Biomass retention and performance of anaerobic fixed-film reactors treating acetic acid wastewater

An acetic-acid-based synthetic wastewater of different organic concentrations was successfully treated at 35 degrees C in anaerobic downflow fixed-film reactors operated at high organic loading rates and short hydraulic retention times (HRTs). Substrate removal and methane production rates close to theoretical values of complete volumetric chemical oxygen demand (COD) removal and maximum methane conversion were obtained. A high concentration of biofilm biomass was retained in the reactor. Steady-state biofilm concentration increased with increased organic loading rate and decreased HRTs, reaching a maximum of 8.3 kg VFS/m(3) at a loading rate of 17 kg COD/m(3) day. Biofilm substrate utilization rates of up to 1.6 kg COD/kg VFS day were achieved. Soluble COD utilization rates at various COD concentrations can be described by half-order reaction kinetics.     

Treatment of slaughterhouse wastewater in a UASB reactor and an anaerobic filter

A study was performed to assess the feasibility of anaerobic treatment of slaughterhouse wastewaters in a UASB (Upflow Anaerobic Sludge Blanket) reactor and in an AF (Anaerobic Filter). Among the different streams generated, the slaughter line showed the highest organic content with an average COD of 8000 mg/l, of which 70% was proteins. The suspended solids content represented between 15 and 30% of the COD. Both reactors had a working volume of 21. They were operated at 37°C. The UASB reactor was run at OLR (Organic Loading Rates) of 1–6.5 kg COD/m³/day. The COD removal was 90% for OLR up to 5 kg COD/m³/day and 60% for an OLR of 6.5 kg COD/m³/day. For similar organic loading rates, the AF showed lower removal efficiencies and lower percentages of methanization. At higher OLR sludge, flotation occurred and consequently the active biomass was washed out from the filter. The results indicated that anaerobic treatment systems are applicable to slaughterhouse wastewaters and that the UASB reactor shows a better performance, giving higher COD removal efficiencies than the AF.     

Anaerobic pre-treatment of slaughterhouse wastewater using fixed-film reactors

The aim of this work was to study the performance of anaerobic fixed-film reactors with non-random support, for poultry slaughterhouse wastewater pre-treatment, including the influence of operating conditions. The work was carried out with two lab-scale reactors, one upflow and the other downflow, both equipped with vertical corrugated PVC tubes as support and a recirculation circuit. Both reactors were operated at 35°C.COD removal efficiencies ranging from 85% to 95% were achieved for organic loading rates of 8 kg COD m⁻³ d⁻¹, while the highest organic loading rates (35 kg COD m⁻³ d⁻¹) led to efficiencies of 55–75%. The reactors did not show destabilization after 12 h shock loads of 50 kg COD m⁻³ d⁻¹ .Reactor stability was easily achieved under intermittent operation, with weekend breaks, after which the reactors rapidly returned to their optimal performance. The influences of the hydraulic retention time, temperature, the recirculation ratio and flow direction were also studied.     

Anaerobic fluidized bed whey treatment

Anaerobic treatment of moderate strength lactic casein why permeate [2000-7000 mg/L soluble chemical oxygen demand (SCOD)] is possible in fluidized bed reactors. Removal efficiencies up to 90% were obtained at organic removal rates of 7.7 kg SCOD M(-3) day(-1) and efficiencies of 70% were obtained at organic removal rates of 19.5 kg SCOD M(-3) day(-1), both at 35 degrees C. A removal rate of 3.0 kg SCOD M(-3) day(-1) at 50% removal efficiency was obtained at 15 degrees C. Nutrient requirements were much lower than for CSTR systems, and no supplemental nitrogen or phosphorus was required. Removal rates increased and removal efficiency decreased as the organic loading increased. Microorganism concentration increased with decreasing temperature, compensating for reduced reaction rates at lower temperatures.     

Assessment of anaerobic wastewater treatment failure using terminal restriction fragment length polymorphism analysis

AIMS: The suitability of genetic fingerprinting to study the microbiological basis of anaerobic bioreactor failure is investigated. METHODS AND RESULTS: Two laboratory-scale anaerobic expanded granular sludge bed bioreactors, R1 and R2, were used for the mesophilic (37 degrees C) treatment of high-strength [10 g chemical oxygen demand (COD) l(-1)] synthetic industrial-like wastewater over a 100-day trial period. A successful start up was achieved by both bioreactors with COD removal over 90%. Both reactors were operated under identical parameters; however, increased organic loading during the trial induced a reduction in the COD removal of R1, while R2 maintained satisfactory performance (COD removal >90%) throughout the experiment. Specific methanogenic activity measurements of biomass from both reactors indicated that the main route of methane production was hydrogenotrophic methanogenesis. Terminal restriction fragment length polymorphism (TRFLP) analysis was applied to the characterization of microbial community dynamics within the system during the trial. The principal differences between the two consortia analysed included an increased abundance of Thiovulum- and Methanococcus-like organisms and uncultured Crenarchaeota in R1. CONCLUSIONS: The results indicated that there was a microbiological basis for the deviation, in terms of operational performance, of R1 and R2. SIGNIFICANCE AND IMPACT OF THE STUDY: High-throughput fingerprinting techniques, such as TRFLP, have been demonstrated as practically relevant for biomonitoring of anaerobic reactor communities.     

