Matching Items (4)
Filtering by
- All Subjects: Carbon, Activated
- Creators: Fox, Peter
Description
Granular activated carbon (GAC) filters are final polishing step in the drinking water treatment systems for removal of dissolved organic carbon fractions. Generally filters are colonized by bacterial communities and their activity reduces biodegradable solutes allowing partial regeneration of GAC's adsorptive capacity. When the bacteria pass into the filtrate due to increased growth, microbiological quality of drinking water is compromised and regrowth in the distribution system occurs. Bacteria attached to carbon particles as biofilms or in conjugation with other bacteria were observed to be highly resistant to post filtration microbial mitigation techniques. Some of these bacteria were identified as pathogenic.
This study focuses on one such pathogen Legionella pneumophila which is resistant to environmental stressors and treatment conditions. It is also responsible for Legionnaires' disease outbreak through drinking water thus attracting attention of regulatory agencies. The work assessed the attachment and colonization of Legionella and heterotrophic bacteria in lab scale GAC media column filters. Quantification of Legionella and HPC in the influent, effluent, column's biofilms and on the GAC particles was performed over time using fluorescent microscopy and culture based techniques.
The results indicated gradual increase in the colonization of the GAC particles with HPC bacteria. Initially high number of Legionella cells were detected in the column effluent and were not detected on GAC suggesting low attachment of the cells to the particles potentially due to lack of any previous biofilms. With the initial colonization of the filter media by other bacteria the number of Legionella cells on the GAC particles and biofilms also increased. Presence of Legionella was confirmed in all the samples collected from the columns spiked with Legionella. Significant increase in the Legionella was observed in column's inner surface biofilm (0.25 logs up to 0.52 logs) and on GAC particles (0.42 logs up to 0.63 logs) after 2 months. Legionella and HPC attached to column's biofilm were higher than that on GAC particles indicating the strong association with biofilms. The bacterial concentration slowly increased in the effluent. This may be due to column's wall effect decreasing filter efficiency, possible exhaustion of GAC capacity over time and potential bacterial growth.
This study focuses on one such pathogen Legionella pneumophila which is resistant to environmental stressors and treatment conditions. It is also responsible for Legionnaires' disease outbreak through drinking water thus attracting attention of regulatory agencies. The work assessed the attachment and colonization of Legionella and heterotrophic bacteria in lab scale GAC media column filters. Quantification of Legionella and HPC in the influent, effluent, column's biofilms and on the GAC particles was performed over time using fluorescent microscopy and culture based techniques.
The results indicated gradual increase in the colonization of the GAC particles with HPC bacteria. Initially high number of Legionella cells were detected in the column effluent and were not detected on GAC suggesting low attachment of the cells to the particles potentially due to lack of any previous biofilms. With the initial colonization of the filter media by other bacteria the number of Legionella cells on the GAC particles and biofilms also increased. Presence of Legionella was confirmed in all the samples collected from the columns spiked with Legionella. Significant increase in the Legionella was observed in column's inner surface biofilm (0.25 logs up to 0.52 logs) and on GAC particles (0.42 logs up to 0.63 logs) after 2 months. Legionella and HPC attached to column's biofilm were higher than that on GAC particles indicating the strong association with biofilms. The bacterial concentration slowly increased in the effluent. This may be due to column's wall effect decreasing filter efficiency, possible exhaustion of GAC capacity over time and potential bacterial growth.
