ارزیابی کیفیت پساب تصفیه‌خانه فاضلاب شهر شیراز جهت استفاده مجدد در بخش کشاورزی در شرایط خشکسالی با استفاده از شاخص‌های irwqi، nsfwqi و owqi

استفاده از آب‌های نامتعارف از جمله آب‌های شور، زه‌آب‌ها و پساب با توجه به محدودیت‌های منابع آبی کشور در مدیریت خشکسالی بسیار موثر است. مهم‌ترین مزیت استفاده از پساب تصفیه‌خانه‌های شهری، ثابت بودن این منابع، سهولت دسترسی و قیمت ارزان آن برای آبیاری زمین‌های کشاورزی یا به بیان دیگر حل مشکل کمبود آب می‌باشد. در این پژوهش شاخص کیفیت آب بنیاد ملی بهداشت آمریکا (nsfwqi) و شاخص کیفیت آب اورگان (owqi) با استفاده از داده‌های روزانه تصفیه‌خانه فاضلاب شهری شیراز طی سال‌های 1397 تا 1398 محاسبه گردید و کیفیت پساب خروجی برای مصارف کشاورزی مورد ارزیابی قرار گرفت. بر اساس نظر افراد متخصص نه پارامتر کدورت، دما، فسفات، نیترات، کلیفرم، اکسیژن مورد نیاز بیولوژیکی (bod)، مواد جامد کل (tds)، اکسیژن محلول (do) و ph جهت محاسبه شاخص nsfwqi برای تصفیه‌خانه شهر شیراز انتخاب گردید. شاخص کیفی owqi همانند شاخص nsfwqi است با این تفاوت که حاوی هشت پارامتر شامل دما، اکسیژن محلول، اکسیژن خواهی بیولوژیکی، ph، نیتروژن، فسفر کل، کل جامدات محلول و کلیفرم مدفدعی می‌باشد. نتایج نشان داد مقادیر میانگین شاخص nsfwqi در ماه‌های مختلف بین 28.73 تا 31.54 بود که در طبقه کیفیت ضعیف قرار می‌گیرد. همچنین بر اساس مقادیر owqi ماهانه که در بازه 4.38 تا 7.95 قرار می‌گیرد کیفیت این پساب خیلی ضعیف است. پساب با چنین کیفیتی را می‌توان صرفاً برای آبیاری گیاهان غیرمثمر و پارک‌های جنگلی اطراف شیراز و حتی قسمتی از فضای سبز شهری به‌کار برد.

evaluating the quality of shiraz wastewater treatment plant effluent for agricultural uses in drought conditions utilizing irwqi, nsfwqi, and owqi indicators

introduction the utilization of non-conventional water sources, such as saline water, drainage, andsewage, has proven to be highly effective in managing droughts given the limitations of the country’s water resources. the primary advantage of utilizing effluent fromurban was tewater treatment plants is the s tability of these sources, their accessibility,and their low cos t for irrigating agricultural lands, which ultimately addresses the issueof water scarcity. s tudies have shown that using sewage for irrigation doesn’t harmagricultural products. however, some long-term s tudies have reported contaminationwith heavy metals and a decrease in soil quality in the irrigated area due to sewageirrigation. water quality indices are an effective and s traightforward method ofassessing the condition and s tatus of water. these indicators use multiple water qualityparameters to determine the water’s health through a mathematical formula, producinga single numerical value. the value is then classified on a relative scale from poor toexcellent, making it useful for managing, analyzing, and monitoring water qualitychanges over time and space.materials and methodsin this s tudy, the quality of shiraz urban sewage treatment plant effluent was evaluatedfor agricultural purposes by calculating the iranian water quality index (irwqi),national sanitation foundation of america water quality index (nsfwqi), andthe oregon water quality index (owqi) using daily data from 2018 to 2019. thewas tewater treatment plant in shiraz city is situated on 72-hectares of land in thesoutheas t region of the city. the plant currently serves a population of 409,000 people,and it is expected to cater for a final population of 584,000 people. the transmissionlines discharge an average of 1360 l/s, with a maximum discharge of 2600 l/s.nine parameters were selected to calculate the nsfwqi index, including turbidity, temperature, phosphate, nitrate, coliform, biological oxygen demand (bod), total dissolved solids(tds), dissolved oxygen (do), and ph. the owqi quality index is similar to the nsfwqi indexbut includes eight parameters: temperature, dissolved oxygen, biological oxygen demand, ph,nitrogen, total phosphorus, total dissolved solids, and fecal coliform.results and discussionthe analysis of the average quality parameters obtained from the relevant tes ts conducted by shirazwater and sewerage company indicates that the biological oxygen demand (bod) concentrationwas consis tently above 30 mg/l in all months. according to the s tandard, since the sub-index met aminimum value of 2, its changes did not affect the water quality index. the ph level was appropriatethroughout all seasons, and it did not vary significantly. therefore, it did not play a significant rolein determining the water quality index. on the other hand, the total dissolved solids concentrationexceeded 500 mg/l in all seasons, and the sub-index met a minimum value of 20. thus, its changesalso did not affect the water quality index. also, the results showed that the average nsfwqivalues varied between 28.73 and 31.54 in different months, indicating poor quality. the monthlyowqi values ranged from 4.38 to 7.95, indicating very poor quality. the irwqi index, which wascalculated using 11 parameters, confirms the results of the other two indices. by using a combinationof treated was tewater and high-quality water, we can irrigate our crops while reducing the amountof freshwater we use. this can be done directly using treated was tewater or by improving its qualitythrough drip irrigation and subsurface irrigation sys tems.conclusionthe results of the s tudied indices revealed that the effluent of the shiraz was tewater treatment plantis of poor quality. therefore, given the low quality of the effluent, it is recommended for use only inirrigating non-productive plants, fores t parks around shiraz, and a limited part of urban green space.