(117f) Choosing the Best Decentralized Wastewater Treatment Systems to be Applied in the Developing Countries

As a result of population growth and urbanization, the traditional centralized wastewater treatment (CWWT) is unable to meet the requirements of wastewater flows, in addition to the high capital and operating costs that burden governments. In this paper, we discussed different types of decentralized wastewater treatment (DWWT) technologies applied worldwide, such as aerobic systems, anaerobic systems, membranes, built wetlands, combined anaerobic and anaerobic system, and chemical treatment. The economic value of decentralized systems lies in their lower capital costs compared to centralized systems, because they require less construction, smaller and less complex networks, and they also require lower operating costs, because they use less energy, lower labor requirements, and are usually cheaper and fewer chemicals and materials to process. Some of them have already been implemented and are in operation in many countries. By studying these technologies we will choose the most suitable method for decentralized wastewater treatment and reuse in semi-arid regions, such as Egypt, in terms of meeting the Egyptian standards for the quality of treated wastewater. Studies showed that different methods achieved better removal efficiencies for some pollutants depending on the wastewater source and system design. The highest economic value was recorded for (aeration tank system + sedimentation tank) and the lowest economic value was recorded for (septic tank + anaerobic filter) system. The results indicate that the promising and effective in terms of lower costs for wastewater treatment is the integrated Up flow anerobic sludge blanket-Continous sequencing batch reactor system (UASB-cSBR), which is one of the anaerobic and aerobic system combination technologies, has proven to be the most suitable method for decentralized wastewater treatment and reuse in semi-arid regions such as Egypt, in terms of meeting the Egyptian standards for the quality of treated wastewater and removal efficiencies for chemical oxygen demand (COD), total suspended solids (TSS), and ammonia (85%, 87%, and 82%, respectively). However using chemical treatment like coagulation followed by adsorption can be applied as it is fast and simple wastewater treatment technology, but further researches is needed for cost reduction which probably can be achieved by using green nanomaterials.