Project Report

Impact of Secondary Wastewater Treatment Processes on Effluent Organic Matter and Partitioning of Emerging Contaminants Patrick Dunlap - EAPSI Singapore Water resources around the world are becoming increasingly taxed due to stressors such as urbanization, climate change, pollution, and agricultural demand. To address these current and future water shortages alternative sources are being turned to. Seawater desalination, wastewater reclamation, and interbasin transfer are all options. Wastewater reclamation has often shown to be advantageous in terms of costs and it is often unavoidable on river systems with high populations where defacto wastewater reuse takes place. With potable water reuse; whether planned or incidental, public health concerns inevitably arise. Of growing concern are emerging organic contaminants such as pharmaceuticals and endocrine disrupting compounds present at trace levels. A better understanding of their removal in conventional and advanced wastewater treatment could lead to significant public health, environmental, and economic benefits. A common method of water reclamation is the use of membranes to clean effluent from a conventional water reclamation process to a reuse quality. The degree to which contaminants are rejected can be influenced by other dissolved organic matter due to mechanisms like partitiong of the contaminant to hydrophobic organic macromolecules. This Effluent Organic Matter (EfOM) was either not removed during the prior stages of treatment or alternatively could have been generated by microbial activity in these prior stages. Research into these impacts has been undertaken and though it is not completely understood what is less investigated is the impact of the secondary treatment processes on the EfOM. In this way the effects of secondary microbial treatments processes on the water could have latent impacts on the rejection of contaminants during advanced treatment. So the goal of my work at the National University of Singapore with Dr. Hu Jiangyong was to relate secondary wastewater treatment processes to the characteristics of the resultant EfOM and to the partitioning of the contaminant to that EfOM. This could aid in predicting what kind of contaminant rejection an advanced wastewater treatment process will achieve given the previous processes and could better inform process design in the future. I collaborated with the Public Utilities Board of Singapore for sampling of wastewater from 3 locations at their Ulu Pandan Water Reclamation Plant and went for these samplings twice. Wastewaters were collected from three treatment processes which treated the same influent wastewater. These processes were all biological secondary treatment processes with different solids retention times (SRTs). SRT is a parameter relating to the amount of time the bacteria which treat the water have to grow before being separated from the water. These processes also had differences in the mechanisms of the separation of the bacteria and the conditions these bacteria grew under. These waters were fractionated using hydrophobic resins to separate the EfOM into chemically distinct classes and to concentrate the EfOM. These fractions were then characterized using Liquid Chromotography – Organic Carbon Detection (LC-OCD) which produced interesting results and yielded insight into the treatment process’s impact on the EfOM. The LC-OCD results suggested that impacts of conventional treatment processes on EfOM was less due to SRT and more the separation mechanism and the conditions which the bacteria were grown in. These differences yield selection pressures cause different bacteria to dominate producing different extracellular organic substances. The other goal of the research was to investigate whether the EfOM from the different processes may complex more or less with emerging contaminants. The hormone Estrone (E1) was chosen because it is relatively poorly removed by membranes and the impact of dissolved organics on E1 rejection by membranes was previously investigated by my research host. The partitioning coefficient for E1 to the hydrophobic acid fraction of EfOMs was attempted using Solid Phase Microextraction (SPME). In this method SPME is used to measure the free concentration of E1 and direct HPLC injection is used to measure the total concentration, from which the partitioning coefficient could be calculated. Due to the low hydrophobicity of E1 this technique proved inappropriate for the measurement of this partitioning. Alternative techniques such as fluorescence quenching should be attempted in future work though unfortunately time was not sufficient to attempt any alternatives. During my time in Singapore I also attended Singapore International Water Week which gave me the opportunity network with and to attend panel discussions by leading researchers, policy makers, consultants, and aid workers in the water industry. I think the conference and the research project this summer led to a very positive experience. Singapore is taking a progressive approach to the management of their water issues and to work with Singapore’s research into water technology and to see the implementation of policies addressing water scarcity taught me lessons which I have been able to bring back to United States where similar water scarcity issues are being addressed.

National Science Foundation (NSF)
Office of International and Integrative Activities (IIA)
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Carter Kimsey
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Dunlap Patrick J
United States
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