Industrial Water Reuse: How Plants Recover, Treat and Reuse Their Own Water
By Sean Alford, Permitting Plus
Industrial water reuse means treating the wastewater a plant has already produced and putting it back to work, instead of drawing new water in and sending used water out. For most industrial sites, the simplest version is this: cooling tower blowdown, process rinse water, and reverse osmosis reject are collected, treated, and returned as cooling tower make-up or process water. Intake falls. Effluent falls. And the permits that govern both get easier to hold.
Reuse used to be a sustainability project run by the environmental department. It is now a compliance and supply project run by operations, with the environmental agency watching. Effluent limits are tightening, water rights and intake permits are harder to expand, and in water-stressed regions the regulator expects a plant to show what it has done with its own water before asking for more.
Permitting Plus delivers brine management projects, project management, engineering, procurement, and construction through to commissioning, together with the permits they need, and water reuse is part of every brine recovery project we deliver. This article covers what industrial water reuse involves, which wastewater can be reused for what, the treatment it takes, and what the regulator asks. Reuse is also the front end of a zero liquid discharge (ZLD) system; our zero liquid discharge page covers that end of the road.
Table of Contents
What counts as industrial water reuse
The Environmental Protection Agency, the EPA, groups industrial reuse into onsite reuse, where a facility recycles its own wastewater, and reuse of water from outside sources, such as treated municipal wastewater supplied to an industrial plant. Both count. Both are growing. This article is mainly about the first, because it is the one a plant controls.
Onsite recycling
A facility collects one or more of its own wastewater streams, treats them to the quality a particular use needs, and sends the water back to that use. The classic loop is cooling tower blowdown, the largest wastewater stream at most plants, treated and returned as make-up. Others include process rinse water returned to rinsing, boiler blowdown returned to the towers, and reverse osmosis reject treated and blended back into low-quality uses such as dust suppression or ash handling.
Reuse of municipal reclaimed water
Many industrial facilities, especially power stations and refineries, take treated municipal wastewater as their cooling water supply instead of fresh water. The municipal treatment works gets a customer for its wastewater and the industrial facility gets a supply that does not compete with drinking water. The quality is variable and the treatment on the receiving side has to handle that.
Where the water comes from
| Stream | Typical quality issue | Common reuse |
|---|---|---|
| Cooling tower blowdown | Concentrated salts, treatment chemicals, some organics | Cooling tower make-up after softening and membranes |
| Reverse osmosis reject | High dissolved salts | Blending into low-quality uses, or concentration for reuse of the permeate |
| Process rinse water | Product residues, low salts | Return to rinsing, tower make-up |
| Boiler blowdown | Hot, treated, moderate salts | Tower make-up, heat recovery first |
| Stormwater from operating areas | Variable, oil and solids | Tower make-up, washdown, after settling and filtration |
| Sanitary wastewater | Organics, nutrients, pathogens | Irrigation, tower make-up after biological treatment and disinfection |
Reuse, recycling, and water management: the terms
The words get mixed up, and the mix-up causes real confusion in permit files.
Water recycling usually means returning water to the same use it came from, often with little treatment: rinse water recycling in a plating line, or cooling water recycling within a closed loop. Water reuse usually means treating wastewater from one use and sending it to a different use. Regulators and the EPA tend to use the two interchangeably, and so do vendors, so the safe practice is to describe each stream by what it is, where it came from, what treatment it gets, and where it goes, rather than by a label.
Water management is the larger discipline both sit inside. A water management plan for an industrial facility covers intake, every internal use, every wastewater stream, treatment, reuse and recycling loops, and the residual effluent, with a water balance that ties them together. Reuse is one lever in that plan. Water management also covers the ones people forget: fixing leaks, running cooling towers at more cycles of concentration, cascading water from clean uses to dirty ones without treatment at all, and metering so that the data exists.
We ask to see the water management plan before we talk about reuse systems. Where there is none, building it is the first task, and it is usually the task that finds the savings.
Why plants reuse water
Three reasons drive almost every industrial water reuse project we see.
