Reduzierung von Fremdwasser bei der Abwasserentsorgung

• Reducing infiltration and inflow to sewers

Hennerkes, Jörg André; Dohmann, Max (Thesis advisor)

Aachen : Publikationsserver der RWTH Aachen University (2006)
Dissertation / PhD Thesis

Aachen, Techn. Hochsch., Diss., 2006

Abstract

Increasing requirements for water pollution control and high financial loads of municipalities aroused the interest in optimizing and cost-reducing investigations in the sewage sector in the past years. From the broad topic particularly the infiltration and inflow moved in the focus of political and technical discussions. Infiltration and inflow water is described as an undesired part of the wastewater flow in sewer systems. Predominantly it consists of groundwater infiltration over leakages in public and/or private sewers and drain pipes as well as the rainfall induced inflow into sanitary sewers. It leads to an additional hydraulic charge, a reduced efficiency of wastewater treatment plants and thus to a higher pollution of water bodies and an increase of sewage costs. In this thesis solutions to avoid and reduce infiltration and inflow are examined taking into account aspects of groundwater management and discharge. For this the national and international state of knowledge is compiled. Finally an integrated view on the topic by an evaluation of measures such as infiltration/inflow reduction and their effects have been achieved. This specifically relates to the possibility of rising groundwater levels with the particular consequences of water-logging or useage restrictions. A sustained and successful reduction of infiltration and inflow can only be achieved by appropriate planning and a supportive tool such as this theses to achieve effective solutions. The significance of groundwater infiltration through leakages in public and lateral sewers are still unknown. Therefore extensive examinations were performed to quantify infiltration volumes into leaking sewers. For this the groundwater infiltration rates into leaking sewers were measured in two separate laboratory test set-ups with varying kinds of surrounding soil, groundwater levels, damages and loads. By evaluating the results of measurements an empirical dependency between groundwater infiltration for point, tearing and sleeve damages and the water permeability of the soil, the damage surface and the hydrostatic pressure can be found. Due to this the success of infiltration-reducing measures, in particular sewer rehabilitation, can be forecasted assuming knowledge of the soil and/or the hydro geological environment. Finally an integrated approach is made to evaluate the measures for infiltration/inflow reduction and their effects. Therefore different scenarios of infiltration/inflow occurrences were developed. By using an efficiency analysis suitable measures were assessed concerning technical, ecological and economic, legal and socio-political criteria. The influence of different weightings of the evaluation criteria is examined by a stability analysis. As a result orders of rank and measure combinations can be determined for infiltration/inflow reduction in each scenario. Thus the expenditure of measures to reduce infiltration/inflow can be calculated more efficiently and a higher planning security can be achieved.