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Biological filters effectively remove ammonium from drinking water via nitrification. In a pilot-scale upflow biological contact filter (U-BCF), complete ammonia oxidizers (comammox), which are capable of oxidizing ammonia to nitrate in one cell, were more abundant than ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB). However, little information is available on the contribution of comammox to nitrification. In this study, we evaluated the autotrophic growth activity of comammox associated with biological activated carbon (BAC) in a U-BCF by DNA-stable isotope probing (DNA-SIP). BAC samples collected from the U-BCF were continuously fed mineral medium containing 0.14 mg N L-1 ammonium and 12C- or 13C-labeled bicarbonate for 20 days. DNA-SIP analysis revealed that comammox (clades A and B) as well as AOA assimilated bicarbonate after 10 days of incubation, proving that dominant comammox could contribute to nitrification. Contrarily, AOB remained inactive throughout the observation period. Amplicon sequencing of the 13C-labeled DNA fractions of comammox revealed that specific genotypes other than the most dominant genotype in the original sample were more enriched under the incubation condition for the DNA-SIP experiment. Thus, dominant genotypes of comammox in a U-BCF might utilize organic nitrogen to fuel nitrification in ammonia-limited environments., (© The Author(s) 2023. Published by Oxford University Press on behalf of Applied Microbiology International.)

Nitrification is a key function of biological activated carbon (BAC) filters for drinking water treatment. It is empirically known that the nitrification activity of BAC filters depends on water temperature, potentially resulting in the leakage of ammonium from BAC filters when the water temperature decreases. However, the ammonium removal capacity of BAC filters and factors governing the capacity remain unknown. This study employed a bench-scale column assay to determine the volumetric ammonium removal rate (VARR) of BAC collected from a full-scale drinking water treatment plant. VARR was determined at a fixed loading rate under different conditions. Seasonal variations of the VARR as well as impacts of the water matrix and water temperature on ammonium removal were quantitatively analyzed. While the VARR in an inorganic medium at 25 °C was maintained even during low water temperature periods and during breakpoint chlorination periods, the water matrix factor reduced the VARR in ozonated water at 25 °C by 33% on average. The VARR in ozonated water was dependent on water temperature, indicating that the microbial activity of BAC did not adapt to low water temperature. The Arrhenius equation was applied to reveal the relationship between VARR and water temperature. The actual ammonium removal performance of a full-scale BAC filter was predicted. VARR is useful for water engineers to reexamine the loading and filter depth of BAC filters.

Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

The presence of pathogenic viruses in drinking water is a major public health concern. Although viability RT-qPCR methods were developed to quantify infectious viruses, they may not always reflect viral infectivity, therefore leading to false-positive results. In this study, sodium deoxycholate (SD) pre-treatment was used to improve the efficiency of viability RT-qPCR methods with respect to exclusive quantification of infectious viruses. The ability of SD pre-treatment to enhance the penetration of three viability markers, namely, ethidium monoazide (EMA, 100 µM), propidium monoazide (PMA, 100 µM), and cis-dichlorodiammineplatinum (CDDP, 1000 µM), into heat-treated (90 °C for 1 min) Aichi virus at various concentrations (0.01-0.5%) was evaluated. The optimal SD concentration was found to be 0.1% for all markers. EMA/PMA/CDDP-RT-qPCR with 0.1% SD pre-treatment was significantly more effective than without SD pre-treatment in determining AiV inactivation after heat (50, 60, 70, 80, or 90 °C for 1 min) or chlorine treatment (1 mgCl 2 /L for 1, 2, 5, or 10 min). Among the viability RT-qPCR methods tested, CDDP-RT-qPCR with SD pre-treatment (SD-CDDP-RT-qPCR) was the most effective in reflecting viral infectivity. Performance testing of SD-CDDP-RT-qPCR in concentrated drinking water samples did not reveal any significant effects of SD-CDDP treatment. Thus, SD-CDDP-RT-qPCR could be a useful tool for monitoring infectious virus presence in drinking water.

