This thesis aimed to evaluate the performance of the treatment of the existing activated sludge wastewater treatment plants in Palestine, under prevailing climatic conditions. A site detection has been done for the selected plants in order to interview the managers responsible for the treatment plants and collect data.

Three wastewater treatment plants in West Bank (Al-Bireh wastewater treatment plant, Nablus wastewater treatment plant and Jericho wastewater treatment plant) were evaluated over a period of nine months. Al-Bireh wastewater treatment plant used as extended aeration activated sludge system, also Jericho wastewater treatment plant used as  extended aeration activated sludge system and Nablus wastewater treatment plant used as a conventional activated sludge system. The study compares the observed effluent quality and the removal efficiencies in terms of BOD, COD, TN, TP and NO3-N according to monthly climatic changes and seasonal variations. Moreover, it compares the sludge quality in terms of MLSS, SVI and F/M ratio, and it compares the energy consumption according to DO concentrations and power consumption. In view of the large performance inconsistent observed, the existence of a relationship between operational parameters and treatment performance was verified. The research has a comparison between the three selected treatment plants regarding to the activated sludge system used, and COD/BOD ratios.

The data collection periods were divided seasonally. The impact of temperature changing on the COD or BOD concentrations was fluctuated over all months, even in Jericho or Al-Bireh wastewater treatment plants. Jericho wastewater treatment plant observed a brilliant performance, which is explained by receiving the typical values for all the parameters that defined the effluent quality, sludge quality and energy consumption, however it has very low F/M ratio and high total energy consumption per COD removed. While, Al-Bireh wastewater treatment plant was evaluated as a good performed system, but in winter and summer 2015 the removal efficiency of COD was not obtained (72.62% and 81.38%), also TN and TP were not given a great attention. MLSS values achieved the required value but SVI described the poor settleability of sludge, additionally it has an acceptable values of F/M ratios but the total energy consumption per COD removed is the lowest. Nablus wastewater treatment plant results analysis showed a good performance but it did not give an attention to TN, TP and NO3. The performance of MLSS and SVI was not as required and exhibited a fair settleability for sludge, also F/M ratios has much less values. Nablus treatment plant was the highest of energy consumption, which had an average value equals 198059 KWh. The concentrations of DO of Jericho treatment plant were the lowest influenced by the high temperature. The comparison that obtained between the three wastewater treatment plants in terms of the activated sludge system type showed that Jericho treatment plant was effective than the two plants, which is based on using diffusers as an aeration system. While, Al-Bireh treatment plant showed approximately high effectiveness when it modified from surface aerators to diffusers.

The study concludes that the three selected wastewater treatment plants were effectively operated, but it should be taken in the considerations to achieve the typical values of the parameters to produce a good quality of effluent and sludge.