Factors affecting removal of NDMA in an ozone-biofiltration process for water reuse

Relating microbial community composition to treatment performance in an ozone-biologically active carbon filtration potable reuse treatment train

Treatment trains that couple ozone (O3) with biologically active carbon (BAC) filtration are of interest as a lower cost, more sustainable, membrane-free approach to water reuse. However, little is known about the microbial communities that are the fundamental drivers of O3-BAC treatment. The objective of this study was to demonstrate microbial community profiling as a diagnostic tool for assessing the functionality, biological stability, and resilience of coupled physical, chemical, advanced oxidative and biological processes employed in water reuse treatment. We utilized 16S rRNA gene amplicon sequencing to profile the bacterial microbiota over time throughout a potable reuse train employing coagulation, flocculation, sedimentation, ozonation, BAC filtration, granular activated carbon (GAC) adsorption, and UV disinfection. A distinct baseline microbiota was associated with each stage of treatment (ANOSIM, p < 0.05, r-stat = 0.52), each undergoing succession with time and operational shifts. Ozonation resulted in the sharpest shifts (i.e., 83.3 % average change in Genus level relative abundances, when adjusted O3:TOC ratio > 1), and also variance, in microbial community composition. Adjustment in O3:TOC ratios, temperature, filter-aid polymer, monochloramine quenching agent, and empty-bed contact time also resulted in measurable changes in the baseline microbial community composition of individual processes, but to a lesser degree. Of these, supplementation of nitrogen and phosphorus resulted in the strongest bifurcation, especially in the microbial communities inhabiting the BAC (ANOSIM: p < 0.05, BAC5 r-stat = 0.32; BAC10 r-stat = 0.54) and GAC (ANOSIM: p < 0.05, GAC10 r-stat = 0.54; GAC20 r-stat = 0.63) units. Additionally, we found that the BAC microbial community was responsive to an inoculation of microbially active media, which resulted in improved TOC removal. The findings of this study improve understanding of bacterial dynamics occurring in advanced water treatment trains and can inform improved system design and operation.

Animal Feedlots and Domestic Wastewater Discharges are Likely Sources of N-Nitrosodimethylamine (NDMA) Precursors in Midwestern Watersheds

N-nitrosodimethylamine (NDMA) precursor concentrations along four major rivers in Minnesota, USA were quantified and correlated with watershed land cover types, anthropogenic activity, and organic matter characteristics. River water samples (36 in total) were chloraminated under uniform formation conditions (UFC) before and after lime-softening treatment, and the resulting NDMA concentrations were quantified (NDMAUFC). Regarding land cover, NDMAUFC in raw river water exhibited weak positive correlations with urban land (ρ = 0.33, p = 0.05) and cropland coverage (ρ = 0.35, p = 0.04). For anthropogenic activity, NDMAUFC in raw river water positively correlated with the number of feedlots (ρ = 0.57), total weight of animals (ρ = 0.68), and total number of domestic wastewater treatment plants (WWTPs; ρ = 0.63) with p < 0.01. NDMAUFC positively correlated with region IV fluorescence intensity from fluorescence excitation-emission spectra (ρ = 0.70, p < 0.01). Lime softening of river water typically increased NDMAUFC and preferentially removed organic matter that fluoresces in region V, suggesting that the organic matter in this region decreases NDMAUFC by competing for available chloramines. Overall, animal feedlots, along with domestic WWTPs, are predominant sources of NDMA precursors in the studied watersheds, while croplands and urban runoff are of lesser importance.

Optimizing Ozone Disinfection in Water Reuse: Controlling Bromate Formation and Enhancing Trace Organic Contaminant Oxidation

