Search

Abstract The objective of this pilot-scale study was to investigate the effectiveness of incorporating ozone (O 3) and advanced oxidation (hydrogen peroxide/ozone: H 2 O 2 /O 3) in combination with biofiltration for taste and odour control, organic carbon removal, and disinfection byproduct (DBP) precursor reduction. Implementation of O 3 and H 2 O 2 /O 3 with and without biofiltration was investigated at pilot-scale in terms of geosmin, 2-methylisoborneol (MIB), and DBP precursor removal efficiency. Two media types (granular activated carbon and anthracite) were compared in conjunction with investigating the impact of pre-oxidation with O 3 (2 mg/L) and varying H 2 O 2 /O 3 mass ratios (0.1, 0.2, 0.35, and 0.5 mg/mg). When O 3 preceded biologically active carbon (BAC) or biologically active anthracite, geosmin removals of 80% and 81%, respectively, were observed at 10 °C; this increased to 89% and 90%, respectively, at 16 °C. Optimal MIB removal (67%) was achieved with 0.1 H 2 O 2 /O 3 (mg/mg) in combination with BAC at 16 °C. In general, geosmin proved to be more amenable to biodegradation than MIB. BAC without pre-oxidation removed 87% geosmin and 85% MIB, at 22 °C. MIB removals decreased to 60% and 46%, respectively at 16 °C and 10 °C. The application of 0.2 H 2 O 2 /O 3 (mg/mg) prior to BAC provided treatment which effectively removed geosmin and MIB. However, in terms of DBP precursor reduction, there was no beneficial impact of H 2 O 2 addition on trihalomethane or haloacetic acid formation potentials. Highlights • BAC alone may serve as a suitable treatment technology for T&O control at warmer temperatures. • Biologically activated anthracite outperformed non-biological anthracite in removing both geosmin & MIB. • O 3 efficiency and BAC biodegradation rates significantly decreased in cold water conditions. • H 2 O 2 /O 3 advanced oxidation improved MIB removal in cold water conditions. • Biopolymers were observed to preferentially react with $OH rather than O 3. [ABSTRACT FROM AUTHOR]

The evolving demands of drinking water treatment necessitate processes capable of removing a diverse suite of contaminants. Biofiltration can employ biotransformation and sorption to remove various classes of chemicals from water. Here, pilot-scale virgin anthracite-sand and previously used biological activated carbon (BAC)-sand dual media filters were operated for ∼250 days to assess removals of 0.4 mg/L ammonia as nitrogen, 50–140 μg/L manganese, and ∼100 ng/L each of trace organic compounds (TOrCs) spiked into pre-ozonated Colorado River water. Anthracite achieved complete nitrification within 200 days and started removing ibuprofen at 85 days. Limited manganese (10%) removal occurred. In contrast, BAC completely nitrified ammonia within 113 days, removed all manganese at 43 days, and exhibited steady state removal of most TOrCs by 140 days. However, during the first 140 days, removal of caffeine, DEET, gemfibrozil, naproxen, and trimethoprim decreased, suggesting a shift from sorption to biotransformation. Acetaminophen and sulfamethoxazole were removed at consistent levels, with complete removal of acetaminophen achieved throughout the study; ibuprofen removal increased with time. When subjected to elevated (1 μg/L) concentrations of TOrCs, BAC removed larger masses of chemicals; with a subsequent decrease and ultimate cease in the TOrCs spike, caffeine, DEET, gemfibrozil, and trimethoprim notably desorbed. By the end of operation, anthracite and BAC exhibited equivalent quantities of biomass measured as adenosine triphosphate, but BAC harbored greater microbial diversity (examined with 16S rRNA sequencing). Improved insight was gained regarding concurrent biotransformation, sorption, and desorption of multiple organic and inorganic contaminants in pilot-scale drinking water biofilters. [ABSTRACT FROM AUTHOR]

N-nitrosodimethylamine (NDMA) is a carcinogen and a disinfection byproduct that is formed by ozone and combined chlorine. Various factors affecting NDMA formation and removal were examined at pilot-scale for a treatment train consisting of ozone, biologically-active carbon (BAC) filtration, and granular activated carbon (GAC) adsorption applied to two distinct feed waters. High concentrations of ozone and monochloramine were added to the influent, demonstrating that ozone removed monochloramine precursors of NDMA. Further, longer empty bed contact times (EBCTs) of 10 min for BAC and 10 and 20 min for GAC removed NDMA to <10 ng/L for both feed waters. NDMA removal by the BAC process was most favorable >22 °C, presumably due to elevated microbial activity. A monochloramine residual of 3 mg/L-Cl 2 in the BAC influent reduced NDMA removal in the 5 min EBCT BAC from 79% to 36% and in the 10 min EBCT BAC from 88.5% to 73.7%. The absence of ozone in the treatment process significantly reduced NDMA formed post ozone, but decreased NDMA removal in BAC, probably due to lower NDMA concentration in the BAC influent. Finally, adding 5 mg/L of allylthiourea, an inhibitor of ammonia-oxidizing bacteria, indicated that removal mechanisms for ammonia and NDMA are distinct. However, nitrification is still a good indicator for NDMA biodegradation potential, because nitrifying bacteria appear to flourish under similar EBCT, temperature. and monochloramine residual conditions during BAC filtration. Image 1 • NDMA formation and removal by O 3 /BAC/GAC was examined at pilot-scale for two plants. • NDMA concentration below 10 ng/L was noted in BAC with 10 versus 5 min EBCT. • Monochloramine-related NDMA precursors were effectively removed by ozone. • 3 mg/L-Cl 2 monochloramine residual reduced NDMA removal by BAC, i.e., NDMA >10 ng/L. • Ammonia removed via nitrification in BAC is a good indicator for NDMA removed. [ABSTRACT FROM AUTHOR]