Browsing by Subject "Drinking water"
Now showing 1 - 3 of 3
- Results Per Page
- Sort Options
Item The effect of nutrient limitations on the production of extracellular polymeric substances by drinking-water bacteria(2013-05) Evans, Ashley Nichole; Kirisits, Mary JoBiological filtration (biofiltration) of drinking-water is gaining popularity due the potential for biodegradation of an array of contaminants not removed by traditional drinking-water processes. However, previous research has suggested that biomass growth on biofilter media may lead to increased headloss, and thus, greater energy and water requirements for backwashing. Research has suggested that the main cause of headloss might be due to extracellular polymeric substances (EPS) rather than the bacterial cells themselves. As EPS production has been shown to increase under nitrogen- and phosphorus-limited or -depleted conditions, the goal of this research was to add to the body of knowledge regarding biofiltration by studying the relationship between EPS production and nutrient limitations in drinking-water. Batch experiments with a synthetic groundwater were run with a mixed community of drinking-water bacteria under nutrient-balanced (a molar carbon to nitrogen to phosphorus ratio [C:N:P] of 100:10:1), nutrient-limited (e.g., C:N:P of 100:10:0.1), and nutrient-depleted conditions (C:N:P of 100:0:1 or 100:10:0). After 5 days, growth was measured as the optical density at 600 nanometers (OD600), and the concentrations of free and bound carbohydrates and proteins, the main components of EPS, were measured. In batch experiments with 2.0 and 0.2 g/L as carbon (mixture of acetic acid, mannitol and sucrose) increases in EPS production per OD600 and decreases in growth were noted under nutrient-depleted conditions. When the same experiments were conducted with a pure culture of Bacillus cereus, bound polysaccharides normalized to OD600 increased under nitrogen- and phosphorus-depleted conditions. Since previous research suggested that Bradyrhizobium would be an important player in EPS production in drinking-water biofilters, similar batch experiments were conducted with Bradyrhizobium. However, due to experimental challenges with Bradyrhizobium japonicum USDA 110, differences in EPS production under nutrient limitations could not be reliably assessed. Additional work is required with Bradyrhizobium. Recommendations for future work include the replication of these batch conditions in steady-state chemostats containing biofilm attachment media and in bench-scale columns. Additionally, future work should include experiments at carbon concentrations as low as 2 mg/L to match typical carbon concentrations in drinking-water biofilters.Item Haloacetic acid formation during chloramination: role of environmental conditions, kinetics, and haloamine chemistry(2006) Pope, Phillip Gregory; Speitel, Gerald E.This dissertation addresses the development of strategies to limit haloacetic acid (HAA) formation resulting from chloramination in drinking water treatment. The impact of several variables that influence HAA formation, such as natural organic matter (NOM), pH, Cl2:N ratio, disinfectant residual concentration, and bromide ion concentration were studied. A multi-factor, two-level, factorial experimental design and statistical analysis of the collected data determined pH and bromide concentration to be the most significant factors contributing to HAA formation. In addition to these variables, the rate of HAA formation during chloramination is a key consideration in determining strategies for minimizing formation. The kinetics of HAA formation during chloramination are characterized by an initial rapid period of formation followed by a period of slower formation. However, many plants now have a significant period of free chlorination prior to ammonia addition for purposes of meeting disinfection requirements. During short periods of prechlorination (5 or 20 minutes), significantly more HAA formation occurred relative to chloramination alone. This research was not only focused on explaining DXAA formation in terms of NOM characteristics and basic water quality and operating parameters, but also expands upon our knowledge of haloamine chemistry with a particular focus on DBP formation. In the presence of bromide, bromine-substituted haloacetic acids, as well as bromine-substituted haloamines, are formed, greatly increasing the number of chemical species that may be relevant in controlling DXAA formation. These bromine-substituted haloamines decay more rapidly and are significantly more reactive than their chlorine-substituted counterparts in forming HAAs. This research provides the fundamental underpinning for new strategies that will help water utilities select operating conditions that minimize the formation of the most reactive haloamine species, thereby leading to decreased HAA formation during chloramination.Item Molecular biology tools for identification and quantification of perchlorate-reduction genes in biotreatment applicatins(2009-08) De Long, Susan Kathleen; Kinney, Kerry A.; Kirisits, Mary JoPerchlorate contamination of drinking water sources in the United States is widespread and represents a public health concern. Biological treatment is an attractive option because perchlorate-reducing bacteria (PRB) are ubiquitous in the environment and can reduce perchlorate completely to chloride. Treatment of perchlorate-contaminated water in fixed-bed bioreactors has been demonstrated at the laboratory- and pilot-scale. However, full-scale development of reliable biological drinking water treatment processes requires a better understanding of the microbial ecology and activity of perchlorate-reducing communities in bioreactors. The objective of this research was to develop molecular biology tools (MBTs) to quantify PRB and expression of genes required for complete perchlorate reduction (pcrA and cld). The development of MBTs targeting specific genes requires that the sequence of the genes be known. In this work, an MBT called prokaryotic Suppression Subtractive Hybridization (SSH) PCR complementary DNA (cDNA) Subtraction was developed to rapidly isolate target genes for sequencing. This new tool was developed and validated using the model bacterium Pseudomonas putida mt-2 and the model pollutant toluene. For this system, over 90% of the isolated gene fragments encoded toluene-related enzymes, and 20 distinct toluene-related genes from three key operons were identified. Based on these results, prokaryotic SSH PCR cDNA Subtraction shows promise as a targeted method for gene identification; however, application to a PRB did not yield new pcrA and cld sequences. Therefore, to support the development of biological perchlorate treatment processes, quantitative PCR (qPCR) and reverse transcription qPCR (RT-qPCR) assays targeting pcrA and cld were developed using existing sequences. The qPCR and RT-qPCR assays were applied to a laboratory-scale bioreactor and two pilot-scale bioreactors treating perchlorate-contaminated water. Higher quantities of perchlorate reduction genes and transcripts generally were observed when bioreactor performance was superior. Although no quantitative correlations were established, these assays detected differences in the quantity of PRB and changes in gene expression levels during the course of bioreactor operation and between bioreactors with different performance levels. Furthermore, these assays provided an additional line of evidence that microbial perchlorate reduction was occurring. This marks the first application of qPCR assays to quantify perchlorate reduction genes and transcripts in bioreactors.