Optimization of biohydrogen production of palm oil mill effluent by ozone pretreatment

The biohydrogen (H₂) production in batch experiments under varying concentrations of raw and ozonated palm oil mill effluent (POME) of 5000–30,000 mg COD.L⁻¹, at initial pH 6, under mesophilic (37 °C), thermophilic (55 °C) and extreme-thermophilic (70 °C) conditions. Effects of ozone pretreatment, substrate concentration and fermentation temperature on H₂ production using mesophilic seed sludge was undertaken. The results demonstrated that H₂ can be produced from both raw and ozonated POME, and the amounts of H₂ production were directly increased as the POME concentrations were increased. H₂ was successfully produced under the mesophilic fermentation of ozonated POME, with maximum H₂ yield, and specific H₂ production rate of 182 mL.g⁻¹ COD_removed (30,000 mg COD.L⁻¹) and 6.2 mL.h⁻¹.g⁻¹ TVS (25,000 mg COD.L⁻¹), respectively. Thus, indicating that the ozone pretreatment could elevate on the biodegradability of major constituents of the POME, which significantly enhanced yields and rates of the H₂ production. H₂ production was not achieved under the thermophilic and extreme-thermophilic fermentation. In both fermentation temperatures with ozonated POME, the maximum H₂ yield was 62 mL.g⁻¹ COD_removed (30,000 mg COD.L⁻¹) and 63 mL.g⁻¹ COD_removed (30,000 mg COD.L⁻¹), respectively. The highest efficiency of total and soluble COD removal was obtained at 44 and 37%, respectively following the mesophilic fermentation, of 24 and 25%, respectively under the thermophilic fermentation, of 32 and 20%, respectively under the extreme-thermophilic fermentation. The production of volatile fatty acids increased with an increased fermentation time and temperature in both raw and ozonated POME under all three fermentation temperatures. The accumulation of volatile fatty acids in the reactor content were mostly acetic and butyric acids. H₂ fermentation under the mesophilic condition of 37 °C was the better selection than that of the thermophilic and extreme-thermophilic fermentation.     

嗜热微生物的耐热机制及应用

首先介绍了嗜热微生物的基本知识,然后从细胞膜组分、蛋白质结构、遗传物质方面阐述了嗜热微生物的嗜热机制,并简要介绍了其应用的研究进展。     

阿维菌素废水处理的研究

采用电化学技术对阿维菌素废水进行预处理,预处理后废水进行生化处理,控制电解时间为30 min,絮凝后高温厌氧48 h,厌氧出水后进行生物碳处理,废水COD和AVM去除率分别达到95.6%和86.3%,出水COD为200～230 mg/L,出水达到生物制药行业的排放标准。     

Development and application of a simulation model for the thermophilic oxic process for treating swine waste

The thermophilic oxic process (TOP) is a composting process that enables simultaneous complete decomposition and evaporation of organic waste under high temperature conditions supported by well-balanced calorific value control. To develop the simulation model for TOP, three-dimensional relationships among decomposition rate constant, temperature (20-70 °C) and moisture content (30-70%) were determined for swine waste and cooking oil based on the oxygen consumption rate during a thermophilic oxic decomposition reaction.The decomposition rate of swine waste and cooking oil under various moisture contents was described by the Arrhenius equation. The optimal temperature and moisture content were 60 °C and 60% for swine waste and 60 °C and 50% for cooking oil, respectively. The simulation model for TOP was constructed on the basis of the carbon, heat, and moisture balance. The validation of the simulation model was examined by comparing the measured temperature in the TOP reactor to that estimated by the simulation. The simulation model was proven by comparing experimental and calculated values. The relationship between the injection calorific value and the process mechanism of TOP was interpreted by the simulation model. On the basis of their relationship during TOP, the appropriate process conditions were discussed.     

Effect of thermosonication in a batch system on the survival of spore‐forming bacteria

Thermosonication may help reduce bacteria counts responsible for spoilage in dairy products. Vegetative cells and spores of Geobacillus stearothermophilus, Anoxybacillus flavithermus and Bacillus subtilis (spores only) were treated with either heat alone or thermosonication in a batch system from 0 to 120 s in tryptic soy broth and 2% fat milk at 72 and 73 °C. D‐values for vegetative cells were calculated and were reduced after thermosonication. Maximum reduction in vegetative cells after thermosonication was 1 log after 30–45 s and for spores was ≤0.2 log after 120 s, which may not influence dairy product quality in scale‐up systems.     

