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.     

Quantitative comparison of stability of ANAMMOX process in different reactor configurations

A new stability evaluating system for ANAMMOX comprising three instability indices i.e. coefficient of variation ratio, coefficient of range ratio and coefficient of regression function derivative was established. Three lab-scale ANAMMOX reactors viz upflow anaerobic sludge blanket (UASB) reactor, upflow stationary fixed film (USFF) reactor and anaerobic sequencing batch reactor (ASBR) were compared for their stability based on the established criterion against the hydraulic and substrate concentration shocks. The results showed that all ANAMMOX reactors under investigation were more tolerant to the hydraulic shock than substrate concentration shock. The UASB reactor was the most stable reactor configuration towards substrate concentration shock, followed by the USFF reactor and ASBR. However, the ASBR proved the most tolerant to hydraulic shock, followed by the UASB reactor and USFF reactor. In terms of stability, UASB reactor was more suitable configuration compared with USFF reactor. The instability indices proved to be effective and explicit for the evaluation of ANAMMOX systems.     

升流厌氧污泥层反应器动力学模型

用碘离子作示踪剂,采用矩形脉冲示踪法测定升流厌氧污泥层(UASB)反应器的流动分布。建立了申级返混加沟流模型。模型简单,能够反映反应器流动分布,具有较强的拟合能力和良好的适用性。运用流动模型和Monod方程,建立了UASB反应器稳态模型,并对模型参数进行了估计。通过灵敏度分析,进水基质浓度S。,废水流量Q,最大比基质降解速率,μmax 对出水基质浓度有较大影响。在稳态模型的基础上又建立了UASB反应器动态模态,利用此模型,对出水基质浓度序列Se,和产气量序列Qg进行计算预测,平均偏差分别5．40％和7．46％,标准偏差分别为7．02％和9．66％。     

Enhanced biodegradation of hexachlorocyclohexane in upflow anaerobic sludge blanket reactor using methanol as an electron donor

Anaerobic dechlorination of technical grade hexachlorocyclohexane (THCH) was studied in a continuous upflow anaerobic sludge blanket (UASB) reactor with methanol as a supplementary substrate and electron donor. A reactor without methanol served as the experimental control. The inlet feed concentration of THCH in both the experimental and the control UASB reactor was 100 mg l(-1). After 60 days of continuous operation, the removal of THCH was >99% in the methanol-supplemented reactor as compared to 20-35% in the control reactor. THCH was completely dechlorinated in the methanol fed reactor at 48 h HRT after 2 months of continuous operation. This period was also accompanied by increase in biomass in the reactor, which was not observed in the experimental control. Batch studies using other supplementary substrates as well as electron donors namely acetate, butyrate, formate and ethanol showed lower % dechlorination (<85%) and dechlorination rates (<3 mg g(-1)d(-1)) as compared to methanol (98%, 5 mg g(-1)d(-1)). The optimum concentration of methanol required, for stable dechlorination of THCH (100 mg l(-1)) in the UASB reactor, was found to be 500 mg l(-1). Results indicate that addition of methanol as electron donor enhances dechlorination of THCH at high inlet concentration, and is also required for stable UASB reactor performance.     

Stimulation of methanol degradation in UASB reactors: in situ versus pre-loading cobalt on anaerobic granular sludge

The effect of pre-loading and in situ loading of cobalt onto a cobalt-limited granular sludge on the performance of methanol fed bioreactors was investigated. One upflow anaerobic sludge bed (UASB) reactor was inoculated with cobalt pre-loaded sludge (24h; 30 degrees C; 1 mM CoCl2) and a second UASB with unloaded sludge. The UASB reactors (30 degrees C; pH 7) were operated for 77 days at 8 h hydraulic retention time and organic loading rates ranging from 5 to 20 g COD.L reactor(-1).d(-1). Cobalt pre-loading clearly stimulated the methanogenic activity of the sludge with methanol as the substrate, e.g., after 30 days of reactor operation this activity was 5.8 times higher than that of the cobalt unloaded sludge. During the experiment, part of the cobalt leached from the pre-loaded sludge, i.e., 54% of the cobalt content was lost during the 77 days of reactor operation. Sequential metal extraction showed that losses mainly occurred from the exchangeable and carbonate fraction and in the sludge remaining cobalt was mainly present in the organic/sulfide fraction of the sludge. In situ loading of cobalt in the unloaded UASB reactor on day 57 by adding 31 microM cobalt to the influent for a 24-h period (16% of the cobalt present in the loaded sludge at day 11) resulted in a 4 time increase of the methanogenic activity of the sludge with methanol as the substrate at the end of the reactor experiment, while the accumulated amount of cobalt in the sludge only amounted to 6% of the cobalt accumulated in the loaded sludge (on day 11). This study showed that both pre-loading sludge and in situ loading are adequate for achieving an increased reactor performance of methanol fed UASB reactors operating under cobalt limitation. However, the in situ dosing procedure needs substantially lower amounts of cobalt, while it also gives significantly smaller losses of cobalt with the effluent.     

