Anaerobic dechlorination of pentachlorophenol in fixed-film and upflow anaerobic sludge blanket reactors using different inocula

Longterm performance and stability of two upflow anaerobic sludge blanket (UASB) reactors inoculated with granular sludge and treating a synthetic waste water containing pentachlorophenol (PCP) and phenol were studied. A similar system consisting of two fixed-film reactors inoculated with anaerobic digested sewage sludge were further studied. One reactor in each series received glucose in addition to the phenols. Dechlorination of PCP proceeded via two different dominating pathways in the respective reactor systems, suggesting that two distinct microbial populations were present, probably originating from the different inocula. Dechlorinating activity was maintained for more than 18 months in the UASB reactors and was generally higher than in the fixed-film reactors. In the fixed-film reactors, dechlorination of PCP suddenly decreased after 15.5 months of operation compared to earlier performance. Since no operational parameters had been changed, this indicated that the enriched culture was unstable on a longterm basis. Addition of yeast extract to the medium restored activity. General process stability in both reactor systems was clearly enhanced by the addition of glucose and was superior in the UASB/granular sludge system. The better performance and the higher stability in the UASB/granular sludge reactor highlights the importance of thorough screening of inocular prior to start-up of processes treating waste waters containing xenobiotic compounds.Abbreviations PCP pentachlorophenol - TeCP tetrachlorophenol - TCP trichlorophenol - DCP dichlorophenol - UASB upflow anaerobic sludge blanket - HRT hydraulic retention time     

Modeling a granule‐based anaerobic ammonium oxidizing (ANAMMOX) process

A mathematical model was developed to describe the anaerobic ammonium oxidation (ANAMMOX) process in a granular upflow anaerobic sludge blanket (UASB) reactor. ANAMMOX granules were cultivated in the UASB reactor by seeding aerobic granules. The granule‐based reactor had a great N‐loading resistant capacity. The model simulation results on the 1‐year reactor performance matched the experimental data well. The yield coefficient for the growth and the decay rate coefficient of the ANAMMOX granules were estimated to be 0.164 g COD g^?1 N and 0.00016 h^?1, respectively. With this model, the effects of process parameters on the reactor performance were evaluated. Results showed that the optimum granule diameter for the maximum N‐removal should be between 1.0 and 1.3 mm and that the optimum N loading rate should be 0.8 kg N m^?3 d^?1. In addition, the substrate micro‐profiles in the ANAMMOX granules were measured with a microelectrode to explore the diffusion dynamics within the granules, and the measured profiles matched the predicted results well. Biotechnol. Bioeng. 2009;103: 490–499. © 2009 Wiley Periodicals, Inc.     

Rapid start-up and performance of denitrifying granular sludge in an upflow sludge blanket (USB) reactor treating high concentration nitrite wastewater

Denitrifying granular sludge reactor holds better nitrogen removal efficiency than other kinds of denitrifying reactors, while this reactor commonly needs seeding anaerobic granular sludge and longer period for start-up in practice, which restricted the application of denitrifying granular sludge reactor. This study presented a rapid and stable start-up method for denitrifying granular sludge. An upflow sludge blanket (USB) reactor with packings was established with flocculent activated sludge for treatment of high concentration nitrite wastewater. Results showed mature denitrifying granular sludge appeared only after 15 days with highest nitrogen removal rate of 5.844 kg N/(m³ day), which was much higher than that of compared anoxic sequencing batch reactor (ASBR). No significant nitrite inhibition occurred in USB and denitrification performance was mainly influenced by hydraulic retention time, influent C/N ratio and internal reflux ratio. Hydraulic shear force created by upflow fluid, shearing of gaseous products and stable microorganisms adhesion on the packings might be the reasons for rapid achievement of granular sludge. Compared to inoculated sludge and ASBR, remarkable microbial communitiy variations were detected in USB. The dominance of Proteobacteria and Bacteroidetes and enrichment of species Pseudomonas_stutzeri should be responsible for the excellent denitrification performance, which further verified the feasibility of start-up method.     

