Pilot Constructed Treatment Wetland and Natural Media Filter

A Natural Media Filter (NMF) and Constructed Treatment Wetland (CTW) pilot study was performed on an industrial landfill leachate site. The pilot study was designed to test if a NMF and CTW could be a low cost replacement option for the current wastewater treatment system. The main contaminates of concern for the leachate were poly-chlorinated biphenyls (PCBs) and ammonia.

The pilot unit consisted of two systems, a subsurface flow CTW and an up-flow NMF that utilize mushroom compost as a media. The two units were run in parallel and were both supplied with untreated leachate. The CTW was operated at a flow rate of 0.3 gpm with a 2.2 day retention time. The goal of the study was to operate the NMF at 0.2 gpm with a half-day retention time, but due to operational issues this flow rate varied throughout the study. The Influent concentration of ammonia varied from non-detectable to 17 mg/l as nitrogen, with effluent concentration from the CTW fluctuating from non-detectable to 16 mg/l. For PCBs, influent concentrations during the majority of the study were non detectable, but during the last few months of the study large spikes in PCBs were recorded. The natural media filter was able to remove PCBs below limits of detection for most of the study, but breakthrough occurred towards the end of the study.

For the constructed treatment wetland, removal of ammonia and nitrate/nitrite were modeled using the both the Plug Flow Model and the Tank-in-Series Model. The CTW was considered to be a Plug Flow unit and was oxygen limited. For the Natural Media Filter, the data collected did not allow for a proper evaluation of the adsorption capacity of the unit. A PCB mass balance was performed on the NMF from data collected from core samples of the compost. The unit was successful in removing PCB loading nine times higher than its designed capacity and the failure of the unit is attributed to short circuiting caused by the unit freezing.