Start-up and steady-state results of a full-scale UASB reactor treating malting wastewater.

An Imhoff tank was reconstructed into a 250 m3 UASB reactor in order to treat a malting plant wastewater. The UASB was inoculated with sludge from an anaerobic lagoon used for slaughterhouse wastewater treatment. After two months of operation the reactor achieved full load with an HRT of 17 h, a COD removal higher than 80% and a biogas production of 300 m3/day (77% average methane content), with an organic loading rate of 3.6 kgCOD/m3.d (0.24 kgCOD/kgVSS.d). A yield coefficient of 0.09 gVSS/gCODrem was found from a mass balance. The fat present in the inoculated sludge (48 mg/gSSV) did not affect the start up performance. Sludge from the inoculum with high content of fat (270 mg/gSSV), was separated by flotation in the first week of operation. The COD removal efficiency was scarcely influenced by the reactor operation temperature (17-25 degrees C).     

On-site treatment of high-strength alcohol distillery wastewater by a pilot-scale thermophilic multi-staged UASB (MS-UASB) reactor.

A pilot-scale multi-staged UASB (MS-UASB) reactor with a working volume of 2.5 m3 was operated for thermophilic (55 degrees C) treatment of an alcohol distillery wastewater for a period of over 600 days. The reactor steadily achieved a super-high rate COD removal, that is, 60 kgCOD m(-3) d(-1) with over 80% COD removal. However, when higher organic loading rates were further imposed upon the reactor, that is, above 90 kgCOD m(-3) d(-1) for barely-based alcohol distillery wastewater (ADWW) and above 100 kgCOD m(-3) d(-1) for sweet potato-based ADWW, the reactor performance somewhat deteriorated to 60 and 70% COD removal, respectively. Methanogenic activity (MA) of the retained sludge in the thermophilic MS-UASB reactor was assessed along the time course of continuous run by serum-vial test using different substrates as a vial sole substrate. With the elapsed time of continuous run, hydrogen-utilizing MA, acetate-utilizing MA and propionate-fed MA increased at maximum of 13.2, 1.95 and 0.263 kgCOD kgVSS(-1) d(-1), respectively, indicating that propionate-fed MA attained only 1/50 of hydrogen-utilizing MA and 1/7 of acetate-utilizing MA. Since the ADWW applied herewith is a typical seasonal campaign wastewater, the influence of shut-down upon the decline in sludge MA was also investigated. Hydrogen-utilizing MA and acetate-utilizing MA decreased slightly by 3/4, during a month of non-feeding period, whereas propionate-fed MA were decreased significantly by 1/5. Relatively low values of propionate-fed MA and its vulnerability to adverse conditions suggests that the propionate degradation step is the most critical bottleneck of overall anaerobic degradation of organic matters under thermophilic condition.     

Grey water treatment in UASB reactor at ambient temperature.

In this paper, the feasibility of grey water treatment in a UASB reactor was investigated. The batch recirculation experiments showed that a maximum total-COD removal of 79% can be obtained in grey-water treatment in the UASB reactor. The continuous operational results of a UASB reactor treating grey water at different hydraulic retention time (HRT) of 20, 12 and 8 hours at ambient temperature (14-24 degrees C) showed that 31-41% of total COD was removed. These results were significantly higher than that achieved by a septic tank (11-14%), the most common system for grey water pre-treatment, at HRT of 2-3 days. The relatively lower removal of total COD in the UASB reactor was mainly due to a higher amount of colloidal COD in the grey water, as compared to that reported in domestic wastewater. The grey water had a limited amount of nitrogen, which was mainly in particulate form (80-90%). The UASB reactor removed 24-36% and 10-24% of total nitrogen and total phosphorus, respectively, in the grey water, due to particulate nutrients removal by physical entrapment and sedimentation. The sludge characteristics of the UASB reactor showed that the system had stable performance and the recommended HRT for the reactor is 12 hours.     

Pretreatment of silk-dyeing industrial wastewater by UASB reactor.

