Anaerobic Sequencing Batch Reactor Research Articles

Methanosarcina domination in anaerobic sequencing batch reactor at short hydraulic retention time

The Archaea population of anaerobic sequential batch reactor (ASBR) featuring cycle operations under varying hydraulic retention time (HRT) was evaluated for treating a dilute waste stream. Terminal-Restriction Length Polymorphism and clone libraries for both 16S rRNA gene and mcrA gene were employed to characterize the methanogenic community structure. Results revealed that a Methanosarcina dominated methanogenic community was successfully established when using an ASBR digester at short HRT. It was revealed that both 16S rRNA and mcrA clone library could not provide complete community structure, while combination of two different clone libraries could capture more archaea diversity. Thermodynamic calculations confirmed a preference for the observed population structure. The results both experimentally and theoretically confirmed that Methanosarcina dominance emphasizing ASBR's important role in treating low strength wastewater as Methanosarcina will be more adept at overcoming temperature and shock loadings experienced with treating this type of wastewater.

Anaerobic Treatment of Industrial Biodiesel Wastewater by an ASBR for Methane Production

A mechanically stirred anaerobic sequencing batch reactor (5 L, 30 °C) containing granular biomass was used to treat the effluent of an industrial biodiesel production process with the purpose to produce methane. Process stability and efficiency were analyzed as a function of applied volumetric organic load (AVOL of 1,000 to 3,000 mgCOD/L), reactor feed time, and cycle length (8-h cycles with 10-min or 4-h feeding and 4-h cycles with 10-min or 2-h feeding). Batch operations (B) with 1,000 to 3,000 mgCOD/L involved 10-min feeding/discharge: (1) 1.0-L influent with 4-h cycle and (2) 2.0-L influent with 8-h cycle. Fed-batch operations (FB) with 1,000 to 3,000 mgCOD/L involved 10-min discharge and the following feeding: (1) 1.0-L influent in 2 h with 4-h cycle and (2) 2.0-L influent in 4 h with 8-h cycle. At 1,000 mgCOD/L (AVOL of 18 to 1.29 gCOD/Lday), kinetic parameter values were 1.03 and 0.92 h(-1) at conditions B-1000-4 h and FB-1000-8/4 h, respectively. At both conditions, removal efficiency was 88 %, and cycle length could be reduced to 3 h (B-1000-4 h) and 5 h (FB-1000-8/4 h). At 2,000 mgCOD/L (AVOL of 2.38 to 2.52 gCOD/Lday), kinetic parameter values were 1.08 and 0.99 h(-1) at conditions B-2000-4/2 h and FB-2000-8/4 h, respectively, and removal efficiencies were 83 and 81 %. Cycle length could be reduced to 3 h (B-2000-4/2 h) and 6 h (FB-2000-8/4 h). At 3,000 mgCOD/L (AVOL of 3.71 to 3.89 gCOD/Lday), conditions allowing stable operation were B-3000-4 h, FB-3000-8/4 h, and FB-3000-4/2 h. Stability could not be obtained at condition B-3000-8 h, and the best results were obtained at condition FB-3000-8/4 h. Specific methane production ranged from 41.1 to 93.7 NmLCH(4)/gCOD, demonstrating reactor application potential and operation flexibility.

Anaerobic digestion of grain stillage at high organic loading rates in three different reactor systems

In this study the anaerobic digestion of grain stillage in three different reactor systems (continuous stirred tank reactor, anaerobic sequencing batch reactor, fixed bed reactor) with and without immobilization of microorganisms was investigated to evaluate the performance during increase of the organic loading rate (OLR) from 1 to 10 g of volatile solids (VS) per liter reactor volume and day and decrease of the hydraulic retention time (HRT) from 40 to 6 days. No significant differences have been observed between the performances of the three examined reactor systems. The changes in OLR and HRT caused a reduction of the specific biogas production (SBP) of about 25% from about 650 to 550 L kg−1 of VS but would also diminish the necessary digester volume and investment costs of about 75% compared to the state of the art.

