New system design to address some of the wastewater treat-ment problems in small settlements

Abstract

A new draft was prepared to amend the Municipal Wastewater Treatment Directive (91/271/EEC), which also affects small settlements. The agglomeration limit is reduced to 1000 PE, and the possibilities of individual wastewater treatment are also limited, prioritizing the sewer system solution. The modification of the sewer system by the connection of the properties to the network with the installation of a septic tank creates more favorable operating conditions than traditional ones in this size category of the settlement, with a small additional investment cost. Smaller diameter pipes can also be used without the risk of clogging and siltation. The septic tanks in this system implement decentralized mechanical wastewater treatment, which avoids the presence of a permanent operating workforce at the small wastewater treatment plant at the end of the network in cases of remote monitoring and control. The system is particularly beneficial and results in a high degree of operational safety for solutions in which the wastewater treatment is nature-based. In most cases, their poor treatment efficiency is caused by poor or missing mechanical pre-cleaning. The installation of the septic tanks results in GHG emissions of 0.063 tons of CO₂e/capita per year. However, this cannot be considered as a net increase compared to traditional sewerage, since GHG emissions also occur in traditional small settlement sewer systems with a long residence time. The modification of the sewerage system excludes the increase in the public health risks, which arise due to decentralized solutions and the free construction of groundwater wells.