The objective of this study was to investigate the performance of the upflow anaerobic sludge blanket (UASB) reactor as the pretreatment system for silk-dyeing wastewater. Two laboratory-scale UASB reactors, with working volume of 15.59 I, were used during May 1998 to June 1999. The actual wastewater was diluted to reduce ammonium ion toxicity on anaerobic bacteria. The experiments were conducted at the organic loading rates (OLRs) of 0.52, 1.01, 1.04, 1.54 and 2.56 kgCOD/(m3 x d), treating only wastewater generated from the acid-dye process of mixed-species raw silk. It took approximately 4 1/2 months to reach the steady-state conditions. It was found that the COD removal was in the ranges of 74.1-85.3%, except at OLR 2.56 kgCOD/(m3 x d) where efficiency significantly dropped to 55.2%. The apparent color removal was in the similar trend as COD. During the study periods, wastewater input had various color shades while the effluent generally looked pale yellowish. The methane generation rates ranged from 0.18-0.31 m3/kg COD removed, with methane composition 81.0-88.1% in biogas. The average granule size in the sludge bed had slowly increased to 0.73 mm in the last experiment. It can be concluded that the UASB reactor is suitable as a pretreatment system for silk-dyeing wastewater. An OLR of 1 kgCOD/(m3 x d) and an influent concentration diluted to 2,600 mgCOD/l are suggested while COD and apparent color removal efficiency of 80% and 70%, respectively, can be expected.     

Anaerobic treatment of a medium strength industrial wastewater at low-temperature and short hydraulic retention time: a pilot-scale experience

The aim of this work was to evaluate the performance of a pilot-scale upflow anaerobic sludge blanket (UASB) reactor during the treatment of cereal-processing industry wastewater under low-temperature conditions (17 degrees C) for more than 300 days. The applied organic loading rate (OLR(appl)) was gradually increased from 4 to 6 and 8 kg COD(sol)/m3d by increasing the influent soluble chemical oxygen demand (COD(sol)), while keeping the hydraulic retention time constant (5.2 h). The removal efficiency was high (82 to 92%) and slightly decreased after increasing the influent COD(sol) and the OLR(appl). The highest removed organic loading rate (OLR(rem)) was reached when the UASB reactor was operated at 8 kg COD(sol)/m3d and it was two times higher than that obtained for an OLR(appl) of 4 kg COD(sol)/m3d. Some disturbances were observed during the experimentation. The formation of biogas pockets in the sludge bed significantly complicated the biogas production quantification, but did not affect the reactor performance. The volatile fatty acids in the effluent were low, but increased as the OLR(appl) increased, which caused an increment of the effluent COD(sol). Anaerobic treatment at low temperature was a good option for the biological pre-treatment of cereal processing industry wastewater.     

Upflow anaerobic sludge blanket (UASB) treatment of supernatant of cow manure by thermal pre-treatment.

Upflow anaerobic sludge blanket (UASB) methane fermentation treatment of cow manure that was subjected to screw pressing, thermal treatment and subsequent solid-liquid separation was studied. Conducting batch scale tests at temperatures between 140 and 180 degrees C, the optimal temperature for sludge settling and the color suppression was found to be between 160-170 degrees C. UASB treatment was carried out with a supernatant obtained from the thermal treatment at the optimal conditions (170 degrees C for 30 minutes) and polymer-dosed solid-liquid separation. In the UASB treatment with a COD(Cr) loading of 11.7 kg/m3/d and water temperature of 32.2 degrees C, the COD(Cr) level dropped from 16,360 mg/L in raw water to 3,940 mg/L in treated water (COD(Cr), removal rate of 75.9%), and the methane production rate per COD(Cr) was 0.187 Nm3/kg. Using wastewater thermal-treated at the optimal conditions, also a methane fermentation treatment with a continuously stirred tank reactor (CSTR) was conducted (COD(Cr) in raw water: 38,000 mg/L, hydraulic retention time (HRT): 20 days, 35 degrees C). At the COD(Cr) loading of 1.9 kg/m3/d, the methane production rate per COD(Cr), was 0.153 Nm3/kg. This result shows that UASB treatment using thermal pre-treatment provides a COD(Cr), loading of four times or more and a methane production rate of 1.3 times higher than the CSTR treatment.     

