| In recent years,the phenomenon that the concentration of nitrogen and phosphorus in the secondary effluent of wastewater plants is higher than the eutrophication threshold of water bodies has attracted wide attention.However,the traditional advanced wastewater treatment methods have disadvantages such as high energy consumption,high carbon emission and pollution transfer.Therefore,sustainable advanced treatment technologies urgently need to be developed.Microalgae have high photosynthetic efficiency and can efficiently absorb pollutants such as nitrogen and phosphorus in wastewater.And microalgae biomass can be used in the production of bioenergy and high value-added products.The application of microalgae in advanced wastewater treatment is of great practical significance and commercial prospect.However,Low-cost biomass harvesting and stable nitrification and phosphorus removal are the bottleneck problems that need to be broken through in the development of microalgae-based wastewater treatment technology.Focusing on these two bottleneck problems,this paper obtained the settleable microalgae with rapid sedimentation potential from municipal wastewater through purification and "wash-out" experiments.On this basis,the growth performance,sedimentation effect and nitrogen and phosphorus removal ablility of experimental algae were compared.The target algae with outstanding comprehensive performance were obtained,and the conditions for nitrogen and phosphorus removal were optimized.Outdoor validation test and economic analysis were carried out under optimized conditions.The feasibility and resource utilization potential of settleable microalgae for advanced wastewater treatment were preliminarily revealed.Four filamentous microalgae were isolated and algae No.1 and No.10 with outstanding comprehensive performance were selected as the target algae.The sedimentation rates of algae No.1 and No.10 at 10 min were 96.18% and 97.56%,respectively,and removal rates of TN were 93.98% and 89.00%,respectively.The removal rates of TP were 96.51% and 96.25%,respectively.The two algae were clumped,and the sizes were about 1 ～ 4 mm and 2 ～ 18 mm,respectively.They mainly rely on gravity to settle quickly.Algae No.1 was Nostoc sp.,and algae No.10 belonged to Pseudanabaenaceae.The multi-factor optimization results of the nitrogen and phosphorus removal conditions of the target algae showed that algae No.10 had more potential for industrial application than algae No.1.The optimal conditions for algae No.10 were as follows: the concentration of algae was 1.64 g/L,and the light intensity was 13254 Lux,and the aeration intensity was 2.03 L/min.At this condition,the TN removal rate was 96.85% and the hydraulic retention time of algae No.10 can be reduced to 9 h.The removal of TN in the system mainly depended on biological assimilation,with a proportion of 89.22 ～ 94.99%.The removal of TP relied on biological adsorption and assimilation.The outdoor experiment of algae No.10 under optimized conditions further verified its potential for advanced wastewater treatment.Within 9 h,the concentrations of NH3-N,TN and TP in the secondary effluent decreased to 0.31mg/L,9.96 mg/L and 0.03 mg/L,respectively.And the sedimentation rate in 10 min was 97.19%.The protein,polysaccharide and oil content of algae No.10 cells were 22.65%,30.27% and 9.32%,respectively.Fatty acids of microalgae were mainly composed of C16 and C18.The cost of wastewater treatment by settleable microalgae is lower and the settleable microalgae can be harvested at no cost.It has technical and economic feasibility to use settleable microalgae for the coupling process of municipal wastewater advanced treatment and microalgae resource utilization. |
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