Advanced oxidation processes (AOPs) such as titanium dioxide (TiO2) photocatalysis have the potential to simultaneously mitigate an array of emerging contaminants. These processes have been shown to effectively mineralize organic contaminants when operated at high energy inputs. However, for successful adoption in the water treatment sector, AOPs must provide a range of benefits when operated at low energy. This research investigated the mitigation of organic matter and estrogenic compounds using low-energy TiO2 photocatalysis coupled with either granular activated carbon (GAC) or membrane filtration processes. Nanopure water was spiked with humic acid sodium salt at 5 to 10 mg/L of dissolved organic carbon (DOC) or an estrogen mixture of approximately 400 µg/L each of EE2, E1, E2, and E3. The estrogen concentrations were assessed using a Shimadzu LC-MS, and total estrogenicity was assessed using the yeast estrogen screen assay. Experiments were performed using a laboratory-scale photocatalysis reactor equipped with a 17 W low-pressure mercury bulb. System energy inputs tested included low levels of 1, 2, and 5 kWh/m3. Additionally, a high energy 80 kWh/m3 control offering more complete oxidation was performed. Treated water was filtered using either rapid small-scale GAC columns or microfiltration membranes. The results demonstrated that significant reductions in DOC, absorbance, and specific UV absorbance (SUVA) could be obtained using low energy photocatalysis (1 – 2 kWh/m3). Using 5 kWh/m3 provided reductions in absorbance and SUVA equivalent to 80 kWh/m3 (although additional reductions in DOC were achieved using 80 kWh/m3). Thus, although the organic matter was not mineralized with low-energy inputs, its chemical character shifted. These changes led to improvements in subsequent filtration processes. Using low-energy photocatalysis significantly increased the volume of water treated prior to membrane fouling. When coupled with GAC filters, photocatalysis using 2 kWh/m3 extended the GAC bed life approximately 300%. With 5 kWh/m3, no organic breakthrough occurred within 100 bed volumes. For the estrogens, high levels of photocatalysis (80 kWh/m3) provided removals to below the detection limit in all cases. However, even at 1 kWh/m3, significant reductions could be observed, which increased with increasing energy input. At 5 kWh/m3, removals were 77% E1, 39% E2, 46% E3, and 44% EE2. Tests on total estrogenicity are ongoing.

Coupled titanium dioxide photocatalysis and filtration to mitigate organic matter and estrogens

253rd National Meeting (2017)

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