الفهرس 
IntroductionOnly 14 pages are availabe for public view
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Abstract
Safe and readily available drinking water is important for public health. Access to safe drinking water is considered to be a human right. Microbiology and chemical contaminants in drinking water can cause acute and chronic health effects. Chlorine is the disinfectants most widely used for water treatment since it is efficient, easily supplied, operated, and cost effective. However, the formation of harmful disinfection by-products (DBPs) such as trihalomethanes (THMs) through the reaction of chlorine with natural organic matter (NOM) is the main drawback of chlorination. These compounds have adverse effects on aquatic environment and human health due to their high mutagenicity, cytotoxicity and carcinogenicity effect. The formation of THMs in drinking water is a function of various factors such as disinfectant concentration, NOM concentration, contact time, temperature and pH. However, in terms of cost, coagulation and flocculation is generally considered to be an effective and economical option for NOM removal compared to other advanced alternatives, especially in the case of large capacity water treatment plants. Water treatment plant (WTP) with high levels of DBPs may need to modify disinfection practices to reduce the formation of DBPs to meet the THM maximum contaminant level requirements. Therefore, The present study aims to reduce high Trihalomethane (THMs) and residual aluminum levels in EL-Nobarya water treatment plant (EL-Nobarya WTP) without affecting adequate pathogen removal. This goal was achieved through performing two studies: 1) Applying Enhanced Coagulation (EC) and 2) Optimization (modifying) of the disinfection process for both the chlorination time and applied dosage according to a disinfection profile. Enhanced coagulation was applied on the treatment plant in a period from January to August 2020. Moreover, a noticeable reduction in THM concentrations was observed compared with conventional treatment and nearly all the samples didn’t exceed the maximum level of 80 μg/L.
By applying enhanced coagulation, residual aluminum never exceeds the limit of 0.2 mg/L as it varied from 0.1-0.13 mg/L compared to 0.18-0.26 mg/L using conventional treatment depending on the pH of the water. The optimum hydrolyzing pH for aluminum salts ranged between 5.5 - 7.7 under which positively charged Al species are produced. Moreover, the average value of clarified water turbidity decreased from 3.2 to 1.66 throughout the year. Consequently, the filter run time increased from 12 hours to 24 hours saving about 250 m3 of washing water for each filter. However, THM concentrations were over the USEPA’s (1998) limit ( 80 μg/L) with high TOC and temperatures. Thus, disinfection optimization (disinfectant dose, and contact time) was applied as a second crucial strategy for further control of THM level without affecting pathogen removal. Chlorine profile was developed for the plant to calculate the CT acheived in the plant compared to the CT required for disinfection by USEPA CT tables to evaluate the disinfection process and whether there is a possibilty to reduce the chlorine dose or the contact time safly. from the chlorine profile for the plant, the total log inactivation achieved was 34.47 and 11.30 for 10 and 25ºC, respectively. 2.5-log of Giardia can be removed through sedimentation and filtration process (USEPA, 1991). The required log inactivation for Giardia by the disinfectant should only be 0.5-log of the 3log set by USEPA. Chlorine dose was reduced from 8 mg/L to 5-5.5 mg/L divided on the three injection points. Flash mixer, contact tank and the secondary disinfectant point. The results of the second profile based on the new chlorine dose and contact time gave 8 log removal of Giardia and 2.7 log inactivation with high and low temperature consequently, so the doses were decided to be used safely on the plant. The results showed sharp, simultaneous and constant reduction in THM level. All THM values were below 64 μg/L which reveals the effect of chlorine dose on THM formation. Biological test for Gardia Lamblia in treated water was carried out to ensure water safety after reducing chlorine dose and contact time. The results revealed complete absence of Gardia cysts in all samples. By this applicable study, EL-Nobarya plant does not need much more costly and sophisticated treatment processes to reduce THM level. The literature review revealed that there were no reported researches on optimization of disinfection process and developing standard operating procedures for chlorination dose calculation according to a disinfection profile in Egypt. The result of the work was applied to the main treatment plant in EL- Behera governor like, Damanhur, Abo-Hommos, Kafr-ELdawar and Shobrakhet WTPs. The study emphasizes the need to apply CT tables and Chlorine Profile with Enhanced Coagulation in all the subsequent water treatment companies under the holding company in Egypt.