The effect of temperature on slaughterhouse wastewater treatment in anaerobic sequencing batch reactors

High strength slaughterhouse wastewater was treated in four 42 l anaerobic sequencing batch reactors (ASBRs) operated at 30 degrees C, 25 degrees C and 20 degrees C. The wastewater contained between 30% and 53% of its chemical oxygen demand (COD) as suspended solids (SS). The ASBRs could easily support volumetric organic loading rates (OLRs) of 4.93, 2.94 and 2.75 kg/m3/d (biomass OLRs of 0.44, 0.42 and 0.14 g/g volatile SS (VSS)/d) at 30 degrees C, 25 degrees C, and 20 degrees C, respectively. At all operating temperatures, the total COD (TCOD) and soluble COD (SCOD) were reduced by over 92%, while average SS removal varied between 80% and 96%. Over the experimental period, 90.8%, 88.7% and 84.2% of the COD removed was transformed into methane at 30 degrees C, 25 degrees C and 20 degrees C, respectively. The decrease in the conversion of the COD removed into methane as operating temperature was lowered, may be partly explained by a lower degradation of influent SS as temperature was reduced. The reactors showed a high average methanogenic activity of 0.37, 0.34 and 0.12 g CH4-COD/gVSS/d (22.4, 12.7 and 11.8 l/d) at 30 degrees C, 25 degrees C and 20 degrees C, respectively. The average methane content in the biogas increased from 74.7% to 78.2% as temperature was lowered from 30 degrees C to 20 degrees C.     

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

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

固定载体卧式厌氧反应器处理糖蜜废水的快速启动

为高效处理高浓度有机废水而设计了固定载体卧式厌氧反应器R1和R2, 它是厌氧折流板反应器(ABR)的改进, 以活性炭纤维作为生物膜载体固定并充当反应器的折流板, 在实验室规模上对R1和R2处理糖蜜废水进行快速启动运行。HRT和ORL是影响R1和R2稳定高效运行及启动的2个重要工艺参数。实验证明: HRT为2 d时, 反应器运行最佳。在第30天时, R1的COD去除率达到84.88%, R2达到81.72%。随着进水ORL由1.25 kg/(m3·d)提升到10 kg/(m3·d), 沼气容积产气率由0.35 L/(L·d)逐渐增加到4.98 L/(L·d)。进水pH值为3.9?4.5之间, 整个启动运行过程中, 未调节pH值, R1和R2的出水pH值均在6.7?7.6之间, 2个反应器均有较强的抗酸能力, R1的pH波动更为平缓。在整个实验过程中, 污泥流失量小, 没有发生堵塞现象, 在处理酸性高浓度有机废水时, 2个反应器均表现出较强的抗负荷冲击能力。     

Community onsite treatment of cold strong sewage in a UASB-septic tank

Two community onsite UASB-septic tanks namely R1 and R2 were operated under two different HRT (2 days for R1 and 4 days for R2) in parallel over a year and monitored over the cold half of the year. During the monitoring period, the sewage was characterised by a high COD(tot) of 905mg/l with a high fraction of COD(ss), viz. about 43.7%, and rather low temperature of 17.3 degrees C. The achieved removal efficiencies in R1 and R2 for COD(tot), COD(sus), COD(col), COD(dis), BOD(5) and TSS were "51%, 83%, 20%, 24%, 45% and 74%" and "54%, 87%, 10%, 28%, 49% and 78%", respectively. The difference in the removal efficiencies of those parameters in R1 and R2 is marginal and was only significant (p<0.05) for COD(sus). The sludge filling period of the reactors is expected to be 4-7 years. In view of that, the UASB-septic tank system is a robust and compact system as it can be adequately designed in Palestine at 2 days HRT.     

