ارزيابي محيط زيستي سامانه هاي آب و فاضلاب شهري از نظر توليد گازهاي گلخانه اي (مطالعة موردي: شهر ساري)

Environmental Assessment of Urban Water and Wastewater Systems from Greenhouse Gasses Production Point of View; Case Study: City of Sari

آب از ضروري‌ترين عوامل توسعه انساني بوده و ايران نيز ازجمله كشورهايي است كه براي تأمين آب در مصارف مختلف، به‌خصوص آب آشاميدني، دچار مشكل بوده و اين مسئله از مهم‌ترين دغدغه‌هاي دولتمردان در راستاي توسعه پايدار بوده است. از طرفي تجهيزات، انرژي و مواد شيميايي مصرف‌شده در تهيه آب آشاميدني، اثرات زيست‌محيطي‌اي در پي‌دارند كه تشديد گرمايش جهاني به دليل افزايش گازهاي گلخانه‌اي، از جمله‌ي اين آثار است. لذا در اين پژوهش ميزان گاز دي‌اكسيد‌كربن معادل كه عامل اصلي گرمايش جهاني است، با ابزار زيست‌محيطي ارزيابي چرخه حيات و با استفاده از نرم‌افزار SimaPro در چرخه‌ي آب آشاميدني تخمين زده‌ شده است. براي اين كار شهر ساري به‌عنوان مطالعه موردي انتخاب شده و تأمين آب از چاه‌هاي آب و همچنين در سه سناريو، جايگزيني منابع آب زيرزميني با آب سد شهيد رجايي بررسي شده است. طبق نتايج بدست آمده چنانچه تأمين آب از محل سد شهيد رجايي انجام پذيرد، ميزان اثرات زيست‌محيطي (مقدار دي‌اكسيد‌كربن معادل توليد شده) به مقدار زيادي كاهش مي‌يابد. همچنين در بين مراحل چرخه‌ي آب آشاميدني، برداشت آب بيشترين تأثير در توليد گاز دي‌اكسيد كربنِ معادل را دارد. از بين عوامل مؤثر در توليد گاز دي‌اكسيد كربن نيز، مصرف برق بيشترين تأثير را داشته است.

Environmental Assessment of Urban Water and Wastewater Systems from Greenhouse Gasses Production Point of View; Case Study: City of Sari Introduction Urban water and wastewater systems should be constructed and designed within the framework of sustainable development. Therefore the assessment of environmental impacts of these systems’ construction and operation is an essential issue. One of the environmental impacts is the global warming in which the equivalent carbon dioxide has the most important role. The equipments, energy and chemical materials used in drinking water cycle (including the phases such as withdrawal water from its resources, water treatment, water distribution, wastewater collection and treatment) have environmental impacts such as the intensification of global warming due to the increase in greenhouse gasses emission. There are various tools for sustainability assessment of water and wastewater systems. Life Cycle Assessment (LCA) is one of these tools. Unlike the three decade records of applying the LCA in the world, this method has been rarely employed in Iran to resolve the problems of real water and wastewater systems. In this study, the LCA of drinking water system has been implemented in order to estimate its impact on global warming and to examine different cases with minimum environmental impacts. Determination of the water cycle phases with the maximum impact on global warming has been also aimed. In this regard, released equivalent carbon dioxide in life cycle of drinking water was estimated by means of SiamPro software. Sari, a city (in north of Iran) in which drinking water is supplied from wells, has been selected as the case study. Three different scenarios for replacing groundwater resources by a dam reservoir (Shahid Rajaee dam) were studied. Materials and Methods In the present research, Sari city is selected as the case study (Figure 1). Population of the city is about 350,000 in which 57,000 inhabitants profit by the wastewater collection and treatment system. Drinking water cycle is divided into four phases including water withdrawal from its resources, water distribution, wastewater collection and wastewater treatment in which the electricity is supplied from thermal power plant. Figure 1. Map of the studied area Because of the nonexistence of required infrastructures, drinking water in Sari city was supplied from underground water resources before July 2015. In other words, drinking water in Sari city was supplied from 28 wells with discharge of 1180 l/s. 18% of this amount was lost due to the leakage. On the other hand, underground water resources have been exposed to pollution due to the usage of farming fertilizers and operating cesspools. Therefore, replacing underground water resources by Shahid Rajaee dam has been mooted. In this regard, water will be transferred from Shahid Rajaee dam to Kiasar water treatment plant. Then the treated water will be transferred to Sari city. Wastewater treatment plant of Sari has been designed in four modules. The first module which has been operated since 2010, serves about 105000 people. The average and the maximum input discharges of this module are 269 and 546 l/s, respectively. Three scenarios have been considered for replacing underground water resources by Shahid Rajaee dam. These scenarios are: 1) Supplying a part of Sari drinking water demand from Shahid Rajaee dam; 2) Supplying the total drinking water demand from Shahid Rajaee dam; and 3) Supplying the total drinking water demand from Shahid Rajaee dam and using hydroelectricity. It should be noted that the environmental impacts of dam construction has not been considered in these Scenarios. SimaPro is one of the common software for assessing the life cycle. In this study, SimaPro 5.1 is employed for calculating the greenhouse gasses produced in water and wastewater systems. Discussion of Results The total amount of the equivalent carbon dioxide produced in drinking water life cycle in Sari city is presented in Figure 2. According to this figure, the total amount of the equivalent carbon dioxide produced in drinking water cycle is 0.392 in which the phase of withdrawal water from its resources has the greatest part (about 60% of the total equivalent carbon dioxide) in producing the greenhouse gasses. Water distribution network, wastewater treatment plant and wastewater collection network have portions of about 20%, 12% and 8% respectively, in producing the greenhouse gasses. Figure 2. The equivalent carbon dioxide produced in drinking water life cycle in Sari According to the obtained results, water supplying from the Shahid Rajaee dam will reduce the environmental impact to a great extent. Scenarios 1 and 2 with common electricity production (in which 500 and 1500 l/s water was respectively supplied from Shahid Rajaee dam and was treated in Kiasr water treatment plant) reduce 84% and 86% of greenhouse gasses production in the water withdrawal phase, in addition to supplying water with higher quality. In scenario 3 with hydroelectricity, 89% of greenhouse gasses produced in the water withdrawal phase is reduced (Figure 3). The equivalent carbon dioxide produced by various agents in itroduced scenarios are shown in Figure 4. Figure 3. The equivalent carbon dioxide produced in the present situation and various scenarios Figure 4. The equivalent carbon dioxide relevant to various agents in scenarios 1-3 Conclusions It can be concluded that operation of Shahid Rajaee dam and Kiasar water treatment plant and using hydroelectricity would lead to a great reduction in electricity consumption and producing greenhouse gasses. Another result is that the biggest share among the factors producing carbon dioxide is associated to electricity. Keywords: Drinking water life cycle, Greenhouse gasses, Life cycle assessment, SimaPro software, Urban water and wastewater systems.