Webinar summary: Indirect potable reuse: from concept to demonstration and full-scale implementation

Indirect potable reuse (IPR) is becoming an increasingly important option for securing resilient water supplies in the UK. But the process requires more than advanced treatment technologies – it also demands continuous verification that those systems are performing as intended.

A recent webinar from Xylem – whose water treatment technologies support major IPR plants worldwide - explored how utilities can achieve this. Drawing on both leading academic research and experience of full-scale operational installations, the speakers discussed how to build confidence in IPR through:

• Designing treatment systems for continous protection of public health
• Monitoring of containments that cannot be measured in real time
• Using critical control points-based frameworks to underpin compliance and confidence

Four principles

The webinar described successful potable reuse systems as being built around four key principles:

• Redundant – addition of measures beyond minimum requirements to ensure goals and targets are met or exceeded, not relying on one single treatment process
• Robust – ability to address broad variety of contaminants
• Reliable – ability to deliver water quality that consistently exceeds requirements
• Resilient – capacity for treatment trains to successfully adapt and respond to failure

The presenters stressed that potable reuse must completely mitigate risks to public health. Rather than depending on one "perfect" technology, advanced treatment combines multiple barriers that together provide protection against pathogens, chemicals and emerging contaminants.

Treatment train design

The speakers compared two dominant approaches currently being adopted around the world, highlighting advantages and trade-offs of each:

Reverse osmosis-based treatment

Often regarded as the California "gold standard", this approach typically combines:

• Membrane filtration
• Reverse osmosis (RO)
• UV advanced oxidation (UV-AOP)

The system provides exceptional removal of dissolved contaminants and salinity but comes with higher operating costs and the challenge of managing concentrated brine streams.

Carbon-based advanced treatment

An alternative approach that often uses:

• Ozonation
• Biological activated carbon filtration
• Granular activated carbon (GAC)
• UV disinfection

This method avoids RO concentrate disposal and generally has lower operating costs, but is not capable of removing salts from source waters with elevated salinity.

Treatment targets

The presenters discussed three established frameworks, including the World Health Organization's Potable Reuse Guidelines (2017) and California's potable reuse regulations.

Although these frameworks differ in detail, they all follow the same fundamental approach:

• Define the maximum concentrations of pathogens expected in raw wastewater
• Establish the acceptable level of health risk in reclaimed water
• Specify the total log reduction values (LRVs) that the treatment train must achieve to protect public health

Demonstrating treatment performance continuously

One of the central questions posed during the webinar was, how do operators continuously demonstrate that treatment targets are being achieved? Since many pathogens and trace contaminants cannot be measured in real time, the speakers described two complementary approaches:

Critical control parameters that demonstrate treatment processes are working correctly, such as measuring CT values for chemical disinfection - the disinfectant concentration at the reactor outlet multiplied by the contact time.

The second approach is the use of surrogate parameters. A surrogate is a parameter that is removed by the treatment process and whose removal can be continuously monitored online and correlates with the removal of the target contaminant or pathogen.

The webinar then explored how critical control point (CCP) frameworks are applied in practice.

SWIFT programme: a practical example

Hampton Roads Sanitation District, Virginia, USA, is implementing major indirect potable reuse schemes through its Sustainable Water Initiative for Tomorrow (SWIFT).

SWIFT takes highly treated water that would otherwise be discharged into the James River and puts it through additional rounds of advanced water treatment to meet drinking water quality standards. The water is then added to the Potomac Aquifer, the primary source of groundwater throughout eastern Virginia.

The district serves a population of around two million people and plans to implement SWIFT technology at three of its major wastewater treatment plants. By 2030, the programme aims to produce approximately 190 megalitres of highly treated water per day through the SWIFT advanced treatment process.

The presenters described how the project has established regulatory limits for every critical treatment stage and, importantly, how operators continuously verify compliance before water enters the aquifer.

Q&A

The questions covered topics including cost - a key message being that while capital investment is required initially, the long-term objective is to deliver the same overall expenditure while providing significantly greater water security.

The speakers noted that operating costs depend on plant scale and treatment configuration, with activated carbon replacement representing one of the largest ongoing operating costs for carbon-based advanced treatment.

When asked about greatest barriers affecting adoption, the speaks concluded:

In Europe, regulatory frameworks remain one of the biggest challenges, with many countries only beginning to establish regulations.

Elsewhere, affordability and public perception can impact progress. However, in severely water-scarce regions, the demand for resilient supplies increasingly drives adoption.

Summing up the discussion, Barry Hopton said: “The webinar really highlighted both the opportunities and the complexities around advanced treatments and indirect potable reuse.

Host

• Xylem’s Barry Hopton, UK head of wastewater treatment – Xylem

Speakers

• Uwe Hübner, senior process engineer, water reuse & advanced oxidation process - Xylem
• Germano Salazar-Benites, water reuse engineer, Hampton Road Sanitation District's Sustainable Water Initiative for Tomorrow (SWIFT), chair of the Water Reuse Program Committee and second vice-chair of the Water Reuse Community at the Water Environment Federation