A treatment wetland was constructed as part of a waste management system for dairy parlour waters and the performance of the wetland in reducing organic matter and nutrients monitored for a two-year period. The wetland was designed 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 were wide fluctuations due to rainfall and water use within the dairy. Average mass loadings to the wetland were 5.6 g/m2/d for Biochemical Oxygen Demand, 2.6 g/m2/d for Organic Nitrogen, 3.2 g/m2/d for Ammonia and 1.5 g/m2/d for Total Phosphorus.
Monitoring results from the system indicated that significant BOD reductions were achieved, while Nitrogen and Phosphorus removals were variable but smaller. Calculated mean monthly pollutant reductions due to the treatment wetland 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 not appear to be suitable as a treatment option for significantly reducing nutrients in this type of agricultural waste.