Inactivation of ANAMMOX communities under concurrent operation of anaerobic ammonium oxidation (ANAMMOX) and denitrification

A concurrent operation of anaerobic ammonium oxidation (ANAMMOX) and denitrification was investigated in a well known UASB reactor seeding with both ANAMMOX and anaerobic granular sludges. ANAMMOX activity was confirmed by hydroxylamine test and the hybridization of biomass using the gene probes of Amx 820 and EUB 338 mixed. Denitrification was observed through the reductions of both COD and nitrate-nitrite concentrations under anaerobic/anoxic conditions. By providing a stoichiometric ratio of nitrite to ammonium nitrogen with addition nitrate nitrogen, a gradual reduction of ANAMMOX activity was found with an increase of COD concentration in a range of 100-400 mg l(-1). This is equivalent to the COD to N ratio of 0.9-2.0. The COD concentration was found to be a control variable for process selection between ANAMMOX reaction and denitrification. A reduction of COD and nitrite-nitrate concentrations in all reactors confirmed the undergone concurrent denitrification which thrives when sufficient organic matter is available. COD concentration over 300 mg l(-1) was found to inactivate or eradicate ANAMMOX communities.     

Controlled shear affinity filtration (CSAF): a new technology for integration of cell separation and protein isolation from mammalian cell cultures

Up-flow anaerobic sludge blanket (UASB) reactors are being used with increasing regularity all over the world, especially in India, for a variety of wastewater treatment operations. Consequently, there is a need to develop methodologies enabling one to determine UASB reactor performance, not only for designing more efficient UASB reactors but also for predicting the performance of existing reactors under various conditions of influent wastewater flows and characteristics. This work explores the feasibility of application of an artificial neural network-based model for simulating the performance of an existing UASB reactor. Accordingly, a neural network model was designed and trained to predict the steady-state performance of a UASB reactor treating high-strength (unrefined sugar based) wastewater. The model inputs were organic loading rate, hydraulic retention time, and influent bicarbonate alkalinity. The output variables were one or more of the following, effluent substrate concentration (Se), reactor bicarbonate alkalinity, reactor pH, reactor volatile fatty acid concentration, average gas production rate, and percent methane content of the gas. Training of the neural network model was achieved using a large amount of experimentally obtained reactor performance data from the reactor mentioned above as the training set. Training was followed by validation using independent sets of performance data obtained from the same UASB reactor. Subsequently, simulations were performed using the validated neural network model to determine the impact of changes in parameters like influent chemical oxygen demand (COD) concentration and hydraulic retention time on the reactor performance. Simulation results thus obtained were carefully analyzed based on qualitative understanding of UASB process and were found to provide important insights into key variables that were responsible for influencing the working of the UASB reactor under varying input conditions.     

Effect of carbon sources and shock loading on the removal of chlorophenols in sequential anaerobic-aerobic reactors

The effect of carbon sources and shock loadings have been studied using two sets of sequential upflow anaerobic sludge blanket (UASB) and rotating biological contactor (RBC) reactors viz., UASB-I followed by RBC-I and UASB-II followed by RBC-II for the removal of two different priority pollutants, 2-CP and 2,4-DCP present in simulated wastewaters. Sodium formate, sodium propionate, glucose and methanol were used separately as four different carbon sources in the feed as co-substrate. Methanol was found to be the best carbon source for UASB reactors showing 95% 2-CP and 81.1% 2,4-DCP removals. The carbon sources formate and propionate were not found suitable in UASB reactors as only 22.6-46.8% 2-CP and 41.9-42.8% 2,4-DCP removals were observed. With glucose as carbon source 93.7% 2-CP and 79.6% 2,4-DCP removals were observed in UASB reactors. For all the four carbon sources more than 97.6% 2-CP and 99.7% 2,4-DCP removals were observed in sequential reactors. Although all the four carbon sources could not serve as good carbon source for UASB reactor alone but could be successfully used by the sequential reactors for the removal of chlorophenols. The Performance of sequential reactors was also evaluated at five different chlorophenolic shock loadings. During shock loading study the concentration of chlorophenols in the wastewaters was increased to 45, 60, 75, 90 and 105 mg/l as compared to the normal feed containing 30 mg/l 2-CP or 2,4-DCP. During shock loading study complete removal of 2-CP and more than 99.6% removal of 2,4-DCP was observed in sequential reactors. Sequential reactors successfully withstood all the shock loadings and produced high quality effluents.     

High-rate treatment of terephthalate in anaerobic hybrid reactors.

