Research On Substrates Selection For Constructed Wetlands

In this paper, a vertical-flow constructed wetlands (VFCWs) system wasestablished to find the best substrates of constructed wetlands for saline waste sewagetreatment. The physical and chemical characters of the substrates, the effects on themunicipal wastewater treatment before and after inoculation, and the effects on thesaline sewage treatment were investigated in this evaluation process.New type substrate, Bio-ceramic, quartz sand, zeolite and medical stone wereused as filtering media for saline sewage treatment. By one hand, the mid-heavenstructure of new type substrate and the higher porosity of sintered clay filtered in thissubstrate contributed to more microorganisms living in it and higher removalefficiency of pollutants. By the other hand, because of larger amounts of Mg, Ca, Fe,Al and Si in the new type substrate, larger amounts of phosphate anion andammonium radical anion could be absorbed on the surface of the substrate.From the result of the treatment to municipal wastewater with differentsubstrates, two conclusions could be made. Firstly, new type substrate and zeolitecould absorb more ammonium radical anion, but Bio-ceramic, quartz san could absorbmore phosphate anion. Secondly, in end of the experiment, large amounts ofphosphate anion were desorbed; therefore, the substrates should be replaced in certaintime.After inoculation, these five-type substrates were used to treat the municipalwastewater, in order to survey their ability of biofilm formation. New type substrateused the shortest time to form the biofilm and its removal efficiency of pollutants ishigher than other four-type substrates.In order to find the most suitable filter for the coastal region, five-type substrateswere used to treat the saline sewage. Removal efficiency of TN was obtained about50%respectively with new type substrate, but removal efficiency of TN was obtainedabout only from30%to40%with other type substrates.Model with first order kinetics and CSTR as well as model with Monod kineticsand CSTR were constructed to fit the experiment data. As a result, model with firstorder kinetics and CSTR is more suitable for this VFCWs system. In sum, the new type substrate was the best filter for the saline sewage treatment,and the model with first order kinetics and CSTR could fit the experiment data.