The effect of temperature fluctuations on psychrophilic anaerobic sequencing batch reactors treating swine manure

Under northern climatic conditions, a temporary decrease in the temperature of anaerobic reactors treating swine manure is likely to happen at the farm. The objective of this study was to evaluate the impact of temperature fluctuations, between 10 and 20 degrees C, on the stability and performance of psychrophilic anaerobic sequencing batch reactors (ASBRs) treating swine manure. Methane yield decreased from 0.266+/-0.014 l/g of total chemical oxygen demand (TCOD) fed to the ASBRs at 20 degrees C to 0.218+/-0.022 and 0.080+/-0.002 l/g TCOD (fed) at 15 and 10 degrees C, respectively. Soluble chemical oxygen demand (SCOD) reduction decreased from 94.2+/-1.1% at 20 degrees C to 78.8+/-3.0% at 15 degrees C and 60.4+/-6.4% at 10 degrees C. Total COD removal also tended to decrease as temperature was lowered, but difference between operating temperatures was not as pronounced. A lower methanogenic activity in the ASBRs operated at 10 degrees C probably favoured quiescent conditions during the settling period, thereby increasing physical removal of the TCOD through sedimentation of the solids with the biomass. When the operating temperature was increased back to 15 and 20 degrees C, methane yield and SCOD reduction improved, but reactor performance remained significantly (P<0.05) lower than that achieved before the cycles at 10 degrees C. Results from this experiment nevertheless suggested that fluctuation in the operating temperature of psychrophilic ASBRs should only have temporary effects on the performance and stability of the process.     

Effects of temperatures and organic loading rates on biomethanation of acidic petrochemical wastewater using an anaerobic upflow fixed-film reactor

The effect of temperature and organic loading rate on the rate of methane production from acidic petrochemical wastewater without neutralization was investigated by continuously feeding an anaerobic upflow fixed-film reactor. The temperatures selected for the studies were 25, 37, 45 and 55 degrees C. Organic loading rate (OLR) for each temperature was varied from 3.6 to 21.7 kg COD m(-3) d(-1). Best performance with respect to COD and BOD reduction, total gas production and methane yield was obtained with the reactor operating at 37 degrees C. OLR could be increased to a maximum of 21.7 kg COD m(-3) d(-1) with 90-95% COD and BOD reduction and methane yield of 0.450 m3 kg(-1) COD d(-1) added. The reactor operating at 55 degrees C gave the highest methane yield of 0.666 m3 kg(-1) COD d(-1) at an OLR of 6 kg COD m(-3) d(-1). This decreased to 0.110 m3 kg(-1) COD d(-1) when the OLR was increased to 18.1 kg COD m(-3) d(-1). The reactor operating at 45 degrees C gave a maximum methane yield of 0.416 m3 kg(-1) COD d(-1) added at an OLR of 6 kg COD m(-3) d(-1). On further increasing the OLR to 9 kg COD m(-3) d(-1), COD reduction was 89%, however, methane yield decreased to 0.333 m3 kg(-1) COD d(-1) added. The highest methane yield of 0.333 m3 kg(-1) COD d(-1) added at an OLR of 6 kg COD m(-3) d(-1) was obtained with reactors operating at 25 degrees C. These studies indicate potential rates of methane production from acidic petrochemical wastewater under different temperatures. This provides a guideline for various kinetic analyses and economic evaluation of the potential feasibility of fermenting acidic wastewater to methane.     

Effects of cationic polymer on performance of UASB reactors treating low strength wastewater

The effect of cationic polymer additives on biomass granulation and COD removal efficiency had been examined in lab-scale upflow anaerobic sludge blanket (UASB) reactors, treating low strength synthetic wastewater (COD 300-630 mg/l). Under identical conditions, two reactors were operated with and without polymer additives in inoculum under four different organic loading rates (OLRs). The optimum polymer dose was adopted based upon the results of jar test and settling test carried out with inoculum seed sludge. With the use of thick inoculum, SS greater than 110 g/l and VSS/SS ratio less than 0.3, granulation was observed in UASB reactor treating synthetic wastewater as well as actual sewage, when OLR was greater than 1.0 kg COD/m(3) d. Polymer additive with such thick inoculum was observed to deteriorate percentage granules and COD removal efficiency compared to inoculum without polymer additives. At OLR less than 1.0 kg COD/m(3) d, proper granulation could not be achieved in both the reactors inoculated with and without polymer additive. Also, under this low loading, drastic reduction in COD removal efficiency was observed with polymer additives in inoculum. Hence, it is rational to conclude that biomass granulation for treatment of low strength biodegradable wastewater depends on the applied loading rate and selection of thick inoculum sludge.     