Optimization of continuous hydrogen production from co-fermenting molasses with liquid swine manure in an anaerobic sequencing batch reactor

This study investigated and optimized the operational conditions for continuous hydrogen production from sugar beet molasses, co-fermented with liquid swine manure in an anaerobic sequencing batch reactor. Results indicated that pH, HRT and total solids content in the swine manure (TS) had significant impact on all the responses such as biogas production rate (BPR), hydrogen content (HC), hydrogen production rate (HPR), and hydrogen yield (HY), although the highest level of each response was achieved at different combination of the three variables. The maximum BPR, HC, HPR and HY of 32.21L/d, 30.51%, 2.23L/d/L and 1.57mol-H2/mol-sugar were estimated at the optimal pH, HRT, and TS of 5.55, 15.78h, and 0.71% for BPR; 5.22, 12.04, and 0.69 for HC; 5.32, 15.62, and 0.78% for HPR; and 5.36, 17.56, and 0.74% for HY, respectively. Good linear relationships of the predicted and tested results for all the parameters were observed.

Laboratory-scale anaerobic sequencing batch reactor for treatment of stillage from fruit distillation

This work describes batch anaerobic digestion tests carried out on stillages, the residue of the distillation process on fruit, in order to contribute to the setting of design parameters for a planned plant. The experimental apparatus was characterized by three reactors, each with a useful volume of 5 L. The different phases of the work carried out were: determining the basic components of the chemical oxygen demand (COD) of the stillages; determining the specific production of biogas; and estimating the rapidly biodegradable COD contained in the stillages. In particular, the main goal of the anaerobic digestion tests on stillages was to measure the parameters of specific gas production (SGP) and gas production rate (GPR) in reactors in which stillages were being digested using ASBR (anaerobic sequencing batch reactor) technology. Runs were developed with increasing concentrations of the feed. The optimal loads for obtaining the maximum SGP and GPR values were 8-9 gCOD L(-1) and 0.9 gCOD g(-1) volatile solids.

Advanced nitrogen removal from landfill leachate without addition of external carbon using a novel system coupling ASBR and modified SBR

In order to achieve advanced nitrogen removal from landfill leachate without the addition of external carbon sources, a novel system coupling an anaerobic sequencing batch reactor (ASBR) and sequencing batch reactor (SBR) was proposed for the treatment of real landfill leachate with NH4+-N and chemical oxygen demand (COD) concentrations of 1100mg/L and 6000mg/L, respectively. ASBR could remove 80% of the influent COD under a volumetric loading rate of 5kg COD/(m3d). Denitritation and simultaneous nitritation–denitritation were responsible for 50% of the TN removal in SBR under alternate anoxic/aerobic modes. Furthermore, advanced nitrogen removal was realized with a total inorganic nitrogen (TIN) removal efficiency of 99% at the expense of endogenous denitritation during a 26h period, which led to effluent COD and TN values of 550–650mg/L and 15–25mgN/L, respectively. For the combined system, removal efficiencies of COD and total nitrogen (TN) were above 90% and 95%, respectively.

생물학적 수소생산을 위한 혐기성 연속 회분식 반응조(ASBR)의 장기운전 특성

Long term hydrogen production was investigated in an anaerobic sequencing batch reactor (ASBR) using mixed microflora. Glucose (about 8,250 mg/L) was used as a substrate for the ASBR operation under the condition of pH 5.5 and 37°C with mixing at 150 rpm. The experiment was carried out over a period of 160 days. Hydrogen yield was 0.8 mol H2/mol glucose with F/M ratio 2 at initial operation period. The hydrogen yield reached to maximum 2.6 mol H2/mol glucose at 80th day operation. However decreased hydrogen yield was observed after 80 days operation and eventually no hydrogen yield. Although well-known hydrogen producer Clostridium sp. was detected in the reactor by PCR-DGGE analysis, changed reactor operation was the major reason of the decreased hydrogen production, such as low F/M ratio of 0.5 and high propionic acid concentration 2,130 mg/L. Consequently the long period operation resulted in MLSS accumulation and then low F/M ration stimulating propionic acid formation which consumes hydrogen produced in the reactor.

Monitoring anaerobic sequential batch reactors via fractal analysis of pH time series

Efficient monitoring and control schemes are mandatory in the current operation of biological wastewater treatment plants because they must accomplish more demanding environmental policies. This fact is of particular interest in anaerobic digestion processes where the availability of accurate, inexpensive, and suitable sensors for the on-line monitoring of key process variables remains an open problem nowadays. In particular, this problem is more challenging when dealing with batch processes where the monitoring strategy has to be performed in finite time, which limits the application of current advanced monitoring schemes as those based in the proposal of nonlinear observers (i.e., software sensors). In this article, a fractal time series analysis of pH fluctuations in an anaerobic sequential batch reactor (AnSBR) used for the treatment of tequila vinasses is presented. Results indicated that conventional on-line pH measurements can be correlated with off-line determined key process variables, such as COD, VFA and biogas production via some fractality indexes.

