By Justin Mattingly
With public safety of primary concern, real-time sensors may be the catalyst for assurance and expansion of potable reuse treatment schemes.
Potable reuse of advanced treated reclaimed water is achieved through multibarrier treatment trains, using a combination of technologies such as microfiltration, reverse osmosis, advanced oxidation, ozonation, and/ or granular activated carbon. To ensure efficacy of treatment, water quality may be evaluated in real time to verify that these barriers are operating as designed and to reassure communities that there are no adverse public health effects from using reclaimed water for potable purposes.
A research team led by Dr. Ian Pepper and Dr. Shane Snyder from the University of Arizona recently completed a study funded by the Water Environment & Reuse Foundation (WE&RF), U.S. Bureau of Reclamation, The Pentair Foundation, and Singapore PUB to evaluate the ability of online sensors to ensure that advanced treatment of reclaimed water before potable reuse eliminates chemical and microbial contaminants. Specifically, the researchers sought to determine if real-time sensors could be used for process control of advanced treatment systems to ensure the safety of potable water for the community. Monitoring for Reliability and Process Control of Potable Reuse Applications (Reuse-11-01) is the research title.
Real-time monitoring offers the opportunity to engage in potable reuse with the ability to detect failures quickly and greatly reduce the response time needed to rectify upsets in a treatment system.
The team conducted the research in four phases:
- Comprehensive literature review
- Laboratory evaluations
- Pilot-scale utility evaluations
- Full-scale utility evaluations
Real-time detection of trace organic compounds was evaluated through sensors for surrogate parameters such as UV254 or fluorescence. For microbial contaminants, techniques such as multi-angle light scattering or measurements of adenosine triphosphate (ATP) were used. Advanced treatment technologies that were evaluated included advanced oxidation, reverse osmosis, and activated carbon.
From Lab To Pilot-Scale
Laboratory evaluations at the University of Arizona Sensors Lab tested eight different advanced treatment methods to determine their efficacy in removing chemical and microbial contaminants. The pilot-scale evaluations involved going beyond bench-scale testing and into monitoring and sensor validation at pilot-scale facilities. The facilities sampled at various critical control points in the system using existing online monitoring systems to monitor the surrogates and indicators proved to be the most useful based on the results of the laboratory evaluation. The last phase conducted full-scale evaluations at facilities that currently implement potable reuse to determine the effectiveness of online monitoring systems.
The pilot-scale evaluations occurred at the Beenyup Wastewater Treatment Plant in Australia, Sacramento Regional Wastewater Treatment Plant, and the Tucson Water Sweetwater Recharge Infiltration Systems. Each facility tested advanced treatment options and identified solutions to improve their process control. Overall, the pilot-scale studies demonstrated that select online sensors were able to provide effective process control. Specifically, ozonation more effectively reduced total microbial load and bacteriophage MS2 levels, indicating that total microbial load may be an effective surrogate for pathogen reduction in treatment trains. Real-time detection methods specific to microorganisms were also shown to have potential to monitor pathogen reduction in treated water.
The Beenyup Wastewater Treatment Plant and Advanced Water Recycling Plant (Perth, Australia) pilot trial identified two key solutions that could improve their process control. First, the implementation of UV254 and fluorescence online sensors may be useful additions to their system. Second, the implementation of a microbial assay like LuminUltra would allow for rapid detection of potential microbial contaminants.
The Sacramento Regional Wastewater Treatment Plant (Sacramento, CA) trial found sensors useful in evaluating the treatment performance and incremental failure events during membrane filtration. The addition of a fluorescence online sensor would also potentially provide additional online process control.
The Tucson Water Sweetwater Recharge Infiltration Systems (Tucson, AZ) pilot found ozonation more effectively reduced total microbial load and MS2 levels over UV-AOP. This implies that total microbial load is an effective surrogate for pathogen reduction in treatment process trains, as it includes a broad spectrum of microorganisms that are more resistant to inactivation than human pathogens typically found in wastewater.
University of Arizona Sensors Lab
The full-scale evaluations occurred at facilities that currently implement potable reuse to determine the effectiveness of online monitoring systems. When combined with the laboratory and pilot-scale evaluations, recommendations for the full-scale facilities were developed to suggest ways to improve their monitoring practices. The facilities that conducted full-scale demonstrations included West Basin Municipal Water District and Orange County Water District.
The results of the full-scale evaluations demonstrated that online sensors can be effective strategies for monitoring process control, and real-time monitoring can detect failures in potable reuse treatment schemes quickly and reduce the response time to rectify the problem.
Based on the laboratory, pilot-scale, and full-scale evaluations, online sensors were shown to be useful for monitoring process control. Overall data from the pilot- and full-scale utility evaluations show that utilities in the U.S. and abroad do use online sensors successfully to monitor for the presence of chemical contaminants in real time, but not microbial contaminants. Currently, utilities rely heavily on sensors for turbidity, conductivity, and total organic carbon (TOC) to act as real-time triggers to alert operators of treatment failure. These sensors could usefully be augmented by an online fluorescence sensor and a real-time assay for microbial contaminants.
These research findings provide meta-data on a variety of different sensors including parameters such as working range, accuracy, precision, response time, and detection mechanism. In addition, the researchers evaluated the ability of different sensors to detect incremental failure of advanced treatment and the efficacy of various sensors in waters with differing water quality. Finally, the team characterized the current status of the use of online sensors at utilities nationally and internationally by evaluating operational pilot and full-scale treatment trains.
Real-time monitoring offers the opportunity to engage in potable reuse with the ability to detect failures quickly and greatly reduce the response time needed to rectify upsets in a treatment system. The research indicates that at the same time, the need for engineered storage in direct potable reuse would be reduced due to the faster response time in monitoring.
The variety of evaluations also identified some gaps and issues in sensor technology:
- Enhanced sensitivity of contaminant detection and removal via surrogates
- Further development of an online sensor for bacterial microbial contaminants
- Development of an online sensor for human pathogenic viruses, perhaps via aptamers or immunoassays coupled to microfluidics
- Enhanced ability to detect minimal incremental failure
- Development of superior software for data maintenance and setting of constantly operational alarm thresholds
- Development of online courses to train utility personnel with respect to new real-time technologies, including sensor maintenance
These topics are among many that may be tackled by the WE&RF water reuse and desalination issue area team in future research efforts.
About The Author
Justin Mattingly is a research manager at the Water Environment & Reuse Foundation focusing on treatment systems for potable reuse, industrial reuse, and water economics and finance. Prior to joining WE&RF, he completed a four-year fellowship at the U.S. EPA in the Clean Water State Revolving Fund program, working with states and communities to develop innovative financing tools and strategies to fund a diverse array of water quality projects. Justin has a bachelor’s degree in biological sciences from the University of Delaware and a master’s degree in environmental science from American University.