Fermentation Of Sewage Sludge Research Articles

Enhanced microalgal biomass and lipid production from a consortium of indigenous microalgae and bacteria present in municipal wastewater under gradually mixotrophic culture conditions

The goal of this study was to investigate the influences of gradually mixotrophic culture conditions on microalgal biomass and lipid production by a consortium of indigenous microalgae and bacteria present in raw municipal wastewater. Lab-scale photobioreactors containing the consortium were operated in repeated batch mode. Initial cultivation (phase I) was performed using only the municipal wastewater, then 10% and 25% of the reactor volumes were replaced with the effluent from a sewage sludge fermentation system producing volatile fatty acids (SSFV) at the beginnings of phase II and phase III, respectively. The highest biomass productivity (117.1±2.7mg/L/d) was attained during phase II, but the lipid productivity (17.2±0.2mg/L/d) was attained during phase III. The increase in the effluent from the SSFV influenced microalgal diversity with a preference for Chlorella sp., but bacterial diversity increased significantly during phase III.

Impact of Adding Biopreparations on the Anaerobic Co-Digestion of Sewage Sludge with Grease Trap Waste

The aim of the study was to evaluate the effect of using biopreparations on efficiency of the co-fermentation process. Commercial bacterial biopreparations DBC Plus Type L, DBC Plus Type R5 and yeast biopreparations were used in the study. The process of cofermentation of sewage sludge with grease trap waste from a production plant that manufactured methyl esters of fatty acids was analysed in the laboratory environment under mesophilic conditions. The sludge in the reactor was replaced once a day, with hydraulic retention time of 10 days. Grease trap waste accounted for 35%wt. of the fermentation mixture. The stabilization process was monitored everyday based on the measurements of biogas volume. Addition of yeast biopreparation to methane fermentation of sewage sludge with grease trap waste caused an increase in mean daily biogas production from 6.9 dm<sup>3</sup> (control mixture) to 9.21dm<sup>3</sup> (mixture M3). No differences in biogas production were found for other cases (mixtures M1, M2). A similar relationship was observed for methane content in biogas.

Appraisal of changes in sewage sludge management

A positive energy balance caused by accelerated production of CH4 and additional financial benefits associated with shorter retention times, reduction in volumes, easier dewatering, enhanced hygiene, etc., are the reasons why most modern wastewater treatment plants are newly equipped with hydrothermal pretreatment units. This study examined how the changes in composition of the pretreated sewage sludge fermentation residues manifested themselves in subsequent processing by pyrolysis, both in terms of technology and financial impacts. It has been found that concentrations of heavy metals and other hazardous inhibitors might increase; however, the overall biotoxicity is lower due to their immobilization in the charred mass. Moreover, charring of the fermentation residues results in significant financial as well as technological benefits.

Comparative Analysis of Performance and Microbial Characteristics Between High-Solid and Low-Solid Anaerobic Digestion of Sewage Sludge Under Mesophilic Conditions

High-solid anaerobic digestion of sewage sludge achieves highly efficient volatile solid reduction, and production of volatile fatty acid (VFA) and methane compared with conventional low-solid anaerobic digestion. In this study, the potential mechanisms of the better performance in high-solid anaerobic digestion of sewage sludge were investigated by using 454 high-throughput pyrosequencing and real-time PCR to analyze the microbial characteristics in sewage sludge fermentation reactors. The results obtained by 454 high-throughput pyrosequencing revealed that the phyla Chloroflexi, Bacteroidetes, and Firmicutes were the dominant functional microorganisms in high-solid and low-solid anaerobic systems. Meanwhile, the real-time PCR assays showed that high-solid anaerobic digestion significantly increased the number of total bacteria, which enhanced the hydrolysis and acidification of sewage sludge. Further study indicated that the number of total archaea (dominated by Methanosarcina) in a high-solid anaerobic fermentation reactor was also higher than that in a low-solid reactor, resulting in higher VFA consumption and methane production. Hence, the increased key bacteria and methanogenic archaea involved in sewage sludge hydrolysis, acidification, and methanogenesis resulted in the better performance of high-solid anaerobic sewage sludge fermentation.

