Exergy analysis and nutrient flows of various sewerage systems

There is an increasing demand for more sustainable sewerage systems. An important tool in the analysis of the sustainability of a sewerage system is exergy analysis. It is possible, by using an exergy analysis, to estimate the consumption of physical resources. In the present study, the demand on resources in the sewerage system of Bergsjon, a district of Goteborg, Sweden, was evaluated through exergy analysis. The case study included the existing system and two sewerage system alternatives. One important aspect of a sustainable sanitary system is nutrients recycling from sewage to agriculture. The exergy analysis has therefore been complemented with an analysis of the mass-flows of phosphorus and nitrogen. The study shows that the hypothetical calculated exergy consumption during operation will be lower in a system with local treatment and urine separation toilets compared with a conventional alternative. The amount of phosphorus that could be recycled is the same for the studied alternatives, but the amount of nitrogen that could be recycled is considerably higher for systems with urine separation techniques. (C) 1997 IAWQ. Published by Elsevier Science Ltd.