The effluent permit. A facility that reuses water sends less out, and a smaller outflow is easier to keep within limits as those limits tighten. In some cases reuse takes the site below a threshold that removes a permit condition altogether.
The intake. Water rights, wells, and municipal supply contracts have limits, and expanding them is slow or impossible. Reuse is the supply that is already on site.
The cost. Intake water is bought, treated, heated, and pumped. Effluent is treated again and often charged for. Water that goes round twice pays for its treatment once.
There is a fourth reason that is becoming the first. In water-stressed regions, the regulator and the community now expect a facility to show what it has done with its own water. A reuse program is the answer to that question, and a facility without one has a harder conversation at every permit renewal.
Matching water quality to the use
The center of any wastewater reuse project is a table like the one below. Water quality has to match the use it goes to, and the treatment is whatever closes the gap.
| Reuse application | Quality the use tolerates | Treatment usually needed |
|---|---|---|
| Cooling tower make-up | Moderate dissolved salts, low hardness, low silica, no organics that foul | Softening, filtration, sometimes reverse osmosis |
| Boiler feed | Very low dissolved salts and silica | Reverse osmosis, ion exchange polishing, deaeration |
| Process water | Depends on the process; often between cooling and boiler | Set by the engineer responsible for that step |
| Washdown and dust suppression | Low; solids and oil removed | Settling, filtration |
| Irrigation and landscape | Low salts, no pathogens | Biological treatment, filtration, disinfection |
| Fire water storage | Low; clean enough not to clog | Filtration only |
Two rules come out of that table. Send each stream to the lowest-quality use that can take it, because treating water to a higher quality than the use needs is wasted money. And do not blend a bad stream into a good one just to get rid of it; blending spreads the problem.
Reuse applications by industry
The same treatment processes serve very different industries, and the reuse applications that make sense differ with them.
Power generation. Cooling tower blowdown is the dominant wastewater stream, and returning it as make-up after softening and membranes is the standard reuse application. Flue gas desulfurization wastewater at coal plants is harder and often ends in a ZLD system.
Oil refining and petrochemicals. Cooling water, production water, and stormwater from operating areas are reused for cooling make-up and firewater after oil removal, biological treatment, and filtration. Many refineries also take reclaimed municipal wastewater as their main supply.
Food and beverage. Clean-in-place rinses, cooling water, and process wastewater are reused for tower make-up, washdown, and non-contact applications after biological treatment and membranes. Food-contact reuse is tightly regulated and rare.
Pulp and paper. Large volumes, high organic load, and long experience with recycling process water within the mill. Reuse applications focus on closing loops inside the mill before any external treatment.
Mining and minerals. Process water reuse from tailings and thickener overflow is routine, and in dry regions it is the only supply. Salinity builds with each cycle, which is where brine treatment and salt recovery come in; our brine management page covers that end.
Semiconductors and electronics. Ultrapure water reuse and reclaim systems recover rinse water for cooling towers, scrubbers, and lower-grade applications, and the industry has some of the highest reuse rates anywhere.
Desalination and chemical plants. Recovered water from concentration and reject streams is reused as process water, as on the project described below.
The point of the list is that the treatment systems overlap almost completely. What is specific to each industry is which applications can take reused water, and at what quality.
The treatment solutions behind industrial water reuse
Reuse solutions are built from the same processes as any industrial wastewater plant. The technologies are the same; what changes is the target: the water has to be good enough for the use, not good enough for the river.
Pretreatment
Suspended solids, oil, and grease come out first, by settling, dissolved air flotation, and filtration. Nothing downstream works if this stage is skipped, and this is part of water management as much as of treatment.
Softening and silica control
Cooling tower blowdown is concentrated by design; the salts, hardness, and silica in the make-up water are three to ten times stronger in the blowdown. Chemical softening with lime or soda ash, or ion exchange, removes hardness. Silica is controlled by softening at high pH or by specific media. This stage decides how far the water can be recycled before it scales.
