Zinc deprivation of methanol fed anaerobic granular sludge bioreactors

The effect of omitting zinc from the influent of mesophilic (30 degrees C) methanol fed upflow anaerobic sludge bed (UASB) reactors, and latter zinc supplementation to the influent to counteract the deprivation, was investigated by coupling the UASB reactor performance to the microbial ecology of the bioreactor sludge. Limitation of the specific methanogenic activity (SMA) on methanol due to the absence of zinc from the influent developed after 137 days of operation. At that day, the SMA in medium with a complete trace metal solution except Zn was 3.4 g CH4-COD g VSS(-1) day(-1), compared to 4.2 g CH4-COD g VSS(-1) day(-1) in a medium with a complete (including zinc) trace metal solution. The methanol removal capacity during these 137 days was 99% and no volatile fatty acids accumulated. Two UASB reactors, inoculated with the zinc-deprived sludge, were operated to study restoration of the zinc limitation by zinc supplementation to the bioreactor influent. In a first reactor, no changes to the operational conditions were made. This resulted in methanol accumulation in the reactor effluent after 12 days of operation, which subsequently induced acetogenic activity 5 days after the methanol accumulation started. Methanogenesis could not be recovered by the continuous addition of 0.5 microM ZnCl2 to the reactor for 13 days. In the second reactor, 0.5 microM ZnCl2 was added from its start-up. Although the reactor stayed 10 days longer methanogenically than the reactor operated without zinc, methanol accumulation was observed in this reactor (up to 1.1 g COD-MeOH L(-1)) as well. This study shows that zinc limitation can induce failure of methanol fed UASB reactors due to acidification, which cannot be restored by resuming the continuous supply of the deprived metal.     

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.     

Effect of sulfur source on the performance and metal retention of methanol-fed UASB reactors

The effect of a sulfur source on the performance and metal retention of methanol-fed upflow anaerobic sludge bed (UASB) reactors was investigated. For this purpose, two UASB reactors were operated with cobalt preloaded granular sludge (1 mM CoCl2; 30 degrees C; 24 h) at an organic loading rate (OLR) of 5 g COD.L reactor(-1).d(-1). One UASB reactor (R1) was operated without a sulfur source in the influent during the first 37 days. In this period the methanol conversion to methane remained very poor, apparently due to the absence of a sulfur source, because once cysteine, a sulfur-containing amino acid, was added to the influent of R1 (day 37) a full conversion of methanol to methane occurred within 6 days. The second reactor (R2) was operated with sulfate (0.41 mM) in the influent during the first 86 days of operation, during which no limitation in the methanol conversion to methane manifested. Cobalt washed out from the sludge at similar rates in both reactors. The leaching of cobalt occurred at two distinct rates, first at a high rate of 22 microg.g TSS(-1).d(-1), which proceeded mainly from the exchangeable and carbonate fraction and later at a relatively slow rate of 9 mug.g TSS(-1).d(-1) from the organic/sulfide fraction. This study showed that the supply of the sulfur source L-cysteine has a pronounced positive effect on the methanogenic activity and the retention of metals such as iron, zinc and molybdenum.     

Assessment of active methanogenic archaea in a methanol-fed upflow anaerobic sludge blanket reactor

Methanogenic archaea enrichment of a granular sludge was undertaken in an upflow anaerobic sludge blanket (UASB) reactor fed with methanol in order to enrich methylotrophic and hydrogenotrophic methanogenic populations. A microbial community assessment, in terms of microbial composition and activity—throughout the different stages of the feeding process with methanol and acetate—was performed using specific methanogenic activity (SMA) assays, quantitative real-time polymerase chain reaction (qPCR), and high-throughput sequencing of 16S ribosomal RNA (rRNA) genes from DNA and complementary DNA (cDNA). Distinct methanogenic enrichment was revealed by qPCR of mcrA gene in the methanol-fed community, being two orders of magnitude higher with respect to the initial inoculum, achieving a final mcrA/16S rRNA ratio of 0.25. High-throughput sequencing analysis revealed that the resulting methanogenic population was mainly composed by methylotrophic archaea (Methanomethylovorans and Methanolobus genus), being also highly active according to the RNA-based assessment. SMA confirmed that the methylotrophic pathway, with a direct conversion of methanol to CH₄, was the main step of methanol degradation in the UASB. The biomass from the UASB, enriched in methanogenic archaea, may bear great potential as additional inoculum for bioreactors to carry out biogas production and other related processes.     

