Wastewater management integrated with farming –an environmental systems analysis of a Swedish country town

Recycling of plant nutrients in sewage products to arable land is considered to be a step towards a more sustainable society. Sewage sludge is the predominant sewage fertiliser product available today, but the use of sewage sludge in agriculture has been questioned as regards hazardous substances. In this respect, blackwater from separating systems seems to better fulfil agricultural requirements regarding fertiliser products. The objective of this paper was to analyse the environmental impact and resource use in a life cycle perspective for three systems, each including both wastewater handling and agricultural production. In the reference system, food waste disposers were installed in houses. Milled food waste and wastewater were treated in a wastewater treatment plant and the sewage sludge was used for producing a soil conditioner. In the sludge utilisation system, food waste from households was composted, wastewater was treated conventionally and sewage sludge was used in oat production. In the blackwater system, toilet water from low-flush toilets and milled organic waste were digested together and spread in growing oats. Data on the wastewater system were derived from simulations by the substance-flow model URWARE/ORWARE. The blackwater system required slightly more primary energy than the other two systems. In particular, construction of storage facilities contributed considerably to energy use. The emissions of greenhouse gases and SO 2 were of the same magnitude for all three systems, while the eutrophying emissions were reduced significantly in the blackwater system. As regards NH 3 and NO X , the emissions were highest for the blackwater system. High substitution of mineral fertiliser, optimal spreading technique and well-designed collection and storage facilities were important factors for the environmental outcome in the blackwater system.