ECONOMIC AND ENVIRONMENTAL ANALYSIS OF THE USAGE OF SOLAR, WIND AND HYDROELECTRIC ENERGY SYSTEMS IN WASTEWATER TREATMENT PLANTS IN TÜRKİYE
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The increasing global demand for water and energy, the limited availability of resources, and the problems caused by the climate crisis are putting significant pressure on water and energy supply systems. Therefore, sustainable energy and clean water supply are among the most critical issues worldwide. The fact that water is the primary material for energy production and energy is needed for water treatment demonstrates a mutual relationship between water and energy. Wastewater treatment plants (WWTPs) are the primary energy consumers in many countries. Approximately 14% of WWTPs in Türkiye cannot be operated due to economic reasons resulting from high energy consumption. This issue is particularly observed in small city municipalities with higher unit energy requirements. Previous studies have shown that renewable energy integration is environmentally and economically feasible for large-scale wastewater treatment plants. However, the primary issue in Türkiye is that many small-capacity WWTPs are not operated due to high electricity demand. Although there are many studies in the literature on integrating renewable energy sources into WWTPs with a certain capacity, there is no study for relatively small-capacity WWTPs in Türkiye that includes renewable energy source types. Therefore, the main aim of this study is to determine a threshold value for the capacity of wastewater treatment plants with feasible renewable energy integration using Particle Swarm Optimization in Python. The study evaluated 79 WWTPs in Türkiye that treat less than 1,000,000 m3 of wastewater and identified nine as viable for renewable energy integration, with a payback period of seven years or less and the potential to meet at least 50% of the electricity demand. The study also indicated that renewable energy integration, including solar, wind, and hydro, is feasible for WWTPs with different capacities, with payback periods ranging from 5.5 to 8.6 years. WWTPs have significant potential for cost and emission reductions. The optimization model developed includes two different scenarios. Scenario 1 is based on generating enough electricity from renewable energy sources to meet the WWTP's electricity consumption and optimize it with minimum cost. Due to the complexity of battery systems, electricity generated from renewable energy sources is assumed to be directly sold to the national grid. Therefore, in Scenario 1, the generation is limited to the amount consumed. In Scenario 2, conversely, more electricity can be generated than needed by using the maximum available photovoltaic area and selling it to the grid. In this case, there is no limitation on electricity generation in Scenario 2, and all the available potential in the area is used for electricity generation. The result of the study indicates that the threshold capacity for renewable energy integration in low-capacity WWTPs is 380,633 m3/year in Scenario 1 and 100,611 m3/year in Scenario 2. This study revealed that the average cost reduction is 22,300 $/y in Scenario 1 and 29,300 $/y in Scenario 2. WWTPs can contribute to a 56% emission reduction in Scenario 1 and 74% in Scenario 2, thanks to the electricity generated from renewable energy sources. Assuming a household's average annual electricity consumption is approximately 4,000 kWh, integrating renewable energy sources in the 79 WWTPs would result in emissions equivalent to the annual electricity consumption of approximately 2,000 households.