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Ronald Gehr


Associate Professor




BSc (Eng) (Witwatersrand, 1972)
MASc (Toronto, 1976)
PhD (Toronto, 1980)


Tel: 514-398-6861
Fax: 514-398-7361



General information

Professor Gehr joined the Department in 1980. He is a specialist in the field of Environmental Engineering, and is Director of the Benedek Integrated Laboratories in Environmental Engineering. He conducts research and teaches in the areas of water and wastewater treatment processes, aquatic chemistry and water and wastewater analysis. As a professional engineer, he has consulted on a variety of projects involving wastewater disinfection and reuse. He has given short courses on these subjects in Canada, South Africa, Mexico, Australia, Israel, and Italy.



  • Editor, Water Quality Research Journal of Canada (November 2003 - December 2013)

Research interests

  • Water and wastewater disinfection by UV, ozone, peracetic acid, and bromine.
  • Water reuse

Current and recent graduate research


  • Biswal, B.K. Using Microarrays to Assess the Impact of Disinfection on the Virulence risk of E. coli. October 2014


  • Enayet, S. Evaluation of Odour Abatement Causes Following Electrodewatering of Biosolids. March 2014
  • Khairallah, R.N. PPA Disinfection Kinetics of E.coli and its Effects on Antibiotic-Resistance Genes. October 2013
  • Yip Woon Sun, M. Virulence of E. coli in Receiving Waters Impacted by Wastewater Effluents.  June 2013
  • Bibi, K. Impact of Particle-Association and UV Disinfection on the Occurrence of Virulent Escherichia coli in Wastewater Effluent as Determined by Microarray Genotyping. May 2011
  • Hamilton, E. Assessing Titanium Coagulants for Municipal Wastewater Treatment. May 2011
  • Charara, N. Water Use Efficiency in the Hotel Sector in Barbados. May 2009
  • Stark, O. Key Factors Affecting the Degradation Behaviour of Peracetic Acid. May 2009
  • Hallmich, C. Effect of Pre- and Post- UV Disinfection Conditions on Photoreactivation of Fecal Coliforms from a Physicochemical Wastewater Effluent. April 2009

Courses offered

  • CIVE 225 Environmental Engineering 4 Credits
      Offered in the:
    • Fall
    • Winter
    • Summer

  • CIVE 421 Municipal Systems 3 Credits
      Offered in the:
    • Fall
    • Winter
    • Summer

  • CIVE 430 Water Treatment&Pollut Control 3 Credits
      Offered in the:
    • Fall
    • Winter
    • Summer

  • CIVE 452 Water Resources in Barbados 3 Credits
      Offered in the:
    • Fall
    • Winter
    • Summer

Highlights recent professional experience

  • Disinfection of wastewater, using novel chemical disinfectants, separately or in combination with UV:

Over the past 20 years, I have been conducting research into disinfection of water and wastewater, using UV, ozone, peracetic acid (PAA), performic acid (PFA), or a combination. Included here are fouling of UV reactors and a new line of research, the effects of disinfection at the gene level. This last-mentioned work is being done in collaboration with researchers from the Biotechnology Research Institute in Montreal.

The research has impacted on several municipal projects which will be upgrading their water or wastewater treatment plants. I was a member of the Expert Committee assessing upgrades to Montreal’s Drinking Water Treatment Plants (February, 2007), and a member of the Technical Review Panel for the Water Environment Research Foundation (WERF) report “Disinfection of Wastewater Effluent – Comparison of Alternative Technologies” (published in 2008). The results of my work on PAA and combined disinfectants have appeared in two widely used books of technical practice (Metcalf & Eddy, Wastewater Engineering, Treatment & Reuse (2003) and Metcalf & Eddy, Water Reuse (2007).

