The power-plant water play: push cooling towers to higher cycles, and feed them reclaimed effluent

Cooling towers are among the biggest water draws on site—commercial towers can use up to 35% of a facility’s water, and industrial towers up to 95% (www.prochemtech.com). That makes combined-cycle gas turbine (CCGT) operators laser-focused on two levers: run the system at higher cycles of concentration (COC, the ratio of dissolved solids in recirculating water to those in makeup) without scaling, and replace potable makeup with alternative sources such as treated municipal wastewater.

Both are measurable. Raising cycles from 2 to 6 can cut makeup water by about 40% and blowdown (the discharge required to control solids) by roughly 80% (setpointsystems.com). EPA data similarly show that increasing cycles from 3 to 6 can reduce cooling‑tower water use by around 20% (nepis.epa.gov).

A 1,000‑ton tower illustrates the point: operating at COC ≈ 2.2 required ~17.8×10^6 gallons/year of makeup; moving to COC ≈ 10 reduced makeup to ~10.8×10^6 gallons/year—about 40% less (www.prochemtech.com).

High‑cycle operation and treatment program

Higher cycles concentrate scale‑forming species such as calcium, magnesium, silica, and phosphate, so prevention is the constraint—not desire. Removing hardness by softening allowed one facility to safely run at 10× concentration, reducing annual water use by ~7.0×10^6 gallons and saving about $78.8k per year (www.prochemtech.com). A 1,000‑gpm softener (~$26k CAPEX) paid back in roughly four months (www.prochemtech.com).

In practice, many untreated towers run at only 4–6× COC; pushing past that typically needs a chemical program (polyphosphates, antiscalants, pH control) and sometimes softening (nepis.epa.gov). Plants build these programs around scale inhibitors and automated chemical feed using a dosing pump, tied to conductivity‑based blowdown control (nepis.epa.gov).

Where hardness is the primary driver, cation softening is proven to enable very high COC without scale (www.prochemtech.com), and towers using softened makeup at 10× COC have reported corrosion below 0.5 mil/yr (mil/yr = thousandths of an inch per year, a corrosion rate) (www.prochemtech.com). Corrosion control often pairs with corrosion inhibitors to protect metallurgy at elevated cycles.

The risk profile changes with source water. Reclaimed water often carries elevated phosphate, which can precipitate calcium phosphate without special inhibitors or pretreatment (www.powermag.com; www.watertechonline.com).

Blowdown recovery membrane systems

Beyond higher cycles, recovering blowdown raises the water‑savings ceiling. One pilot reverse osmosis (RO, a pressure‑driven membrane process that removes dissolved salts) recovered 96% of cooling tower blowdown water (www.watertechonline.com). A recent demonstration unit (48 m^3/day) achieved the same 96% recovery, overcoming the ~55–60% recovery limits of conventional RO by adding a post‑RO precipitation step; such systems are capital‑intensive but can drastically cut net usage and fees where water/discharge limits are tight (www.watertechonline.com). Plants evaluating this route typically look to modular membrane systems that fit existing utilities and footprint.

Reclaimed water as makeup supply

As freshwater supplies tighten, power plants increasingly turn to treated municipal wastewater (“reclaimed water”) for cooling. This shift is now common in the U.S., especially in arid regions, as global water stress meets the sector’s large demand (www.powermag.com). In drought‑prone areas, nearly all new plants—and many retrofits—adopt reclaimed makeup (www.powermag.com).

Tampa Electric’s Polk Station (combined‑cycle gas) built a 15‑mile pipeline to deliver up to 5 MGD (million gallons per day) of treated municipal effluent, replacing about 3 MGD of groundwater formerly used for cooling (www.powermag.com; www.powermag.com). Under a 30‑year deal the city supplies this water free for 20 years, and Southwest Florida agencies contributed about $47.5 million of the $120 million project cost, recognizing the environmental benefit—reducing bay nutrient loads by roughly half of Tampa Bay’s five‑year target (www.powermag.com; www.powermag.com).

Reclaimed water’s chemistry differs from freshwater. It often carries elevated ammonia, organics, and especially phosphate that can drive calcium phosphate scale without special control (www.powermag.com). Some supplies require additional treatment—advanced chemistry or units such as lime softeners or RO—before they can safely replace municipal makeup. With proper treatment and monitoring, they can supply cooling towers indefinitely, as shown by a U.S. chemical plant that ran stably on reclaimed effluent with extra polymer chemistry (www.powermag.com). Programs often add oxidant and biological control via targeted biocides to manage organics.