ContributorsSharma, Harsha (Author) / Abbaszadegan, Morteza (Thesis advisor) / Alum, Absar (Committee member) / Fox, Peter (Committee member) / Arizona State University (Publisher)
Created2014
Description
Research in microbial biofuels has dramatically increased over the last decade. The bulk of this research has focused on increasing the production yields of cyanobacteria and algal cells and improving extraction processes. However, there has been little to no research on the potential impact of viruses on the yields of these phototrophic microbes for biofuel production. Viruses have the potential to significantly reduce microbial populations and limit their growth rates. It is therefore important to understand how viruses affect phototrophic microbes and the prevalence of these viruses in the environment. For this study, phototrophic microbes were grown in glass bioreactors, under continuous light and aeration. Detection and quantification of viruses of both environmental and laboratory microbial strains were measured through the use of a plaque assay. Plates were incubated at 25º C under continuous direct florescent light. Several environmental samples were taken from Tempe Town Lake (Tempe, AZ) and all the samples tested positive for viruses. Virus free phototrophic microbes were obtained from plaque assay plates by using a sterile loop to scoop up a virus free portion of the microbial lawn and transferred into a new bioreactor. Isolated cells were confirmed virus free through subsequent plaque assays. Viruses were detected from the bench scale bioreactors of Cyanobacteria Synechocystis PCC 6803 and the environmental samples. Viruses were consistently present through subsequent passage in fresh cultures; demonstrating viral contamination can be a chronic problem. In addition TEM was performed to examine presence or viral attachment to cyanobacterial cells and to characterize viral particles morphology. Electron micrographs obtained confirmed viral attachment and that the viruses detected were all of a similar size and shape. Particle sizes were measured to be approximately 50-60 nm. Cell reduction was observed as a decrease in optical density, with a transition from a dark green to a yellow green color for the cultures. Phototrophic microbial viruses were demonstrated to persist in the natural environment and to cause a reduction in algal populations in the bioreactors. Therefore it is likely that viruses could have a significant impact on microbial biofuel production by limiting the yields of production ponds.
ContributorsKraft, Kyle (Author) / Abbaszadegan, Morteza (Thesis advisor) / Alum, Absar (Committee member) / Fox, Peter (Committee member) / Arizona State University (Publisher)
Created2014
Description
Granular activated carbon (GAC) is effectively used to remove natural organic matter (NOM) and to assist in the removal of disinfection byproducts (DBPs) and their precursors. However, operation of GAC is cost- and labor-intensive due to frequent media replacement. Optimizing the use of GAC is necessary to ensure treatment efficiency while reducing costs. This dissertation presents four strategies to reduce improve GAC usage while reducing formation of DBPs. The first part of this work adopts Rapid Small Scale Tests (RSSCTs) to evaluate removal of molecular weight fractions of NOM, characterized using size exclusion chromatography (SECDOC). Total trihalomethanes (TTHM), haloacetic acids (HAA5) and haloacetonitriles (HAN) formation were quantified after treatment with GAC. Low MW NOM was removed preferentially in the early bed volumes, up until exhaustion of available adsorption sites. DBP formation potential lowered with DOC removal. Chlorination prior to GAC is investigated in the second part of this work as a strategy to increase removal of NOM and DBP precursors. Results showed lower TTHM formation in the effluent of the GAC treatment when pre-chlorination was adopted, meaning this strategy could help optimize and extend the bed life if GAC filters. The third part of this work investigates in-situ GAC regeneration as an alternative to recover adsorption capacity of field-spent GAC that could potentially offer new modes of operation for water treatment facilities while savng costs with reactivation of spent GAC in an external facility. Field-spent GACs were treated with different oxidant solutions and recovery in adsorption capacity was evaluated for NOM and for two micro pollutants. Recovery of GAC adsorption capacity was not satisfactory for most of conditions evaluated. This indicates that in-situ GAC regeneration could be more effective when the adsorbates are present at high concentrations. Lastly, this work investigates the impact of low molecular weight polyDADMAC on N-nitrosodimethylamine (NDMA) formation. Water treatment facilities rely on polyDADMAC as a coagulant aid to comply with NOM removal and turbidity requirements. Since polymer-derived NDMA precursors are not removed by GAC, it is essential to optimize the use and synthesis of polyDADMAC to reduce NDMA precursors during water treatment.
ContributorsFischer, Natalia (Author) / Westerhoff, Paul (Thesis advisor) / Hristovski, Kiril (Committee member) / Fox, Peter (Committee member) / Arizona State University (Publisher)
Created2017
Description
Specific inorganic and organic pollutants in water (As(V), Cr(VI), THMs, and hardness) cause health concerns or aesthetic problems. The goal of this dissertation is to demonstrate novel approaches to improve the performance of point of use and municipal activated carbon processes to provide safe and reliable water to the public at distributed centralized locations.
