Influence of Hydraulic Loading Rate on UASB Reactor Treating Phenolic Wastewater

[[abstract]]A recirculated upflow anaerobic sludge blanket (RUASB) reactor was operated with three effluent recirculation ratios (5:1, 4:1, and 3:1) to evaluate the influence of hydraulic loading rate on the RUASB treatment of concentrated phenolic wastewater. The results indicate that following an adjustment of the recirculation ratio, a 2- or 3-week lag in methane production occurred, and the effluent concentrations of volatile suspended solid and phenol apparently increased. The results obtained emphasize that the sludge loading rate of 1.4 g phenol chemical oxygen demand/g volatile suspended solid per day was a threshold limit for the methanogens to generate methane. A substrate metabolic activity experiment was carried out to measure the biogas converting capacity of the phenol-consuming granular sludge. A modified Gompertz equation then was applied to evaluate the biogas production potential and rate. The phenolic biodegradation characteristics were described using the Haldane relationship. The half-saturation constant (K\ds) decreased with a decrease in the recirculation ratio, indicating that the granules inside the RUASB reactor had a higher substrate affinity under a low hydraulic loading rate than at a high hydraulic loading rate

Interaction between homoacetogens and methanogens in lake sediments

[[abstract]]The interaction between homoacetogens and methanogens in lake sediments was investigated using hydrogen consumption as an indicator. Sediments samples were obtained from Lake Izunuma, Miyagi prefecture, Japan, a wintering place for migratory birds from Siberia. A batch experiment using View the MathML source as a substrate was conducted to determine the acetate generation and methane production potential of the sediments. Incubation for 4 d at 37°C gave the following stoichiometric equation: 88H2 + 39HCO3− + 22H+ → 17CH3COO− + 5CH4 + 83H2O. The activities, νm, of hydrogen-utilizing homoacetogens and methanogens respectively ranged from 3.2 to 48 and from 1.8 to 3.2 mgCOD·gVSS−1·h−1. The population of hydrogen-utilizing homoacetogens was determined to be 2.6 × 108 MPN·gVSS−1, which was approximately two orders of magnitude higher than that of hydrogen-utilizing methanogens. The results suggest that homoacetogens in the sediments functioned not only as hydrogen consumers but also as major degraders of organic matter, forming acetate as the major reduction product

Methane release rate and methanogenic bacterial populations in lake sediments

[[abstract]]Methane release rates from the sediment in the lake were estimated by a batch culture. The methane release rates were decreased from 6.1 ± 0.7 mgCH4-m−2-h−1 at top 5 cm depth to 2.6 mgCH4-m−2-h−1 at 20–30 cm depth of sediments. Overall methane release rate from sediments was 19.9 mgCH4-m−2-h−1. The maximum specific acetate- and H2-utilization rates, νm, were 5.2 × 10−5 to 7.96 × 10−6 and 0.9 × 10−5 to 1.0 × 10−4 gCOD-gVSS−1-h−1 for the sediments collected in the depths of sediments, respectively. The half-velocity constant, Ks, were from 21 to 65.5 and 27 to 194 mgCOD-1−1 for acetate-and H2-utilizing methanogens in the depths of sediments, respectively. The acetate-utilizing methanogens were enumerated by the most probable number (MPN) technique, and showed the number of acetate-utilizing methanogens increases as the νm increases. The populational distributions were 5.27 × 108 to 2.8 × 108, and 1.2 × 108 MPN-gVSS−1 at the sediments of top 20 and 20–30 cm, respectively. The specific methane production rates of sediments ranged from 1.2 × 10−11 to 3.3 × 10−11 mgCH4-MPN−1-h−1 (average = 2.1 × 10−11 mgCH4-MPN−1-h−1) and are reasonably close to values reported in anaerobic treatment reactors and marine sediments. The sediment of top 20 cm had high microbial activity compared with the deeper section at 20–30 cm depth. In addition, the number of H2-utilizing methanogens was smaller than that of acetate-utilizing methanogens in the sediments

Influence of chemical nature of organic wastes on their conversion to hydrogen by heat-shock digested sludge

