RESUMEN

Chloraminated drinking water systems commonly use free chlorine conversions (FCCs) to prevent or control nitrification, but unintended water quality changes may occur, including increased disinfection by-product and metal concentrations. This study evaluated water quality in a chloraminated drinking water system and residential locations before, during, and after their annual, planned FCC. Water quality alternated between relatively consistent and variable periods when switching disinfectants. During the FCC, regulated four trihalomethane and five haloacetic acid concentrations increased by four and seven times, respectively, and exceeded corresponding maximum contaminant levels. Implications of disinfection by-product sampling during an FCC were assessed, and an approach to account for increased FCC disinfection by-product concentrations was proposed. For metals, the FCC had minor impacts on distribution system concentrations and did not appear to impact residential concentrations. Overall, observed variable water quality appeared primarily associated with switching disinfectants and depended on distribution system hydraulics.

RESUMEN

ELISA assays are a potential tool to screen for dissolved or cell bound microcystins in drinking water treatment sludges. In order to evaluate this potential more thoroughly, experiments were performed in alum sludges to: (1) evaluate the impacts of sample storage times, temperatures, and sludge composition on spiked microcystin-LR recovery by ELISA; (2) examine the linearity of ELISA responses to spiked microcystin-LR as a function of sludge composition; and (3) examine the sensitivity ELISA and LC/MS/MS to five different concentrations of microcystin-producing cyanobacteria entrained in sludges of two different compositions. During storage experiments, microcystin recovery efficiencies ranged from 85% to 125% across the range of 12 storage time and temperature combinations with recovery efficiencies in 7 of the 12 combinations falling into the 90% to 110% range. During the linearity experiments, linear models fit ELISA responses in all sludge compositions with R2 values ≥ 0.95. During the sensitivity studies, simple freeze/thaw/centrifugation processing combined with ELISA or LC/MS/MS analyses resulted in detection of microcystins in thickened sludges derived from pre-coagulation cell suspensions of 102-106 cells/mL. In addition, the relationships between toxin concentrations in sludges and the original cell titers were linear regardless of analytical method.

RESUMEN

Existing heterotrophic denitrification reactors rely on microorganisms to consume dissolved oxygen (DO) and create conditions suitable for denitrification, but this practice leads to excessive microbial growth and increased organic carbon doses. An innovative reactor that uses nitrogen gas sparging through a contactor to strip DO was developed and tested in the lab. It reduced influent nitrate from 15 to <1 mg/L as N with nitrite accumulation <1 mg/L as N. It maintained a consistent flow rate and developed minimal headloss, making it easier to operate than the denitrifying dual-media filter that was operated in parallel. Gravel, polyvinyl chloride pieces, and no packing media were assessed as options for the nitrogen-sparged contactor, and gravel was found to support denitrification at the highest loading rate and was resilient to nitrogen-sparging shutoffs and intermittent operation. This innovative reactor appears promising for small drinking water systems.

RESUMEN

Aerobic plate count assays are an industry standard method for the enumeration of microbial products. Colony swarming among industrial Bacillus isolates on solid medium can impact a counting technician's interpretation of colony count, promote inter-technician variance and reduce the agreement of plate counts with growth-independent enumeration methods. In the present study, we examined swarming behavior among four industrial Bacillus species as a function of culture medium brand choice. Colony diameter for three Bacillus species was found to be influenced by culture medium brand, as was colony count interpretation among three out of four plate counting technicians. Estimations of Bacillus endospore concentration were likewise influenced by culture medium brand, leading to an increased incidence of QC failure for replicate samples of a Bacillus-based microbial product as a function of brand choice. Results suggest that culture medium brand choice may be an additional source of variance when plate counting is used for the enumeration of Bacillus-based microbial products. We recommend that plating medium brand availability in testing laboratories be considered by microbial product manufacturers when considering sources of variance in customer and regulatory laboratories.

Asunto(s)

Bacillus/crecimiento & desarrollo , Bacillus/aislamiento & purificación , Recuento de Colonia Microbiana/métodos , Medios de Cultivo/química , Técnicas Bacteriológicas/métodos , Microbiología de Alimentos , Esporas Bacterianas

RESUMEN

Growth-independent microbial enumeration methods such as quantitative PCR require the efficient extraction of genomic DNA from targeted cells. Bacillus endospores are popular inclusions in commercial products due to their hardiness and metabolic dormancy; however, this hardiness is known to render Bacillus endospores resistant to traditional DNA isolation techniques. Metagenomic studies have sought to address this resistance through nutrient-based germination of bacterial endospores in environmental samples. In the present study, we sought to apply this technique to the enumeration of microbial products using an industrial strain of Bacillus subtilis as a model organism. Germination was induced through incubation of axenic spore suspensions in an AGFK-based rich medium. Total spore count, dipicolinic acid release and OD600 absorbance were monitored over time to track the progression of spore populations through the stages of germination and outgrowth. Aerobic plate counts and flow cytometry were used to monitor cell populations for proliferation during the incubation period. Finally, quantitative PCR with taxon-specific primers was used to examine DNA recovery as a function of time. Results show that customized germination protocols, once appropriately validated for the species and product matrix under consideration, can result in more efficient DNA extraction and thus lower limits of detection for qPCR assays targeting industrial Bacillus endospores in microbial products.