الفهرس 
AcknowledgmentOnly 14 pages are availabe for public view
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Abstract
Alexandria is the second largest city and main port of Egypt; it lies north west of the Nile Delta and stretches along a narrow land strip between the Mediterranean Sea and lake Maryut. In past, the city was planned to discharge its sewage either by dilution into the sea through Kait Bay outfall and another 20 minor outfalls located along the city beaches or into lake Maryut. These small outfalls were designed to serve as an emergency relief during the rainy season in winter, but actually these outfalls were used to dispose raw sewage to the beach even during the summer season due to overloaded conditions of the sewerage system. Now, most of the collected sewage from the city is pumped to two wastewater treatment plants. The first on is the East Treatment Plant with a design capacity of 410,000 m3/d and the second is the West Treatment Plant, which has a design capacity of 175,000 m3/d. Both plants use primary treatment technology and discharge their primary treated effluents into lake Maryut, therefore the discharge of these plants has been resulted in more deterioration of the lake. Accordingly, these plants should be upgraded to produce a satisfactory effluent in compliance with the environmental regulations to protect the lake or to get the benefits of reusing this large quantity of treated effluents. Wastewater treatment is divided into preliminary, primary, secondary and advanced treatment. Preliminary treatment includes measurement and regulation of the incoming flow and removal of large floating solids and grit. Primary treatment processes remove settleable and floatable pollutants. However non settleable and most of dissolved pollutants could be removed by secondary treatment. The most common approaches to secondary treatment are activated sludge and trickling filters. There are many modifications of the activated sludge process in use today such as complete mix, step feed, contact stabilization, extended aeration, sequencing batch reactor, and pure oxygen activated sludge process. In the pure oxygen activated sludge process pure oxygen is used instead of air for achieving biological oxidation. The use of pure oxygen has the ability to operate at food to microorganism ratio higher than the air systems. Furthermore, pure oxygen systems can be operated at relatively shorter hydraulic detention time when compared to the air systems while producing lower sludge quantities than the air systems. This study was carried out to compare the efficiency of the pure oxygen activated sludge with the air activated sludge system, to determine the optimum operating conditions for pure oxygen and air activated sludge processes, and to study the feasibility of applying pure oxygen in the activated sludge process as an alternative for treating wastewater of Alexandria city. In this study, two pilot scale activated sludge units with internal solids circulation were constructed in the East Treatment Plant. One of these units was operated with compressed air and the second was operated with pure oxygen. Both units were fed with the primary settled sewage of the East Treatment Plant. The air activated sludge unit was operated at detention time ranged from 9 hours to 4 hours, and a sludge age from 3 days to 8 days. The pure oxygen activated sludge unit was operated at detention time raged from 4 hours to 2 hours, and sludge age from 3 days to 8 days. Both units were operated towards the reduction of detention time and consequently increasing sludge age to overcome the effect of reducing detention time. Results obtained from this study revealed the following A satisfactory effluent quality could be obtained from the air and pure oxygen activated sludge systems at sludge age of 6 days. At this sludge age the air system can be operated at detention time in the range of 5.5 to 9 hours, while the pure oxygen system can be operated at detention time ranging from 2 to 3 hours. Operation at sludge age of 3 days and 4.2 days for both systems failed to achieve a satisfactory effluent quality in compliance with the law 48 for the year 1982. The removal percentages of SS, BOD, and COD for the pure oxygen unit were greater than the air unit operated at the same F/M ratio. Accordingly the pure oxygen system can be operated at higher F/M ratio then the air system while producing either better or even similar effluent quality. Pure oxygen can produce a good settling activated sludge compared with the air activated sludge system. Furthermore, lower sludge quantities could be obtained for the pure oxygen system compared to the air system operated at the same sludge age. Nitrification occurred in both systems during all the applied operating conditions even at short sludge age of 3 days. Microbiological examination revealed that both systems are not designed for complete removal of coliforms and parasites. Application of pure oxygen as an alternative for the treatment of the East Treatment Plant could reduce about 31 of the total land required for the air system, and about 46 of the dry solids wasted each day.