Effect of long-term cobalt deprivation on methanol degradation in a methanogenic granular sludge bioreactor

The effect of the trace metal cobalt on the conversion of methanol in an upflow anaerobic sludge bed (UASB) reactor was investigated by studying the effect of cobalt deprivation from the influent on the reactor efficiency and the sludge characteristics. A UASB reactor (30 degrees C; pH 7) was operated for 261 days at a 12-h hydraulic retention time (HRT). The loading rate was increased stepwise from 2.6 g chemical oxygen demand (COD) x L reactor(-1) x d(-1) to 7.8 g COD x L reactor(-1) x d(-1). Cobalt deprivation had a strong impact on the methanogenic activity of the sludge. In batch tests, the methanogenic activity of the sludge with methanol as the substrate increased 5.3 (day 28) and 2.1 (day 257) times by addition of 840 nM of cobalt. The sludge had an apparent K(m) for cobalt of 948 nM after 28 days of operation and 442 nM at the end of the run. Cobalt deprivation during 54 days of operation led to a methanol conversion efficiency of only 55%. Continuous addition of cobalt (330 nM) for 33 days improved the methanol removal efficiency to 100%. In this period of cobalt dosing, the cobalt concentration in the sludge increased 2.7 times up to 32 microg x g TSS(-1). Upon omission of the cobalt addition, cobalt washed-out at a stable rate of 0.1 microg x g VSS(-1) x d(-1). At the end of the run, the cobalt concentration of the sludge was similar to that of the seed sludge.     

Role of nickel in high rate methanol degradation in anaerobic granular sludge bioreactors

The effect of nickel deprivation from the influent of a mesophilic (30 degrees C) methanol fed upflow anaerobic sludge bed (UASB) reactor was investigated by coupling the reactor performance to the evolution of the Methanosarcina population of the bioreactor sludge. The reactor was operated at pH 7.0 and an organic loading rate (OLR) of 5-15 g COD l(-1) day(-1) for 191 days. A clear limitation of the specific methanogenic activity (SMA) on methanol due to the absence of nickel was observed after 129 days of bioreactor operation: the SMA of the sludge in medium with the complete trace metal solution except nickel amounted to 1.164 (+/-0.167) g CH(4)-COD g VSS(-1) day(-1) compared to 2.027 (+/-0.111) g CH(4)-COD g VSS(-1) day(-1) in a medium with the complete (including nickel) trace metal solution. The methanol removal efficiency during these 129 days was 99%, no volatile fatty acid (VFA) accumulation was observed and the size of the Methanosarcina population increased compared to the seed sludge. Continuation of the UASB reactor operation with the nickel limited sludge lead to incomplete methanol removal, and thus methanol accumulation in the reactor effluent from day 142 onwards. This methanol accumulation subsequently induced an increase of the acetogenic activity in the UASB reactor on day 160. On day 165, 77% of the methanol fed to the system was converted to acetate and the Methanosarcina population size had substantially decreased. Inclusion of 0.5 muM Ni (dosed as NiCl(2)) to the influent from day 165 onwards lead to the recovery of the methanol removal efficiency to 99% without VFA accumulation within 2 days of bioreactor operation.     

