the selected parameters were performed (Table 1), the LSD (significance level < 0.05) was calculated for the determined chemical properties for a 107-day period, the mean and standard deviation (3 repetitions for each parameter) for the replicates at the defined sampling times.

3. Results and Discussion

3.1. Changes in the Temperature and Humidity of the Composted Waste

The intensity of the OM transformation and decomposition processes during composting depends on the temperature and humidity which affect the microbiological activity in the composted material [3,9,35]. The average temperature of the initial mixture was about 30.3 °C and after 34 days, it reached the value of 55 °C—the lower limit of the thermophilic phase. This phase, with an average temperature > 55 °C lasted 4 weeks (between 34th and 62nd days) and the highest average daily temperature (61.8 °C) was observed on the 47th day of composting (Figure 2). Following this period, a regular drop in temperature to an average 27.8 °C degrees was observed (107th day).
Many authors indicated [3,9,36] that a water content of 40 to 60% H2O in the composted mass is the most optimal for successful composting processes. Analysis of the changes in this parameter (Figure 2) indicated that the moisture of the investigated compost was in this range, regardless of the thermal phase of the process. However, it should be noted that the moisture deficiencies have been corrected after 7, 28, 42 and 56 days of the experiment. This indicates the need for the regular monitoring of the parameters during the biological, aerobic processing of the municipal biodegradable waste and to intervene when the negative phenomena occur.
Both temperature and moisture levels showed a significant influence on the quantitative changes of most of the analysed groups of organic compounds (Table 1). The obtained results confirm the previous studies [3,5,8,11,36], which showed that the mentioned parameters support the maintenance and/or stimulate the physico-chemical and chemical processes, as well as the activity of microorganisms responsible for the dynamics of the organic compounds transformation.

3.2. Changes in TOC, TN and the TOC/TN Ratio during the Composting of MSW

The most suitable and very widely used parameters describing the biotransformation conditions during composting [36,37,38,39] are the quantitative changes of TOC and TN in different phases of this process and the accompanying changes of the TOC/TN ratio (Figure 3a–c).
Based on the results obtained, during the 15 weeks of the experiment, the TOC content decreased from 352.66 to 168.73 g kg−1, while the amount of TN increased from 10.75 to 14.23 g kg−1 (Figure 3a,b). The most intense decrease in the TOC content and increase in TN content were observed during the first 8 weeks of composting. These changes were statistically correlated with the temperature and moisture contents (Figure 2 and Figure 3a,b, Table 1) and were associated with the thermal phases of composting, particularly the thermophilic phase. The observed changes in the TOC and TN contents are compatible with the results of previous studies [3,9,10,36,38,39]. It should also be noted that for both TOC and TN, a stabilisation phase was observed after 70 days of the experiment (Figure 3a,b, Table 2). Furthermore, the results from Ciavatta et al. [3], Bernat et al. [40] and Gariglio et al. [41] indicated that these optimal carbon and nitrogen transformations may be due to the properties of the substrates used, in particular the proportion of the components highly carbon-rich (UGW), in relation to the components rich in other nutrients—mainly nitrogen (DKW).
The study also indicated a decrease in the TOC/TN ratio (Figure 3c). Although the changes in the values of this parameter were determined by the changes in the TOC and TN contents, but the processes involved in the carbon mineralisation during composting had the greatest influence [38,40,42,43].
Additionally, it should be noted that the analysis of the intensity of the changes in the value of the TOC/TN index (Figure 3c) indicated that the studied product reached maturity (TOC/TN ≤ 12) after 90 days (TOC/TN = 11.9), which suggests the optimal technological conditions of the process [3,5,8,38,42].
Regardless of the determined TOC and TN content and the technology used, the EU international fertiliser regulations define the principles for the use of biodegradable municipal waste as a substrate for the production of organic or organic-mineral fertiliser substances or soil substitutes [2,3,8,12,30]. Therefore, the possibility of using the investigated product as a component of alternative soil conditioners and/or substrates for agricultural, remediation and environmental purposes should be considered [1,3,7,18,26,28].

