تصفيه تكميلي شيرابه كمپوست با استفاده از فرايند فتوكاتاليستي UV/TiO2

UV-TiO2 Photocatalytic Degradation of Compost Leachate

يكي از اقدامات لازم در خصوص مديريت پسماند، جمع آوري و تصفيه شيرابه است. تاكنون از روش هاي مختلفي جهت تصفيه شيرابه استفاده گرديده كه يكي از اين روش ها كه اخيرا مورد توجه قرار گرفته فرايند فتوكاتاليستي مي باشد. در اين تحقيق تصفيه تكميلي شيرابه كمپوست با استفاده از نانو ذرات TiO2 تثبيت شده بر بستر بتني و تحت تابش نور UV، در مقياس آزمايشگاهي مورد بررسي قرار گرفت. شيرابه مورد استفاده از خروجي تصفيه خانه يكي از مراكز توليد كمپوست كشور كه در دو مرحله مورد تصفيه بيولوژيكي قرار گرفته تامين گرديد. در اين فرايند از لامپ هاي UV-C با توان هاي مختلف در محدوده 107-8 وات كه در فاصله ثابت 10 سانتي متر از سطح شيرابه قرار داشت استفاده شد. در ابتدا به منظور تعيين تاثير هر يك از پارامترهاي اصلي موثر بر فرايند، آزمايش هاي شاهد در شرايط تاريكي مطلق، بستر بتني بدون پوشش نانو ذرات و اشعه UV تنها انجام و تاثير هر يك از عوامل مذكور به صورت مجزا بر حذف بار آلي از شيرابه ارزيابي گرديد. در ادامه تاثير همزمان عوامل ياد شده مورد بررسي قرار گرفته و در شرايط بهينه حداكثر حذف COD و رنگ به ترتيب 62 و 33 درصد در 5pH=، زمان ماند 20 ساعت، پوشش دهي نانو ذرات به ميزان 60 گرم بر متر مربع و با استفاده از لامپ UV با توان 77 وات حاصل شد. با در نظر گرفتن استانداردهاي سازمان حفاظت محيط زيست كشور، فرايند فتوكاتاليستي UV/TiO2 قادر به كاهش بار آلي شيرابه جهت استفاده در كشاورزي مي باشد

The growing rate in solid wastes production leads to considerable generation of leachate. Leachate is defined as the aqueous effluent generated as a consequence of precipitation percolation through wastes, biochemical processes in wastes body and the inherent water content of wastes themselves. Since the leachate contains significant amount of organic and inorganic compounds, it is not allowed to be directly discharge to the environment. Conventional treatment techniques to remove organic matters from leachate include physical, chemical and biological processes. Most of these techniques are non-destructive and do not solve the environmental problems because the wastes are simply transferred from water to another phase creating secondary wastes pollution. Biological method was regarded as the most efficient and cheapest process to eliminate organic materials from leachate. However, biological process cannot usually remove refractory substances. Therefore, the effluent values of the organic content do not meet the standards of the treated wastewater with respect to persistent contaminants. Due to limited biodegradability, the treatment of leachate, apart from biological methods necessitates the application of other methods, which complement and support the main process. Advanced oxidation process has been intensively studied in the past decade to improve the removal of these large refractory organic molecules or to transform them into more easily biodegradable substances. Among them photocatalytic process is one of the appropriate methods for final treatment of these kinds of waste. In this study, application of photocatalytic process via UV light and TiO2 Nano particles immobilized on concrete surface in post-treatment of composting leachate was investigated. This investigation was conducted in laboratory scale and batch mode. A biological pre-treated leachates sample which contains some macromolecular organic substances that were resistant to biological degradation were collected from the effluent of leachate treatment facility, of Gorgan composting plant (Golestan, Iran). UV-C lamps with different power in the range of 8-107 W at a constant distance of 10 cm from the surface of the leachate were used as the source of irradiation. Pervious concrete was constructed using LECA lightweight aggregates with the dimension of 30*10*10 cm. Immobilization of TiO2 on concrete surface was done by using concrete sealer. In order to investigate the effect of each parameter individually, some experiments were carried out. The results showed that the presence of nanoparticles and UV radiation alone did not significantly affect on the COD removal. According to the conducted experiments the maximum COD removal of 62% was achieved after 20 hr radiation with 7.5 mW.Cm-2 intensity in pH value of 5 and in presence of 60 g.m-2 of TiO2 coated on concrete. According to Iranian environmental standards and with regard to organic loading of leachate, removal efficiency of this process was in such a way that it could be directly discharged into the environment.