Hybrid Upflow Anaerobic Sludge Blanket Reactor Research Articles

EFFECT OF TRACE METAL FECL3 ON BIOGAS PRODUCTION IN INDUSTRIAL WASTEWATER TREATMENT WITH HIGH ORGANIC LOAD

Wastewater from the food industry that contains a high organic load, such as wastewater from the tofu manufacturing process, requires an appropriate and efficient treatment system to reduce pollutants before being discharged into water bodies. The most suitable treatment for high organic loads is the anaerobic treatment system. The anaerobic treatment process is a system of suspended media, attached media, or the combination thereof as a hybrid. This study uses a Hybrid Upflow Anaerobic Sludge Blanket (HUASB) reactor with the consideration that this reactor has advantages in maintaining high concentrations of biomass, high operating load rates, good decomposition capabilities, and good solid-liquid separation due to suitable granulation. The purpose of this study was to determine the effect of the addition of the trace metal FeCl3 on biogas production and the ability to remove pollutants in the tofu industrial process wastewater treatment in the HUASB reactor. The operation of the reactor uses variations in the concentration of tofu industrial waste water (75 and 100%) and trace metal concentrations (0.3–0.6 mg/L). The optimum biogas production was obtained with 8190 mL at a concentration of 75% tofu industrial waste water, a trace metal concentration of 0.6 mg/L FeCl3, and removal of COD and TSS of 94.09% and 94.2%, respectively. The role of the trace metal FeCl3in the anaerobic process shows that it is a source of nutrition for increasing the growth of microorganisms in anaerobic systems so that biogas production and pollutant removal are increased.

A comparative study for hybrid UASB reactor performance using polyethylene media and luffa sponge as biofilm support.

This paper study the performance of a lab-scale hybrid up-flow anaerobic sludge blanket (UASB) reactor treating low-strength synthetic wastewater using different biofilm supporting materials. Two identical reactors are constructed and operated at constant up-flow velocity of 0.1m/hr., inflow rate of 9.76L/d, and hydraulic retention time (HRT) of 8.26hours. The Start-up phase, using seed sludge for existing wastewater treatment plant, lasted until the efficiency of chemical oxygen demand (COD) removal of both reactors reached 80%. Polyethylene (PE) media are added to one of the reactors and luffa sponge is used in the second reactor. Results show increased COD removal efficiency up to about 90% at 20°C and biogas production rates from 3.8*10-3 till 7.5*10-3m3 CH4/kg CODr using PE media. The COD removal efficiency reaches about 95% at 20°C using luffa sponge and biogas production rates up to 6.5*10 -3m3 CH4/kg CODr are achieved before clogging problem is observed. Effect of HRT reduction, from 8.26 to 4.13hours, on removing clogging is investigated. Reduction in COD removal efficiencies is observed at low ambient temperatures during seasonal variations of 15-25°C. AFM and SEM analysis are used to examine sludge granulation and biofilm formation.

Performance evaluation and kinetics modeling of a hybrid UASB reactor treating bovine slaughterhouse wastewater.

This work aimed to analyze the performance of a hybrid upflow anaerobic sludge blanket (HUASB) reactor packed with natural zeolite for slaughterhouse wastewater treatment through kinetics modeling. Wastewater samples from a municipal bovine slaughterhouse were sieved through a 1-mm mesh screen and thermally pretreated in an autoclave. Then, biological treatment was carried out in a HUASB reactor packed with a zeolite filter at the top. Slaughterhouse wastewater was diluted with municipal wastewater during the start-up period to achieve a low organic loading rate (OLR) (3.4kg chemical oxygen demand (COD)/m3/day); afterward, it gradually increased until dilution was eliminated, reaching 14.4kg COD/m3/day. At this OLR, the maximum percentage removals of total COD, soluble COD, total solid, and volatile solid (67.7%, 68.3%, 55.2%, and 72.1%, respectively) were found. Moreover, the zeolite filter enabled NH4+-N and PO43--P removal, with the highest values (32.8% and 35%, respectively) at 9.8kg COD/m3/day. Thus, the natural zeolite filter improved the reactor's performance. Among all equations analyzed, the modified Stover-Kincannon equation correctly fitted the results and provided the best prediction of the HUASB reactor's performance.

