Carbon based advanced treatment (CBAT), including ozone (O3), bioactive filtration (BAF), and adsorption by granular activated carbon (GAC), is gaining substantial momentum for potable reuse as this treatment train is more environmentally sustainable and cost effective. CBAT has been shown to be effective for the transformation and removal of effluent organic matter (EfOM), which are substantial precursors for DBPs. However, little is known regarding the formation and control of regulated and non-regulated DBPs by CBAT. The objective of this study was to systematically evaluate the transformation and removal of precursors for a wide range of regulated and non-regulated DBPs by CBAT. Municipal treated wastewater effluents were evaluated at bench-scale. The treatment train consisted of alum enhanced coagulation, ozonation at different O3:TOC ratios, BAF wtih biological activated carbon (BAC) and anthracite at two EBCTs, and GAC rapid small-scale column test (RSSCT) at two EBCTs. Treated effluents were collected at each treatment step and evaluated for DBP precursor removal. Precursors were assessed via formation potential tests under uniform formation conditions (UFC). A list of 50 priority regulated and non-regulated DBP compounds were analyzed, including 4 THMs, 9 HAAs, 10 HANs, 7 HALs, 7 HAMs, 7 HNMs, and 6 I-THMs. As anticipated, TTHM and HAA9 formation accounted for more than 70% (by mass) of DBPs formed in the wastewater, whereas HALs are the most predominant non-regulated DBPs formed, followed by HANs and HAMs. Enhanced coagulation was effective in removing all but HAN precursors, and the precursor removal rates correlate with the amount of TOC that was removed. Ozonation alone yielded 20% lower TTHM and HAA9 formation, and 50% lower HAN formation regardless of ozone dose, but ozone significantly enhanced HNM, HAM, and HAL formation, particularly at high doses. However, ozone-induced HNM, HAM, and HAL precursors were effectively controlled by downstream BAF, especially with BAC media. Anthracite generally underperformed BAC at the same EBCT, indicating the potential role of residual adsorption by GAC. Unlike non-regulated DBPs, O3-BAF treatment had little impact on TTHM and HAA9 precursor removal regardless of ozone dose, BAF media type, and BAF EBCT. Further DBP precursor removal post O3-BAF by GAC adsorption is being investigated using RSSCTs. Overall, this study demonstrates that CBAT processes can substantially mitigate DBP formation from EfOM.

Control of regulated and non-regulated disinfection byproduct precursors by carbon based advanced treatment (CBAT) for potable reuse

ACS Fall 2021

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