پديد آورندگان :
شريفي، شهرام دانشگاه نوشيرواني بابل , حسيني، مرتضي دانشگاه نوشيرواني بابل - گروه مهندسي شيمي , اميني راد، حسن دانشگاه نوشيرواني بابل - گروه مهندسي عمران
كليدواژه :
منعقدكنندة طبيعي , بنه , حذف كدورت , بهينه سازي , انعقاد , RSM
چكيده فارسي :
انعقاد يكي از مهمترين فرآيندها در تصفيه آب است. نگراني روزافزون جهاني در مورد مسائل زيست محيطي علاقه به تحقيق در مورد منعقدكننده‌هاي طبيعي را افزايش داده است. در حال حاضر ثابت شده است كه منعقد كننده‌هاي طبيعي به دليل در دسترس بودن ، مقرون به صرفه بودن، ماهيت غيرسمي و زيست تخريب‌پذير بودن، جايگزين خوبي براي منعقد كننده‌هاي شيميايي هستند. در اين مطالعه پتانسيل، مناسب بودن ، اثربخشي و كارايي دانه بنه به عنوان منعقد كننده طبيعي براي تصفيه آب با كدورت اوليه NTU100 بررسي شد. از طرف ديگر ، روش سطح پاسخ (RSM) از نوع طراحي مركب مركزي (CCD) در 5 سطح براي ارزيابي و بهينه سازي شرايط واكنش فرآيند انعقاد-لخته سازي در تصفيه آب آشاميدني به كار گرفته شد. از سه پارامتر غلظت منعقد كننده، pH و زمان تماس كه از عوامل مهم و تأثيرگذار بر فرآيند انعقاد-لخته سازي هستند به عنوان متغير در طراحي آزمايش استفاده شد. يك مدل چند جمله‌اي درجه دوم با مقدار0.9654=R2 (ضريب تشخيص) به داده‌ها ارائه شد. آزمايش‌هاي صحت مدل، مطابقت خوب بين مقادير واقعي و مقادير پيش‌بيني شده را نشان داد. در تصفيه آب آشاميدني حاصل از نتايج تجربي، كاهش قابل ملاحظه كدورت يعني 95.13 درصد با غلظت 90.53 ميلي گرم در ليتر ، 9.79= pHو زمان تماس 44.86 دقيقه براي منعقدكننده بنه حاصل شد. با توجه به نتايج بهينه‌سازي، دانه بنه به عنوان منعقدكننده در تصفيه آب آشاميدني پتانسيل بالايي را از خود به نمايش گذاشت.
چكيده لاتين :
Coagulation is one of the most important processes in water treatment. Water sources can be contaminated with pathogenic microorganisms, soluble and suspended solids, particles that change the taste, odor and color of water and make water unsafe for human consumption. Such impurities and contaminants which reduce water quality must be effectively removed. Coagulation- flocculation is performed as the first step in water treatment processes to remove turbidity from suspended solids and colloidal particles. The materials used in this stage of water treatment can be inorganic coagulants, synthetic organic polymers or coagulants of natural origin. Aluminum sulfate (alum) is a common coagulant used worldwide in water treatment. Despite the high efficiency of alum in removing turbidity, the volume of sludge produced after the coagulation process is high, that raises concerns about its harmful environmental effects. Apply of synthetic polymers and the presence of residual monomers is undesirable due to nerve toxicity and strong carcinogenicity. Therefore, the use of natural coagulants received more attention. In contrast to chemical coagulants, natural coagulants are safe, eco-friendly and generally toxic free. Natural coagulants have been found to generate not only a much smaller sludge volume (up to five times lower), but also a higher nutritional sludge value. As such, lower costs of sludge treatment and handling canmake it a more sustainable. The raw plant extracts are often available locally and hence, a low cost alternative to chemical coagulants. Since natural coagulants do not consume alkalinity unlike alum, pH adjustments can be omitted that provides extra cost savings. Natural coagulants are also non-corrosive. In this study, Pistacia atlantica seeds were used as a natural coagulant. The seeds were obtained from coriander tree in the Zagros Mountains (Rig region, Lordegan province, Iran). Husks of the seeds were removed manually. This biomass was madecoarse grind using a hand mill. Then, it came to fine grind by a Bosch electric Kaolin mill. Afterward, 5 g/l of fine milled seeds was mixed with distilled water and stirred at 500 rpm, using electric stirrer for 10 min at room temperature. The filtered extract containing the active coagulant was then used in the coagulation process. Synthetic turbid water was prepared by adding kaolin to distilled water to gain a stock kaolin suspension for all coagulation experiments. The stock kaolin suspension was prepared by dissolving 10 g of kaolin powder in 1 L of distilled water. The suspension was stirred at 20 rpm for 1 h to achieve uniform dispersion of the kaolin particles. The suspension was then permitted to stand for 24 h to achieve a complete hydration of the kaolin. This suspension was used as a stock solution for the preparation of water samples of varying turbidity for the coagulations tests. Then, one molar solution of HCl and NaOH were added into the synthetic turbid water to adjust the pH value. The coagulation activity of Pistacia atlantica extract was determined by Jar test, during which 300 ml of Synthetic turbid water of different initial turbidities was poured into 600 ml beakers. Pistacia atlantica extracts with variable doses and densities were added to these beakers and mixed at 100 rpm for 4 min for rapid mixing using mechanical stirrer. The mixing speed was reduced to 40 rpm for another 25 min. The suspensions were then allowed to settle down. After 30 min of sedimentation, clarified samples from beakers were collected and their residual turbidities were measured using turbidity meter. The initial turbidity was studied 100 NTU and the solvent with 0.5 M NaCl were employed. All the experiments were repeated at least twice for consistency and results average. Moreover, the response surface methodology (RSM) of central composite design (CCD) was used at 5 levels to evaluate and optimize the reaction conditions of the coagulation-flocculation process in drinking water treatment. Three parameters of dose, pH and contact time, which are important and influential factors on the coagulation-flocculation process, were used as variables in the experimental design. A quadratic polynomials model with a value of R2 = 0.9654 (correlation coefficient) was presented to the data. Model accuracy tests showed a good correlation between actual and predicted values. In the treatment of drinking water obtained from experimental results, a significant reduction in turbidity was obtained for Pistacia atlantica coagulant, i.e. 95.13% with the dose of 90.53 mg/l, pH = 9.97 and a contact time of 44.86 minutes. Consequently, Pistacia atlantica seed had high potential as a coagulant in drinking water treatment.
