Methane production in an UASB reactor operated under periodic mesophilic-thermophilic conditions

Methane production was studied in a laboratory-scale 10 L anaerobic upflow sludge bed (UASB) reactor with periodic variations of the reactor temperature. On a daily basis the temperature was varied between 35 and 45 degrees C or 35 and 55 degrees C with a heating period of 6 h. Each temperature increase was accompanied by an increase in methane production and a decrease in the concentration of soluble organic matter in the effluent. In comparison to a reactor operated at 35 degrees C, a net increase in methane production of up to 22% was observed. Batch activity tests demonstrated a tolerance of mesophilic methanogenic populations to short-term, 2-6 h, temperature increases, although activity of acetoclastic methanogens decreased after 6 h exposure to a temperature of 55 degrees C. 16S sequencing of DGGE bands revealed proliferation of temperature-tolerant Methanospirillum hungatii sp. in the reactor.     

Continuous ethanol production by immobilized yeast reactor

Summary Saccharomyces cerevisiae yeast immobilized in calcium alginate gel beads was employed in packed-bed column reactors for continuous ethanol production from glucose or cane molasses, and for beer fermentation from barley malt wort. With properly balanced nutrient content or periodical regeneration of cells by nutrient addition and aeration, ethanol production could be maintained for several months. About 7 percent (w/v) ethanol content could be easily maintained with cane molasses diluted to about 17.5 percent (w/v) of total reducing sugars at about 4 to 5 h residence time. Beer of up to 4.5 percent (wv) of ethanol could be produced from barley wort at about 2 h residence time without any addition of nutrients.     

Performance of an UASB reactor treating synthetic wastewater at low-temperature using cold-adapted seed slurry

The present study is an attempt to investigate if a long-term acclimation of digester contents to low-temperatures would improve wastewater treatment at low-temperatures similar to mesophilic ranges. The feasibility of low-temperature (15 °C) anaerobic treatment of synthetic wastewater in an upflow anaerobic sludge blanket reactor was studied using inoculum from a cattle manure digester adapted to 15 °C. The effect of varying hydraulic retention time was studied by decreasing the retention time from 7 days to 1 day. Under a constant temperature of 15 °C with a hydraulic retention time of 1 day and a corresponding loading rate of 7.2 g-chemical oxygen demand (COD)/l/day, 90–95% removal efficiency was achieved. The methane production of 250 l/kg-COD removed at standard temperature pressure (STP) is a major highlight of the study complementing the high treatment efficiency achieved. Loading rates >5 g-COD/l/day was accompanied by increase in effluent volatile fatty acids (VFA) concentrations. Due to the presence of a high concentration of active granular sludge in the lower compartment of the reactor, 80% reduction of COD occurred within the granular bed of the reactor. Treatment of low strength wastewater for a short period showed 70–75% removal efficiencies with methane yield of 300 l/kg-COD removed. Specific methanogenic activity profiles of the anaerobic biomass revealed low-temperature (15 °C) optima, indicating selection of cold-active microorganisms during the acclimation process. The SMA assays also indicate the development of a putatively psychrophilic acetoclastic methanogenic community and biogas analysis showed 75% efficiency in energy recovery as methane.     

Continuous ethanol production by immobilized yeast in a fluidized reactor

Summary In order to minimize the adverse effect of CO₂ gas in a packed bed immobilized yeast reactor, a fluidized bed reactor was used for the continuous production of ethanol from glucose. Immobilized yeast was prepared by entrapping whole cells of Saccharomyces cerevisiae within a Caalginate matrix. It was found that the efficiency of the ethanol production in a fluidized bed reactor was 100% better than that for a packed bed reactor system. The alcohol productivity obtained was 21 g/l/hr in a fluidized bed reactor at 94% of conversion level.     

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.     

