الفهرس 
CHAPTER (1) INTRODUCTIONOnly 14 pages are availabe for public view
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Abstract
Climate change is having a multitude of immediate and long term impacts on water resources in Egypt and other African countries. These include flooding, drought, drying up of rivers, poor water quality in surface and groundwater systems, precipitation and water vapor pattern distortions. Therefore, the decrease in the amount of fresh water availability together with a simultaneous increase in the amount of wastewater production is an alarming issue. The solution lies in conservative use of water and development of sustainable treatment technologies and rehabilitation and/or upgrading of many existing wastewater treatment plants.
This study compares the ability of four secondary treatment systems: conventional activated sludge (CAS), integrated fixed film activated sludge (IFAS), moving bed biofilm reactor (MBBR), and membrane bioreactor (MBR) for sewage treatment under different operating conditions (HRT, DO). To accomplish this objective, four tanks with the same volume each were manufactured and operated. The IFAS and MBBR contain an innovative plastic biofilm carrier at fixed ratio (60 % of the reactor volume). In the IFAS the media was fixed without motion while in the MBBR the media was freely moving into the reactor by aeration. The fourth system was a cloth-media submerged membrane bioreactor (MBR).
The results obtained indicated that Both DO concentration and HRT have significant impact, directly or indirectly, on the four systems. Economically, the system operation at low DO concentration (2 ppm) and HRT (6 hrs.) was cost-effective, sustainable and provided treated effluent complying physico-chemically with reuse standards. The treatment efficiency at HRT 6 hr. and DO 2 mg/l of the CAS system based on COD, BOD and TSS removal was 83.6 %, 85.5% and 86.5 %, respectively. The corresponding results of the MBBR system were 86 %, 88.4%, and 89.1% , respectively, and results of the IFAS system were 88.3 %, 90 %, and 91.2 %, respectively. Also, the corresponding results of the MBR system were 93.3%, 93.5% and 97.3 %, respectively.
Comparing the treatment efficiency of the four alternative treatment processes, it can be concluded that the descending order of effluent quality for all considered parameters is as follows: MBR > IFAS > MBBR > CAS. The MBR and IFAS provide better effluent quality.
The economic evaluation is made for the proposed CAS, MBBR, IFAS and MBR systems, capable of treating 10000 m3/d of medium strength wastewater generated from a small community. The proposed system consists of aeration tank of volume 2500 m3 and final clarifier of volume 1320 m3. The MBR is the more expensive technology among the four selected technologies. The cost of the MBR is about three folds the cost of IFAS or MBBR. The cost of the MBR is seven times the cost of the conventional CAS. The cost estimation of the four systems indicted sustainability of the MBBR comparing to the MBR which is highly expensive. Also MBBR is more sustainable than IFAS which is susceptible to sludge bulking problems in addition to little higher capital cost and higher daily operation cost.