UASB reactor for domestic wastewater treatment at low temperatures: a comparison between a classical UASB and hybrid UASB-filter reactor.

The performance of an upflow anaerobic sludge blanket (UASB) reactor and a hybrid UASB-filter reactor was investigated and compared for the treatment of domestic wastewater at different operational temperatures (28, 20, 14 and 10 degrees C) and loading rates. For each temperature studied a constant CODt removal was observed as long as the upflow velocity was lower than 0.35 m/h. At these upflow velocities similar removals were observed for both reactor types at 28 and 20 degrees C, 82 and 72% respectively. However, at 14 and 10 degrees C the UASB reactor showed a better COD removal (70% and 48%, respectively) than the hybrid reactor (60% and 38%). COD removal resulted from biological degradation and solids accumulation in the reactors. At 28 degrees C, a constant 200 g sludge mass was observed in both reactors and COD removal was attributed to biological degradation only. At lower temperatures, solids accumulation was observed in addition to biological degradation with an increase in reactor sludge as the temperature decreased. The decrease in biological degradation at lower temperatures was offset by solids accumulation and explains the similar overall COD removal efficiency observed at 28 degrees C, 20 degrees C and 14 degrees C. The decrease in temperature was also followed by an increase in the effluent TSS concentration in both reactors. At 14 and 10 degrees C a lower effluent TSS concentration and better performance was observed in the UASB reactor.     

Application of an anaerobic hybrid reactor for petrochemical effluent treatment

An anaerobic hybrid reactor (UASB/Filter) was used for petrochemical wastewater treatment in mesophilic conditions. The seeded flocculent sludge from a UASB plant treating dairy wastewater, acclimatized to the petrochemical wastes in a two-stage operation. After start up, under steady-state conditions, experiments were conducted at OLRs of between 0.5 and 24 kg TCOD m(-3) d(-1), hydraulic retention times (HRT) of 4-48 h and up-flow velocities 0.021-0.25 mh(-1). Removal efficiencies in the range of 42-86% were achieved at feed TCOD concentrations of 1,000-4,000 mg L(-1). The results of reactor performance at different operational conditions and its relations are presented and discussed in this paper. Then, the obtained data are used for determination of kinetic models. The results showed that a second-order model and a modified Stover-Kincannon model were the most appropriate models for this reactor. Finally, the biogas production data were used for the determination of biogas production kinetics.     

Optimization of the performance of an integrated anaerobic-aerobic system for domestic wastewater treatment

A promising system consisting of Up-flow Anaerobic Sludge Blanket (UASB) and Down-Flow Hanging Sponge (DHS) system was investigated for removal of COD, BOD(5) fractions, ammonia and faecal coliform from domestic wastewater. The combined system was operated at different HRTs of 16, 11 and 8 h. The results indicate that increasing the total HRT from 8 to 16 h significantly (p < 0.05) improves the COD(total) and BOD(5 total) removal mainly as a result of a higher removal of COD(soluble), BOD(soluble), COD(particulate) and BOD(particulate). The main part of coarse suspended solids was removed in the UASB reactor (76.4+/-18%) and the remaining portion was adsorbed and/or enmeshed and degraded in the biomass of the DHS system. The combined system achieved a substantial reduction of total suspended solids (TSS) resulting in an average overall percentage removal of 94+/-6% (HRT = 16 h) and 89.5+/-7.8% (HRT = 8 h). Faecal coliform reduction was significantly improved when increasing the total HRT from 8 to 16 h. Residual counts of faecal coliform were 3.1 x 10(3)/100 ml at a total HRT of 16 h, and 2.8 x 10(4)/100 ml at total HRT of 8 h, corresponding to overall removal efficiency of 99.97+/-0.03 and 99.6+/-0.3% respectively. Despite the increase of ammonia concentration as a result of protein hydrolysis in the UASB reactor, a substantial removal of ammonia was achieved in the DHS system. The results obtained show that decreasing the OLR imposed to DHS system from 2.6 to 1.6 kg COD/m(3).d significantly (p < 0.05) improves the removal efficiency of ammonia by a value of 29%. However, the removal efficiency of ammonia is not further increased when decreasing the OLR from 1.6 to 1.3 kg COD/m(3).d. The discharged sludge from UASB + DHS system exerts a good settling property and partially stabilized.DHS profile results have shown that the major part of COD, BOD(5), and TSS was removed in the upper part of the system, consequently, the nitrification process was occurring in the lower part of the DHS system.     