The influence of petroleum products on the methane fermentation process

In this study the influence of the petroleum products: diesel fuel and spent engine oil on the sewage sludge digestion process and biogas production efficiency was investigated. Microbiological, chemical and enzymatic analyses were applied in the survey. It was revealed that the influence of the petroleum derivatives on the effectiveness of the methane fermentation of sewage sludge depends on the type of the petroleum product. Diesel fuel did not limit the biogas production and the methane concentration in the biogas, while spent engine oil significantly reduced the process efficacy. The changes in physical–chemical parameters, excluding COD, did not reflect the effect of the tested substances. The negative influence of petroleum products on individual bacterial groups was observed after 7 days of the process, while after 14 days probably some adaptive mechanisms appeared. The dehydrogenase activity assessment was the most relevant parameter to evaluate the effect of petroleum products contamination. Diesel fuel was probably used as a source of carbon and energy in the process, while the toxic influence was observed in case of spent engine oil.

Multi-system Nernst–Michaelis–Menten model applied to bioanodes formed from sewage sludge

Bioanodes were formed under constant polarization at −0.2V/SCE from fermented sewage sludge. Current densities reached were 9.3±1.2Am−2 with the whole fermented sludge and 6.2±0.9Am−2 with the fermented sludge supernatant. The bioanode kinetics was analysed by differentiating among the contributions of the three redox systems identified by voltammetry. Each system ensured reversible Nernstian electron transfer but around a different central potential. The global overpotential required to reach the maximum current plateau was not imposed by slow electron transfer rates but was due to the potential range covered by the different redox systems. The microbial communities of the three bioanodes were analysed by 16S rRNA gene pyrosequencing. They showed a significant microbial diversity around a core of Desulfuromonadales, the proportion of which was correlated with the electrochemical performance of the bioanodes.

Filtration characteristics of anaerobic fermented sewage sludge for fatty acids production

The filtration characteristics of untreated sewage sludge, thermal alkaline pretreated and anaerobic fermented sewage sludge were investigated in the process of fatty acids production. The filtration resistance, viscosity, particle size, extracellular polymeric substances (EPS) and soluble microbial products (SMP) were determined to identify the filtration characteristics of the sewage sludge. The results indicated that thermal alkaline pretreatment significantly increased the filtration resistance and viscosity of the sewage sludge, while anaerobic fermentation decreased the filtration resistance. The particle size of the sewage sludge decreased after pretreatment and fermentation. Moreover, the EPS concentration in the sludge sharply decreased after thermal alkaline pretreatment and then increased after the following fermentation. The mechanism of the increase of sludge filtration resistance after pretreatment could be attributed to the release of EPS from the microbial cells of the sludge. The degradation and conversion of SMP into volatile fatty acids could explain the decrease in the filtration resistance after fermentation.

Recovery of volatile fatty acids from fermentation of sewage sludge in municipal wastewater treatment plants

This work investigated the pilot scale production of short chain fatty acids (SCFAs) from sewage sludge through alkaline fermentation and the subsequent membrane filtration. Furthermore, the impact of the fermentation liquid on nutrient bioremoval was examined. The addition of wollastonite in the fermenter to buffer the pH affected the composition of the carbon source produced during fermentation, resulting in higher COD/NH4-N and COD/PO4-P ratios in the liquid phase and higher content of propionic acid. The addition of wollastonite decreased the capillary suction time (CST) and the time to filter (TTF), resulting in favorable dewatering characteristics. The sludge dewatering characteristics and the separation process were adversely affected from the use of caustic soda. When wollastonite was added, the permeate flux increased by 32%, compared to the use of caustic soda. When fermentation liquid was added as carbon source for nutrient removal, higher removal rates were obtained compared to the use of acetic acid.

Effects of pH control and concentration on microbial oil production from Chlorella vulgaris cultivated in the effluent of a low-cost organic waste fermentation system producing volatile fatty acids

The objective of this study was to investigate the feasibility of applying volatile fatty acids (VFAs) produced from low-cost organic waste to the major carbon sources of microalgae cultivation for highly efficient biofuel production. An integrated process that consists of a sewage sludge fermentation system producing VFAs (SSFV) and mixotrophic cultivation of Chlorella vulgaris (C. vulgaris) was operated to produce microbial lipids economically. The effluents from the SSFV diluted to different concentrations at the level of 100%, 50%, and 15% were prepared for the C. vulgaris cultivation and the highest biomass productivity (433±11.9mg/L/d) was achieved in the 100% culture controlling pH at 7.0. The harvested biomass included lipid contents ranging from 12.87% to 20.01% under the three different effluent concentrations with and without pH control. The composition of fatty acids from C. vulgaris grown on the effluents from the SSFV complied with the requirements of high-quality biodiesel. These results demonstrated that VFAs produced from the SSFV are favorable carbon sources for cultivating C. vulgaris.

