Chemical Inhibition of Nitrification: Evaluating Methods to Detect and Characterize Inhibition and the Role of Selected Stress Responses Upon Exposure to Oxidative and Hydrophobic Toxins

dc.contributor.authorKelly, Richard Thomas, IIen
dc.contributor.committeechairLove, Nancy G.en
dc.contributor.committeememberDaigger, Glen T.en
dc.contributor.committeememberNovak, John T.en
dc.contributor.committeememberVikesland, Peter J.en
dc.contributor.committeememberStevens, Ann M.en
dc.contributor.departmentEnvironmental Engineeringen
dc.date.accessioned2014-03-14T20:13:35Zen
dc.date.adate2005-07-21en
dc.date.available2014-03-14T20:13:35Zen
dc.date.issued2005-06-21en
dc.date.rdate2007-07-21en
dc.date.sdate2005-06-29en
dc.description.abstractThis research first examined nitrification inhibition caused by different classes of industrially relevant chemicals on activated sludge and found that conventional aerobic nitrification was inhibited by single pulse inputs of every chemical tested, with 1-chloro-2,4-dinitrobenzene (oxidant) having the most severe impact, followed by alkaline pH 11, cadmium (heavy metal), cyanide, octanol (hydrophobic) and 2,4-dinitrophenol (respiratory uncoupler). Of the different chemicals tested, the oxidative and hydrophobic chemicals showed severe nitrification inhibition relative to other treatment processes and therefore deserved further investigation. For oxidative chemicals, we hypothesized that the more severe inhibition was because nitrifying bacteria lack one or more of the microbial stress response mechanisms used to mediate the toxic effect of oxidative chemicals. During these experiments, we showed that a rapid (minutes) antioxidant potassium efflux mechanism does not exist in two nitrifying bacteria, Nitrosomonas europaea and Nitrospira moscoviensis. Furthermore, we showed that another important antioxidant molecule, glutathione, was not oxidized as readily as in a non-nitrifying bacterium. Furthermore, we hypothesized that hydrophobic chemical-induced nitrification inhibition recovered more quickly because of the presence of membrane modification stress response mechanisms. While testing this hypothesis, we showed that N. europaea modified its cell membrane in response to hydrophobic chemicals using a long-term (hours) membrane modification mechanism that required the synthesis of new fatty acids, but it did not contain a short-term (minutes) response mechanism involving a cis/trans isomerase. Therefore, investigating these nitrifier stress responses showed that nitrifiers lack short-term stress responses that may be used to rapidly detect inhibition, indicating that conventional methods of detecting nitrification inhibition, like differential respirometry and nitrate generation rate (NGR), are still the fastest and easiest methods to use. Because several conventional methods exist, we also investigated differences between differential respirometry and a UV method we developed to measure NGR. During these tests, we showed that the UV NGR method provided a more reliable measure of nitrification inhibition than differential respirometry, and that the time to maximum nitrification inhibition depended on the properties of the chemical toxin, which implies that longer exposure times may be needed to accurately predict nitrification inhibition.en
dc.description.degreePh. D.en
dc.identifier.otheretd-06292005-113813en
dc.identifier.sourceurlhttp://scholar.lib.vt.edu/theses/available/etd-06292005-113813/en
dc.identifier.urihttp://hdl.handle.net/10919/28151en
dc.publisherVirginia Techen
dc.relation.haspartKellyIIETDnew.pdfen
dc.rightsIn Copyrighten
dc.rights.urihttp://rightsstatements.org/vocab/InC/1.0/en
dc.subjectchemical inhibitionen
dc.subjectfatty aciden
dc.subjectcell membraneen
dc.subjectpotassium effluxen
dc.subjectglutathioneen
dc.subjectstress responseen
dc.subjectdetectionen
dc.subjectactivated sludgeen
dc.subjectnitrificationen
dc.titleChemical Inhibition of Nitrification: Evaluating Methods to Detect and Characterize Inhibition and the Role of Selected Stress Responses Upon Exposure to Oxidative and Hydrophobic Toxinsen
dc.typeDissertationen
thesis.degree.disciplineEnvironmental Engineeringen
thesis.degree.grantorVirginia Polytechnic Institute and State Universityen
thesis.degree.leveldoctoralen
thesis.degree.namePh. D.en

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