Search Results (17)

This study aims to explore anaerobic co-digestion (AcoD) of cassava (EUM) and poultry (FP) effluents using one inoculum/substrate ratio (30%) and three EUM vs. FP substrate composition ratios (25:75, 50:50, and 75:25). The AcoD process was therefore designed for 20 L batch digesters, under mesophilic conditions, with less than 5% total solids for 66 days. The results showed that EUMs were highly resistant to degradation, while FPs were the most easily degradable. Kinetic analysis indicated specific organic matter (MO) reduction rates of 0.28% per day for EUM and 0.76% per day for FP. EUM alone produced 45.47 mL/g MO, while the 50:50 substrate produced 1184.60 mL/g MOV. The main factors contributing to EUM inefficiency were the inability to tame acidic conditions and the accumulation of volatile fatty acids. AcoD produced 23 to 50 times more methane than EUM alone, 2 to 5 times more than FP alone, and 2 to 4 times more than inoculum. As a result, the AcoD of both types of waste had a qualitative and quantitative effect on biogas production. CH₄ content increased from around 2 to 75%, depending on the amount of organic nitrogen added. The addition of nitrogen by AcoD, even under mesophilic conditions, improves the kinetics and quality of anaerobic digestion of low-nitrogen substrates. Its impact on thermophilic and psychrophilic conditions needs to be verified. Full article

This study endeavors to develop an economical and user-friendly biological sulfide oxidation system and explore its mechanism for generating biological elemental sulfur under micro-aerobic conditions using psychrophilic anaerobically digested media (liquid/solid inoculums obtained from agricultural livestock wastes) for sulfide-free biogas production. With an initial hydrogen sulfide concentration of 5000 ppm, a biogas flow rate ranging from 0.9 to 1.8 L/h-L_inoculum-mix, and an air injection rate of 0.6–1% (oxygen concentration in biogas), a remarkable biodesulfurization efficiency of 99–100% was attained using solid inoculum as the biodesulfurization medium. This efficiency was achieved without compromising the methane quality in the treated biogas. Compared to liquid inoculum, solid inoculum requires less than half the volume and no mixing equipment, such as bubble column reactors. The biodesulfurization reactor requires only 1 m³, which is approximately 1.5% of the volume of a wet anaerobic digester and 3% of a dry anaerobic digester, while processing cow manure (Total Solids: 20%) at 1.03 m³ of manure per day. Moreover, it can be operated at (19–20 °C), leading to substantial reductions in cost and footprint. Full article

At psychrophilic temperatures (<20 °C), anaerobic digestion produces less methane (CH₄). For psychrophilic anaerobic digestion (PAD) to be successful, investigation of cold-adapted microbial consortia involved in methane production is critical. This study aimed to investigate the microbial community driving enhanced methane production from the cold-adaptation process and bioaugmentation of PAD with cold-adapted inoculum (BI). Microbial consortia in cattle manure (CM) and food waste (FW) were adapted and applied during batch PAD of CM and FW to bioaugment methane production at 15 °C. Cold adaptation and PAD with BI resulted in cumulative specific methane yields of 0.874 ± 0.231 and 0.552 ± 0.089 L CH₄ g⁻¹ volatile solids, respectively, after 14 weeks, while the absence of BI (control) led to acidification and no methane production during PAD. Following 16S rRNA V4–V5 amplicon sequencing and metagenomic analyses, Methanosarcina was revealed as a key driver of methanogenesis during cold adaptation and PAD bioaugmentation. Furthermore, based on the predictive functional and metabolic analysis of the communities, possible synergies were proposed in terms of substrate production and utilization by the dominant microbial groups. For instance, during methane production, Bacteroides and Methanobrevibacter were possibly involved in a syntrophic relationship, which promoted methanogenesis by Methanosarcina. These findings provide insight into the prospective microbial synergies that can be harnessed and/or regulated in cold-adapted inoculum for the improvement of methane production during PAD. Full article