Ultraviolet light emitting diodes (UV-LEDs) are small mercury-free devices that can be installed at the point of use (POU) of water for disinfection. Considering that heterotrophic bacteria are of concern in drinking water systems, we applied a flow-through UV-LED apparatus to dechlorinated tap water, and determined the heterotrophic plate count (HPC) in samples after UV-LED exposure (UV+) compared to samples without UV-LED application (UV-). The UV+ and UV- samples were maintained at 20°C to track HPC profiles during storage for 7 days. It was confirmed that UV+ samples showed negative HPC or lower HPC than UV- for 5 days of storage after the flow-through test. HPC bacteria formed colonies with different morphological characteristics, and yellow colonies were closest to Novosphingobium sp., with 99% identity, while white and pale pink colonies were closest to Methylobacterium sp., with 99-100% identity, based on 16S rRNA gene sequences. White colonies became dominant in UV+, indicating that UV-LED exposure can select UV-resistant species such as Methylobacterium. This study shows the effects of UV-LED application on HPC bacteria in tap water and implies that future research is required on the significance and impacts of microbial selection by UV-LED exposure., (© 2018 The American Society of Photobiology.)

Molecular changes in dissolved organic matter (DOM) from treatment processes at two drinking water treatment plants in Japan were investigated using unknown screening analysis by Orbitrap mass spectrometry. DOM formulas with carbon, hydrogen and oxygen (CHO-DOM) were the most abundant class in water samples, and over half of them were commonly found at both plants. Among the treatment processes, ozonation induced the most drastic changes to DOM. Mass peak intensities of less saturated CHO-DOM (positive (oxygen subtracted double bond equivalent per carbon (DBE-O)/C)) decreased by ozonation, while more saturated oxidation byproducts (negative (DBE-O)/C) increased and new oxidation byproducts (OBPs) were detected. By Kendrick mass analysis, ozone reactions preferred less saturated CHO-DOM in the same alkylation families and produced more saturated alkylation families of OBPs. Following ozonation, biological activated carbon filtration effectively removed <300 Da CHO-DOM, including OBPs. Following chlorination, over 50 chlorinated formulas of disinfection byproducts (DBPs) were found in chlorinated water samples where at least half were unknown. Putative precursors of these DBPs were determined based on electrophilic substitutions and addition reactions. Ozonation demonstrated better decomposition of addition reaction-type precursors than electrophilic substitution-type precursors; over half of both precursor types decreased during biological activated carbon filtration.

Ammonia is a precursor to trichloramine, which causes an undesirable chlorinous odor. Granular activated carbon (GAC) filtration is used to biologically oxidize ammonia during drinking water purification; however, little information is available regarding the abundance and diversity of ammonia-oxidizing archaea (AOA) and bacteria (AOB) associated with GAC. In addition, their sources and fates in water purification process remain unknown. In this study, six GAC samples were collected from five full-scale drinking water purification plants in Tokyo during summer and winter, and the abundance and community structure of AOA and AOB associated with GAC were studied in these two seasons. In summer, archaeal and bacterial amoA genes on GACs were present at 3.7 × 10(5)-3.9 × 10(8) gene copies/g-dry and 4.5 × 10(6)-4.2 × 10(8) gene copies/g-dry, respectively. In winter, archaeal amoA genes remained at the same level, while bacterial amoA genes decreased significantly for all GACs. No differences were observed in the community diversity of AOA and AOB from summer to winter. Phylogenetic analysis revealed high AOA diversity in group I.1a and group I.1b in raw water. Terminal-restriction fragment length polymorphism analysis of processed water samples revealed that AOA diversity decreased dramatically to only two OTUs in group I.1a after ozonation, which were identical to those detected on GAC. It suggests that ozonation plays an important role in determining AOA diversity on GAC. Further study on the cell-specific activity of AOA and AOB is necessary to understand their contributions to in situ nitrification performance.

