Environmental impacts of alternative water treatment strategies of process water from a herring processing plant

Abstract

Throughout human existence, the oceans have been used as recipient for residues of man’s activities, which is still causing great environmental damages on the marine environment. Today, eutrophication of coastal areas is one of the most difficult environmental challenges humans are facing and the gradual increase of eutrophying emissions to the oceans shows the importance of creating and using sustainable solutions in order to mitigate as much emissions as possible. Hence, stricter legislations and requirements regarding wastewater treatment have been implemented as a strategy to reduce eutrophication. In Sweden, the Swedish herring company Scandic Pelagic AB (owned by the Danish company Skagen FF) have since the 1990’s rented part of the WWTP of the municipality in Orust, north of Göteborg for treatment of industrial wastewater. However, due to new emission requirements they are only allowed to use this solution until the end of 2021, meaning that Scandic Pelagic needs to find another solution for their wastewater treatment. The goal of this work was to compare the environmental impacts of the current wastewater treatment with a number of proposed alternative solutions using a life cycle assessment (LCA). The environmental categories global warming (kg CO2-eq) and eutrophication (kg N-eq) were considered. The goal was also to compare the removal efficiencies of organic matter and nutrients (BOD, N and P). The assessed alternatives are: Scandic Plagics’ current WWTP; pretreatment plant + mussel farm, using boat for transporting process water to mussel farm; pretreatment plant + mussel farm, using pipelines for transporting process water to mussel farm; pre-treatment plant + MBBR technology; pre-treatment plant + SBR technology; and pretreatment plant + SBR technology + surge tank. The results showed that the alternative pre-treatment plant + mussel farm (boat) has the highest global warming and eutrophication impact (132kg CO2-eq and 0.013kg N-eq) and the lowest contributor is pre-treatment plant + SBR (61kg CO2-eq resp 0.0016kg N-eq). Pre-treatment plant + MBBR was the highest emission contributor (89kg CO2-eq resp 0.024kg N-eq) among the assessed WWTPs mainly operated on land but has the highest nutrient reduction capacity. A correlation of the nutrient and organic removal efficiency levels and the environmental impact of the assessed alternatives could be observed. Since this work indicated that an increase of chemical, energy and material use generate a greater reduction of organic matter and nutrients in CHALMERS Architecture and Civil Engineering, Master Thesis ACEX30 process water. Based on this LCA study, pre-treatment plant + SBR should be implemented as a future solution by Scandic Pelagic since this is the most environmentally friendly treatment method and at the same time has sufficient organics removal.