Shigeki Uemura

Interaction between sulfate-reducing bacteria and methane-producing bacteria in UASB reactors fed with low strength wastes containing different levels of sulfate

Abstract The mutual interaction between sulfate-reducing bacteria (SRB) and methane-producing bacteria (MPB) in anaerobic sludge consortia was investigated using three identical laboratory-scale UASB reactors. Reactors were fed in parallel with a synthetic low strength waste (starch and sucrose, 500 mg COD l−1), but with different levels of sulfate (30, 150, 600 mg SO42- l−1, respectively). The mass balances of COD and sulfur over the experimental period of 180 days operation indicated that the higher the level of sulfate the less methane production caused since a greater electron flow was distributed to the SRB. Namely, at the last stage of the experiment in which the highest sulfate level was imposed, 75% of the total COD removal was performed by SRB. The specific methanogenic activities (SMAs) of the respective sludges were evaluated using the serum vial test using different substrates and by setting different sulfate levels. SMA was not affected by the presence of sulfate in the vials when acetate was used as the vial substrate. In the case of glucose as the test substrate, SMA increased with an increase in sulfate level. On the other hand, SMA decreased with increasing sulfate level when hydrogen was employed as the test substrate. A large amount of propionate accumulation was observed during vial tests, in which glucose was fed to the sludge grown at higher levels of sulfate, when zero or low levels of sulfate were added to the vials. This result suggests that SRB played an important role in the breakdown of propionate either through direct utilization or through a so-called interspecies hydrogen transfer.

Treatment of sewage by a UASB reactor under moderate to low temperature conditions

Abstract The feasibility of sewage treatment by an upflow anaerobic sludge blanket (UASB) reactor was studied using actual sewage at a fixed hydraulic retention time (HRT) of 4.7 h, and at temperatures in the range of 25–13°C, for six months. The average total COD removals and solid COD removals achieved were 70% and 80%, respectively. Total COD removal rate depended on influent strength, especially solid COD concentration, rather than operational temperature. Particulate organic matter in the influent was effectively removed by entrapment in the sludge bed. The hydrolysis rate of the entrapped organics was significantly affected by temperature, that is, 58% of the entrapped particulate organics was liquefied at 25°C, decreasing to 33% at 13°C. The methanogenic activity of the retained sludge decreased eventually to 4–10% of the seed granular sludge which had been formed on carbohydrate wastewater. Microscopic observation of the morphology of the sludge revealed that even though the sludge remained in granular form as a whole, the granules tended to be partly broken in a state of autolysis.

Anaerobic treatment of a recalcitrant distillery wastewater by a thermophilic UASB reactor

The feasibility of thermophilic (55°C) anaerobic treatment of an alcohol distillery wastewater (cane molasses vinasse) was studied using a 140 l upflow anaerobic sludge blanket (UASB) reactor for a period of 430 days. Organic loading rates were applied up to 28 kg chemical oxygen demand (COD) m−3 d−1 by reducing hydraulic retention time (HRT) at a fixed influent concentration of 10 g COD l−1. Chemical oxygen demand removals during the entire experimental period were relatively low (39–67%), while biochemical oxygen demand (BOD) removals were more satisfactory (more than 80%). The biodegradability of the vinasse used in this study was assessed by a serum vial test. The test revealed that methane production rates from the vinasse were only 136, 132, 125 and 123 as great as those from H2CO2, acetate, glucose and another type of vinasse (malt), respectively. The poor performance of the reactor for COD elimination can probably be attributed to the low degradability of the waste itself. Methanogenic activity of the retained sludge increased 24 times, for acetate, and 13 times, for H2CO2, as much as that of the inoculum sludge. The optimum temperature of methanogenic activity of the sludge depended on the substrate used; i.e. 60°C for acetate, 60–65°C for H2CO2, and around 55°C for the waste.

