Treatment of dairy soiled water using an aerobic woodchip filter and a sand filter

Abstract

The milking process produces dairy soiled water (DSW) that contains variable concentrations of nutrients. The most common method of disposal is by application to land. However, this practice can result in the pollution of nearby receiving water bodies. It is proposed that aerobic woodchip filters would decrease contaminant concentrations of nutrients in DSW. A laboratory-based experiment investigated woodchip as a filter medium to treat DSW. Subsequently, farm-scale filters investigated the system under normal farm conditions. The effectiveness of two types of sand filters (SFs), single-layer and stratified, were compared to treat effluent from the farm-scale woodchip filters. 0.5, 1, and 1.5 m-deep laboratory filters (n=3) containing Sitka Spruce (Picea sitchensis (Bong.) Carr.) treated DSW at two loading rates: 280 g suspended solids (SS) m-2 d-1 (S1) and 840 g SS m-2 d-1 (S2). Average chemical oxygen demand (COD), SS and total nitrogen (TN) decreases of 95, 99 and 88 %, respectively, were achieved and the effect of depth was negligible. Based on these findings, three replicated farm-scale 1 m-deep filters, each with a surface area of 100 m2, were constructed and loaded at 30 L m-2 d-1 for 11 months. Average decreases of 65, 84 and 60 % for COD, SS and TN, respectively, were achieved. Three replicated single-layer SFs and stratified SFs were operated for 82 days and loaded at 20 L m-2 d-1 with the effluent from the farm-scale filters. Average influent COD, SS and TN concentrations were decreased by an average of 39, 52 and 36 % for the single-layer SFs and 56, 62 and 57 % for the stratified SFs, respectively. These results demonstrate the potential use of woodchip as a filter medium for treating DSW to produce an effluent for re-use in washing yards, or for application to land as an organic fertiliser. This would reduce water usage and the environmental risks associated with land spreading. Woodchip filters are a low cost, minimal maintenance treatment system, using a renewable resource, which can be easily integrated into existing farm infrastructure.