3.3. Changes in the HSC, WEOC, CAC, CCEL, CALK and CR Contents of the Composted Waste

Although the TOC content decreased by over 50% during the 107 days of the experiment (Figure 3a), the intensity and direction of the changes in the carbon content of the extracted organic compounds varied (Figure 4a,b). Analysis of the results showed that, except for the CALK fraction, the organic carbon of the other fractions analysed decreased with the progression of the composting time (Table 1).
Changes in the C contents of HSC, WEOC and CAC fractions showed a significantly negative correlation (Table 1) with composting, the temperature while CAC, CCEL, CALK and CR indicated a significantly positive correlation with the moisture content. Furthermore, the quantitative changes in the HSC and WEOC fractions were highest up to the 47th day and the CR up to the 70th day of the experiment, which may be related to the intensive biological-chemical-physical processes in the thermophilic and in the early 2nd mesophilic phases (Figure 4a,b). These results are in accordance with the studies of Ryckeboer et al. [15], Bekier et al. [22] and Amir et al. [44], especially in the intensity of the transformation of the hydrophobic compounds (HSC). The authors indicated that the intensity of the decomposition of the hydrophobic substances, was significantly correlated with the composting parameters, mainly the temperature and time (Table 1). Similar correlations for the water-extractable organic compounds were described in the experiments by Kałuża-Haładyn et al. [45,46] and Jamroz et al. [33]. Although the intensity of the HSC transformation can be used as an indicator of the advancement of transformation processes during composting, some authors [3,15,22,45] indicate that the carbon content of the hydrophobic compounds in the composted mass should not exceed 15% of TOC. The analysis of the transformation intensity of water-extractable organic compounds indicated a similarity with the results obtained in the experiments by Kałuza-Haładyn et al. [45,46] and Jamroz et al. [33]. Furthermore, other authors [17,19,38,43] indicated the organic components of WEOC are the main, available and important source of carbon and energy for microorganisms involved in composting processes. For this reason, the quantitative changes of this fraction were observed during the intense thermophilic phase. However, the intensity of the decrease in the WEOC content (Figure 4a) may also be caused by the leaching of these fractions from the composted MSW with the effluents. Analysis of the decrease in the CR content (Figure 4c), represented mainly by humin, with the progress of composting, did not show a significant influence of the temperature on the intensity of these changes (Table 1 and Table 2). Regardless of the extraction and/or isolation methods used and the biological activity of the environment, the CR fractions represent the highest part in the TOC content, as confirmed by the studies of Kononova [47], Stevenson [17] and Weber et al. [34]. However, it should be noted that the interpretation of the biotransformation of the fractions very resistant to microbial activity, is a major scientific challenge. The lack of solubility, the difficulty to determine the structure and complex interactions with the mineral components make research on this fraction much more complicated.
The study showed a systematic decrease in the organic matter content represented by CAC and CCEL (Figure 4a,b) during the MSW composting. While the stability of the CCEL fraction, regardless of the thermal composting phases (Table 1) has been confirmed by the experimental results of Ryckeboer et al. [15], Amir et al. [44], Bekier et al. [22,38] and Kałuża-Haładyn et al. [46], the decrease in the CAC content was significantly correlated with all composting parameters. Although wood is very frequently present in biodegradable municipal waste, the direction of its biotransformation during composting is a major scientific problem. The presence of lignin indicates a transformation to humic substances [3,16,17,31], however, too high a proportion can lead to increased mineralisation processes and the move of humification towards low molecular acidophilic compounds [3,40,41,46]. However, it should be noted that the intensity of the CAC changes is in accordance with the work of other authors [48,49]. Senesi et al. [50] and Jerzykiewicz [51], Kulikowska and Sindrewicz [52] indicated that the transformations of small-molecule, mostly aliphatic compounds representing this fraction may have a crucial influence on the direction of the humification processes and the quality of organic matter obtained during composting. Furthermore, studies by Chefetz et al. [10], Chen et al. [48], Koivula and Hänninien [49] indicated that the contents of the acidophilic organic carbon increase in the thermophilic phase and achieves a stabilisation and then remains on a decreasing trend. Therefore, the significant correlations of the CAC fraction transformations with time and moisture content are appropriate, indicating the suitable quality of the substrate used for composting and the optimal process parameters.
The study indicated an increase in the CALK content during composting (Figure 4a). This fraction is commonly classified as lignino-humic compounds, obtained by the biotransformation of lignino-protein complexes [14,16,17,18]. Therefore, the organic compounds contained in the CALK extract should be considered as a mixture of the proper humic substances, also defined as a core-HS. The results obtained are in accordance with the performed studies confirming the increase of the HS content in composts [8,10,14,31,40]. The increase of the CALK content with the composting time, moisture and temperature was observed (Table 1). Furthermore, the dynamics of the quantitative changes in carbon of this fraction indicated a stabilisation after the thermophilic phase (from day 56) with a slight increasing trend until the end of the experiment (Figure 4a, Table 2).
It should be noted that the significantly negative correlations of time and temperature with the content of the hydrophobic fractions, WEOC, CCEL and CR (Table 1), are in agreement with the studies of other authors [9,10,11,15,49,52] indicating that hydrolysis products formed in the thermophilic phase should be considered as a substrate in the mesophilic biotransformation processes and formation of HS.