Methane fermentation of coastal mud sediment by a two-stage upflow anaerobic sludge blanket (UASB) reactor system

The removal of organic matter from a coastal mud sediment was carried out by a methane fermentation process under anaerobic conditions. In a batch acidogenic fermentation, the addition of vitamins containing thiamine, nicotinic acid and biotin dramatically enhanced acetate production from the mud sediment (200 g wet wt l(-1) artificial sea water), yielding 77 mM acetate after 6 days, which corresponded to 77% of the organic matter in the mud sediment, measured on the basis of chemical oxygen demand. Thereafter, the two-fold diluted, post-acidogenic fermentation liquor (PAF liquor) was continuously treated at 2.4x original dilution rate day(-1) for 30 days, using an upflow anaerobic sludge blanket methanogenic reactor containing the acclimated methanogenic sludge from the mud sediment. Acetate, 42 mM in the PAF liquor, was converted to methane at a maximum methane production rate of 96 mmol l(-1) day(-1); and 87.5% of the acetate and 88.7% of the total organic carbon in the PAF liquor were removed. Moreover, an efficient treatment of the mud sediment was carried out by a semi-continuous, two-stage reactor system, where the culture broth was circulated between acidogenic and methanogenic reactors. This two-stage reactor system gave a stable operation at 4-day intervals for one treatment period, yielding 112 mmol methane from the wet mud in the PAF liquor (278 g l(-1)).     

Study of the microbial diversity in a full-scale UASB reactor treating domestic wastewater

The microorganisms diversity in a full-scale UASB reactor treating domestic sewage was studied by molecular techniques, with the objective of identifying the population differences associated with the specific methanogenic activity (SMA) of the sludges. Samples were collected at levels A (0.8 m; bottom), B (1.3 m), C (1.8 m), D (2.3 m) and E (2.8 m). Actinobacteria was dominant at the three lower points and should have been primarily responsible for the degradation of organic matter. DNA sequences belonging to Methanomicrobiales order of Archaea domain was detected in all five levels with the majority producing methane from hydrogen and carbon dioxide. Points A and E showed similar bacteria variety. The SMA of point A was the highest (0.374 g COD-CH₄/g SSV.d); however, the point E showed much lower value, probably due to the predominance of Proteobacteria phylum, including sulfate-reducing bacteria. In the overall, the results obtained can be considered important because data from full-scale UASB reactors treating domestic sewage remain scarce.     

Start-up of an anaerobic hybrid (UASB/filter) reactor treating wastewater from a coffee processing plant

The ability of an anaerobic hybrid reactor, treating coffee wastewater, to achieve a quick start-up was tested at pilot scale. The unacclimatized seed sludge used showed a low specific methanogenic activity of 26.47 g CH4 as chemical oxygen demand (COD)/kg volatile suspended solids (VSS) x day. This strongly limited the reactor performance. After a few days of operation, a COD removal of 77.2% was obtained at an organic loading rate (OLR) of 1.89 kg COD/m3 x day and a hydraulic retention time (HRT) of 22 h. However, suddenly increasing OLR above 2.4 kg COD/m3 x day resulted in a deterioration in treatment efficiency. The reactor recovered from shock loads after shutdowns of 1 week. The hybrid design of the anaerobic reactor prevented the biomass from washing-out but gas clogging in the packing material was also observed. Wide variations in wastewater strength and flow rates prevented stable reactor operation in the short period of the study.     

Enhancing the start-up of a UASB reactor treating domestic wastewater by adding a water extract of Moringa oleifera seeds

