بازیابی منعقدکننده از لجن تصفیه‌خانه‌ی آب به روش هضم اسیدی
محورهای موضوعی : تکنولوژی آب و فاضلاب
سیده الهه مهدویان آهق
1
(دانشگاه تهران)
فریبا استوار
2
(پژوهشکده محیط زیست جهاددانشگاهی)
کلید واژه: منعقدکننده هضم اسیدی تصفیه‌خانه‌ی آب لجنآلومینیوم,
چکیده مقاله :
انعقاد فرایندی است که تمایل ذرات کوچک موجود در سوسپانسیون آبی را جهت چسبیدن به یکدیگر و به سطوحی مانند مدیا در صافی شنی افزایش می‌دهد و از طریق مخلوط کردن منعقدکننده‌هایی نظیر سولفات آلومینیوم (آلوم)، کلرید فریک و پلی‌آلومینیوم کلراید با آب خام انجام می‌شود. لجن‌های حاوی منعقدکننده پس از عمل انعقاد و به واسطه‌ی ته‌نشینیِ کدورت طبیعی تشکیل می‌شوند. وجود مقدار زیادی منعقدکننده در لجن تصفیه‌خانه‌ی آب، ریسک‌های محیط‌زیستی و هزینه‌های مربوط به دفع را افزایش می‌دهد. از سوی دیگر، منعقدکننده‌های موجود در لجن ارزش اقتصادی بالایی دارند. بنابراین چنانچه بازیابی شوند، علاوه بر کاهش ریسک‌های مربوط به دفع لجن، ممکن است هزینه‌های تأمین منعقدکننده‌ی تازه در تصفیه‌خانه‌ی آب و یا فاضلاب نیز کاهش یابد. در این مقاله پژوهش‌های انجام شده به روش هضم اسیدی جهت بازیابی منعقدکننده از لجن تصفیه‌خانه‌ی آب بررسی شده‌اند. میزان بازیابی منعقدکننده‌ها، نقاط قوت و ضعف و جنبه‌های اقتصادی این روش، مواردی هستند که به آنها پرداخته شده است. نتایج بررسی‌های انجام شده مشخص نمود استفاده از سولفوریک اسید، به دلیل ارزان و در دسترس بودن، بهترین گزینه برای انجام فرایند هضم اسیدی است. همچنین چنانچه هدف از بازیابی منعقدکننده، دستیابی به کیفیتی مشابه نمونه‌ی تجاری باشد، روش هضم اسیدی استانداردهای مربوطه را ارضاء نخواهد نمود.
Coagulation is a process that increases the tendency of small particles in an aqueous suspension to attach to one another and to surfaces such as the media in a filter bed and is applied through mixing coagulants such as aluminum sulfate (alum), ferric chloride and polyaluminum chloride with raw water. Sludge containing coagulant is formed after coagulation and through sedimentation of natural turbidity. Presence of high amounts of coagulant in waterworks sludge, increases environmental risks and disposal costs. Coagulants in sludge have high economic value. Therefore, if these coagulants recover, not only sludge disposal risks but also expenses related to supply of fresh coagulant in water or wastewater treatment plant may decrease. In this paper, researches conducted by acid digestion method for coagulant recovery from waterworks sludge are investigated. Amounts of coagulant recovery, advantages and disadvantages and economic aspects of this method are studied. Results of the investigation showed that using sulfuric acid is the best option for conducting acid digestion process because it is cheap and available. Moreover, if the purpose of recovering process is to achieve a recovered coagulant with a similar quality to the commercial ones, acid digestion method will not satisfy related standards.
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