تصفيه خاك آلوده به شيرابه توسط فرايند ازن زني

اندكي پس از توليد مواد زائد، توليد شيرابه آغاز شده كه از منابع آلاينده خاك و آب‌هاي زير‌‌زميني به شمار مي‌رود. امروزه فرآيند ازن زني به‌عنوان يك روش پركاربرد در تصفيه خاك‌هاي آلوده مورد‌استفاده قرار مي‌گيرد. ازن در تصفيه گستره وسيعي از آلاينده‌ها كاربرد دارد. از آنجايي‌كه شيرابه در برگيرنده مجموعه‌اي از آلاينده‌هاي آلي و معدني است، بنابراين فرايند ازن زني مي‌تواند نقش مفيدي در ‌تصفيه خاك‌هاي آلوده به شيرابه داشته باشد. در اين مطالعه كاربرد فرايند ازن زني جهت پالايش خاك آلوده به شيرابه حاصل از فرايند كمپوست زباله شهري در مقياس آزمايشگاهي موردبررسي قرارگرفته است. در اين تحقيق اثر پارامترهاي زمان واكنش، دبي ازن زني، pH محيط، پيش‌تصفيه ازن، ميزان مواد آلي خاك و همچنين حضور اكسيدهاي فلزي بر راندمان حذف مواد آلي از خاك موردبررسي قرارگرفته است. بر اساس نتايج آزمايش‌ها حداكثر راندمان حذف به ميزان 2/11% پس از 120 دقيقه ازن زني با دبي200 ميلي‌ليتر بر دقيقه و در pH حدود 9 حاصل شد. همچنين با افزايش آلودگي اوليه خاك راندمان حذف مواد آلي افزايش يافت. در اين پژوهش حضور اكسيد آهن 3 ظرفيتي باعث افزايش 42 درصدي در راندمان حذف مواد آلي خاك گرديد. براساس آزمايشات صورت پذيرفته، ازن پس از عبور از مجاورت اسيد توانسته است در pH حدود 9، پس از گذشت 120 دقيقه، مواد آلي خاك مورد مطالعه را به ميزان 2/21 درصد كاهش دهد كه در مقايسه با راندمان حذف با استفاده از گاز ازن بدون پيش‌تصفيه نزديك به90% افزايش، نشان مي‌دهد.

By developing of the consumerism and rapidly progress of industrial and commercial lifestyle in most of the countries, the solid waste production has been growth rapidly in the recent years. The leachate production starts shortly after the production of waste and cause the pollution of environment and especially contamination of the soil. Chemical processes are usually considered as the most effective processes for degradation of soil pollutants. In these processes, the chemical reagents are added to make the desired reactions take place. But it is sometimes necessary to increase the amount of reagents so that the reactions take place completely. This may cause chemical reagents to remain in the soil. Ozone, which acts as a powerful oxidizer, is capable of degrading organic pollutants in a short period of time without producing any toxic residuals. Nowadays ozonation has become one of the most favorable processes in soil remediation technologies. Ozone is used in the treatment of a wide range of pollutants. Due to the high diffusion coefficient of ozone, all of the present pollutants in soil are theoretically available for this oxidant. Since leachate contains a range of organic and inorganic pollutants, ozonation process is therefore can be a useful process in treating soils contaminated with leachate. In this study, application of ozonation process as an ex-situ method on the treatment of composting leachate polluted soil was studied in laboratory scale and in batch mode. Experiments were conducted using a cylindrical Plexiglas reactor with the diameter of 3 cm and the height of 60 cm. Ozone gas was continuously passed through a diffuser at the bottom of the reactor. Ozone generator with 5 g/h nominal capacity was used to produce ozone gas from pure and dry oxygen. Ozone content was measured with a digital ozone analyzer. A rotameter was also applied to measure the volume of gas injected to the reactor. The leachate used in this study has been collected from one of composting plant in north of Iran. The soil used in this study was mainly silica with the particle size of 0.12-0.3 mm. In order to pollute the soil; a certain amount of leachate was well mixed with the soil and then dried to the desired humidity. According to the results the maximum removal of soil organic content was obtained at pH=9 after 120 minutes ozonation with a flow of 200 ml/min. By increasing the initial organic content of the soil, the removal via ozonation has been also increased. In other word the soil with higher initial contaminations has shown better removal efficiencies compared with the one with lower initial pollutants. In this study, the presence of trivalent iron oxide caused 42% increases in soil organic content removal efficiency. In this research applying gas washing technique with acid also greatly enhanced the removal efficiency of ozonation process. According to the conducted experiments, after pre washing of ozone with acid, the removal of soil organic content with nearly 90% increase, reached to 21.2%. The results were also shown that, the change in the type of acid did not have a significant effect on the soil organic matter removal efficiency.