Simultaneous saccharification and fermentation of cellulose for bio-hydrogen production by anaerobic mixed cultures in elephant dung

The objective of this study was to optimize the culture conditions for simultaneous saccharification and fermentation (SSF) of cellulose for bio-hydrogen production by anaerobic mixed cultures in elephant dung under thermophilic temperature. Carboxymethyl cellulose (CMC) was used as the model substrate. The investigated parameters included initial pH, temperature and substrate concentration. The experimental results showed that maximum hydrogen yield (HY) and hydrogen production rate (HPR) of 7.22 ± 0.62 mmol H₂/g CMC_added and 73.4 ± 3.8 mL H₂/L h, respectively, were achieved at an initial pH of 7.0, temperature of 55 °C and CMC concentration of 0.25 g/L. The optimum conditions were then used to produce hydrogen from the cellulose fraction of sugarcane bagasse (SCB) at a concentration of 0.40 g/L (equivalent to 0.25 g/L cellulose) in which an HY of 7.10 ± 3.22 mmol H₂/g cellulose_added. The pre-dominant hydrogen producers analyzed by polymerase chain reaction-denaturing gel gradient electrophoresis (PCR-DGGE) were Thermoanaerobacterium thermosaccharolyticum and Clostridium sp. The lower HY obtained when the cellulose fraction of SCB was used as the substrate might be due to the presence of lignin in the SCB as well as the presence of Lactobacillus parabuchneri and Lactobacillus rhamnosus in the hydrogen fermentation broth.     

Pilot-scale of biohythane production from palm oil mill effluent by two-stage thermophilic anaerobic fermentation

The pilot-scale of two-stage thermophilic (55 °C) for biohythane production from palm oil mill effluent (POME) was operated at hydraulic retention time (HRT) of 2 days and organic loading rate (OLR) of 27.5 gCOD/L⋅d) for first stage and HRT of 10 days and OLR of 5.5 gCOD/L⋅d for second stage. Biohythane production rate was 1.93 L-gas/L⋅d with biogas containing 11% H₂, 37% CO₂, and 52% CH₄. Recirculation of methane effluent mixed with POME at a ratio of 1:1 can control pH in the first stage at an optimal range of 5.0–6.5. Microbial community in hydrogen stage dominated by Thermoanaerobacterium sp., while methane stage dominated by Methanosarcina sp. The H₂/CH₄ ratio of biohythane was 0.13–0.18 which suitable for vehicle fuel. Biohythane production from POME could be promising cleaner biofuel with flexible and controllable H₂/CH₄ ratio.     

嗜热侧孢霉固体发酵产纤维素酶条件研究

采用单因子实验和正交试验对嗜热侧孢霉(Thermophilic sporotrichum)固体发酵产纤维素酶条件进行了研究,并测定了CMC酶、滤纸酶和棉花酶活力,以CMC酶和FPA酶为主要参考指标,最适产酶条件为:麸皮∶甘蔗渣(1∶2)50 g,(NH4)2SO4 1.0 g,K2HPO4 0.1 g,MgSO4·7H2O 0.03 g,含水量60%,pH5.5,培养温度为45℃,250 mL三角瓶盛放培养料40 g,培养4 d,测得CMC酶、FPA酶和棉花酶活力分别为320.04 IU,38.65 IU,180.31 IU.     

Dephytinization of food stuffs by phytase of Geobacillus sp. TF16 immobilized in chitosan and calcium-alginate

In this work, Geobacillus sp. TF16 phytase was separately immobilized in chitosan and Ca-alginate with the efficiency of 38% and 42%, respectively. These enzymes exhibited broad substrate specificity. Maximal relative phytase activity was measured at pH 5.0 and 95°C and pH 3.0 and 75°C for chitosan and Ca-alginate, respectively. The enzymes were highly stable in a wide pH and temperature range. Values of K_m and V_max were determined as 2.38 mM and 3401.36 U/mg protein for chitosan, and 7.5 mM and 5011.12 U/mg protein for Ca-alginate. The immobilized enzymes showed higher resistance to proteolysis. After 4 h incubation, hydrolysis capacities of chitosan- and Ca-alginate immobilized enzymes for soymilk phytate were calculated as 24% and 33%, respectively. The chitosan- and Ca-alginate immobilized phytases conserved its original activity after 8 and 6 cycles of reuse, respectively. The features of the enzymes were very attractive and they might be useful for some industrial applications.     

