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Lyophilization and Reconstitution of Reverse Osmosis Concentrated Natural Organic Matter
McCurry, D. L. AND J. G. PRESSMAN. Lyophilization and Reconstitution of Reverse Osmosis Concentrated Natural Organic Matter. Presented at AWWA Water Quality Technology Conference, Savannah, GA, November 14 - 18, 2010.
To inform the public.
Disinfection by-product (DBP) research can be complicated by difficulties in shipping large water quantities and changing natural organic matter (NOM) characteristics over time. To overcome these issues, it is advantageous to have a reliable method for concentrating and preserving NOM with minimal loss and maximum shelf-life. NOM concentration and preservation by lyophilization (freeze-drying) has been practiced for many years; however, no detailed method for lyophilizing and reconstituting NOM exists in the published literature and no lyophilized drinking water relevant NOM samples are commercially available. The purpose of this research was both to optimize the lyophilization process by determining key thermodynamic properties of concentrated NOM solution, and to determine the appropriate conditions (pH, mixing time, and concentration factor) under which to reconstitute NOM for maximum total organic carbon (TOC) and ultra-violet at 254nm absorbance (UV254) recovery. First, thermal and resistivity analyses were performed on reverse-osmosis (RO) 150x concentrates. From these analyses, the equilibrium freezing and autonucleation temperatures of the concentrate were determined, however, no clearly defined eutectic point could be found. Next, based on these data, a lyophilization ‘recipe’ was created, and 12L concentrate was lyophilized. The lyophilized concentrate was reconstituted at 36 combinations of pH (6, 8, & 10), mixing time (1h, 4h, & 24h) and concentration factor (1, 10, 100, & 1000 times raw water DOC). TOC and UV254 samples were taken from each reconstitution before and after filtering (0.45µm). No statistically significant correlations between TOC or UV254 recovery and pH, mixing time, or concentration factor could be made. At pH 10, reconstitutions recovered slightly more UV254 absorbance than did pH 6 or pH 8, but the difference was within one standard deviation. The lack of correlation between mixing time and recovery suggests that one hour of mixing time is sufficient. Filtration removed 1.0% of TOC and 2.63% of UV254 absorbance, on average, but both results were within one standard deviation of their respective unfiltered values. The mean TOC and UV254 recovery of all filtered samples was 101 ± 10% and 91 ± 11%, respectively. These results confirm that NOM can be concentrated and preserved by RO and lyophilization, and later reconstituted with minimal loss of NOM surrogate analytes. This method shows promise for effectively concentrating large volumes (~15000L/month) of drinking water relevant NOM for future use in disinfection, health effects, and other research.