Ozone and biofiltration as an alternative to reverse osmosis for removing PPCPs and EDCs from wastewater
A lot of attention has been paid to trace amounts of pharmaceuticals and personal care products (PPCPs) and endocrine disrupting compounds (EDCs) in drinking water supplies. Current water and wastewater treatment techniques, such as coagulation, flocculation, and sedimentation for water treatment and the conventional activated sludge process for wastewater treatment, have shown only limited success in their removal. Although there is a lack of evidence linking these emerging microconstituents to adverse human health effects, not a lot is known about the effects of long term exposure to these compounds and more research is still needed. This study examined advanced wastewater treatment processes, such as membrane bioreactors (MBRs), along with processes that are not normally used for treating wastewater to remove these emerging contaminants. The processes include oxidation with ozone coupled with biological active filtration (BAF) to increase the removal efficiencies of these compounds. A pilot scale membrane bioreactor (MBR) was set up at the Albuquerque Bernalillo County Water Utility Authority (ABCWUA) Southside Water Reclamation Plant (SWRP). The MBR was continuously fed primary treated wastewater. The MBR effluent was used to feed an ozone contactor, which then fed a BAF column. The MBR was operated at an SRT of 10 days throughout the duration of the experiments. Three ozone doses where examined. The applied ozone doses were 2, 4, and 8 mg/L, which correspond to a ratio of 0.5, 1, and 2 mg ozone/mg TOC. After ozone treatment, the water was pumped to the BAF column. The BAF column used anthracite media that was seeded with MLSS and soaked in MBR feedwater for a week to establish a bio-growth prior to the experiments. The system was run for at least one week between sampling events to establish steady state conditions at each new ozone dose. To determine steady state conditions, TOC, UV254, SUVA, and BDOC removal were evaluated. This study also investigated the removal of microconstituents using a reverse osmosis (RO) system that ran concurrent to the Ozone/BAF treatment train for two of the ozone doses. The concentrations of the compounds of interest were tested in the effluents of the MBR, ozone, BAF, and RO. Significant removal of the selected compounds was observed at all selected ozone doses. Although removal of microconstituents increased with increasing ozone dose, little additional removal occurred at ozone concentrations greater than 4 mg/L. The change in percent removal of both organics and microconstituents was larger going from an ozone dose of 2 to 4 mg/L than going from 4 to 8 mg/L. The BAF column did not dramatically decrease the concentrations of these compounds after the initial decrease due to ozonation, although additional TOC removal was achieved. This can be contributed to oxidation breaking the compounds down to smaller, more biodegradable compounds. Bulk organic analysis such as TOC, UV254 absorbance, SUVA, and BDOC show that organic compounds are not mineralized to CO2 and H2O by ozonation alone. However, the data also shows that additional destruction of TOC occurred in the BAF column following ozonation. Although the organic analyses do not indicate the fate of individual microconstituents, the microconstituents can be expected to have the same fate as other organics.
Sewage--Purification--Organic compounds removal, Sewage--Purification--Ozonization, Sewage--Purification--Fixed-film biological process, Membrane reactors
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