Anaerobic Digestion Research Articles

A novel tubular single-chamber microbial electrolysis cell for efficient methane production from industrial potato starch wastewater

The integration of microbial electrolysis cells (MEC) with anaerobic digestion (AD) shows great promise for enhancing methane production from high-COD wastewater. However, an efficient MEC-AD reactor design remains elusive. Here, a novel tubular single-chamber MEC-AD reactor was constructed to treat potato starch wastewater (COD over 20000mg/L). The concentric and compact design of the stainless-steel cathode and anode reduced internal resistance, resulting in enhanced methane production. Applying -0.2V vs. Ag/AgCl to the anode increased methane production by 1.73 times compared to the open circuit and halved hydraulic retention time. Moreover, the reactor achieved an average methane content of 82.57%, which was 23.89% higher than the open circuit. The reactor showed a total COD removal of 92.2%, which was 24% higher than the open circuit. Additionally, base consumption to maintain pH was reduced to one-sixth of that in conventional AD, preventing volatile fatty acid accumulation. Microbial analysis showed Geobacter (63.4%) and Methanobacterium (96.8%) were highly enriched in the anode and cathode biofilms, respectively. The proportion of fermentative bacteria also increased in the MEC-AD system. These results demonstrate the effectiveness of the tubular single-chamber MEC-AD reactor in enhancing methane production from potato starch wastewater, with strong potential for scale-up applications.

Robust methane production from anaerobic digestion of maize silage: Feeding control using sliding mode control strategy with Anaerobic Digestion Model N°01

This paper introduces a robust control approach based on the Sliding Mode Control (SMC) strategy for the AD process. We use the Anaerobic Digestion Model N°01 (ADM1), the most detailed and comprehensive model for AD, as a virtual AD plant. The proposed control scheme is derived from a reduced model. This control law uses the state variables of the reduced AM2HN model as well as the stoichiometric and kinetic parameters. An interface block between the ADM1 and AM2HN state variables has been designed in a closed loop. The performance of SMC has been enhanced by the use of a low-pass filter, which completely eliminates chattering and provides smooth dilution rates (chatter-free) while rapidly reaching the target methane production (in less than 5 days) in a noisy environment.

Cobalt-modified digestate-derived biochar enhances kitchen waste anaerobic dry digestion: Performance, microbial mechanisms, and metabolic pathways

To achieve simultaneous in-situ high-value utilization of digestate and efficient resource recovery of kitchen waste (KW). In this work, Co-modified digestate-derived biochar (DDB-Co) was prepared for the first time, the effects of DDB-Co on KW mesophilic dry anaerobic digestion were investigated, and the underlying mechanisms were elucidated. The results showed that the specific surface area of DDB-Co increased to 98.7 m2/g, which was 37.4 % higher than that of the unmodified group (DDB). DDB-Co exhibited a dose-dependent effect on biogas production from the KW dry digestion, with the optimal dose of 4.0 g/L (calculated on a solid content) DDB-Co yielding 205.3 mL/(g·VS) of biogas, representing an 80.9 % increase compared to the CK group. However, higher doses, such as 8.0 g/L DDB-Co, reduced the cumulative biogas production. Mechanistic analysis indicated that 4.0 g/L DDB-Co facilitated the dissolution of particulate organic matter and accelerates the conversion process of volatile fatty acids (VFA) in KW, thereby preventing excessive acidification. Microbial community structure analysis revealed that DDB-Co reduced microbial richness and diversity but selectively enriched microorganisms such as Lactobacillus and Methanothrix, accelerating the direct interspecific electron transfer (DIET) reaction rate and increasing biogas production. Metagenomic analysis demonstrated that DDB-Co primarily upregulated the relative abundances of key enzymes in the acetate decarboxylation methanogenesis pathway, such as acetate kinase (ackA), phosphate acetyltransferase (pta), and acetyl-CoA synthetase (acs), enhancing biogas yield and maintaining system stability. The findings of this work expand the high-value utilization pathways for digestate and provide an alternative solution for the efficient resource recovery of KW.

