New method for wastewater pre-treatment in the sewage system DIANA ROBESCU * , RALUCA MOCANU ** , DAN ROBESCU * * Department of Hydraulics, Hydraulical Machinery and Environmental Engineering University Politehnica Bucharest Splaiul Independentei, nr. 313, sect 6, Bucharest ROMANIA ** National Research and Development Institute for Gas Turbines – COMOTI Bd. Iuliu Maniu, nr 220 D, sect 6, Bucharest ROMANIA e-mail: diarobescu@yahoo.com; r.mocanu@yahoo.com; dan.robescu@upb.ro. Abstract: - The paper presents a new method, currently unused, for the practical application of the sewage network as a wastewater pre-treatment stage. This can be achieved by using alternative aeration systems along the sewage system, which lead to alternative aerobic and anaerobic areas and allow the development of the biological processes. The microorganisms that occurred partially decompose the organic pollutants from the wastewater in the sewage system. Besides the rationally and efficiently used of the sewage system for facilitating the operation of the wastewater treatment plant, another important advantage is the modified gaseous medium that lead to quickly and safety interventions of the operators in the sewage network, without danger. In this paper the mathematical model and numerically simulations are presented, which were done to obtain the optimum horizontally distribution of aeration equipment in aerobic zones and the optimum length of aerobic and anaerobic zones. It was found that the removing of the organic substances was around 15 – 17% using this method on 10 kilometers of the sewage system. Key-Words: - aeration, wastewater, pre-treatment, modeling, oxygen dispersion, sewage systems 1 Introduction Currently the sewage system is used to assure the wastewater gravitationally flow to the wastewater treatment plant. The length of the sewage system depends on the relative position of the wastewater treatment plant from the locality and it is around 5 to 15 kilometers. It is necessary several hours for wastewater covers this distance. During this time the organic substances are anaerobically decomposed, eliminating toxic gasses (CH 4 , CO 2 , H 2 S) and unpleasant smells through the apertures of the sewage system, with major implications for the safety of the maintenance personnel. A new wastewater pre-treatment method is proposed for rationally and efficiently use of the length of the sewage system, [1]. This method consists of the alternation of the aerobic and anaerobic areas into the sewage, using aeration systems, which allow the development of the biological processes. The grown bacteria partially degrade the organic substances from the sewer system. By aerating the wastewater from the sewer the gaseous medium is modified and this lead on quickly and safety interventions in the sewer system, without dangers for the operators. The aeration systems assure the oxygen needed in the aerobic areas for the decomposition of the organic pollutants, for the metabolism of the microorganisms and for the multiphase fluid mixing. In this way the microorganisms are in continuous contact with the dissolved organic substances. To improve the efficiency of the biological process, in the upstream of the sewage excess activated sludge from wastewater treatment plant could be injected. On the sewage walls a biological film occurred after a period of time that biochemical decomposes the organic matter. Due to the biomass fixed on the sewage walls the pipes corrosion will be prevented. The cases presented in this paper consider the oxygen dispersion in the sewer at different flow conditions. The mathematical model and numerically simulations are compared with the experimental data. 2 Mathematical model The purpose of mathematical modeling and numerical simulation is to identify the best position of the aeration equipment to have the optimum oxygen concentration in aerobic zones of wastewater, around 2 mg/l. Also, it is necessary to provide anaerobic zones, for denitrification. The optimization of pre-treatment method is needed Proceedings of the 10th WSEAS International Conference on MATHEMATICS and COMPUTERS in BIOLOGY and CHEMISTRY ISSN: 1790-5125 153 ISBN: 978-960-474-062-8