Ronald Gehr

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Papers by Ronald Gehr

Collimated beam tests: their limitations for assessing wastewater disinfectability by UV, and a proposal for an additional evaluation parameter

Journal of Environmental Engineering and Science, May 1, 2007

This study examines the effects of the liquid matrix on the disinfectability of waters and wastew... more This study examines the effects of the liquid matrix on the disinfectability of waters and wastewaters by ultraviolet (UV) light. Collimated beam (CB) curves, which are routinely used to assess disinfectability, and to provide the average fluence (in microjoules per square centimetre) necessary to reach a target effluent microbial count, eliminate the effect of UV transmission (UVT), using the Morowitz equation. However, this calculation has the consequence of masking the differences between samples of differing UVT, which may indeed require the same average UV fluence to reach the target, but require considerably different energy input and number of lamps in the full-scale system. An additional parameter, called herein an "energy factor'', is proposed in addition to the CB curve to evaluate disinfectability. The energy factor is the applied UV energy per unit volume divided by the average fluence experienced by the microbes in the liquid matrix. Synthetic data and actual CB curves from various types of samples are used to assess the effects of UVT, the depth of sample in the petri dish, the slope of the CB curve, the target microbial count, and, finally, the original microbial count on the energy factor. Key words: ultraviolet disinfection, collimated beam, energy factor.

Peracetic Acid (Paa) as a Disinfectant for Municipal Wastewaters: Encouraging Performance Results from Physicochemical as Well as Biological Effluents

Proceedings of the Water Environment Federation, 2002

ABSTRACT

Acid mine drainage as a coagulant

Minerals Engineering, Sep 1, 1992

Abstract Chemical analysis of two AMD samples from a Canadian source showed the presence of catio... more

Wastewater disinfection with UV or PAA: Are those surviving microbes really benign?

Elucidate the dynamics of: A) pathogenic and non-pathogenic strains of E. coli, and B) their deve... more

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Pilot Studies and Assessment of Downstream Effects of UV and Ozone Disinfection of a Physicochemical Wastewater

Water Quality Research Journal of Canada, May 1, 1996

W radiation and ozonation were investigated as disinfection alternatives for the Montreal Urban C... more W radiation and ozonation were investigated as disinfection alternatives for the Montreal Urban Community physicochemical wastewater treatment plant. The final effluent flows through a 5-km-long outfall tunnel before discharge into the St Lawrence River; the critical point for microbial quality is 4 km downstream. The study, therefore, also examined possible biofilm growth in the tunnel and dilution behaviour in the river. For UV disinfection, a newly developed, high-intensity medium-pressure lamp unit was tested because of its space-saving features. Typical two-stage dose-response curves were obtained with the transition between disinfection of free-swimming and particulateassociated organisms occurring at approximately 25 mW's/cmz. Disinfection behaviour improved when alum was substituted for FeC13 as the coagulant. Photoreactivation decreased with increasing UV dose. Ozonation was adversely effected by changes in COD and H,S in the wastewater. A dose of 17 mg/L was needed to reach target disinfection levels of <5,000 CFU/100 mL in 90% of the cases; the CT value was approximately 0.4 mg*min/L. Replacement of FeCl, by alum reduced the required dose by 35%. Effects of biofilm growth in the tunnel were inconsistent: effluent SS and microbial concentrations were sometimes higher at the exit than at the entrance, and vice versa. Effective dilution of microbes in the river decreased as water temperature increased, reaching a minimum of approximately 20.

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Performic acid (PFA): tests on an advanced primary effluent show promising disinfection performance

Water Science and Technology, 2009

Performic acid, or PFA (CH 2 O 3 ), is a well-known oxidizing agent and disinfectant in the medic... more Performic acid, or PFA (CH 2 O 3 ), is a well-known oxidizing agent and disinfectant in the medical field and food industry. It has recently become available on a commercial scale for potential use in wastewater disinfection. This study investigated its application to an advanced primary effluent which is recalcitrant to disinfection by UV and peracetic acid (PAA). Methods were developed for determining PFA concentrations in stock solutions as well as in residual concentrations in the wastewater. Batch and continuous-flow pilot studies showed a correlation between log fecal coliform removals and PFA doses. A PFA dose of approximately 3.4 mg/L and a contact time of 45 minutes could achieve 3-logs removal, and almost total disinfection could be achieved using a dose of 6 mg/L. The by-products of PFA addition are hydrogen peroxide and formic acid (CHOOH), neither of which is considered to be toxic to aquatic fauna at the doses required for disinfection.