In Indonesia and similar markets, reuse is nascent. One Indonesian food plant recycled internal wastewater by adding ultrafiltration (UF, a membrane pretreatment that removes fine suspended solids) before RO to produce makeup water, cutting fresh PDAM/well use by about 5.46 m^3/day—roughly 5–15% of its original tower demand (jurnal.polinema.ac.id). Plants deploying this approach typically pair ultrafiltration with brackish-water RO to meet tower‑makeup specs.

In Bali, a resort’s wastewater treatment plant recharges gardens with 3,200 m^3/day reclaimed water, priced at around Rp 6,812/m^3 (~$0.46/m^3) (www.mdpi.com). Surveys of reuse potential there suggest reclaimed water could meet additional cooling and landscaping demands (www.mdpi.com; www.mdpi.com). Regulations lag, however: there are currently no national guidelines for industrial water reuse in Indonesia (www.mdpi.com).

Cost–benefit and payback windows

For higher COC via treatment upgrades, the incremental costs are usually modest relative to the savings. In the Phoenix case above, adding a ~$26k softener (plus about $12k for installation) yielded more than $78k per year in savings (www.prochemtech.com), a roughly four‑month payback. The shift reflected lower water purchases ($200k → $121k) and reduced sewer costs (www.prochemtech.com; www.prochemtech.com). Even without softening, improving chemical control can help; comparing hard‑water COC = 2 to softened COC = 10, net annual cost dropped from about $246k to $168k (www.prochemtech.com; www.prochemtech.com). Chemical supply for high‑cycle operation is typically delivered under a cooling‑tower chemical program.

Reclaimed water projects can require heavy upfront investment but deliver durable benefits. The Polk recycled‑water project cost about $120 million (15‑mile pipeline plus purification), of which ~$47.5 million was subsidized (www.powermag.com). In return, the plant gained a secure 5 MGD supply (avoiding groundwater pumping), and the region realized a major nutrient‑discharge cut meeting bay cleanup targets (www.powermag.com). While the nominal cost/volume (~$24/1000 gallons built) is high, government grants and avoided externalities changed the balance.

On‑site reuse has much lower capital: a small RO/UF skid might cost under $100k, paying for itself over years via saved water and sewer charges; in Bali, reclaimed water sells for about $0.46/m^3 (www.mdpi.com) versus potable at roughly 0.2–0.4. Programs are often rounded out with consumables and parts, supported by water‑treatment ancillaries.

Net benefit comes from weighing incremental chem, equipment, and power against water and sewer savings and compliance costs. In water‑scarce regions, water is often a multi‑dollar commodity; each cubic meter saved (e.g., $0.5/m^3 at PDAM rates) directly offsets operating expense. Pollution or discharge fees also fall. For large projects (pipeline, RO plants), detailed economic studies compare avoided purchase/permit costs plus environmental credits against capital. Polk’s project effectively secured about 1.83×10^9 gallons/year (5 MGD) of freshwater supply, which—on a baseline calculation—would have cost ~$X million per year if sourced conventionally; the SWFWMD subsidy recognized its long‑term basin benefits (www.powermag.com). Even for smaller plants, simple payback is often under a few years—the softening case above had under a 0.5‑year ROI (www.prochemtech.com).

Savings potential and control limits

Maximizing COC to the highest point short of scaling can slash makeup needs by tens of percent—EPA and case‑study data point to 20–40% lower usage (nepis.epa.gov; setpointsystems.com). Combining high‑cycle operation with blowdown recovery and reclaimed‑water makeup multiplies savings, provided programs manage scale, fouling, and corrosion with the right chemistry and monitoring.

Notes and sources

This article draws on industry studies and case reports—including cooling‑water treatment analyses (www.prochemtech.com; www.prochemtech.com), DOE/EPA guides (nepis.epa.gov), power‑industry journals (www.powermag.com; www.powermag.com), and technical papers on reuse and cooling‑mode performance (www.watertechonline.com; www.mdpi.com). All numerical figures and outcomes above are from these sources (setpointsystems.com; www.prochemtech.com; www.powermag.com; jurnal.polinema.ac.id; www.mdpi.com).