Membranes
Reverse osmosis produces water clean enough for tower make-up and, with polishing, for boiler feed. Recovery on reuse duty is limited by scaling, which is why softening comes first. High-recovery solutions push 80 to 95 percent of the water back to the plant; the rest is a concentrate that goes to the outfall, to a small evaporator (usually a mechanical vapor recompression unit; see our article on those evaporators), or, in a ZLD plant, to a crystallizer. We cover the middle option in our article on minimal liquid discharge.
Biological treatment and disinfection
Where the wastewater carries organics, as food, pulp, and chemical wastewater usually does, or where the reuse involves people, such as irrigation or washdown, biological treatment and disinfection are added. Sanitary wastewater reused on site always needs both, whatever else is done to it.
Polishing
Ion exchange, second-pass reverse osmosis, or electrodeionization take reverse osmosis permeate to boiler-feed quality. Ion exchange is the oldest of the three technologies and still the most common, mixed-bed ion exchange remains the final step at most boilers, and ion exchange resins need their own regeneration waste route. Each step is small, and each step matters at the boiler.
A reuse loop inside a large brine project
On our project in Indonesia, water reuse is built into a much larger recovery plant. The reject brine from a seawater desalination plant, tens of thousands of cubic meters a day, is being turned into salt and chlor-alkali chemicals with no liquid returned to the sea. The design is preliminary and subject to confirmation in detailed engineering.
Inside that plant, the reuse loops are ordinary. Water recovered from the brine concentration stage is reused as process water. Dechlorinated brine leaving the electrolysis cells returns to the concentration loop as feedstock. Each modular chemical plant draws process water and demineralized water, and the recovered water offsets both. The water balance names every stream, including cooling blowdown, laboratory waste, and site effluent, because a reuse or ZLD claim that leaves streams out does not survive review.
The lesson for an ordinary industrial facility is the same one: start with the water balance. Every stream in, every stream out, every internal loop, with flows confirmed or estimated and the basis stated. That document is the reuse plan, the permit file, and the business case in one.
Permitting industrial water reuse
Reuse changes permits in both directions, and owners are sometimes surprised by the second.
What gets easier
Less effluent means less to comply with. A facility that cuts its outflow by half has half the pollutant load to report and more margin under every limit. Where an effluent permit is up for renewal with tighter limits, a reuse program is often the cheapest way to meet them. Intake permits and water rights are easier to hold when the plant can show it has reduced demand.
What gets harder
The concentrate. Reuse concentrates whatever the plant does not consume. A stream that met effluent limits at full flow can exceed them once it is one-fifth the volume and five times the strength. The permit for the residual outflow has to be checked against the concentrated stream, not the original one. Where the concentrate has nowhere to go, the facility is on the road to ZLD whether it planned to be or not, and we cover the disposal options in our guide to brine disposal methods.
Regulations that apply to reuse itself
In the United States there is no single federal permit for onsite industrial reuse. The EPA publishes guidance and resources, the effluent that remains is governed by the facility’s National Pollutant Discharge Elimination System permit or its industrial user permit from the local treatment works, and the state sets any rules for reuse quality, especially where people may contact the water or where reclaimed municipal water is involved. Some states have detailed reuse regulations; others treat industrial onsite reuse as a design matter within the existing permits. Outside the United States the pattern is similar, with the environmental agency reviewing the water balance and the residual outflow together.
Our job on a reuse project is to map exactly which permits and environmental approvals change, which new approvals are needed, and in what order, and to assemble the file that shows the regulator the whole water balance rather than one stream.
Data, targets, and reporting
A reuse program lives or dies on data. Flow meters on intake, on each major use, on each wastewater stream, and on the reuse line are the minimum. Without that data the water balance is a guess, the reuse rate cannot be proved, and the regulator has nothing to accept.
Targets follow from data. A reuse target expressed as a percentage of wastewater returned, an intake target expressed in cubic meters per unit of production, and an effluent target expressed as a volume or a load give the plant something to manage against and give the regulator something to verify. Corporate water targets set at head office are only useful when they are translated into site targets like these, with the data behind them.
