Two - Stage AnMBR for Removal of UV Quenching Organic Carbon from Landfill Leachates: Feasibility and Microbial Community Analyses

Autor: Pathak, Ankit Bidhan
Rok vydání: 2017
Předmět:
Druh dokumentu: Dissertation
Popis: Landfilling is the most widely used method for the disposal of municipal solid wastes (MSW) in the United States due to its simplicity and low cost. According to the 2014 report on Advancing Sustainable Materials Management by the USEPA, only 34% of the total MSW generated in the US was recycled, while 13% was combusted for energy recovery. In 2014, 53% of the MSW generated, (i.e. 136 million tons) in the US was landfilled. The treatment of landfill leachates, generated by percolation of water through the landfill, primarily due to precipitation, has been found to be one of the major challenges associated with landfill operation and management. Currently, leachates from most landfills are discharged into wastewater treatment plants, where they get treated along with domestic sewage. Issues associated with treatment of landfill leachates due to their high nitrogen and heavy metal content have been widely studied. Recently, it has been observed that the organic carbon in landfill leachates, specifically humic and fulvic acids (together referred to as "humic substances") contain aromatic groups that can absorb large amounts of ultraviolet (UV) light, greatly reducing the UV transmissivity in wastewater plants using UV disinfection as the final treatment step. This interference with UV disinfection is observed even when landfill leachates constitute a very small fraction (of the order of 1%) of the total volumetric flow into wastewater treatment plants. Humic substances are present as dissolved organic matter (DOM) and typically show very low biodegradability. Removing these substances using chemical treatment or membrane processes is an expensive proposition. However, the concentrations of humic substances are found to be reduced in leachates from landfill cells that have aged for several years, suggesting that these substances may be degraded under the conditions of long-term landfilling. The primary objective of this research was to use a two-stage process employing thermophilic pretreatment followed by a mesophilic anaerobic membrane bioreactor (AnMBR) to mimic the conditions of long-term landfilling. The AnMBR was designed to keep biomass inside the reactor and accelerate degradation of biologically recalcitrant organic carbon such as humic substances. The treatment goal was to reduce UV absorbance in raw landfill leachates, potentially providing landfills with an innovative on-site biological treatment option prior to discharging leachates into wastewater treatment plants. The system was operated over 14 months, during which time over 50% of UV-quenching organic carbon and 45% of UV absorbance was consistently removed. To the best of our knowledge, these removal values are higher than any reported using biological treatment in the literature. Comparative studies were also performed to evaluate the performance of this system in treating young leachates versus aged leachates. Next-generation DNA sequencing and quantitative PCR (qPCR) were used to characterize the microbial community in raw landfill leachates and the bioreactors treating landfill leachate. Analysis of microbial community structure and function revealed the presence of known degraders of humic substances in raw as well as treated landfill leachates. The total number of organisms in the bioreactors were found to be higher than in raw leachate. Gene markers corresponding to pathogenic bacteria and a variety of antibiotic resistance genes (ARGs) were detected in raw landfill leachates and the also in the reactors treating leachate, which makes it necessary to compare these ARG levels with wastewater treatment in order to determine if leachates can act as sources of ARG addition into wastewater treatment plants. In addition, the high UV absorbance of leachates could hinder the removal of ARBs and ARGs by UV disinfection, allowing their release into surface water bodies and aiding their proliferation in natural and engineered systems.
Ph. D.
Municipal solid waste is most often disposed by dumping it in landfills. Percolation of water through these landfills due to precipitation or the intrusion of surface or groundwater, results in the formation of landfill leachate, a mixture of organic and inorganic contaminants, at the bottom of the landfill. Landfills are therefore lined with special materials to prevent leachate from seeping into soil or groundwater and have sophisticated collection systems to periodically extract and dispose leachate. Perhaps the most commonly used method for the disposal of landfill leachates is discharge into wastewater treatment plants, where leachates can cause toxicity to biological processes due to their high organic load as well as their substantial heavy metal content. In the last decade or so, it has been established that leachates can absorb UV light considerably by virtue of aromatic organic compounds present in them, causing inhibition of UV disinfection in wastewater treatment. Thus, leachates must be appropriately treated to reduce their capacity to absorb UV light prior to discharge into wastewater treatment plants. This study employed a novel two – stage reactor system to treat landfill leachates in order to reduce their UV-quenching ability. The system was successfully operated over 14 months and was able to remove more than half of the UV light absorbing organic carbon from landfill leachate. Additionally, samples of biomass isolated from untreated landfill leachates and the reactors treating them revealed the potential presence of pathogenic bacteria and antibiotic resistance genes. Preliminary data suggests that landfill leachates might have large antibiotic resistance content, higher than that observed in wastewater and other engineered systems.
Databáze: Networked Digital Library of Theses & Dissertations
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