Illumina sequencing-based analyses of bacterial communities during short-chain fatty-acid production from food waste and sewage sludge fermentation at different pH values.

Short-chain fatty acids (SCFAs) can be produced by primary and waste activated sludge anaerobic fermentation. The yield and product spectrum distribution of SCFAs can be significantly affected by different initial pH values. However, most studies have focused on the physical and chemical aspects of SCFA production by waste activated sludge fermentation at different pH values. Information on the bacterial community structures during acidogenic fermentation is limited. In this study, comparisons of the bacterial communities during the co-substrate fermentation of food wastes and sewage sludge at different pH values were performed using the barcoded Illumina paired-end sequencing method. The results showed that different pH environments harbored a characteristic bacterial community, including sequences related to Lactobacillus, Prevotella, Mitsuokella, Treponema, Clostridium, and Ureibacillus. The most abundant bacterial operational taxonomic units in the different pH environments were those related to carbohydrate-degrading bacteria, which are associated with constituents of co-substrate fermentation. Further analyses showed that during organic matter fermentation, a core microbiota composed of Firmicutes, Proteobacteria, and Bacteroidetes existed. Comparison analyses revealed that the bacterial community during fermentation was significantly affected by the pH, and that the diverse product distribution was related to the shift in bacterial communities.

Effect of temperature on short chain fatty acids (SCFAs) accumulation and microbiological transformation in sludge alkaline fermentation with Ca(OH)2 adjustment

The effects of temperatures (15–55 °C) on the alkaline fermentation of sewage sludge were investigated in semi-continuous stirred tank reactors (semi – CSTR) at the pH of 10. The highest soluble chemical oxygen demand (SCOD) yield was obtained at 55 °C (764.2 mg/(gVS L d)), while the highest short chain fatty acids (SCFAs) yield was observed at 35 °C (319.8 mg/(gVS L d)), 1.5 times higher than SCFAs yield at 55 °C (209.5 mg/(gVS L d)). The proportion of the intercellular organic substances being transferred to the slime layer of sludge flocs increased from 29% at 15 °C to 54% at 55 °C. But only a small part of soluble organic substances in the slime layers was converted to SCFAs at 55 °C. The dewaterability of sludge was better at 35 °C than that at 55 °C. Microbiological community analysis showed the acid-producing microorganisms at the medium temperatures (25 °C and 35 °C) were more diverse and abundant than those at the low (15 °C) and high temperatures (55 °C). Clodtridium and Bacillus in Firmicutes and Gamma proteobacterium in Proteobacteria were the dominant functional bacterial species for high SCFA accumulation.

Trophic link between syntrophic acetogens and homoacetogens during the anaerobic acidogenic fermentation of sewage sludge

Acetate production during anaerobic sludge treatment has significant economic and environmental benefits. In this study, trophic links between syntrophic acetogens and homoacetogens in the anaerobic acidogenic fermentation of sewage sludge were investigated using methanogenic inhibitor 2-bromoethanesulfonate (BES) to block the methanogenesis pathway and butyrate to enhance syntrophic acetogenesis. The Gibbs free energies (ΔG) of the butyrate-degrading and homoacetogenic processes were close to the thermodynamic threshold of the reaction activity (−15kJ/mol). In addition, microbial quantification analysis revealed that the growth of syntrophic acetogenic bacteria and homoacetogens in the treatment incubations was higher than that of the control. The results indicated that hydrogen-producing butyrate degraders are stimulated with homoacetogens when methanogenesis was specifically inhibited.

Hydrogen production and microbial diversity in sewage sludge fermentation preceded by heat and alkaline treatment

Combined pretreatment of heat treatment with alkaline condition was applied to the sewage sludge in order to acquire the effective method for sludge solubilization and bio-hydrogen production. Solubilization ratio of the sludge with heat treatment at alkaline condition (pH 13) was as high as 85.0%, resulting in an increase of COD concentration in aqueous solution, but the ratio of sludge with heat treatment or alkaline treatment alone was 32.2% and 56.3%, respectively. During the fermentation of the pretreated sludge, a significant increase of hydrogen production was observed with a low strength of ammonia, showing that ammonia in the aqueous phase could inhibit bio-hydrogen production. Klebsiella, Enterobacter or Clostridium genus were mostly related on the hydrogen production.

