Asian Jr. of Microbiol. Biotech. Env. Sc. Vol. 17, No. (3) : 2015 : 593-601 © Global Science Publications ISSN-0972-3005 *Corresponding author’s email: hussein.alkaisy@gmail.com MODELLING OF SEWAGE QUALITY DURING RAINY SEASON A.O. HUSSEIN* 1 , S. SHAHID 1 , K.N. BASIM 2 AND S. CHELLIAPAN 3 1 Department of Hydraulics and Hydrology, Faculty of Civil Engineering, Universiti Teknologi Malaysia, 81310, Skudai, Johor Bahru, Malaysia 2 Department of Civil Engineering, Karbala University, Karbala, Iraq 3 Razak School of Engineeringand Advance Technology, Universiti Teknologi Malaysia, Kuala Lumpur, Malaysia Key words: Pollution loading, Storm Water Management Model, Wastewater concentrations, Geographic information systems. Abstract–In the previous four decades, methodical research has been concentrated on the protection of water resources, and especially on the contaminating consequence of the inner city of natural water bodies. One approximation to this investigation has concerned the advancement of instruments to illustrate the phenomena which takes place in the city watershed throughout both wet and dry times. This article aims to determine the significant differences of the changes of Biochemical Oxygen Demand (BOD), and total suspended solids (TSS) parameters in a wastewater in the sewer networks during rainy seasons for the historic rainfall time series using SWMM5. For this purpose, thirty years (1980-2010) of rainfall, temperature and sewer flow data of Karbala city of Iraq were collected, processed and employed for the modelling of the pollution loading. The effects of land-use, population and impervious surface cover on the quality of storm water were also analyzed. The results showed that the concentrations of BOD 5 and TSS increase significantly after raining in the study area. The statistical tests showed the differences were significant (p<0.05). The increase of the BOD5 was very high compared to TSS. It can be expected that the long-term simulations of storm water pollution loading would be help to compare the benefits of different scenarios of the sewage- treatment plan for the reduction of the pollution in the storm discharge. INTRODUCTION Modelling pollution loading in urban storm water is important for non-point source pollution control and water treatment. Majority of older urban area centres including many old metropolitan towns in the U.S. and Europe (New York City, Washington, Paris, London, etc.) are discharged by merging sewer systems. The magnitude of wet weather flow (WWF) contaminant loads (Chebbo and Saget, 1995; Veldkamp and Wiggers, 1997; Brombach et al., 2005; Suarez and Puertas, 2005; Gasperi et al., 2010) and subsequently caused acute impact on receiving waters. With the advances of civilization, agricultural lands, forests, and wetlands are converted into municipal land uses. Urbanization adversely alters watershed hydrology, contributing to the deterioration of water resources and water quality. The urban runoff is one of the factors that have the most influence on the water quality of water bodies (Characklis and Wiesner, 1997). The cities where the rainfall is very sporadic and sparse, sudden rainfall after a long dry spell often causes a high level of pollution of the storm water. This alteration includes increased runoff volumes and peaks, decreased time of concentration, decreased base flow recharge (Burns et al., 2005), and increases as the non-point source (NPS) pollution in the runoff (Ying and Sansalone, 2010a; Ying and Sansalone, 2010b). Urban NPS pollutants include suspended and dissolved solids, nutrients, oxygen- demanding organisms, bacteria, pesticides, metals, oil and grease. The transport of pollutants in the runoff from the land areas into water bodies is a natural process. However, urban city NPS pollution is intensified by activities associated with domestication. The most prevalent of these activities include increased impervious surfaces (e.g., roads, parking lots, sidewalks, roofs, and compacted areas), increased application of fertilizers, pesticides on municipal lawns and gardens, erosion from land disturbance due to the construction activities. Increasing use of vehicles also causes pollutant inputs into the air and subsequent atmospheric