The use of ozone/biofiltration advanced treatment has become more prevalent in recent years, with many utilities seeking an alternative to membrane/RO based treatment for water reuse. Ensuring efficient pathogen reduction while controlling disinfection byproducts and maximizing oxidation of trace organic contaminants remains a major barrier to implementing ozone in reuse applications. Navigating these challenges is imperative in order to allow for the more widespread application of ozonation. Here, we demonstrate the effectiveness of ozone for virus, coliform bacteria, and spore forming bacteria inactivation in unfiltered secondary effluent, all the while controlling the disinfection byproduct bromate. A greater than 6-log reduction of both male specific and somatic coliphages was seen at specific ozone doses as low as 0.75 O3:TOC. This study compared monochloramine and hydrogen peroxide as chemical bromate control measures in high bromide water (Br- = 0.35 ± 0.07 mg/L). On average, monochloramine and hydrogen peroxide resulted in an 80% and 36% decrease of bromate formation, respectively. Neither bromate control method had any appreciable impact on virus or coliform bacteria disinfection by ozone; however, the use of hydrogen peroxide would require a non-Ct disinfection framework. Maintaining ozone residual was shown to be critical for achieving disinfection of more resilient microorganisms, such as spore forming bacteria. While extremely effective at controlling bromate, monochloramine was shown to inhibit TrOC oxidation, whereas hydrogen peroxide enhanced TrOC oxidation.

Surface-modified activated carbon for N-nitrosodimethylamine removal in the continuous flow biological activated carbon columns

The carcinogenic nitrogenous disinfection by-product, N-nitrosodimethylamine (NDMA), is challenging to adsorb due to its high polarity and solubility. Our previous research demonstrated that the adsorptive removal of NDMA can be improved using surface-modified activated carbon (AC800). The current study evaluated the efficacy of AC800 in removing NDMA in a continuous-flow column over 75 days, using both granular activated carbon (GAC) and biologically activated carbon (BAC) columns. The AC800 GAC column demonstrated extended breakthrough and exhaustion times of 10 days and 22 days, respectively, compared to the conventional GAC column at 4 days and 10.5 days. The surface modification effect persisted for 25 days before the removal trends became indistinguishable. The AC800 BAC column outperformed the conventional BAC column with a longer breakthrough time of 11.3 days compared to 7.4 days. BAC columns consistently showed greater NDMA removal, emphasizing the role of biodegradation in NDMA removal on carbon. The higher NDMA removal in the inoculated columns was attributed to increased microbial diversity and the dominance of six specific genera, Methylobacterium, Phyllobacterium, Curvibacter, Acidovorax, Variovorax, and Rhodoferax. This study provides new insights into using modified activated carbon as GAC and BAC media in a real-world continuous-flow setup.

Air Pollutants Removal Using Biofiltration Technique: A Challenge at the Frontiers of Sustainable Environment

Air pollution is a central problem faced by industries during the production process. The control of this pollution is essential for the environment and living organisms as it creates harmful effects. Biofiltration is a current pollution management strategy that concerns removing odor, volatile organic compounds (VOCs), and other pollutants from the air. Recently, this approach has earned vogue globally due to its low-cost and straightforward technique, effortless function, high reduction efficacy, less energy necessity, and residual consequences not needing additional remedy. There is a critical requirement to consider sustainable machinery to decrease the pollutants arising within air and water sources. For managing these different kinds of pollutant reductions, biofiltration techniques have been utilized. The contaminants are adsorbed upon the medium exterior and are metabolized to benign outcomes through immobilized microbes. Biofiltration-based designs have appeared advantageous in terminating dangerous pollutants from wastewater or contaminated air in recent years. Biofiltration uses the possibilities of microbial approaches (bacteria and fungi) to lessen the broad range of compounds and VOCs. In this review, we have discussed a general introduction based on biofiltration and the classification of air pollutants based on different sources. The history of biofiltration and other mechanisms used in biofiltration techniques have been discussed. Further, the crucial factors of biofilters that affect the performance of biofiltration techniques have been discussed in detail. Finally, we concluded the topic with current challenges and future prospects.

Highly effective electrocatalytic reduction of N-nitrosodimethylamine on Ru/CNT catalyst