My laboratory was one of the first in Canada to perform collimated beam testing for UV disinfection, and we perform such tests for municipalities in North America. Montreal is intending to disinfect its treated domestic effluent before discharge into the St Lawrence River, and I have directed 10 laboratory or pilot studies on wastewater from the Montreal Wastewater Treatment Plant regarding UV, ozone, peracetic acid or performic acid as alternatives to chlorine disinfection. The most recent was a study with Kemira Canada into the feasibility of using performic acid as a disinfectant; this has lead to further pilot work in Ottawa and elsewhere. I have also collaborated with Dr Pierre Payment of the Institut Armand Frappier to assess the disinfection of Montreal’s wastewaters using UV, ozone, or peracetic acid. The unique aspect of this study was the use of four indicator microorganisms – fecal coliforms, enterococci, Clostridium perfringens, and MS-2 coliphage – to give a more complete picture of the effects of these disinfectants on pathogens. I have supervised pilot testing at Fabreville (Que) for two separate full-scale projects, and have consulted on projects for the cities of Saskatoon, Winnipeg, Vancouver and several in Quebec. In February, 2005 I was invited by the Quebec Ministry of Municipal Affairs to be their official “witness” for validation testing of a drinking water UV disinfection system at L’Epiphanie, Quebec. Since 1994 I have given 8 sets of short courses on wastewater disinfection and physicochemical treatment, in Australia, Israel, Italy, Mexico, and South Africa.

  • Impact of disinfection of wastewaters on antibiotic resistance and virulence genes in bacteria:

Disinfection of wastewater does not generally lead to zero counts of viable indicator bacteria, as is the case with drinking water. Depending on the disinfection technology which is used, those organisms which survive may be able to do so because of their specific genetic makeup. The virulence gene pool in these survivors could, in turn, yield bacteria which are pathogenic to humans. Disinfection may also select for those strains which are more resistant to antibiotics. My research is therefore moving from simply assessing the performance of various disinfectants under a variety of conditions, to the impact of the disinfection process at the genetic level.


Association Québécoise des Techniques de l'eau: Distinction, Article Scientifique, 2004. Paper by Payment and Gehr (2004) which appeared in Vecteur Environnement.

Lady Davis Visiting Professor Scholarship, Hebrew University, Jerusalem, November 2002.

Association Québécoise des Techniques de l'eau: Distinction, Article Scientifique. 1997. Paper by Gosselin et al (1996) which appeared in Vecteur Environnement.

Canadian Association on Water Quality, Service Award, February 1995.

Professional committees and activities with professional societies

  • Reviewer for Environmental Science and Technology, Journal of Environmental Engineering, Water Research, Water Environment Federation (research journal), Canadian Journal of Civil Engineering, Journal of Hazardous Materials, etc.
  • Reviewer for EPA-SBIR, EPA-STAR, Hong Kong Research Grants Council, etc.
  • Reviewer for the Walkerton Inquiry

