The short answer. First decide what kind of help you need: independent advice, an engineered design, equipment, or an operated service. Each type of provider earns money differently, and that shapes what it recommends. Then compare proposals on scope, the accuracy class of any cost estimate, and how they calculate return on investment. A credible ROI for zero liquid discharge (ZLD) is always measured against the next-best option, usually minimum liquid discharge (MLD) or keeping a managed discharge, not against doing nothing.
Four kinds of ZLD provider
| Provider type | What they sell | Accountable for | Watch for |
|---|---|---|---|
| Independent consultant | Advice: water balances, option studies, cost ranges, vendor evaluation | The quality of the analysis and recommendation | Whether they take commissions from suppliers or later bid to build what they recommend |
| Engineering firm or EPC contractor | Design, procurement and construction | Delivering the specified plant on time and budget | The study may lean toward a scope they can build |
| Technology vendor | Equipment and process packages, often with a performance guarantee | Their equipment meeting its guaranteed performance | Free studies that only consider their own technology |
| Operator or service provider | Build-own-operate contracts, mobile units, O&M | Running the plant to contract | Long contracts that are hard to exit if needs change |
None of these is wrong. The mistake is asking one type of provider to do another’s job, for example asking a vendor whether you need their equipment.
How to compare ZLD consultants on cost
For advisory and study work, a good proposal states:
- The scope by phase, such as data review, site water balance, option screening and pre-feasibility, with a fixed fee per phase or a clear time-based estimate
- The deliverables: mass balances, option comparison, cost ranges, risks and recommended next steps
- The accuracy of any cost estimate it will produce, and the assumptions behind it
- Who collects the data, including sampling and lab analysis, and who pays for it
- Any financial relationship with suppliers
On estimate accuracy, the process industries use the AACE International classification (Recommended Practice 18R-97). At concept stage (Class 5), the expected range can be as wide as about -50% to +100%. At feasibility stage (Class 4) the typical range narrows to -15% to -30% on the low side and +20% to +50% on the high side. A precise single CAPEX number at concept stage is a warning sign, not a strength.
How to judge ZLD ROI honestly
ZLD rarely pays back through savings alone. Its value usually comes from avoided discharge costs, water you no longer buy, production that would otherwise be constrained, and compliance risk removed. Research on process plants points the same way: whether ZLD is economic depends on the relationship between the cost of regenerating water, the price of fresh water, and the allowed discharge concentration.
So the right question is not “what does ZLD save?” but “what does ZLD save compared with the realistic alternative?” The example below uses hypothetical figures, except for the 2026 Dutch levy range of roughly EUR 67 to EUR 115 per pollution unit.
A Dutch site discharges 35,000 m³ a year of saline effluent. A ZLD plant would cost EUR 4 million to build, EUR 7.00 per m³ to run, and produce 300 tonnes of salt a year at EUR 250 per tonne to dispose of. It would recover 30,000 m³ of water worth EUR 1.50 per m³.
| Scenario 1: discharge stays available | Scenario 2: discharge route closes | |
|---|---|---|
| Avoided cost | Levy of about EUR 120,000 a year (about 1,300 pollution units at EUR 92) | Haulage at EUR 40 per m³, so EUR 1.4 million a year |
| Water no longer bought | EUR 45,000 | EUR 45,000 |
| ZLD operating cost including solids | EUR 320,000 | EUR 320,000 |
| Net effect per year | Loses EUR 155,000 | Saves about EUR 1.1 million |
| Simple payback on EUR 4 million | Never | About 3.6 years |
The plant is identical. Only the counterfactual changes. In scenario 1, the site should test MLD or source reduction before ZLD. In scenario 2, ZLD may be the clear choice. Any provider who shows you an ROI without stating the counterfactual has not done the analysis.
Our ZLD cost guide covers the cost drivers, and the MLD vs ZLD Decision Screener helps you test which endpoint deserves a full study. For the trade-offs in more depth, see minimum vs zero liquid discharge.
Questions to ask any provider
- Do you sell, represent or receive commissions on any equipment you might recommend?
- Which projects have you worked on with water chemistry like ours, and can we speak to the client?
- What will we receive at the end of each phase, and in what form?
- What accuracy class will your cost estimates be, and what assumptions sit behind them?
- Against which baseline will you calculate ROI?
- How will you handle the solids and any purge stream in your options?
- If we go ahead, will you also bid to design or build the plant?
Red flags
- An ROI that compares ZLD with doing nothing
- A study that only evaluates one technology
- Recovered salt revenue counted without a named buyer
- A single CAPEX number at concept stage
- No mention of solids classification or disposal cost
Where an independent adviser fits
An independent consultant is most useful before money is committed: deciding whether ZLD, MLD or a managed discharge is right, defining the design basis, and comparing vendor proposals on equal terms. Brine Consulting sells no treatment equipment and does not build plants. When a project moves to detailed design and construction, you will need an engineering firm or supplier, and we can help you specify and evaluate that work.
“…a great business acumen which makes the difference.”
Castor Criado Madrigal, Sr. Director, Global Sales, in a testimonial published on the Brine Consulting website.
Request a consultation to discuss your project, or see how to evaluate ZLD vendor proposals.
Frequently asked questions
Is an independent study worth paying for if a vendor offers one free?
Usually, yes. A vendor study tells you how that vendor would solve the problem. An independent study tells you which approach fits, including options the vendor does not sell. For a multi-million euro decision, the second question usually matters more.
How accurate should a cost estimate be at feasibility stage?
Under the AACE classification, a feasibility-stage (Class 4) estimate typically carries a range of -15% to -30% on the low side and +20% to +50% on the high side. Ask every provider to state the class of their estimate.
Can ZLD pay for itself?
Sometimes, mainly when discharge is closed, very expensive, or limiting production. Where a discharge route remains available and affordable, MLD or source reduction usually gives a better return.
What is the difference between a consultant and an EPC contractor?
A consultant advises on what to do and how to judge it. An EPC contractor designs, buys and builds the chosen solution and is accountable for delivering it.
Sources
- AACE International Recommended Practice 18R-97, as summarised by EPCLand and in a WPWMA concept evaluation
- Koppol, Bagajewicz, Dericks and Savelski: On zero water discharge solutions in the process industry, 2004
- Brine Consulting: Dutch wastewater levy calculator, including 2026 tariffs
- Brine Consulting: ZLD guide, chapter 13
Written by the Brine Consulting advisory team. The Brine Consulting advisory practice includes Osis G. Kalache, P.Eng., a senior wastewater process engineer with more than 17 years in industrial wastewater treatment and process optimization, and Cesar J.M. Chu Ortega, a water-tech strategist with expertise in water reuse, zero liquid discharge and industrial wastewater treatment. Meet our experts.