The anaerobic degradation of terephthalate as sole substrate was studied in three anaerobic upflow reactors. Initially, the reactors were operated as upflow anaerobic sludge bed (UASB) reactors and seeded with suspended methanogenic biomass obtained from a full-scale down-flow fixed film reactor, treating wastewater generated during production of purified terephthalic acid. The reactors were operated at 30, 37, and 55 degrees C. The terephthalate removal capacities remained low in all three reactors (<4 mmolxL-1xday-1, or 1 g of chemical oxygen demand (COD)xL-1xday-1) due to limitations in biomass retention. Batch experiments with biomass from the UASB reactors revealed that, within the mesophilic temperature range, optimal terephthalate degradation is obtained at 37 degrees C. No thermophilic terephthalate-degrading culture could be obtained in either continuous or batch cultures. To enhance biomass retention, the reactors were modified to anaerobic hybrid reactors by introduction of two types of reticulated polyurethane (PUR) foam particles. The hybrid reactors were operated at 37 degrees C and seeded with a mixture of biomass from the UASB reactors operated at 30 and 37 degrees C. After a lag period of approximately 80 days, the terephthalate conversion capacity of the hybrid reactors increased exponentially at a specific rate of approximately 0.06 day-1, and high removal rates were obtained (40-70 mmolxL-1xday-1, or 10-17 g of CODxL-1xday-1) at hydraulic retention times between 5 and 8 h. These high removal capacities could be attributed to enhanced biomass retention by the development of biofilms on the PUR carrier material as well as the formation of granular biomass. Biomass balances over the hybrid reactors suggested that either bacterial decay or selective wash-out of the terephthalate fermenting biomass played an important role in the capacity limitations of the systems. The presented results suggest that terephthalate can be degraded at high volumetric rates if sufficiently long sludge ages can be maintained, and the reactor pH and temperature are close to their optima.     

Comparison of long-term performances and final microbial compositions of anaerobic reactors treating landfill leachate

Laboratory scale anaerobic upflow filter, sludge blanket and hybrid bed reactors were operated for 860 days in the treatment of high ammonia landfill leachate. Organic loading was gradually increased from 1.3 to 23.5 kg COD/m3 day in the start-up period and then fluctuated according to the COD concentration of raw leachate. To prevent free ammonia inhibition, influent pH was reduced to 4.5 after Day 181 and consequently COD removal efficiencies above 80% were achieved in all reactors. However, the anaerobic filter and hybrid bed reactor were generally found slightly more efficient and stable than the UASB reactor. In addition to conventional anaerobic reactor control parameters, the complementary techniques of denaturing gradient gel electrophoresis (DGGE), cloning and fluorescent in situ hybridization (FISH) were used to identify and compare the microbial profiles in the reactors at Day 830. Molecular analyses revealed that acetoclastic Methanosaeta species were prevalent in all reactors and configuration did not have an impact on microbial diversity in the long-term.     

Kinetics of anaerobic treatment of slaughterhouse wastewater in batch and upflow anaerobic sludge blanket reactor

The kinetics of anaerobic treatment of slaughterhouse wastewater in batch and upflow anaerobic sludge blanket (UASB) reactors was investigated. Different concentrations of organic matter in slaughterhouse wastewater did not change the first order kinetics of the reaction. In batch digesters, methane and nitrogen production stopped after 30-40, 20-30 h, respectively, and in UASB reactors it was terminated after 30-40 days. The constant of velocity was 3.93 and 0.23 h(-1) respectively, for methane and nitrogen production. The yield coefficient, Yp was 343 and 349 ml CH4 per g of chemical oxygen demand at standard temperature and pressure conditions for batch reactors and UASB reactor, respectively.     

Effects of process stability on anaerobic biodegradation of LAS in UASB reactors

Anaerobic biodegradation of linear alkylbenzene sulfonates (LAS) was studied in upflow anaerobic sludge blanket (UASB) reactors operated under mesophilic (37 degrees C) and thermophilic (55 degrees C) conditions. LAS C12 concentration in the influents was 10 mg.L(-1), and the hydraulic retention time in the reactors was 2 days. Adsorption of LAS C12 was assessed in an autoclaved control reactor and ceased after 115 days. The reactors were operated for a minimum of 267 days; 40-80% removal of LAS C12 was observed. A temperature reduction from 55 degrees C to 32 degrees C for 30 h resulted in process imbalance as indicated by increase of volatile fatty acids (VFA). The imbalance was much more intense in the LAS amended reactor compared with an unamended reactor. At the same time, the process imbalance resulted in discontinued LAS removal. This finding indicates that process stability is a key factor in anaerobic biological removal of LAS. After a recovery period, the removal of LAS resumed, providing evidence of biological anaerobic LAS degradation. The removal remained constant until termination of experiments in the reactor. Biodegradation of LAS in the mesophilic reactor was at the same level as in the thermophilic reactor under stable conditions.     