Water extract of Moringa oleifera seeds (WEMOS) was used to enhance the start-up of a self-inoculated upflow anaerobic sludge blanket (UASB) reactor treating raw domestic wastewater. Two reactors labelled control (RC) and WEMOS addition (RM) were started without special inoculum. Both reactors were fed continuously for 22 weeks with domestic wastewater containing an average total chemical oxygen demand (COD) of 320 mg O2/l and suspended solid (SS) of 165 mg/l. The reactors operated during the entire experimental period at 29 degrees C and at a hydraulic retention time (HRT) of 4 h. The RM reactor received 2 ml WEMOS per litre of influent. WEMOS solution was prepared on the basis of 2.5% (w/v) ground M. oleifera seeds in water. The results of 22 weeks' operation showed an improvement in the performance of the RM compared to that of the RC. The dosage of WEMOS in the feed (1) shortened the biological start-up period by 20%, (2) increased acidogenic and methanogenic activity by a factor of 2.4 and 2.2 respectively, (3) increased the specific biogas production by a factor of 1.6, (4) favoured fast growth of the sludge bed, and (5) allowed the aggregation of coccoid bacteria and growth of microbial nuclei, which are precursors of anaerobic granulation.     

The production of ethanol from lactose in a tubular reactor by immobilized cells of Kluyveromyces fragilis

Summary An immobilized-cell tubular reactor for the continuous fermentation of lactose by Kluyveromyces fragilis was developed. Two types of supporting media were successfully tested; beechwood cubes and activated charcoal pellets. Ethanol productivity of 17.2 g/l/h was achieved from a 15% whey-lactose solution using K. fragilis immobilized on charcoal pellets, with a final ethanol concentration of 18 g/l. The use of two reactors in series demonstrated that it is possible to obtain up to 50 g/l of ethanol in the final product. No decrease in biological activity of the immobilized yeast cells occurred over a period of up to 31 days of continuous operation.     

Comparative study of ethanol production by an immobilized yeast in a tubular reactor and in a multistage reactor

Summary The productivity of continuous ethanol fermentation has been increased using fixed bed reactors where a high density of yeast cells was maintained on a packing of wood chips. Two different systems have been used: 1. A tubular reactor which produced alcohol solutions containing up to 13.5% (V/V) ethanol. High CO₂ retention and a poor mass transfer between bulk medium and immobilized biomass prevented production rates higher than 2.2 g/l·h. 2. A multistage reactor where a better utilisation of the reactor volume led to improved performances. Solutions containing 132 g/l of ethanol (16.5% V/V) were produced with a productivity increased up to 4.8 g/l·h. A better distribution of the active biomass and a lower gradient of alcohol concentration between support and bulk medium are possible reasons for this improvement.     

A cell retention internal filter reactor for ethanol production using tapioca hydrolysates

Summary Ethanol fermentation with Saccharomyces cerevisiae was carried out in a bioreactor equipped with a sintered stainless steel filter to obtain a high cell density as well as a high productivity. With a 100 g glucose/l feed, the maximum yeast concentration was 208 g/L similar to that obtained in external membrane cell recycle cultures. However, with tapioca hydrolysates, treated with activated carbon column, the yeast concentration attained was 42g/L.     

Biodiesel production using a membrane reactor

The immiscibility of canola oil in methanol provides a mass-transfer challenge in the early stages of the transesterification of canola oil in the production of fatty acid methyl esters (FAME or biodiesel). To overcome or rather, exploit this situation, a two-phase membrane reactor was developed to produce FAME from canola oil and methanol. The transesterification of canola oil was performed via both acid- or base-catalysis. Runs were performed in the membrane reactor in semi-batch mode at 60, 65 and 70 degrees C and at different catalyst concentrations and feed flow rates. Increases in temperature, catalyst concentration and feedstock (methanol/oil) flow rate significantly increased the conversion of oil to biodiesel. The novel reactor enabled the separation of reaction products (FAME/glycerol in methanol) from the original canola oil feed. The two-phase membrane reactor was particularly useful in removing unreacted canola oil from the FAME product yielding high purity biodiesel and shifting the reaction equilibrium to the product side.     

Microbiota adaptation after an alkaline pH perturbation in a full-scale UASB anaerobic reactor treating dairy wastewater

Bioprocess and Biosystems Engineering - The aim of this study was to understand how the microbial community adapted to changes, including a pH perturbation, occurring during the start-up and...     

