Regional wastewater treatment–an economical solution? Data from 40 years of operation gives the answer

Economic data from 40 years of operation of three regional wastewater treatment companies have been compiled and analysed. The transport systems consist mainly of gravity flow tunnels with lengths of 55–120 km. In spite of the heavy initial investments <20% of the cumulative total costs can be allocated to the transport systems. The treatment plants all remove 90% or more of the influent Biological Oxygen Demand (BOD) and phosphorus and 65–80% of the nitrogen. The wastewater treatment is responsible for about 90% of the cumulative operation costs while the transport system is responsible for 20–40% of the cumulative capital costs. Over time the cost of the transport systems has decreased considerably and is after 40 years of operation only 4–13% of the total costs. Although the main benefit of the regional solutions has been the transfer of wastewater from sensitive inland streams and lakes, the data presented give strong evidence that the regional solutions also has been advantageous from an economic point of view.