Using Upflow Anaerobic Sludge Blanket Research Articles

Improving CH4/O2 energy ratio of meat processing wastewater treatment systems through micro-sieving

ABSTRACT Micro-sieving is an effective way to prevent organic pollutants enter the main biological process and reduce aeration intensity and sludge production. However, few researchers quantified the effect of micro-sieving on meat processing wastewater treatment. The current study developed Excel-based models to compare the energy consumption and production of historical, conventional and innovative systems. Historical and conventional systems employ activated sludge (AS), nitrification, and denitrification as the main biological processes. Innovative systems are designed by using up-flow anaerobic sludge blanket (UASB) and partial nitrification/Anammox (PN/A) as the main treatment processes. Results show that the CH4/O2 energy ratios of the innovative treatment system are as high as 10 times of the historical and conventional systems. Therefore, innovative system can achieve electrical self-sufficiency. Micro-sieving reduces 5% of aeration demand. Furthermore, the impact of micro-sieving on the innovative treatment systemis assessed by cost-benefit analysis. System with micro-sieving has the shortest payback time of 2.1 years and reduces cost of the innovative treatment system. An excel-based model was developed to quantify the impact of micro-sieving on energy and cost of innovative treatment system, thereby providing a valuable reference for future sustainable engineering design of meat processing wastewater treatment.

Comparison of three anaerobic digestion reactors for low-carbon wastewater treatment.

In this study, three anaerobic digestion reactors using up-flow anaerobic sludge blanket (UASB), anaerobic sequencing batch reactor (AnSBR), and anaerobic membrane bioreactor (AnMBR) were studied. The chemical oxygen demand (COD), gas production, sludge performance, and microbial characteristics of the anaerobic digestion process were assessed. The results showed that the average COD removal efficiencies reached 86%, 83%, and 85%, with corresponding removed rates of 2.49, 0.48, and 0.79 kg COD m-3d-1 in UASB, AnSBR, and AnMBR, respectively. After the reactors attained stable operation, both extracellular polymeric substances and soluble microbial products decreased in all the reactors compared with the seed sludge. Methanothrix was the dominant archaea for methane production in the UASB, the relative abundance of which increased from 58.3% to 83.4%. These results identify UASB as the most suitable reactor for anaerobic digestion when treating wastewater with low carbon. Such reactors are important for the application and development of the energy self-sufficiency in sewage treatment. PRACTITIONER POINTS: UASB, SBR, and MBR were adopted to treat low-carbon wastewater using anaerobic digestion process. UASB performed the highest COD removal from low-carbon wastewater. The main microorganisms in UASB were Methanothrix, Methanomassiliicoccus, and Methanobacterium.

A comparative long-term operation using up-flow anaerobic sludge blanket (UASB) and anaerobic membrane bioreactor (AnMBR) for the upgrading of anaerobic treatment of N, N-dimethylformamide-containing wastewater

Synthetic industrial wastewater containing approximately 2000 mg/L N, N-dimethylformamide (DMF) was treated using a lab-scale anaerobic sludge blanket (UASB) and an anaerobic membrane bioreactor (AnMBR) in this study. The inoculum consisted of two sources of sludge: Co-culture of anaerobic digested sludge (ADS) with DMF-hydrolyzing activated sludge (DAS) for the AnMBR, and co-culture of anaerobic granular sludge (AGS) with DAS for the UASB. Effective DMF methanogenic degradation of nearly 100% removal was achieved in both reactors on the first day. Both reactors obtained excellent DMF removal efficiency and high methane production under a low organic loading rate (OLR) of around 3–4 g COD/L/d. However, excessive elevation of OLR significantly limited DMF hydrolysis. When OLR exceeded 6 g COD/L/d, the removal efficiency and methane production in both reactors dramatically dropped. Despite their different forms and shapes, the ADS and AGS both provide methanogens which are responsible for methanogenesis. The UASB tolerated a higher OLR while the AnMBR was limited by membrane fouling due to the increased sludge concentration. However, the AnMBR obtained high-quality effluent without suspended solid. Whether DMF can be effectively degraded depends on DAS, in which abundant DMF-hydrolyzing bacteria (DHB) provide sufficient quantities of the hydrolytic enzyme for effective hydrolysis of DMF. However, these DHB were facultative and were also identified as denitrifying bacteria which require nitrate as the electron acceptor or otherwise survive under the aerobic condition. They gradually decayed rather than proliferated and were outcompeted by methanogens. Therefore, it is conceivable that a slight dosage of nitrate would enrich the abundance of DHB in both the UASB and the AnMBR, and provide a sufficient quantity of enzymes for the DMF hydrolysis. The cultivation of the anaerobic DMF-degrading granular sludge using the UASB is considered an upgraded solution to the effective treatment of DMF-containing wastewater.

