2016 Progress Report: Contaminant Removal Using Membrane Distillation for Sustainable Drinking Water TreatmentEPA Grant Number: R835333
Title: Contaminant Removal Using Membrane Distillation for Sustainable Drinking Water Treatment
Investigators: Childress, Amy E , Kolodziej, Edward P. , Park, Chanwoo
Institution: University of Nevada - Reno
Current Institution: University of Southern California
EPA Project Officer: Packard, Benjamin H
Project Period: September 1, 2013 through February 15, 2017
Project Period Covered by this Report: October 1, 2015 through September 30,2016
Project Amount: $499,743
RFA: Research and Demonstration of Innovative Drinking Water Treatment Technologies in Small Systems (2011) RFA Text | Recipients Lists
Research Category: Drinking Water , Water
The main objectives of the investigation are to characterize the range of drinking water contaminants and contaminant classes that can be removed by membrane distillation (MD) and to develop and test a small-scale pilot MD system that can operate using waste heat for small water treatment systems. The steps toward achieving the goals of the research project are to perform bench-scale testing of MD to evaluate membrane performance for spiked feed waters; to evaluate potential small system test sites; to design and construct a modular, small pilot-scale MD system with heat exchanger; and to test the small pilot system using source water spiked with contaminants that are relevant to small systems.
Progress during the 2015-2016 period focused on the identification of relationships between physical and chemical contaminant parameters with contaminant rejection as well as further development of the small pilot-scale system. Correlations between a wide range of physical and chemical contaminant parameters with rejection of nitrosamine species have been developed using data from the custom closed bench-scale membrane distillation (MD) system. The promising relationship between nitrosamine rejection and log Henry’s constant (pKH) was further investigated by introducing the concept of equilibrium rejection. Equilibrium rejection was shown to have a very high correlation (R2=0.97) with pKH of the nitrosamines. The relationship between equilibrium rejection and pKH was also demonstrated for phenols and anilines, resulting in a combined correlation coefficient (R2) of 0.95 for nitrosamines, phenols, and anilines. Results for boron are also presented, demonstrating a final rejection of 99.9%. The final small pilot-scale MD system has been constructed and tested for use with a simulated liquid waste heat source. The pilot system uses a recirculated warmed/cooled bath to simulate the variable temperature data that characterizes the autoclave discharge waste heat source at the James Hardie Building Products facility. The pilot system has been tested for leaks and validity of data, and will be used to perform experiments evaluating contaminant removal while using a variable waste heat source. Separately from the pilot system, a control system was developed to allow the MD feed water to be held at a specified setpoint temperature, when using a variable waste heat source. Plans for bench-scale investigations before the final report include further analysis of existing data and data collection regarding pharmaceuticals and personal care products and bromide. Plans for small pilot-scale system investigations include final identification of feed solution contaminants of interest and performance of contaminant removal experiments while using a simulated variable waste heat source.
In the upcoming quarter, an additional bench-scale direct contact membrane distillation (DCMD) experiment will be performed with bromide in the feed solution. Like boron, bromide is a contaminant that has relatively low rejection in traditional reverse osmosis systems, and thus could be a target contaminant for DCMD as a polishing process. An additional experiment is planned with the mega-mix of volatile and semi-volatile organic components using a modified experimental setup. Significant effort has gone into designing and fabricating a gas-tight DCMD system; in doing so the experimental setup is inherently batch. At large scale, the DCMD process will likely need to be operated in a continuous or semi-continuous fashion, thus we plan to perform a test where the feed side remains closed but the distillate side receives a constant supply of fresh DI water rather than circulating the accumulated distillate solution. By comparing the feed side concentrations with and without distillate recycle, additional insight into the transport mechanisms and the tendency towards equilibrium observed in the previous experiments will be gained. Additionally, important insight into scale-up (batch to continuous operation) will be provided by the experiment.
Experiments for the small pilot-scale MD system also will be completed during the upcoming quarter. The final contaminant(s) of interest for the pilot system will be identified, with perchlorate as a likely candidate. Experiments will be performed using the pilot system that will evaluate the ability of the system to remove the selected contaminant(s) of interest with a larger membrane module in a concentrative system with periodic blowdown of the feed solution to limit scale formation. The importance of waste heat source variability in waste-heat-driven MD systems will be highlighted with these experiments, and the thermal response of the MD system to operation with a variable waste heat source will be characterized at multiple points throughout the system.