Effects of Operation Conditions on the Performance of the ASBR Methane Fermentation of Syrup Wastewater

Methane fermentation of the syrup wastewater was conducted using the anaerobic sequencing batch reactor (ASBR). Organic loading rate (OLR), which is calculated by dividing the substrate concentration in the wastewater by hydraulic retention time (HRT), was set at the same value in two runs; R1 with longer HRT and higher concentration of substrate, and R2 with shorter HRT and lower concentration of substrate. The effects of HRT and substrate concentration on the performance of the methane fermentation were tried to be elucidated by comparing two experimental runs. The OLR was increased stepwisely from 2.6 to 20.4 g-COD/L/d. No significant difference was observed until the OLR of 10.2 g-COD/L/d. After the OLR increased to 20.4 g-COD/L/d, oxidation reduction potential (ORP) in R2 with short HRT of 3.1 days increased immediately and methane gas production rate (MPR) decreased drastically. In contrast, the ORP of R1 with long HRT of 6.2 days was in the range from -450 to -350mV, and high MPR was maintained for a while though the OLR in R1 was the same with that in R2. More than 10 days of operation with the OLR of 20.4 g-COD/L/d, however, the pH in R1 decreased abruptly and the MPR also decreased rapidly. It was revealed that the collapse of methane fermentation caused by the too short HRT occurred faster than that caused by the too high concentration of substrate.

Influence of linoleic acid, pH and HRT on anaerobic microbial populations and metabolic shifts in ASBRs during dark hydrogen fermentation of lignocellulosic sugars

In this study, controlling an anaerobic microbial community to increase the hydrogen (H2) yield during the degradation of lignocelluosic sugars was accomplished by adding linoleic acid (LA) at low pH and reducing the hydraulic retention time (HRT) of an anaerobic sequencing batch reactor (ASBR). At pH 5.5 and a 1.7 d HRT, the maximum H2 yield for LA treated cultures fed glucose or xylose reached 2.89 ± 0.18 mol mol−1 and 1.94 ± 0.17 mol mol−1, respectively. The major soluble metabolites at pH 5.5 with a 1.7 day HRT differed between the control and LA treated cultures. A metabolic shift toward H2 production resulted in increased hydrogenase activity in both the xylose (13%) and glucose (34%) fed LA treated cultures relative to the controls. In addition, the Clostridia population and the H2 yield were elevated in cultures treated with LA. A flux balance analysis for the LA treated cultures showed a reduction in homoacetogenic activity which was associated with reducing the Bacteriodes levels from 12% to 5% in the glucose fed cultures and 16% to 10% in the xylose fed cultures. Strategies for controlling the homoacetogens and optimal hydrogen production from glucose and xylose are proposed.

Kinetics of psychrophilic anaerobic sequencing batch reactor treating flushed dairy manure

In this study, a new strategy, improving biomass retention with fiber material present within the dairy manure as biofilm carriers, was evaluated for treating flushed dairy manure in a psychrophilic anaerobic sequencing batch reactor (ASBR). A kinetic study was carried out for process control and design by comparing four microbial growth kinetic models, i.e. first order, Grau, Monod and Chen and Hashimoto models. A volumetric methane production rate of 0.24L/L/d of and a specific methane productivity of 0.19L/gVSloaded were achieved at 6days HRT. It was proved that an ASBR using manure fiber as support media not only improved methane production but also reduced the necessary HRT and temperature to achieve a similar treating efficiency compared with current technologies. The kinetic model can be used for design and optimization of the process.