High-rate nitrogen removal from waste brine by marine anammox bacteria in a pilot-scale UASB reactor

Applied Microbiology and Biotechnology - The goal of this study was to develop a startup strategy for a high-rate anaerobic ammonium oxidation (anammox) reactor to treat waste brine with high...     

Treatment of distillery spentwash by hybrid UASB reactor

A laboratory-scale hybrid UASB reactor, which combined an UASB in the lower part and a filter in the upper part, was used for the treatment of distillery spentwash. The reactor was operated under ambient conditions for 380 days. Using anaerobically digested sewage sludge as a seed, the start-up of the reactor and the cultivation of active granular sludge was completed within three months period. Scanning electron microscopic (SEM) observation of the granules showed the presence of Mehtanonthrix-like bacteria as the dominant species. Following the start-up the organic loading rate (OLR) was increased, stepwise, to 36 kg COD/m³ · d at a constant hydraulic retention time (HRT) of 6 h. COD removal efficiency was 80% even at a high OLR of 36 kg COD/m³ · d. Biogas rich in methane content (80%), with a maximum specific biogas yield of 0.40 m³ CH₄/kg · COD was produced. Polypropylene pall rings filter medium in the upper-third of the reactor was very effective as a gas-liquid-solid (GLS) separator, and retained the biomass in addition. The study indicated that hybrid UASB is a very feasible alternative for the treatment of high-strength wastewaters like distillery spentwash.     

Microbial production of hydrogen and ethanol from glycerol-containing wastes discharged from a biodiesel fuel production plant in a bioelectrochemical reactor with thionine

H(2) and ethanol production from glycerol-containing wastes discharged from a biodiesel fuel production plant by Enterobacter aerogenes NBRC 12010 was demonstrated in bioelectrochemical cells. Thionine as an exogenous electron transfer mediator was reduced by E. aerogenes, and was re-oxidized by a working electrode applied at +0.2 V against a Ag/AgCl reference electrode by a potentiostat (electrode system). At the initial glycerol concentration of 110 mM, 92.9 mM glycerol was consumed in the electrode system with 2 mM thionine after 48 h. On the other hand, the concentration of glycerol consumed was only 50.3 mM under the control conditions without thionine and the electrodes (normal fermentation). There are no differences in the yields of H(2) and ethanol against glycerol consumed between the control conditions and the conditions with the electrode system. A pH of 6.0 was suitable for the H(2) production in the range between pH 6 and pH 7.5 in the electrode system. At pH values of 7.0 and 7.5, H(2) production decreased and formate was remarkably produced in the reaction solution. The rates of both glycerol consumption and the H(2) and ethanol production increased as the thionine concentration and the surface area of the working electrode increased. After 60 h, 154 mM of the initial 161 mM glycerol concentration in the wastes was consumed in the electrode system, which is a 2.6-fold increase compared to the control experiment. Biotechnol. Bioeng. 2007;98: 340-348. (c) 2007 Wiley Periodicals, Inc.     

Recovery strategies for tackling the impact of phenolic compounds in a UASB reactor treating coal gasification wastewater

The impact of phenolic compounds (around 3.2 g/L) resulted in a completely failed performance in a mesophilic UASB reactor treating coal gasification wastewater. The recovery strategies, including extension of HRT, dilution, oxygen-limited aeration, and addition of powdered activated carbon were evaluated in batch tests, in order to obtain the most appropriate way for the quick recovery of the failed reactor performance. Results indicated that addition of powdered activated carbon and oxygen-limited aeration were the best recovery strategies in the batch tests. In the UASB reactor, addition of powdered activated carbon of 1 g/L shortened the recovery time from 25 to 9 days and oxygen-limited aeration of 0-0.5 mgO₂/L reduced the recovery time to 17 days. Reduction of bioavailable concentration of phenolic compounds and recovery of sludge activity were the decisive factors for the recovery strategies to tackle the impact of phenolic compounds in anaerobic treatment of coal gasification wastewater.