Effect of non-feeding period length on the intermittent operation of UASB reactors treating dairy effluents

Recent environmental concerns have prompted a re-evaluation of conventional management strategies and refueled the search of innovative waste management practices. In this sense, the anaerobic digestion of both fat and the remaining complex organic matter present in dairy wastewaters is attractive, although the continuous operation of high rate anaerobic processes treating this type of wastewaters causes the failure of the process. This work accesses the influence of non-feeding period length on the intermittent operation of mesophilic UASB reactors treating dairy wastewater, in order to allow the biological degradation to catch up with adsorption phenomenon. During the experiments, two UASB reactors were subject to three organic loading rates, ranging from 6 to 12 g(COD) x L(-1) x d(-1), with the same daily load applied to both reactors, each one with a different non-feeding period. Both reactors showed good COD removal efficiencies (87-92%). A material balance for COD in the reactors during the feeding and non-feeding periods showed the importance of the feedless period, which allowed the biomass to degrade substrate that was accumulated during the feeding period. The reactor with the longest non-feeding period had a better performance, which resulted in a higher methane production and adsorption capacity for the same organic load applied with a consequent less accumulation of substrate into the biomass. In addition, both reactors had a stable operation for the organic load of 12 g(COD) x L(-1) x d(-1), which is higher than the maximum applicable load reported in literature for continuous systems (3-6 g(COD) x L(-1) x d(-1)).     

Anaerobic digestion of long-chain fatty acids in UASB and expanded granular sludge bed reactors

Solutions of sodium caprate and sodium laurate were digested in upflow anaerobic sludge bed (UASB) reactors inoculated with granular sludge and in expanded granular sludge bed (EGSB) reactors. UASB reactors are unsuitable if lipids contribute 50% or more to the COD of waste water: the gas production rate required to obtain sufficient mixing and contact cannot be achieved. At lipid loading rates exceeding 2–3 kg COD m⁻³ day⁻¹, total sludge wash-out occurred. At lower loading rates the system was unreliable, due to unpredictable sludge flotation. EGSB reactors do fulfil the requirements of mixing and contact. They accommodate space loading rates up to 30 kg COD m⁻³ day⁻¹ during digestion of caprate or laurate as sole substrate, at COD removal efficiencies of 83–91%, and can be operated at hydraulic residence times of 2 h without any problems. Augmentation of granular sludge in lab-scale EGSB reactors was demonstrated. The new granules had excellent settling properties. Floating layer formation, as well as mixing characteristics in full-scale EGSB reactors require further research.     

Methane recovery from water hyacinth through whole-cell immobilization technology

The concepts of feed pretreatment, phase separation, and whole-cell immobilization technology have been incorporated in this investigation for the development of rational and cost-effective two- and three-stage methane recovery systems from water hyacinth (WH)Analyses of laboratory data reveal that a three-stage system could be designed with an alkali pretreatment stage [3.6% Na(2)CO(3) + 2.5% Ca(OH)(2) W/W, 24 h HRT] followed by an open acid reactor (2.1 days HRT) and closed immobilized methane reactor (12 h HRT), providing steady-state COD conversion of 62-65%, TVA conversion of 91-95%, and gas productivity of 4.08-5.36 L/L reactor volume/day with 82% methane. A gas yield of 50 L/kg WH/day (dry wt basis) at 35-37 degrees C is possible with this system. Insulation bricks, with particle size distribution of 500-3000 mum, were used as support material in the reactors at organic loading rate of 20 kg COD/m(3) day. The reactors matured in 15-18 weeksSubstantial reduction in retention time for the conversion of volatile acids in immobilized methane reactors prompted further research on the combined immobilized reactor to make possible an additional reduction in the cost of a WH-based biogas system. Evaluation of laboratory data reveals that a two-stage system could be designed with an open alkali pretreatment stage and a combined immobilized reactor (12 h HRT), providing steady-state COD conversion of 53% and gas productivity of 3.1 L/L reactor volume/day with 86% methane. A gas yield of 44 L/kg WH/day (dry wt basis) at 35-37 degrees C could be obtained from this system. Insulation bricks, with 500-1000 mum particle size distribution, was used as support material at an organic loading rate of 15 kg COD/m(3) day. Notwithstanding the fact that the technology in this study has been developed with water hyacinth as substrate, the implicit principles could be extended to any other organic substrate.     

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

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

Pentachlorophenol (PCP) dechlorination in horizontal-flow anaerobic immobilized biomass (HAIB) reactors

This study verifies the potential applicability of horizontal-flow anaerobic immobilized biomass (HAIB) reactors to pentachlorophenol (PCP) dechlorination. Two bench-scale HAIB reactors (R1 and R2) were filled with cubic polyurethane foam matrices containing immobilized anaerobic sludge. The reactors were then continuously fed with synthetic wastewater consisting of PCP, glucose, acetic acid, and formic acid as co-substrates for PCP anaerobic degradation. Before being immobilized in polyurethane foam matrices, the biomass was exposed to wastewater containing PCP in reactors fed at a semi-continuous rate of 2.0 μg PCP g⁻¹ VS. The applied PCP loading rate was increased from 0.05 to 2.59 mg PCP l⁻¹ day⁻¹ for R1, and from 0.06 to 4.15 mg PCP l⁻¹ day⁻¹ for R2. The organic loading rates (OLR) were 1.1 and 1.7 kg COD m⁻³ day⁻¹ at hydraulic retention times (HRT) of 24 h for R1 and 18 h for R2. Under such conditions, chemical oxygen demand (COD) removal efficiencies of up to 98% were achieved in the HAIB reactors. Both reactors exhibited the ability to remove 97% of the loaded PCP. Dichlorophenol (DCP) was the primary chlorophenol detected in the effluent. The adsorption of PCP and metabolites formed during PCP degradation in the packed bed was negligible for PCP removal efficiency.     