Ambient temperature treatment of low strength wastewater using anaerobic sequencing batch reactor

Low strength wastewater having chemical oxygen demands (COD) concentrations of 1000, 800, 600 and 400mg/l were treated at 35, 25, 20 and 15¡C using four anaerobic sequencing batch reactors (ASBRs). Reactor 1 was operated at hydraulic retention time (HRT) of 48h, reactor 2 at 24h HRT, reactor 3 at 16h HRT and reactor 4 at 12h HRT. 80 to 99% soluble COD was removed at the various operational conditions, except during 15¡C treatment of 1000 and 800mg/l COD wastewater at 12h HRT and 1000mg/l COD wastewater at 16h HRT, where excessive loss of biological solids occurred. The ASBR process can be an effective process for the treatment of low concentrated wastewaters which are usually treated aerobically with large amount of sludge production and higher energy expenditures.     

Anaerobic treatment of low-strength wastewater with a high fraction of particulate matter in an unconventional two-phase ASBRs system

The results of a two-phase anaerobic system using anaerobic sequencing batch reactors (ASBRs), treating low-strength wastewater (COD ∼ 500 mg/L) with a high fraction of particulate organic matter (70%, COD basis), are presented. Two reactors in series were used; the first one was hydrolytic–acidogenic, while the second one was methanogenic. This configuration was proposed to promote high efficiency solids removal. During the experiment, 69% and 50% efficiencies of total COD removal were obtained for OLRs of 0.63 and 1.22 kgCOD/(m³ d), respectively. Values of the solubilized organic fraction (SOF) achieved in the hydrolytic–acidogenic reactor were within the range of 0.3–0.6 gCOD_solubilized/gpCOD_removed, and the average acidified organic fraction (AOF) was 0.6 gCOD_VFA-produced/gsCOD_fed. The methanogenic reactor had a VFA removal fraction (VFARF) between 0.4 and 0.6 gCOD_VFA-removed/gCOD_VFA-fed for the OLR of 0.63 and 1.22. The two-phase ASBR system is suitable, and can be implemented, for the anaerobic treatment of this kind of wastewater.     

The effects of digestion temperature and temperature shock on the biogas yields from the mesophilic anaerobic digestion of swine manure

In order to obtain basic design criteria for anaerobic digesters of swine manure, the effects of different digesting temperatures, temperature shocks and feed loads, on the biogas yields and methane content were evaluated. The digester temperatures were set at 25, 30 and 35 degrees C, with four feed loads of 5%, 10%, 20% and 40% (feed volume/digester volume). At a temperature of 30 degrees C, the methane yield was reduced by only 3% compared to 35 degrees C, while a 17.4% reduction was observed when the digestion was performed at 25 degrees C. Ultimate methane yields of 327, 389 and 403 mL CH(4)/g VS(added) were obtained at 25, 30 and 35 degrees C, respectively; with moderate feed loads from 5% to 20% (V/V). From the elemental analysis of swine manure, the theoretical biogas and methane yields at standard temperature and pressure were 1.12L biogas/g VS(destroyed) and 0.724 L CH(4)/g VS(destroyed), respectively. Also, the methane content increased with increasing digestion temperatures, but only to a small degree. Temperature shocks from 35 to 30 degrees C and again from 30 to 32 degrees C led to a decrease in the biogas production rate, but it rapidly resumed the value of the control reactor. In addition, no lasting damage was observed for the digestion performance, once it had recovered.     