Residues from the production of biofuels for transportation: Characterization and ash sintering tendency

The continuously growing demand for fuels in the transportation sector has led to the increased use of liquid biofuels, with a corresponding increase in the amounts of production residues. With energy recovery, these residues could become a source of biomass fuels. The current work investigated the behaviour of four potential biomass fuels during combustion. Fermented sewage sludge (FSS) is the residue from biogas production via anaerobic fermentation; distillers' dried grains with solubles (DDGS) are a residue from barley bioethanol production; and rapeseed cake (RC) and palm kernel cake (PKC) are both oil extraction residues from first generation biodiesel production plants. Since the main challenges during biomass combustion are related to ash behaviour, this paper focuses on the ash-forming matter in the fuels and its effect on the ash sintering tendency. Three different types of tests were applied to study ash sintering: compression strength, microsample sintering, and standard ash sintering. The latter was carried out using hot stage microscopy and computer aided image analysis, and the results were compared with those from the compression strength and microsample tests. To obtain additional information about the nature and extent of the sintering, ash samples before and after sintering were examined with a scanning electron microscope equipped with energy dispersive X-ray (SEM/EDX) technology and a stereomicroscope incorporating a digital camera. To make it possible to study the ash-forming matter, chemical fractionation were performed accompanied by fuel proximate analyses by means of thermogravimetric analyzer.The results clearly showed that the lowest initial sintering temperatures were below 800°C for RC and DDGS in all the sintering tests, while PKC and FSS did not exhibit any significant sintering below 900°C. This could be interpreted to mean that when the combustion temperature is below 900°C, no significant ash-related problems will occur. The chemistry of the fuel ashes investigated is dominated by phosphorus, and the shift between alkali metal and alkaline earth metal phosphates governs the sintering behaviour. The FSS sintering tendency is dominated by the iron oxide chemistry.

Behaviour of PAHs during sewage sludge fermentation in the presence of sulphate and nitrate

In this study, the changes of polycyclic aromatic hydrocarbons (PAHs) in sewage sludge and supernatants during anaerobic digestion under nitrate- and sulphate-reducing conditions were investigated. NaNO 3 or Na 2 SO 4 were added to the mixed sludge in order to obtain denitrification and sulphate reduction conditions, respectively. Abiotic loses of PAHs simultaneously were observed. Abiotic samples (with sodium azide) were also prepared. All sludge samples (biotic and abiotic) were incubated at 35°C in the dark. PAHs concentration was determined before incubation, after 13 d and after 20 d of incubation. Quantification of 16 PAHs (EPA) was carried out by GC-MS. PAHs were determined both in sewage sludge and in supernatants. During hydrolysis of organic compounds (first phase of fermentation) in the control samples (in sewage sludge and in superna tants) the increase of PAHs concentration occurred (especially naphthalene and 3-ring PAHs). The concentration of 16 PAHs in sewage sludge was reduced by 30% on average under nitrate-reducing conditions after 20 d and by 32% on average under sulphate-reducing conditions, respectively. The effectiveness of reducing of individual hydrocarbons was different. The concentration of carcino genic PAHs in sewage sludge was reduced by 73% on average under nitrate-reducing conditions and by 79% on average under sulphate-reducing conditions, respectively.

Material and Energy Flow Analysis in Sewage Sludge Incineration and Composting Treatment Processes

This study aims to clarify the material and energy flows in a well-known sewage sludge treatment plant in Japan; the treatment processes include composting, drying, incineration, and incineration with ash melting. We used not only statistical data but also data such as carbon, nitrogen, and moisture content in sludge obtained through our on-site observations. Material and energy flow analysis of sewage sludge composting is seldom reported in comparison with the analysis of other recycling and treatment methods. Therefore, we have performed material and energy flow analysis on sewage sludge composting to estimate factors such as environmental load and energy balance. We investigate the energy consumption of sewage sludge composting in one company that produces manure through aerobic fermentation of sewage sludge. In addition, we compare sewage sludge composting with incineration and evaluate their respective characteristics regarding sewage treatment and production of manure. It has been found that the use of anaerobic digestion of sewage sludge can reduce the overall energy consumption in sewage sludge treatment if power generation using biogas is adopted; however, the digestion of sewage sludge lowers the heating value of the digested sludge, requiring more energy to operate the digester. The energy consumption in a wastewater treatment plant accepting returned water from sludge digestion was increased by 10% to 20% compared to the process without sludge digestion. The overall energy consumption in both wastewater treatment and sludge digestion should be considered. The electric power was 60% of the overall energy consumption and 70% of the energy consumption in the plant's production sector.