Psychrophilic anaerobic digestion emerges as an appealing integrated solution for the management of agricultural waste, particularly for farmers in regions where the average temperature does not exceed 26 °C, as seen in coffee cultivation. Therefore, this study seeks to assess the biomethane potential of thermochemical-treated coffee husk through psychrophilic anaerobic digestion (C3-20 °C-w/pretreatment). To examine its viability, outcomes were compared with reactors operating at both mesophilic (C1-35 °C) and psychrophilic (C2-20 °C) conditions, albeit without the use of pretreated coffee husk. The C3-20 °C-w/pretreatment test demonstrated a 36.89% increase (150.47 NmL CH₄/g VS; 161.04 NmL CH₄/g COD), while the C1-35 °C test exhibited a 24.03% increase (124.99 NmL CH₄/g VS; 133.77 NmL CH₄/g COD), both in comparison to the C2-20 °C test (94.96 NmL CH₄/g VS; 101.63 NmL CH₄/g COD). Notably, the C3-20 °C-w/pretreatment trial yielded superior outcomes, accompanied by an associated energy output of 3199.25 GWh/year, sufficient to meet the annual energy demands of 494 residences. This marks an increase of 83 and 182 million residences compared to the mesophilic and psychrophilic AD of CH without pretreatment, respectively. Full article

Food waste has emerged as a pressing concern, and thus advanced techniques to valorize food waste into nutrition rich materials as well as renewable energy are highly important. The exceptional biodegradability of food waste renders it a highly suitable substrate for anaerobic treatment. This leads to energy production and a reduction in the carbon footprint. Nevertheless, in frigid territories like Canada, the conventional mesophilic anaerobic digestion at 30–40 °C can require substantial amounts of energy. Consequently, this study introduces a new approach to treat food waste at psychrophilic temperatures (1–20 °C). Lower temperatures can negatively impact cellular processes during anaerobic treatment, rendering substrates less accessible to microscopic organisms. To address this challenge associated with lower temperatures, the study introduces an innovative biogas recirculation strategy. The primary objectives of this study are to assess the viability of anaerobic treatment for food waste at psychrophilic temperatures and to investigate the effectiveness of reintroduction of the produced biogas to the anaerobic system in enhancing biomethane generation and stability of the system. Batch experiments were conducted on food waste in various assessments, both with and without biogas recirculation. The outcomes revealed a methane concentration ranging from 68% to 93% when biogas recirculation was employed, whereas without this technique, methane concentration varied between 10% and 45%. Moreover, with biogas recirculation, the reduction in volatile solids reached a maximum of 92%, and there was an 82% decrease in chemical oxygen demand. In conclusion, the utilization of the recirculation of biogas at the psychrophilic temperature range enhanced biomethane production and reduction of volatile solids and chemical oxygen demand. This study underscores the potential of employing anaerobic treatment with reintroduction of produced biogas into the system in cold regions as an economically viable and sustainable choice for treating food waste with nominal energy consumption. Full article

The rapid growth of the Malaysian poultry and palm oil industries has led biomass waste generation in abundance specifically chicken manure and empty fruit bunch (EFB). Anaerobic digestion (AD) is a circular economy-based approach which converts chicken manure and EFB into biogas which can be utilized for heating and power generation. Operating temperature is an imperative consideration for AD hence the objective of the study is to evaluate the effect of different temperature profiles namely, psychrophilic (20 °C), mesophilic (35 °C) and thermophilic (50 °C) on AD of chicken manure and EFB. The kinetic parameters are also evaluated using five kinetic models to enable readers to comprehend the kinetic behaviours of the systems. The volume and composition of biogas is measured every five days for a 50-day retention time. The findings observed that mesophilic condition is the most favourable with cumulative methane, CH₄ composition of up to 17.07%, almost two folds that of thermophilic (9.12%) and five folds that of psychrophilic (3.49%). The CH₄ generation rate, R_b based on the modified Gompertz model which is deemed the best fit further supports these findings as the R_b under mesophilic condition is significantly higher (0.330 mL/g_vs day) compared to psychrophilic (0.088 mL/g_vs day) and thermophilic (0.120 mL/g_vs day) conditions. Full article

