This study aimed to find out the optimum pH range and a buffer feeding method for butyric acid production from rice straw by undefined mixed culture. A serial experiment was conducted at various pH levels from 5.0 to 7.0. The results showed that neutral pH improved rice straw conversion and hence carboxylic acid production. The highest butyric acid production was achieved at pH range of 6.0 to 6.5. Another serial experiment was performed at pH 6.0 to 6.5 buffered with CaCO3, NaHCO3, NH4HCO3 and their combinations, respectively. The results indicated that different buffers had different effects on product spectrum, and that CaCO3 combined with NaHCO3 was an effective buffer for butyric acid production. This study presents an alternative way for butyric acid production from lignocellulosic biomass without supplementary cellulolytic enzyme.
Dry methane fermentation is an innovative anaerobic digestion technique to treat solid bio-wastes without dilution for potential energy recovery with nutrient rich fertilizer and sustainable waste management. Although dry anaerobic fermentation offers great advantages like utilization of wastes in its produced form, high organic loading rate, no liquid effluent and comparable amount of biogas production with wet fermentation, commercial dry anaerobic digestion is scarcely used so far. In order to develop feasible dry fermentation process, it is important to review the optimization techniques and suggested possible areas where improvements could be made, including the reactor configuration, mixing, feed stocks, co-digestion, pretreatment and environmental conditions within the digester.
Low nitrogen removal efficiency caused by the lack of carbon source in low C/N ratio wastewater restricts the wastewater biological treatment. Advances in wastewater biological treatment at low C/N ratio are reviewed in the paper from three aspects, including modifying traditional biological nitrogen removal process, developing novel biological nitrogen removal processes and optimizing traditional carbon source and developing new types of carbon sources. The mechanisms, advantages, and applications of these processes are also summarized and analyzed.
Leather processing is an important industry in China, and the discharge of chromium waste has been severely circumscribed. Though traditional processes for treating chromium waste have been widely used in tannery plants, technology adopting high efficiency and economic simultaneously is deficient. In order to develop an economic treatment for tannery waste, a mixed alkali of sodium hydroxide and magnesium oxide and diluted mineral acids were tested to improve the sedimentation effect of trivalent chromium from tannery wastewater. The results showed that the most feasible alkali was a mixture of sodium hydroxide and magnesium oxide with a mass ratio of 5:1 to balance the cost performance. The high chromium removal as 99.1% was obtained with a mixed alkali dosage only 0.2 g/L at pH 9.5, with a very low Cr-sludge yield. The effects of various factors on the extraction of trivalent chromium from Cr-sludge using mineral acids were investigated further more, and the results indicated that the feasible condition for chromium recovery from wet chromium sludge was as follows: 4% sulfuric acid as the leaching acid, chromium sludge (dry weight) load 23.55 g/L, extraction time 60 min, and reaction temperature 30°C. A chromium recovery of 20.86 mg/g was obtained under the feasible condition with a recovery rate of 91.8%. The method developed in the present study provided an effective solution to balance the cost performance for tannery waste treatment.
A anaerobic baffled reactor (ABR) with an effective volume of 28.7 L was adopted, and the hydrogen production efficiency was investigated with diluted molasses as the substrate. Using a mixture of aerobic and anaerobic activated sludge, the ABR was start-up with a hydraulic retention time (HRT) of 24 h and 35°C. When the influent chemical oxygen demand (COD) concentration was gradually increased from 500 mg/L to 6000 mg/L after a 63-day operation, the ABR kept a steady state. The increase of influent COD concentration, from 6000 mg/L to 8000 mg/L stage by stage, had the remarkable changes on the fermentative system. The ethanol-type fermentation was formed in the first three compartments, while butyric acid-type fermentation in the 4th compartment. In the steady stage at the influent COD of 8000 mg/L, the biogas (H2) yield was found 61.54 L/d (12.85 L/d) while specific H2 production rate of the activated sludge was 48 L/kgMLVSS∙d. Although the ABR system accumulated hydrogen-producing acetogen, due to the hydrogen-consuming bacteria (methanogen and homoacetogenic bacteria), the hydrogen production efficiency was badly inhibited.
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