Ultrsonic Enhanced The Lipid Synthesis Of Microalgae By Using Primary Settling Tank Effluent

Water is the resource that people live on.Our country is lack of water,so it is imminent to search for a green,efficient purification of sewage.As the third generation of a source of raw materials for biodiesel,microalgae have many irreplaceable advantages.For example,they can survive in harsh environments,decompose organic matter in the effluent,remove nitrogen and phosphorus,complete the accumulation of lipid at the same time.The high culture cost restricts the development of microalgae biodiesel,studies have shown that the conversion rate of biodiesel preparation could be improved in a short time by means of low-intensity ultrasonic wave.In this study,we used the domestic sewage to culture microalgae to produce lipid,increased the production of lipid with ultrasonic wave,and established the method of combining waste water resources and microalgae culture to produce biomass energy.In this study,the primary and secondary effluent were used seperately to culture the microalgae Z-4 in order to investigate the feasibility of culturing microalgae in wastewater.Simultaneously,the effects of different pretreatment methods(raw,centrifugal,filter wastewater)on the cultivation were explored.It is concluded that the raw primary tank effluent is the most suitable medium for the growth and lipid production of microalgae Z-4.The biomass and the lipid yield of microalgae Z-4 in the primary tank effluent medium reached 0.68 g / L and 0.16 g/L respectively.The COD,TN and TP of the culture medium were reduced from the initial values of 150 mg/L,50 mg/L and 6 mg/L to 30 mg/L,10 mg/L and 0.5 mg/L,respectively.After that the BG-11 medium was cosidered as reference to optimize the concentration of nutrient,and the optimal concetration of Na NO3 and K2HPO4 was 0.4 g/L and 0.02 g/L respectively.Compared with unoptimized primaty tank effluent medium,the biomass and the lipid yield of micralgae Z-4 reached 1.4 g/L and 0.19 g/L,which was increased by 105% and 18% respectively in the optimal me dium.Ultrasonic wave has less influence on the quality of the effluent of the reactors.Then the ultrasonic strengthening apparatus were combined with photobioreactor to culture microalgae Z-4 in this study.The reactors were designed and assembled,and the microalgae culture was enhanced by ultrasonic device.The optimal ultrasonic parameters were determined to be 18 k Hz and 20 W for 10 min in logarithmic growth phase of the microalgae Z-4 in the reactor.Under the condition of optimal medium and ultrasonic parameters,the biomass and the lipid yield of microalgae Z-4 were improved to 1.56 g/L and 0.24 g/L,which was increased by 11% and 26% respectively compared with controlled group.In order to have a further exploration of the mechanism of ultrasonic enhancement,the high-throughput sequencing of the system in the reactor before and afer the ultrasonic wave was used as analyzed method in this study.The results showed that ultrasonic wave could promote the stability of the community in the wastewater system and accelerated the microalgae Z-4 to become the dominant population.To a certain extent,ultrasonic wave might promote the expression of functional ralated to the lipid transport and metabolism in microalgae cells.