Template Assisted Crystallization system would adjust saturation index (SI) value of TAC treated water to zero when SI value of influent water was in the range at 0.08~0.3. However, the reduction in SI when SI values were higher (e.g. 0.7~1.3) was similar to the reduction at lower SI values which could be due to limitations in kinetics or mass transfer with the template on TAC media.
Pre-chlorination prior to municipal-scale granular activated carbon (GAC) treatment was evaluated to control THM formation in distribution systems. Pre-chlorination decreased UVA, shift the dissolved organic carbon (DOC) molecular weight distribution and pre-formed trihalomethanes (THM). GAC treatment of pre-chlorinated water achieved lower THM formation in distribution systems.
To add functionality in POU systems to remove As(V) and Cr(VI), activated carbon was nano-tized to fabricate nano-enabled carbon block (CB) by (1) impregnating iron or titanium metal oxides chemically or (2) attaching titanium based P25 through electrostatic attraction force. Nanoparticle loadings of 5 to 10 wt % with respect to activated carbon enables reduction of As(V) or Cr(VI) from levels of common occurrence to below regulatory levels across carbon block designs. Minimal impacts on As(V) and Cr(VI) sorption were observed up to a nanoparticle pre-treatment temperature of 200 C, which is the temperature for CB production. Through controlling pH at 4.5 during mixing of nanoparticles with pH IEP=6 and activated carbon with pH IEP=3, electrostatic attachment of nanoparticles to activated carbon could be achieved prior to fabricating carbon block. A mini carbon block test device was designed, fabricated, and validated to mimic performances of full-scale carbon block using less volumes of test water. As(V) removal tests showed Fe impregnated CB achieved the highest As(V) removal while P25 attached CB had the lowest among three nanoparticles loaded CBs.
Template Assisted Crystallization system would adjust saturation index (SI) value of TAC treated water to zero when SI value of influent water was in the range at 0.08~0.3. However, the reduction in SI when SI values were higher (e.g. 0.7~1.3) was similar to the reduction at lower SI values which could be due to limitations in kinetics or mass transfer with the template on TAC media.
Pre-chlorination prior to municipal-scale granular activated carbon (GAC) treatment was evaluated to control THM formation in distribution systems. Pre-chlorination decreased UVA, shift the dissolved organic carbon (DOC) molecular weight distribution and pre-formed trihalomethanes (THM). GAC treatment of pre-chlorinated water achieved lower THM formation in distribution systems.
To add functionality in POU systems to remove As(V) and Cr(VI), activated carbon was nano-tized to fabricate nano-enabled carbon block (CB) by (1) impregnating iron or titanium metal oxides chemically or (2) attaching titanium based P25 through electrostatic attraction force. Nanoparticle loadings of 5 to 10 wt % with respect to activated carbon enables reduction of As(V) or Cr(VI) from levels of common occurrence to below regulatory levels across carbon block designs. Minimal impacts on As(V) and Cr(VI) sorption were observed up to a nanoparticle pre-treatment temperature of 200 C, which is the temperature for CB production. Through controlling pH at 4.5 during mixing of nanoparticles with pH IEP=6 and activated carbon with pH IEP=3, electrostatic attachment of nanoparticles to activated carbon could be achieved prior to fabricating carbon block. A mini carbon block test device was designed, fabricated, and validated to mimic performances of full-scale carbon block using less volumes of test water. As(V) removal tests showed Fe impregnated CB achieved the highest As(V) removal while P25 attached CB had the lowest among three nanoparticles loaded CBs.
ContributorsLee, Heuidae (Author) / Westerhoff, Paul (Thesis advisor) / Fox, Peter (Committee member) / Hristovski, Kiril (Committee member) / Arizona State University (Publisher)
Created2018