Effects of different quorum sensing signal molecules on alleviation of ammonia inhibition during biomethanation

Anaerobic digestion (AD) is a promising technology for achieving both organic wastes treatment and energy recovery. However, challenges such as ammonia inhibition still remain. Quorum sensing (QS) system is relevant with the regulation of microbial community behaviors by releasing and sensing signal molecules, which could improve methane production during AD process. Therefore, the current study explored the effects of different quorum sensing signal molecules on alleviation of ammonia inhibition. The results showed that both secretion of N-butyryl-DL-homoserine lactone (C4-HSL) and N-(β-ketocaproyl)-DL-homoserine lactone (3OC6-HSL) could be inhibited by high ammonia stress while stimulation of N-hexanoyl-L-homoserine lactone (C6-HSL) and N-octanoyl-DL-homoserine lactone (C8-HSL) secretion might be triggered by ammonia toxicity. Moreover, the alleviation of ammonia inhibition could be achieved by both introducing 3OC6-HSL (0.5 μM) and combination of 3OC6-HSL (0.1 μM) and biochar (4 g/L). Exogenous 3OC6-HSL could regulate microbial social behaviors and enhance the secretion of extracellular polymeric substances (EPS) to promote anaerobic digestion. In addition, the mitigation of ammonia inhibition through exogenous 3OC6-HSL and biochar were confirmed by microbial community changes (Methanobacterium, Propionicicella and Petrimonas). Critical enzymes involved in both acidification and methanogenic steps were enhanced after adding the combination of 3OC6-HSL and biochar. The combination of low levels of 3OC6-HSL and biochar could promote both direct interspecies electron transfer (DIET) process and communication between different anaerobic microorganisms to mitigate ammonia inhibition. The current study will provide primary insights for conquering ammonia inhibition during biomethanation.

Effects of quaternary ammonium disinfectants on human pathogenic bacteria in anaerobic sludge digestion: Dose-response and resistance variation

Sewage sludge is a critical reservoir for biological pollutants, and its harmless disposal remains a major issue. Quaternary ammonium compounds (QACs) as typical household disinfectants are inevitably concentrated in sewage sludge, and have the potential to affect human pathogenic bacteria (HPBs) that remain poorly understood. This study found that the relative abundance of HPBs in digesters was decreased by 10 − 20 % at low QACs dose, but increased by 238 − 591 % at high QACs dose. Mechanistic analysis revealed that low QACs doses promoted functional hydrolytic/fermentative bacteria and their metabolism by stimulating extracellular polymeric substances secretion and enhancing resistance to QACs. Conversely, high QAC doses decreased microbial biomass and developed QACs and antibiotic resistance of HPBs by increasing cell membrane permeability and triggering oxidative stress, resulting in deteriorating sanitation performance. These findings provide advanced insights into the potential function and hazards of exogenous QACs on the biosafety of digestate.

Efficient resource recovery from food waste digestate via hydrothermal treatment and its application as organic fertilizer

With the continuous recognition of green, organic and non-polluting products, organic fertilizers play an increasingly vital role in agricultural production. Among them, hydrochar-based organic fertilizer has attracted widespread attention recently. The present study evaluated the potential of digestate from anaerobic digestion of food waste for the preparation of hydrochar-based organic fertilizer by straw-based, FeCl3-catalyzed hydrothermal carbonization (HTC). Under the optimal conditions, a hydrochar-based organic fertilizer with > 25 wt% humus content and limited pollution risk was successfully prepared. The pot experiment demonstrated the feasibility of improving the physicochemical properties of red soil and promoting crop growth after adding hydrochar in place of commercial fertilizer. In addition, the function of zeolite on nutrient recovery in hydrothermal liquid (HTL) was analyzed, and preparing the slow-release organic fertilizer by mixing the nutrient-rich zeolite with hydrochar in a mass ratio of 1:4 was proposed. This work has significant implications for achieving the efficient resource recovery of digestate.

Facultative anaerobic bacteria enable syntrophic fatty acids degradation under micro-aerobic conditions.

Trace amounts of oxygen stimulate facultative anaerobic bacteria (FAB) within anaerobic bioreactors, which was shown to correlate with enhanced methane production from long-chain fatty acids. The relationship between FAB and fatty acid-degrading syntrophic communities under micro-aerobic conditions is still not clear. In this work, two syntrophic co-cultures, Syntrophomonas wolfei + Methanospirillum hungatei and Syntrophomonas zehnderi + Methanobacterium formicicum, were assembled and incubated with short, medium and long-chain fatty acids, with 0-10 % O2, in the presence and absence of FAB, here represented by Pseudomonas spp. Without Pseudomonas, the syntrophic activity was inhibited by 79 % at 0.5 %O2, but with Pseudomonas, the syntrophic co-cultures successfully converted the fatty acids to methane with up to 2 %O2. These findings underscore the pivotal role of FAB in the protection of syntrophic fatty acid-degrading communities under micro-aerobic conditions and emphasizes its significance in real-scale anaerobic digesters where strictly anaerobic conditions may not consistently be maintained.

