Effects of biologically active discharges into acquatic ecosystems: Review of treatment systems and standards

Over the last ten years there has been an increasing awareness of the impacts of uncontrolled biological waste discharge into the receiving waters. The types of impact such discharges produce in the receiving waters are discussed. Early standards were based on overseas research but there is now a substantial body of New Zealand based work. Initial research concentrated on dairy shed discharges and domestic sewage pond discharges but has broadened to include piggeries wastes, meat industry wastes and various others. In the main this work has shown that traditional oxidation pond systems do not treat the water to a high enough standard. Currently many discharges are high in suspended solids, biochemical oxygen demand, nitrogen (often in the form of ammonia), phosphorus and faecal coliforms. The effectiveness of additional treatment in wetlands, either natural or constructed is being investigated. Early results are encouraging and suggest that low cost, low maintenance wetlands can be constructed to polish effluent from oxidation ponds. Research into other methods such as spraying onto land is continuing. The dilution factors required to achieve various receiving water standards are presented for both domestic and dairy shed oxidation pond discharges. Some wastes, such as those from piggeries, are proving difficult to treat to the required standard and work on this and other problems is continuing. Department of Conservation staff involved in vetting resource consents for discharge to water involving biological wastes should consider recommending further polishing in wetlands.