مدل‌سازی آلودگی چاه‌های جذبی بر آب زیرزمینی

نوع مقاله : علمی - پژوهشی

نویسندگان

1 گروه محیط زیست، دانشکده منابع طبیعی و محیط زیست، دانشگاه ملایر، ملایر، ایران

2 معاونت پژوهش و فناوری، وزارت علوم، تحقیقات و فناوری، تهران، ایران

چکیده

سابقه و هدف: چاه‌های جذبی از رایج‌ترین انواع تاسیسات بهداشتی در بیشتر کشورهای در حال توسعه هستند. این چاه‌ها به‌عنوان مکانیزمی برای جداسازی فاز مایع از جامد هستند، اما در بیشتر آنها شرایط برای نیتروژن‌دهی محلول حاوی سرب فراهم بوده که می‌تواند حجم قابل‌توجهی از آلودگی را وارد منابع آب زیرزمینی کند. ازاین‌رو برای بررسی نیترات ورودی به آب‌های زیرزمینی در نواحی استقرار چاه‌های جذبی از روش مدل‌سازی استفاده ‌شده است.مواد و روش‌ها: در این مدل یک آبخوان با ویژگی‌های عادی یک آبخوان واقعی به صورت فرضی درنظر گرفته شد. فاصله سطح آب زیرزمینی تا کف (ته) چاه جذبی را 5، 10 یا 30 متر در نظر گرفته و این عمق به تمام سطح آب در آبخوان فرضی تعمیم داده شد. همچنین برای نیترات نیمه‌عمر 500 تا 1500 روز با مقیاس زمانی 6 ماه تا چند سال در نظر گرفته شد. سپس در نرم‌افزار MATLAB نمودار مربوط به تغییرات غلظت نیترات به عمق ترسیم شد.نتایج و بحث: نتایج از بالا بودن احتمال آلودگی نیترات در سطح آب زیرزمینی نسبت به استاندارد سازمان بهداشت جهانی (50 میلی‌گرم درلیتر) برای آشامیدن در چاه‌هایی با فاصله 5 متر بین کف چاه جذب تا سطح آب در دوره 5 ساله با نیمه‌عمر متوسط تا طولانی نیترات حکایت داشت. مکان‌یابی نواحی دور از سطح آب زیرزمینی، تخلیه مکرر چاه، تعویض آن و تفکیک فاضلاب قبل از ورود به چاه از راه‌حل‌های مؤثر برای کاهش ورود نیترات از چاه‌های فضولات انسانی به آب زیرزمینی است. هرچند راهکارهای فوق ممکن است به دلایل اجتماعی، فنی و محدودیت‌های اقتصادی همیشه قابل‌اجرا نباشد.نتیجه‌گیری: بررسی‌‌ گسترده در سطوح مختلف و با داده‌های دقیق‌تر با نیمه‌عمرهای متفاوت نیترات می‌تواند اطلاعات درباره شدت آلایندگی چاه‌های فضولات انسانی را افزایش دهد.

کلیدواژه‌ها

عنوان مقاله [English]

Modeling of absorptive wells pollution on groundwater

نویسندگان [English]

  • Balal Oroji 1
  • Hosain Bahrami 1
  • Mohammad Sadegh Oliaei 2
1 Department of Environmental Science, Faculty of Natural Resources and Environmental Science, Malayer University, Malayer, Iran
2 Department of Research and Technology, Ministry of Science, Research and Technology, Tehran, Iran
چکیده [English]

Introduction: Absorptive wells are one of the most common forms of onsite sanitation facilities in many developing countries. These latrines are suitable as a means of isolating human waste; however, conditions within pits often lead to nitrification of the contained waste. In areas with a near-surface aquifer, the potential for nitrate pollution arising from Absorptive wells cannot be ignored.Material and methods: In this study, Hypothetical aquifer was made, to gather relevant information about the Absorptive wells in use and the soil and groundwater underneath the Hypothetical aquifer. Modeling was then conducted to demonstrate the potential for nitrate pollution of the groundwater from the latrines in such settings. The depth from the bottom of the pits to the water table was considered as 5, 10 or 30 m, to represent the range of aquifer depths at the study sites. Nitrate half-lives ranging from 500 to 1500 days were considered, and time scales from 6 months to several years were modeled.Results and discussion: The results highlighted the high likelihood of nitrate pollution of groundwater reaching levels exceeding the World Health Organization guideline value for nitrate in drinking water of 50 mg/L after as short a period as two years for the aquifer situated 5 m below the pits, when considering moderate to long nitrate half-lives in the subsurface. Careful siting of latrines away from high water table areas, more frequent pit emptying, or switching to urine diversion toilets may be effective solutions to reduce nitrate passage from Absorptive wells into groundwater, although these solutions may not always be applicable, because of social, technical and economic constraints.Conclusion: The study highlights the need for more reliable data on the typical nitrate concentrations in Absorptive wells and the nitrate half-life in different subsurface conditions.

کلیدواژه‌ها [English]

  • Keywords: Nitrate
  • Groundwater
  • Absorptive well
  • Pollution
  • Modeling

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فصلنامه علوم محیطی
دوره 14، شماره 4
دی 1395
صفحه 75-90

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