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Dissolved free amino acid pool composition and size in a hypertrophic, warm lake

The Effects of Short-Term Storage and Elevated Temperatures on the Flocculation Activity of Aqueous Polymer Solutions

Water Quality Research Journal of Canada, Feb 1, 1983

of the requirements f~r the degree of Master of Engineering ~ .

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Capturing the sensitivity of land-use regression models to short-term mobile monitoring campaigns using air pollution micro-sensors

Environmental Pollution, 2017

The development of reliable measures of exposure to traffic-related air pollution is crucial for ... more The development of reliable measures of exposure to traffic-related air pollution is crucial for the evaluation of the health effects of transportation. Land-use regression (LUR) techniques have been widely used for the development of exposure surfaces, however these surfaces are often highly sensitive to the data collected. With the rise of inexpensive air pollution sensors paired with GPS devices, we witness the emergence of mobile data collection protocols. For the same urban area, can we achieve a 'universal' model irrespective of the number of locations and sampling visits? Can we trade the temporal representation of fixed-point sampling for a larger spatial extent afforded by mobile monitoring? This study highlights the challenges of short-term mobile sampling campaigns in terms of the resulting exposure surfaces. A mobile monitoring campaign was conducted in 2015 in Montreal; nitrogen dioxide (NO 2) levels at 1395 road segments were measured under repeated visits. We developed LUR models based on sub-segments, categorized in terms of the number of visits per road segment. We observe that LUR models were highly sensitive to the number of road segments and to the number of visits per road segment. The associated exposure surfaces were also highly dissimilar.

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Peracetic Acid (Paa) as a Disinfectant for Municipal Wastewaters: Encouraging Performance Results from Physicochemical as Well as Biological Effluents

Proceedings of the Water Environment Federation, 2002

ABSTRACT

Wastewater Disinfection by PAA: Relating Residual Measurements and Inactivation

With its potential for low (if any) disinfection byproduct (DBP) formation and easy retrofit for ... more With its potential for low (if any) disinfection byproduct (DBP) formation and easy retrofit for chlorine contactors, peracetic acid (PAA) or use of PAA in combination with other disinfectant technologies may be an attractive alternative to chlorine-based disinfection. Examples of systems that might benefit from use of PAA are water reuse schemes or plants discharging to sensitive receiving bodies. Though PAA is in use in numerous wastewater treatment plants in Europe, its chemical kinetics, microbial inactivation rates and mode of action against microorganisms are not thoroughly understood. This paper presents results from experimental studies of PAA demand, PAA decay and microbial inactivation together with a complementary modeling analysis. Model results are used to evaluate techniques for measurement of PAA concentration and to develop hypotheses regarding the mode of action of PAA in bacterial inactivation. Kinetic and microbial inactivation rate data were collected for typical wastewaters and may be useful for engineers in evaluating whether to convert from chlorine to PAA disinfection.

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UV disinfection of wastewater coagulated with ferric chloride: Recalcitrance and fouling problems

Water Science and Technology, 1998

Collimated beam and pilot tests using low pressure or medium pressure UV lamps were conducted to ... more Collimated beam and pilot tests using low pressure or medium pressure UV lamps were conducted to assess the disinfection performance of a municipal wastewater which had been pretreated by ferric chloride coagulation followed by sedimentation. The feed to the UV systems contained high levels of Fe (often above 3 mgll); suspended solids and UV2S4 transmission values were also not ideal (mean approximately 30 mgll and 32% respectively). The collimated beam tests indicated that the target level of 2jOO coliform forming unitsilOO ml often could not be reached. and the pilot tests revealed significant fouling after only a few hours. Thus physicochemical effluents of this nature likely require upstream filtration (or a relaxation of the target level) and a continual. automated cleaning system to ensure that performance levels can be maintained.