Continuous fermentative hydrogen production from cheese whey wastewater under thermophilic anaerobic conditions

Hydrogen (H₂) production from cheese processing wastewater via dark anaerobic fermentation was conducted using mixed microbial communities under thermophilic conditions. The effects of varying hydraulic retention time (HRT: 1, 2 and 3.5 days) and especially high organic load rates (OLR: 21, 35 and 47 g chemical oxygen demand (COD)/l/day) on biohydrogen production in a continuous stirred tank reactor were investigated. The biogas contained 5–82% (45% on average) hydrogen and the hydrogen production rate ranged from 0.3 to 7.9 l H₂/l/day (2.5 l/l/day on average). H₂ yields of 22, 15 and 5 mmol/g COD (at a constant influent COD of 40 g/l) were achieved at HRT values of 3.5, 2, and 1 days, respectively. On the other hand, H₂ yields were monitored to be 3, 9 and 6 mmol/g COD, for OLR values of 47, 35 and 21 g COD/l/day, when HRT was kept constant at 1 day. The total measurable volatile fatty acid concentration in the effluent (as a function of influent COD) ranged between 118 and 27,012 mg/l, which was mainly composed of acetic acid, iso-butyric acid, butyric acid, propionic acid, formate and lactate. Ethanol and acetone production was also monitored from time to time.To characterize the microbial community in the bioreactor at different HRTs, DNA in mixed liquor samples was extracted immediately for PCR amplification of 16S RNA gene using eubacterial primers corresponding to 8F and 518R. The PCR product was cloned and subjected to DNA sequencing. The sequencing results were analyzed by using MegaBlast available on NCBI website which showed 99% identity to uncultured Thermoanaerobacteriaceae bacterium.     

Trace metal chemistry and silicification of microorganisms in geothermal sinter, Taupo Volcanic Zone, New Zealand

As part of a pilot study investigating the role of microorganisms in the immobilisation of As, Sb, B, Tl and Hg, the inorganic geochemistry of seven different active sinter deposits and their contact fluids were characterised. A comprehensive series of sequential extractions for a suite of trace elements was carried out on siliceous sinter and a mixed silica-carbonate sinter. The extractions showed whether metals were loosely exchangeable or bound to carbonate, oxide, organic or crystalline fractions. Hyperthermophilic microbial communities associated with sinters deposited from high temperature (92–94°C) fluids at a variety of geothermal sources were investigated using SEM. The rapidity and style of silicification of the hyperthermophiles can be correlated with the dissolved silica content of the fluid. Although high concentrations of Hg and Tl were found associated with the organic fraction of the sinters, there was no evidence to suggest that any of the heavy metals were associated preferentially with the hyperthermophiles at the high temperature (92–94°C) ends of the terrestrial thermal spring ecosystems studied.     

Enzymatic hydrolysis and anaerobic biological treatment of fish industry effluent: Evaluation of the mesophilic and thermophilic conditions

Enzymatic hydrolysis and anaerobic treatment of effluent similar to that generated in the fish processing industry were evaluated at 30 °C and 50 °C. Hydrolysis used lipase produced by fungus Penicillium simplicissimum in solid state fermentation with babassu cake as substrate, which has optimal activity at 50 °C. Hydrolysis kinetics was conducted with mixtures of effluent (containing 1500 mg oils and greases/L) and different lipase activities (0–0.67 U/ml of effluent), verifying that with 0.16 U/ml of effluent, 9.69 μmol/ml of free acids were produced after 4 h at 50 °C. Anaerobic biodegradation assays were conducted with effluent submitted to three different treatments: thermophilic (hydrolysis and anaerobic treatment at 50 °C), mesophilic (hydrolysis and anaerobic treatment at 30 °C) and hybrid (hydrolysis at 50 °C and anaerobic treatment at 30 °C). The best results (97.5% of chemical oxygen demand [COD] removal and 105.4 ml CH₄/g COD_removed) were obtained with the hybrid treatment in only 68 h. The thermophilic hydrolysis not only reduced the amount of enzyme and the hydrolysis time but also reduced the time and the cost of mesophilic anaerobic treatment, favoring the application of this treatment on an industrial scale.     

Pre-treatment mechanisms during thermophilic-mesophilic temperature phased anaerobic digestion of primary sludge

Pre-treatment is used extensively to improve degradability and hydrolysis rate of material being fed into digesters. One emerging process is temperature phased anaerobic digestion (TPAD), which applies a short (2 day) 50-70 °C pre-treatment step prior to 35 °C digestion in the main stage (10-20 days). In this study, we evaluated a thermophilic-mesophilic TPAD against a mesophilic-mesophilic TPAD treating primary sludge. Thermophilic-mesophilic TPAD achieved 54% VS destruction compared to 44% in mesophilic-mesophilic TPAD, with a 25% parallel increase in methane production. Measurements of soluble COD and NH₄⁺-N showed increased hydrolysis extent during thermophilic pre-treatment. Model based analysis indicated the improved performance was due to an increased hydrolysis coefficient rather than an increased inherent degradability, suggesting while TPAD is suitable as an intensification process, a larger main digester could achieve similar impact.