Strategic carbon emission assessment in sludge treatment: A dynamic tool for low-carbon transformation

The carbon–neutral target presents a significant challenge for the sewage sludge treatment and disposal (SSTD) industry, necessitating strategic planning for a low-carbon transition. However, flexible and comprehensive carbon emission analysis tools to support this goal remain lacking. This study presents a carbon emission analysis tool to evaluate the carbon emission characteristics and future mitigation potentials of SSTD. The tool integrates life cycle inventory (LCI) modeling-based analysis, sensitivity analysis, regression analysis, and scenario analysis. Carbon emissions are dynamically calculated based on sludge properties, technological level, and industry external parameters, providing a foundation for adaptable evaluation tailored to local conditions. The framework considers the potential effects of multi-parameter and multi-aspect changes in scene design, both within and outside the industry, to achieve dynamic and comprehensive simulations. A case study conducted in Wuhan, China, demonstrated the usability and application processes of the framework. The results indicated that carbon emissions from SSTD are projected to more than double from 2021 to 2060 without interventions. Among the mitigation measures, energy and chemical savings would yield the largest reduction potential, followed by the technical layout adjustment and the promotion of energy efficiency. Operational optimization in the sludge industry and outside the industry would contribute the least. With all mitigation measures applied, emissions could decrease to –82.91 kt CO2-eq in 2060, equivalent to 13.03% compensation for emissions from the sewage treatment line. Among all the processes, incineration routes are recommended due to their current and future low carbon emissions. The cooperative resource route of anaerobic digestion and land use also shows promise as it progressively demonstrates superior performance with increasing organic matter and nutrient content of sludge. Critical factors, sub-processes, and emission types for different routes were identified and can be optimized accordingly. The developed method demonstrates sufficient flexibility to be applied to other cities and larger-scale regions, thereby offering technical and strategic support for SSTD towards carbon–neutral operation.

Optimizing anoxic/oxic intervals in intermittent aeration for STHP-AD filtrate treatment: Restoring partial nitrification and community dynamics in the SPNAD system

Currently, partial nitrification (PN) processes are commonly used to improve efficiency in high ammonia nitrogen wastewaters. However, initiating and restoring damaged PN performance is crucial for optimizing nitrogen removal efficiency without the use of chemical additives. In this study, a simultaneous partial nitrification and denitrification coupled with anammox (SPNAD) sequencing batch biofilm reactor was constructed to treat anaerobic digestion after sludge thermal hydrolysis pretreatment (STHP-AD) filtrate. The PN performance was successfully recovered through optimizing the operation mode of anoxic/oxic alternation within 120 days. Result showed that Nitrosomonas increased from 0.68 % to 3.43 %, while Nitrospira decreased to 0.06 %. The PN recovery also promoted anammox, with the only anammox bacterium of Candidatus Brocadia, detected in the mixing and biofilm sludge of 1.73 % and 1.41 %, respectively. The autotrophic denitrifying bacteria Thermomonas (increasing from 0.47 % to 23.85 %) and Truepera (rising from 2.31 % to 6.54 %) rapidly accumulated. After adjusting to the anoxic/oxic alternation ratio, the hydraulic retention time was shortened from 50 h to 37.5 h, and the oxic time was reduced to half of the initial operation. The PN recovery and anammox enrichment resulted in improving nitrogen removal approximately 20 %. Eventually, the SPNAD system realizes stable and efficient nitrogen removal with the influent nitrogen loading rate of 0.43 kgN/(m3·d), the ammonium removal efficiency of 94.73 ± 3.27 %, and the nitrogen removal efficiency of 72.98 ± 1.27 %. In this study, a new strategy using intermittent aeration while appropriately extending the oxic time was proposed to restore the system’s ability to treat STHP-AD filtrate after PN disruption.

