THE DESIGN AND PERFORMANCE OF A VERTICAL FLOW REED BED FOR THE TREATMENT OF HIGH AMMONIA, LOW SUSPENDED-SOLIDS ORGANIC EFFLUENTS

A design approach for vertical flow constructed wetlands based on sele ction of not only bed size, but also substrate characteristics, config uration, plant species/variety and management is piloted in a trial sy stem to treat sugar beet processing wastes. In the beer processing sea son these wastes are hot, low in suspended solids and relatively high in ammoniacal nitrogen. The pilot system consists of a small, coarse s ubstrate first stage followed by a larger, fine substrate second stage . Results in the beer processing season show 87.3% COD removal, 87.7% TSS removal and a 79.5% reduction in ammoniacal nitrogen. Treating lar ger volumes of cooler stored wastes out of season, the mean removal ef ficiencies were 73.9% for COD, 88.0% for TSS and 93.4% for ammoniacal nitrogen. TSS removal m(-2) was found to be independent of influent co ncentration and temperature, whilst COD removal m(-2) was found to be independent of temperature, but not influent concentration. Removal of ammoniacal nitrogen appeared to be dependent upon influent concentrat ion and, in particular, upon temperature. Infiltration rates were show n to be negatively correlated to length of dosing cycle. Simple models of substrate permeability based on substrate particle size distributi on are seen to be inadequate for describing infiltration rates in vert ical downflow systems, even those treating low strength wastes. (C) 19 97 IAWQ. Published by Elsevier Science Ltd.