| After researching examines the physico-chemical properties of zeolite and steel slag,the constructed wetland system consists of a vertical downflow reactor in where quartz sand zeolite and steel slag were layered?a vertical upflow reactor in where quartz sand zeolite and steel slag were layered and a horizontal flow reactor in where steel slag and zeolite are filled to study the performance of the system for deep treatment of domestic sewage.TP,TN,ammonia nitrogen and COD is considered to be the main evaluation indexes of constructed wetland system;In two different operating modes including planting plants and non-planting plants,each mode including five different working conditions(0.092m~3/(m~2·d)?0.138m~3/(m~2·d)?0.184m~3/(m~2·d)?0.270m~3/(m~2·d)?0.553m~3/(m~2·d)),the combined constructed wetland system obtains the optimal operation mode,and the optimal treatment load of nitrogen and phosphorus pollutants was proposed.The following conclusions are drawn from this experimental study:?The isothermal adsorption process of zeolite adsorbing ammonia nitrogen conform to the Freundlish isothermal adsorption equation,maximum adsorption for0.41mg/g.The isothermal adsorption process of steel slag adsorbing phosphorus,maximum adsorption for 0.56mg/g.?The optimal mode and working condition of the combined constructed wetland for the deep treatment of domestic sewage are:planting plant mode,the hydraulic load of 0.138 m~3/(m~2·d),in where the removal rates of TP,TN,ammonia nitrogen and COD are respectively 90.07%,58.89%,99.8%and 56.38%.?The removal rate of total phosphorus in the constructed wetland was between87.12%and 95.57%,and the average effluent TP concentration was 0.07mg/L.The removal of total phosphorus is mainly concentrated in the steel slag layer of vertical flow constructed wetland.?The removal rate of total nitrogen in the planted wetland was 2.9 times higher than that in the unplanted wetland.The removal of total nitrogen in the constructed wetland was mainly concentrated in the vertical flow constructed wetland.In the model of planting plants,the removal effect of combined constructed wetlands on total nitrogen is mainly concentrated in the zeolite layer.Regardless of planting or not,the removal tendency of total nitrogen in vertical flow constructed wetland increased first and then decreased.?The removal rate of ammonia nitrogen in the combined constructed wetland was basically maintained above 80%,and the removal rate of ammonia nitrogen in the planting plant mode could be maintained above 99%stably.Under the working conditions of 0.092 m~3/(m~2·d),0.134 m~3/(m~2·d)and 0.184 m~3/(m~2·d),vertical flow constructed wetlands play the major role in ammonia nitrogen removal.Under the working conditions of 0.27 m~3/(m~2·d)and 0.553 m~3/(m~2·d),the constructed wetlands with horizontal flow and vertical flow work together to remove ammonia nitrogen.The removal of ammonia nitrogen is mainly concentrated in the quartz sand layer and zeolite layer in the vertical downflow reactor,and with the gradual increase of hydraulic load,the contribution of ammonia nitrogen removal increases.?The combined artificial wetland was stable in COD removal,and the removal of COD was mainly concentrated in the quartz sand layer and zeolite layer in the vertical downflow reactor;Plants improve the stability of COD removal in each part of the system and increase the impact resistance of the system.?In the constructed wetland system,the nitrogen and phosphorus contents in the mature reed were 25.4mgN/g and 2.93mgP/g,respectively;The nitrogen and phosphorus contents in the mature cynosure were 19.5 mgN/g and 2.36 mgP/g,respectively.?In the working condition of hydraulic load of 0.039 m~3/(m~2·d),the amount of TP into the artificial wetland and plant absorption amount of TP are in balance,and TN concentration in effluent reaches class A in the discharge standard of pollutant for municipal wastewater treatment plant. |
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