Effect of effluent recycling and shock loading on the biodegradation of complex phenolic mixture in hybrid UASB reactors

This study describes the feasibility of anaerobic treatment of synthetic coal wastewater using four identical 13.5L (effective volume) bench scale hybrid up flow anaerobic sludge blanket (HUASB) reactors (R1, R2, R3 and R4) under mesophilic (27+/-5 degrees C) conditions. Synthetic coal wastewater with an average chemical oxygen demand (COD) of 2240 mg/L and phenolics concentration of 752 mg/L was used as substrate. Effluent recirculation was employed at four different effluent to feed recirculation ratios (R/F) of 0.5, 1.0, 1.5 and 2.0 for 100 days to study the effect of recirculation on the performance of the reactors. Phenolics and COD removal was found to improve with increase in effluent recirculation. An effluent to feed recycle ratio of 1.0 resulted in maximum removal of phenolics and COD. Phenolics and COD removal improved from 88% and 92% to 95% each, respectively. The concentration of volatile fatty acids in the effluent was lower than the influent when effluent to feed recirculation was employed. Effect of shock loading on the reactors revealed that phenolics shock load up to 2.5 times increase in the normal input phenolics concentration in the form of continuous shock load for 4days did not affect the reactors performance irreversibly.     

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.     

Effect of COD/N ratio and salinity on the performance of sequencing batch reactors

The effects of COD/N ratio (3-6) and salt concentration (0.5-2%) on organics and nitrogen removal efficiencies in three bench top sequencing batch reactors (SBRs) with synthetic wastewater and one SBR with fish market wastewater were investigated under different operating schedules. The solids retention time (SRT, 20-100 days) and aeration time (4-10h) was also varied to monitor the performance. For synthetic wastewater, chemical oxygen demand (COD) removal efficiencies were consistently greater than 95%, irrespective of changes in COD/N ratio, aeration time and salt concentrations. Increasing the salt concentrations decreased the nitrification efficiency, while high COD/N ratio's favored better nitrogen removal (>90%). The treatment of real saline wastewater ( approximately 3.2%) from a fish market showed high COD (>80%) and nitrogen (>40%) removal efficiencies despite high loading rate and COD/N fluctuations, which is due to the acclimatization of the biomass within the SBR.     

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

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

Design of acidogenic reactors for the anaerobic treatment of the organic fraction of solid food waste

Volatile Fatty Acids (VFA) production by anaerobic fermentation of organic solid wastes was studied at laboratory scale. The influence of initial substrate concentration was evaluated on VFA production. Completely mixed reactors (0.9?l) were used at mesophilic temperature (35?°C). Food wastes had 43.8% Total Solids content. Three dilutions of substrate (1/25, 1/10 and 1/5) corresponding to 1.75%, 4.38% and 8.76% of Total Solids and five values of Organic Loading Rates: 2, 5, 10, 12.5 and 25?kg COD/m³?d were studied. It was found that substrate 1/10 led to 14?g VFA/l at a loading rate of 12.5?kg COD/m³?d and an hydraulic retention time of 3.7 d. The main VFA produced were especially acetate and butyrate. Substrate diluted 1/5 led to 26.1?g VFA/l at a loading of 5?kg COD/m³?d and an hydraulic retention time of 15.1 d, but biomass production was not optimal. In a second study, a cascade of three reactors was used. An effluent with 42?g VFA/l was obtained at steady-state conditions at a loading of 12.5?kg of COD/m³?d and an hydraulic retention time of 12.5?d. The distribution of VFA was the following: 36% of propionate, 34% of acetate and 22.5% of butyrate.     

Determination of kinetic constants for a two-stage anaerobic upflow packed-bed reactor for dairy wastewater

A two-stage upflow packed-bed (reactors in series) system was used for the treatment of dairy wastewater. Nylon pads were used as supporting media for the biomass. This investigation aimed at the determination of various kinetic constants for substrate, biomass and biogas based on various models. The maximum loadings that could be applied to reactor I and reactor II were 14·29 and 5·0 kg of chemical oxygen demand (COD) per m³ per day, respectively. The maximum COD removal efficiencies at various loading rates were in the ranges of 93·8–98·5% and 72·5–84% for the two reactor systems, respectively. The combined biogas yield was between 0·196 and 0·386 m³ gas/kg COD_a.