An integrated approach to explore UASB reactors for energy recycling in pulp and paper industry: a case study in Brazil

Brazil is currently focused on its energy matrix transition in favor of increasing of the share of renewable energy carriers for both enhanced energy security and mitigation of greenhouse gas emissions. In this context, the country`s pulp and paper industry whose different wastes teams are not generally exploited, could play a critical role. Accordingly, the main objective of this work is to develop a conceptual ‘systemic’ biorefinery framework integrating the treatment of pulp and paper mill wastewater using upflow anaerobic sludge blanket (UASB) reactor with energy recovery through biogas production and its conversion into heat and power in stationary engines and boilers, respectively. Based on the results obtained through the present case study, it was revealed that the adoption of UASB reactors by the paper mill industry could properly addresses the environmental concerns faced while could contribute to the national agenda favoring an increasing share of renewable energies in the country`s energy matrix. The financial analysis showed that the investment required for the implementation of UASB reactors within a biorefinery platform would be minor vs. the investment in the whole mill and would be returned in 6.4 yr with a high return on investment even when operated at half of operational capacity. Moreover, through the developed UASB reactor-based biorefinery, the Brazilian pulp and paper industry as a whole could avoid 1.06 ×105 CO2eq tons, effectively contributing to the decarbonization of the country`s economy.

Potential enhancement of direct interspecies electron transfer for anaerobic degradation of coal gasification wastewater using up-flow anaerobic sludge blanket (UASB) with nitrogen doped sewage sludge carbon assisted

Waste sewage sludge was converted into the novel conductive material of nitrogen doped sewage sludge carbon (N-SC) to enhance anaerobic degradation of coal gasification wastewater (CGW). The results indicated that N-SC played a significant role in enhanced efficiencies, with chemical oxygen demand (COD) removal efficiency increased by 25.4%, methane production rate improved by 68.1% and total volatile fatty acids (VFA) decreased by 37.5% than that of controlled reactor. The conductivity, activity of electron transport, and extracellular polymeric substances (EPS) of anaerobic sludge were remarkably enhanced with N-SC, which promoted sludge granulation and supplied better conductive environment for microorganisms. The microbial community analysis revealed that potential enhancement of direct interspecies electron transfer (DIET) was achieved by electrical connection between enriched Geobacter, Pseudomonas and Methanosaeta with N-SC assisted, which enhanced the anaerobic degradation of CGW. Moreover, anaerobic degradation with N-SC had higher capacity to resist acidic shocks, facilitating the process stability.

Simultaneous recovery of calcium phosphate granules and methane in anaerobic treatment of black water: Effect of bicarbonate and calcium fluctuations

Calcium phosphate (CaP) granules were discovered in the anaerobic treatment of vacuum collected black water (BW), using upflow anaerobic sludge blanket (UASB) technology. This allows simultaneous recovery of CaP granules and methane in the UASB reactor. However, the role of BW composition on CaP granulation is not yet understood. Moreover, CaP granulation was not observed in previous research on anaerobic treatment of BW, although similar treatment conditions were applied. Therefore, this study shows specifically the influence of bicarbonate and calcium fluctuations in BW on the phosphorus accumulation in the UASB reactor, which directly affects CaP granulation. Without calcium addition, 5% of the total phosphorus (P) fed was found as CaP granules in the reactor (61 mgP g−1dried matter), after 260 days of operation. Simultaneously, 65% of the COD in BW was efficiently converted into methane at 25 °C. Variations of bicarbonate and calcium concentrations in raw BW showed a significant influence on phosphorus accumulation in the UASB reactor. Geochemical modelling showed that the increase of soluble calcium from 39 to 54 mg L−1 in BW triggers supersaturation for calcium phosphate precursors (Cax(PO4)y). Concurrently, bicarbonate decreased from 2.7 to 1.2 g L−1, increasing further the ionic activity of calcium. Formation and accumulation of seed particles possibly enhanced CaP granulation. Preliminary results showed that addition of calcium (Ca2+/PO43− molar ratio of 3) increased the accumulation of total P in the UASB reactor to more than 85%. This further increases the granulation rate and consequently, the process feasibility.