Recent publications

Journal articles

  • Navab-Daneshmand, T., Enayet, S., Gehr, R. and Frigon, F. (2014) "Bacterial Pathogen Indicators Regrowth and Reduced Sulphur Compounds’ Emissions During Storage of Electro-Dewatered Biosolids", Chemosphere, 113, 109-115. http://dx.doi.org/10.1016/j.chemosphere.2014.04.012
  • Biswal, B.K., Khairallah, R., Bibi, K., Mazza, A., Gehr, R., Masson, L. and Frigon, D. (2014) "UV and  PAA Disinfection Reduce the Prevalence of Uropathogenic Escherichia coli in  Wastewater Effluents", Applied and Environmental Microbiology, 80, 12, 3656–3666. http://dx.doi.org/10.1128/AEM.00418-14
  • Frigon, D., Biswal, B.K., Mazza, A., Masson, L., and Gehr, R. (2014) "Impact of Wastewater Treatment  Processes on Antimicrobial Resistance Genes and their Co-occurrence with Virulence  Genes  in Escherichia coli", Water Research, 50, 245-253. http://dx.doi.org/10.1016/j.watres.2013.11.047
  • Frigon, F., Biswal, B., Mazza, A., Masson, L. and Gehr, R. (2013) "Biological and Physicochemical  Wastewater Treatment Processes Reduce the Prevalence of Virulent Escherichia coli", Applied and Environmental Microbiology, 79, 3, 835-844. http://dx.doi.org/10.1128/AEM.02789-12
  • Navab Daneshmand, T., Beton, B., Hill, R.J., Gehr, R. and Frigon, D.F. (2012) "Inactivation Mechanisms  of Bacterial Pathogen Indicators During Electro-dewatering of Activated Sludge  Biosolids", Water Research, 46, 13, 3999–4008. http://dx.doi.org/10.1016/j.watres.2012.05.009
  • González, A., Gehr, R., Vaca, M. and López, R. (2012) "Disinfection of an Advanced Primary Effluent with PAA and UV Combined Treatment: a Continuous-flow Pilot Plant Study", Water Environment Research, 84, 3, 247-253. http://dx.doi.org/10.2175/106143012X13347678384765
  • Charara, N., Cashman, A., Bonnell, R and Gehr, R. (2011)  "Water Use Efficiency in the Hotel Sector of Barbados",  Journal of Sustainable Tourism, 19, 2, 231–245. http://dx.doi.org/10.1080/09669582.2010.502577
  • Hallmich, C. and Gehr, R.: (2010)  "Effect of Pre- and Post- UV Disinfection Conditions on Photoreactivation of Fecal Coliforms in Wastewater Effluents",  Water Research, 44, 2885-2893. http://dx.doi.org/10.1016/j.watres.2010.02.003
  • Gehr, R., Parent Uribe, S., Da Silva Baptista, I. F. and Mazer, B. (2008)  "Concentrations of Endotoxins in Waters Around the Island of Montreal, and Treatment Options",  Water Quality Research Journal of Canada, 43, 4, 291-303.
  • Falsanisi, D., Gehr, R., Liberti, L. and Notarnicola, M. (2008)  "Effect of Suspended Particles on Disinfection of a Physicochemical Municipal Wastewater with Peracetic Acid",  Water Quality Research Journal of Canada, 43, 1, 47-54.
  • Martin, N. and Gehr, R. (2007)  "Reduction of Photoreactivation with the Combined UV/Peracetic Acid Process or by Delayed Exposure to Visible Light", Water Environment Research, 79, 9, 991-999.
  • Santoro, D., Gehr, R., Bartrand, T.A., Liberti, L., Notarnicola, M., Dell’Erba, A., Falsanisi, D. and Haas, C.N. (2007)  "Wastewater Disinfection by PAA: Relating Residual Measurements and Inactivation",  Water Environment Research Journal, 79, 7, 775-787.
  • Gehr, R.  (2007)  "Collimated Beam Tests: Their Limitations for Assessing Wastewater Disinfectability by UV, and a Proposal for an Additional Evaluation Parameter", Technical Note,  Journal of Environmental Engineering and Science, 6: 265–270.

Full papers in proceedings of refereed conferences

  • Navab Daneshmand, T., Enayet, S., Gehr, R. and Frigon, D. (2013) "Control of the Regrowth of Bacterial Pathogen Indicators and Odour Production in Electro-dewatered Biosolids", International Water Association (IWA) Holistic Sludge Management Conference, Västerås, Sweden, May 6-8.
  • Biswal, B.K., Gehr, R., Khairallah, R., Bibi, K., Mazza, A., Masson, L. and Frigon, D. (2013) "UV or PAA for Wastewater Disinfection: A Comparison of the Impact on Virulence Genes", Disinfection and Public Health Conference, Water Environment Federation (WEF), Indianapolis, Indiana, February 24–26,19 pp.
  • Charara, N., Cashman, A., Bonnell, R and Gehr, R. (2009) "Water Use Efficiency in the Hotel Sector of Barbados", 18th Annual Caribbean Water and Wastewater Association's 2009 Conference: A Green Future Developing Caribbean Water and Waste Resources, St Thomas, US Virgin Islands, October 5-9.
  • Hallmich, C. and Gehr, R. (2010) "Effect of Pre- and Post- UV Disinfection Conditions on Photoreactivation of Fecal Coliforms from a Physicochemical Wastewater Effluent", International Ultraviolet Association and International Ozone Association (IUVA/IOA) North American Conference, Cambridge, Massachusetts, USA, May 4-5, 2009.  Also published in IUVA News, Issue #2, 2010.
  • Gehr, R., Chen, D. and Moreau, M. (2008) "Performic Acid (PFA) Tests on an Advanced Primary Effluent Show Promising Disinfection Performance", International Water Association (IWA) World Congress, Vienna, Austria, September 7–12.

Professional registration

  • Member of the Professional Engineers Association of the Province of Ontario

Association memberships

  • American Water Works Association
  • Association of Environmental Engineering Scientists and Professors
  • Canadian Association on Water Quality
  • Canadian Society of Civil Engineers
  • International Ultraviolet Association
  • Water Environment Federation