Recurring plans for building a large crude oil pipeline in the immediate neighborhood of the Saint Lawrence River and connected watercourses raise concerns about potential threats to this drinking water source serving over 3 million Canadians. Quebec has the lowest drinking water threshold for benzene in North America (0.5 μg L ⁻¹) - a toxic hydrocarbon present in crude oil. With powdered activated carbon (PAC) being an effective benzene adsorbent several municipalities around Montréal consider its application as an emergency barrier. Their current and primary PAC application is taste and odor removal caused by 2-methylisoborneol (MIB) and geosmin. Ideally, a single PAC would be selected as a suitable barrier against all three pollutants. The adsorption of MIB/geosmin was studied on 11 PAC in 3 source waters characterized by different concentrations of low molecular weight natural organic matter - the main competitor for adsorption sites on PAC. Results show that taste and odor removal was low in water with high fractions of small competitive natural organic matter. Benzene removal was studied separately in adsorption tests with 3 selected PAC. The highest (40 to 75%) and the lowest (10 to 15%) benzene removal was achieved by the same PAC types that also performed best and worst respectively for MIB/geosmin.

Biological ion exchange (BIEX) refers to operating ion exchange (IX) filters with infrequent regeneration to favor the microbial growth on resin surface and thereby contribute to the removal of organic matter through biodegradation. However, the extent of biodegradation on BIEX resins is still debatable due to the difficulty in discriminating between biodegradation and IX. The objective of the present study was to evaluate the performance of BIEX resins for the removal of organic micropollutants and thereby validate the occurrence of biodegradation. The removals of biodegradable micropollutants (neutral: caffeine and estradiol; negative: ibuprofen and naproxen) and nonbiodegradable micropollutants with different charges (neutral: atrazine and thiamethoxam; negative: PFOA and PFOS) were respectively monitored during batch tests with biotic and abiotic BIEX resins. Results demonstrated that biodegradation contributed to the removal of caffeine, estradiol, and ibuprofen, confirming that biodegradation occurred on the BIEX resins. Furthermore, biodegradation contributed to a lower extent to the removal of naproxen probably due to the absence of an adapted bacterial community (Biotic: 49% vs Abiotic: 38% after 24 h batch test). The removal of naproxen, PFOS, and PFOA were attributable to ion exchange with previously retained natural organic matter on BIEX resins. Nonbiodegradable and neutral micropollutants (atrazine and thiamethoxam) were minimally (6%–10%) removed during the batch tests. Overall, the present study corroborates that biomass found on BIEX resins contribute to the removal of micropollutants through biodegradation and ion exchange resins can be used as biomass support for biofiltration.

Subsequent to an oil spill, conventional physico-chemical treatment processes such as ballasted flocculation would serve as the principal barrier in drinking water treatment plants (DWTP) against contamination from toxic soluble contaminants such as benzene. Benzene is a well-known carcinogenic compound and its maximum threshold concentrations in drinking water are regulated at 5 μg/L and 0.5 μg/L in the United States and in Quebec, Canada, respectively. Our study focused on ballasted flocculation in order to determine its removal efficiency for traces of dissolved petroleum hydrocarbons originating from diesel and gasoline contamination. Results show that ballasted flocculation alone, using alum or ferric sulphate as coagulant, is not efficient for benzene reduction below regulations. Addition of an adsorbent such as powdered activated carbon (PAC) is necessary. From PAC adsorption isotherms and kinetics, we found an optimal dose of 80 mg PAC/L and contact times of 15 and 30 min for diesel and gasoline-contaminated waters, respectively. The simultaneous addition of PAC and coagulant during ballasted flocculation showed that although benzene concentration declined substantially, alum treatment could not decrease concentrations below the Canadian threshold (0.5 μg/L) while the US regulation value was met. Analysis of PAC-ballasted flocculation tests demonstrated the likelihood of PAC pore blockage in the presence of coagulants. Although PAC doses as high as 80 mg PAC/L were introduced during ballasted flocculation, settled water quality was not negatively impacted. Findings from this study will help DWTP in their effort to prepare emergency response plans for the event of an oil spill.