Introduction With the development of economy and industry, traditional fossil fuel is approaching depletion. This induces urgent demand of renewable energy like biodiesel. It has been proved that volatile fatty acids (VFAs) derived from organic wastes can be used by oleaginous microorganism to produce microbial lipids, which can be processed to biodiesel. Among organic wastes, municipal sludge is a fine option to produce VFAs by anaerobic fermentation due to its large quantity and high ratio of organics. Newly developed two-stage anaerobic fermentation, of which physical or chemical pretreatments are attached before fermentation, can obtain more biodegradable organics than the direct fermentation pattern. Based on this, two-stage anaerobic fermentation of sludge was adopted and the fermentation liquid was used to cultivate oleaginous yeast through different cultivation strategies. Results and Discussion Three kinds of physic-chemical pretreatment methods were compared, i.e. pyro-hydrolysis, thermal-alkaline (TAH) and ultrasonic treatment. Among them, TAH showed the best performance in terms of organics, VFAs yield and protein utilization ratio. Then TAH was used to pretreat different sources of sludge, including waste activated sludge, concentrated sludge and dewatered sludge. The derived VFAs concentrations varied from around 4 to 15 g/L. It was found that if linear VFAs corresponded to higher sludge concentrations were required to obtain, stronger TAH should provide. Substances composition especially the molecular weight of proteins was analyzed. High-throughput sequencing technology was applied to reveal the relative abundances and the structures of microbial community. Anaerobic fermentation liquids were then sterilized and used as the medium to cultivate Cryptococcus curvatus, a kind of oleaginous yeast. Batch cultivation and sequencing batch cultivation (SBC) were applied for different concentrations of VFAs. The highest lipid yield of 3.5 g/L was achieved from 15 g/L of VFAs cultivated by SBC. Based on the data, life cycle assessment was used to compare different strategies through resource consumption, acidification and eutrophication potential value, etc. Some improvement suggestions were offered specifically.

Bioconversion of anaerobic fermentation liquid of municipal sludge into microbial lipids by Cryptococcus curvatus using different cultivation strategies

255th National Meeting (2018)

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