Dye decomposition by combined ozonation and anaerobic treatment: Cost effective technology

Abstract To control the total treatment cost of textile dye effluent a new advanced combined treatment technology has been investigated. Advanced oxidation processes like ozonation have much potential to degrade dye but its main drawback is high cost. To reduce the cost of ozonation for dye degradation and decolourization, ozonation followed by anaerobic biodegradation using upflow anaerobic sludge blanket (UASB) reactor was carried out. The synthetic textile wastewater containing Reactive Black 5 has been used in this study by this combined treatment process. The system of ozonation and anaerobic treatment by UASB reactor showed that the chemical oxygen demand (COD) reduction has reached to about 90% and dye removal 94% respectively. Combined treatment enhanced the overall color removal up to 10 on platinum cobalt (Pt–Co) scale. Thus the combined treatment process results in high color, COD and total organic carbon (TOC) removal efficiency which would minimize the overall treatment cost. Dye degradation products were analyzed by ion chromatography (IC) and UV–vis spectroscopy.

Fermentation of hydrogen, 1,3-propanediol and ethanol from glycerol as affected by organic loading rate using up-flow anaerobic sludge blanket (UASB) reactor

The influences of organic loading rate (OLR) on the production of biohydrogen, 1,3-propanediol (1,3-PD) and ethanol from glycerol in an up-flow anaerobic sludge blanket (UASB) by anaerobic mixed cultures were investigated. UASB reactor was firstly operated using pure glycerol as the substrate at various OLRs of 25, 37.5, 50, 62.5 g/L d. Results showed that a change in OLR led to a change in hydrogen production, hydrogen production rate (HPR), hydrogen yield (HY), 1,3-PD and ethanol production as well as glycerol consumption, and microbial community. The optimal OLR for hydrogen and ethanol production was found to be 50 g/L d when the UASB was fed with pure glycerol, while the optimal OLR for 1,3-PD production was 62.5 g/L d. After the optimum OLR was obtained, the reactor was fed with crude glycerol. Maximum hydrogen, ethanol and 1,3-PD production from crude glycerol was obtained at the same OLR as of pure glycerol. A maximum hydrogen production, HY, ethanol and 1,3-PD production of 134.2 mmol/L, 579.8 mmol H2/mol glycerol, 78.9 mmol/L and 60.9 mmol/L, respectively, were obtained when pure glycerol was used as the substrate. However, when crude glycerol was used as the substrate, a maximum hydrogen production, HY, ethanol and 1,3-PD production were lower than that of using pure glycerol as the substrate. Analysis of microbial community by polymerase chain reaction-denaturing gradient gel electrophoresis indicated that the predominant hydrogen producers at the optimum OLR of 50 g/L d, when crude glycerol was used as the substrate, were Clostridium sp., Enterobacter sp., uncultured Firmicutes bacterium, and uncultured Actinobacterium while Enterobacter sp., Klebsiella sp., were the predominant 1,3-PD producers and Clostridium sp., as well as Enterobacter sp., were the predominant ethanol producers.

Reduction of greenhouse gases emissions during anoxic wastewater treatment by strengthening nitrite-dependent anaerobic methane oxidation process

Nitrite-dependent anaerobic methane oxidation (n-damo) is a recently discovered process performed by NC10 phylum, which plays an important role in greenhouse gases (GHG) reduction. In this study, co-existence of n-damo bacteria and methanogens was successfully achieved by using upflow anaerobic sludge blanket (UASB) reactor. Reactor with inorganic carbon source (CO2/H2) showed the highest abundance of n-damo bacteria and the highest n-damo potential activity, resulted in its highest nitrogen removal rate. Significant reduction in GHG was obtained after introduction of n-damo process, especially for N2O. Furthermore, GHG emissions decreased with the increase of n-damo bacteria abundance. Community structure analysis found carbon source could influence the diversity of n-damo bacteria indirectly. And phylogenetic analysis showed that all the obtained sequences were assigned to group B, mainly due to in situ production and consumption of CH4.

Upflow Anaerobic Sludge Blanket Reactor Codigestion of Algae and Acetate to Produce Methane.

