Techno-economic analysis of a decentralized wastewater treatment plant operating in closed-loop. A Finnish case study

The study analyzes a potential to improve the local waste and wastewater management in a Finnish community. The Lappeenranta wastewater treatment plant (WWTP) is used as a case study. Two different technological setups are considered for improving the wastewater treatment plant. These are used to construct four alternative wastewater reclamation scenarios. The mass and energy balances for the considered scenarios are developed and used as input for the profitability evaluation. The utilization of the sewage sludge from the WWTP and municipal solid waste fraction that cannot be recycled for the generation of heat and electricity at the CHP plant is investigated with the aim to improve the economic performance of the wastewater treatment facility. The studied scenarios are initially compared based on their investment and operational costs. The cost of water treatment increases significantly in the case of the investigated tertiary treatment systems: higher amounts of chemicals and electricity are needed to improve the water quality. At the same time, the study indicates that the profitability of a WWTP integrated with a CHP plant can be reasonably high in a wide range of likely price scenarios for alternative wastewater purification systems. The results of the analysis showed a significant potential for the investigated wastewater reclamation systems to improve the efficiency of solid waste and wastewater management in the community.