Solid-state anaerobic digestion of sweet corn waste: The effect of mixing and recirculation interval

The mixing and sludge recirculation interval is one of the key successes of the solid-state anaerobic digestion process, a promising technology for converting high-solid agro-industrial wastes to renewable energy. This study employed a pilot-scale completely stirred tank reactor to examine biogas production from sweet corn waste, including corn cobs, husks, and seeds. The reactor was operated as solid-state anaerobic digestion at an ambient temperature. The mixing and recirculating intervals were set to non-mixing and mixing for 10 minutes every 3, 6, and 12 hours. The initial total solid of the feedstock was 25%, while the hydraulic retention time was 30 days. The results showed that during the mixing and recirculation every three hours, the highest chemical oxygen demand, total solid, and volatile solid (VS) removal efficiencies were 85.42%, 62.92%, and 64.59%, respectively. The ratio between volatile fatty acid and alkalinity ranged between 0.20 and 0.30 without any sign of system failure. The highest specific methane yield of 766 L/kg VSadded was obtained in the experiment with mixing and recirculating intervals every 3 hours. It was found that the modified Gompertz model could effectively fit the methane yields with an R2 of 0.9667. The modeled methane production potential and the maximum methane production rate were 867.40 NL/kg VSadded and 132.01 NL/kg VSadded-d, respectively. Additionally, the levelized cost of the biogas produced from the solid-state anaerobic digestion of the sweet corn waste was calculated to be 0.61 USD/kg. The findings of this study can serve as a guide for the design and operation of the SS-AD system, which aims to transform various types of lignocellulosic waste into environmentally friendly energy.

Valorization of paper-mill sludge laden with 2-chlorotoluene using hydroxyapatite@biochar nanocomposite to enrich methanogenic community: A techno-economic approach

While several studies have investigated the anaerobic digestion of paper-mill sludge (PMS), this technology suffers from nutrient insufficiency, inhibition by aromatic compounds, and low bio-CH4 yield. Hence, PMS was anaerobically co-digested with chicken manure (CM) and supplemented by hydroxyapatite@biochar (HAP@BC) nanocomposite for enhancing 2-chlorotoluene degradation and enriching the methanogenic archaea. Multiple continuous stirred tank reactors (CSTRs) were operated at 12.6 h hydraulic retention time (HRT), using PMS (R1), CM (R2), PMS + CM (R3), PMS + CM+100 mg HAP/L (R4), and PMS + CM+100 mg HAP@BC/L (R5). The maximum bio-CH4 yield of 147.5 ± 9.1 mL/g COD and 2-chlorotoluene removal of 91.2 ± 6.8 % were obtained from R5, experiencing a sufficient C/N ratio of 14.7 and the highest activities of acidogenesis (42.0 %), acetogenesis (37.9 %), and methanogenesis (42.1 %). The abundances of Euryarchaeota, Bacteroidota, and Chloroflexi at the phylum level, and Pseudomonas, and Bacillus at the genus level could highly contribute to the dechlorination mechanism and acetate transformation into CH4. This biomass-to-bioenergy project (10 m3/d capacity) could benefit from pollution reduction, biogas recovery, and carbon credit, giving 5.6 yr payback-period, 3503 USD net present value, and 12.1 % internal rate of return. Because R5 exhibited an efficient techno-economic anaerobic biodegradation performance, future studies are required to optimize its HRT condition and HAP@BC dosage.

The effect of Fenton sludge on anaerobic digestion of papermaking wastewater in an upflow anaerobic sludge blanket reactor

An upflow anaerobic sludge blanket (UASB) reactor was used to investigate the effect of adding Fenton sludge (FS) on the anaerobic digestion of actual papermaking wastewater. The results showed that a one-time addition of 10 g/L FS could sustainably promote the performance of UASB for more than 40 days. The organic matter removal efficiency increased by 15.56%, and the biogas production increased by 24.52%. The proportion of methane in biogas increased by 12.87%. Adding FS increased the capacitance values of sludge extracellular polymeric substances and the electron transfer system activity in reactor increased by 1.76 times. The dehydrogenase activity and coenzyme F420 of the sludge increased by 1.54 and 2.11 times, respectively. Adding FS enriched the iron-reducing bacteria (Thermodesulfobacteriota) and hydrolytic acid-producing bacteria (Chloroflexota and Synergistota), thereby promoting the hydrolysis and acidification process. Adding FS was beneficial to the enrichment of methanogen, especially Methanosaeta, significantly increasing the methane production.