Algae grown in wastewater treatment lagoons are a potentially important substrate for biofuel production. The feasibility of using upflow anaerobic sludge blanket (UASB) reactors in anaerobic digestion of algae to produce methane was investigated. A favorable carbon to nitrogen (C/N) weight ratio of 21/1 was determined in batch reactor experiments in which the ratio was adjusted by blending algal biomass with sodium acetate as a carbon source. This blend of algae and acetate was used in the feedstock applied to the UASB reactors. Duplicate, 34-L, UASB reactors initially received an organic loading rate (OLR) of 0.9 g chemical oxygen demand (COD)/L.d at a 7.2-day hydraulic retention time (HRT). The OLR was gradually increased to 5.4 g/L.d and the HRT was decreased to 5.5 days resulting in a methane production increase from 247 to 298 mL/g COD biodegraded. The COD removal efficiency was 80% with a biogas methane composition of 90%.

Treatment of slaughterhouse wastewater in an upflow anaerobic sludge blanket reactor: Sludge characteristics

Aims: Present study was done by using upflow anaerobic sludge blanket (UASB) reactor to investigate the effect of influent chemical oxygen demand (COD) and organic load rate on the formation of anaerobic granules in wastewater treatment. Martials and Methods: Upflow anaerobic sludge blanket reactor with working volume 30 L was studied using actual slaughterhouse wastewater at a hydraulic retention time of 1.24 d and at temperatures in the range of 35°C ± 0.5°C for 320 days. The inoculum was extracted from the anaerobic digester of municipal sewage treatment plant, and the UASB reactor was filled with 8 L of sludge. Results: The results indicated that under the optimal conditions, about 94.6% of COD could be effectively removed from slaughterhouse wastewater with the UASB. The highest and lowest COD removal efficiency was 40.5 and 94.6% corresponding to influent COD of 1266.8 and 1222.2 mg/L, respectively. The fluctuation of solution pH in UASB operation was in the range of 6.68-8.03. The average of solution pH was 7.46 ± 0.36. The solution pH was gradually improved with UASB operation. Different granule sizes coexisted in the UASB reactor, but granules with the size of 1-3 mm were predominant. The maximum observed size of anaerobic granule was 7 mm. Conclusion: Application of slaughterhouse wastewater as feed wastewater demonstrated that the slaughterhouse wastewater to be more effective in promoting the formation of anaerobic granules and granule size in UASB reactor.

Towards biohythane production from biomass: Influence of operational stage on anaerobic fermentation and microbial community

Biohythane consisting of biohydrogen and biomethane via two-stage fermentation is a promising energy carrier for vehicle use. In this study, one-stage biomethane system using upflow anaerobic sludge blanket (UASB) and packed bed reactor (PBR) was shifted to the two-stage biohythane system to study the influence of operational stage. Compared with biomethane system, the biohythane process achieved higher COD removal and energy recovery. Particularly, the total COD removal in the PBR system rose significantly from 74.0 to 97.3%, corresponding to an increased energy recovery from 54.2 to 67.1%. The first-stage hydrogen fermentation had a positive effect on subsequent biomethane production in biohythane system. The analysis of microbial diversity using Illumina MiSeq sequencing showed significant changes of microorganisms in biomethane reactor, which revealed the variation of biochemical pathways. Compared to biomethane system, the relative abundance of acidogenesis bacteria was reduced in biohythane system, such as family Clostridiaceae. By contrast, the amount of acetogens (Syntrophaceae, Syntrophomonadaceae and Desulfovibrionaceae) and acetate-oxidizing bacteria (Spirochaetes) was increased. The archaea community remained stable, and mainly consisted of acetoclastic methanogens from family Methanosaetaceae. These results indicated the biomethane reactors in biohythane system had more efficient acidogenesis and acetate-utilizing microbial community.

