Normalising impacts in an environmental systems analysis of wastewater systems.

In an environmental systems analysis of four wasterwater systems, the environmental aspects were prioritised by normalisation of predicted impacts from the studied systems to the total impacts from society. Priority Group 1 (highest priority) consisted of discharges (flows) of nitrogen, cadmium, lead and mercury to water, recycling of nitrogen and phosphorus to arable land and flows of heavy metals to arable land. A conventional wastewater system (A) was compared to irrigation of energy forest with biologically treated wastewater (B), liquid composting of toilet wastewater (C) and a conventional system supplemented with urine separation (D). Analysing the aspects in priority group one, systems B-D improved the management of plant nutrients and decreased the flow of heavy metals to water, while the flow to arable land increased, especially for system B. The suggested method is useful in municipal environmental planning and when choosing a wastewater system.