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Sabren Yahya
Sahar Khalid
Sondos Saleh
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The efficient and economical treatment of waste waters requires great attention to the settle ability of activated sludge. Efficient settlement in the secondary sedimentation tank is required to keep the desired effluent quality and to sustain the necessary amount of microorganisms in the aeration tank. The settle ability of microorganisms in the secondary clarifier dependents to great extent on the physiological and biochemical nature of activated sludge floc, which is mostly determined by the conditions of the aeration tank. Research about various treatment processes in water and wastewater treatment and dewater ability showed that temperature and pH are important factors affecting efficiency of flocculation and settling properties. The floc formation is completed by release of the natural poly electrolytes. These poly-electrolytes consist mainly of proteins and polysaccharides, and lipids that may be affected by temperature. Therefore, variation in temperature may results in change in polymer structure and bacterial cell wall. Also, the pH in biological systems affects the enzymatic activities of microbial community. This study will be performed to determine the effects of pH and temperature on the settle ability of sludge. In this research, effects of temperature and pH of sludge samples from a local municipal wastewater were studied.  Floc-structure, turbidity; BOD, and settleability, evaluated using Sludge Volume Index (SVI), were measured following standard method. The study was run in two phases. The first one was to study the effect of changes in pH (5 to 9) on settleability and dewater ability of sludge samples at a constant temperature. The second phase was to study the effect of temperature (5 to 35) on settle ability and dewater ability at constant pH value. The data were analyzed using statistical techniques including linear regression. This research study shows that the temperature and the pH affect the settle ability of activated sludge, and the lowest sludge volume index (SVI ml/g) was at 35 C and at pH = 6.   The relationship between SVI and temperature was best described by a linear regression . The linear regression line seems to fit the data very closely with very high coefficient of determination (R2) of 0.91. The relationship between pH and SVI was tested and found to be a perfect fit of cupic curve with coefficient of determination of 0.99. A prediction equation was derived and it was SVI = 16,992 - 7,170X + 1014.9X2 - 46 X3.  The SVI decreased when pH increased from 5 to 6 but increased when pH increased from 6 to 9 at decreasing rate.