[[abstract]]The influence of the chemical nature of high-solid organic wastes (HSOW) on their biohydrogen generation was investigated using simulated high-solid bioreactors under mesophilic conditions. The bioreactors were filled with 10% total solid of rice, potato, fat meat, chicken skin, egg, and lean meat. Experimental results indicate that hydrogen-producing potential of carbohydrate-rich HSOW (rice and potato) was approximately 20 times larger than that of fat-rich HSOW (fat meat and chicken skin) and of protein-rich HSOW (egg and lean meat). According to development trends of pH and hydrogen, pH around 6.0 might be threshold for heat-shock digested sludge; that is Clostridium-rich sludge, converting fat- and protein-rich HSOW to hydrogen; but pH threshold for Clostridium-rich sludge consuming carbohydrates-rich HSOW occurred at around 5.0. In bulk solution, volatile fatty acids (VFA) and alcohols occurred concurrently and the trends of carbohydrate-rich HSOW were similar to those of protein-rich HSOW. Considering developments of carbohydrates and VFAs together with that of hydrogen one infers that lipids would be hydrolyzed to carbohydrates and the carbon flow would proceed through acetate/H2+CO2 cleavage. Indications from cluster analysis of pH development trends are that a cometabolism would be obtained in wastes rich in carbohydrate and protein

Feasibility of biological hydrogen production from organic fraction of municipal solid waste

[[abstract]]Organic municipal solid waste (OFMSW) and two seed microorganisms, namely heat-pretreated digested sludge and hydrogen-producing bacteria enriched from soybean-meal silo, were varied according to a full factorial central composite experimental design with the aim of assessing the feasibility of hydrogen production from OFMSW. A simple model developed from the Gompertz equation was suitable for estimating the hydrogen production potential and rate. Through response surface methodology, empirical equations for specific hydrogen production potential and rate were fitted and plotted as contour diagrams in order to facilitate examination of experimental results. The contour plots showed that high hydrogen production potentials of 140 and 180 ml H2·g TVS−1 occurred when the pretreated digested sludge and the hydrogen-producing bacteria consumed OFMSW, respectively. A high hydrogenic activity for the pretreated digested sludge (45 ml·g VSS−1·h−1) was obtained at a high food-to-microorganism (F/M) ratio; however, that for the hydrogen-producing bacteria (36 ml·g VSS−1·h−1) was found at a low F/M ratio. The experimental results showed that the hydrogen composition of the biogas was greater than 60% except for initial incubation and no significant methane was found throughout this study. Further experiments confirmed that the results of this study were highly reliable and the OFMSW had a considerable potential on biological hydrogen production. Metabolic responses confirmed that characteristics of the heat-pretreated digested sludge converting the OFMSW into hydrogen were similar to that of anaerobic spore-forming bacteria of the genus Clostridium

The influence of pH and ammonia concentration on the methane production in high-solids digestion processes

[[abstract]]The influence of pH and ammonium-nitrogen on methane production in a high-solids sludge digestion process was investigated using a mesophilic batch digester fed with a sludge cake. A simple model developed from the Gompertz equation was applied to the quantitative measurement of the methane production rate and lag-phase time at pHs ranging from 6.5 to 9.0 and ammonium-nitrogen concentrations ranging from 100 to 6 000 mg/L. The results indicate that the ammonium-nitrogen concentration was a more significant factor than the free ammonia in affecting the methanogenic activity of a well-acclimatized system. The simulated results reveal that the methanogenic activity decreased with an increase in ammonium-nitrogen, dropped 10% at an ammonium-nitrogen concentration of 1 670 to 3 720 mg/L, dropped 50% at 4 090 to 5 550 mg/L, and dropped to zero at 5 880 to 6 000 mg/L. The lag-phase time in the batch experiment was dependent on the ammonia level, but not ammonium, and when the free ammonia concentration was higher than 500 mg/L, a notable shock load was observed. In addition, the maximum methane-converting capacity of sludge changed from 28 to 0.9 mL CH4/g VS·d when the ammonium-nitrogen concentration increased from 100 to 6 000 mg/L

Factors Affecting Hydrogen Production from Food Wastes by Clostridium-Rich Composts

[[abstract]]This study used the technique of response surface approach to analyze the combined effects of heat-shocking temperature and time on anaerobic grass composts. Results indicate that the grass composts under heat-shocking temperature and time of 80°C and 3 h, respectively, could yield high populations of hydrogen-producing microorganisms. Metabolic results demonstrate that the composts are reliable, having considerable hydrogen-producing Clostridia. The multivariate analysis with response surface by considering specific hydrogen-producing potential and rate simultaneously indicate that the cultural media with Fe²+=132 mg/L; NH\(+4) =537 mg/L; and PO\(34)-=1,331 mg/L were optimal for the hydrogen-producing Clostridia -rich composts using high-solids food wastes. The specific hydrogen production potential and rate were 77±3 mL H2/gTVS and 52020 mL H2/g TVS/day, respectively. The former was 38% of theoretical hydrogen-producing potential of Clostridium sp. using glucose. Of these factors, ammonium and phosphate are nutrients for the hydrogen-producing Clostridia growth while iron exerts a synergistic influence on them in the conversion of the food wastes into hydrogen