Influence of hydraulic retention time on UASB post-treatment with UF membranes

A pilot UASB reactor coupled with an external ultrafiltration (UF) membrane was operated under three different hydraulic retention times (HRT) for domestic wastewater treatment. The aim was to assess the HRT influence on system performance and fouling. The highest concentrations of COD, total solids, extracellular polymeric substances (EPS) and soluble microbial products (SMP) in UASB effluent and permeate were found when the UASB reactor was operated under the lowest HRT studied (4 hours); although the fulfillment of Mexican Standard for wastewater reclamation was not compromised. This fact could be attributed to the higher shear stress forces inside the UASB reactor when it was operated at low HRT, which promoted the release of biopolymeric substances in its effluent. Besides, the fouling propensity in the UASB effluent was worsened with HRT reduction, by increasing the fouling rate and the specific cake resistance. Based on these results, it is recommended to avoid operating the UASB reactor at low HRTs (less than 4 hours) in order to control SMP and EPS fouling potential. The results presented also suggest that HRT reduction has a detrimental effect on performance and fouling.     

Treatment of organic synthesis wastewater using anaerobic packed bed and aerobic suspended growth bioreactors.

The performance of an anaerobic mesophilic packed bed reactor, with a mixture of GAC and tezontle, followed by an aerobic suspended growth system was studied for the treatment of organic chemical wastewater with a high COD concentration (22-29 g/L). The testing of the anaerobic-aerobic system was conducted in an experimental set-up for almost 2.5 years. Different operational conditions were evaluated. The anaerobic reactor showed performance stability and COD removals higher than 80% were obtained with loads up to 16.6 kg x m(-3) x d(-1). The acclimation of the aerobic biomass to the substrate in the anaerobic effluent was very quick and COD removals higher than 94% were obtained even at high organic loads. The combined anaerobic-aerobic system allowed total COD removals higher than 99.5% and the accomplishment of the discharge requirements of 200 mgCOD/L when the anaerobic reactor was operated with loads of 8-11 kg x m(-3)x d(-1) and the aerobic reactor with 0.33 kg x kg(-1) x d(-1), being the total HRT of 4.4. The average TKN removal in the anaerobic-aerobic system was 97%, the average for the anaerobic reactor being 52% and that one for the aerobic system being 94%.     

Influence of effluent-recirculation condition on the process performance of expanded granular sludge bed reactor for treating low strength wastewater.

A 2.0 L volume of EGSB reactor was operated at 20 degrees C for more than 500 days with 0.3-0.4 g COD/L of sucrose base wastewater to investigate the influence of effluent-recirculation on the process performance. At the start up period, the reactor was operated in EGSB mode with 5 m/h upflow velocity by continuous effluent recirculation. The COD loading was set to 7.2-9.6 kg COD/m(3) day with HRT of 1 hour. However, in this mode, EGSB reactor exhibited insufficient COD removal efficiency, i.e., 50-60%. Therefore, UASB mode (without recirculation, 0.7 m/h upflow velocity) was used for 30 minutes in every 40 minutes cycle to increase the COD concentration in the sludge bed. As a result, an excellent process performance was shown. The COD removal efficiency increased from 65% to 91% and the reactor could maintain a good physical property of retained sludge (sludge concentration: 33.4 g VSS/L and SVI: 25 mL/g VSS). Furthermore, retained sludge possessed sufficient level of methanogenic activity at 20 degrees C.     