Degradation of 4-chlorophenol in UASB reactor under methanogenic conditions

Treatment of simulated wastewater containing 40 mg/l of 4-chlorophenol (4-CP) was carried out in an upflow anaerobic sludge blanket (UASB) reactor under methanogenic condition. The performance of this test UASB reactor was evaluated in terms of 4-CP removal. Hydraulic retention time (HRT) and substrate:co-substrate ratio for the 4-CP removal was optimized by varying the influent flow rate (13-34.7 ml/min) and sodium acetate concentration (2-5 g/l), respectively. A control UASB reactor, which was not exposed to 4-CP was also operated under similar conditions. Organic loading rate (OLR) was varied in the range of 2-5.3 kg/m(3)/d and 1.7-4.2 kg/m(3)/d, respectively, for HRT and substrate:co-substrate ratio studies, respectively. The optimum HRT and substrate:co-substrate ratio for the removal of 4-CP was 12h and 1:75, respectively. Removal of 4-CP achieved at optimum HRT and substrate:co-substrate ratio was 88.3+/-0.7%. Removal of 4-CP occurred through dehalogenation and caused increase in chloride ion concentration in the effluent by 0.23-0.27 mg/mg 4-CP removed. The ring cleavage test showed the ortho mode of ring cleavage of 4-CP. Change in the elemental composition of the anaerobic biomass of UASB reactors was observed during the study period. Concentration of Ca(2+) increased in the biomass and this could be attributed to the biosoftening. Specific methanogenic activity of the sludge of control and test UASB reactor was 0.832 g CH(4) COD/g VSS d and 0.694 g CH(4) COD/g VSS d, respectively.     

Microbial diversity and dynamics in multi- and single-compartment anaerobic bioreactors processing sulfate-rich waste streams

We investigated bacterial and archaeal community structures and population dynamics in two anaerobic bioreactors processing a carbohydrate- and sulfate-rich synthetic wastewater. A five-compartment anaerobic migrating blanket reactor (AMBR) was designed to promote biomass and substrate staging, which partially separates the processes of methanogenesis and sulfidogenesis in the middle and outer compartment(s) respectively. The second reactor was a conventional, single-compartment upflow anaerobic sludge blanket (UASB) reactor. Both reactors, which were seeded with the same inoculum, performed well when the influent chemical oxygen demand (COD)/SO(4) (2-) mass ratio was 24.4. The AMBR performed worse than the UASB reactor when the influent COD/SO(4) (2-) mass ratio was decreased to 5.0 by raising the sulfate load. Terminal restriction fragment length polymorphism analyses of bacterial 16S rRNA genes showed that the increase in sulfate load had a greater impact on bacterial diversity and community structure for the five AMBR compartments than for the UASB reactor. Moreover, bacterial community profiles across AMBR compartments became more similar through time, indicating a converging, rather than a staged community. While similar populations were abundant in both reactors at the beginning of the experiment, fermenting bacteria (clostridia, streptococci), and sulfate-reducing bacteria became more abundant in the AMBR, after shifting to a higher sulfate load, while a novel Thermotogales-like population eventually became predominant in the UASB reactor. A similar shift in the community structure of the hydrogenotrophic methanogens in the AMBR occurred: representatives of the Methanobacteriaceae out-competed the Methanospirillaceae after increasing the sulfate load in the AMBR, while the archaeal community structure was maintained in the UASB.     

The inhibitory effects and removal of dieldrin in continuous upflow anaerobic sludge blanket reactors

The inhibitory effects and removal efficiency of dieldrin (DLD) in anaerobic reactors were investigated. Anaerobic toxicity assay (ATA) experiments conducted in batch reactors revealed that 30 mg/l DLD had inhibitory effects on the unacclimated mixed anaerobic cultures. Continuous reactor experiments performed in a lab-scale two-stage upflow anaerobic sludge blanket (UASB) reactor system which was fed with ethanol as the sole carbon source, indicated that anaerobic granular cultures could be successfully acclimated to DLD. Chemical oxygen demand (COD) removal efficiencies were 88-92% for the two-stage system. The influent DLD concentration of 10 mg/l was removed by 44-86% and 86-94% in the second stage and overall UASB system, respectively. Biosorption of DLD on granular anaerobic biomass was found to be a significant mechanism for DLD removal in the UASB system. The maximum DLD loading rate and minimum HRT achievable for the first stage UASB reactor were 0.5 mg/lday (76 microg DLD/g VSS.day) and 10 h, respectively, which resulted in the overall COD removal efficiency of 85%.     

