Studies on the Phosphorus Sorption Capacity of Substrates Used in Constructed Wetlands

Substrate is the most vital component in the constructed wetland, playing an important role in the purification of sewage especially phosphorus removal. And the cost of a constructed wetland depends mainly on the substrates filled within it. In this study, we selected six substrates: slag, ashes, honeycomb slag, waste slag cement, gravel and oyster shells as the substrates to study their phosphorus adsorption properties. The static adsorption results indicated: six wetland substrates of the phosphorus adsorption processes all can be described by the Freundlich and Langmuir equation, where the waste slag cement had the best adsorption effect among them, and the adsorption effect order of the others was as follows: Slag > honeycomb cinder > ashes > oyster shell > gravel. The order of the theoretical saturated adsorption value was as follows: waste slag cement > slag > ashes = oyster shell > gravel> honeycomb cinder. Dynamic adsorption results showed that: the waste slag cement had high phosphorus removal ability, it´s average removal rate was above 98%, followed by the slag, honeycomb cinder, oyster shell, ash. Gravel had the minimum removal rate.This suggests that more attention should be paid to chemical composition during the selection and assembly of substrates for both constructed wetland study and its engineering application.