The role of hydraulic retention time on controlling methanogenesis and homoacetogenesis in biohydrogen production using upflow anaerobic sludge blanket (UASB) reactor and packed bed reactor (PBR)

Methanogenesis and homoacetogenesis are two notorious hydrogen-consuming reactions during dark fermentation for biohydrogen production. The focus of this study was on the role of hydraulic retention time (HRT) to control methanogenesis and homoacetogenesis in an upflow anaerobic sludge blanket (UASB) reactor and a packed bed reactor (PBR). The HRT was changed from 24 to 4 h and 24 to 2 h in the UASB and PBR, respectively. A maximal hydrogen yield of 1.47 mol/mol glucoseadded with a high hydrogen production rate of 4.38 L/L/d was achieved at 8 h HRT in UASB. In comparison, a maximal hydrogen yield of 0.89 mol/mol glucoseadded with a high hydrogen production rate of 10.66 L/L/d was achieved at 2 h in PBR. With the reduction of the HRT, the volumic hydrogen consumption due to methanogenesis in the UASB was decreased from 12.1 to 3.1%. As for PBR, the value was reduced from 66.9 to 31.4%. Homoacetogenesis in the UASB and PBR was dramatically suppressed when the HRT was decreased to 8 and 4 h, respectively. However, these hydrogen-consuming microbes cannot be completely removed. Microbial diversity analysis using Illumina MiSeq sequencing revealed the existence of Clostridium ljungdahlii, a homoacetogen, in UASB and PBR at low HRT. In addition, the low HRT reduced relative abundance of Clostridiaceae and accelerated the proliferation of lactic acid producers and ethanol producers in the UASB and PBR, which were mainly from the families Ruminococcaceae and Leuconostocaceae.

Anaerobic Digestion of Pulping Wastewater Using Up-flow Anaerobic Sludge Blanket (UASB) Reactor at Mesophilic Condition

The waste considered for this study was the effluent of the pulping process produced during the manufacture of pulp and paper in the Rakta integrated pulp and paper mill in Alexandria. The pulping process in Rakta mill is conducted under pressure of 7-8 bar, 165°C using 10% NaOH based on straw weight for 2 h. The spent liquor after alkali cooking contains any where 8 to 15% solids in solution and primarily these dissolved solids are lignin and dissolved carbohydrates. The effect of some operating parameters on the performance of the Using Up-flow Anaerobic Sludge Blanket was studied; these include mainly the organic loading rate and hydraulic retention time. The gas production rate increased to 3.43 m3 biogas/(m3 reactor volume. day), by increasing the Biochemical Oxygen Demand (BOD) loading rate to 16 kg BOD feed/(m3 reactor volume. day), with a gas yield of 0.66 m3 biogas/(kg reduced organic matter). The efficiency was reduced by increasing the loading rate. Thus by increasing the BOD loading rate from 0.4 to 16 kg BOD feed/(m3 reactor volume. day), the reduction in BOD decreased from 79% to 42%.

Nitrogen and phosphorus removal in an anaerobic (UASB)-aerobic (ABF) sewage treatment system

Anaerobic sewage treatment process using upflow anaerobic sludge blanket (UASB) coupled with aerated biofilter (ABF) was tested for the removal of nitrogen and phosphorus by recycling the final effluent and by adding alum to the influent. TCOD Removal efficiency was about 60% in UASB without recycling of the ABF effluent, while it increased to 90% at recycling ratio of 3. Complete denitrification had occurred in the UASB, and removal efficiencies of both total nitrogen (TN) and NH4+-N were also improved to 74 and 96%, respectively, by recycling the nitrified ABF effluent. Total phosphorus (TP) removal was not improved by recycling of the ABF effluent. TP and soluble phosphorus were effectively removed in UASB by adding alum to the influent. 90% removal of TP was possible with alum dose at Al/P mole ratio of 2.6. In the final effluent, concentrations of TCOD, TN, and TP were below 14.0, 7.0, and 0.27 mg/L, respectively, in the UASB-ABF sewage treatment system at recycling ratio of 3 with alum.

Decolorization of methyl orange using upflow anaerobic sludge blanket (UASB) reactor—An investigation of co-substrate and dye degradation kinetics

Decolorization of a synthetic wastewater containing Methyl Orange (MO) azo dye was performed in an upflow anaerobic sludge blanket (UASB) reactor. Color removal efficiencies approaching 94, 90 and 96% were obtained with influent MO concentrations of 50, 100 and 150 mg l−1 respectively. COD removal decreased with respect to the increasing of color concentration. Maximum COD removal was attained 69% in 50 mg l−1 of MO. Cleavages of azo bond tends to the accumulation of aromatic amines which contributed COD in the effluent. Zero-, first-, and second-order reaction kinetics were used to find out the suitable COD removal and decolorization kinetics. The COD removal process was suitable to second-order reaction kinetic, and the degradation of MO approximates was suitable to the first-order kinetic model. The regression coefficient (R2) for both decolorization and COD degradation was around 0.9 which ensures the high-degree linear relationship between the concentration and time.