Application of the upflow anaerobic sludge bed (UASB) process for treatment of complex wastewaters at low temperatures

The feasibility of the upflow anaerobic sludge bed (UASB) process for the treatment of potato starch wastewater at low ambient temperatures was demonstrated by operating two 5.65-L reactors at 14 degrees C and 20 degrees C, respectively. The organic space loading rates achieved in these laboratory-scale reactors were 3 kg COD/m(3)/day at 14 degrees C and 4-5 kg COD/m(3)/day at 20 degrees C. The corresponding sludge loading rates were 0.12 kg COD/kg VSS/day at 14 degrees C and 0.16-0.18 kg COD/kg VSS/day at 20 degrees C.These findings are of considerable practical importance because application of anaerobic treatment at low ambient temperatures will lead to considerable savings in energy needed for operating the process. As compared with various other anaerobic wastewater treatment processes, a granular sludge upflow process represents one of the best options developed so far. Although the overall sludge yield under psychrophilic conditions is slightly higher than under optimal mesophilic conditions, this doesn't seriously hamper the operation of the process. The extra sludge yield, due to accumulation of slowly hydrolyzing substrate ingredients, was 4.75% of the COD input at 14 degrees C and 1.22% of the COD input at 20 degrees C.     

Treatment of low strength soluble wastewaters in UASB reactors

Low strength wastewaters can be those with chemical oxygen demand (COD) below 2,000 mg/l. The anaerobic treatment of such wastewaters has not been fully explored so far. The suboptimal reaction rates with low substrate concentrations, and the presence of dissolved oxygen in the influent are regarded as possible constraints. In this study, the treatment of low strength soluble wastewaters containing ethanol or whey was studied in lab-scale upflow anaerobic sludged bed (UASB) reactors at 30°C. The high treatment performance obtained demonstrates that UASB reactors are viable for treating both types of wastewaters at low COD concentrations. The treatment of the ethanol containing wastewater resulted in COD removal efficiencies exceeding 95% at organic loading rates (OLR) between 0.3 to 6.8 g COD/l-d with influent concentrations in the range of 422 to 943 mg COD/l. In the case of the more complex whey containing wastewater, COD removal efficiencies exceeded 86% at OLRs up to 3.9 g COD/l·, as long as the COD influent was above 630 mg/l. Lowering the COD influent resulted in decreased efficiency with sharper decrease at values below 200 mg/l. Acidification instead of methanogenesis was found to be the rate limiting step in the COD removal at low concentrations, which was not the case when treating ethanol. The effect of dissolved oxygen in the influent as a potential danger in anaerobic treatment was investigated in reactors fed with and without dissolved oxygen. Compared with the control reactor, the reactor receiving oxygen showed no detrimental effects in the treatment performance. Thus, the presence of dissolved oxygen in dilute wastewaters is expected to be of minor importance in practice.     

Neutral fat hydrolysis and long-chain fatty acid oxidation during anaerobic digestion of slaughterhouse wastewater

Neutral fat hydrolysis and long-chain fatty acid (LCFA) oxidation rates were determined during the digestion of slaughterhouse wastewater in anaerobic sequencing batch reactors operated at 25 degrees C. The experimental substrate consisted of filtered slaughterhouse wastewater supplemented with pork fat particles at various average initial sizes (D(in)) ranging from 60 to 450 microm. At the D(in) tested, there was no significant particle size effect on the first-order hydrolysis rate. The neutral fat hydrolysis rate averaged 0.63 +/- 0.07 d(-1). LCFA oxidation rate was modelled using a Monod-type equation. The maximum substrate utilization rate (kmax) and the half-saturation concentration (Ks) averaged 164 +/- 37 mg LCFA/L/d and 35 +/- 31 mg LCFA/L, respectively. Pork fat particle degradation was mainly controlled by LCFA oxidation rate and, to a lesser extent, by neutral fat hydrolysis rate. Hydrolysis pretreatment of fat-containing wastewaters and sludges should not substantially accelerate their anaerobic treatment. At a D(in) of 450 microm, fat particles were found to inhibit methane production during the initial 20 h of digestion. Inhibition of methane production in the early phase of digestion was the only significant effect of fat particle size on anaerobic digestion of pork slaughterhouse wastewater. Soluble COD could not be used to determine the rate of lipid hydrolysis due to LCFA adsorption on the biomass.     

Acetate Degradation at 70 degrees C in Upflow Anaerobic Sludge Blanket Reactors and Temperature Response of Granules Grown at 70 degrees C

Anaerobic acetate degradation at 70 degrees C and at 55 degrees C (as a reference) was studied by running laboratory upflow anaerobic sludge blanket (UASB) reactors inoculated with mesophilic granular sludge. In UASB reactors fed with acetate-containing media (3 g of chemical oxygen demand [COD] per liter, corresponding to 47 mM acetate) approximately 50 days was needed at 70 degrees C and less than 15 days was needed at 55 degrees C to achieve an effluent COD of 500 to 700 mg/liter. In the UASB reactors at both 70 and 55 degrees C up to 90% of the COD was removed. Batch assays showed that sludges from two 70 degrees C UASB reactors, one run at a low effluent acetate concentration and the other run at a high effluent acetate concentration, exhibited slightly different responses to temperatures in the range from 37 to 70 degrees C. Both 70 degrees C sludges, as well as the 55 degrees C sludge, produced methane at temperatures of 37 to 73 degrees C. The 55 degrees C sludge exhibited shorter lag phases than the 70 degrees C sludges and higher specific methane production rates between 37 and 65 degrees C.     

