Sorterande avloppssystem: kostnads- och nyttoanalys i stadsdelen H+, Helsingborg

Sammanfattning: The urban renewal project H+, in the city of Helsingborg, is considering a source separating wastewater system, which could potentially help the municipality to fully or partly reach environmental targets. Advantages of blackwater separation include increased production of biogas and a more convenient recycling of plant nutrients, in comparison to a conventional system. However, existing literature clearly indicates a conflict between environmental benefits and financial considerations. It follows that uncertainty related to the cost of source separating wastewater systems needs to be reduced. The aim of this master’s thesis was to find the most cost effective source separating system, which in addition could maximize societal economic benefits. This goal was reached by an evaluation of three options (Systems 2 - 4) based on costs and benefits and by comparing these to a conventional reference alternative (System 1). Further, the aim was to evaluate the sustainability of the studied systems and to appraise their applicability not only in H+ but other cities as well. In the source separating systems the blackwater is collected via vacuum technology. Anaerobic treatment of the blackwater is considered in Systems 2 and 3, while the treatment of System 4 centers around aerobic hygienisation. All systems are focused on the production of biogas and/or the return of plant nutrients to farmland. The results show that System 3 is the least costly sorting alternative. However, source separating wastewater systems in this study are 35 - 50 % more expensive than System 1. While Systems 2 - 4 have more environmental and societal economic advantages, they are associated with higher installation and operating costs. The annual income from the source separating systems correspond to approximately 4 % of the annual investment and operating costs. By a sensitivity analysis it is shown that larger systems are cheaper per person compared to systems that are dimensioned for fewer people. However, bigger systems are more expansive in total, which will increase the risk of the investment. The sensitivity analysis also shows that a doubling in price of the commercial fertilizers, which is a likely scenario in the future, does not affect the results significantly. However, a less advanced treatment for source separated graywater could reduce the overall costs by approximately 20 %. The method to calculate this is not well established and further studies regarding the costs of graywater treatment are necessary. Some factors which significantly impact the outcome are the selected imputed cost of capital and the length of the sewage net, which determine the applicability of the studied systems in other cities.