Biological tannery wastewater treatment using two stage UASB reactors

Wastewater discharged from tannery industries is highly complex, concentrated, and toxic. In view of the varying nature of discharged wastewater and the numerous small industries in Egypt, there is a need for highly efficient treatment processes that are simple to operate and have low/reasonable construction and operation costs. This study investigated the possibility of applying innovative low cost biological treatment using upflow anaerobic sludge blanket (UASB) in providing adequate treatment for tannery wastewater. The anaerobic treatment application was thus evaluated through using two stage UASB reactors connecting in series, each with volume of 94l. Five hydraulic retention times (HRT) were used along the experimental works, which lasted for a year, starting by HRT of 24h then 18, 12, 8 and finally 5h for each UASB reactor. The proposed process at 12h HRTs could pre-treat the tannery wastewater to be disposed to the municipality sewers. The study created best fit equations to predict the efficiency of the system.

Comparison of UASB and EGSB reactors performance, for treatment of raw and deoiled palm oil mill effluent (POME)

Anaerobic digestion of palm oil mill effluent (POME) and deoiled POME was investigated both in batch assays and continuous reactor experiments using up-flow anaerobic sludge blanket (UASB) and expanded granular sludge bed (EGSB) reactors. The methane potential determined from batch assays of POME and deoiled POME was 503 and 610 mL-CH 4/gVS-added, respectively. For the treatment of POME in continuously fed reactors, both in UASB and EGSB reactors more than 90% COD removal could be obtained, at HRT of 5 days, corresponding to OLR of 5.8 gVS/(L-reactor.d). Similar methane yields of 436–438 mL-CH 4/gVS-added were obtained for UASB and EGSB respectively. However, for treatment of deoiled POME, both UASB and EGSB reactors could operate at lower OLR of 2.6 gVS/(L-reactor.d), with the methane yield of 600 and 555 mL-CH 4/gVS-added for UASB and EGSB, respectively. The higher methane yield achieved from the deoiled POME was attributed to lower portion of biofibers which are more recalcitrant compared the rest of organic matter in POME. The UASB reactor was found to be more stable than EGSB reactor under the same OLR, as could be seen from lower VFA concentration, especially propionic acid, compared to the EGSB reactor.

Factors affecting the activity of anammox bacteria during start up in the continuous culture reactor

Factors affecting cultivation of extremely slow-growing bacteria (anaerobic ammonium oxidiser, doubling time 11 days) were investigated by using upflow anaerobic sludge blanket (UASB) reactors which can maintain high solid retention time. The effects of concentrations of DO, free ammonia (FA), and nitrite on activation of anammox activity were tested during the start-up period. The reactor was inoculated with granular sludge collected from a full-scale UASB reactor used for treating brewery wastewater, and sludge from a piggery wastewater treatment plant and rotating biological contactor treating sewage. Results of continuous operation showed that concentrations of DO, free ammonia (FA) and nitrite in the reactors played a key role in stimulating the anammox activity during start-up period. It is crucial to keep DO below 0.2 ppm, FA below 2 mg/L and nitrite nitrogen below 35 mg/L to cultivate anammox cells in the continuous bioreactor. When the levels of DO, FA and nitrite in the influent were controlled at less than the inhibition levels, the anammox activity increased gradually in the anaerobic condition. Addition of hydrogen sulphide into the reactor enhanced anammox activity in the continuous culture. Through the SEM, TEM and FISH analysis, anammox bacteria were detected in the granular sludge after 3 months of continuous operation.

Effect of loading rate on the granulation process and granular activity in a bench scale UASB reactor

The effect of organic loading rate (OLR) on the granulation process was evaluated using upflow anaerobic sludge blanket (UASB) reactors running under different conditions. Results showed that increase of OLR, extracellular polymer (ECP) content and granulation were closely related to one another. ECP in the sludge accumulated over a short period under overloading conditions, which greatly enhanced the granulation process. Treatment performance could be recovered after the ECP accumulation when the overloading was suitably exerted. However, too high loading rate should be avoided because it could cause the unrecoverable decay of methanogenic activity and the serious unbalance between the feedstuff and biological requirement.