Organic, inorganic, and biological contaminant occurrence and removal in a carbon-based potable water reuse mobile demonstration system

Direct potable reuse (DPR) is becoming an increasingly important option for communities facing water scarcity, but it comes with a clear expectation: utilities must be able to demonstrate that finished water meets health-based standards. Because DPR starts with an impaired source (treated municipal wastewater), the proof has to address a wide range of potential contaminants, from PFAS and trace organics to pathogens and disinfection byproducts.

A recent article in ACS ES&T Water addresses that question head-on. As part of a broader research team, Carollo’s John Rehring and Jason Assouline co-authored “Organic, Inorganic, and Biological Contaminant Occurrence and Removal in a Carbon-Based Potable Water Reuse Mobile Demonstration System,” summarizing results from a demonstration-scale DPR system designed to assess the long-term performance of a carbon-based treatment train. Their work provides practical insights for inland communities interested in potable reuse without using reverse osmosis (RO).

Why Carbon-Based DPR Matters for Inland Communities

Many potable reuse facilities rely on advanced treatment trains that include RO membranes, which are highly effective at removing a broad range of dissolved contaminants. But RO also produces a concentrated brine stream that can be difficult and costly to manage, especially for inland utilities.

That’s why alternative multibarrier approaches are gaining attention. As the authors note, carbon-based systems use multiple treatment steps—each contributing to risk reduction—rather than relying heavily on a single barrier. In this study, the demonstration-scale treatment train combined ozone, biologically active carbon (BAC), microfiltration (MF), granular activated carbon (GAC), and ultraviolet light with advanced oxidation (UV/AOP), followed by disinfection.

Inside the Mobile Direct Potable Reuse Demonstration System

The first stop for the mobile DPR demonstration system was a five-month period treating tertiary effluent from the J.D. Phillips Water Resource Recovery Facility in Colorado Springs. The demonstration system tracked water quality through each step of the process, and additional sampling measured a broad suite of constituents.

The goal was not just to confirm that contaminant concentrations could be reduced, but to understand where removal happened, what could form during treatment, and how performance shifted over time.

The results of the testing demonstrate that the multibarrier system “reduced all regulated contaminants to concentrations below regulatory standards and removed most unregulated contaminants below detection.” They also emphasize that pathogens were consistently present in the influent but “not in the finished water,” reinforcing the value of multiple barriers working together.

Microbial Safety and the Value of a True Multibarrier Approach

Because municipal wastewater can contain a wide range of pathogens, microbial performance is essential for producing safe DPR water. One of the most compelling real-world lessons in the paper comes from variability in ozone performance on certain dates. Even when the ozone system was less effective, downstream barriers helped maintain finished-water quality—an important demonstration of what “multibarrier” means in practice.

The authors summarize the big picture clearly: the study “demonstrated that a GAC-based DPR treatment train, as an alternative to reverse osmosis-based DPR, can reliably mitigate the risk of chemical and microbial contaminants.”

What This Means for the Future of Direct Potable Reuse

As DPR expands, utilities will need both robust treatment and monitoring strategies that align with regulatory requirements and the system’s risk profile. This research reinforces the idea that carbon-based DPR can be a strong option, especially for inland communities, while underscoring the importance of planning for media exhaustion and redundancy across barriers.

Read the full article in ACS ES&T Water to dive deeper into the treatment train performance and what it could mean for future DPR projects.