Basic Research On The Biodiesel Production From Dewatered Primary Sludge In Municipal Wastewater Plant

As the global energy is shortage and the increasingly environmental degradation,the human need to find an alternative renewable energy,especially biodiesel.However,the high cost of raw materials for the production of biodiesel is the main limiting factor for its large-scale production.Since the quantity of sludge from municipal sewage treatment plant is huge.And the sludge contains a certain amount of lipid that can be converted into biodiesel oil,it is a kind of potential raw materials for biodiesel production from sludge.However,the cost of using the dry sludge as raw materials for producing biodiesel is high at present.Therefore,this paper try to use dewatered sludge as raw materials for producing biodiesel,which not only has economic benefits but also has the environmental benefits.The dewatered primary sludge of Xi'an fifth wastewater treatment plant was used to extract lipid in this research.Based on optimizing the method of lipid extraction,different solid catalysts were used to catalyze the produce biodiesel and the optimum conditions were obtained.Later the optimum conditions for the production of biodiesel were compared with those of traditional in-situ acid catalysis from dry sludge.The life cycle of biodiesel was analyzed by means of life cycle assessment method to find out the main factors affecting the environmental condition for improving the production process further.The main conclusions are as follows:(1)The maximum lipid yield was 13.37% when the dewatered sludge was pretreated with sulphuric ac id and extracted with hexane under 50? for 8h.This lipid yield was more than three times of the yield without acidification pretreatment.(2)Through AlC l3�6H2O catalyzed the lipid extracted from dewatered primary sludge under the optimum conditions for the production of biodiesel was: the reaction temperature of 45 ?,the dosage of catalyst for 4%,the reaction time of 5h.According to the optimum conditions of the above,the maximum biodiesel yield of attained was 6.66% under ex-situ transesterification using AlC l3�6H2O catalyst from dewatered sludge.(3)Through lipase Novozym435 catalyzed the lipid extracted from dewatered primary sludge under the optimum conditions for the production of biodiesel was: the reaction temperature of 50?,the dosage of catalyst for 10%,the reaction time of 24 h.According to the optimum conditions of the above,the maximum biodiesel yield of attained was 4.76% under ex-situ transesterification using lipase Novozym435 catalyst from dewatered sludge.In addition,its type and percentage of fatty acid methyl esters in biodiesel were very similar of biodiesel production under ex-situ transesterification using AlC l3�6H2O catalyst from dewatered sludge and in-situ acid catalysis from dry sludge.(4)The Zn/Al composite was prepared by co-preparation method as the catalyst for producing biodiesel.The best preparation condition for Zn/Al catalyst with co-preparation method was: Zn/Al molar ratio of 2,calcination 3h at 500?.The optimum reaction conditions were as follows: methanol 125 ml,reaction temperature of 75 ?,the dosage of catalyst for 8%,reaction time of 4h,the highest yield of biodiesel was 4.90%.(5)The life cycle assessment method was used to evaluate the life cycle energy consumption and emissions of biodiesel from the four scenarios described in the paper.In the viewpoint of energy demand,the energy consumption in biodiesel production by ex-situ heterogeneous catalysis with AlC l3�6H2O from dewatered primary sludge,was no more than one third of the energy consumption for 1g biodiesel production by in-situ acid catalysis from dry sludge,and the global warming potential of life cycle was minimal.(6)According to the yield of the biodiesel and composition,the energy consumption and environmental emissions in three aspects of comprehensive consideration,it was an advantageous method to produce biodiesel by ex-situ heterogeneous catalysis from dewatered primary sludge when compared with in-situ acid catalysis from dry sludge.Thus AlC l3� 6H2 O as a catalyst to produce biodiesel from dewatered sludge was a better choice.