Mathematical approach towards non-stepwise performance assessment in HUASB reactor for wastewater treatment from pulp and paper mills

A lab-scale Hybrid Upflow Anaerobic Sludge Blanket (HUASB) reactor with a working volume of 6.5 litres has been taken for the performance analysis, in the treatability study of pulp and paper mill wastewater. In order to analyze the performance of the reactor, operational parameter like hydraulic retention time (HRT) was varied from 10, 20, 30 and 40 h. In addition to that, performance parameters like chemical oxygen demand (COD), pH, volatile fatty acids (VFA), alkalinity, gas production and VFA/alkalinity ratio are analyzed to check the reactor efficacy. The maximum COD removal efficiency of 81.3% is obtained at 40 h HRT, with gas production (methane content of 58%). Also, the obtained results are fitted to the kinetic models like the standard first order, first order and second order to evaluate the performance of the HUASB reactor.

Textile wastewater treatment by anaerobic sludge blanket reactor

In this study, performance of a lab-scale hybrid up-flow anaerobic sludge blanket (HUASB) reactor treating textile wastewater was evaluated under several operating conditions such as i) textile wastewater mixed up with glucose as food, ii) textile wastewater seeded with sewage sludge and glucose and iii) textile wastewater only. In all cases, two days of incubation period was provided for bacterial growth. In the first case, Klebsiella was the primary Species of bacteria growing in the reactor and the removal efficiency of COD and color was 25% and 56.4% respectively. In the second case, Klebsiella and Escherichia coli were the major bacteria and removal efficiency of COD and color was found to be 38% and 65% respectively. In the last case, Pseudomonas bacterium was dominant in the reactor and removal efficiency of COD, BOD and color was 84%, 93%, and 97% respectively. Wastewater treatment without glucose favored the growth of Pseudomonas which has been found to be effective in degrading organics present in textile wastewater. For all cases, reactor performance decreased after the third or fourth cycle of treatment. However, the removal of sludge after the third cycle allowed a high degradation efficiency of organics to be maintained in the reactor. With proper bacterial growth and maintenance, the HUASB reactor can be a huge upgrade from conventional UASB and a suitable alternative to conventional processes for the treatment of textile wastewater.
 Bangladesh J. Sci. Ind. Res.55(3), 165-172, 2020

Effect of Hydraulic Retention Time on the Treatment of Real Cattle Slaughterhouse Wastewater and Biogas Production from HUASB Reactor

Anaerobic digestion technology provides an alternative route for sustainable management of organic waste. In this study, the performance of the hybrid upflow anaerobic sludge blanket (HUASB) reactor consisting of synthetic grass media as attached growth surface was investigated for the treatment of cattle slaughterhouse wastewater under mesophilic (35 ± 1 °C) condition. After acclimatization with synthetic wastewater, the reactor was loaded up to OLR 10 g L−1d−1, corresponding to 20 g COD/L at a varying hydraulic retention time (HRT) of 24, 30, 36, 42, and 48 h. The system attained a maximum COD removal efficiency of 97% total suspended solids (TSS), volatile suspended solids (VSS), fats, oil, and grease (FOG), color removal, and turbidity were found as 97%, 284 mg/L, 79%, 78%, and 91% respectively. The biogas production after 48 h was found as 38 L/d, with about 85% methane and specific methane production of 0.24 LCH4/gCODadded. The ratio of alkalinity was 0.22, while ammonia nitrogen concentration reached a maximum of 839 mg/L at a steady state. Scanning electron microscopic (SEM) analysis revealed a predominance of Methanosarcina bacteria with the coccoidal shape at the end of the performance study. Therefore, the results of the experiment showed that increasing HRT significantly affects the performance of the system.

Start-up of Hybrid Upflow Anaerobic Sludge Blanket Reactor with Organic Wastewater

In the process of treating wastewaters from different industries by using anaerobic reactor, initially the start-up process is the first step to stabilize the reactor. The aim of this research is to conduct the start-up process and to evaluate the characterization of synthetic organic wastewater using Hybrid up flow Anaerobic Sludge Blanket reactor (HUASBR) with the effective volume of 20L. Initially the reactor was processed with synthetic organic wastewater with COD of 3200 mg/l. The processes were continuously operated with hydraulic retention time of 24 hours for 48 days. The results obtained after the process of stabilization were, COD removal is 87.8%, VFA was Stable for the operating condition, Biogas production was increased as 13.2 l/d during the maximum removal of COD and the pH value of outlet is ranging from 5.5-7.9.