Combustion Characteristics of Biomass Residues and Biowastes: Fate of Fuel Nitrogen

Biomass residues and wastes will have an important role in the future energy mix. Residues from agriculture or industrial processes are usually cheap, widespread, and continuously produced, and their heating value is comparable to that of wood. However, many of these materials are rich in proteins and, thus, nitrogen. Therefore, to be able to exploit these materials in an efficient way, fundamental research on their nitrogen chemistry is essential. In the work presented here, the release of gaseous compounds from five biomass residues from different processes was tested in a bench-scale single-particle reactor. The tested fuels were dry distiller’s grains and solubles (DDGS), palm kernel cake (PKC), rapeseed cake (RC), fermented sewage sludge (FSS), and chicken manure (CM). All of these materials have sufficiently high heating values and are either already used or projected to be used soon in industrial-scale boilers. The setup allowed us to study the total C and N release and the nitrogen partitioning be...

Comparison between disintegrated and fermented sewage sludge for production of a carbon source suitable for biological nutrient removal

There is a need to investigate processes that enable sludge re-use while enhancing sewage treatment efficiency. Mechanically disintegrated thickened surplus activated sludge (SAS) and fermented primary sludge were compared for their capacity to produce a carbon source suitable for BNR by completing nutrient removal predictive tests. Mechanically disintegration of SAS using a deflaker enhanced volatile fatty acids (VFAs) content from 92 to 374 mg l(-1) (4.1-fold increase). In comparison, primary sludge fermentation increased the VFAs content from 3.5 g l(-1) to a final concentration of 8.7 g l(-1) (2.5-fold increase). The carbon source obtained from disintegration and fermentation treatments improved phosphate (PO(4)-P) release and denitrification by up to 0.04 mg NO(3)-Ng(-1)VSS min(-1) and 0.031 mg PO(4)-Pg(-1)VSS min(-1), respectively, in comparison to acetate (0.023 mg NO(3)-Ng(-1)VSS min(-1)and 0.010 mg PO(4)-Pg(-1)VSS min(-1)). Overall, both types of sludge were suitable for BNR but disintegrated SAS displayed lower carbon to nutrient ratios of 8 for SCOD:PO(4)-P and 9 for SCOD:NO(3)-N. On the other hand, SAS increased the concentration of PO(4)-P in the settled sewage by a further 0.97 g PO(4)-P kg(-1)SCOD indicating its potential negative impact towards nutrient recycling in the BNR process.

