On-farm treatment of dairy soiled water using aerobic woodchip filters

Dairy soiled water (DSW) is produced on dairy farms through the washing-down of milking parlours and holding areas, and is generally applied to land. However, there is a risk of nutrient loss to surface and ground waters from land application. The aim of this study was to use aerobic woodchip filters to remove organic matter, suspended solids (SS) and nutrients from DSW. This novel treatment method would allow the re-use of the final effluent from the woodchip filters to wash down yards, thereby reducing water usage and environmental risks associated with land spreading. Three replicate 100 m² farm-scale woodchip filters, each 1 m deep, were constructed and operated to treat DSW from 300 cows over an 11-month study duration. The filters were loaded at a hydraulic loading rate of 30 L m⁻² d⁻¹, applied in four doses through a network of pipes on the filter surface. Average influent concentrations of chemical oxygen demand (COD), SS and total nitrogen (TN) of 5750 ± 1441 mg L⁻¹, 602 ± 303 mg L⁻¹ and 357 ± 100 mg L⁻¹, respectively, were reduced by 66, 86 and 57% in the filters. Effluent nutrient concentrations remained relatively stable over the study period, indicating the effectiveness of the filter despite increasing and/or fluctuating influent concentrations. Woodchip filters are a low cost, minimal maintenance treatment system, using a renewable resource that can be easily integrated into existing farm infrastructure.