Effect of HRT on performance of hybrid upflow anaerobic sludge blanket (HUASB) reactor using bio balls in treatment of pulp and paper mill bagasse wash water

Abstract Enormous quantities of bagasse are being used as raw material in agro based large integrated pulp and paper mills. Anaerobic technology is an effective means of biodegradation of organic substance in wastewater and energy production of biogas that can be used as an alternative fuel. This study illustrates the effect of HRT on performance of lab scale hybrid upflow anaerobic sludge blanket (HUASB) reactor on treatment of pulp and paper mill bagasse wash water. The lab scale HUASB reactor was designed for an effective volume of 0.013 m3 with bio balls as packing media at the top of reactor and operated under mesophilic condition. After startup period, the reactor was operated with HRTs of 23.55, 15.98, 12.00, 10.03 and 7.97 h for the average influent COD concentrations of 2503.6 mg/L, 3918 mg/L, 5432 mg/L, 6608 mg/L and 7996 mg/L respectively. The results showed that the maximum COD removal efficiencies and TSS removal efficiencies were in the range of 68.60–92.19% and 89.56–94.66% respectively. The minimum and maximum biogas yield of 0.32 and 0.53 m3/kg CODa were obtained at influent concentration of 2503.6 mg/L and 7996 mg/L respectively.

Performance study on organic carbon, total nitrogen, suspended solids removal and biogas production in hybrid UASB reactor treating real slaughterhouse wastewater

The performance of slaughterhouse wastewater treatment was studied in Hybrid Upflow Anaerobic Sludge Blanket Reactor (HUASBR) consisting of polypropylene media as attached growth surface. During acclimation phase, the amount of real slaughterhouse wastewater was gradually increased, whereas the amount of synthetic wastewater was proportionally decreased in a mixed feed to the reactor. The batch performance was evaluated by feeding 1000 ml of raw slaughterhouse wastewater and observing consistent Chemical Oxygen Demand (COD) removal over a batch period of 72 h. After attaining maximum COD removal efficiency and maximum methane gas production, the reactor was operated under continuous mode with gradually increasing Total Organic Carbon (TOC) loading rate. The reactor showed steady increase in the TOC removal efficiency as well as incremental biogas production. In this study, TOC loading rate was varied in the range of (1.12–14.19)kg TOC/m3/d corresponding to decremental Hydraulic Retention Time (HRT) of (24–6) hours. The HUASBR enhanced the TOC removal efficiency in slaughterhouse wastewater up to maximum of 95.85% under the TOC loading rate of 6.97 kg TOC/m3/d for 10 h HRT. The TSS removal efficiency was observed to be in the range of (72–98) % throughout the study. Similarly, The TN removal was also recorded between (48–78) % out of all the continuous operations. The maximum methane gas production rate was observed as 61.5 L/d at 10 h HRT.

Influence of Organic Loading Rates (OLR) in Treatment of Pulp and Paper Mill Wastewater with Hybrid Upflow Anaerobic Sludge Blanket Reactor (HUASBR) with Hexagonal Polypropylene Inert Material

Abstract The present work illustrates the effective treatment of raw pulp and paper mill effluent using a model hybrid upflow anaerobic sludge blanket reactor (HUASBR). The physico-chemical and biological characteristics of wastewater were observed to be critical from the pollution potential aspect. The design features of model HUASBR had a respective total and effective working capacity of 7.5 and 6.5l, together with 25 cm depth of packing by polypropylene hexagonal inert material at the top of the reactor. Start-up of the reactor was carried out using an inoculum mixture containing rumen liquid of goat and cow dung slurry at an appropriate ratio of 3 : 1(v/v). Also, the reactor was effectively started up at the end of 36 days. Based on the performance of model HUASBR, under the respective variations of organic loading rates (OLRs) of 1, 2 and 4 kg COD m−3 d−1, the stepwise COD removals were found to be about 41, 69 and 87%. However, a hydraulic loading rate (HRT) of 20 h was appropriately maintained throughout the studies.

