On-Site Pilot Study - Removal of Uranium, Radium-226 and Arsenic from Impacted Leachate by Reverse Osmosis – 13155 McMurray,

Conestoga-Rovers & Associates (CRA-LTD) performed an on-site pilot study at the Welcome Waste Management Facility in Port Hope, Ontario, Canada, to evaluate the effectiveness of a unique leachate treatment process for the removal of radioactive contaminants from leachate impacted by low-level radioactive waste. Results from the study also provided the parameters needed for the design of the CRA-LTD full scale leachate treatment process design. The final effluent water quality discharged from the process to meet the local surface water discharge criteria. A statistical software package was utilized to obtain the analysis of variance (ANOVA) for the results from design of experiment applied to determine the effect of the evaluated factors on the measured responses. The factors considered in the study were: percent of reverse osmosis permeate water recovery, influent coagulant dosage, and influent total dissolved solids (TDS) dosage. The measured responses evaluated were: operating time, average specific flux, and rejection of radioactive contaminants along with other elements. The ANOVA for the design of experiment results revealed that the operating time is affected by the percent water recovery to be achieved and the flocculent dosage over the range studied. The average specific flux and rejection for the radioactive contaminants were not affected by the factors evaluated over the range studied. The 3 month long on-site pilot testing on the impacted leachate revealed that the CRA-LTD leachate treatment process was robust and produced an effluent water quality that met the surface water discharge criteria mandated by the Canadian Nuclear Safety Commission and the local municipality. INTRODUCTION Conestoga-Rovers and Associates Limited (CRA-LTD) was retained by the Atomic Energy of Canada Limited (AECL) to provide a design for a full-scale treatment plant for the removal of contaminants of concern (COC) from impacted leachate at the Welcome Waste Management Facility (WMF), an existing low-level radioactive waste site located in Port Hope, Ontario. The main COC are uranium (U), radium-226 (Ra-226), and arsenic (As). The effluent quality objectives for the full-scale plant include: a high level of assurance for human health, a reduction of radiological discharge in discharge water to levels as low as reasonably achievable, and minimization of the total treated leachate loading to Lake Ontario. CRA-LTD concluded from its bench scale test results that the chemical pre-treatment of the leachate followed by clarification then concentration of the COC with the Rochem Spacer Tube (ST) reverse osmosis (RO) WM2013 Conference, February 24 – 28, 2013, Phoenix, Arizona, USA 2 membrane module as potentially feasible [1]. Radioactive contaminants have been effectively concentrated by RO in leachate pre-treatment [2, 3, 4, 5, 6], drinking water pre-treatment [7], and radioactive waste processing [8]. The RO technology was identified as the best demonstrated technology for removal of radium-226, radium-228, and uranium from leachate by the United States of America Environmental Protection Agency (USEPA) [9]. The focus herein is of the on-site pilot study performed by CRA-LTD, which utilized a fractional factorial statistical design of experiment (SDOEX) to evaluate the identified approach on a pilot scale as well as determine if the approach is practical and robust in removing and concentrating COC. Additional objectives included determining the operating envelope of the Rochem ST RO modules, the impact of recovery of Rochem ST RO module on performance, chemical pre-treatment and influent quality on module performance, and design parameters needed for the full-scale plant design. These objectives were identified by the USEPA as being important in assessing the overall effectiveness of a treatment technology for the management of radioactive residuals from drinking water [10]. DESCRIPTION The on-site pilot testing was performed for three consecutive months. The pilot system was contained in a 2.4 m by 12.2 m metal wind/water tight tunnel style containerized intermodal freight container; referred to as the “pilot trailer”. The aerial photo in Figure 1 is of the Welcome WMF site in Port Hope with the location of the pilot trailer relative to the existing leachate treatment building shown. The pilot system was comprised of a mixing and storage tank, chemical metering equipment, an inclined plate clarifier, a clarifier supernatant storage tank, and the Rochem RO-510 PT2 pilot unit with permeate and concentrate storage tanks. The process flow diagram of the pilot system is shown in Figure 2. The photos displayed in Figure 3a and 3b are of the chemical pre-treatment equipment and pilot Rochem RO-510 PT2 unit, respectively, in the pilot trailer. The study applied a fractional factorial SDOEX to determine the influence of the factors: percent recovery, pre-treatment, and TDS spike. The factor percent recovery refers to the percentage of the total permeate flow to that of the influent flow to the first RO module. The levels evaluated were: 75%, 80%, and 85%. The factor pre-treatment refers to the ferric chloride dosage levels applied in the clarifier; ferric chloride applied as a flocculating agent. The levels evaluated were: pre-treatment (ferric chloride dosage of 130 ppm) and no pre-treatment (no ferric chloride added). The levels evaluated for the TDS spike factor were: TDS spike (increased electrical conductivity of first RO module influent between 1,000 and 1,200 uS/cm) and no TDS spike (unaltered influent electrical conductivity to the first RO module). The design matrix of the SDOEX involved nine runs the factor levels for each of the runs are provided in Table I. This design was applied to minimize the number of runs, evaluate main effects, and evaluate error. The conditions of run 2 were replicated in run 3 and 8 to obtain a measure of error. The chemical analysis was performed by a laboratory accredited by the Canadian Association for Environmental Analytical Laboratories.

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