Nitrification is an important biological function of granular activated carbon (GAC) used in advanced drinking water purification processes. Newly discovered ammonia-oxidizing archaea (AOA) have challenged the traditional understanding of ammonia oxidation, which considered ammonia-oxidizing bacteria (AOB) as the sole ammonia-oxidizers. Previous studies demonstrated the predominance of AOA on GAC, but the contributions of AOA and AOB to ammonia oxidation remain unclear. In the present study, DNA-stable isotope probing (DNA-SIP) was used to investigate the autotrophic growth of AOA and AOB associated with GAC at two different ammonium concentrations (0.14 mg N/L and 1.4 mg N/L). GAC samples collected from three full-scale drinking water purification plants in Tokyo, Japan, had different abundance of AOA and AOB. These samples were fed continuously with ammonium and (13)C-bicarbonate for 14 days. The DNA-SIP analysis demonstrated that only AOA assimilated (13)C-bicarbonate at low ammonium concentration, whereas AOA and AOB exhibited autotrophic growth at high ammonium concentration. This indicates that a lower ammonium concentration is preferable for AOA growth. Since AOA could not grow without ammonium, their autotrophic growth was coupled with ammonia oxidation. Overall, our results point towards an important role of AOA in nitrification in GAC filters treating low concentration of ammonium., (Copyright © 2013 Elsevier Ltd. All rights reserved.)

Abstract: Ozonation followed by granular activated carbon (GAC) is one of the advanced drinking water treatments. During GAC treatment, ammonia can be oxidized by ammonia-oxidizing microorganisms associated with GAC. However, there is little information on the abundance and diversity of ammonia-oxidizing microorganisms on GAC. In this study, the nitrification activity of GAC and the settlement of ammonia-oxidizing archaea (AOA) and bacteria (AOB) in GAC were monitored at a new full-scale advanced drinking water treatment plant in Japan for 1 year after plant start-up. Prechlorination was implemented at the receiving well for the first 10 months of operation to treat ammonia in raw water. During this prechlorination period, levels of both AOA and AOB associated with GAC were below the quantification limit. After prechlorination was stopped, 105 copies g-dry−1 of AOA amoA genes were detected within 3 weeks and the quantities ultimately reached 106–107 copies g-dry−1, while levels of AOB amoA genes still remained below the quantification limit. This observation indicates that AOA can settle in GAC rapidly without prechlorination. The nitrification activity of GAC increased concurrently with the settlement of AOA after prechlorination was stopped. Estimation of in situ cell-specific ammonia-oxidation activity for AOA on the assumption that only AOA and AOB determined can contribute to nitrification suggests that AOA may account for most of the ammonia-oxidation. However, further validation on AOB contribution is required. [ABSTRACT FROM AUTHOR]

The effects of different placements of rapid sand filtration on nitrification performance of BAC treatment in a pilot-scale plant were evaluated. In this plant, rapid sand filtration was placed after ozonation-BAC treatment in Process (A), while it preceded ozonation-BAC treatment in Process (B). Analysis of amoA genes of ammonia-oxidizing archaea (AOA) and bacteria (AOB) combined with nitrification potential test was conducted. BAC from Process (A) demonstrated slightly higher nitrification potential at every sampling occasion. This might be due to higher abundances of AOB on BAC from Process (A) than those on BAC from Process (B). However, AOA rather than AOB could be predominant ammonia-oxidizers in BAC treatment regardless of the position of rapid sand filtration. The highest nitrification potential was observed for BAC from both processes in February when the highest abundances of AOA-amoA and AOB-amoA genes were detected. Since rapid sand filtration was placed after BAC treatment in Process (A), residual aluminum concentration in BAC influent was higher in Process (A). However, adverse effects of aluminum on nitrification activity were not observed. These results suggest that factors other than aluminum concentration in different treatment processes could possibly have some influence on abundances of ammonia-oxidizing microorganisms on BAC. [ABSTRACT FROM AUTHOR]