Sustainability effects of water reuse and infiltration and inflow on a wastewater treatment plant - a Multi Criteria Decision Analysis

Examensarbete på grundnivå
Ceder, Jakob
Backeström, Emmy
To lower the environmental impact of wastewater treatment in the Gothenburg area, Rya wastewater treatment plant (WWTP) is constantly working towards a more environmentally friendly and efficient wastewater treatment process. The function of the WWTP is dependent on the inflow of wastewater. In this study, the sustainability effects of increased and decreased infiltration and inflow (I/I), which is water that reaches the sewer system that is not sewage water, are analyzed. Since the WWTP is connected to the entire sewer system of the connected municipalities, the wastewater inflow can increase significantly because of the excess water from I/I in the system. The sustainability effects of two types of water reuse, upstream reuse and downstream reuse, were also analyzed. Upstream water reuse refers to water that is reused before it reaches the WWTP and downstream refers to treated wastewater that is used in some type of industry. To assess the sustainability effects, six scenarios that represented increased or decreased fast and slow runoff I/I, as well as upstream and downstream water reuse were constructed and compared to a base case scenario using Multi Criteria Decision Analysis (MCDA). The criteria analyzed in the MCDA were Effluent quality, Heavy metal content in sludge, Climate impact, Water use, Energy use, Sphere of action/Political support, Local environment quality & amenity, Working environment, Safety/Risks, Operating costs, Vulnerability and Flexibility. Data and information for each criterion were gathered from measurements done at Rya WWTP, literature study and interviews with Gryaab employees and analyzed for wastewater inflow series constructed for each of the scenarios. The data and information were then presented to an expert panel that graded and weighed each criterion. The results showed that an increase in I/I has a negative effect on overall sustainability at the WWTP, while decreased I/I has a positive effect. Fast runoff I/I was deemed to be the most preferred to lower since it had the largest effect on sustainability and was mostly due to increased combined sewer overflows caused by the selective increase of wastewater inflow. Upstream reuse is preferable to downstream since it lowers drinking water use and reduces wastewater inflow to the WWTP which has positive sustainability effects at the WWTP.
Wastewater , Wastewater treatment , Wastewater treatment plant (WWTP) , Sustainability , Infiltration and inflow (I/I) , Greywater reuse , Water reuse , Multi Criteria Decision Analysis (MCDA)
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