Improvement of Landfill Leachate Biodegradability with Ultrasonic Process

et al. (2012) Improvement of Landfill Leachate Biodegradability with Ultrasonic Process. PLoS ONE 7(7): e27571. doi:10.1371/journal.pone.0027571 Improvement of Landfill Leachate Biodegradability with Ultrasonic Process Amir Hossein Mahvi 0 Ali Akbar Roodbari 0 Ramin Nabizadeh Nodehi 0 Simin Nasseri 0 Mohammad 0 Hadil Dehghani 0 Mahmood Alimohammadi 0 Vanesa Magar, Plymouth University, United Kingdom 0 1 School of Public Health, Tehran University of Medical Sciences , Tehran , Iran , 2 National Institute of Health Research, Tehran University of Medical Sciences , Tehran , Iran , 3 Center for Solid Waste Research, Institute for Environmental Research, Tehran University of Medical Sciences , Tehran , Iran Landfills leachates are known to contain recalcitrant and/or non-biodegradable organic substances and biological processes are not efficient in these cases. A promising alternative to complete oxidation of biorecalcitrant leachate is the use of ultrasonic process as pre-treatment to convert initially biorecalcitrant compounds to more readily biodegradable intermediates. The objectives of this study are to investigate the effect of ultrasonic process on biodegradability improvement. After the optimization by factorial design, the ultrasonic were applied in the treatment of raw leachates using a batch wise mode. For this, different scenarios were tested with regard to power intensities of 70 and 110 W, frequencies of 30, 45 and 60 KHz, reaction times of 30, 60, 90 and 120 minutes and pH of 3, 7 and 10. For determining the effects of catalysts on sonication efficiencies, 5 mg/l of TiO2 and ZnO have been also used. Results showed that when applied as relatively brief pre-treatment systems, the sonocatalysis processes induce several modifications of the matrix, which results in significant enhancement of its biodegradability. For this reason, the integrated chemical-biological systems proposed here represent a suitable solution for the treatment of landfill leachate samples. - The generation of leachate remains an inevitable consequence of the practice of waste disposal in sanitary landfills [1]. Leachate from mature landfills contains less biodegradable carbon due to loss from the landfill via methane gas production and is typically characterized by high ammonium (NH4+) content, low biodegradability (low BOD5/COD ratio) and high fraction of refractory and large organic molecules such as humic and fulvic acids [2]. Usually young landfill leachates contain low organic compound concentrations and are treated more easily as compared to the old one [3]. Biodegradable organic compounds and ammonia are leachate constituents that pose the most significant environmental threats [4,5]. Biological treatment of leachate is often the most costeffective alternative when compared to other treatment options [6]. Nevertheless, mature leachate effluents are known to contain recalcitrant and/or non-biodegradable organic substances and biological processes are not efficient in these cases [7,8]. Studies have demonstrated that the major fraction of dissolved organic carbon (DOC) in biologically pre-treated landfill leachates consists of humic substances, mainly in humic and fulvic acids. Traditionally, the degradation of organic compounds and the removal of nitrogen can be achieved by advanced oxidation processes (AOP) [9,10]. AOP have been used to enhance the biotreatability of wastewaters containing various organic compounds that are nonbiodegradable and/or toxic to common microorganisms [11,12]. Ultrasonic process is one of AOP and involve the generation of the hydroxyl radical (NOH) and pyrolysis phenomenon, which has a very high oxidation potential and is able to oxidize almost all organic pollutants and volatile matter such as NH3. Although these processes are very effective in completing mineralization of pollutants, if they are applied as the only treatment process, they will be expensive. A promising alternative to complete oxidation of biorecalcitrant leachate is the use of ultrasonic process as pretreatment to convert initially biorecalcitrant compounds to more readily biodegradable intermediates, followed by biological oxidation of these intermediates to biomass and water. The major pollutants contained in leachate are biodegradable/non-biodegradable organic material, ammonia and inorganic salts, with anthropogenic organic chemicals, such as phthalates and other endocrine disrupting compounds becoming an increasing concern [13,14]. Because of the variation in leachate composition and the wide range of pollutants contained in leachate, it is difficult to predict a treatment technique that will be effective for leachate. Usually combinations of physical, chemical and biological methods are used for effective treatment of landfill leachate, since it is difficult to obtain satisfactory results by using any of those methods alone. Sedimentation, air stripping, adsorption, membrane filtration are the major physical methods used for leachate treatment [15,16]. These methods are usually used in combination with chemical and biological methods. Coagulationflocculation [17,18], chemical precipitation [19,20], chemicalelectrochemical oxidations [21,22] are the major chemical methods used for the landfill leachate treatment. Biological treatment methods used for the leachate treatment can be classified as aerobic, anaerobic and anoxic processes which are widely used for the removal of biodegradable compounds. Physicochemical methods are used along with the biological methods mainly to remove nonbiodegradable compounds from the leachate [23,24,25]. As a result, parameters have been developed to characterize leachate and predict its treatment efficiency. The ratio of biochemical oxygen demand (BOD) to chemical oxygen demand (COD) (BOD/COD) is a common classification approach. Leachate is classified as stabilized, intermediate, or fresh given BOD/COD values of ,0.1, 0.10.5, and .0.5, respectively [26,27,28]. The BOD/COD ratio indicates that biological processes are appropriate for treatment of fresh leachate because of a higher fraction of biodegradable organic material, while physicalchemical processes are more appropriate for treatment of stabilized leachate because of the high fraction of non-biodegradable organic material. The objectives of this study are to investigate the effect of ultrasonic process on leachate biodegradability improvement. Results and Discussion Effect of Sonocatalyst on Biodegradability of Leachate The results indicated that sonocatalyst process can improve leachate biodegradability (BOD5/COD ratio). BOD5/COD ratio for raw leachate was 0.35 but it reached to 0.786 (with TiO2) and 0.783 (with ZnO) after sonication. Independent Samples T-test showed there is significant difference between BOD5/COD ratio of raw leachate and pretreated leachate with sonocatalysis process. (pvalue = 0.000 for both TiO2 and ZnO). The results indicated that the system operates with gre (...truncated)