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.     

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.     

Kinetic Modelling and Characterization of Microbial Community Present in a Full-Scale UASB Reactor Treating Brewery Effluent

The performance of a full-scale upflow anaerobic sludge blanket (UASB) reactor treating brewery wastewater was investigated by microbial analysis and kinetic modelling. The microbial community present in the granular sludge was detected using fluorescent in situ hybridization (FISH) and further confirmed using polymerase chain reaction. A group of 16S rRNA based fluorescent probes and primers targeting Archaea and Eubacteria were selected for microbial analysis. FISH results indicated the presence and dominance of a significant amount of Eubacteria and diverse group of methanogenic Archaea belonging to the order Methanococcales, Methanobacteriales, and Methanomicrobiales within in the UASB reactor. The influent brewery wastewater had a relatively high amount of volatile fatty acids chemical oxygen demand (COD), 2005 mg/l and the final COD concentration of the reactor was 457 mg/l. The biogas analysis showed 60–69 % of methane, confirming the presence and activities of methanogens within the reactor. Biokinetics of the degradable organic substrate present in the brewery wastewater was further explored using Stover and Kincannon kinetic model, with the aim of predicting the final effluent quality. The maximum utilization rate constant U _max and the saturation constant (K _B) in the model were estimated as 18.51 and 13.64 g/l/day, respectively. The model showed an excellent fit between the predicted and the observed effluent COD concentrations. Applicability of this model to predict the effluent quality of the UASB reactor treating brewery wastewater was evident from the regression analysis (R ²?=?0.957) which could be used for optimizing the reactor performance.     

Effect of ferrous ion on the biological activity in a UASB reactor: mathematical modeling and verification

The effect of ferrous ion on the biological activity in a upflow anaerobic sludge blanket (UASB) reactor was studied. A mathematical model was developed and validated in order to simulate the dynamic behavior of a UASB reactor. This model took into consideration of all the biological and physicochemical reactions. The model was able to simulate the accumulation of iron in the sludge bed and its effect on the biological activity of the anaerobic sludge. A significant increase in the maximum uptake rate of methanogens and acidogens was revealed when iron was supplemented to the UASB reactor. The addition of ferrous iron induced a stable and excellent COD conversion rate. The model can be a useful tool for the prediction of process performance in the future and can be used to assist in the operation of biogas plants. The ferrous ion addition proved to enhance the biological activity of UASB sludge. Thus, the model can be used for the design of treatment plants that will take advantage of the benefits of iron addition.     

Performance evaluation and kinetic modeling of the start-up of a UASB reactor treating municipal wastewater at low temperature

A kinetic modeling-based study was carried out to evaluate the start-up performance of a 10-L up-flow anaerobic sludge blanket (UASB) reactor treating municipal wastewater under different organic and hydraulic loading conditions. The reactor was operated for 105 days (around 4 months) below 20 °C and with three different hydraulic retention times of 24, 12 and 5 h. Imposed volumetric organic loading rates (OLR) ranged from 0.57 (±0.05) to 11.78 (±0.85) kg TCOD/m³-day. Although relatively high incoming volumetric OLR values were employed to the system, the UASB reactor demonstrated a favorable performance on the anaerobic treatability of municipal wastewater, and no process failure was recorded in the start-up stage. On the basis of experimental results, the modified Stover–Kincannon model was successfully applied to define the start-up kinetics with a very high value of the correlation coefficient (R = 0.9729). Maximum substrate utilization rate constant and saturation constant of the modified Stover–Kincannon model were determined as U _max = 1.996 g/L-day and K _B = 1.536 g/L-day, respectively.     

High strength sewage treatment in a UASB reactor and an integrated UASB-digester system

The treatment of high strength sewage was investigated in a one-stage upflow anaerobic sludge blanket (UASB) reactor and a UASB-digester system. The one-stage UASB reactor was operated in Palestine at a hydraulic retention time (HRT) of 10h and at ambient air temperature for a period of more than a year in order to asses the system response to the Mediterranean climatic seasonal temperature fluctuation. Afterwards, the one-stage UASB reactor was modified to a UASB-digester system by incorporating a digester operated at 35 degrees C. The achieved removal efficiencies in the one-stage UASB reactor for total, suspended, colloidal, dissolved and VFA COD were 54, 71, 34, 23%, and -7%, respectively during the first warm six months of the year, and achieved only 32% removal efficiency for COD total over the following cold six months of the year. The modification of the one-stage UASB reactor to a UASB-digester system had remarkably improved the UASB reactor performance as the UASB-digester achieved removal efficiencies for total, suspended, colloidal, dissolved and VFA COD of 72, 74, 74, 62 and 70%. Therefore, the anaerobic treatment of high strength sewage during the hot period in Palestine in a UASB-digester system is very promising.     