Yersinia enterocolitica and Y. pseudotuberculosis are Gram-negative, facultative anaerobic bacteria that cause yersiniosis—one of the most important zoonotic diseases of the digestive tract. The aim of this study was to determine the prevalence of potentially human-pathogenic Y. enterocolitica and Y. pseudotuberculosis strains in free-living and farmed fallow deer, and to evaluate their sensitivity to chemotherapeutics. A total of 372 rectal swabs were analyzed, including 262 from free-living and 110 from farmed fallow deer. Due to the psychrophilic properties of Yersinia, two samples were collected from each animal. Seven Y. enterocolitica strains were isolated from free-living fallow deer, while two strains were isolated from farmed fallow deer. Yersinia pseudotuberculosis strains were not identified. All isolated Y. enterocolitica strains were ystB-positive, and phylogenetic analysis based on the nucleotide sequences of this gene revealed the presence of two phylogenetic groups. Yersinia enterocolitica strains isolated from fallow deer belonged to biotype 1A, and serotyping analysis demonstrated that the vast majority did not agglutinate with any diagnostic sera. All strains were multiple drug resistant and were not sensitive to at least four of the tested chemotherapeutics (amoxicillin with clavulanic acid, ampicillin, cefalexin, and streptomycin). One Y. enterocolitica strain isolated from a free-living animal was resistant to nine out of the 13 analyzed chemotherapeutics and was intermediately sensitive to the four remaining chemotherapeutics. The highest sensitivity was noted in case of ciprofloxacin (five strains) and trimethoprim-sulfamethoxazole (three strains). Only one strain isolated from a free-living animal was sensitive to three out of the 13 examined antibiotics, whereas the remaining strains were sensitive to only one drug or were not sensitive to any of the chemotherapeutics used. The results of this study indicate that multiple drug-resistant Y. enterocolitica strains can be carried by free-living and farmed fallow deer. This observation gives serious cause for concern because the meat of fallow deer and other ruminants is often consumed semi-raw (steak) or raw (tartar steak). Full article

The experiment was conducted using a single-stage steel biodigester of 75 L working volume, charged with 75% pig manure and 25% pine wood sawdust and operated under batch mode at a psychrophilic temperature range (13.16–24.69 °C). The total viable count was determined via the spread plate method on selective microbiological media to determine viable numbers of the selected bacterial pathogens in samples collected from the biodigesting chamber every seven or fourteen days over the duration of study. Multiple linear regression models including the log bacterial counts (response) and number of days, pH, and average daily temperature as predictors were developed using Matlab for each bacterium. The reduction (90–99.9%) in numbers of isolates of E. coli, Salmonella, Yersinia, Campylobacter, and Listeria varied with time (days) from their initial respective counts of 2 × 10⁶, 7 × 10⁴, 3 × 10⁵, 9 × 10⁵, and 1 × 10⁴ cfu/g to concentrations lower than the detection limit (DL = 10² cfu/g substrate). E. coli demonstrated the least resistance to the environmental conditions in the biodigester and survived only for 77 days, unlike L. monocytogenes that lasted for 175 days and was the most resistant bacterium. From the models, the number of days and temperature were directly and inversely related to log Listeria counts, respectively, contrary to the others. The predictors, number of days, pH, and average daily temperature, were described as either primary or secondary factors based on the bacteria via the reliefF test. Full article