3.4. Changes in the Share of the Organic Carbon of the Extracted Fractions in Relation to TOC

Considering the different durabilities of the organic compounds contained in the waste to the biotransformation processes during composting, many authors indicates the necessity to express the percentage of organic carbon of the extracted substances in relation to the TOC content [9,18,37,40,42,46]. This method of interpreting allows one to trace which compounds and to what extent they determine the organic carbon pool in the different composting phases. The study showed that the CR fraction was dominant both in quantity and in share of TOC (Figure 4c and Figure 5). Furthermore, this relation was observed in all samples tested, regardless of the compost maturity stage. It should be noted that, despite the significant decrease of the CR content (Figure 4c), the organic carbon of this fraction represented the largest resource of the total organic carbon in the composts studied. The observed phenomena are confirmed by studies performed by other authors [3,8,31,34,35,53].
A different interaction was observed for the carbon of the CAC and CCEL fractions. Despite a systematic quantitative decrease in the cellulose and acidophilic fractions, an increase in the share of CCEl and very irregular changes in CAC were observed (Figure 4a,b and Figure 5). While for cellulose these changes are acceptable [3,14,52,54,55,56,57], for the CAC fraction the results are unusual and difficult to explain, indicating the need for research into the transformations of small-molecule acidophilic compounds during composting.
The results obtained confirm the previous studies [3,8,18,20,22,23,46,48], indicating that both the carbon content of the hydrophobic and WEOC fractions and their share of TOC (Figure 4a and Figure 5) decrease with the duration of composting. Furthermore, in samples composted for 107 days, the summed share of the HSC and WEOC fractions did not exceed 3.5% of TOC, indicating that the maturation and stabilisation of the composted waste was correct [3,9,32,35,48]. The results confirmed the formation and accumulation of the CALK (core-HS) compounds. A quantitative increase in the CALK carbon content resulted in an increase in the share of this fraction in TOC [14,16,17,18]. These phenomena occurred with different dynamics, and the most intense changes were observed between 28 and 70 days of composting (Figure 4a and Figure 5). In the last 30 days of the experiment, these processes stabilised (Table 2), which indicates the optimal course of the composting process and indicates the maturity of the final product [8,10,14,31,40].

