Evaluation and optimisation of the environmental footprint of the Braunschweig sanitation concept with Life Cycle Assessment

This paper presents the results of an evaluation of the environmental footprint of the Braunschweig wastewater scheme with Life Cycle Assessment. All relevant inputs and outputs of the system are quantified in a substance flow model and evaluated with a set of environmental indicators for cumulative energy demand, carbon footprint, acidification, eutrophication, and human and ecotoxicity. The analysis shows that energy demand and carbon footprint of the Braunschweig system are to a large extent offset by credits accounted for valuable products such as electricity from biogas production, nutrients and irrigation water. The eutrophication of surface waters via nutrient emissions is reduced in comparison to a conventional system discharging all effluent directly into the river, because some nutrients are diverted to agriculture. For human and ecotoxicity, a close monitoring of pollutant concentrations in soil is recommended to prevent negative effects on human health and ecosystems. Normalised indicators indicate the importance of the primary function of the wastewater system (= protection of surface waters) before optimisation of secondary environmental impacts such as energy demand and carbon footprint. A further decrease of the energy-related environmentalfootprint can be reached by applying optimisation measures such as the addition of grass as co-substrate into the digestor, thermal hydrolysis of excess sludge, or nutrient recovery from sludge liquors.

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