Biogas is produced in Bangladesh mostly through fixed-dome anaerobic digesters, which usually operate without any temperature controller. An experiment was conducted to monitor the seasonal temperature variation inside a fixed-dome type digester and its effect on biogas composition. A commercial-scale digester with a working volume of 350 m³ was used for this study. Three k-type thermocouple sensors were used to monitor the ambient, biogas, and slurry temperatures in real-time. The results showed that the average ambient temperature in the autumn, late autumn, and winter was 29.05, 22.90, and 17.64 °C, respectively. The average slurry temperature in the autumn (30.38 °C) was higher than in the late autumn (29.36 °C) and in the winter (25.76 °C). The highest and lowest slurry temperatures were found to be 31.11 and 24.47 °C, respectively, which indicated that the digester worked within a wide temperature range, establishing both psychrophilic and mesophilic operational conditions. Higher methane concentrations were observed in the autumn than in the late autumn and winter. The CO₂ and H₂S concentrations were higher in the winter than those of in the autumn and late autumn. The electricity generation in the winter was 47.85% and 45.15% lower than in the autumn and late autumn, respectively. Full article

Small-scale anaerobic digestion (AD) can be an effective organic waste management system that also provides energy for small businesses and rural communities. This study measured fuel production from digestions of single and mixed feedstocks using an unheated, 2 m³ digester operated continuously in a temperate climate for over three years. Using local food waste, brewery waste, grease waste, and agricultural residues, this study determined that small-scale AD co-digestions were almost always higher yielding than single feedstocks during psychrophilic operation and seasonal temperature transitions. Agricultural residues from Miscanthus x giganteus had the greatest impact on biomethane production during co-digestion (4.7-fold greater average biogas %CH₄), while mesophilic digestion of brewery waste alone produced the most biogas (0.76 gCH₄ gVS⁻¹ d⁻¹). Biogas production during the transition from mesophilic to psychrophilic was temporarily maintained at levels similar to mesophilic digestions, particularly during co-digestions, but biogas quality declined during these temperature shifts. Full-time operation of small-scale, unheated AD systems could be feasible in temperate climates if feedstock is intentionally amended to stabilize carbon content. Full article

This study evaluates the anaerobic digestion (AD) of the organic fraction of municipal solid waste (OFMSW) and digested sewage sludge (DSS) at lowered temperatures. AD batch tests for CH₄ yield determination were carried out with DSS as inoculum between 23 and 40 °C. All results were related to organic dry matter and calculated for standard conditions (1013 hPa, 0 °C). The AD experiments at 40 °C and at 35 °C delivered specific CH₄ yields of 325 ± 6 mL/g and 268 ± 27 mL/g for OFMSW alone. At lower temperatures, specific CH₄ yields of 364 ± 25 mL/g (25 °C) and 172 ± 21 mL/g (23 °C) were reached. AD at 25 °C could be beneficial regarding energy input (heating costs) and energy output (CH₄ yield). Plant operators could increase AD efficiencies by avoiding heating costs. The co-digestion of OFMSW together with DSS could lead to further synergies such as better exploitation of the energy potentials of DSS, but the digestate utilization could become problematic due to hygienic requirements. Efficiency potentials through lowered operating temperatures are limited. In further research, lowered process temperatures could be applied in the AD of energy crops due to large numbers of existing plants. Full article

Most biogas plants in the world run under psychrophilic conditions and are operated by small and medium farmers. There is a gap of knowledge on the performance of these systems after several years of operation. The aim of this research is to provide a complete evaluation of a psychrophilic, low-cost, tubular digester operated for eight years. The thermal performance was monitored for 50 days, and parameters such as pH, total volatile fatty acid (tVFA), chemical oxygen demand (COD) and volatile solids (VS) were measured every week for the influent and effluent. The digester operated at a stabilized slurry temperature of around 17.7 °C, with a mean organic load rate (OLR) equal to 0.52 kg VS/m³_digester *d and an estimated hydraulic retention time (HRT) of 25 days. The VS reduction in the digester was around 77.58% and the COD reduction was 67 ± 3%, with a mean value for the effluent of 3.31 ± 1.20 g COD/Lt, while the tVFA decreased by 83.6 ± 15.5% and the presence of coliforms decreased 10.5%. A BioMethane potential test (BMP) for the influent and effluent showed that the digester reached a specific methane production of 0.40 Nm³CH₄/kg VS and a 0.21 Nm³CH₄/m³_digester d with 63.1% CH₄ in the biogas. These results, together with a microbiological analysis, show stabilized anaerobic digestion and a biogas production that was higher than expected for the psychrophilic range and the short HRT; this may have been due to the presence of an anaerobic digestion microorganism consortium which was extremely well-adapted to psychrophilic conditions over the eight-year study period. Full article

