[USA] Cooling tower blowdown becomes a water source: ROTEC's reverse-flow Reverse Osmosis (RO) wins a water reuse project at a 330 MW power plant in California, with the goal of eliminating surface water discharge.

2026 年 9 月 23 日, U.S. Reverse Osmosis technology supplier ROTEC USA announced it will provide an advanced water treatment system for the Imperial Irrigation District (IID) El Centro Generating Station in California, treating chemically softened cooling tower blowdown, with a process of Membrane Microfiltration + High-Recovery Flow Reversal Reverse Osmosis (FR-RO), along with a boiler makeup water Reverse Osmosis system. The generating station has an installed capacity of more than 330 MW. The project is part of IID's wastewater reduction program, with the goal of eliminating surface water discharge from the station and enhancing in-plant reuse, with the concentrate significantly reduced in volume before being sent to evaporation ponds.

What Is Being Targeted Is Not Wastewater, but Cooling Tower Blowdown

To control scaling and corrosion, the circulating cooling system of thermal power generating units must continuously discharge a portion of water with relatively high salinity, namely cooling tower blowdown. This type of water is large in volume, high in salinity, and relatively stable in composition at power plants, and has long been regarded as a waste stream requiring disposal.

The entry point of ROTEC's system is precisely to turn this waste stream into a makeup water source.

• Influent is first chemically softened — cooling tower blowdown first undergoes chemical softening to remove hardness, reducing scaling risk for the downstream membrane system. This step determines whether the entire system can operate stably in a higher recovery range.
• Membrane Microfiltration as pretreatment — Membrane Microfiltration intercepts Suspended Solids and colloids, replacing the traditional combination of multi-media filtration plus Activated Carbon. It occupies less space, delivers more stable effluent quality, and also provides reliable feedwater protection for Reverse Osmosis.
• High-recovery Flow Reversal Reverse Osmosis is the core — FR-RO (Flow Reversal Reverse Osmosis) periodically changes the flow direction within the membrane elements, inhibiting thickening of the boundary layer on the concentrate side and scale deposition, thereby operating at higher recovery with more permeate and less concentrate.
• Permeate then enters the boiler makeup water system — FR-RO permeate serves as feedwater for the dedicated boiler makeup water Reverse Osmosis system, achieving secondary purification for in-plant reuse; the concentrate significantly reduced in volume by FR-RO is discharged to evaporation ponds.

The chain is clearly designed: volume reduction + quality upgrading + reuse. The ultimate goal is for the station to no longer discharge to surface water bodies while squeezing more usable output from its own water volume.

Water Resource Pressure Behind a 330 MW Power Station

The El Centro Generating Station has an installed capacity of more than 330 MW and is an important part of IID's power generation assets, providing electricity to the Imperial Valley and Coachella Valley. The project's location determines that its water resource constraints are quite rigid.

• The region itself is water-scarce — the Imperial Valley is located in an arid area of southeastern California, where agricultural and municipal water use compete intensely. Colorado River water rights allocation has long been in a sensitive state, and the social and approval costs for industrial users to obtain additional water are very high.
• Discharge permits continue to tighten — ROTEC explicitly stated in its announcement that the new system was built "to respond to increasingly stringent wastewater discharge requirements." For existing units, retrofitting water treatment systems is often easier to approve than building new water intake facilities.
• Evaporation ponds are the final containment endpoint — discharging concentrate to evaporation ponds means the system still retains an end-of-pipe disposal pathway, but by increasing recovery, the volume of water entering the evaporation ponds is significantly reduced, thereby extending the service life of existing evaporation ponds.

This logic is not unfamiliar to Chinese readers: in many domestic thermal power and coal chemical wastewater Zero Liquid Discharge retrofits, "first reduce volume, then solidify" is also the mainstream pathway. The only difference lies in whether the endpoint is evaporative crystallization or evaporation ponds.

Delivery Method and Team Composition

The project is being delivered by W. M. Lyles Co. using a progressive design-build approach, with Aqua Engineering and Albert A. Webb Associates participating in engineering design.

The meaning of progressive design-build is that the owner brings in the contractor before the project scope and budget are fully fixed, and both parties iterate repeatedly between design and constructability before locking in the final cost. For projects like water treatment where "influent quality — process selection — investment scale" are highly coupled, this approach can better avoid late-stage changes than the traditional design-bid-build method. This is worth referencing for domestic Industrial Wastewater projects: for projects with large water quality fluctuations, the earlier the process party is involved, the fewer detours will be taken.

Bruce Alderman, CEO of ROTEC, stated that cooling tower blowdown is a major opportunity for water reuse in the power generation industry. In El Centro, reverse-flow Reverse Osmosis will help the Imperial Irrigation District recover more usable water from this wastewater stream while discharging less to evaporation ponds.

Why High-Recovery Reverse Osmosis Has Gained Momentum in the Past Two Years

In its announcement, ROTEC listed the target industries for reverse-flow Reverse Osmosis, including municipal water supply, power generation, data centers, semiconductor manufacturing, food and beverage, oil and gas, and other high water-consuming sectors. This list itself is a demand map.

• Data centers and semiconductors are the strongest driving forces — both types of facilities consume large volumes of water, have high water quality requirements, and new projects are often constrained by local water withdrawal quotas, giving owners incentive to pay a premium for "less intake, less discharge."
• Every percentage point increase in recovery rate reduces the concentrate volume — brine disposal costs are typically the most expensive segment of a Zero Liquid Discharge project. The end-of-pipe reduction effect brought by improved front-end recovery is multiplicative, which is also the source of the economic viability of high-recovery processes.
• Membrane lifespan and cleaning frequency determine the true cost — the value of the reverse-flow design goes beyond recovery rate; it also includes extending membrane lifespan, reducing chemical consumption, and decreasing cleaning frequency. Owners should evaluate total lifecycle cost rather than focusing solely on initial investment.

Our Assessment

TIANYI TECH has long provided wastewater treatment and Reclaimed Water Reuse system solutions for municipal and Industrial Park clients. We believe the most valuable reference from this project is not "what membrane was used," but rather the approach of separating cooling tower blowdown for resource recovery. In water balance testing at domestic industrial enterprises, cooling tower blowdown is often mixed into comprehensive wastewater for combined treatment, resulting in diluted salinity and underestimated treatment difficulty. We recommend that before developing a Reclaimed Water Reuse plan, wastewater should first be classified by water quality into "high-salinity, difficult-to-treat" and "low-salinity, easy-to-reuse" categories, with reuse pathways demonstrated separately: the low-salinity portion can be directly reused, while the high-salinity portion should be separately reduced in volume. This approach often requires less investment and operates more stably than "collect everything and treat it uniformly."

About TIANYI LIMITED: TIANYI TECH is deeply engaged in the fields of wastewater treatment and Reclaimed Water Reuse, committed to providing efficient, low-carbon, and sustainable water treatment solutions for municipal and industrial clients.