Thermophilic (55-65 degrees C) and extreme thermophilic (70-80 degrees C) sulfate reduction in methanol and formate-fed UASB reactors

The feasibility of thermophilic (55-65 degrees C) and extreme thermophilic (70-80 degrees C) sulfate-reducing processes was investigated in three lab-scale upflow anaerobic sludge bed (UASB) reactors fed with either methanol or formate as the sole substrates and inoculated with mesophilic granular sludge previously not exposed to high temperatures. Full methanol and formate degradation at temperatures up to, respectively, 70 and 75 degrees C, were achieved when operating UASB reactors fed with sulfate rich (COD/SO4(2-)=0.5) synthetic wastewater. Methane-producing archaea (MPA) outcompeted sulfate-reducing bacteria (SRB) in the formate-fed UASB reactor at all temperatures tested (65-75 degrees C). In contrast, SRB outcompeted MPA in methanol-fed UASB reactors at temperatures equal to or exceeding 65 degrees C, whereas strong competition between SRB and MPA was observed in these reactors at 55 degrees C. A short-term (5 days) temperature increase from 55 to 65 degrees C was an effective strategy to suppress methanogenesis in methanol-fed sulfidogenic UASB reactors operated at 55 degrees C. Methanol was found to be a suitable electron donor for sulfate-reducing processes at a maximal temperature of 70 degrees C, with sulfide as the sole mineralization product of methanol degradation at that temperature.     

Influence of pH shocks on trace metal dynamics and performance of methanol fed granular sludge bioreactors

The influence of pH shocks on the trace metal dynamics and performance of methanol fed upflow anaerobic granular sludge bed (UASB) reactors was investigated. For this purpose, two UASB reactors were operated with metal pre-loaded granular sludge (1mM Co, Ni and Fe; 30°C; 96h) at an organic loading rate (OLR) of 5gCOD l reactor^–1d^–1. One UASB reactor (R1) was inoculated with sludge that originated from a full scale reactor treating alcohol distillery wastewater, while the other reactor (R2) was inoculated with sludge from a full scale reactor treating paper mill wastewater. A 30h pH shock (pH 5) strongly affected the metal retention dynamics within the granular sludge bed in both reactors. Iron losses in soluble form with the effluent were considerable: 2.3 and 2.9% for R1 and R2, respectively, based on initial iron content in the reactors, while losses of cobalt and nickel in soluble form were limited. Sequential extraction of the metals from the sludge showed that cobalt, nickel, iron and sulfur were translocated from the residual to the organic/sulfide fraction during the pH shock in R2, increasing 34, 47, 109 and 41% in the organic/sulfide fraction, respectively. This is likely due to the modification of the iron sulfide precipitate stability, which influences the extractability of iron and trace metals. Such a translocation was not observed for the R1 sludge during the first 30h pH shock, but a second 4day pH shock induced significant losses of cobalt (18%), iron (29%) and sulfur (29%) from the organic/sulfide fraction, likely due to iron sulfide dissolution and concomitant release of cobalt. After the 30h pH shock, VFA accumulated in the R2 effluent, whereas both VFA and methanol accumulated in R1 after the 4day pH shock. The formed VFA, mainly acetate, were not converted to methane due to the loss of methanogenic activity of the sludge on acetate. The VFA accumulation gradually disappeared, which is likely to be related to out-competition of acetogens by methanogens. Zinc, copper and manganese supply did not have a clear effect on the acetate removal and methanol conversion, but zinc may have induced the onset of methanol degradation after day 152 in R1.     

Effect of nickel deprivation on methanol degradation in a methanogenic granular sludge bioreactor

The effect of omitting nickel from the influent on methanol conversion in an Upflow Anaerobic Sludge Bed (UASB) reactor was investigated. The UASB reactor (30°C, pH 7) was operated for 261 days at a 12-h hydraulic retention time (HRT) and at organic loading rates (OLRs) ranging from 2.6 to 7.8 g COD l reactor⁻¹ day⁻¹. The nickel content of the sludge decreased by 66% during the 261-day reactor run because of washout and doubling of the sludge bed volume. Nickel deprivation initially had a strong impact on the methanogenic activity of the sludge with methanol; e.g., after 89 days of operation, this activity was doubled by adding 2 μM nickel. Upon prolonged UASB reactor operation, methanol and VFA effluent concentrations decreased whereas the sludge lost its response to nickel addition in activity tests. This suggests that a less nickel-dependent methanol-converting sludge had developed in the UASB reactor. Received 09 April 2002/ Accepted in revised form 13 July 2002     

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.     

