Experimental Study On The N And P Removal From Secondary Effluent And Resource Recovery By Settleable Microalgae

Water resource has always been taking for granted and overlooked by human beings for a long time.The scarcity of water resource is getting more and more significant and is hard to reverse this situation,which highlights the indispensable role of water for human beings.To protect the shrinking water stock,advanced treatment of wastewater to protect the aquatic environment is a must.However,the conventional paradigm of wastewater treatment is a process of"pollution transfer"with"high energy consumption".In another word,the acceptable water quality is obtained at the sacrifice of air pollution.Thus,it is necessary to shift the wastewater treatment to resource recovery to offset the adverse environmental impact.The present study aimed to achieve simultaneous removal of nitrogen and phosphorus by settleable microalgae as well as obtain high value-added products,which is expected to alter the environmental impact from conventional wastewater treatment.Firstly,microscopic classification and identification of settleable microalgae were carried out,providing a theoretical research basis for the following study.More than ten species of green algae were observed in the reactors.The ratio of different algae in the reactor was not significantly correlated with the treatment efficiency.Then,the growth condition(biomass,algal pigment),the change of sedimentation efficiency of the settleable microalgae,and the water quality under the outdoor light level were studied.High light intensity(800?mol/(m~2·s))can induce severe photoinhibition on the settleable microalgae.However,settleable microalgae was suitable for advanced wastewater treatment after adaptation.The removal efficiencies of phosphate and nitrate were nearly 90%or more,which could further remove N and P from secondary effluent.Finally,for the purpose of valorization of microalgae this present study analyzed the resource recovery in terms of lipid and PHB(poly-?-hydroxybutyrate)from settleable microalgae.The traditional strategy promoting lipid accumulation had no obvious effect on settleable microalgae.However,it did stimulate a small number of microalgae although the overall performance was poor.An addition of 8 mg/L sodium acetate in the cyanobacteria dominant group,the maximum PHB increased by about 6 times during the culture process and reached to 30.16%(dcw,dry cell weight).