High upflow velocity and organic loading rate improve granulation in upflow anaerobic sludge blanket reactors

Five laboratory scale upflow anaerobic sludge blanket (UASB) reactors were seeded with nongranular sewage sludge. Granulation was obtained after 15–35 days when between 0.5 and 2.0m/h upflow liquid velocity was applied, with an organic loading rate (OLR) of 8g COD/l.d (COD is the chemical oxygen demand). Granules had different physical characteristics and specific activity (g COD_REMOVED/g volatile suspended solids) depending on the upflow liquid velocity applied. Granules were obtained in short startup periods (5 and 14 days) when a pilot-scale (180l) UASB reactor with a height of 4.7m was used to study hydraulic effects on the granulation process.     

Design,Construction, and Starting-up of an Anaerobic Reactor for the Stabilisation,Handling, and Disposal of Excess Biological Sludge Generated in a Wastewater Treatment Plant

Design, construction, and starting-up of an upflow anaerobic sludge blanket reactor was carried out. This system was proposed for excess sludge stabilisation, particularly that generated at an activated sludge wastewater treatment facility installed in a sugarcane mill. The upflow anaerobic sludge blanket (UASB) reactor built, had a working volume of 22.3 m³and a hydraulic residence time of 22 days. Methane production was at a maximum of 79% volume with an average of 60% for this treatment. For starting up the anaerobic reactor, a suitable inoculum from a neighboring plant was used. As the waste characteristics in both plants were different, an acclimation procedure was followed to achieve granulation. Control and stability of anaerobic reactions were monitored with alkalinity data, using the so-called ‘alfa alkalinity’ to try to keep its value at around 0.4. Once pseudosteady-state conditions were reached (chemical oxygen demand reduction and methane-rich biogas production within ±10 percent), the organic load was steadily increased up to feeding 100% excess sludge. The UASB reactor used to stabilise the excess biomass generated a sludge with a much lower volume than that originally fed. Its design ensured adequate hydraulic flow and biogas production with a high methane content. The bacteria were attached constituting spheres and very minor maintenance operations were required.     

亚硝酸盐型同步厌氧生物脱氮除硫工艺的运行性能

采用上流式厌氧污泥床(UASB)反应器研究了亚硝酸盐型同步厌氧生物脱氮除硫工艺的性能。该工艺具有很高的硫化物和亚硝酸盐转化潜能,最大容积硫化物去除率和容积硝酸盐去除率分别为13.4kg/(m3·d)和2.3kg/(m3·d);所能耐受的最大进水硫化物和亚硝酸盐浓度分别为880mg/L和252.7mg/L;最适进水硫化物和亚硝酸盐浓度分别为460mg/L和132.3mg/L,最适水力停留时间为4h。硫化物和亚硝酸盐的表观半抑制浓度分别为403.9mg/L和120.8mg/L,两者之间的联合毒性为拮抗作用。     

Distribution and change of microbial activity in combined UASB and AFB reactors for wastewater treatment

A thermophilic upflow anaerobic sludge blanket (UASB) reactor was combined with a mesophilic aerobic fluidized bed (AFB) reactor for treatment of a medium strength wastewater with 2,700?mg COD?l^?1. The COD removal efficiency reached 75% with a removal rate of 0.2 g COD?l^?1 h^?1 at an overall hydraulic retention time 14 hours. The distribution of microbial activity and its change with hydraulic retention time in the two reactors were investigated by measuring ATP concentration in the reactors and specific ATP content of the biomass. In the UASB reactor, the difference in specific ATP was significant between the sludge bed and blanket solution (0.02?mg ATP g VS^?1 versus 0.85?mg ATP g VS^?1) even though the ATP concentrations in these two zones were similar. A great pH gradient up to 4 was developed along the UASB reactor. Since a high ATP or biological activity in the blanket solution could only be maintained in a narrow pH range from 6.5 to 7.5, the sludge granules showed a high pH tolerance and buffering capacity up to pH 11. The suspended biomass in AFB reactor had a higher specific ATP than the biomass fixed in polyurethane carriers (1.6?mg ATP g VS^?1 versus 1.1?mg ATP g VS^?1), which implies a starvation status of the immobilized cells due to mass transfer limitation. The aerobes had to work under starvation conditions in this polishing reactor. The anaerobic biomass brought into AFB reactor contributed to an increase in suspended solids, but not the COD removal because of its fast deactivation under aerobic conditions. A second order kinetic model was proposed for ATP decline of the anaerobes. The results on distribution of microbial activity in the two reactors as well as its change with hydraulic retention time lead to further performance improvement of the combined anaerobic/aerobic reactor system.     