Biohydrogen Generation by Mesophilic Anaerobic Fermentation of Microcrystalline Cellulose

[[abstract]]Sixteen batch experiments were performed to evaluate the stability, kinetics, and metabolic paths of heat-shocked digester (HSD) sludge that transforms microcrystalline cellulose into hydrogen. Highly reproducible kinetic and metabolic data confirmed that HSD sludge could stably convert microcrystalline cellulose to hydrogen and volatile fatty acids (VFA) and induce metabolic shift to produce alcohols. We concluded that clostridia predominated the hydrogen-producing bacteria in the HSD sludge. Throughout this study the hydrogen percentage in the headspace of the digesters was greater than 50% and no methanogenesis was observed. The results emphasize that hydrogen significantly inhibited the hydrogen-producing activity of sludge when initial microcrystalline cellulose concentrations exceeded 25.0 g/L. A further 25 batch experiments performed with full factorial design incorporating multivariate analysis suggested that the ability of the sludge to convert cellulose into hydrogen was influenced mainly by the ratio of initial cellulose concentration (So) to initial sludge density (Xo), but not by interaction between the variables. The hydrogen-producing activity depended highly on interaction of So x (So/Xo). Through response surface analysis it was found that a maximum hydrogen yield of 3.2 mmol/g cellulose occurred at So = 40 g/L and So/Xo = 8 g cellulose/g VSS. A high specific rate of 18 mmol/(g VSS-d) occurred at So = 28 g/L and So/Xo = 9 g cellulose/g VSS. These experimental results suggest that high hydrogen generation from cellulose was accompanied by low So/X

Modeling and optimization of anaerobic digested sludge converting starch to hydrogen

[[abstract]]The pH and hydraulic retention time (HRT) of a chemostat reactor were varied according to a central composite design methodology with the aim of modeling and optimizing the conversion of starch into hydrogen by microorganisms in an anaerobic digested sludge. Experimental results from 23 runs indicate that a maximum hydrogen production rate of 1600 L/m3/d under the organic loading rate of 6 kg starch m3/d obtained at pH = 5.2 and HRT = 17 h. Throughout this study, the hydrogen percentage in the biogas was approximately 60% and no methanogenesis was observed. while the reactor was operated with HRT of 17 h, hydrogen was produced within a pH range between 4.7 and 5.7. Alcohol production rate was greater than hydrogen production rate if the pH was lower than 4.3 or higher than 6.1. Supplementary experiments confirm that the optimum conditions evaluated in this study were highly reliable; while a hydrogen production yield of 1.29 l H2/g starch-COD was obtained. An examination of the response surfaces, including hydrogen, volatile fatty acids (VFA) and alcohols production, led us to the belief that clostridium sp. predominated in the anaerobic hydrogen-producing microorganisms in this study. Experiment results obtained emphasize that the response of metabolites was a more useful indicator than hydrogenic activity for obtaining efficient hydrogen production. Furthermore, expressions of contour plots indicate that Response-Surface Methodology may provide easily interpretable advice on the operation of a hydrogen-producing bioprocess

Influences of pH and moisture content on the methane production in high-solids sludge digestion

[[abstract]]The effects of pH and moisture content on high-solids sludge digestion were investigated using a mesophilic batch digester fed with sludge cake. The experiments were carried out by changing the initial moisture contents from 90 to 96% and the initial pH from 5.0 to 10.0. A simple model developed from the Gompertz equation was applied to estimate the methane production rate and the lag-phase time under various conditions, based on the cumulative methane production curves. The relative methanogenic activity decreased with the decrease of moisture content and dropped from 100 to 53% when the moisture content decreased from 96 to 90%. The rate of the methane production of the high-solids digestion at moisture contents of 90 to 96% functioned over a range of 6.6–7.8 with an optimum of pH 6.8, whereas the process may fail if the pH is lower than 6.1 or higher than 8.3. Moreover, a minimum lag-phase time for methane production was also found at around pH 6.8. In addition, a modified Haldane equation was suitable to represent the effect of pH on methanogenic activity at various moisture contents. The maximum specific methane production rate, Km, and the saturation rate constants for hydrogen ion, KH, and hydroxyl ion, KOH, were 14.5-7.5 ml CH . g−1 dry weight . d−1, 5.0 × 10−1–8.0 × 10−5 [M] and 2.0 × 10−9–8.0 × 10−9 [M], respectively