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Although significant progress has been achieved in the field of environmental impact assessment in many engineering disciplines, the impact of wastewater treatment plants has not yet been well integrated. In light of this remarkable scientific progress, the outputs of the plants as treated water and clean sludge have become potential sources of irrigation and energy, not a waste. The aim of this study is to assess the environmental impacts of upgrading the wastewater treatment plants from primary to secondary treatment. The Lifecycle Assessment Framework (ISO 14040 and 14044) was applied using GaBi Software. Abu Rawash wastewater treatment plant (WWTP) has been taken as a case study. Two scenarios were studied, Scenario 1 is the current situation of the WWTP using the primary treatment units and Scenario 2 is upgrading the WWTP by adding secondary treatment units. The study highlighted the influence and cumulative impact of upgrading all the primary WWTPs in Egypt to secondary treatment. With the high amount of energy consumed in the aeration process, energy recovery methods were proposed to boost the circular economy concept in Abu Rawash WWTP in order to achieve optimal results from environmental and economic perspectives.

a b s t r a c tEnergy and water are essential components to any civilization. Both are important for industrial, agricultural and societal development. Desalination seems to be one of the most suitable solutions to the water problem. The integration of renewable energy into water desalination systems has become increasingly attractive due to the growing demand for water and energy. In this paper, a proposed model consists of a solar photovoltaic (PV) powered seawater reverse osmosis desalination plant for the southern region of the Gaza Strip. The proposed system of reverse osmosis plant with a capacity of 2,400 m 3 /h is designed using ROSA software. As the solar PV plant is designed using System Advisor Model software that does not rely on expensive batteries, the water production cost is nearly the same as the current expenses (0.56 USD/m 3 ). The simple payback period for PV plant was found to be 5.9 years, the nominal levelized cost of energy was 9.3 cents/kWh, the net present value was around $800,000 and the investor internal rate of return was 10.6% (which is greater than the interest rate 6%). The system reduces the emission of greenhouse gases. Comparing the results obtained with the conventional values, this model would provide a much needed efficient compensator of the shortage of water and energy, making it more sustainable and economically feasible.

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