Grey water treatment in upflow anaerobic sludge blanket (UASB) reactor at different temperatures

The treatment of grey water in two upflow anaerobic sludge blanket (UASB) reactors, operated at different hydraulic retention times (HRTs) and temperatures, was investigated. The first reactor (UASB-A) was operated at ambient temperature (14-25 degrees C) and HRT of 20, 12 and 8 h, while the second reactor (UASB-30) was operated at controlled temperature of 30 degrees C and HRT of 16, 10 and 6 h. The two reactors were fed with grey water from 'Flintenbreite' settlement in Luebeck, Germany. When the grey water was treated in the UASB reactor at 30 degrees C, total chemical oxygen demand (CODt) removal of 52-64% was achieved at HRT between 6 and 16 h, while at lower temperature lower removal (31-41%) was obtained at HRT between 8 and 20 h. Total nitrogen and phosphorous removal in the UASB reactors were limited (22-36 and 10-24%, respectively) at all operational conditions. The results showed that at increasing temperature or decreasing HRT of the reactors, maximum specific methanogenic activity of the sludge in the reactors improved. As the UASB reactor showed a significantly higher COD removal (31-64%) than the septic tank (11-14%) even at low temperature, it is recommended to use UASB reactor instead of septic tank (the most common system) for grey water pre-treatment. Based on the achieved results and due to high peak flow factor, a HRT between 8 and 12 h can be considered the suitable HRT for the UASB reactor treating grey water at temperature 20-30 degrees C, while a HRT of 12-24 h can be applied at temperature lower than 20 degrees C.     

Low temperature anaerobic biotreatment of priority pollutants.

The effect of low operating temperature and pollutant concentration on the performance of five anaerobic hybrid reactors was investigated. Stable and efficient long-term (>400 days) treatment of a cold (6-13 degrees C), volatile fatty acid (VFA)-based, wastewater was achieved at applied organic loading rates (OLRs) of 5 kg chemical oxygen demand (COD) m(-3) d(-1) with COD removal efficiencies c. 84% at 6 degrees C (sludge loading rate (SLR) 1.04-1.46 kg COD kg [VSS](-1) d(-1)). VFA-based wastewaters, containing up to 14 g pentachlorophenol (PCP) m(-3) d(-1) or 155 g toluene m(-3) d(-1) were successfully treated at applied OLRs of 5-7 kg COD m(-3) d(-1). Despite transient declines in reactor performance in response to increasing toxicant loading rates, stable operation (COD removal efficiencies > 90%) and satisfactory toxicant removal efficiencies (>88%) were demonstrated by the systems.     

UASB treatment of liquid residues from grass bioraffination.

In 2001 the first green biorefinery started operation in Switzerland with a design load of 5,000 tons dm of grass per year and a combined output of fibres (0.4 tons per ton input), protein (160 t/t) and bioenergy (500 kWh/t). Bioenergy was produced in a 570 m3 UASB reactor which has been monitored intensively during its first year of operation. Anaerobic treatment of liquid residues with > 80% degradation of organics was shown up to high f/m ratios and loading rates of 12 -15 kg COD/m3 d and specific biogas production of 0.5-0.65 Nm3 of gas per kg of COD added. A mass flow analysis of solids and pellets leads to the conclusion, that due to a low sludge bed volume of only 16% of the reactor combined with a low actual organic loading of 1.5 kg COD/m3 d there was a restricted adsorption and a low degradation of substrate solids.     

Anaerobic digestion potential for ecological and decentralised sanitation in urban areas.

The potential of anaerobic digestion in ecological and decentralised sanitation has been investigated in this research. Different anaerobic digestion systems were proposed for the treatment of sewage, grey water, black water and faeces. Moreover, mathematical models based on anaerobic digestion model no.1 (ADM1) were developed for determination of a suitable design for each system. For stable performance of an upflow anaerobic sludge blanket (UASB) reactor treating sewage, the model results indicated that optimisation of wastewater conversion to biogas (not COD removal) should be selected for determination of the hydraulic retention time (HRT) of the reactor. For the treatment of sewage or black water in a UASB septic-tank, the model results showed that the sludge removal period was the main parameter for determination of the HRT. At such HRT, both COD removal and wastewater conversion are also optimised. The model results demonstrated that for treatment of faeces in an accumulation (AC) system at temperature > or = 25 degrees C, the filling period of the system should be higher than 60 days. For maximisation of the net biogas production (i.e. reduction of biogas losses as dissolved in the effluent), the separation between grey water, urine and faeces and reduction of water consumption for faeces flushing are required. Furthermore, the faeces and kitchen organic wastes and grey water are digested in, respectively, an AC system and UASB reactor, while the urine is stored.     

