Cement plants lean on closed-loop cooling to keep bearings, lube‑oil coolers, and compressors running — but biofilms and corrosion don’t care that the water recirculates. The fix is a disciplined biocide program, rigorous monitoring, and scheduled cleaning and flushing.
Closed-loop cooling circuits recirculate the same water — often high‑grade condensate or demineralized water — with minimal makeup. In fact, a closed loop “should retain ~90% of its water annually,” which means contaminants like nutrients, metals, oxygen, and microbial biomass can accumulate over time (Chardon Labs).
That accumulation is enough to support biofilms (slime-like microbial communities) including nitrifying, sulphate-reducing, aerobic bacteria, and even fungi, degrading heat transfer and corroding pipes. Industry reviews bluntly note that neglecting water treatment and monitoring “can lead to corrosion and fouling” even in closed circuits (Water Tech Online; POWER Magazine).
The stakes are high: failure of a closed loop can shut down critical plant systems, with cascading operational risk (POWER Magazine). That is why microbiological control is embedded in preventive maintenance guidance for closed circuits (WCS Group).
Oxidizing and non‑oxidizing biocides
Biocides used in cooling water fall into oxidizing and non‑oxidizing classes. Oxidizing biocides — chlorine, bromine, ozone, peracetic acid, hydrogen peroxide, chlorine dioxide — kill via strong redox reactions. They act fast and broadly but can clash with corrosion inhibitor films commonly used in closed loops. Free halogens, for example, can consume nitrite or molybdate inhibitors and even accelerate stress corrosion cracking in susceptible alloys (Water Tech Online; ChemTreat).
There are exceptions: chlorine dioxide (selective, tolerant of higher pH, not fouled by ammonia) and monochloramine (a combined chlorine species designed to penetrate biofilm) can be used when the inhibitor program allows. Both demand tight control — stabilizers, on‑site generation — and are uncommon in standard cement‑plant loops (ChemTreat; ChemTreat).
By contrast, non‑oxidizing biocides are the norm in closed loops because they do not strip protective films. Typical actives include glutaraldehyde (a dialdehyde biocide), isothiazolinones (heterocyclic biocides), DBNPA (dibromo‑nitrilopropionamide), and quaternary ammonium compounds. They disrupt cell walls or metabolism without halogens, so they generally do not react with nitrite/molybdate corrosion programs. Glutaraldehyde, for instance, is broad‑spectrum, breaks down to carbon–oxygen compounds (no halogens or sulfur), and remains stable at high pH and hardness; isothiazolones are popular too, though they can introduce low levels of chloride (Water Tech Online). In practice, programs draw from standardized biocide packages within broader closed‑loop chemical programs.
Non‑oxidizers often have a slower kill curve and may be applied as periodic “shock” doses or maintained at low continuous feed. Typical feeds are on the order of hundreds of ppm, subject to site-specific guidance; one field guideline cites “1.5% isothiazolinone (i.e., 15,000 ppm stock)” as a basic dose for chiller loops, with alternating glutaraldehyde to prevent microbial resistance (Chardon Labs).
Combined dosing strategies and compatibility
Many operators blend approaches. One case study found that continuous chlorination plus weekly glutaraldehyde “effectively controlled bacterial populations” in cooling loops, even though some biofilm persisted (PMC). Other plants feed an oxidizer 1–2 hours per day and a non‑oxidizing biocide once per week, cutting halogen usage while sustaining control (ChemTreat). Where an oxidizer is used, stabilized forms and bio‑penetrants are common to slow non‑productive reactions (ChemTreat).
The compatibility rule remains: unless the corrosion inhibitor program is non‑nitrite (e.g., phosphate or molybdate), oxidizers are generally avoided because of adverse reactions with nitrite films (Water Tech Online; ChemTreat). Accurate metering via a dedicated dosing pump helps maintain effective levels without overfeed.
Corrosion control remains foundational alongside biocides. Plants typically maintain nitrite or molybdate films with corrosion inhibitors, and may add scale inhibitors when water chemistry warrants it.
Monitoring parameters and action levels
Frequent biomonitoring is non‑negotiable. Periodic plate counts of heterotrophic bacteria (colony forming units per milliliter, CFU/mL) are used with targets of less than 10^4–10^5 CFU/mL; many plants set “action levels” so a spike above 10^4 CFU/mL triggers investigation and dosing (Veolia Water Technologies Handbook; WO2022026240A2). In nitrite‑treated systems, a rapid drop in nitrite residual is an early warning because some microbes can consume nitrite; adding more nitrite can then fuel growth if biofilms have taken hold (POWER Magazine).