Effect of temperature on performance and microbial diversity in hyperthermophilic digester system fed with kitchen garbage

The objective of this study was to evaluate the performances and microbial diversities for development of the effective hyperthermophilic digester system that consists of hyperthermophilic reactor and hyperthermophilic or thermophilic reactor in series. Lab-scale reactors were operated continuously fed with artificial kitchen garbage. The effect of temperature on the acidification step was firstly investigated. Results indicated that 43.1% of COD solubilization was achieved at 70 degrees C, while it was about 21% at 80 degrees C. The average protein solubilization reached to 31% at 80 degrees C. Methane conversion efficiency following the acidification was around 85% in average at 55 degrees C, but decreased with increasing temperature and methane gas was not produced over 73 degrees C. The upper temperature limits for growth of microbes were secondly observed and shown to be 73 degrees C for acetate oxidizers, 65 degrees C for propionate oxidizers, 70 degrees C for iso-butyrate oxidizers, 80 degrees C for lactate oxidizers and 65 degrees C for protein degrading bacteria in the methane fermenter. As well as, microbes affiliated with methanogens dominated the population below the 65 degrees C, while those affiliated with acidogens were predominant over the 73 degrees C. These results indicated that the hyperthermophilic processes have considerable benefits to treat wastewater or waste containing high concentration of protein.     

Performance evaluation of a mesophilic anaerobic fluidized-bed reactor treating wastewater derived from the production of proteins from extracted sunflower flour

A study of the anaerobic digestion of wastewater derived from the production of protein isolates from extracted sunflower flour was carried out in a laboratory-scale, mesophilic (35 degrees C) fluidized-bed reactor with saponite as bacterial support. Chemical oxygen demand (COD) removal efficiencies in the range of 98.3-80.0% were achieved in the reactor at organic loading rates (OLR) of between 0.6 and 9.3 g COD/I d, hydraulic retention times (HRT) of between 20.0 and 1.1 d and average feed COD concentration of 10.6 g/l. Eighty percent of feed COD could be removed up to OLR of 9.3 g COD/l d. The yield coefficient of methane production was 0.33 l of methane (at STP) per gram of COD removed and was virtually independent of the OLR applied. Because the buffering capacity of the experimental system was maintained at favorable levels with excess total alkalinity present at all loadings, the rate of methanogenesis was not affected by loading. The experimental data indicated that a total alkalinity in the range of 2,000-2,460 mg/l as CaCO3 was sufficient to prevent the pH from dropping to below 7.0 for OLR of up to 9.3 g COD/l d. The volatile fatty acid (VFA) levels and the VFA/alkalinity ratio were lower than the suggested limits for digester failure (0.3-0.4) for OLR and HRT up to 9.3 g COD/l d and 1.1 d, respectively. For a HRT of 0.87 d (OLR of 12.1 g COD/l d) the start of acidification was observed in the reactor.     

Bioenergy conversion studies of organic fraction of MSW: kinetic studies and gas yield--organic loading relationships for process optimisation

Batch digestion of municipal garbage was carried out for 100 days at room temperature (26+/-4 degrees C; average temperature 25 degrees C) and at ambient temperature (32+/-10 degrees C; average temperature 29 degrees C) conditions for total solids concentrations varying between 45 and 135 g/l. A first order model based on the availability of substrate as the limiting factor was used to perform the kinetic studies of batch anaerobic digestion system. Effect of organic solids concentration and digestion time on biogas yield was studied and mass and energy balance analysis was conducted for batch digestion. The net bioenergy yield from municipal garbage and corresponding bioprocess conversion efficiency over the length of the digestion time were observed to be 12,528 kJ/kg volatile solids and 84.51% respectively. The methane content of the biogas generated from the reactors was in the range of 62-72% with the overall average methane content of the biogas, computed over the total digestion period was 65 vol%.     

