The treatment of run-off from a fertiliser plant for nitrification, denitrification and phosphorus removal by use of constructed wetlands: a demonstration study

摘要

The paper describes an evaluation carried out on demonstration scale to show that it wasnpossible to use a Hybrid Reed Bed System comprising a Horizontal flow and a Vertical Flow Bednfor treating the high strength run-off from a fertiliser packaging plant. The site is located closento an estuary which is sensitive to nutrients. The environmental regulators were thereforenconcerned that excessive mass flows of nitrate, ammoniacal nitrogen and phosphate, potentiallynarising from the site run-off, were not discharged into the estuary. The fertiliser manufacturingncompany required a simple, low maintenance system for removing nitrogen and phosphorus.nA series of experimental runs were carried out to characterise the performance of the HybridnSystem, establishing the effluent quality that could be achieved and the mass removal ratenwhich was appropriate for acceptable treatment. These tests showed that it was possiblento achieve a reduction of 79% in Total N whilst using molasses as a carbon source forndenitrification. When using a 4:1 recycle ratio this produced an effluent with concentrationsnof 14mgNH4-N/litre and 18mgNO3-N/litre from treating site run-off containing concentrationsnin the order of 75mg/litre of both NH3N and NO3-N. Chemical dosing with an iron salt broughtnthe P concentration down to around 0.5mg PO4-P/litre.