امكان سنجي استفاده از شبكه‌هاي جمع‌آوري نوين فاضلاب به عنوان تاسيسات پيش تصفيه

Evaluation of Conventional sewers as wastewater pre-treatment facilities

در اين پژوهش تاثير واكنش‌هاي بيولوژيكي در حذف مواد آلي فاضلاب موجود در شبكه‌هاي جمع‌آوري نوين بررسي شد. براي اين منظور شبكه‌هاي جمع‌آوري فاضلاب از جنس PVC تحت جريان ثقلي در مقياس آزمايشگاهي طراحي و ساخته شد. از چسباندن توري پلاستيكي به عنوان واسطه به سطوح داخلي لوله، براي رشد و الحاق ميكروارگانيسم‌ها، استفاده شد. جهت افزايش غلظت ميكروبي و همچنين سرعت بخشيدن به تشكيل بايوفيلم، از لجن فعال تصفيه خانه شهرك يثرب استفاده گرديد. فاضلاب مصنوعي با آلودگي مشابه با فاضلاب خانگي در اين مطالعه استفاده گرديد. در اين مطالعه تجربي پارامترهايي مانند BOD، COD، TN، NH3N ، NO3N ، TSS، مقاديرDO و ضخامت بيوفيلم در شرايط آزمايشگاهي اندازه گيري شد.نتايج نشان مي دهد بايوفيلم ايجاد شده بر روي سطح يكنواخت نبود و ضخامت آن بين 4.7-3 ميلي‌متر و چگالي سطحي بايوفيلم بين33.1-22.3 گرم بايومس بر متر مربع بدست آمد. نرخ مصرف اكسيژن تقريبا به 0.21 ميلي‌گرم بر ليتر بر دقيقه بود. غلظت مواد معلق با كاهش 82 درصدي از 105 به 19 ميلي‌گرم بر ليتر رسيد. بيشترين راندمان حذف مواد آلي در شبكه، در بار گذاري هاي مختلف بهره برداري براي ‍ BOD , COD به ترتيب به 59 و54 درصد رسيد. با افزايش بار آلي 70% به شبكه فاضلاب، ميزان راندمان حذف COD فقط 9% كاهش يافت . در هر دو حالت بارگذاري آلي شبكه، با توجه به غلظت بالايCOD پساب خروجي، شرايط رشد باكتري هاي نيترات ساز ويا فرآيند نيتريفيكاسيون شكل نگرفت و تغييرات غلظت ‌‌‌تركيبات نيتروژني ناچيز بود.

The composition of wastwwater in sewer lines are changing due to their nature. Wastewater contains large amount of organic materials, therfore it is suseptible to biological disintegritaion. Normally the conditions of sewers dicctate and promote the type of growth of bacteria being either aerobic or anaerobic. Previous studies have shown that large number of concrete sewer lines were found to beeffected by anaerobic bacteria activites. In this experimental investigation the aerobic biological transformation of organic matter in small diameter gravity slope wastewater collection system is evaluated. In this study a sewer network reactor at pilot scale was designed and built. The reactor consists of 15 meters length of PVC with 0.1 m diameter, two storage tanks and re circulating pump. The whole system was set up on a platform with adjustable slope. To ease the Formation of attached growth of micro organism a plastic net was attached on the inner surface of PVC pipe, thus a rough surface for attachment of microorganisms was formed. Due to the variation of hydraulic mean diameter, contact area with flowing wastewater was ranged from 1.88 to 3.77 m2 (half or full). Synthetic wastewater with characteristic municipal wastewater was used. A settled activated sludge fromYasreb wastewater treatment plant in Qaemshahr city was used to start and accelerate the biofilm growth in the reactor. In order to study biofilm attachment rate two P.V.C square plates in dimensions of 10*10 cm were placed perpendicular on the direction flow of wastewater. The reactor was conducted under aerobic conditions in a hydraulic retention time of 7 hours under constant temperature changed about 20 ±3 C. In this study parameter such as BOD, COD, TN and NH3N and NO3N were measured on daily basis. The thickness of biofilm increased and formed as irregular with thickness of 34.7 mm. Biofilm characteristics analysis showed that density and surface density were respectively 55 mg Ts/cm3 and between 22.3 and 33.1 m2. The concentration of suspended biomass was varied from1015 mgl1 at optimum COD removal. Oxygen consumption rate was estimated from decreasing rate of soluble oxygen concentration which reached to 0.21 mg l1 min1 after 3 weeks of operation. The highest reduction in COD and biological oxygen demand (BOD) concentration were 59% and 54% respectively . By increasing the chemichal oxygen demand (COD) loading by 70 %, removal rate of COD reduced by only 9%. Due to high COD concentration of wastewater effuluent, the nitrification process was limited. In order to nitrify the waste water, a longer hydraulic retention time(HRT) or higher recirculation is required. From the results and analysis it can seen be seen that proposed innovative method is applicable in many fields such as mountainous area, area with water stress ratio, water scarce area and ... which normally an application of conventional wastewater treatment either are costly or impractical. And also with regard to publicized incentives for using waste water reclaimation as a source of water for agricultral irrigation, thus with more precision in desigin and operation, an effluent of these new configuration of PVC pipes can be used in agriindustry