| Anaerobic digestion process is capable of treating sewage sludge for reduction, resource recovery and stabilization, being one of the key technologies for sewage sludge disposal and treatment. Nowadays, the sludge anaerobic digestion of wastewater treatment plants(WWTPs) in China are unsatisfying due to the low methane producing efficiency and the lack of engineering operational experience. Therefore, it is quite necessary to study how to improve the efficiency of anaerobic digestion in WWTPs.Firstly, a review was given on the principle of anaerobic digestion and technical development in domestic and abroad. After that, a thorough process analysis was conducted for anaerobic digestion process in Beijing Xiaohongmen WWTP based on the data of 2011-2012. As the results, the anaerobic digestion system was more stable and efficient in 2012 than in 2011, due to the more homogeneic quantity and quality of influent sludge and the more constant operational temperature. The organic matters removal rate was about 57. 1% in year average of 2012, which increased by 7.9% than that of 2011. The rate of gas production per volatile solids degraded was about 0.56 m3/kg VS, increased by 69.7% from 2011.Secondly, statistical analysis including correlation analysis and redundanc y analysis(RDA) was performed to investigate the variation of influence factors of each year and identify the important factors to affect the anaerobic digestion process. The results of 2012 showed that both feed sludge characteristics(especially volatile fatty acids and solid concentration of primary sludge) and anaerobic digestion temperature had significant positive correlation with gas production efficiency. Therefore, improving sludge properties and rising the digestion temperature were proposed as t he priorities for optimizing operation.Thirdly, laboratory experiments of controlling digestion temperature and thermal hydrolysis pretreatment were conducted to find the feasible operation conditions to enhance the methane producing. Results showed the b iogas production efficiency and organic matter removal rate were increased for primary settled sludge at 40 ℃ than those at 35 ℃. Thermal hydrolysis pretreatment was found useful for enhancing activated sludge anaerobic digestion for excessive sludge, but less effective for primary sludge. The experimental data was well interpreted by Bio WIN process simulation of whole plant models.Finally, a full scale operation by extending sludge retention time in primary sedimentation tank and increasing digestion temp erature from 35℃ to 40℃ was conducted and evaluated in 2013. Results proved that the VFA on inlet sludge was 24% more than that of 2012. And the biogas production could be greatly enhanced by improving sludge properties and rising digestion temperature. The biogas production rate in 2013 was 1.06m3/kgVS, which was 1.89 times more than that of 2012. And the economic benefits of WWTP in 2013 was 596.5 thousand Yuan more than that of 2012.This paper applied the systematic methodology to optimize the biogas production in Xiaohongmen WWTP, including process analysis, lab oratory experiments, process simulation and full scale operation. The methods and results in this study could be good reference for operators in WWTPs. |
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