Fate of pharmaceutical and personal care products (PPCPs) during anaerobic digestion of sewage sludge

The behaviour of 13 pharmaceutical and personal care products (PPCPs) has been studied during anaerobic digestion of sewage sludge: two musks (Galaxolide and Tonalide), one tranquilliser (Diazepam), one anti-epileptic (Carbamazepine), three anti-phlogistics (Ibuprofen, Naproxen and Diclofenac), two antibiotics (Sulfamethoxazole and Roxithromycin), one X-ray contrast medium (Iopromide) and three oestrogens (Estrone, 17beta-oestradiol and 17alpha-ethinyloestradiol). Two parallel processes have been carried out, one in mesophilic range (37 degrees C) and the other in thermophilic range (55 degrees C). The influence of temperature and sludge retention time (SRT) has been analysed. Among the substances considered, the higher removal efficiencies were achieved for the antibiotics, natural oestrogens, musks and Naproxen. For the other compounds, the values ranged between 20% and 60%, except for Carbamazepine, which showed no elimination. The removal of oestrogens, Diazepam and Diclofenac occurred after sludge adaptation. In general, no influence of SRT and temperature on PPCPs removal was observed. Considering the difficulty of obtaining reliable PPCPs concentrations, especially those corresponding to the fractions sorbed onto sludge, a methodology to validate the experimental data has been developed and successfully applied.     

Thermophilic treatment of acidified and partially acidified wastewater using an anaerobic submerged MBR: Factors affecting long-term operational flux

The long-term operation of two thermophilic anaerobic submerged membrane bioreactors (AnSMBRs) was studied using acidified and partially acidified synthetic wastewaters. In both reactors, cake formation was identified as the key factor governing critical flux. Even though cake formation was observed to be mostly reversible, particle deposition proceeds fast once the critical flux is exceeded. Very little irreversible fouling was observed during long-term operation, irrespective of the substrate. Critical flux values at the end of the reactors operation were 7 and 3L/m(2)h for the AnSMBRs fed with acidified and partially acidified wastewaters, respectively, at a gas superficial velocity of 70m/h. Small particle size was identified as the responsible parameter for the low observed critical flux values. The degree of wastewater acidification significantly affected the physical properties of the sludge, determining the attainable flux. Based on the fluxes observed in this research, the membrane costs would be in the range of 0.5euro/m(3) of treated wastewater. Gas sparging was ineffective in increasing the critical flux values. However, preliminary tests showed that cross-flow operation may be a feasible alternative to reduce particle deposition.     

Influence of high gas production during thermophilic anaerobic digestion in pilot-scale and lab-scale reactors on survival of the thermotolerant pathogens Clostridium perfringens and Campylobacter jejuni in piggery wastewater

Safe reuse of animal wastes to capture energy and nutrients, through anaerobic digestion processes, is becoming an increasingly desirable solution to environmental pollution. Pathogen decay is the most important safety consideration and is in general, improved at elevated temperatures and longer hydraulic residence times. During routine sampling to assess pathogen decay in thermophilic digestion, an inversely proportional relationship between levels of Clostridium perfringens and gas production was observed. Further samples were collected from pilot-scale, bench-scale thermophilic reactors and batch scale vials to assess whether gas production (predominantly methane) could be a useful indicator of decay of the thermotolerant pathogens C. perfringens and Campylobacter jejuni. Pathogen levels did appear to be lower where gas production and levels of methanogens were higher. This was evident at each operating temperature (50, 57, 65 °C) in the pilot-scale thermophilic digesters, although higher temperatures also reduced the numbers of pathogens detected. When methane production was higher, either when feed rate was increased, or pH was lowered from 8.2 (piggery wastewater) to 6.5, lower numbers of pathogens were detected. Although a number of related factors are known to influence the amount and rate of methane production, it may be a useful indicator of the removal of the pathogens C. perfringens and C. jejuni.     

Waste activated sludge hydrolysis and short-chain fatty acids accumulation under mesophilic and thermophilic conditions: Effect of pH

