رفع آلودگي از خاك‌هاي كايولينيتي آلوده به BTEX با استفاده از فناوري ديواره هاي تراواي واكنش زا (PRB) و نانوذرات آهن

Remediation of BTEX-contaminated groundwaters by Nano scale zero-valent Iron based PRBs

آلاينده هاي خانواده BTEX (شامل بنزن، تولوين، اتيل بنزن و زايلين) از آلاينده هاي زيست محيطي مونوآروماتيك بسيار مهم است، تركيب BTEX در گازوييل، بنزين و ديگر محصولات صنايع پتروشيمي يافت مي شوند، اين تركيبات كه بخش عمده‌اي از محصولات نفتي را تشكيل مي دهند بسيار سمي بوده، و علاوه بر آثار بسيار زيان آور بر سلامتي انسان، سبب صدمه شديد به كليه اشكال حيات مي شوند. در اين پژوهش با به كار بردن نانو ذرات آهن در يك ديواره تراواي واكنش زا (PRB) اثر اين نانوذرات به عنوان عامل واكنش زاي به كار رفته در PRB ، در رفع آلودگي از خاك‌هاي اشباع كايولينيتي آلوده به BTEX به صورت كمي بررسي شده است. در اين آزمايش‌ها مشاهده شد غلظت آلاينده هاي BTEX موجود در آب، در اثر عبور از لايه هاي PRB قرار گرفته در سلول مورد آزمايش، تا 60% غلظت اوليه كاهش يافته است. يكي ديگر از مسايلي كه در اين پژوهش بررسي شده مقدار بهينه نانو آهن به كار رفته در لايه هاي واكنش زا است، در اين پژوهش در چند مرحله آزمايش، براي آلاينده هاي مورد مطالعه مقاديري به عنوان مقادير بهينه نانو آهن در هر لايه ارايه شده است. در آزمايش هاي انجام شده در اين مطالعه پارامتر دما به عنوان يكي از عوامل تاثيرگذار بر فرايندهاي رفع آلودگي، به صورت كنترل شده و هدفمند تغيير داده شده تا امكان بررسي اثر دما روي نتايج آزمايش‌ها وجود داشته باشد. نتايج به دست آمده از اين پژوهش مي تواند در طراحي سيستم هاي رفع آلودگي از آب هاي زير زميني استفاده شود.

Benzene, toluene, ethylbenzene and xylenes, commonly referred to as BTEX, are critical monoaromatic environmental contaminants around the World, of which the major aromatic contaminants in gasoline pose serious environmental health problems. Leaking tanks or ruptured pipelines pollute soil and groundwater with these compounds. Because of their polarity and very soluble characteristics, these compounds will be able to enter the soil and groundwater systems and cause serious contamination problems and threats to the public safety and environment. One of the most promising ground water remediation technologies is the use of permeable reactive barriers (PRBs) packed with reactive material to intercept and decontaminate plumes in the subsurface. The concept of PRBs is rather simple. Reactive material is placed in the subsurface to intercept a plume of contaminated groundwater which must move through it as it flows, typically under its natural gradient. As the contaminant moves through the Reactive material, reactions occur that alter it to less harmful or immobile species. The PRB is not a barrier to the groundwater, but it is a barrier to the contaminant. The key advantage of a reactive barrier is the passive nature of the treatment. That is, for the most part, its operation does not depend on any external labor or energy inputs. Once installed, the barrier takes advantage of the in situ groundwater flow to bring the pollutants in contact with the reactive material. The reactive material used in the barrier may vary depending on the type of contaminants being treated. The most common reactive agent used to date has been granular iron. For contaminants of unknown treatability or media of unknown reactivity, addressing these issues will involve laboratory studies using both batch and column techniques. As for any remedial technology, it is imperative to fully understand the factors that can result in either effective implementation and successful remediation or failure to achieve the remedial design objectives. Iron nanoparticles are increasingly being applied in soil and grounwater remediation and hazardous waste treatment. Nearly two decades after iron nanoparticle was first proposed, the iron nanoparticle technology is at a critical point of its development process. Extensive laboratory studies have verified that nanoscale iron particles are effective for the treatment of a wide range of common groundwater pollutants such as chlorinated organic solvents, organochlorine pesticides, polychlorinated biphenyls (PCBs), organic dyes, and various inorganic compounds. Numerous field trials have also demonstrated the favorable prospective for in situ remediation. Nonetheless, there are still substantial knowledge gaps on many fundamental scientific issues. In this Experimental study, A series of laboratory experiments in various temperatures and contaminant concentrations were conducted on Nano sized zero-valet iron (nZVI) to determine its removal efficiency as PRB reactive materials against BTEX compounds in saturated Kaolinite clays, And the initial Concentration of BTEX is reduced to 60%. Obtained results may provide required data in groundwater remediation PRB systems design.