Enhancing anaerobic digestion in urban wastewater management

Abstract: The thesis investigates how anaerobic digestion could be utilized to improve wastewater management,specifically in regards to future expected regulation on sludge management in Sweden.Two possible paths of applying anaerobic digestion are investigated. First, the usage of thermophilic anaerobicdigestion of sludge in order to achieve pathogen hygienization. Second, the usage of anaerobic digestion totreat wastewaters at decreased temperature. The evaluation of each path was made through practical labscale experiments. Additionally, the benefits of each path was compared through desk top environmentalimpact studies and economic analysis.The results for the first path showed that thermophilic anaerobic digestion renders high pathogen hygienizationeven at relative short exposure times. However no additional beneficial impact on biogas production or thereduction of organic micropollutants was found. The results for the second path showed that the difficulty ofoperating the sensitive anaerobic digestion process at low temperatures can be partly overcome by simpleengineering batch tests. Furthermore, the dissolved methane in the effluent wastewaters can be extractedusing membrane contactors. Finally, the environmental impact assessment showed that increased resourcerecovery from wastewater, as well as decreased climate impact, can be achieved by applying anaerobicdigestion on source separated domestic wastewaster.The economic evaluation of the two paths showed that the implementation of source separation systems isexpensive compared to implementing the needed thermophilic hygienization. However, source separationsystems would greatly boost nutrient recovery from cities to agriculture which complies well with the goals ofthe Swedish Environmental Protection Agency.