4. Summary and Conclusions

Both the type of technology and the selected physico-chemical properties of the substrate indicate the optimal composting conditions, enabling a positive evaluation of the experiment. The applied technical solutions stimulated the formation and accumulation of the core-HS compounds. The relatively low content (Figure 4a) and share of the HSC and WEOC fractions in TOC (Figure 5), the dominance of the CR and CCEL compounds and the optimal TOC/TN ratio may result from the properties of the substrate [3,9,17,26,28,30,39]. Furthermore, the results and observations obtained indicate that the studied compost produced from the selectively collected biodegradable waste can have a wide spectrum of applications [1,2,3,4,30]. In addition, the lack of substances considered to be contaminants is an advantage of the tested product [2,3,4,5]. Based on the results obtained, it can be stated that the final product studied, resulting from the applied mechanical-biological treatment (MBT), confirmed the benefits of the biological, aerobic methods for recycling organic compounds contained in the waste [1,2,3,4,5,6,30,58,59,60,61,62].
Considering the results obtained and the interpretation of the observed transformations, the following conclusions can be drawn: (1) The quantitative changes in total carbon and total nitrogen, observed during composting, showed significant correlations with time, temperature and moisture content of the composted mass; (2) The most intense changes of the organic carbon contents were observed in the hydrophilic, core-HS and residual fractions; (3) The composting conditions, the technology applied and the properties of the substrate stimulated both the quantitative increase in CALK and the share of this fraction in TOC; (4) The study showed that the highest share of organic carbon in the final product was incorporated in the residual, cellulose and core-HS fractions, respectively; (5) The contents of TOC, TN, the origin and quality of the substrate used allow to qualify the studied product as organic or organic-mineral fertilizer; (6) The investigated composts from selectively collected biodegradable municipal waste meet the legal and ecological criteria for products of biological recycling, thus can be used as a good organic amendment to improve the soil organic matter balance, stimulate soil biodiversity and carbon sequestration. Further investigations determining the soil and plant response to the compost application are needed to confirm its benefits as an attractive option for the soil amendment.

Author Contributions

Conceptualization J.B. and E.J.; methodology J.B. and E.J.; validation E.J., M.D. and I.Ć.-P.; formal analysis J.B. and E.J.; investigation J.B.; resources J.B., E.J. and M.D.; data curation J.B., E.J. and I.Ć.-P.; writing—original draft preparation J.B.; writing—review and editing E.J., A.K., M.D. and I.Ć.-P.; visualization J.B.; supervision E.J. and I.Ć.-P.; project administration J.B. All authors have read and agreed to the published version of the manuscript.

Funding

This research has been supported by a grant from the National Science Centre, Poland, project no. N N305 395738.

Institutional Review Board Statement

Not applicable.

Data Availability Statement

The data presented in this study are available upon request from the corresponding author.

Acknowledgments

The authors would like to acknowledge the technical staff of the Waste Management Plant in Zielona Gora.

Conflicts of Interest

The authors declare no conflict of interest.