Multi‑parameter trending — pH, conductivity, dissolved oxygen, and ORP (oxidation–reduction potential) — is common. Some sites deploy online microbial monitors such as ATP assays (adenosine triphosphate) or impedance devices, and nitrate sensors that watch for conversion to nitrite as a proxy for anaerobic biofilm. In one patented control scheme, rising nitrite prompts automated non‑oxidizing biocide feed, with a goal of keeping denitrifying bacteria below 10^5 CFU/mL (WO2022026240A2; WO2022026240A2; WO2022026240A2). Routine weekly checks are widely advised, with more frequent testing in problem loops. The BSRIA closed‑system standard (BG50) even recommends an hourly pump circulation for seasonal systems to discourage stagnation (WCS Group), and closed‑circuit guidance emphasizes that any sign of growth should trigger investigation and, if needed, a more aggressive treatment routine (WCS Group; WCS Group).
Cleaning and flushing procedures
Chemical dosing alone cannot remove established deposits. Periodic cleaning and flushing physically strip biofilm and rust sludge and expose fresh metal for inhibitor coverage. A typical sequence is: drain and line flush at the system low point until clear; circulate an approved cleaning solution (with defoamer and iron/sequestrant chemistry) for 2–4 days; flush until key parameters (e.g., conductivity) match makeup water; then refill with fresh corrosion inhibitor and biocide (Chardon Labs; Chardon Labs). As a rule of thumb, flushing may take roughly 12 hours per 1,000 gallons of loop volume before the water “runs clear” (Chardon Labs). For a 50 m³ (~13,000 gal) system, that is on the order of 6–12 hours at 2 gpm, and badly fouled systems may need multiple cycles.
Closed loops tend to accumulate iron until saturation, then precipitate rust sludge. Without flushing, “ferrous by‑products rapidly exceed the ability of leaks [to] control iron,” resulting in deposits (Chardon Labs). When biodispersants are applied, all filters and drip legs should be cleaned promptly, because dislodged biofilm can plug small‑bore sections; in some layouts, dispersants can cause blockages if not carefully managed (WCS Group). Plants often incorporate dispersant chemicals in controlled, supervised steps and rely on replaceable cartridge filters to capture suspended debris dislodged during cleanup.
Hardware helps. Post‑flush straining and periodic solids interception with rugged steel filter housings or a properly sized strainer reduce re‑circulation of fines. Many facilities follow BSRIA BG29/2020 practices at commissioning for a biocidal pre‑startup clean (WCS Group) and then schedule annual or biannual flushes, aligned with 1–3‑year shutdowns common in Asian cement plants. The consensus is straightforward: “it is easier and more cost‑effective to maintain microbiological control than to clean a badly fouled system” (WCS Group).
Performance metrics and regulatory context
Done well, these programs deliver measurable outcomes. Shock dosing aims for >99% inactivation of planktonic bacteria; in one pilot, weekly glutaraldehyde plus daily chlorination gave near‑complete kill of planktonic Pseudomonas and Klebsiella (biofilm communities required persistent dosing) (PMC). Cement loop programs target similarly high log‑reduction (4–5 log kill in bulk water during pulses), while operators aim for final colony counts below 10^3–10^4 CFU/mL and clean surfaces verified by corrosion coupons and titration kits.
The business case is compelling. Neglected loops erode efficiency (heat exchange, pump head) and can cause sudden failures; one engineering perspective warns that in a closed circuit, “once corrosion has a foothold… critical data equipment may be damaged to the point where it affects the ability of the plant to operate” (POWER Magazine). Vendors estimate that preventing a single clogged or corroded cooler can avoid ~$100–300k per incident in large plants — savings driven by pre‑emptive dosing and filter maintenance.
Regulatory framing matters, even with minimal blowdown. While there is no specific Indonesian law for closed‑loop biocide use, wastewater standards such as PP 82/2001 apply to any bleed stream. Oxidizers may form compounds above discharge limits (e.g., halides), so any residuals must meet municipal standards (BOD, halogens, heavy metals, etc.). In practice, closed loops minimize blowdown and rely on pre‑filtered potable makeup water. Broader trends are pushing away from older chemistries; oxidizing halides face scrutiny under legislation like Indonesia’s PERMEN on hazardous discharge, encouraging some sites toward peracetic acid or stabilized chlorine dioxide where compatible. Non‑oxidizers continue to evolve into multi‑component blends that pair bactericides with biodispersants.
Across the board, authoritative references reinforce these practices (Water Tech Online; ChemTreat; Veolia Water Technologies Handbook; WCS Group; PMC; ChemTreat; WCS Group; Chardon Labs), and plants operationalize them through coherent chemical programs and fit‑for‑purpose equipment — from closed‑loop chemicals and biocides to precision dosing pumps and solids capture hardware.
