Transformation of organic matter during reclamation of wastewater by soil aquifer treatment and membranes

The objective of this research was to compare structural transformation of organic matter in natural water reuse systems against high-technology water reuse systems. Organic matter removal during long-term soil aquifer treatment (SAT, more than 6 months travel time) and advanced membrane treatment using nanofiltration or reverse osmosis (RO) were compared at three different field sites in Arizona. The two SAT field sites were the “Northwest Water Reclamation Plant” in Mesa and the “Sweetwater Underground Storage and Recovery Site” in Tucson, and the membrane field site was the Scottsdale Water Campus.; In this study, it was found that the DOC of the reclaimed water was reduced by 80–93% at the Mesa and Tucson field sites. During membrane treatment, 97% of the DOC was removed. The molecular weight distribution of the SAT treated water showed that 76% of the final product water had a molecular weight of 1000 Dalton or less. Ultrafiltration results and liquid chromatography-organic carbon detection results after membrane treatment showed that the permeate was composed of molecular weight compounds with less than 500 Dalton.; An isolation approach was developed to analyze the structure of the effluents, the SAT product water and the membrane permeate. Applying the RO-XAD approach higher carbon recovery (CR = 45–55%) was achieved compared to the conventional approach (CR = 20%). Spectroscopic methods such as Fourier transform infrared (FT-IR) spectroscopy and nuclear magnetic resonance (NMR) spectroscopy (1-dimensional (1D) and 2D: correlation spectroscopy, heteronuclear multiple quantum coherence and heternuclear multiple bond correlation) were used to elicit information about the DOC for the reclaimed water, SAT treated water and RO permeate. According to spectroscopic results, it can be concluded that both systems result in differently structured DOC. The structural composition of the SAT product water remains during treatment and the structural composition after membrane treatment is a more uniform class of low molecular weight hydrophilic compounds. From the obtained results in this study, predictive characterization can be used to estimate water quality for SAT and membrane treatment.