Excess Sludge To Improve Microbial Lipids And Sludge Reduction By Bio-Transformation

Sewage sludge is natruly produced during wastewater treatment.The large quantity sludge production required proper management.Under the concept of sustainable development,sludge management should foucs on the conversion of sludge to value-added product production.Sludge mianly contains organic and inorganic matters,microorganisms.Lipid is an energy source of microorganism;hence sludge contains some portion of lipid.It was found that the lipids could be used as raw material for biodiesel production.The organic matters in the sludge are great source for microorganism growth.The current problem is that the method of resource recycling from sewage sludge is limited.Utilization of sewage sludge for production of microbial lipids,which can be further transferred to biodiesel,provides an option for sustainable utilization of sludge.In this study,the microorganism and organic matter in the sewage sludge was utilized in different ways to increase the content of lipids in the sludge,and to evaluate the effects of different pathways on sludge reduction and resource utilization.The lipids content in the sludge collected directly from wastewater treatment plant was only 6% to 8%(w/w dry sludge).In order to improve the lipids content of sludge,different carbon sources including glucose and food waste were employed to cultivate sludge.The study showed that in the case of glucose as the carbon source,the lipids content in the sludge increased with the increase of C/N ratio.When the C/N ratio was 70,the lipids content in the sludge was up to 33.34%(w/w),which was 3.2 times of the initial lipids content.Taking the food waste pretreated with mechanical crushing and microwave as the carbon source,the sludge lipids content was up to 13.95%(w/w).In fact,there are substances in the sludge that are difficult to be utilized by microorganisms.To improve the biodegradability of sludge,acidoc,alkaline,microwave,and ultrasonic pretreatment on sludge were performed prior to fermentation.Thereafter,the sludge was inoculated with L.starkeyi.The study showed that the maximum lipids contents obtained were 13.49,18.04,14.31 and 36.67%(w/w)with acid,alkali,microwave and ultrasonic pretreated sludge,respectively.Ultrasonic pretreatment on sludge provided the best results for lipids accumulation on L.starkeyi.The C/N ratio of raw sludge(5:1~8:1)is low.In order to supplement the shortage of carbon source in the sludge,the feasibility of producing microbial lipids by using the food waste as an external carbon source to enrich the ultrasonic pretreatment sludge for cultivating the L.starkeyiwas was explored.The study showed that the sludge lipid content was up to 23.68%(w/w)under the condition of addition of NaHCO3 to control pH.It indicates that the food waste is not a suitable carbon source L.starkeyi to accumulate lipid.The main components of biodiesel prepared by transesterification were palmitic acid(C16:0),stearic acid(C18:0),oleic acid(C18:1),and linoleic acid(C18:2).According to the experiment results,the sludge reduction performances of the different ways of using sludge to produce microbial lipids were evaluated.The results showed that the sludge treated with ultrasonication as a nutrient to clutivate L.starkeyi provided the maxiumun microbial lipid production,which was up to 36.37%(w/w),and the sludge reduction reached 40%.After microbial lipids extraction,the sludge reduction was even up to 62%.It suggests that sludge has the potential to be used as biodiesel production source.