تاثير تخلخل و شدت بارش بر راندمان تصفيه رواناب شهري توسط روسازي بتني متخلخل

The Effect of Porosity and Rainfall Intensity on Performance of Urban Runoff Treatment Via Previous Concrete Pavement

رواناب شهري شامل آلاينده هايي همچون مواد مغذي، فلزات سنگين و مواد آلي مانند هيدروكربن ها بوده كه از سطح جاده شسته شده و منجر به آلوده شدن منابع آب و خاك مي شود. در اين ميان روسازي بتني متخلخل قادر به كاهش قابل توجه حجم رواناب هاي شهري و در نتيجه كاهش بار هيدروليكي رواناب و اثرات جانبي آن بر تاسيسات شهري مي باشد. همچنين اين نوع روسازي شرايط لازم براي تصفيه و مديريت آلودگي هاي منتشر شده شهري در نزديكي و يا خود منبع را فراهم مي كند. هدف از انجام اين تحقيق بررسي كارايي سيستم روسازي بتني متخلخل بر كميت و كيفيت رواناب سنتزي بوده و اثرات تغيير تخلخل و شدت بارش بر پارامترهاي مختلف مورد بررسي قرار گرفته است. در مطالعه حاضر بيشترين راندمان حذف tss و cod به ترتيب برابر 88% و 15% حاصل گرديد. همچنين سيستم توانايي كمي در حذف tds و ec از خود نشان داد. سيستم روسازي مورد بررسي در اين مطالعه توانايي قابل قبولي در حذف كدورت از رواناب سنتزي را دارا بوده و بيشترين ميزان حذف در شدت بارش 37 ميلي متر بر ساعت و تخلخل 9/22% به ميزان 70% حاصل شد. با مقايسه نتايج حاصل از بررسي پارامترهاي فوق مشخص گرديد كه تغيير تخلخل تاثيري بر كيفيت پساب خروجي ندارد. همچنين با افزايش شدت بارش ميزان كارايي سيستم در حذف آلاينده ها هرچند با شيب بسيار كم، كاهش يافت. به طور كلي اين روش توانايي خوبي در حذف tss و كدورت از خود نشان داد ولي كارايي مناسبي در حذف بار آلي و جامدات محلول نداشت.

Urban development is always associated with infrastructure surfaces icreasment such as road and building construction and other impermeable surfaces that lead to precipitations runoff. Urban runoff contains heavy contaminants such as nutrients, heavy metals and organic substances including hydrocarbons and polycyclic aromatic hydrocarbons (PAHs). This pollutants can infect water and soil resources by road surface washing and discharging into the receiving waters or infiltrating into surrounding area soils. Stormwater management has recently shifted towards a focus on site level low impact development (LID) techniques that aim to reduce the total stormwater runoff volumes in addition to attenuating peak flows and removing pollutants at or near the source of runoff. Permeable pavement systems (PPS) are a subset of LID stormwater best management practices (BMPs) of particular interest in dense urban areas because they can be installed in parking lots and low traffic roadways where the availability of land space for more traditional BMPs is not available. Such information is necessary to improve the selection of BMP/LIDs for stormwater management. Previous concrete pavement are subset of PPS and able to reduce the volume of urban runoff significantly which leads to hydraulic differentia reduction and its specific side effects urban utilities in addition to providing requirements for treatment processes and in-situ urban pollution management. In this study, porous concrete pavement performance has been surveyed in terms of quantitative and qualitative reduction of synthetic runoff. The effect of porosity and rainfall intensity were investigated. To investigate the effect of concrete porosity, four levels including 15%, 20%, 25% and 30% have studed and for evaluating rainfall intensity effect, a range of precipitation between 25 to 250 mm/h concidered according the recent studies considered. The pilot used for this study consisted of a tank made of galvanized steel that simulated PCP was replaced layer by layer at the bottom of tank. Synthetic runoff sprinkled on the previous concrete surface with specified flow rate. Effluent is collected from the orifice that embedded under the tank then effluent quality parameters were evaluated. Befor run the pilot Previous concrete mixed designs calculated and prosity, percolation rate and Compressive strength were verified. The parameters examined in this study including COD, TDS, TSS, turbidity and EC of pervious concrete pavement system was compared to synthetic runoff. According to study outcomes, the system efficiency in TSS removal was between 75.7% to 88.6%, highest COD removal detected was 15% in case the porosity was 22.9%. Effluent quality analysis demonstrated that PCPS had little ability in TDS and EC removal. However PCPS was able to remove turbidity from syntetic runoff. The maximum efficiency of turbidty removal was detected 70.3% at rainfall intensity of 37 mm/h and the porosity of 22.9%. By comparing the results of the above parameters, it was determined that porosity has almost no effect on runoff quality. Results showed the rainfall intensity dose not have significant effect on PCPS efficency although the systems overall removal efficiency was drastically deacrased due to rainfall intensity increase even in cases with low emissions gradients.