Design of a constructed wetland prototype for nitrate removal

Abstract

Constructed wetlands have become a recognized alternative to conventional wastewater treatment for low strength effluents. Nitrate is one of the major contaminants considered for removal from wastewater using constructed wetlands. The purpose of this project was to examine the use of constructed wetlands to remove nitrates, through the design of a wetland prototype. The main objectives of the study were to: 1) Research the feasibility of constructed wetlands, 2) Design a constructed wetland prototype, 3) Build and operate the prototype, and 4) Introduce nitrate to the flow and examine the nitrate removal rates over time. Constructed wetlands were found to be feasible for the treatment of low concentration effluents, based on previous research in this area and the results received from the prototype. The prototype tank was constructed of plywood which was fibreglassed, and silicon sealed. It measured 1.83 m by 0.7 m by 0.5 m and contained silica sand to a depth of 0.027 m, between two meshed and filtered slots for water infiltration. The prototype was housed in the Biology Department's greenhouse complex, where ample light and heat could be provided for cattail growth. Cattails were planted in the silica sand at low densities in comparison to natural conditions. Once the prototype set-up was operational, nitrate addition was monitored for 20 days. The removal rate for nitrate, based on a one week retention time was approximately 75% to 100%. This is a significant removal rate for a low plant density wetland. Denitrification was assumed to be the main removal mechanism, based on findings in the literature reviewed and low plant densities present in the wetland.