Development of anaerobic sludge bed (ASB) reactor technologies for domestic wastewater treatment: motives and perspectives

During the treatment of raw domestic wastewater in the upflow anaerobic sludge blanket (UASB) reactor, the suspended solids (SS) present in the wastewater tend to influence negatively the methanogenic activity and the chemical oxygen demand (COD) conversion efficiency. These problems led to the emergence of various anaerobic sludge bed systems such as the expanded granular sludge bed (EGSB), the upflow anaerobic sludge blanket (UASB)-septic tank, the hydrolysis upflow sludge bed (HUSB), the two-stage reactor and the anaerobic hybrid (AH) reactor. However, these systems have, like the UASB reactor, limited performance with regard to complete treatment (e.g., removal of pathogens). In this respect, a new integrated approach for the anaerobic treatment of domestic wastewater is suggested. This approach combines a UASB reactor and a conventional completely stirred tank reactor (CSTR) for the treatment of the wastewater low in SS and sedimented primary sludge, respectively. The principal advantages of the proposed system are energy recovery from organic waste in an environmentally friendly way; lowering the negative effect of suspended solids in the UASB reactor; production of a high quality effluent for irrigation; and prevention of odour problems.     

Effect of reactor configuration on biogas production from wheat straw hydrolysate

The potential of wheat straw hydrolysate for biogas production was investigated in continuous stirred tank reactor (CSTR) and up-flow anaerobic sludge bed (UASB) reactors. The hydrolysate originated as a side stream from a pilot plant pretreating wheat straw hydrothermally (195 °C for 10–12 min) for producing 2nd generation bioethanol [Kaparaju, P., Serrano, M., Thomsen, A.B., Kongjan, P., Angelidaki, I., 2009. Bioethanol, biohydrogen and biogas production from wheat straw in a biorefinery concept. Bioresource Technology 100 (9), 2562–2568]. Results from batch assays showed that hydrolysate had a methane potential of 384 ml/g-volatile solids (VS)_added. Process performance in CTSR and UASB reactors was investigated by varying hydrolysate concentration and/or organic loading rate (OLR). In CSTR, methane yields increased with increase in hydrolysate concentration and maximum yield of 297 ml/g-COD was obtained at an OLR of 1.9 g-COD/l d and 100% (v/v) hydrolysate. On the other hand, process performance and methane yields in UASB were affected by OLR and/or substrate concentration. Maximum methane yields of 267 ml/g-COD (COD removal of 72%) was obtained in UASB reactor when operated at an OLR of 2.8 g-COD/l d but with only 10% (v/v) hydrolysate. However, co-digestion of hydrolysate with pig manure (1:3 v/v ratio) improved the process performance and resulted in methane yield of 219 ml/g-COD (COD removal of 72%). Thus, anaerobic digestion of hydrolysate for biogas production was feasible in both CSTR and UASB reactor types. However, biogas process was affected by the reactor type and operating conditions.     

Acidification of methanol-fed anaerobic granular sludge bioreactors by cobalt deprivation: Induction and microbial community dynamics

The acidification of mesophilic (30 degrees C) methanol-fed upflow anaerobic sludge bed (UASB) reactors induced by cobalt deprivation from the influent was investigated by coupling the reactor performance (pH 7.0; organic loading rate 4.5 g COD . L(-1) . d(-1)) to the microbial ecology of the bioreactor sludge. The latter was investigated by specific methanogenic activity (SMA) measurements and fluorescence in situ hybridization (FISH) to quantify the abundance of key organisms over time. This study hypothesized that under cobalt limiting conditions, the SMA on methanol of the sludge gradually decreases, which ultimately results in methanol accumulation in the reactor effluent. Once the methanol accumulation surpasses a threshold value (about 8.5 mM for the sludge investigated), reactor acidification occurs because acetogens outcompete methylothrophic methanogens at these elevated methanol concentrations. Methanogens present in granular sludge at the time of the acidification do not use methanol as the direct substrate and are unable to degrade acetate. Methylotrophic/acetoclastic methanogenic activity was found to be lost within 10 days of reactor operation, coinciding with the disappearance of the Methanosarcina population. The loss of SMA on methanol can thus be used as an accurate parameter to predict reactor acidification of methanol-fed UASB reactors operating under cobalt limiting conditions.     

