Environmental Systems Analysis of Wastewater Management

Doctoral thesis, 2000

The history of wastewater management tells us that efforts have been made at solving only one problem at the time; sanitation during the first half of the 20th Century followed by eutrophication of lakes and sea and, for the past ten years, recycling of nutrients. After the "Brundtland Report", 1987, a reversal of the debate occurred where water management was discussed in a more holistic manner than before. The concept sustainable development became widely accepted and was put into practice. This thesis suggests a framework for evaluating the sustainability of wastewater systems, which contains the use of criteria and system analytical evaluation methods matching each criterion. The main categories of criteria are identified as: Health and Hygiene, Social and Cultural, Environmental, Economic and Functional and Technical. The usability of different concepts of Environmental Systems Analysis for evaluating environmental criteria of wastewater systems is also investigated. These studies show that a substance-flow model combined with evaluation methods from Life Cycle Assessment (LCA), sometimes complemented with Exergy Analysis or Analysis of Primary Energy, is a beneficial approach for evaluating environmental impacts and the usage of resources. However, none of these concepts can provide a complete Environmental Impact Assessment since they lack, for example, the ability to analyse local environmental impacts and risks. The substance-flow model ORWARE (ORganic WAste REsearch) combined with LCA was used to compare four systems structures for the management of household wastewater and solid organic waste, namely Conventional System, Irrigation of Energy Forests, Liquid Composting and Urine Separation. This study shows a potential for further develop the three alternative systems since they increase the recycling of nitrogen and reduce the discharge of nitrogen to receiving waters compared to the Conventional system. Their management of phosphorus and heavy metals is, on the other hand, not obviously an improvement on the Conventional System. Urine Separation systems seem to be beneficial both in sparsely and densely populated areas, while Irrigation of Energy Forests is of most interest for large scale systems where land for cultivating energy forests is available near the treatment plant. Liquid Composting systems are probably most convenient where there is a potential to co-treat wastewater from toilets with other substrates, e.g. solid organic household waste or manure. It is, furthermore, important to develop more energy efficient collection and treatment systems for source separated toilet water and solid organic waste. The comparative study also included some development of system analytical methods. This thesis shows how the contribution from oxidisation of ammonia should be included in the eutrophication impact category. Furthermore, a method is given for prioritisation of the most relevant impacts from wastewater management by using normalisation of these impacts in relation to those from the society as a whole. Further analysis of the four system structures described above gave the basis for formulation of four strategies for less environmental impact and less resource usage of wastewater management: 1) Handle nutrient-rich flows separately from other waste flows, 2) Recycle nutrients and use energy efficiently, 3) Avoid contamination of wastewater flows and 4) Put unavoidable pollution on landfill.