A hybrid anaerobic solid-liquid bioreactor for food waste digestion

A hybrid anaerobic solid-liquid (HASL) bioreactor is an enhanced two-phase anaerobic system, that consists of a solid waste reactor as the acidification reactor and a wastewater reactor, i.e. an upflow anaerobic sludge blanket (UASB) reactor as the methanogenic reactor. Food waste digestion in HASL bioreactors with pre-acidification and HASL operation stages was investigated in two separate runs. After 8 days of pre-acidification in Run A and 4 days in Run B, total volatile fatty acid (TVFA) and chemical oxygen demand (COD) concentrations in the leachates of both acidification reactors were similar. During HASL operation stage, TVFA and COD removal in the methanogenic phase were 77–100% and 75–95%, respectively. Some 99% of the total methane generated was from the methanogenic phase with a content of 68–70% methane. At the end of operation, about 59–60% of the added volatile solids (VS) were removed with a methane yield of 0.25 l g^–1 VS.     

Effect of loading rate on the granulation process and granular activity in a bench scale UASB reactor

The effect of organic loading rate (OLR) on the granulation process was evaluated using upflow anaerobic sludge blanket (UASB) reactors running under different conditions. Results showed that increase of OLR, extracellular polymer (ECP) content and granulation were closely related to one another. ECP in the sludge accumulated over a short period under overloading conditions, which greatly enhanced the granulation process. Treatment performance could be recovered after the ECP accumulation when the overloading was suitably exerted. However, too high loading rate should be avoided because it could cause the unrecoverable decay of methanogenic activity and the serious unbalance between the feedstuff and biological requirement.     

A study of the effects of methanol in start-up of UASB reactors

Upflow anaerobic sludge blanket reactors were started up, using a stepped loading regime, on a dairy waste prepared from raw ice-cream production waste from an ice-cream manufacturing plant. One UASB was supplemented with methanol. Granules were detected in the methanol-fed UASB at 3 weeks after start-up. The maximum load of 6·7 kgCOD m⁻³ day⁻¹ with an HRT of 0·75 days could not be sustained during the 73 days of operation. Complete granulation had, however, occurred by the 4th week. Methanol addition at start-up aided rapid biomass granulation, and enhanced the settling velocity and specific activity of the sludge. However, wash-out was severe and residual biomass was sensitive to methanol withdrawal and produced no net growth.     

Effect of cobalt on the anaerobic degradation of methanol

The effect of trace elements on the methanogenesis from methanol and acetate was studied utilizing granular sludge obtained from an anaerobic wastewater treatment plant. The methanogenic activity from methanol was dramatically stimulated by the addition of a cocktail of trace elements in the basal medium. When trace elements were supplied individually, cobalt greatly stimulated methanogenesis which equalled the stimulation observed with the complete trace element mixture. No remarkable influence of any trace element was observed when acetate was used as the substrate. Two Upflow Anaerobic Sludge Blanket (UASB) reactors were operated with and without supplementation of cobalt. Cobalt greatly stimulated both acetogenesis in the initial operational phase and later methanogenesis. The cobalt sufficient column provided almost 3 times the methane productivity compared to the cobalt deprived column. At an organic loading rate of 8 g COD/l·d, 87% of the COD was converted to methane in the cobalt sufficient column. Under low cobalt concentration, methanogens compete better for cobalt than acetogens.     

Thermophilic sulfate reduction and methanogenesis with methanol in a high rate anaerobic reactor