Microbial characteristics of methanogenic sludge consortia developed in thermophilic U ASB reactors

The effect of temperature on granulation and microbial interaction of anaerobic sludges grown in thermophilic upflow anaerobic sludge bed (UASB) reactors was investigated at two different temperatures, 55°C (Run 1) and 65°C (Run 2). Each run consisted of two phases. Phase 1 was conducted by feeding acetate for a period of 200 days. In Phase 2, both reactors were fed a mixture of acetate and sucrose for a further 100 days. During Phase 1, no granulation occurred in the sludge of either run. Microscopic observation revealed that the predominant methanogen was Methanothrix in Run 1, whereas Methanobacterium-like bacteria existed to a significant extent in Run 2. The acetate-utilizing methanogenic activity of both sludges increased with increasing test temperature in the range 55–65°C. Since the acetate-grown sludges exhibited far higher H2-utilizing methanogenic activity than acetate-utilizing methanogenic activity, it is suggested that a syntrophic association of acetate-oxidizing bacteria with hydrogenotrophic methanogens was responsible for a considerable portion of the overall acetate elimination in thermophilic anaerobic sludge. During Phase 2, granules coated with either filamentous bacteria or cocci-type bacteria (both presumably acid-forming bacteria) were successfully established in Run 1 and Run 2, respectively. Since the acetate-utilizing methanogenic activities of the granular sludges were four to five times higher than those of the acetate-grown sludges (Phase 1), the co-existence of these “coating bacteria” appeared to contribute to the enclosing of acetate consumers inside granules.

Inorganic composition and microbial characteristics of methanogenic granular sludge grown in a thermophilic upflow anaerobic sludge blanket reactor

An upflow anaerobic sludge blanket reactor was operated under thermophilic conditions (55° C) for 160 days by feeding a wastewater containing sucrose as the major carbon source. The reactor exhibited a satisfactory performance due to the formation of well-settling granulated sludge, achieving a total organic carbon (TOC) removal of above 80% at an organic loading rate of 30 kg total organic C m−3 day−1. Structural and microbial properties of the methanogenic granular sludge were examined using scanning electron microscope X-ray analyses and serum vial activity tests. All the thermophilic granules developed showed a double-layered structure, comprised of a black core portion and a yellowish exterior portion. The interior cope portion contained abundant crystalline precipitates of calcium carbonate. Calcium-bound phosphorus was also present more prominently in the core portion than in the exterior portion. Methanogenic activities of the thermophilic granules both from acetate and from H2 increased with increasing vial-test temperature in the range of 55–65° C [from 1.43 to 2.36 kg CH4 chemical oxygen demand (COD) kg volatile suspended solids (VSS)−1 day−1 for acetate and from 0.85 to 1.11 kg CH4 COD kg VSS−1 day−1 for H2]. On the other hand, propionate-utilizing methanogenic activity was independent of vial-test temperature, and was much lower (0.1–0.12 kg CH4 COD kg VSS−1 day−1) than that from either acetate or H2. Acetate consumption during vial tests was considerably inhibited by the presence of H2 in the headspace, indicating that a syntrophic association between acetate oxidizers and H2-utilizing methane-producing bacteria was responsible for some portion of the overall acetate elimination by the theromophilically grown sludge.

Characterization of the retained sludge in a down-flow hanging sponge (DHS) reactor with emphasis on its low excess sludge production

Experiments to characterize retained sludge in a down-flow hanging sponge (DHS) reactor fed with upflow anaerobic sludge blanket (UASB) treated sewage under moderate conditions were conducted. Plenty of oxygen was supplied through the DHS reactor without aeration and the effluent qualities after the reactor were comparable to activated sludge processes. The average excess sludge production rate was 0.09 g SS g(-1) COD removed. The DHS reactor maintained a high sludge concentration of 26.9 g VSS L(-1) sponge, resulting in a low loading rate of 0.032 g COD g(-1) VSS day(-1). The endogenous respiration rate of DHS sludge was comparable to previously reported aerobic sludges. The numbers of microfauna were one order of magnitude greater than those in activated sludge. The results indicated that low excess sludge production was attributable to the high sludge concentration, sufficient oxygen supply, adequate endogenous respiration rate, and a high density and diversity of microfauna.