The start-up and saline adaptation of mesophilic anaerobic sequencing batch reactor treating sludge from recirculating aquaculture systems

Treatment of sludge from aquaculture is a matter of special importance and there is a need for salt-tolerant biological wastewater treatment to coincide with the development of brackish/marine aquaculture. The aims of the current study were to determine the ability of anaerobic sequencing batch reactor (ASBR) to anaerobically digest sludge from fresh-water recirculating aquaculture systems and the ability of adaptation to low saline conditions. The mesophilic ASBR were evaluated with loading rates between 0.12 and 0.41g chemical oxygen demand (COD)/day at a 20-day hydraulic retention time (HRT) for start-up and with organic loading rates (OLR) of 0.39–0.41gCOD/Lday at a 20-day HRT for saline adaptation. The average removal rate of total chemical oxygen demand (TCOD), total suspended solids (TSS) and volatile suspended solids (VSS) of the ASBR were above 97%, 96% and 91% during the stabilization period of the experimental reactors. The average daily gas production of ASBR was between 0.013 and 0.022L/g TCOD from day 118. A sludge-mass reduction of up to 94±2.3%, TCOD reduction of 44±13% and VSS/SS of 39–70% were demonstrated for the reactor performance during the gas production period. However, the process of gas production was obviously inhibited, presumably by salt, and unstable due to the dissolved COD (DCOD), total ammonium nitrogen (TAN) and alkalinity of the effluents of the experimental reactors and TSS and sludge volume index (SVI) observed within the reactors. The daily gas production was observed to decrease during the saline adaptation period and stopped when the salinity of the effluents was higher than 8.7ppt until the end of the experiment.

Molecular diversity of bacterial community of dye wastewater in an anaerobic sequencing batch reactor

Anaerobic sequencing batch reactor has proven more effective than aerobic systems in treating dye-containing wastewaters which usually contain refractory dyes and organic chemicals. In this study, the composition and diversity of bacterial community present in an anaerobic sequencing batch reactor used for treating dye wastewater were determined by both high-through pyrosequencing and screening environmentally derived gene library based on 16S rRNA gene sequences. Our results demonstrated that Bacteroidetes represented the dominant phylum in dye wastewater, while the second and third most abundant phyla were Firmicutes and Proteobacteria. The genus Enterococcus from phylum Firmicutes was the dominant genus in the bacterial community of wastewater, followed by the genus Novispirillum, which was classified into phylum Alphaproteobacteria. The majority of sequences from environmental Alphaproteobacteria specific 16S rRNA gene library were assigned into genus Novispirillum and Rhodobacter, which were in agreement with our pyrosequencing results. The aforementioned two genera represented dominant Alphaproteobacteria community, which may perform important roles in degrading refractory dyes and organic chemicals in the anaerobic sequencing batch reactor. The results demonstrated that a wide variety of bacterial species were identified at the genera level and some potential degraders such asEnterococcus, Lactobacillus, Novispirillum and Rhodobacter were abundant in the reactor, which potentially contributed to the strong dye reduction ability. Key words: Dye wastewater, anaerobic sequencing batch reactor, 16S rRNA gene, pyrosequencing, bacterial diversity.

Treatment of wastewater from dairy plants using Anaerobic Sequencing Batch Reactor (ASBR) following by Aerobic Sequencing Batch Reactor (SBR) aiming the removal of organic matter and nitrification

Studies on the environmental impacts of the food industry are important because the wastewater produced by these industries contains large amounts of organic matter and nutrients. Nitrogenous compounds released into the environment stimulate the greenhouse effect and threaten biodiversity. Sequencing batch reactors (SBR) have received a considerable amount of attention in recent years and have been used in the treatment of dairy wastewater in bench scale studies. Dairy plants are operated in batch regime and offer a good opportunity for wastewater treatment via sequential batch processes. Accordingly, the present article describes the results obtained in the first 100 days of operation of a system composed of an anaerobic sequencing batch (ASBR) followed by an aerobic reactor operated under SBR mode, for the treatment of wastewater generated by the USP Pirassununga dairy plant. SBR was used as post-treatment of ASBR to remove residual organic matter and to promote the nitrification of the effluent of the ASBR. Within a 24-h cycle, the ASBR removed 91.1 ± 5.0% of organic matter (chemical oxygen demand (COD) total). The initial concentration of total COD was approximately 4.5 g/L, and the organic loading rate was equal to 4.5 kg/m³ day. The SBR was operated for 24 h at a dissolved oxygen concentration of 3 mg/L, and NH4+-N was effectively converted to NO3−-N. At the end of the cycle, the concentration of NO3−-N and NO2−-N was equal to 26.0 ± 20.7 mg/L and 4.9 ± 2.97 mg/L, respectively. The SBR removed 75.5 ± 22.4% of the total total Kjeldahl nitrogen (TKN-N) of which 50% was converted to nitrate and 9% was converted to nitrite. It is believed that 41% of TKN-N removed may have been assimilated by microorganisms or converted to gaseous nitrogen by the denitrification during the stage of sedimentation. Moreover, phosphorus was also efficiently removed from the effluent, and the concentration of total phosphorous at the end of the cycle was equal to 4.9 ± 0.8 mg/L. Regarding the employment of the effluents from reactors for agricultural reuse, it was not observed sodification risk of soil; however the high values of electrical conductivity indicated a high potential for soil salinization.

