Research On The Substrates Performance For Constructed Wetland Wastewater Treatment System

In this paper,haydite,carbonized rice husk,oyster shell and vermiculite were researched as the substrates for constructed wetland through the research system of micro-features, chemical compositions,static adsorption properties,dynamic processing effects and price.From the four substrates photographs of SEM,it can be discovered that haydite has porous structure with a wide range of aperture,carbonized rice husk and vermiculite has layered structure,oyster shell has clay structure.From the chemical composition analysis,it can be discovered that haydite and vermiculite contains Al,Ca,Fe,and oyster shell contains a large number of Ca.From the results of static adsorption experiments,three conclusions can be made.Firstly, haydite,oyster shell and vermiculite were more obvious for phosphorus adsorption.But carbonized rice husk almost had no adsorption for phosphorus.Secondly,Carbonized rice husk and vermiculite were more obvious for NH₄⁺-N adsorption.But haydite and oyster shell almost has no adsorption for NH₄⁺-N.At last haydite,oyster shell,vermiculite and carbonized rice husk were all obvious for organics adsorption.Under intermittent operation condition(retention time 48h:aerobic 24h,anaerobic 24h alternatively conducted) haydite,oyster shell and carbonized rice husk all had the average removal rate of TP more than 75%when the influent was simulated wastewater.They also had the average removal rate of TN more than 80%,and the average removal rate of NH₄⁺-N and COD more than 95%.With the influent changing from simulated wastewater to domestic sewage,the three substrates average removal rate of TP was as follows:hadite> oyster shell> carbonized rice husk.The three substrates average removal rate of TN was as follows:carbonized rice husk> haydite> oyster shell.With the increasing organic load of influent,the three substrates removal rate for TN was all significantly increased.The three substrates average removal rate of NH₄⁺-N and COD were still able to maintain more than 90%.Under continuous operation condition(retention time 24h,aerobic processing mode) the three substrates average removal rate of TP was as follows:haydite> oyster shell> carbonized rice husk when the influent organic load was low.And this sequence was according to the intermittent operation.The three substrates average removal rate of TN was as follows:oyster shell> carbonized rice husk> haydite.The three substrates average removal rate of NH₄⁺-N were all more than 99%.Their average removal rate of COD was as follows:carbonized rice husk> oyster shell> haydite.This sequence was according to the intermittent operation.After all,compared with the intermittent operation,the substrates removal capacities of TP,TN and COD were all obviously decreased under the continuous operation.Above all,haydite and oyster shell had high removal rate of TP,so they could be used as the constructed wetland substrates to treat the phosphorus-containing wastewater.Carbonized rice husk and haydite had high removal rate of TN and NH₄⁺-N,so they can be used as the constructed wetland substrates to treat the nitrogen-containing wastewater.