Application of a fluorescence EEM-PARAFAC model for direct and indirect potable water reuse monitoring: Multi-stage ozone-biofiltration without reverse osmosis at Gwinnett County, Georgia, USA.

Periods of drought coupled with increasing population growth have prompted increased interest in potable water reuse in Gwinnett County, Georgia, USA. However, such inland water recycling facilities are challenged with treatment approaches where reverse osmosis (RO) membrane concentrate disposal is a barrier to implementation of potable reuse. To evaluate alternative treatment processes, testing of two side-by-side pilot systems using multi-stage ozone and biological filtration without RO was conducted to compare indirect potable reuse (IPR) to direct potable reuse (DPR). Two water sources were investigated-influent from Lake Lanier for the IPR pilot, and a blend of 25 % reclaimed water mixed with lake water (75 %) for the DPR pilot. To assess the nature of organic matter removed during potable reuse, excitation-emission matrix (EEM) fluorescence spectroscopy/PARAllel FACtor (PARAFAC) analyses were examined as a fingerprinting tool. The objectives were to determine (a) if a DPR scenario, when preceded by advanced wastewater treatment, could achieve drinking water quality comparable to IPR and (b) if water quality monitoring using EEM/PARAFAC methods could predict results for DPR and IPR water quality, comparable to parameters obtained in a supplementary study that required more expensive, time-consuming, and complicated analytical techniques. Sample scores representing relative concentrations of fluorescing organic matter derived from the EEM-PARAFAC model decreased in the order of reclaimed water > lake water > DPR pilot > IPR pilot, demonstrating that EEM/PARAFAC could distinguish between DPR and IPR water quality. An assessment of a comprehensive list of individual organic compounds (reported separately) validated that blend ratios of 25 % reclaimed water, or higher mixed with lake water (75 %) did not meet primary and secondary drinking water standards. Likewise, in this study, EEM/PARAFAC analysis demonstrated the 25 % blend did not provide drinking water quality indicating this simple, inexpensive method could be used for potable reuse monitoring.

Pilot testing of direct and indirect potable water reuse using multi-stage ozone-biofiltration without reverse osmosis.

Pilot testing of direct potable reuse (DPR) using multi-stage ozone and biological filtration as an alternative treatment train without reverse osmosis (RO) was investigated. This study examined four blending ratios of advanced treated reclaimed water from the F. Wayne Hill Water Resources Center (FWH WRC) in Gwinnett County, Georgia, combined with the existing drinking water treatment plant raw water supply, Lake Lanier, for potable water production. Baseline testing with 100 percent (%) Lake Lanier water was initially conducted; followed by testing blends of 15, 25, 50, and 100% reclaimed water from FWH WRC. Finished water quality from the DPR pilot was compared to drinking water standards, and emerging microbial and chemical contaminants were also evaluated. Results were benchmarked against a parallel indirect potable reuse (IPR) pilot receiving 100% of the raw water from Lake Lanier. Finished water quality from the DPR pilot at the 15% blend complied with the United States primary and secondary maximum contaminant levels (MCLs and SMCLs, respectively). However, exceedances of one or more MCLs or SMCLs were observed at higher blends. Importantly, reclaimed water from FWH WRC was of equal or better quality for all microbiological targets tested compared to Lake Lanier, indicating that a DPR scenario could lower acute risks from microbial pathogens compared to current practices. Finished water from the DPR pilot had no detections of microorganisms, even at the 100% FWH WRC effluent blend. Microbiological targets tested included heterotrophic plate counts, total and fecal coliforms, Escherichia coli, somatic and male-specific coliphage, Clostridium perfringens, Enterococci, Legionella, Cryptosporidium, and Giardia. There were water quality challenges, primarily associated with nitrate originating from incomplete denitrification and bromate formation from ozonation at the FWH WRC. These challenges highlight the importance of upstream process monitoring and control at the advanced wastewater treatment facility if DPR is considered. This research demonstrated that ozone with biological filtration could achieve potable water quality criteria, without the use of RO, in cases where nitrate is below the MCL of 10 mg nitrogen per liter and total dissolved solids are below the SMCL of 500 mg per liter.