Effects of chlortetracycline amended feed on anaerobic sequencing batch reactor performance of swine manure digestion

The effects of antimicrobial chlortetracycline (CTC) on the anaerobic digestion (AD) of swine manure slurry using anaerobic sequencing batch reactors (ASBRs) was investigated. Reactors were loaded with manure collected from pigs receiving CTC and no-antimicrobial amended diets at 2.5g/L/d. The slurry was intermittently fed to four 9.5L lab-scale anaerobic sequencing batch reactors, two with no-antimicrobial manure, and two with CTC-amended manure, and four 28day ASBR cycles were completed. The CTC concentration within the manure was 28mg/L immediately after collection and 1.02mg/L after dilution and 250days of storage. CTC did not inhibit ASBR biogas production extent, however the volumetric composition of methane was significantly less (approximately 13% and 15% for cycles 1 and 2, respectively) than the no-antimicrobial through 56d. CTC decreased soluble chemical oxygen demand and acetic acid utilization through 56d, after which acclimation to CTC was apparent for the duration of the experiment.

Anaerobic biodegradation of methyl tert-butyl ether and tert-butyl alcohol in petrochemical wastewater

A laboratory-scale anaerobic sequencing batch reactor was used to evaluate treatment of a synthetic substrate mixture representing petrochemical wastewater containing methyl tert-butyl ether (MTBE), ethanol and acetic acid. Influent MTBE concentrations were 5, 10 and 50 mg/l (corresponding to MTBE loading rates of 0.2, 0.4 and 2 mg/l.d) with overall organic loading rates (OLRs) of 1.51, 3.23 and 3.25 g COD/l.d, respectively. These OLRs resulted in removal efficiencies for MTBE of 78%, 98% and 88%. Removal efficiencies for chemical oxygen demand were 85% and 90% with influent MTBE concentrations of 5 and 10 mg/l, but were significantly reduced to 72% with influent MTBE concentrations of 50 mg/l. During all reactor runs, effluent concentrations of tert-butyl alcohol (TBA) were below the detection limit. Batch degradation of the organic substrate mixture demonstrated initial inhibitory effects when exposed to MTBE concentrations of 50 mg/l and complete inhibition with MTBE concentrations above 2000 mg/l. It is interesting to note that in batch tests using MTBE as the sole organic substrate (initial MTBE concentrations of 50, 100 and 200 mg/l), the specific methanogenic activity decreased to below detection within the first 96 hours, but following a 72-hour lag phase the methane production increased again. Based on low volatile fatty acid (VFA) concentration, disappearance of TBA peaks and no findings of any other intermediate via gas chromatography/mass spectrometry, while the MTBE concentration is still high, it can be suggested that during the batch tests the breakdown of gas production and the following lag phase were the direct effect of higher MTBE concentrations (more than 50 mg/l) and not because of the TBA or VFA accumulations.

Continuously-stirred anaerobic digester to convert organic wastes into biogas: system setup and basic operation.

