Benefits and Challenges Associated with Raw Water Augmentation for DPR

Advanced treated water (ATW) can be a reliable water source, which can help address challenges faced by water industry due to ever-increasing population and climate change. Direct potable reuse (DPR) can be advantageous over indirect potable reuse (IPR) due to:
• Limited infrastructure requirements
• Low energy, and overall operation and maintenance (O&M) costs, and
• Greater provision for monitoring and controlling process performance.
For DPR, raw water augmentation (RWA) is an option, in which ATW is blended with raw water sources upstream of a surface water treatment plant (SWTP). However, it is critical to understand the effects of blending ATW on plant operation and overall treatment performance. Recognizing this, in collaboration with the California Water Boards, the Water Research Foundation (WRF) implemented Project 5049: Public Health Benefits and Challenges for Blending of Advanced Treated Water Upstream of a Surface Water Treatment Plant in DPR.
Bench-scale tests were conducted with raw water and ATW collected from RO-based and carbon-based advanced treatment systems (i.e., RBAT and CBAT systems) from across the country. Tests were conducted with 0% to 50% ATW blends. In most cases, blending ATW reduced turbidity and TOC in the blended water, reducing coagulant dose requirement.
Pilot-scale tests were conducted at Plants A, C, and D, simulating conventional or direct filtration system. Compared to the 0% blend (i.e., raw water), the ATW-blended water resulted:
• Similar or better TOC removal
• Similar or better effluent turbidity
• Lower headloss accumulation rate in the filter, and
• Similar or lower disinfection byproduct formation potential in filtered effluent
MS2 and PMMoV spiking tests conducted at Plants A and C showed better pathogen log removal with the ATW-blended water.
Overall, the bench- and pilot-scale results demonstrated that RWA does not negatively impact SWTP operation and/or performance. Rather, filter performance can improve when using ATW-blended water.