Water Online

MAR 2017

Water Innovations gives Water and Wastewater Engineers and end-users a venue to find project solutions and source valuable product information. We aim to educate the engineering and operations community on important issues and trends.

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By Justin Mattingly A s communities in water-stressed regions look to pursue new and more sustainable water supplies, direct potable reuse (DPR) is expected to become an increasingly common option. DPR is the introduction of advanced treated water from a wastewater treatment facility directly into a drinking water treatment facility or distribution system without the use of an environmental buffer. The advanced treatment used in a DPR system will include processes such as reverse osmosis (RO) that are largely uncommon in conventional wastewater and drinking water facilities. Understanding how to manage these processes is a critical component for making DPR a reality. Recent research from the Water Environment & Reuse Foundation (WE&RF), led by Troy Walker and Dr. Ben Stanford of Hazen and Sawyer, breaks down the treatment trains expected to be part of DPR systems to identify the operational points of most importance, as well as strategies for effective maintenance (see below). This research is part of WE&RF's Direct Potable Reuse Initiative aimed at supporting efforts in California and elsewhere to advance DPR. Safety First: Ensuring Water Quality The first project in this bundle of research, Critical Control Point Assessment to Quantify Robustness and Reliability of Multiple Treatment Barriers of a DPR Scheme (Reuse-13-03), used the hazard analysis and critical control point (HACCP) method to identify the critical control points (CCPs) of two advanced treatment trains for DPR. Originally developed by the food industry, the HACCP method is a means of controlling microbial hazards. It is used to develop operational controls to detect and correct deviations in quality at the earliest possible opportunity before a health hazard occurs, which is accomplished through a focus on monitoring and maintaining the barriers of treatment, rather than on end-of-pipe sampling and testing. For this research, a CCP is a point in a treatment process whereby controls to reduce, prevent, or eliminate process failure can be applied, and whereby monitoring is conducted to confirm that the control point is functioning correctly. The ozone-biological activated carbon (BAC) based treatment train is an example. Initially, BAC could not be considered a CCP because there was no control mechanism to adjust its ability to achieve pathogen reduction or contaminant removal. Yet, by modifying the process to incorporate a coagulation step ahead of filtration, BAC became a control point. BAC effectively reduced turbidity and hence levels of microorganism removal if operated as a biological filter. The HACCP method facilitated this decision, although it was straightforward from a process design and selection viewpoint. On top of identifying the CCPs in DPR treatment trains, the robustness of those treatment processes was also evaluated. The researchers conducted a Monte Carlo simulation with full-scale data to model contaminant removals across the multiple barriers for both treatment trains studied. The two treatment trains exceeded the current California regulations for groundwater injection of 12-log removal of viruses, 10-log removal of Cryptosporidium, and 10-log removal of Giardia, the results confirmed. The only exception was removal of Cryptosporidium in ozone-BAC treatment. However, the processes in that treatment train could be further optimized within a specific facility to reach the removal targets. This research is clear in its determination that non-RO based treatment is adequate for removal of Cryptosporidium, bringing DPR another step closer to reality in many communities. 12 wateronline.com n Water Innovations Overcoming Operations Challenges For Direct Potable Reuse The Water Environment & Reuse Foundation introduces a "bundle of research" to help direct potable reuse and its practitioners reach full potential. Ozone-BAC treatment train RO-based treatment train

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