Combinative treatment of phenol-rich retting-pond wastewater by a hybrid upflow anaerobic sludge blanket reactor and solar photofenton process

In this study, recalcitrant rich retting-pond wastewater was treated primarily by anaerobic treatment and subsequently treated with a solar photofenton process to remove phenol and organics. The anaerobic treatment was carried out in a granulated laboratory scale hybrid upflow anaerobic sludge blanket reactor (HUASBR) with a working volume of 5.9 L. It was operated at different hydraulic retention times (HRT) from 40 to 20 h over a period of 140 days. The optimum HRT of the anaerobic reactor was found to be 30 h, with corresponding chemical oxygen demand (COD) and phenol removal of 60% and 47%, respectively. Primary anaerobically treated wastewater was subjected to secondary solar photofenton treatment which was carried out at pH 3.5. Response surface methodology (RSM) was used to design and optimize the performance of the solar photofenton process. Regression quadratic model describing COD removal efficiency of the solar photofenton process was developed and confirmed by analysis of variance (ANOVA). Optimum parameters of the solar photofenton process were found to be: 4 g/L of fenton as catalysts, 25 mL of hydrogen peroxide, and 30 min of reaction time. After the primary anaerobic treatment, solar photofenton oxidation process removed 94% and 96.58% of COD and phenol, respectively. Integration of anaerobic and solar photofenton treatment resulted in 97.5% and 98.4% removal of COD and phenol, respectively, from retting-pond wastewater.

Treatment of a low-strength bilge water of Caspian Sea ships by HUASB technique

Oily bilge water is one of the major pollutants that threats marine environment due to its direct discharge from ships into sea. The aim of this paper is to investigate the possibility of dilute bilge water treatment by using hybrid up-flow anaerobic sludge blanket (HUASB) bio-reactor. The reactor operated at two hydraulic retention times (HRTs) of 10h and 8h. The organic loading rate (OLR) was gradually increased from 0.12g to 0.6g chemical oxygen demand (COD)/lday. After the immobilization of sludge on the surface of the support materials and 10 days of batch feeding of the reactor with the waste water as acclimation period (with COD removal of 59%), the continuous operation of the reactor started. At the end of the experiment, with the HRT of 8h and OLR of 0.6g COD/lday, the COD removal efficiency reached the amount of 75%. Furthermore, the bio-reactor showed a good performance in removing oil from the waste stream which was significantly lower than the standard value which has been laid down for the discharge of the bilge water from ships by the International Maritime Organization (IMO). The obtained data demonstrated that the HUASB reactor is an appropriate system for the treatment of a low-strength bilge water.

Comparative Study of Treatment of Sago Wastewater using HUASB Reactor in the Presence and Absence of Effective Microorganisms

This study evaluates the performance of HUASB reactors in anaerobic treatment of sago industry wastewater using Effective Microorganism. A laboratory scale Hybrid Up flow Anaerobic Sludge Blanket (HUASB) reactor, having a volume of about 4.7 L was operated and Polypropylene rings were used as packing media. The initial OLR (Organic Loading Rate) range was about 0.75 Kg.COD/m3.day and further increased. Various effluent characteristics like pH, COD, Total Suspended Solids, VFA, Alkalinity and biogas production were studied until the attainment of steady state. The pH of treated effluent during steady state condition was almost neutral for both reactors even though the influent had an acidic pH. The maximum COD and TSS removal efficiencies were as high as 88% and 77% in HUASB reactor in the presence of effective microorganisms with an OLR of 9kg.COD/m3.day as compared with HUASB reactor in the absence of effective microorganisms of 76% and 68% with an OLR of 9kg.COD/m3.day during the steady state period. The gas production was increased with increased OLR. The maximum gas production of 2.8 L/d and 2.0 L/d for HUASB reactor in the presence of effective microorganisms and HUASB reactor in the absence of effective microorganisms were obtained.

Back propagation neural network modelling of biodegradation and fermentative biohydrogen production using distillery wastewater in a hybrid upflow anaerobic sludge blanket reactor.

In a hybrid upflow anaerobic sludge blanket (HUASB) reactor, biodegradation in association with biohydrogen production was studied using distillery wastewater as substrate. The experiments were carried out at ambient temperature (34±1°C) and acidophilic pH of 6.5 with constant hydraulic retention time (HRT) of 24h at various organic loading rates (OLRs) (1-10.2kgCODm(-3)d(-1)) in continuous mode. A maximum hydrogen production rate of 1300mLd(-1) was achieved. A back propagation neural network (BPNN) model with network topology of 4-20-1 using Levenberg-Marquardt (LM) algorithm was developed and validated. A total of 231 data points were studied to examine the performance of the HUASB reactor in acclimatisation and operation phase. The statistical qualities of BPNN models were significant due to the high correlation coefficient, R(2), and lower mean absolute error (MAE) between experimental and simulated data. From the results, it was concluded that BPNN modelling could be applied in HUASB reactor for predicting the biodegradation and biohydrogen production using distillery wastewater.