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Reduction of Photoreactivation with the Combined UV/Peracetic Acid Process or by Delayed Exposure to Visible Light

Water Environment Research, 2007

Photoreactivation of microorganisms following UV inactivation is a well-known, but complex, pheno... more Photoreactivation of microorganisms following UV inactivation is a well-known, but complex, phenomenon. It is affected by several factors, including UV fluence, wavelength, light intensity, and exposure time to photoreactivating light. The effect on photoreactivation of a combined peracetic acid (PAA)/UV process has not been investigated. Accordingly, this study compared the degree of photoreactivation, under both sunlight and artificial lights, following UV and combined PAA/UV inactivation of fecal coliforms. Effluent samples from the Montreal Wastewater Treatment Plant (MWTP) (Quebec, Canada) were exposed, for 3 hours, to both low-and high-intensity artificial lights and sunlight. All resulted in similar photoreactivation levels. However, average photoreactivation for UV-treated wastewater samples was 1.2 logs, compared with 0.1 log for the combined PAA/UV treatment. Hence, the use of PAA in combination with UV can significantly reduce the potential for photoreactivation. To simulate the photoreactivation conditions of the MWTP effluent (which passes through a 4-km outfall tunnel with approximately 3 hours detention time), UV-treated samples were kept in the dark for 3 hours before photoreactivating light exposure. After this period, photoreactivation levels were close to zero. Hence, the effects of photoreactivation may be diminished by use of a combined disinfection scheme and/or by delaying exposure of the disinfected wastewater to light. Water Environ. Res., 79, 991 (2007).

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Removal of extracellular material techniques and pitfalls

Water Research, 1983

ABSTRACT

Evaluación del proceso combinado Ácido Peracético-Luz Ultravioleta para desinfección de agua residual tratada para utilizarse en riego de áreas verdes

This project is focused in disinfection processes, looking for alternatives to override certain o... more This project is focused in disinfection processes, looking for alternatives to override certain objectionable aspects of chlorination. The main objective of this project was to evaluate the disinfection process combining the use of peracetic acid and UV irradiation (PAA-UV process) in order to achieve microbiological standards stated in Mexican legislation for recreational landscape irrigation. A second objective was to establish the synergy effect of combined disinfectants compared with the addition of their individual effects.

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Wastewater disinfection: long-term laboratory and full-scale studies on performic acid in comparison with peracetic acid and chlorine

Water Research, 2020

This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

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Desorption of Cationic Polyacrylamide from Bleached Kraft Pulp Fibers

Water Science and Technology, 1987

The adsorption and desorption behaviour of a cationic polyelectrolyte contacted with wood pulp fi... more The adsorption and desorption behaviour of a cationic polyelectrolyte contacted with wood pulp fibers was determined by total nitrogen analysis using a pyrolysis/chemiluminescence detection system. Dialysed polymer generated an adsorption isotherm of higher affinity than did non-dialysed polymer. Capacity adsorption was maximized at pH 7, but decreased in the presence of alum depending on the dosage. Desorption of non-dialysed polymer was caused by changes in pH above or below 7.0 as well as by addition of alum. However for the alum doses typically encountered in paper manufacturing, significant desorption is unlikely. Nevertheless, the contaminants in non-dialysed polymers do hinder adsorption, and effluents from those processes using both alum and polymer may contain quantities of unadsorbed or desorbed polyelectrolytes which could be damaging to receiving water bodies.

Wastewater disinfectant showdown: A techno-economic and life cycle assessment of sodium hypochlorite, peracetic acid, and performic acid

Proceedings of the Water Environment Federation, 2018

Assessing chemical disinfectant alternatives using I-CT dose response kinetics for multiple microorganisms

Proceedings of the Water Environment Federation, 2018

Fouling of Uv Lamps with Varying Influent Water Quality

Proceedings of the Water Environment Federation, 2000

As part of an ongoing study by our group into fouling phenomena of UV lamps, the fouling of UV la... more As part of an ongoing study by our group into fouling phenomena of UV lamps, the fouling of UV lamps was examined at the St. Eustache, Que., wastewater treatment facility. This plant provides biological treatment to mainly domestic wastewaters via biofilters. Alum is used in the summer months only for phosphorous removal. A pilot plant study was performed there in order to compare the composition and quantity of foulant material formed with biologically-treated versus physicochemically-treated effluents. The Trojan UV 3000 pilot plant consisted of 3 modules with two lamps each. The modules were separated with baffles enabling each channel to work independently of the others. Only one module irradiated UV light, while the other two served as controls: one was off ("OFF"), and one emitted visible light only ("VIS"). Tracer studies were performed, and the dispersion number was found to be approximately 0.01 in each channel, indicating uniformity of flow and low to moderate dispersion through the three channels. The composition of the foulant formed on the lamps was quantified in terms of organic, inorganic, and biological material. Furthermore, water quality parameters were monitored to assess any correlation found between the influent quality and the foulant composition.

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