Predicting RO Removal of Toxicologically Relevant Unique Organics
Project: 14-19
Product: Report
Estimated Release: TBD
Program: Principal
Total Investment: $225,000 (Cash: $225,000)
Background
Reverse osmosis (RO) is an effective barrier to the majority of contaminants of known health concern. However, studies conducted by others have shown that some low molecular weight organics can penetrate even current thin film composite membranes. Examples such as NDMA and 1, 4-dioxane have actually led to the addition of supplemental treatment processes like UV photolysis and UV advanced oxidation.
Modeling techniques can be used to evaluate compounds that have been identified by state or federal regulators as posing potential health risks in drinking water supplies. One of the challenges is to identify the concentration of these compounds that poses a threat to human health. Factors such as molecular weight, chemical structure, charge, etc. can be used to predict removal efficiency of untested compounds.
The purpose of this project is to reduce the risk of future surprises regarding breakthrough of compounds of health concern. In addition to compounds of direct health concern, with Direct Potable Reuse (DPR) there may be concerns with compounds that can form disinfection byproducts of health concern when exposed to typical water distribution system residuals.
Quantitative structure-activity relationship (QSAR) models can be used to predict both RO removal and DBP formation with a minimum of experimental data in the form of model training sets.
Goals and Objectives
The project will predict removal efficiency of compounds identified by state or federal regulatory agencies of potential public health concern by reverse osmosis (RO), and predict removal of compounds that may be precursors of disinfection byproducts (DBPs) of potential health concern.
Research Approach
Task 1: Background Research. Examine, analyze, and assemble (identify and specify lists from USEPA, others) lists of low molecular weight organic chemicals within states considering DPR. Data sources may include, but are not limited to: occurrence information, Unregulated Contaminant Monitoring (UCMR) programs, Federal Contaminant Candidate List (CCL), and California notification list. Review RO removal efficiency of compounds reported by both DPR and Indirect Potable Reuse (IPR) facilities at full-scale, bench-scale, and pilot-scale. Evaluate and quantify the difference in rejection of the identified organic compounds between “loose” low pressure RO and tighter brackish RO membranes through the review of literature, discussions with manufacturers, and/or modeling.
Task 2: Develop and Apply QSAR Models. Develop and apply QSAR models to listed compounds identified in Task 1 (Background Research), relative to removals identified in current potable reuse facilities, and known RO removals of other structurally-related compounds. Include an assessment of the sensitivity of predicted RO removal efficiencies to changes in temperature, water flux, and percent water recovered.
Task 3: DBP Precursors. Identify potential compounds for formation of DBPs that are capable of passing through RO systems in the permeate stream. Test specific DBPs (in the QSAR models) identified in the review of the literature, particularly those that are structurally related to or known to be derived from the parent compounds employed in the original QSAR models.
Task 4: Evaluation. Conduct an evaluation of need for supplemental treatment processes in order to address potential health risk compounds that pass through RO. The effectiveness of removal may be reduced if breach in membrane or membrane system integrity occurs or as the membranes age. The result of this study should provide information on this aspect as well.
Task 5: Source Control. Evaluate source control vulnerability to compounds capable of penetrating RO systems. Spikes of industrial chemicals released through dumping are of potential concern to efforts to develop potable reuse. Develop a list of at least 20 organic industrial chemicals commonly discharged to Publicly Owned Treatment Works (POTWs) and regulated under source control, and review their occurrence in treated wastewater effluent and their expected removal through RO membranes using the QSAR model.
Task 6: Additional Research. Based on the results of this research, recommendations for additional research including bench, pilot, full-scale confirmation of the models via laboratory analysis and evaluation will be identified.
Task 7: Final Report. This task will summarize Tasks 1 through 6 into a final report for the WateReuse Research Foundation. It will include the background research, QSAR model data, DBP precursors, evaluation results, source control information, and additional research. The final report should also include:
A list of compounds that have been identified as vulnerabilities from the QSAR model
Recommendations for remediation, including:
- Source controls monitoring and accountability (local limits)
- Secondary treatment upgrades
- Addition of supplemental treatment
- An analysis of the relative efficacy of each remediation step.