Potentials of anaerobic treatment for catalytically oxidized olive mill wastewater (OMW)

The catalytically oxidized olive mill wastewater (OMW) was subjected to continuous anaerobic treatment using two treatment schemes. The 1st step in both schemes was an up-flow anaerobic sludge blanket (UASB) reactor (2 0 l). The 2nd step was either a hybrid UASB reactor or a classical one (1 0 l, each). The 1st stage was operated at constant hydraulic retention time (HRT) of 24 h. The organic loading rate (OLR) varied from 3.4 to 4.8 kgCOD/m 3 d depending on the quality of the pretreated wastewater. The results obtained indicated that, the 1st step UASB reactor achieved a COD percentage removal value of 53.9%. Corresponding total BOD 5 and TSS removal were 51.5% and 68.3%, respectively. The results obtained indicated that the hybrid UASB reactor as a 2nd step produced better quality effluent as compared to the classical one. This could be attributed to the presence of the packing curtain sponge with active biomass in the sedimentation part of hybrid UASB reactor which minimizes suspended solids washout, consequently enhancement of the efficiency of the reactor. Available data showed that a two stage system consisting of a classical and a hybrid UASB reactor operated at a total HRT of 48 h and OLR of 2.0 kgCOD/m 3 d provided promising results. Removal values of COD total, BOD 5 total , TOC, VFA, oil and grease were 83%, 84%, 81%, 93% and 81%, respectively. Based on the available data, the use of a two stage anaerobic system consisting of a classical UASB reactor followed by a hybrid UASB as a post-treatment step for catalytically oxidized OMW is recommended.

Effect of COD/NO 3−-N ratio on the performance of a hybrid UASB reactor treating phenolic wastewater

The effect of COD/O 3 −-N ratio on the biodegradation of complex phenolic mixture was studied in bench scale hybrid upflow anaerobic sludge blanket (HUASB) reactors. HUASB reactor is a combination of a UASB unit at the lower part and an anaerobic fixed film at the upper end. The aim of this study was to evaluate the biodegradability of phenolic mixture (from synthetic coal wastewater) as the only carbon and energy source in continuous experiments using nitrate as the final electron acceptor. Synthetic coal wastewater contained phenol (490 mg/L); m-, o-, p-cresols (123.0 mg/L, 58.6 mg/L, 42 mg/L); 2,4-, 2,5-, 3,4- and 3,5 dimethyl phenols (6.3 mg/L, 6.3 mg/L, 4.4 mg/L and 21.3 mg/L) as major phenolic compounds representing the complex phenolic mixture. Nitrate nitrogen loading was increased from 0.11 g/m 3/d to 0.5 g/m 3/d in order to keep COD/NO 3 −-N ratio as 20.1, 14.85, 9.9, 6.36 and 4.45. An input phenolics concentration of 752 mg/L and hydraulic retention time (HRT) of 24 h was maintained through out the study. Removal of phenolic mixture was found to increase with the lowering of COD/NO 3 −-N ratio. Maximum phenolics removal of 98% was achieved at a COD/NO 3 −-N ratio of 6.36. However, phenolics removal got adversely affected when COD/NO 3 −-N ratio was reduced below 6.36. A nitrogen production efficiency of 78% was obtained according to nitrate consumption. Simultaneous denitrification and methanogenesis was observed in all the reactors throughout the study, demonstrating that denitrification is a feasible alternative for the treatment of coal wastewater. Granules degrading complex phenolic mixture were of diameter 1.6–2.25 mm.

Anaerobic treatment of a chemical synthesis-based pharmaceutical wastewater in a hybrid upflow anaerobic sludge blanket reactor