Integration of biogas and liquid recirculation enhance methane production in high-solid anaerobic digestion of pig manure and rice husks

High-solid anaerobic digestion (HSAD) is a promising technology for treating livestock manure and agricultural waste; however, the wide application has been limited due to homogenization problems. This study established a novel HSAD system by integrating liquid and biogas recirculation (RBL), aiming to enhance the biogas conversion efficiency of high-solid substrates at low costs. Results showed that the highest methane yield was 357 mL/gVSadded in the novel HSAD system (RBL), 30.7 % and 251.7 % higher than those with only liquid recirculation (RL) or with no recirculation (RNo). Biogas recirculation helped enhance dissolution and degradation of organic matter, and prevented the VFAs accumulation, contributing to the enhanced methane production in the novel HSAD system. The net electric energy benefit of RBL was 301.2 kWh for treating 1-ton raw materials, suggesting the high economic feasibility of the novel HSAD system for the sustainable treatment of high-solid organic wastes.

Optimizing feedstock organic composition to regulate humification and heavy metal passivation during solid-state anaerobic digestion

This study uncovered the impacts of feedstock organic composition, comprising proteins, lignocellulose, and lipids, on humification and passivation of heavy metals (HMs) in solid-state anaerobic digestion (SSAD). Mantel tests and partial least squares structural equation modeling (PLS-SEM) results revealed that copper (Cu) and zinc (Zn) passivation predominantly occurred through complexation with humic acid (HA). In contrast, lead (Pb) and chromium (Cr) passivation were pH-dependent as influenced by substrate conditions in SSAD. Increasing protein content in the feedstock facilitated lignocellulose biodegradation to enhance HA formation, and thus augmenting Cu and Zn passivation. Furthermore, the improved biodegradation of organic components elevated the substrate pH, further enhancing Pb and Cr passivation. Such improvement was notable when the protein: lignocellulose: lipid ratio of feedstock was regulated to 4.1:3.7:2.2, which increased HA contents to 35.25% and pH to 9 to enhance the passivation of Cu, Pb, and Cr by 0.48%, 52.0%, and 17.9%, respectively.

Mechanism of extracellular polymeric substance production and its contribution to anaerobic digestion foaming: Insights from cellular signalling

Mechanism of extracellular polymeric substance production and its contribution to anaerobic digestion foaming: Insights from cellular signalling

Bioaugmented ensiling pretreatment to improve bioconversion of sweet sorghum: Effect of bio-additives on enzymatic saccharification and biomethane potential

This study proposes a novel strategy to integrate ensiling preservation with pretreatment of sweet sorghum (SS) biomass. Bio-additives, including cellulase, xylanase, liquid anaerobic digestate (LD), and rumen fluid (RF) were applied in ensiling process to improve the silage quality, sugar production by enzymatic hydrolysis, and anaerobic biomethane production of SS. Compared with others additives, LD could alter microbial community compositions and reduce the crystallinity of SS, thus improving ensiling pretreatment performance and achieving the highest reducing sugar yield of 84.73%. The methane production of LD silages was increased by 32.84% compared with the un-ensiled SS, indicating that ensiling pretreatment with LD could be an effective strategy to achieve the trans-seasonal preservation and improving the methane production of SS. Furthermore, taking techno-economic factors into account (energy net income of 96.07 USD/ton), LD additive was recommended for the bioaugmented ensiling pretreatment and downstream methane production of SS, which also contribute to recirculate the liquid digestate from biogas plant.

Deciphering the function of Fe3O4 in alleviating propionate inhibition during high-solids anaerobic digestion: insights of physiological response and energy conservation

Deciphering the function of Fe3O4 in alleviating propionate inhibition during high-solids anaerobic digestion: insights of physiological response and energy conservation

Soil application potential of post-sorbents produced by co-sorption of humic substances and nutrients from sludge anaerobic digestion reject water