Petroleum coke supplementation for enhanced biogas production and phosphate removal under mesophilic conditions

The use of carbon-based conductive materials has been shown to lead to an increase in biogas and methane yields during anaerobic digestion (AD). The effect of these additives on AD using synthetic substrates has been extensively studied, yet their significance for wastewater sludge digestion has not been adequately investigated. Therefore, the aim of this research was to optimize the concentration of petroleum coke (PC) that is a waste by-product of oil refineries, for the anaerobic digestion of wastewater sludge and investigation of phosphate removal in the AD process in the mesophilic temperature range. According to the results of the experiments, supplementing reactors with PC could significantly improve biogas and methane production. Supplementation of reactors with 1.5 g/L PC led to 23.40 ± 0.26% and 42.55 ± 3.97% increase in biogas production and methane generation, respectively. Moreover, the average volatile solids (VS), phosphate, and chemical oxygen demand (COD) removals were 43.43 ± 0.73, 46.74 ± 0.77%, and 60.40 ± 0.38%, respectively.     

Use of the UASB reactor for the anaerobic treatment of stillage from sugar cane molasses

The feasibility of applying the UASB concept for the anaerobic treatment of stillage of distilleries in the sugar producing area of Argentina was subject to study. Results obtained in a 100-L UASB reactor treating stillages with COD values between 35 and 100 g COD/L are presented. Loading rates of up to 24 g COD/L/day were applied with an average COD removal of 75% and a biogas production of more than 9 L/L/day, with an average methane content of 58%. The settling velocity distribution of sludge particles would indicate a good formation of biomass pellets. System interruptions of months without feed and at ambient temperature (20-24 degrees C) were well tolerated.     

Treatment of strong domestic sewage in a 96 m3 UASB reactor operated at ambient temperatures: two-stage versus single-stage reactor

A 96 m3 UASB reactor was operated for 2.5 years under different conditions to assess the feasibility of treating strong sewage (COD(tot) = 1531 mg/l) at ambient temperatures with averages of 18 and 25 degrees C for winter and summer respectively. During the first year, the reactor was operated as a two-stage system at OLRs in the range of 3.6-5.0 kg COD/m3 d for the first stage and 2.9-4.6 kg COD/m3 d for the second stage. The results of the first stage showed average removals of 51% and 60% for COD(tot) and COD(ss) respectively without significant effect of temperature. The second stage reactor was unstable. The temperature affected sludge stabilization. During the second year, the first stage was operated as a single-stage UASB reactor at half of the previous loading rates. The results showed an average removal efficiency of 62% for COD(tot) during summer, while it dropped to 51% during wintertime. However, the effluent suspended solids were stabilized with VSS/TSS ratio around 0.50 all over the year. The sludge in the single-stage reactor was well-stabilized and exerted an excellent settlability. During the last three months of research, sludge was discharged regularly from the single-stage UASB reactor. The results showed no significant improvement in the performance in terms of COD(tot). Based on the results of the experiment, a single-stage UASB reactor operated at relatively long HRT is preferred above two-stage system at the Jordanian conditions.     

Nitrogen removal in an anaerobic baffled filter reactor with aerobic post-treatment

A new sewage treatment system was studied, which consisted of an anaerobic baffled filter reactor and the following aerobic post-treatment. One of the two studied systems (AN-I) was inoculated with psychrophilic digested sludge, the second one (AN-II) was operated without inoculation. The HRT in anaerobic and aerobic parts of the reactors were about 15 and 4 h, respectively. The temperature in both reactors varied during the year from 4.5 to 23 degrees C. All monitored parameters were removed with relatively high efficiencies (COD = 78.6-83.0%, BOD5 = 92.5-94.0% and SS = 80.9-92.7%). An intensive nitrification process was observed during the whole year in both reactors (under average temperature of 5.9 degrees C in January 2000, also). The average removal of the NH4-N varied during the year from 46.4% to 87.3%. In both systems a partial denitrification process was observed, too.     