N-Nitrosodimethylamine (NDMA) is a commonly identified carcinogenic and genotoxic pollutant in water. In this study, we prepared Ru catalysts supported on carbon nanotube (Ru/CNT) and studied the electrocatalytic reduction of N-nitrosamines on Ru/CNT electrode in a three-electrode system. The results show that Ru-based catalyst exhibits a high activity of 793.3 μmol L^-1 gCat^-1 h^-1 for electrochemical reduction of NDMA. Reaction mechanism study discloses that the electrocatalytic reduction of NDMA is accomplished by both direct electron reduction and atomic H* mediated indirect reduction pathways. Further product analysis indicates that NDMA is finally reduced to dimethylamine (DMA) and ammonia. The reduction efficiency of NDMA strongly relies on cathode potential, initial NDMA concentration and solution pH. To verify the universality of Ru/CNT electrode, electrocatalytic reduction of three dialkyl N-nitrosamines with different alkyl groups was performed and Ru catalyst has high catalytic activities for the three N-nitrosamines, while the catalytic efficiency differs with their structures. Simultaneous electrochemical reduction of the three N-nitrosamines indicates that the reduction rates of N-nitrosamines follow the same order in the multiple-component system as that in the single-component system. Catalyst recycling results demonstrate that after 5 consecutive recycling runs Ru/CNT electrode remains almost identical catalytic activity to the fresh catalyst, manifesting the high catalytic stability of Ru/CNT electrode.

Evaluation of preformed monochloramine for bromate control in ozonation for potable reuse

Bromate, a regulated disinfection byproduct, forms during the ozonation of bromide through reactions with both ozone and hydroxyl radical. In this study, preformed monochloramine was evaluated for use as a bromate suppression method in pilot testing of wastewater reuse with an average bromide concentration of 422±20 µg/L. A dose of 3 mg/L NH₂Cl-Cl₂ decreased bromate formation by an average of 82% and was sufficient to keep bromate below the MCL at ozone doses up to 8.6 mg/L (1.2 O₃:TOC). Removal of 1,4-dioxane through ozonation decreased with increasing NH₂Cl dose, confirming that monochloramine suppresses bromate formation, at least in part, by acting as a hydroxyl radical scavenger. This may negatively impact oxidation objectives of ozonation in reuse applications. Increasing monochloramine contact time did not improve bromate suppression, indicating that monochloramine probably did not mask bromide as NHBrCl or other haloamines prior to ozonation. However, NHBrCl and NH₂Br may be formed from reactions between HOBr and NH₂Cl and excess free ammonia during ozonation. NDMA was formed by ozonation at concentrations up to 79 ng/L and was not enhanced by NH₂Cl addition.

Demonstration-scale evaluation of ozone-biofiltration-granular activated carbon advanced water treatment for managed aquifer recharge

The Sustainable Water Initiative for Tomorrow (SWIFT) program is the effort of the Hampton Roads Sanitation District to implement indirect potable reuse to recharge the depleted Potomac Aquifer. This initiative is being demonstrated at the 1-MGD SWIFT Research Center with a treatment train including coagulation/flocculation/sedimentation (floc/sed), ozonation, biofiltration (BAF), granular activated carbon (GAC) adsorption, and UV disinfection, followed by managed aquifer recharge. Bulk total organic carbon (TOC) removal occurred via multiple treatment barriers including, floc/sed (26% removal), ozone/BAF (30% removal), and adsorption by GAC. BAF acclimation was observed during the first months of plant operation which coincided with the establishment of biological nitrification and dissolved metal removal. Bromate formation during ozonation was efficiently controlled below 10 µg/L using preformed monochloramine and preoxidation with free chlorine. N-nitrosodimethylamine (NDMA) was formed at an average concentration of 53 ng/L post-ozonation and was removed >70% by the BAFs after several months of operation. Contaminants of emerging concern were removed by multiple treatment barriers including oxidation, biological degradation, and adsorption. The breakthrough of these contaminants and bulk TOC will likely determine the replacement interval of GAC. The ozone/BAC/GAC treatment process was shown to meet all defined treatment goals for managed aquifer recharge. PRACTITIONER POINTS: Floc/sed, biofiltration, and GAC adsorption provide important barriers in carbon-based treatment trains for bulk TOC and trace organic contaminant removal. Biofilter acclimation was observed during the first three months of operation in each operating period as evidenced by the establishment of nitrification. Bromate was effectively controlled during ozonation of a high bromide water with monochloramine doses of 3-5 mg/L. NDMA was formed at an average concentration of 53 ng/L by ozonation and complete removal was achieved by BAFs after several months of biological acclimation. An average 25% removal of 1,4-dioxane was achieved via oxidation by hydroxyl radicals during ozonation.