This study introduces a novel soil conditioning approach using humic substances (HSs) and nutrients co-recovered from reject water from sewage sludge anaerobic digestion. For the first time, HSs and nutrients were simultaneously recovered through sorption on low-cost, environmentally inert materials: natural rock opoka (OP) and waste autoclaved aerated concrete (WAAC). This innovative application of OP and WAAC as carriers and delivery agents for soil-relevant substances offers potential for resource recovery and soil conditioning. Results indicate that the post-sorption opoka (PS-OP) and post-sorption waste autoclaved aerated concrete (PS-WAAC) effectively release retained HSs at 350–480 μg g⁻1 d⁻1, respectively. These materials also show potential as NPK fertilizers, releasing 280–430 μg g⁻1 d⁻1 N-NH₄⁺, 80–150 μg g⁻1 d⁻1 P-PO₄³⁻, and 270–350 μg g⁻1 d⁻1 K⁺. Additionally, PS-OP demonstrated promising fungicide properties, reducing P. diachenii growth by 31% at a concentration of 1 g L⁻1. A two-way ANOVA indicated that the effects of PS-OP and PS-WAAC on soil physicochemical and biological parameters varied with plant species. Both post-sorbents improved the quality of soil collected from sand mining area, increasing cation exchange capacity by 7%–85% and organic matter content by 10%–58%. They also enhanced the functional potential of soil microbial communities, increasing their metabolic activities by 23%–36% in soils sown with clover and by 33%–39% in soils sown with rapeseed. An opposite effect was observed in soils sown with sorghum, suggesting these amendments may not universally act as plant biostimulants. The effectiveness of these post-sorbents in enhancing plant growth varied depending on plant species and the mineral base of the post-sorbent. PS-OP increased the total length of clover and sorghum by 41% and 36%, and their fresh biomass by 82% and 80%, respectively. In turn, PS-WAAC increased the total length of clover and sorghum by 76% and 17%, and their fresh biomass by 29% and 15%, respectively. It was notably more effective than PS-OP for rapeseed. This study proposes a strategy to decrease reliance on non-renewable resources and costly sorbents while minimizing environmental impact. It shows that PS-OP and PS-WAAC can enhance soil quality, microbial activity, and plant growth. Given their origins, these amendments are recommended for soil remediation, particularly in degraded areas. Future research should focus on optimizing their application across various plant species to maximize effectiveness.

Enabling modern bioenergy deployment in Nigeria to support industry and local communities

Nigeria intends to rank among the top 20 global economies by 2030 by focusing on industrialisation. However, limiting energy access may slow the rate of industrialisation. Bioenergy integration into Nigeria's energy mix can accelerate the industrialisation agenda due to the co-benefits it offers. We used a disaggregated approach to map agri-residue availability and identify knowledge gaps in agri-residue application to support modern and sustainable bioenergy integration into Nigeria's energy mix. Expert interviews with stakeholders from government departments, small- and large-scale industries, and feedstock producers were used to validate the biomass mapping. The output of the biomass mapping shows that residues from yam, sorghum, wheat, palm, cassava, rice, sugarcane, etc, have knowledge gaps in agri-residue application and they could support the industrialisation agenda of Nigeria. The output of the stakeholder engagement shows that fossil fuels are the main energy source for productive uses in Nigeria. Current waste management practices involve onsite burning and disposal on land. Bioenergy technologies currently deployed in Nigeria are predominantly anaerobic digestion and combustion. Stakeholders have a strong preference for electricity to be the predominant energy vector. However, awareness of modern bioenergy applications and technologies was limited even though Nigeria's Energy Masterplan supports the efficient use of biomass to generate clean heat, electricity and biofuel for industrial, transport and household applications. Based on these findings, we have developed a suite of novel bioenergy case studies to support biomass integration into Nigeria's energy system.

Management of Tanning Waste from Leather Processing by Anaerobic Digestion Using a Dynamic Method on a Semi-Technical Scale

In the context of climate policy, measures are being taken around the world to reduce pollution. These have been intensified in the areas of transport, industry, and energy, with the goal of zero emissions. The role of the biogas plant in energy transition and as a waste treatment plant for disposal is very important. This article describes research on a dynamic anaerobic digestion (AD) process plant. The subject of this study was leather shavings, which is a problematic waste. The research presented here is intended to demonstrate the decomposition of the flesh in the process, to confirm its biogas yield, and to evaluate the biological and technical parameters of the process. High biochemical stability was achieved for each of the tests evaluated, and no specific technical requirements were demonstrated. The only technical aspect to be addressed during operation was sedimentation, which can be solved by preparing the mixture earlier or by changing the mixing method. This made it reasonable to investigate the material further in the context of an industrial project. The characteristics of protein degradation in the AD process resulted in a high methane content in the biogas, above 65%. It was also observed that the long conditioning time of biogas in the gas cushion favourably affected the proportion of methane in biogas. Analytical results confirmed 77.5% methane content, which was a very good result. This paper presents the results of a surprising effect of chromium, primarily Cr (III), on the performance of anaerobic digestion.