The effect of pH (4.0–11.0) on waste activated sludge (WAS) hydrolysis and short-chain fatty acids (SCFAs) accumulation under mesophilic and thermophilic conditions were investigated. The WAS hydrolysis increased markedly in thermophilic fermentation compared to mesophilic fermentation at any pH investigated. The hydrolysis at alkaline pHs (8.0–11.0) was greater than that at acidic pHs, but both of the acidic and alkaline hydrolysis was higher than that pH uncontrolled under either mesophilic or thermophilic conditions. No matter in mesophilic or thermophilic fermentation, the accumulation of SCFAs at alkaline pHs was greater than at acidic or uncontrolled pHs. The optimum SCFAs accumulation was 0.298 g COD/g volatile suspended solids (VSS) with mesophilic fermentation, and 0.368 with thermophilic fermentation, which was observed respectively at pH 9.0 and fermentation time 5 d and pH 8.0 and time 9 d. The maximum SCFAs productions reported in this study were much greater than that in the literature. The analysis of the SCFAs composition showed that acetic acid was the prevalent acid in the accumulated SCFAs at any pH investigated under both temperatures, followed by propionic acid and n-valeric acid. Nevertheless, during the entire mesophilic and thermophilic fermentation the activity of methanogens was inhibited severely at acid or alkaline pHs, and the highest methane concentration was obtained at pH 7.0 in most cases. The studies of carbon mass balance showed that during WAS fermentation the reduction of VSS decreased with the increase of pH, and the thermophilic VSS reduction was greater than the mesophilic one. Further investigation indicated that most of the reduced VSS was converted to soluble protein and carbohydrate and SCFAs in two fermentations systems, while little formed methane and carbon dioxide.     

Thermophilic bacilli and their importance in dairy processing

The thermophilic bacilli, such as Anoxybacillus flavithermus and Geobacillus spp., are an important group of contaminants in the dairy industry. Although these bacilli are generally not pathogenic, their presence in dairy products is an indicator of poor hygiene and high numbers are unacceptable to customers. In addition, their growth may result in milk product defects caused by the production of acids or enzymes, potentially leading to off-flavours. Dairy thermophiles are usually selected for by the conditions during dairy manufacture. These bacteria are able to grow in sections of dairy manufacturing plants where temperatures reach 40-65 °C. Furthermore, because they are spore formers, they are difficult to eliminate. In addition, they exhibit a wide temperature growth range, exhibit a fast growth rate (generation time of approximately 15-20 min) and tend to readily form biofilms. Many strategies have been tested to remove, prevent and/or delay the formation of thermophilic bacilli biofilms in dairy manufacture, but with limited success. This is, in part, because little is known about the structure and composition of thermophilic bacilli biofilms in general and, more specifically, in milk processing environments. Therefore, new cleaning regimes often do not target the problem optimally. A greater understanding of the structure of thermophilic biofilms within the context of the milk processing environment and their link with spore formation is needed to develop better control measures. This review discusses the characteristics and food spoilage potential, enumeration and identification methods for the thermophilic bacilli, as well as their importance to dairy manufacture, with an emphasis on biofilm development and spore formation.     

Biological hydrogen production in suspended and attached growth anaerobic reactor systems

Biological production of hydrogen gas has received increasing interest from the international community during the last decade. Most studies on biological fermentative hydrogen production from carbohydrates using mixed cultures have been conducted in conventional continuous stirred tank reactors (CSTR) under mesophilic conditions. Investigations on hydrogen production in reactor systems with attached microbial growth have recently come up as well as investigations on hydrogen production in the thermophilic temperature range. The present study examines and compares the biological fermentative production of hydrogen from glucose in a continuous stirred tank type bioreactor (CSTR) and an upflow anaerobic sludge blanket bioreactor (UASB) at various hydraulic retention times (2–12 h HRT) under mesophilic conditions (35 °C). Also the biohydrogen production from glucose in the CSTR at mesophilic and thermophilic (55 °C) temperature range was studied and compared. From the CSTR experiments it was found that thermophilic conditions combine high hydrogen production rate with low production of microbial mass, thus giving a specific hydrogen production rate as high as 104 mmole _H2/h/l/g${\mathrm{H}}_2/\mathrm{h}/\mathrm{l}/\mathrm{g}$ VSS at 6 h retention time compared to a specific hydrogen production rate of 12 mmole _H2/h/l/g${\mathrm{H}}_2/\mathrm{h}/\mathrm{l}/\mathrm{g}$ VSS under mesophilic conditions. On the other hand, the UASB reactor configuration is more stable than the CSTR regarding hydrogen production, pH, glucose consumption and microbial by-products (e.g. volatile fatty acids, alcohols etc.) at the HRTs tested. Moreover, the hydrogen production rate in the UASB reactor was significantly higher compared to that of the CSTR at low retention times (19.05 and 8.42 mmole _H2/h/l${\mathrm{H}}_2/\mathrm{h}/\mathrm{l}$, respectively at 2 h HRT) while hydrogen yield (mmole _H2/mmole${\mathrm{H}}_2/\mathrm{mmole}$ glucose consumed) was higher in the CSTR reactor at all HRT tested. This implies that there is a trade-off between technical efficiency (based on hydrogen yield) and economic efficiency (based on hydrogen production rate) when the attached (UASB) and suspended (CSTR) growth configurations are compared.