Estimating the diffusion of decentralized wastewater and storm water management on the basis of land use data

In Europe and in most other parts of the world, centralized systems of wastewater collection and treatment are state-of-the-art. They and their proper functioning are however questioned by challenges such as climate and demographic change. An alternative to centralized systems of wastewater and storm water treatment and management are decentralized systems, including small-scale treatment plants for wastewater and on-site infiltration of storm water and treated wastewater run-off. However, especially the small-scale treatment plants can face a lock-out by their centralized counterpart. This lock-out is based on arguments that hold in many, but by far not all, conditions and regions. It is important to identify those regions where the alternative, decentralized infrastructure, is not locked out because it tells policy makers and business persons where and when the support and adoption of elements of the alternative approach should best be started. In order to identify possible starting points for the diffusion of decentralized wastewater and storm water management in the Elbe region, we use geographically differentiated data concerning today's (2004) population, settlement area, sealed surface area, the installed small-scale wastewater treatment devices as well as size and load factors of the existing urban centralized installations. We then and extrapolate these data to the year 2020. It turns out that it is possible to identify regions where the employment of decentralized management of wastewater and storm water, respectively, is much more favorable than in others, and thus adoption of it is much more probable.