Anaerobic digestion (AD) is a bioprocess that is commonly used to convert complex organic wastes into a useful biogas with methane as the energy carrier. Increasingly, AD is being used in industrial, agricultural, and municipal waste(water) treatment applications. The use of AD technology allows plant operators to reduce waste disposal costs and offset energy utility expenses. In addition to treating organic wastes, energy crops are being converted into the energy carrier methane. As the application of AD technology broadens for the treatment of new substrates and co-substrate mixtures, so does the demand for a reliable testing methodology at the pilot- and laboratory-scale. Anaerobic digestion systems have a variety of configurations, including the continuously stirred tank reactor (CSTR), plug flow (PF), and anaerobic sequencing batch reactor (ASBR) configurations. The CSTR is frequently used in research due to its simplicity in design and operation, but also for its advantages in experimentation. Compared to other configurations, the CSTR provides greater uniformity of system parameters, such as temperature, mixing, chemical concentration, and substrate concentration. Ultimately, when designing a full-scale reactor, the optimum reactor configuration will depend on the character of a given substrate among many other nontechnical considerations. However, all configurations share fundamental design features and operating parameters that render the CSTR appropriate for most preliminary assessments. If researchers and engineers use an influent stream with relatively high concentrations of solids, then lab-scale bioreactor configurations cannot be fed continuously due to plugging problems of lab-scale pumps with solids or settling of solids in tubing. For that scenario with continuous mixing requirements, lab-scale bioreactors are fed periodically and we refer to such configurations as continuously stirred anaerobic digesters (CSADs). This article presents a general methodology for constructing, inoculating, operating, and monitoring a CSAD system for the purpose of testing the suitability of a given organic substrate for long-term anaerobic digestion. The construction section of this article will cover building the lab-scale reactor system. The inoculation section will explain how to create an anaerobic environment suitable for seeding with an active methanogenic inoculum. The operating section will cover operation, maintenance, and troubleshooting. The monitoring section will introduce testing protocols using standard analyses. The use of these measures is necessary for reliable experimental assessments of substrate suitability for AD. This protocol should provide greater protection against a common mistake made in AD studies, which is to conclude that reactor failure was caused by the substrate in use, when really it was improper user operation.

Anaerobic digestion technology in livestock manure treatment for biogas production: A review

This article reviews the potential of anaerobic digestion (AD) for biogas production from livestock manure wastes and compares the operating and performance data for various anaerobic process configurations. It examines different kinds of manure waste treatment techniques and the influence of several parameters on biogas and methane yield. The comparison indicates that a variety of different operational conditions, various reactor configurations such as batch reactors, continuously stirred tank reactor (CSTR), plug flow reactor (PFR), up‐flow anaerobic sludge blanket (UASB), anaerobic sequencing batch reactor (ASBR), temperature phased anaerobic digestion (TPAD), and continuous one‐ and two‐stage systems, present a suitable technology for the AD of livestock manure waste. Main performance indicators are biogas and methane yield, degradation of volatile solids (VS), higher loading, and process stability with a short retention time.

Factors Influencing Iron Reduction–Induced Phosphorus Precipitation

Abstract An iron-amended anaerobic sequencing batch reactor, fed with synthetic sewage, was used to evaluate the factors influencing iron reduction–induced phosphorus precipitation from a simulated septic system. Results revealed that soluble phosphate could be effectively removed from the reactor when the added amorphous ferric oxyhydroxide (α-FeOOH) was increased from a molar ratio of 1.5 to 3. Whereas cycle time, substrate concentration, and temperature did not have a noticeable effect on iron reduction and the subsequent phosphorus removal, agitation was found to be an important factor, enabling better contact between α-FeOOH and the microorganisms during phosphorus removal. Precipitates collected from the reactor were analyzed by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD). Results demonstrated that the precipitate was mainly vivianite [Fe3(PO4)2·8H2O], which suggests that phosphorus was removed through iron reduction–induced precipitatio...

Hydrogen production from alcohol wastewater by an anaerobic sequencing batch reactor under thermophilic operation: Nitrogen and phosphorous uptakes and transformation

The objective of this study was to investigate hydrogen production from alcohol wastewater using an anaerobic sequencing batch reactor (ASBR) under thermophilic operation and at a constant pH of 5.5. Under the optimum COD loading rate of 68 kg/m3d, the produced gas contained 43% H2 without methane and the system provided a hydrogen yield and specific hydrogen production rate of 130 ml H2/g COD removed and 2100 ml H2/l d, respectively, which were much higher than those obtained under the mesophilic operation. Under thermophilic operation, both nitrogen and phosphate uptakes were minimal at the optimum COD loading rate for hydrogen production and most nitrogen uptake was derived from organic nitrogen. Under the thermophilic operation for hydrogen production, the nutrient requirement in terms of COD:N:P was found to be 100:6:0.5, which was much higher than that for the methenogenic step for methane production under both thermophilic and mesophilic operations and for the acidogenic step for hydrogen production under mesophilic operation.