Study On The Effect Of Constructed Wetland Substrates Composite On Nitrogen And Phosphorus Removal In Reclaimed Water

At present,China's water resources are scarce and per capita is low.With the development of society,the situation of water environment pollution will become more severe.The development and utilization of traditional water resources can no longer meet the water requirements of production and living.Regardless of whether it is from the perspective of ecological benefits or sustainability,reclaimed water is the best alternative to water sources.By using constructed wetland technology to treat the reclaimed water to meet the corresponding water requirements.Aiming at the problem of excessively high nitrogen and phosphorus content in the reclaimed water,this paper combined the composition and structure of the substrate to conduct static adsorption and release experiments.The characteristics of the adsorption and release of N and P by each substrate were studied.Through the combination of substrate,a dynamic adsorption experiment was carried out to simulate the change of each key water quality parameter under different influent concentration and hydraulic load conditions.By using high-throughput sequencing technique of molecular biology,the characteristics of biological diversity under different substrate combinations were described,and a systematic scheme for deep removal of N and P was formed.The results of static adsorption showed that Freundlich equation and Langmuir equation better described the adsorption features of the substrate on TP and NH₄⁺-N.Through the parameter fitting,the theoretical saturation adsorption capacity of vermiculite,limestone and volcanic rock on TP were 0.40mg/g,0.36 mg/g and 0.17 mg/g,respectively;The theoretical saturation adsorption capacity of vermiculite,zeolite and volcanic rock for NH₄⁺-N were 0.40 mg/g,0.24 mg/g and 0.12 mg/g,respectively.Dynamic fitting and static adsorption were basically consistent.The physical properties of the substrate showed that the permeability was positively correlated with pore structure and particle size.Volcanic rock has a high permeability coefficient of 60.07 cm/s.Simulated dynamic adsorption experiments were carried out on different configurations of substrate.The results showed that the combined substrate had better purification effect than the single substrate,and the volcanic rock-limestone combined had a good removal effect on each pollutant.The removal rates of TP,COD,NH₄⁺-N,NO₃-N and TN were 35.7%,68.5%,82.5%,80.0%and 85.3%,respectively.A further pilot test of the volcanic rock-limestone showed that when the hydraulic load was 0.25 m/d,the pollutant outflow of the system was relatively stable.At the influent concentration A,a group of canna,cattail,and reed planted on each key the removal effect was slightly better.When it was further reduced to concentration B,the average removal rates of effluent COD,NH₄⁺-N,TP,NO₃-N and TN were 75.9%,93.4%,57.6%,79.9%and 84.1%,respectively.The TP effluent concentration was controlled at 0.19 m/L,and the NH₄⁺-N effluent concentration was about 0.8 mg/L.The volcanic rocks were modified by Mg Al-LDHs.Compared with the original volcanic rocks,the result showed that the surface area of the modified volcanic rocks increased,and the TP adsorption capacity increased from 0.0630 mg/g to 0.0854 mg/g.the adsorption rate increased from 0.99 to 1.40.The adsorption amount of NH₄⁺-N increased from 0.0926 mg/g to 0.1255 mg/g,and the adsorption rate increased from 0.72 to 2.32.Dynamic experiments showed that the average removal rate of TP increased from 32.5%to 49.2%;The average removal rate of ammonia nitrogen by modified volcanic rock has been improved to a certain extent.