Trussell Technologies Explains the 4Rs in Potable Reuse

Bryan Trussell, P.E., BCEE, CWEA Los Angeles Basin Section Past President

Bryan Trussell, P.E., BCEE, CWEA Los Angeles Basin Section Past President

Reliability | Redundancy | Robustness | Resilience

Trussell Technologies, a family run environmental engineering firm focused on process and water quality was recently cited by the DPR Expert Panel Report for their significant work on WateReuse. The firm has played and continues to play a significant role in the development of treatment processes for reuse projects. We interviewed Bryan Trussell, P.E., BCEE and CWEA Los Angeles Basin Section Past President on the role Trussell Technologies plays in the DPR report.  

What was Trussell Technologies role in the State Water Board’s Expert Panel report on DPR? 

Trussell Technologies had no direct role in the expert panel report on DPR. Our founder Rhodes Trussell was originally appointed chair of the State Expert Panel, but he rescinded the position because it became clear that our work on WateReuse Research Foundation (14-12), Demonstrating Redundancy and Monitoring to Achieve Direct Potable Reuse, was developing salient information that would be evaluated by this panel. The Expert Panel cited our work under WRRF 14-12 throughout portions of their report, particularly in their reliability assessment. The Expert Panel concluded that DPR was in fact feasible, using data from 14-12 as evidence that DPR systems can provide consistent protection of public health.

Representation of a reliability framework for direct potable reuse. The two strategies for achieving reliability are failure prevention (through redundancy and robustness) and failure response (through resilience)

Representation of a reliability framework for direct potable reuse. The two strategies for achieving reliability are failure prevention (through redundancy and robustness) and failure response (through resilience)

Can you explain the 4Rs and why they are important in Trussell’s planning for water reuse projects?

The concept of the 4Rs is to provide a framework for delivering safe water to our consumers. The 4Rs work together to build a solid foundation for our treatment systems. The first ‘R’ is reliability and is truly the fundamental goal of the 4Rs framework–to provide a reliable source of safe drinking water to our consumers. To achieve this goal of reliability, the remaining 3 R’s provide the foundation. Redundancy provides additional treatment or monitoring that goes beyond the minimum requirements to ensure treatment goals are more reliably met or that performance is more reliably demonstrated. Robustness provides the treatment train with a variety of different treatment mechanisms, thus addressing a broad range of contaminants and providing resistance to failure. Resilience addresses the ability of the treatment train to recover and/or respond to a treatment failure. In combination, these 3Rs (redundancy, robustness, and resilience) combine to both prevent failures and properly respond to any that do occur. Through this foundation, reliability is achieved. These are the basic tenets of the 4Rs concept. Download the AWWA Journal article on the 4Rs .

Where did Trussell Tech get inspiration for the 4Rs?

The 4Rs concept was developed within Trussell Technologies over several years of conducting research projects in potable reuse. All safe potable reuse systems employ certain elements to prevent and respond to failures, though the way we balance these elements differs as we move from groundwater recharge to surface water augmentation to DPR. With the 4Rs we began to conceptualize how planned potable reuse could be accomplished.

The concept is broader than the critical control points framework. In fact, critical control points are a necessary component of any reliable potable reuse facility and must be incorporated into the 4Rs framework to achieve their common goal. Specifically, one element of the 4Rs, redundancy, can be informed by a careful review of the protections provided by the critical control points of the treatment system. Based on the findings, additional treatment and monitoring may be added to improve the overall reliability of the treatment system.

How did the 4Rs concept end up in the State Water Board’s draft report on DPR feasibility?

We had several published documents on the 4Rs in performing our work with both the City of San Diego and Padre Dam Municipal Water District, both of whom are pursuing non-traditional potable reuse projects. As a result of these projects, we have also been in constant communication with DDW about the developing regulatory landscape. It is likely that the Expert Panel, through our published documents and through dialoguing with DDW, took hold of the 4Rs concept, saw its broad application and inclusion of other common concepts, and included it in their report as a result.

What’s Trussell Tech’s confidence in the safety of DPR? Do your engineers sample the purified water at your pilot projects? 

We are confident that DPR can be done safely. The primary concern of a DPR system is to prevent the acute impacts of pathogens, which can have an immediate impact on the consumers. Microfiltration and reverse osmosis in combination with advanced oxidation provide effective barriers to these pathogens and, work in WRRF 14-12 has shown that these, in combination with ozone, biological carbon filtration and chlorination can make safe drinking water from a nitrified wastewater effluent.  Many of our engineers have tasted the reuse water at various pilot and demonstration projects, including projects that are not led by Trussell Technologies. The key focus of the 4Rs and developing DPR treatment is to ensure that the approach provided proves to be reliable and can stand the test of time.

Trussell Tech’s research in California is frequently mentioned in prestigious research reports such as the State Water Board’s draft report on DPR. What advice do you give to young engineers who want to join a cutting edge firm such as yours?

Our firm was founded by my father, Rhodes Trussell, under the tenet that emerging issues in water would be best addressed by uniting our experience in engineering with the principles of science. My advice would be to never forget the fundamental tenets that your profession relies upon as they will continue to provide insight into the complex challenges that we all run into on a day-to-day basis.

Download the Journal AWWA article “Achieving Reliability in Potable Reuse: The Four Rs”


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Megan Barillo

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