Biogas from waste and renewable resources: an introduction

Preface. Abbreviations. Acknowledgement. Part I General thoughts about energy supply. 1 Energy supply - today and in the future. 1.1 Primary energy sources. 1.2 Secondary energy sources. 1.3 End-point energy sources. 1.4 Effective energy. 2 Energy supply in the future - scenarios. 2.1 Amount of space. 2.2 Potential yield from biomass. 2.3 Technical potential. 2.4 Economic potential. 2.5 Realizable potential. 3 History and status to date in Europe. 3.1 First attempts at using biogas. 3.2 Second attempts at using biogas. 3.3 Third attempts at applying biogas. 3.4 Status to date and perspective in Europe. 4 History and status to date in other countries. 4.1 History and status to date in China. 4.2 History and status to date in India. 4.3 Status to date in Latin America. 4.4 Status to date in the CIS states. 5 General aspects of the recovery of biomass in the future. Part II Substrate and biogas. 1 Biogas. 1.1 Biogas compared to other methane-containing gases. 1.2 Detailed overview of biogas components. 2 Substrates. 2.1 Liquid manure and co-substrates. 2.2 Bio waste from collections of residual waste and trade waste similar to domestic waste. 2.3 Landfi ll for residual waste. 2.4 Sewage sludge and co-substrate. 2.5 Industrial waste water. 2.6 Waste grease or fat. 2.7 Cultivation of algae. 2.8 Plankton. 2.9 Sediments in the sea. 2.10 Wood, straw. 3 Evaluation of substrates for biogas production. 4 Benefi ts of a biogas plant. Part III Formation of biogas. 1 Biochemical reaction. 2 Biology. 2.1 Bioreactions. 2.2 Process parameters. 3 Bacteria participating in the process of degradation . 3.1 Hydrolyzing genera. 3.2 Acidogenic genera. 3.3 Acetogenic genera. 3.4 Methanogenics. 3.5 Methanotropic species. Part IV Laws and guidelines concerning biogas plants. 1 Guidelines and regulations. 1.1 Construction of plants. 1.2 Utilized biomass. 1.3 Biomass to be used preferentially. 1.4 Distribution of the residues. 1.5 Feeding biogas to the gas network. 1.6 Risk of explosion. 1.7 Risk of fire. 1.8 Harmful exhaust gases. 1.9 Noise protection. 1.10 Prevention of injuries. 1.11 Protection from water. 2 Building a biogas plant. 2.1 Feasibility study. 2.2 Preliminary planning. 2.3 The construction process. 3 Financing. Part V Process engineering. 1 Parts of biogas plants. 1.1 Tanks and reactors. 1.2 Equipment for tempering the substrate. 1.3 Thermal insulation. 1.4 Piping system. 1.5 Pump system. 1.6 Measurement, control, and automation technology. 1.7 Exhaust air cleaning. 2 Area for the delivery and equipment for storage of the delivered biomass. 3 Process technology for the upstream processing. 3.1 Adjustment of the water content. 3.2 Removal of disturbing/harmful substances. 3.3 Comminution. 3.4 Hygienization. 3.5 Disintegration. 3.6 Feeding. 4 Fermentation technology. 4.1 Batchwise and continuous processes without separators. 4.2 Existing installations by different suppliers. 4.3 Installation with substrate dilution and subsequent water separation. 4.4 Installation with biomass accumulation. 4.5 Plants with separation of non-hydrolyzable biomass. 4.6 Residue storage tank and distribution. 5 Special plant installations. 5.1 Combined fermentation of sewage sludge and bio waste. 5.2 Bio waste plants. 5.3 Purifi cation of industrial waste water. Part VI Biogas to energy. 1 Gas pipelines. 2 Biogasholder. 2.1 Biogasholder types. 2.2 Gas flares. 3 Gas preparation. 3.1 Removal of hydrogen sulfide. 3.2 Removal of the carbon dioxide. 3.3 Removal of oxygen. 3.4 Removal of water. 3.5 Removal of ammonia. 3.6 Removal of siloxanes. 4 Liquefaction or compression of the biogas. 4.1 Liquefaction. 4.2 Compression. 5 Utilization of biogas for the generation of electric power and heat. 5.1 Supply of current to the public electricity network. 5.2 Heat. 5.3 Combined heat and power generator (CHP). 5.4 Lessons learnt from experience. 5.5 Economy. 5.6 CHP manufacturers. 6 Biogas for feeding into the natural gas network. 6.1 Biogas for feeding into the natural gas network in 6.2 Biogas for feeding into the natural gas network in Sweden. 6.3 Biogas for feeding into the natural gas network in Germany. 7 Biogas as fuel for vehicles. 7.1 Example project: chain of restaurants in Switzerland. 7.2 Example projects in Sweden. Part VII Residues and waste water. 1 Residues. 2 Waste water. Attachment I Typical design calculation for an agricultural biogas plant. Attachment II Economy of biogas plants for the year 2007 (Calculation on the basis of the example of Attachment I). Literature. Index.

Kinetic investigations of methane co-fermentation of sewage sludge and organic fraction of municipal solid wastes

In the presented study the co-fermentation, fermentation of sewage sludge (SS) and fermentation of organic fraction of municipal solid waste (OFMSW) were compared. The goal of experiments was determination of the processes carbon balance and proposal of the simple kinetic model of anaerobic digestion. Three batch experiments with above mentioned feedstocks were conducted in large scale laboratory reactor of working volume of 40 dm 3. The cumulative biogas production for sewage sludge (180.59 dm 3) was lower than that for co-fermentation (232 dm 3) or OFMSW (228.34 dm 3). During fermentation of the OFMSW an accumulation of volatile fatty acids (VFA) caused pH decrease and strongly inhibited gas production. The addition of co-substrate improved buffering capacity of fermentation broth. The suggested mathematical descriptions of carbon division in anaerobic digestion processes gave the satisfying conformity with the experimental values.