Flocculants effect in biomass retention in a UASB reactor treating dairy manure

The performance and biomass retention of an upflow anaerobic sludge bed (UASB) reactor treating liquid fraction of dairy manure has been investigated at several organic loading rates. Two identical UASB reactors were employed. The biomass of one UASB reactor (FBR) had previously been treated with a cationic polyacrylamide, the other reactor was operated as a control reactor (CR). At 3 and 2 days of HRT both reactors functioned similarly, but at 1.5 days HRT some differences were observed between both effluents. Mean COD(T) removal percentages were 83.4% and 76.5%; COD(VFA) values in effluents were 977 and 2682 mg l(-1) for the FBR and the CR respectively. The VSS initial value in both reactors was 25.66 g VSS, whereas after the experiment the quantities were 31.83 g VSS in the FBR and 23.18 g VSS in the CR reactors. Polymer addition resulted in a higher degree of biomass retention and better performance in the FBR reactor.     

Biological hydrogen production in a UASB reactor with granules. II: Reactor performance in 3-year operation

The experiment was conducted to evaluate the performance of an upflow anaerobic sludge blanket (UASB) with granules for H(2) production from a sucrose-rich synthetic wastewater at various substrate concentrations (5.33-28.07 g-COD/L) and hydraulic retention times (HRTs) (3-30 h) for over 3 years. The kinetics of H(2) production was evaluated, and the sludge yield and endogenous decay coefficient of the H(2)-producing granules were estimated to be 0.334 g-VSS/g-COD and 0.004/h, respectively. Based on Gibbs free energy calculations, the formation thermodynamics of caproate, an important aqueous product, were analyzed. Experimental results show that the H(2) partial pressure in biogas decreased with increasing substrate concentration, but was not sensitive to the variation of HRT in a range of 6-22 h. The H(2) production rate increased with increasing substrate concentration, but decreased with increasing HRT. The H(2) yield was in the range of 0.49-1.44 mol-H(2)/mol-glucose. Acetate, butyrate, caporate, and ethanol were the main aqueous products in the reactor, and their concentrations were dependent on both substrate concentration and HRT. An elevated substrate concentration resulted in a shift of fermentation from butyrate- to caporate-type in the reactor and the formation of caproate was dependent on the H(2) partial pressure. The 3-year experimental results demonstrate that H(2) could be produced continuously and stably from the acidogenic-granule-based UASB reactor.     

Two-stage UASB design enables activated-sludge free treatment of easily biodegradable wastewater

A two-stage lab-scale UASB reactor, incorporating a selector-type UASB prior to the main reactor was operated at 37 °C with an easily biodegradable food wastewater having a COD of 3,000 mg/L. Varying the hydraulic retention time from 25 to 5 h, the removal of COD by the two-stage process was higher than 95%. Effluent soluble COD was consistently below 75 mg/L and the methane production rate close to theoretical values. The selector UASB removed the majority of the organic load (70–90%) at high organic loading rate, i.e. between 6 and 30 g/(Ld) and the granular sludge developed was characterized by dense microbial colonies, high volatile suspended solids’ content and high substrate degradation efficiency. Design of a two-stage process, incorporating a selector and a second UASB reactor, was able to achieve stable and complete substrate degradation at overall loading rates of the order of ~10–15 g/(Ld).     

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.     

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     

Effects of acetate, propionate, and butyrate on the thermophilic anaerobic degradation of propionate by methanogenic sludge and defined cultures.

The effects of acetate, propionate, and butyrate on the anaerobic thermophilic conversion of propionate by methanogenic sludge and by enriched propionate-oxidizing bacteria in syntrophy with Methanobacterium thermoautotrophicum delta H were studied. The methanogenic sludge was cultivated in an upflow anaerobic sludge bed (UASB) reactor fed with propionate (35 mM) as the sole substrate for a period of 80 days. Propionate degradation was shown to be severely inhibited by the addition of 50 mM acetate to the influent of the UASB reactor. The inhibitory effect remained even when the acetate concentration in the effluent was below the level of detection. Recovery of propionate oxidation occurred only when acetate was omitted from the influent medium. Propionate degradation by the methanogenic sludge in the UASB reactor was not affected by the addition of an equimolar concentration (35 mM) of butyrate to the influent. However, butyrate had a strong inhibitory effect on the growth of the propionate-oxidizing enrichment culture. In that case, the conversion of propionate was almost completely inhibited at a butyrate concentration of 10 mM. However, addition of a butyrate-oxidizing enrichment culture abolished the inhibitory effect, and propionate oxidation was even stimulated. All experiments were conducted at pH 7.0 to 7.7. The thermophilic syntrophic culture showed a sensitivity to acetate and propionate similar to that of mesophilic cultures described in the literature. Additions of butyrate or acetate to the propionate medium had no effect on the hydrogen partial pressure in the biogas of an UASB reactor, nor was the hydrogen partial pressure in propionate-degrading cultures affected by the two acids.(ABSTRACT TRUNCATED AT 250 WORDS)