New Techniques for Real-Time Monitoring of Membrane Integrity for Virus Removal Using Submicron Particle Characterization Methods
Project: 09-06 (Phase A)
Year Released: 2013
Funding Partner: Bureau of Reclamation
Total Investment: $263,319.44 (Cash: $149,984.92, In-Kind: $113,334.52)
Principal Investigators: Joon Min, Ph.D., Consultant to Psomas, Christopher Yu, Ph. D., Consultant to Psomas, and Sunny Jiang, Ph.D., University of California, Irvine
The priority in water reclamation is public safety. Microorganisms such as bacteria, viruses, and protozoa cysts are potential health hazards to the public if not properly removed. The typical advanced treatment systems today use membrane systems with various removal efficiencies depending on the pore size of the membrane. Verifying the integrity of these membranes requires real time virus monitoring to ensure public safety. Currently, there are no direct, online instruments or protocols available for membrane integrity assessments for compliance monitoring for virus removal.
Goals and Objectives
- Identifies feasible, reliable, and cost-effective monitoring devices for virus and/or submicron particle detection for various types of membranes including microfiltration (MF), ultrafiltration (UF), nanofiltration (NF), and reverse osmosis (RO);
- Correlates results from submicron particle analyzers with epifluorescence direct viral counts;
- Conducts challenge tests by introducing defects to the membrane and validate the sensitivity of the test protocols; and
- Assesses cost of real-time integrity monitoring with a submicron particle analyzer as a surrogate for virus removal.
The study was conducted using bench- and pilot-scale testing at the Water Replenishment District of Southern California’s Leo J. Vander Lans Water Treatment Facility and West Basin Municipal Water District’s Edward C. Little Water Recycling facility.
Bench-scale testing was performed to develop sampling logistics and locations and to determine which instrumentation to use for the reverse osmosis (RO) pilot testing phase. Samples were taken from two locations: WRD and WBMWD. The samples were analyzed using the DLS systems, EFM virus count, and a TOC analyzer. To verify the validity of utilizing DLS submicron detection for virus removal, the results for DLS were compared to the EFM virus count results.
A RO pilot unit was installed on site at the LVLWTF to enable on-line monitoring as well as collection of grab samples to assess sensitivity of a number of analytical instruments for detecting leakage from the RO membrane under varying conditions. After flushing out the preservatives from the RO membranes in the first hour, a baseline of steady parameters was established.
There are a number of potential leakage points in a RO membrane element. One scenario is a mechanical failure where the O-rings can be flattened or cracked with age and as a result, leaks may develop. RO pressure vessels may be probed to find faulty O-rings (Hydranautics, 2001). Probing also helps in determining the exact fault with the pressure vessel. The problem, however, may be either a poorly performing membrane element, an O-ring leak at an interconnector or end adapter, or possibly even a cracked adapter (Hydranautics, 1998). Accordingly, the connector O-ring on the pressure vessel adapter on the high pressure side that connects to the RO element was determined to be the most vulnerable in terms of leakage. This specific O-ring was then progressively compromised to observe the sensitivities in the instrument response.
Response from dynamic light scattering (DLS) was compared with other on-line measurements, including total organic carbon (TOC), turbidity and total dissolved solids (TDS). Samples were also analyzed at University of California Irvine (UCI) to confirm viral particle detection using epifluorescence microscopy (EFM).
Findings and Conclusions
After conducting the literature review, the core method chosen to be evaluated for virus detection was EFM. The core technology evaluated as a potential indirect surrogate for virus monitoring was the DLS technology. After the literature review phase was completed, steps were taken towards a bench-scale phase.
Samples from WRD and WBMWD were analyzed for particle count during the bench-scale phase. Various parameters including TOC were measured for all the samples. Two different DLS nanoparticle analyzers were tested for ease of operation, sensitivity and reproducibility. Due to limited samples, the NanoDLS analyzer was not tested. The particle count was compared with the EFM results to evaluate if DLS is a feasible surrogate method for virus monitoring by comparing to a direct virus monitoring method (EFM). The correlation shows a good match for the particle count with a R2 value of 0.91. The NanoSight DLS has the advantage of displaying a visual image of particles. It can be used as a single particle analyzer as it provides an absolute concentration in particles/mL.
The output from the two DLS instruments was not directly comparable as the Nanotrac provided particle distribution and not the absolute particle count as NanoSight. Nanotrac was more reliable and sensitive to detect particles less than 10 nm, much less than the cut-off of 25 nm for the NanoSight. Considering the ease of operation, Nanotrac also has the advantage of an independent sensitive probe which can be easily used to detect particles, along with the much larger sample cell volume to mitigate the sensitivity issue. Since Nanotrac provides more reliable measurement and lower detection limit, it was used as a primary instrument during the pilot phase. In addition to DLS, the TOC analyzer and EC meter was considered for the pilot phase to detect small changes in the fluctuation because these instruments are sensitive to detect small changes.
DLS was used as a primary instrument during the pilot phase. In addition to DLS, the TOC analyzer, turbidimeter and conductivity meter were used to detect small changes in water quality fluctuations. Moreover, these instruments confirmed detections for different degrees of O-ring compromise.
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