Study On Two-stage Process Consisting Growth With Lipid Production Of Scenedesmus Sp. Based On Anaerobic Digested Effluent Combing Municipal Wastewater

In view of high cost of microalgae cultivation and contradiction between biomass and lipid content,anaerobic digested effluent from cattle manure rich in nitrogen and phosphorus and municipal wastewater were applied in this work as a cost-effective microalgae culture medium,and the pretreatment of dilution was optimized.A two-stage process was then introduced into microalgae cultivation based on anaerobic digested effluent combing municipal wastewater to enhance microalgal biomass and lipid production by optimizing conditions of growth and lipid production independently.Time-course comparisons of growth,lipid production and nutrient removal efficiency were carried out between two-stage process based on anerobic digested effluent and single-stage process based on BG-11 medium finally.This study was expected to provide theoretical basis for microalgae lipid production and wastewater treatment.The results showed that Scenedesmus sp.L-1 had the potential of growth,lipid production and wastewater treatment in inactivated wastewater medium containing10%anerobic digested effluent from cattle manure with 90%secondary sedimentation tank effluent.Two-stage process based on wastewater medium could enhance the biomass and lipid yield of microalgae,as well as intracellular polysaccharide and protein production.The optimum conditions of growth culture were as following:glucose 10 g/L,NaNO₃ 0.3 g/L,K₂HPO₄·3H₂O 0.01 g/L,MgSO₄·7H₂O 0.075 g/L,A5 1 mL/L,with initial pH of 7.0 and light intensity of5000 lux.The biomass and lipid yield during 7-d cultivation reached 4.65 g/L and0.57 g/L,respectively.The removal efficiency of NH₄⁺-N,NO₃^--N,PO₄^3--P and COD in wastewater medium were 94.24%,98.11%,86.90%and 96.37%,and the residual concentrations were 4.42,1.24,0.035 and 344 mg/L,respectively.The optimum conditions for lipid production were as following:glucose 4 g/L,NaNO₃0.3 g/L,K₂HPO₄·3H₂O 0.01 g/L,citric acid 0.006 g/L with continuous light intensity of 2500 lux.The biomass concentration,lipid yield,intracellular polysaccharides and proteins yield were 4.84,0.925,0.11 and 0.028 g/L,respectively.The removal efficiency of NH₄⁺-N,NO₃^--N,PO₄^3--P and COD in wastewater medium were 96.50%,99.74%,51.78%and 94.23%,and the residual concentrations were 3.09,0.16,0.042 and 209 mg/L,respectively.In contrast to single-stage cultivation based on BG-11 medium,two-stage process based on anaerobic digested effluent combing municipal wastewater has the following characteristics:?1?There is no obvious lag period for microalgal growth in the growth medium based on anaerobic digested effluent.And the biomass,lipid content and lipid yield in the first stage are similar with those of BG-11 medium,indicating that the growth medium based on anaerobic digested effluent could replace for BG-11 medium.?2?The lipid yield of microalgae in lipid-production medium based on anaerobic digested effluent reached 0.98 g/L,which was 55.56%higher than that at the beginning of inoculation in the second stage.And the promoting of lipid yield was as a result to the both increase of biomass and lipid content.?3?Microalgae cultured by two-stage process based on anerobic digested effluent can obtain higher production of intracellular polysaccharide and protein,which has the potential for biorefinery.?4?Scenedesmus sp.performed excellent in nutrient removal efficiency during two-stage cultivation based on anaerobic digested effluent.Among them,Scenedesmus sp.mainly utilizes NH₄⁺-N,NO₃^--N and PO₄^3--P in anaerobic digested effluent combing secondary effluent for growth and metabolism.