Reporting closes the loop. Many plants now report water data publicly, and permit renewals increasingly ask for it. The EPA maintains water reuse resources and guidance for industrial applications, and several states publish reuse data of their own. Using the EPA’s categories and definitions in your own reporting saves argument later, because the reviewer recognizes them.
Data collection and targets belong in the reuse plan from the start, because a reuse system that cannot demonstrate its reuse rate is a system the regulator will discount.
Working with engineers, equipment suppliers, and the regulator
Industrial water reuse projects involve three outside parties, and owners do better when the roles are clear.
The engineers define the problem: the water balance, the quality targets, the reuse applications, and the permitting map. On our brine projects that is us and our technology partner, and the same team carries the work through procurement, construction, and commissioning. On other reuse projects our role is the permitting side: the water balance and the file the regulator sees.
Vendors supply the systems and package them as solutions. Good vendors have reference plants on similar wastewater, publish specific performance data, and will let you contact their references. New systems without operating references are a risk the owner carries.
The regulator approves the result. The agencies want to see the whole water balance, the treatment for each reuse application, the residual effluent, and the monitoring that proves it. Early contact with the agency, with the water management plan in hand, shortens the review and often changes the design for the better.
Owners sometimes bring in the engineers after a vendor has quoted. The order should be the other way round: the specification is set first, the equipment is bought against it, and the regulator sees a coherent file. Contact us before the vendors do, and the project usually costs less.
What a reuse project looks like
Our approach on industrial water reuse follows the same sequence as our brine and ZLD work, and the treatment technologies overlap.
Get the numbers. Every wastewater stream, its flow, and its quality, from sampling rather than assumption.
Confirm what happens today. Where each stream goes now, what the permits say, and what headroom exists.
Match streams to uses. The lowest-quality use that can take each stream, and the treatment that closes the gap.
Map the approvals. Which permits get easier, which get harder, and what the residual outflow will look like.
Select technology you can go and see. Treatment systems with reference plants, not pilots.
Sequence the work. Readiness reviews before commissioning, and a plan for the upset case when treatment is down and reuse stops.
What industrial water reuse costs, and what it saves
We do not publish project cost figures, but the shape of the numbers is consistent from site to site, whichever solutions are chosen.
On the cost side: the collection piping and tanks to bring wastewater streams to one place, the softening and membrane systems sized for the reuse rate, the polishing for any boiler-grade duty, the concentrate handling, and the instruments and data systems that prove the reuse rate. Energy for membranes is modest compared with evaporation; chemicals for softening and cleaning are a steady operating line; membrane replacement is a periodic one.
On the savings side: intake water no longer bought or pumped, effluent no longer treated or charged for, heat recovered from warm blowdown, and, harder to price but often decisive, the permit margin that reuse buys at renewal. In water-stressed regions add the value of a supply that does not depend on a well or a contract that may not be renewed.
The payback varies with water prices and effluent charges, which differ enormously between regions. Where water is cheap and effluent limits are loose, reuse is a long payback. Where water is scarce or effluent limits are tight, it is often the cheapest compliance option available, and the plant that has already done it holds a stronger position with the environmental agency than the one that has not. Reuse rates also tend to rise over time as operators learn which wastewater streams can be pushed further, so the first year’s figure is rarely the final one.
New systems and retrofits
Most industrial water reuse is retrofitted onto plants that were designed to use water once. That shapes the project and the solutions that fit it. Space is tight, the existing wastewater collection was designed for disposal rather than reuse, and streams that should be kept separate were combined years ago. A retrofit usually starts by separating the wastewater streams again, so that clean streams can be reused with little treatment and dirty ones get the treatment they need.
New plants have an easier time. A new facility designed for reuse from the start segregates wastewater at source, cascades water from clean uses to dirty ones, sizes the cooling and boiler systems for reused water, and leaves room for the treatment technologies and for a later step toward ZLD if the regulator moves that way. The new plant’s water balance is a design document rather than a forensic one. Where an owner is building new, we push for the reuse plan to be part of the process design, not a package added after the process is fixed.