In this study, performance of a lab-scale hybrid up-flow anaerobic sludge blanket (UASB) reactor, treating a chemical synthesis-based pharmaceutical wastewater, was evaluated under different operating conditions. This study consisted of two experimental stages: first, acclimation to the pharmaceutical wastewater and second, determination of maximum loading capacity of the hybrid UASB reactor. Initially, the carbon source in the reactor feed came entirely from glucose, applied at an organic loading rate (OLR) 1 kg COD/m 3 d. The OLR was gradually step increased to 3 kg COD/m 3 d at which point the feed to the hybrid UASB reactor was progressively modified by introducing the pharmaceutical wastewater in blends with glucose, so that the wastewater contributed approximately 10%, 30%, 70%, and ultimately, 100% of the carbon (COD) to be treated. At the acclimation OLR of 3 kg COD/m 3 d the hydraulic retention time (HRT) was 2 days. During this period of feed modification, the COD removal efficiencies of the anaerobic reactor were 99%, 96%, 91% and 85%, and specific methanogenic activities (SMA) were measured as 240, 230, 205 and 231 ml CH 4/g TVS d, respectively. Following the acclimation period, the hybrid UASB reactor was fed with 100% (w/v) pharmaceutical wastewater up to an OLR of 9 kg COD/m 3 d in order to determine the maximum loading capacity achievable before reactor failure. At this OLR, the COD removal efficiency was 28%, and the SMA was measured as 170 ml CH 4/g TVS d. The hybrid UASB reactor was found to be far more effective at an OLR of 8 kg COD/m 3 d with a COD removal efficiency of 72%. At this point, SMA value was 200 ml CH 4/g TVS d. It was concluded that the hybrid UASB reactor could be a suitable alternative for the treatment of chemical synthesis-based pharmaceutical wastewater.

High rate anaerobic treatment of Sago wastewater using HUASB with PUF as carrier

Sago industry is one of the major small-scale sectors in India and over 800 units are located in the southern State of Tamilnadu. Processing of sago generates enormous quantities of high strength wastewater requiring systematic treatment prior to disposal. The present study is an attempt to treat the sago wastewater using Hybrid Upflow Anaerobic Sludge Blanket (HUASB) reactor, which offers the advantages of both fixed film and up flow anaerobic sludge blanket treatment. HUASB reactor with a volume of 5.6 L was operated at Organic Loading Rates varying from 10.7 to 24.7 kg COD/m3.day. After 130 days of startup, the reactor produced appreciable decrease in COD of wastewater and removed solids efficiently. The COD removal varied from 91–87%. While the removal of Total Solids was in the range of 61–57%, that of volatile solids varied from 70–67%. The ideal OLR for the reactor was 23.5 kg COD/m3.day. The findings of the study open up newer possibilities of design low cost and compact onsite treatment systems with very short retention periods.

Anaerobic treatment of swine wastewater using hybrid UASB reactors

Two hybrid upflow anaerobic sludge blanket (UASB) reactors were used to treat screened swine wastewaters. In order to achieve the advantages of both suspended growth and attached-growth anaerobic reactor systems, this type of reactor has a rope matrix inserted as a fixed-film medium in its mid section. The study examined the reactor performance in terms of its treatment efficiency and membrane production, and evaluated the effect which the absence of seeding in the start-up process had on the efficiency of reactor performance. The conclusion reached was that this hybrid UASB reactor could be used without seeding in the treatment of screened swine manure if the organic loading rates were moderate. Under these conditions, over 57% COD removal and 0.71 litres CH 4/litre reactor day were obtained. While sludge loss did occur, methane production increased and the concentrations of VFA in the effluents were kept below 100 mg/litre. It is believed that the additional biofilm in this hybrid reactor increased the stability of the reactor and helped maintain steady methane production. The results also confirm that granulation of the sludge is an essential requirement for satisfactory operation.

Hybrid Upflow Anaerobic Sludge Blanket Reactor (HUASBR) Treatment of Dairy Effluents

This paper covers the treatability results of a laboratory-scale hybrid upflow anaerobic sludge blanket reactor (HUASBR) treating dairy effluents from a large integrated industry with a maximum production capacity of 500 tons of milk per day. The study began wilb the determination of effluent characteristics and pollution profile for the investigated dairy industry. As a result of observations, by-product recovery and waste reduction alternatives were investigated by in-plant control measures. Anaerobic treatability studies were conducted by a laboratory-scale hybrid upflow anaerobic reactor with an effective volume of 81. The reactor was operated more that 270 days under mesophilic conditions and it was fed wilb the combined effluents from the investigated dairy industry. The hydraulic retention times ranged from 0.21 to 0.96 days under normal operating conditions after the start up. COD removal efficiencies of more than 87% were achieved at an organic loading rate (OLR) of 8.5 kg COD/m3·d OLR was gradually increased from 2.54 to 7.1 kg COD/m3·d within 15 days but the anaerobic reactor performances did not change significantly. The reactor was operated under varying feed characteristics to test the response of the system to high strength acid whey. The system can tolerate OLRs as high as 17 kg COD/m3·d with an average COD removal efficiency of 75% for two weeks. Although the reactor was fed by diluted effluent with an average COD of 1070 mg/l at very high hydraulic loadings (HRT=5 hours), 75% removals of COD were achieved under these conditions.