Suitability of a treatment wetland for dairy wastewaters

A treatment wetland was constructed as part of a waste management system fo r dairy parlour waters and the performance of the wetland in reducing organ ic matter and nutrients monitored for a two-year period. The wetland was de signed for a herd size of 110 with a detention time Of approximately 10-14 days. Hydraulic loads to the wetland averaged 25 mm/day, although there wer e wide fluctuations due to rainfall and water use within the dairy. Average mass loadings to the wetland were 5.6 g/m(2)/d for Biochemical Oxygen Dema nd, 2.6 g/m(2)/d for Organic Nitrogen, 3.2 g/m(2)/d for Ammonia and 1.5 g/m (2)/d for Total Phosphorus. Monitoring results from the system indicated that significant BOD reduction s were achieved, while Nitrogen and Phosphorus removals were variable but s maller. Calculated mean monthly pollutant reductions due to the treatment w etland were 61% for BOD, 43% for Organic Nitrogen, 26% for NH3 and 28% for TP. The wetland received high hydraulic and pollutant loads and appeared to act as a sink for the nutrients which were removed. At this scale it did n ot appear to be suitable as a treatment option for significantly reducing n utrients in this type of agricultural waste. (C) 1999 IAWQ Published by Els evier Science Ltd. All rights reserved.