Introduction of a de novo bioremediation ability, aryl reductive dechlorination, into anaerobic granular sludge by inoculation of sludge with Desulfomonile tiedjei.

Methanogenic upflow anaerobic granular-sludge blanket (UASB) reactors treat wastewaters at a high rate while simultaneously producing a useful product, methane; however, recalcitrant environmental pollutants may not be degraded. To impart 3-chlorobenzoate (3-CB)-dechlorinating ability to UASB reactors, we inoculated granular sludge in UASB reactors with either a pure culture of Desulfomonile tiedjei (a 3-CB-dechlorinating anaerobe) or a three-member consortium consisting of D. tiejei, a benzoate degrader, and an H2-utilizing methanogen. No degradation occurred in an uninoculated control reactor which was started with the same granular sludge, but inoculated reactors and granules from the inoculated UASB systems rapidly transformed 3-CB (54 mumol/day/g of granule biomass). After several months at a hydraulic retention time of 0.5 day, much shorter than the generation time of D. tiedjei, the reactors still dechlorinated 3-CB. This indicated that the bacteria were immobilized in the reactor granules, and by using an antibody probe for D. tiedjei, we demonstrated that this microorganism had colonized the sludge granules. These results represent the first addition of a pure culture or a defined microbial mixture to a viable waste treatment process to introduce a specific de novo degradative pathway into a granular-sludge consortium.     

Introduction of a de novo bioremediation ability, aryl reductive dechlorination, into anaerobic granular sludge by inoculation of sludge with Desulfomonile tiedjei.

Methanogenic upflow anaerobic granular-sludge blanket (UASB) reactors treat wastewaters at a high rate while simultaneously producing a useful product, methane; however, recalcitrant environmental pollutants may not be degraded. To impart 3-chlorobenzoate (3-CB)-dechlorinating ability to UASB reactors, we inoculated granular sludge in UASB reactors with either a pure culture of Desulfomonile tiedjei (a 3-CB-dechlorinating anaerobe) or a three-member consortium consisting of D. tiejei, a benzoate degrader, and an H2-utilizing methanogen. No degradation occurred in an uninoculated control reactor which was started with the same granular sludge, but inoculated reactors and granules from the inoculated UASB systems rapidly transformed 3-CB (54 mumol/day/g of granule biomass). After several months at a hydraulic retention time of 0.5 day, much shorter than the generation time of D. tiedjei, the reactors still dechlorinated 3-CB. This indicated that the bacteria were immobilized in the reactor granules, and by using an antibody probe for D. tiedjei, we demonstrated that this microorganism had colonized the sludge granules. These results represent the first addition of a pure culture or a defined microbial mixture to a viable waste treatment process to introduce a specific de novo degradative pathway into a granular-sludge consortium.     

Solids removal in upflow anaerobic reactors,a review

This desk study deals with the mechanisms and parameters affecting particles separation from wastewater in mainly upflow anaerobic reactors. Despite the fact that the functioning of upflow anaerobic sludge blanket (UASB) systems depends on both physical parameters and biological processes, the physical parameters have been barely reported in the literature. The reason is that the underlying mechanisms are very complex and depend on various interrelated parameters. In addition, the lack of a serious attempt to gather the entire physical theme into one picture has resulted in just a superficial understanding of this field of science. Better understanding of the interaction and role of these parameters is essential for the development of anaerobic treatment technologies. In this study, the various parameters that might affect the solid liquid separation process by filtration through the sludge bed of a UASB have been elaborated. These parameters have been classified into (1) reactor operational conditions (temperature, organic loading rate, hydraulic retention time and upflow velocity), (2) influent characteristics (influent concentration, influent particle size and influent particle charge) and (3) sludge bed characteristics (particle size distribution, extracellular polymeric substances, and charge). The overall output of this study includes (1) a literature review, (2) structuring of this field of science, and (3) highlighting fields where research is needed.