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Evaluating Pilot Scale Slow Sand Filtration Columns to Effectively Remove Emerging Contaminants in Recycled Water

  • Author(s): Phu, Nancy
  • Advisor(s): Wu, Laosheng
  • et al.
Abstract

Slow sand filter columns are a high efficiency system proposed to reduce a multitude of physical and chemical contaminants while remaining cost effective and not land intensive. We concluded using SSF is a low cost alternative for the treatment of contaminants in recycled water, in particular a greenhouse utilizing reclaimed water with a variety of emerging contaminants. While slow sand filter is not a new concept, its research on removing emerging contaminants has yet to be discussed. Much of the literature has focused on bank filtration systems to manage aquifer systems, or biofilters that have some combination of chemical treatment or various granular media that could bolster the effectiveness of the biofilters such as activated carbon. However, with only utilizing the inoculation supplied by the tertiary treated waterwater plant leachate in our greenhouse, biofilm was able to grow in these conditions. In certain cases, utilization of the biological degradable organic carbon supplied with the plant leachate could have been the reason of biological degradation as biofilm layer is growing and using the micropollutants as a secondary source. The redox conditions have been known to be crucial in the sorption of pharmaceutically active compounds, since they tend to exist in ionic forms under certain pH conditions. Although removals have occurred, it is difficult to distinguish whether removal is occurring based on adsorption or biodegradation. There were many factors to consider, as this is a preliminary study, more tests concerning the following issues should be addressed. Adsorption is primarily based on the hydrophobicity of the compound to adhere to binding sites, usually an indication of larger log Kow values. However, we have seen signs of oversaturation of compounds with large Kow values and decreases in removal. Given the short amount of time that our study was conducted, it is insufficient to know the extent of the compounds’ removal and thus further studies should be conducted. Given the limits of our preliminary study and analytical method, we have successfully analyzed 29 compounds able to undergo derivatization and maintain quality recoveries, and have used SSF to remove a mean 20-60%. This project has shown that columns have developed unique microbial communities and averaging removals between columns may not be an accurate representation. To understand a compound’s removal, it is crucial to observe trends over time. Even under 60 days, certain compounds, like 17β-estradiol, estrone, 4-methyl-benzylidene camphor, diazinon, chlorpyrifos, and salicylic acid have all shown capability to be highly degraded. The highest removals experienced were >90% for some days of the project. There is promise that the conditions provided by our greenhouse system and design of the SSF allows for sufficient, at least moderate, removals of our emerging contaminants.

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