The excessive H₂S presence in water and wastewater can lead to corrosion, toxicity, and biological processes inhibition—i.e., anaerobic digestion. Production of H₂S can occur in psychrophilic conditions. Biological removal of HS⁻ by addition of NO₃⁻ as an electron acceptor under psychrophilic (10 °C) conditions in a continuous flow experiment is evaluated here. Four different N/S molar ratios—0.35, 0.40, 0.60, and 1.30—were tested in an expanded granular sludge bed (EGSB) reactor. Samples were analyzed daily by ion chromatography. Efficient psychrophilic HS⁻ removal with sulfur products oxidation control by NO₃⁻ supply is documented. The highest HS⁻ removal was obtained at N/S = 0.35 and 1.30 (89.1 ± 2.2 and 89.6 ± 2.9%). Removal of HS⁻ was less at mid-N/S with the lowest value (76.9 ± 2.6%) at N/S = 0.60. NO₃⁻ removal remained high for all N/S ratios. N/S molar ratio influenced the sulfur products distribution with less S⁰ and increase in SO₄²⁻ effluent concentration with increasing N/S ratio. Oxidation of HS⁻ and accumulated S⁰ occurred simultaneously at N/S ratios >0.35. The observations are explained by culture flexibility in utilizing available resources for energy gain. Full article

Increasing the feed total solids to anaerobic digester improves the process economics and decreases the volume of liquid effluent from current wet anaerobic digestion. The objective of this study was to develop a novel psychrophilic (20 °C) anaerobic digestion technology of undiluted cow feces (total solids of 11%–16%). Two sets of duplicate laboratory-scale sequence batch bioreactors have been operated at organic loading rates (OLR) of 6.0 to 8.0 g total chemical oxygen demand (TCOD) kg⁻¹ inoculum day⁻¹ (d⁻¹) during 210 days. The results demonstrated that the process is feasible at treatment cycle length (TCL) of 21 days; however, the quality of cow feces rather than the OLR had a direct influence on the specific methane yield (SMY). The SMY ranged between 124.5 ± 1.4 and 227.9 ± 4.8 normalized liter (NL) CH₄ kg⁻¹ volatile solids (VS) fed d⁻¹. Substrate-to-inoculum mass ratio (SIR) was 0.63 ± 0.05, 0.90 ± 0.09, and 1.06 ± 0.07 at OLR of 6.0, 7.0, and 8.0 g TCOD kg⁻¹ inoculum d⁻¹, respectively. No volatile fatty acids (VFAs) accumulation has been observed which indicated that hydrolysis was the rate limiting step and VFAs have been consumed immediately. Bioreactors performance consistency in terms of the level of SMYs, VFAs concentrations at end of the TCL, pH stability and volatile solids reduction indicates a stable and reproducible process during the entire operation. Full article

Degrading antibiotics discharged in the livestock manure in a well-controlled bioprocess contributes to a more sustainable and environment-friendly livestock breeding. Although most antibiotics remain stable during manure storage, anaerobic digestion can degrade and remove them to various extents depending on the concentration and class of antibiotic, bioreactor operating conditions, type of feedstock and inoculum sources. Generally, antibiotics are degraded during composting > anaerobic digestion > manure storage > soil. Manure matrix variation influences extraction, quantification, and degradation of antibiotics, but it has not been well investigated. Fractioning of manure-laden antibiotics into liquid and solid phases and its effects on their anaerobic degradation and the contribution of abiotic (physical and chemical) versus biotic degradation mechanisms need to be quantified for various manures, antibiotics types, reactor designs and temperature of operations. More research is required to determine the kinetics of antibiotics’ metabolites degradation during anaerobic digestion. Further investigations are required to assess the degradation of antibiotics during psychrophilic anaerobic digestion. Full article