Performance characteristics of a two-stage dark fermentative system producing hydrogen and methane continuously

The performance of a mesophilic two-stage system generating hydrogen and methane continuously from sucrose (10-30 g/L) was investigated. A hydrogen-generating CSTR followed by an upflow anaerobic filter were both inoculated with anaerobically digested sewage sludge, and ORP, pH, gas output, %H(2), %CH(4) and %CO(2) monitored. pH was controlled with NaOH, KOH or Ca(OH)(2). Using NaOH as alkali with 10 g/L sucrose, yields of 1.62 +/- 0.2 mol H(2)/mol hexose added and 323 mL CH(4)/gCOD added to the hydrogen and methane reactors respectively were achieved. The overall chemical oxygen demand (COD) reduction was 92.6% with 0.90 +/- 0.1 g/L sodium and 316 +/- 40 mg/L residual acetate in the methane reactor. Operation at 20 g/L sucrose and NaOH as alkali led to impaired volatile fatty acid (VFA) degradation in the methane reactor with 2.23 +/- 0.2 g/L sodium, 1,885 mg/L residual acetate, a hydrogen yield of 1.47 +/- 0.1 mol/mol hexose added, a methane yield of 294 mL/gCOD added and an overall COD reduction of 83%. Using Ca(OH)(2) as alkali with 20 g/L sucrose gave a hydrogen yield of 1.29 +/- 0.3 mol/mol hexose added, a methane yield of 337 mL/gCOD added and improved the overall COD reduction to 91% with residual acetate concentrations of 522 +/- 87 mg/L. Operation at 30 g/L sucrose with Ca(OH)(2) gave poorer overall COD reduction (68%), a hydrogen yield of 1.47 +/- 0.2 mol/mol hexose added, a methane yield of 138 mL/gCOD added and residual acetate 7,343 +/- 715 mg/L. It was shown that sodium toxicity and overloading are important issues for successful anaerobic digestion of effluent from biohydrogen reactors in high rate systems.     

Effect of pH on phase separated anaerobic digestion

A pilot scale experiment was performed for a year to develop a two-phase anaerobic process for piggery wastewater treatment (COD: 6,000 mg/L, BOD: 4,000 mg/L, SS: 500 gm/L, pH 8.4, alkalinity 6,000 mg/L). The acidogenic reactor had a total volume of 3 m³, and the methanogenic reactor, an, anaerobic up-flow sludge filter, combining a filter and a sludge bed, was also of total volume 3 m³ (1.5 m³ of upper packing material). Temperatures of the acidogenic and methanogenic reactors kept at 20°C and 35°C., respectively. When the pH of the acidogenic reactor was controlled at 6.0–7.0 with HCl, the COD removal efficiency increased from 50 to 80% over a period of six months, and as a result, the COD of the final effluent fell in the range of 1,000–1,500 mg/L. BOD removal efficiency over the same period was above 90%, and 300 to 400 mg/L was maintained in the final effluent. The average SS in the final effluent was 270 mg/L. The methane production was 0.32 m³ CH₄/kg COD_removed and methane content of the methanogenic reactor was high value at 80–90%., When the pH of the acidogenic reactor was not controlled over the final two months, the pH reached 8.2 and acid conversion decreased compared with that of pH controlled, while COD removal was similar to the pH controlled operation. Without pH control, the methane content in the gas from methanogenic reactor improved to 90%, compared to 80% with pH control.     

Enhancing the start-up of a UASB reactor treating domestic wastewater by adding a water extract of Moringa oleifera seeds

Water extract of Moringa oleifera seeds (WEMOS) was used to enhance the start-up of a self-inoculated upflow anaerobic sludge blanket (UASB) reactor treating raw domestic wastewater. Two reactors labelled control (RC) and WEMOS addition (RM) were started without special inoculum. Both reactors were fed continuously for 22 weeks with domestic wastewater containing an average total chemical oxygen demand (COD) of 320 mg O2/l and suspended solid (SS) of 165 mg/l. The reactors operated during the entire experimental period at 29 degrees C and at a hydraulic retention time (HRT) of 4 h. The RM reactor received 2 ml WEMOS per litre of influent. WEMOS solution was prepared on the basis of 2.5% (w/v) ground M. oleifera seeds in water. The results of 22 weeks' operation showed an improvement in the performance of the RM compared to that of the RC. The dosage of WEMOS in the feed (1) shortened the biological start-up period by 20%, (2) increased acidogenic and methanogenic activity by a factor of 2.4 and 2.2 respectively, (3) increased the specific biogas production by a factor of 1.6, (4) favoured fast growth of the sludge bed, and (5) allowed the aggregation of coccoid bacteria and growth of microbial nuclei, which are precursors of anaerobic granulation.