Sulfate reduction outcompeted methanogenesis at 65 degrees C and pH 7.5 in methanol and sulfate-fed expanded granular sludge bed reactors operated at hydraulic retention times (HRT) of 14 and 3.5 h, both under methanol-limiting and methanol-overloading conditions. After 100 and 50 days for the reactors operated at 14 and 3.5 h, respectively, sulfide production accounted for 80% of the methanol-COD consumed by the sludge. The specific methanogenic activity on methanol of the sludge from a reactor operated at HRTs of down to 3.5 h for a period of 4 months gradually decreased from 0. 83 gCOD. gVSS(-1). day(-1) at the start to a value of less than 0.05 gCOD. gVSS(-1). day(-1), showing that the relative number of methanogens decreased and eventually became very low. By contrast, the increase of the specific sulfidogenic activity of sludge from 0. 22 gCOD. gVSS(-1). day(-1) to a final value of 1.05 gCOD. gVSS(-1). day(-1) showed that sulfate reducing bacteria were enriched. Methanol degradation by a methanogenic culture obtained from a reactor by serial dilution of the sludge was inhibited in the presence of vancomycin, indicating that methanogenesis directly from methanol was not important. H(2)/CO(2) and formate, but not acetate, were degraded to methane in the presence of vancomycin. These results indicated that methanol degradation to methane occurs via the intermediates H(2)/CO(2) and formate. The high and low specific methanogenic activity of sludge on H(2)/CO(2) and formate, respectively, indicated that the former substrate probably acts as the main electron donor for the methanogens during methanol degradation. As sulfate reduction in the sludge was also strongly supported by hydrogen, competition between sulfate reducing bacteria and methanogens in the sludge seemed to be mainly for this substrate. Sulfate elimination rates of up to 15 gSO(4)(2-)/L per day were achieved in the reactors. Biomass retention limited the sulfate elimination rate.     

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     

Application of DNA amplification fingerprinting (DAF) to mixed culture bioreactors

Summary The use of DNA amplification fingerprinting (DAF) as a tool for monitoring mixed microbial populations in bioreactors was evaluated. Short (8-mer or 10-mer) oligonucleotides were used to prime DNA extracts from various biological reactors during polymerase chain reaction (PCR) amplification. The reactors examined in this study included two sets of anaerobic stirred tank continuous flow bioreactors. One set of anaerobic reactors was operated under methanogenic conditions and one set was operated under sulfate-reducing conditions. The anaerobic reactor communities in the methanol-fed reactors showed extensive DAF homology. DAF was also applied to a fixed-film azo dye degrading reactor to examine the degree of uniformity of colonization of the substratum in representative regions of the reactor. This method is a quick and relatively inexpensive means of monitoring microbial community structure during biological processes. Since no cultivation of the sample is involved, the genetic profile of the community is not biased by outgrowth conditions. DAF profiles may be useful for comparisons of population changes over time or of bench-scale vs pilot-scale reactors but not adequate for assessing community diversity.     

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

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

An integrated UASB-sludge digester system for raw domestic wastewater treatment in temperate climates

To improve the performance of an upflow anaerobic sludge blanket (UASB) reactor treating raw domestic wastewater under temperate climates conditions, the addition of a sludge digester to the process was investigated. With the decrease in temperature, the COD removal decreased from 78% at 28 °C to 42% at 10 °C for the UASB reactor operating alone at a hydraulic retention time of 6 h. The decrease was attributed to low hydrolytic activity at lower temperatures that reduced suspended matter degradation and resulted in solids accumulation in the top of the sludge blanket. Solids removed from the upper part of the UASB sludge were treated in an anaerobic digester. Based on sludge degradation kinetics at 30 °C, a digester of 0.66 l per liter of UASB reactor was design operating at a 3.20 days retention time. Methane produced by the sludge digester is sufficient to maintain the temperature at 30 °C.     

Evaluation of UASB reactor performance during start-up operation using synthetic mixed-acid waste

A start-up experiment was performed in a laboratory-scale, upflow anaerobic sludge blanket (UASB) reactor using seed sludge from a domestic waste treatment plant at 3.8-33.3gCODl(-1)day(-1) loading rates. Analysis over the height of the reactor with time showed that the VSS in the reactor was initially differentiated into active and non-active biomass at increasing gas production and upflow velocities, and specific update rates of the volatile fatty acids (VFA) components were pronounced at the bottom 10% of the reactor. During start-up, specific methanogenic activity and chemical oxygen demand (COD) uptake rate increased from 0.075 to 0.75gCOD-CH(4)(gVSS)(-1)day(-1) and from 0.08 to 0.875gCOD removed (gVSS)(-1)day(-1), respectively. When seed sludge from a distillery waste treatment plant was used, improved performance due to a predominance of active biomass was evident when the loading rate was increased from 9.4 to 28.7gCODl(-1)day(-1). The proposed start-up evaluation is an effective tool to successfully monitor performance of UASB reactors.