Water crises are already stressing societies, economies, and the environment worldwide and especially developing countries. The expected growth in population, urbanization and economic activity, as well as the impact of climate change, will exacerbate the situation in the coming decade. In developed countries, conventional water supply and wastewater disposal systems ensure safe access to drinking water, sanitation and wastewater services. The worldwide application of conventional systems is, however, only possible to a limited extent. The reason for this is that these systems are designed for certain climatic conditions and also do not consider the varying requirements regarding water supply and wastewater disposal typical for developing countries. Although there are alternative water supply and wastewater disposal systems that have proved to be successful throughout the developing world, there are still several barriers to their worldwide adoption. To increase the establishment of these approaches this paper focuses on aspects of particular relevance for developing countries, namely: water reuse (untreated wastewater), alternative sewerage (settled and simplified sewerage), alternative wastewater treatment (waste stabilization ponds, constructed wetlands and up-flow anaerobic sludge blanket reactors) and management of water losses (real and apparent losses).
The present design of stormwater tanks is based on the creation of storage volume to retain stormwater and the prevention or reduction of stormwater overflows. The treatment of stormwater is often improved with mechanical equipment. The general layout rules do usually not include the appropriate choice of design inflow related to the chosen treatment equipment. In the following investigations it was the task to analyze the hydraulic efficiency and the overflow behaviour of a lamella particle separator inside a stormwater tank under different design approaches regarding the chosen design inflow. Therefore six scenarios with different precipitation yield approaches were chosen and applied to a given constant sized catchment to calculate the design inflows. For a given minimum particle size, the necessary number of lamellas were determined for the scenarios and standard stormwater tanks were dimensioned. These stormwater tanks were modelled in the hydrologic model SMUSI to investigate the overflow behaviour of the different tank sizes. The number of overflow events, their duration and maximum flow rates were the results of the modelling. Comparisons to the design inflows were carried out. The treated particles sizes at the overflow events were determined reversible and compared to the original chosen minimum particle sizes.
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