Textile effluent treatment in a UASB reactor followed by submerged aerated biofiltration

An upflow anaerobic sludge bed (UASB)-submerged aerated biofilter (SAB) system that treats effluents from a jeans factory was evaluated. The 210-day operational period was divided into three phases (PI, PII and PIII), each with a different hydraulic retention time (HRT in h) and organic loading rate (OLR in kg COD/m3.d). In PI, the best performance was achieved using the UASB (HRT 24, OLR 1.3) with COD and color removal efficiencies of 59 and 64%, respectively; the corresponding values were 77 and 86% for the final effluent. In PII, the efficiencies were 50 and 55% using the UASB (HRT 16, OLR 1.2), respectively, and 69 and 81% for the final system effluent, respectively. In PIII, the UASB (HRT 12 and ORL 3.2) showed the poorest performance; the efficiencies decreased to 48 and 50%, respectively. The same phenomenon occurred in the system with corresponding efficiencies decreasing to 69 and 61%. Throughout the experiment, the system removal efficiencies were between 57 and 88% for nitrogen and between 14 and 63% for sulfate. The final effluent showed relatively non-toxicity or moderate toxicity using Daphnia magna as an indicator. Therefore, the overall results showed that the use of a sequential anaerobic-aerobic system is promising for treatment of textile industrial wastewater.     

黄姜废水处理实践与分析

基于黄姜废水处理工程运行实际,着重分析了pH值、温度、COD及容积负荷等因素对UASB反应器启动的影响。该工程利用预处理＋厌氧＋好氧＋混凝、脱色组合工艺处理黄姜废水,在进水COD和色度分别达12000mg/L和600倍的情况下,出水COD和色度分别为110mg/L和50倍,COD去除率达99%。废水经处理后出水水质符合《皂素工业水污染排放标准》（GB20425-2006）。     

Combined biological and physico-chemical treatment of baker's yeast wastewater.

The UASB reactor (35 degrees C) was quite efficient for removal of bulk COD (52-74%) from the raw and diluted cultivation medium from the first separation process of baker's yeasts (the average organic loading rates varied in the range 3.7-16 g COD/I/d). The aerobic-anoxic biofilter (19-23 degrees C) can be used for removal of remaining BOD and ammonia from anaerobic effluents; however, it had insufficient COD to fulfil the denitrification requirements. To balance COD/N ratio, some bypass of raw wastewater (approximately 10%) should be added to the biofilter feed. The application of iron (III)-, aluminium- or calcium-induced coagulation for post-treatment of aerobic effluents can fulfil the limits for discharge to sewerage (even for colour mainly exerted by hardly biodegradable melanoidins), however, the required amounts of coagulants were relatively high.     

Comparing the performance of UASB and GRABBR treating low strength wastewaters

Anaerobic technologies have proved successful in the treatment of various high strength wastewaters with perceptible advantages over aerobic systems. The applicability of anaerobic processes to treat low strength wastewaters has been increasing with the evolution of high-rate reactors capable of achieving high sludge retention time (SRT) when operating at low HRT. However, the performance of these systems can be affected by high variations in flow and wastewater composition. This paper reports on the comparative study carried out with two such high rate reactors systems to evaluate their performances when used for the treatment of low strength wastewaters at high hydraulic rates. One of the two systems is the most commonly used upflow anaerobic sludge blanket (UASB) reactor in which all reactions occur within a single vessel. The other is the granular bed baffled reactor (GRABBR) that encourages different stages of anaerobic digestion in separate vessels longitudinally across the reactor. The reactors, with equal capacity of 10 litres, were subjected to increasing organic loading rates (OLRs) and hydraulic retention times (HRTs) of up to 60 kg COD m(-3) d(-1) and 1 h respectively. Results show that the GRABBR has greater processes stability at relatively low HRTs, whilst the UASB seems to be better equipped to cope with organic overloads or shockloads. The study also shows that the GRABBR enables the harvesting of biogas with greater energetic value and hence greater re-use potential than the UASB. Biogas of up to 86% methane content is obtainable with GRABBR treating low strength wastewaters.