Effluent treatment for flow through systems and European Environmental Regulations

Abstract

The average production of salmonids in European land-based farms, comprising coastal farming of smolt and inland farming of portion size rainbow trout, has increased significantly due to intensification attempts and better management. Typical conditions in intensive Norwegian and German flow through systems are flow rates of 100–300 l min −1 per ton of fish stock and effluent loads prior treatment of 150–200 kg suspended solids (SS), 7 kg phosphorus and 40 kg nitrogen per ton of fish produced. An increasing number of land-based farms are installing effluent treatment systems in order to meet discharge consent requirements. Effluent solids are commonly removed by screens, such as intermittently back-washed disc or drum filters. Biofiltration as an integrated end-of-pipe device has proven high removal efficiency in a SW Germany based farm. Post-mechanical treatment, nutrient uptake by hydrophytes is sometimes applied in trout farms before discharging the effluent into the recipient. The diversity of regulations and standards controlling fish farming in Europe reflects the differences in environmental conditions, fish farming technology, species farmed, and quantity and nature of wastes discharged. In land-based farms, regulations typically include limitations on the amount of water to be abstracted and on the effluent volume and concentrations of nutrients and organic matter to be discharged. Most of the environmental legislation controlling fish farming has briefly remained unchanged over the last decade. The Water Framework Directive was adopted by the EU countries in 2000 and is intended to provide protection for groundwater, coastal, estuarine and surface waters. Fish farming is not specifically addressed in the Directive but it will undoubtedly affect regulation of the industry. Norway is no member of EU and thus the Framework Directive is not binding for this country.