Study On Biological Ecological Coupling System Based On Microalgae Culture And Constructed Wetland To Enhance Wastewater Nitrogen And Phosphorus Removal

Vigorously developing advanced sewage treatment and reuse technology is an important way to alleviate the shortage of water resources and prevent water pollution.Nitrogen and phosphorus assimilation technology based on microalgae culture and constructed wetland technology are typical biological ecological sewage deep purification technology.Coupling the two technologies can not only achieve efficient removal of nitrogen and phosphorus pollutants,but also have high resource potential.In this study,the two combination modes of constructed wetland microalgae culture coupling system and microalgae culture constructed wetland coupling system were explored,the purification effect and resource level of pollutants by the two coupling systems were evaluated,and the scheme of transferring part of microalgae biomass produced in microalgae treatment technology and adding it to the denitrification section of constructed wetland to strengthen the denitrification capacity of the system was put forward.Through FISH,qPCR,high-throughput and other means,From the perspective of microorganism,the mechanism of algae powder addition on enhancing nitrogen and phosphorus removal in constructed wetland was revealed.The main conclusions of this study are as follows:(1)In the effluent of constructed wetland microalgae culture coupling system,the removal rates of TN and TP can reach 40%-78%and 77%-85%respectively,and the microalgae accumulation efficiency of about 7.84×103 mg/m3/d can be realized.Compared with the treatment of constructed wetland alone,the coupling system significantly improves the removal effect of TP(p<0.05).The poor denitrification in the constructed wetland section of the coupling process is the reason for the high TN in the effluent of the system.For microalgae culture section,higher phosphorus concentration(TP:1.5-3.0 mg/L)is more conducive to the accumulation of microalgae biomass;The culture mode affects the accumulation of microalgae biomass and the maximum light energy conversion efficiency.The suspension attachment mixed culture with low carrier addition density(0.25 g/L)is more conducive to the accumulation of microalgae biomass than single suspension or attachment culture.When the carrier density of suspension attachment mixed culture mode is set too high,the growth of microalgae will be inhibited due to the obstruction of light propagation.Compared with suspended microalgae,attached microalgae have higher maximum light energy conversion efficiency.(2)n the microalgae culture constructed wetland coupling system,when the HRT of microalgae treatment section is set to 3 d and 5 d,the removal rates of TN and TP are 40.9±3.4%and 48.8±2.0%respectively,75.7±5.7%and 86.3±3.0%respectively,which can realize the microalgae biomass accumulation efficiency of 4.3 ×10-2 mg/mL/d and 3.7× 10-2 mg/mL/d respectively.By analyzing the resource utilization of the system,it is found that the resource conversion rate of phosphorus(25.34%,44.54%)is significantly higher than that of nitrogen(13.72%,24.13%),and the change of HRT has little effect on the resource efficiency of carbon,nitrogen and phosphorus.Comparing the two combinations of constructed wetland and microalgae culture coupling system,it is found that the water quality treatment effects of them are similar,but the microalgae treatment technology in microalgae culture constructed wetland coupling system has higher influent nutrient concentration,better microalgae growth and higher biomass accumulation efficiency,that is,higher resource conversion rate.It is a better choice for the biological ecological coupling system based on microalgae culture and constructed wetland.(3)Aiming at the improvement of microalgae culture constructed wetland coupling system,the problem of low TN removal rate caused by insufficient carbon source in constructed wetland is identified.It is proposed to add some microalgae produced by microalgae treatment system to the denitrification section of constructed wetland,which significantly improves the TN removal capacity of wetland(p<0.05).When the addition amount of algae powder is less than 1 g,the fluctuation of effluent quality is small,which is a more appropriate addition amount of algae powder.Under this addition amount,the effluent TN can be maintained at 7-12 mg/L during the stable period of water quality,and the maximum removal rate of the system can reach 94.42±3.61%.Through the microbial analysis of the constructed wetland,it is found that when the influent pollutant load is higher and the anaerobic environment at the addition position of algae powder is more sufficient,the number and diversity of microorganisms in the wetland are more abundant.The abundance of Proteobacteria,a key horizontal strain that can realize the efficient transformation of carbon and nitrogen substances,increased from 25.90%to 29.87%,indicating that adding algae powder in a more sufficient anaerobic environment is more conducive to the denitrification of constructed wetland.From an economic point of view,the water quality treatment effect of microalgae culture constructed wetland coupling system is similar under the two settings of HRT in microalgae culture section,but the setting of HRT for 3 d has better water purification efficiency and can save construction and operation costs.