Either way, the wastewater treatment plant that serves reuse is usually modular and can be expanded. Starting with the largest, cleanest wastewater stream and adding others as the data comes in is a sound way to build a reuse program without over-investing on day one.
Resources worth knowing
The EPA’s water reuse program publishes resources for industrial applications, including case studies, state regulation summaries, and technical guidance on reuse technologies, and it is the first place to look for the definitions a US regulator will use. State environmental agencies publish their own reuse rules and resources, and the level of detail varies widely. Industry associations in power, refining, food, and semiconductors publish reuse guidance specific to their wastewater. And the vendors’ own reference lists, checked directly, remain one of the most useful resources of all.
We keep current with these resources so that a reuse plan uses the definitions and the data the reviewing agency expects, in the United States and worldwide.
Mistakes we see in industrial water reuse
Purifying to the wrong quality. Boiler-grade water sent to a cooling tower, or cooling-grade water sent to a boiler.
Ignoring the concentrate. Reuse was planned as a supply project and nobody checked what the smaller, stronger effluent would do to the permit.
Skipping softening. The membranes scaled at 60 percent recovery and the reuse rate never reached the design figure.
No water balance. Streams nobody measured turned out to be the largest, and the design was sized on the wrong ones.
Forgetting the upset case. When the reuse plant is down, the cooling towers still need make-up, and the intake permit did not allow for it.
Treating reuse as a bolt-on. The best reuse projects change how the plant uses water in the first place, cascading water from high-quality uses to low-quality ones before any treatment at all.
Frequently asked questions
What percentage of industrial water can be reused?
It depends on the streams and the uses. Facilities with large cooling loads routinely reuse 50 to 80 percent of their wastewater as cooling make-up. Facilities that add membrane technologies and go toward minimal liquid discharge reach 90 to 98 percent. Zero liquid discharge recovers effectively all of it, at a much higher energy cost.
Is treated municipal wastewater safe for industrial reuse?
Yes, with the right treatment on the receiving side. Power stations and refineries have used reclaimed municipal water for cooling for decades. The variability of the supply is the design challenge, not the safety.
Does water reuse need a permit?
Onsite reuse usually changes existing permits rather than needing a new one, but the residual effluent has to be re-evaluated, and some states regulate reuse quality directly. Where reclaimed municipal water is brought in, or where the reuse involves irrigation or human contact, specific approvals apply.
What is the difference between water reuse and water recycling?
In practice, recycling usually means returning water to the same use with little treatment, and reuse means treating wastewater for a different use. Regulators use the terms loosely, so describe each stream by source, treatment, and destination rather than by label.
Can wastewater with high salinity be reused?
Yes, but the salinity has to go somewhere. Membranes separate the water from the salts, and the salts leave in a concentrate. High-salinity wastewater is where reuse meets brine management, and the concentrate route decides how far reuse can go.
Where should a plant start with reuse?
With the largest, cleanest wastewater stream it has, which at most sites is tower blowdown, and with a water balance that shows where it goes now and which systems it passes through. The first loop pays for the meters and the sampling that make the second loop possible.
How is reuse water quality monitored?
Continuous conductivity and flow on the reuse line, periodic sampling for the parameters that matter to the use, and a record the regulator can inspect. Cooling systems are watched for scaling and corrosion; boilers for silica and conductivity.
In short
Industrial water reuse is a set of treatment solutions aimed at a use rather than at a river. Match each stream to the lowest-quality use that can take it, treat only as far as that use needs, and check what the smaller, stronger effluent does to the permit. Start with the water balance. It is the plan, the permit file, the system specification, and the business case in one document.
If you are being asked to cut intake, cut effluent, or show a reuse plan at your next permit renewal, send us your water balance, or let us build it. Call (470) 714-8564 or request a consultation. Our zero liquid discharge page explains where reuse ends and ZLD begins.
Talk to us about your wastewater
Send us the analysis, the flows, and a description of every stream that leaves the site, and we will tell you whether zero liquid discharge is required, what the regulator will ask, and how long it will take.