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Agriculture 12 02058 g001 550
Figure 1. Simplified diagram of the extraction method by Stevenson [17] and Adani et al. [31,32].
Figure 1. Simplified diagram of the extraction method by Stevenson [17] and Adani et al. [31,32].
Agriculture 12 02058 g001
Agriculture 12 02058 g002 550
Figure 2. Changes in: temperature and moisture during the composting of municipal waste.
Figure 2. Changes in: temperature and moisture during the composting of municipal waste.
Agriculture 12 02058 g002
Agriculture 12 02058 g003 550
Figure 3. Changes in: (a) TOC and (b) TN and (c) TOC/TN during the composting of MSW (markers: measured values; lines: mean values).
Figure 3. Changes in: (a) TOC and (b) TN and (c) TOC/TN during the composting of MSW (markers: measured values; lines: mean values).
Agriculture 12 02058 g003
Agriculture 12 02058 g004 550
Figure 4. Changes in: (a) HSC, WEOC, CAC and CALK, and (b) CCEL and CR during the composting of MSW (markers: measured values; lines—mean values).
Figure 4. Changes in: (a) HSC, WEOC, CAC and CALK, and (b) CCEL and CR during the composting of MSW (markers: measured values; lines—mean values).
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Agriculture 12 02058 g005 550
Figure 5. Changes in the share of the organic carbon of the extracted fractions in relation to TOC during the experiment.
Figure 5. Changes in the share of the organic carbon of the extracted fractions in relation to TOC during the experiment.
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Table
Table 1. Correlation coefficients between the investigated chemical properties and the basic composting parameters (time, temperature moisture) in the studied samples.
Table 1. Correlation coefficients between the investigated chemical properties and the basic composting parameters (time, temperature moisture) in the studied samples.
ParameterTimeTemperatureMoistureTOCTNHSCWEOCCACCCELCALKCR
Time-ns−0.587−0.9740.915−0.861−0.930−0.927−0.9800.895−0.951
Temperaturens-0.593−0.5750.519−0.583−0.494−0.682nsnsns
Moisture−0.5870.593-0.4960.487nsns0.5100.5290.6030.517
TOC−0.974−0.5750.496-−0.9320.8970.9490.9300.960−0.9340.992
TN0.9150.5190.487−0.932-−0.884−0.950−0.929−0.8660.924−0.914
HSC−0.861−0.583ns0.897−0.884-0.9560.8290.879−0.9240.853
WEOC−0.930−0.494ns0.949−0.9500.956-0.9360.914−0.9790.915
CAC−0.927−0.6820.5100.930−0.9290.8290.936-0.881−0.9120.906
CCEL−0.980ns0.5290.960−0.8660.8790.9140.881-−0.8800.928
CALK0.8950.5120.603−0.9340.924−0.924−0.979−0.912−0.880-−0.915
CR−0.951−0.5420.5170.992−0.9140.8530.9150.9060.928−0.915-
Significant at p < 0.05; ns—not significant.
Table
Table 2. Changes in means and standard deviations for the replicates at defined sampling times and LSD (p < 0.05) for the 90-day period of investigated chemical properties.
Table 2. Changes in means and standard deviations for the replicates at defined sampling times and LSD (p < 0.05) for the 90-day period of investigated chemical properties.
Composting TimeParameterTOCTNHSCWEOCCACCCELCALKCR
[Days][g kg−1]
1Mean352.6610.9519.4129.8518.7385.4328.02171.22
St. dev12.700.410.710.540.341.550.5111.81
14Mean316.9311.5511.4123.3718.2677.4930.44155.96
St. dev1.460.540.660.490.382.080.642.43
28Mean292.0811.669.9919.1419.3171.8935.50136.25
St. dev2.770.490.070.570.573.021.052.91
45Mean263.3113.266.267.5312.0869.5941.76126.10
St. dev2.490.110.110.280.121.221.302.53
56Mean232.8513.505.707.0110.4665.8244.8499.02
St. dev1.450.280.210.270.241.800.382.18
70Mean185.6813.775.135.228.9261.7345.3859.30
St. dev1.650.260.270.280.621.570.670.10
90Mean175.7014.334.462.819.3954.8445.9258.27
St. dev0.720.210.180.200.521.060.590.80
107Mean168.7314.234.052.136.5549.5545.0561.39
St. dev1.140.250.090.210.570.760.480.35
LSD16.621.211.311.341.594.762.6415.77
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Bekier, J.; Jamroz, E.; Dębicka, M.; Ćwieląg-Piasecka, I.; Kocowicz, A. Quantitative Carbon Changes of Selected Organic Fractions during the Aerobic Biological Recycling of Biodegradable Municipal Solid Waste (MSW) as a Potential Soil Environment Improving Amendment—A Case Study. Agriculture 2022, 12, 2058. https://doi.org/10.3390/agriculture12122058

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Bekier J, Jamroz E, Dębicka M, Ćwieląg-Piasecka I, Kocowicz A. Quantitative Carbon Changes of Selected Organic Fractions during the Aerobic Biological Recycling of Biodegradable Municipal Solid Waste (MSW) as a Potential Soil Environment Improving Amendment—A Case Study. Agriculture. 2022; 12(12):2058. https://doi.org/10.3390/agriculture12122058

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Bekier, Jakub, Elżbieta Jamroz, Magdalena Dębicka, Irmina Ćwieląg-Piasecka, and Andrzej Kocowicz. 2022. "Quantitative Carbon Changes of Selected Organic Fractions during the Aerobic Biological Recycling of Biodegradable Municipal Solid Waste (MSW) as a Potential Soil Environment Improving Amendment—A Case Study" Agriculture 12, no. 12: 2058. https://doi.org/10.3390/agriculture12122058

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