Development of a sixth-generation down-flow hanging sponge (DHS) reactor using rigid sponge media for post-treatment of UASB treating municipal sewage

A sixth-generation down-flow hanging sponge reactor (DHS-G6), using rigid sponge media, was developed as a novel aerobic post-treatment unit for upflow anaerobic sludge blanket (UASB) treating municipal sewage. The rigid sponge media were manufactured by copolymerizing polyurethane with epoxy resin. The UASB and DHS system had a hydraulic retention time (HRT) of 10.6 h (8.6 h for UASB and 2 h for DHS) when operated at 10-28 °C. The system gave reasonable organic and nitrogen removal efficiencies. The final effluent had a total biochemical oxygen demand of only 12 mg/L and a total Kjeldahl nitrogen content of 6 mg/L. The DHS reactor gave particularly good nitrification performance, which was attributed to the new rigid sponge media. The sponge media helped to provide a sufficient HRT, and retained a high biomass concentration, extending the solids retention time. The DHS reactor maintained a high dissolved oxygen concentration under natural ventilation.

Removal of organic substances and oxidation of ammonium nitrogen by a down-flow hanging sponge (DHS) reactor under high salinity conditions.

A down-flow hanging sponge (DHS) reactor, constructed by connecting three identical treatment units in series, was fed with highly saline artificial coke-plant wastewater containing 1400 mg L(-1) of phenol in terms of chemical oxygen demand (COD) and 500 mg-NL(-1) of ammonium nitrogen. The COD was removed by the 1st unit, achieving 92% removal at an average COD loading rate of 3.0 kg-COD m(-3)d(-1) for all units, with oxidation of ammonium nitrogen occurring primarily in the two downstream units. Microbial assays of the different units of the reactor revealed greater numbers of nitrifying bacteria in the 2nd and 3rd units than in the 1st unit, corresponding with the observed ammonium oxidation pattern of the reactor. These findings suggest that a succession of microflora was successfully established along the DHS.

On-site evaluation of the performance of a full-scale down-flow hanging sponge reactor as a post-treatment process of an up-flow anaerobic sludge blanket reactor for treating sewage in India.

A down-flow hanging sponge (DHS) reactor is a novel, unaerated, aerobic, biofilm reactor that is used to polish effluent received from an up-flow anaerobic sludge blanket (UASB) reactor for treating municipal sewage. A full-scale DHS reactor was constructed for post-treatment of a full-scale UASB reactor at a municipal sewage treatment plant in India. Performance of the DHS reactor was evaluated with respect to organic removal over 1800 days of continuous operation. The UASB+DHS system consistently produced effluent with chemical oxygen demand (COD), biochemical oxygen demand (BOD), and suspended solids (SS) values of 37, 6.0 and 19 mg L(-1), on average, respectively. The sludge yield of the DHS reactor was estimated to be 0.04 kg SS kg(-1) COD removed or 0.12 kg SS kg(-1) BOD removed, which is considerably lower than other aerobic treatment methods that have been employed for polishing UASB effluent.

Microbial-ecological significance of sulfide precipitation within anaerobic granular sludge revealed by micro-electrodes study.

Micro-electrodes were applied to anaerobic granular sludge, which was developed in a UASB reactor, to examine intra-granule profiles with respect to pH, glucose and sulfide. When glucose was employed as a bulk liquid substrate, the micro-electrodes study demonstrated the pH behavior along granule depth: pH decrement at the granule exterior portion due to acid formation (buildup of acidity), and subsequent pH increment at the granule inner portion due to the consumption of acid (buildup of alkalinity). Sulfide micro-electrode proved sulfate reduction that mostly occurred at the granule exterior portion. Chemical equilibrium consideration evidently explained the occurrence of ferric sulfide predominantly in the interior portion, which accounts well for the morphology of a representative double-layered structure of granules grown on a low level of sulfite. Inorganic elements distribution within anaerobic granule was examined by electron probe X-ray micro analysis (EPMA) and ICP methods. The presence of crystalline calcium carbonate (calcite) was identified by X-ray diffraction analysis.