Reuse, Recovery & Stormwater
Zero Liquid Discharge (ZLD) Companies
ZLD integrators combining membranes, evaporators, and crystallizers to eliminate liquid effluent and recover salts.
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Zero Liquid Discharge Systems: Evaporation, Crystallisation, and Brine Management Technologies
Zero liquid discharge (ZLD) systems treat industrial wastewater and concentrate streams to the point where no liquid effluent is discharged to environment, producing only solid waste (salt cake, crystals, or sludge) for disposal or reuse. ZLD is driven by water scarcity regulations (India Ministry of Environment, Forest and Climate Change ZLD mandate for textile, leather, pharmaceutical, and power sectors since 2016), zero-discharge environmental permits for high-TDS industrial effluents, and water recovery maximisation in water-stressed regions. ZLD technology train: high-recovery RO or brine concentrators (BC) concentrate wastewater TDS from 5,000 to 200,000+ mg/L; evaporators (mechanical vapour recompression, MVR, or multiple-effect evaporation, MEE) further concentrate to 25 to 35 percent solids; crystallisers (forced circulation, evaporative crystalliser) produce dry salt or crystal slurry. Applications: power plant flue gas desulphurisation (FGD) wastewater (high sulphate, chloride); coal mine drainage; textile dye wastewater (India, Bangladesh); pharmaceutical and chemical plant effluent; semiconductor and electronics manufacturing; offshore oil and gas produced water.
Brine concentrator technology: mechanical vapour recompression (MVR) evaporators are the most energy-efficient single-effect evaporation technology for ZLD applications. MVR principle: vapour generated from boiling brine is mechanically compressed (by centrifugal compressor or blower), raising its temperature and pressure, and then used as heating steam to evaporate more feed; closed loop reuses latent heat; SEC: 15 to 35 kWh per tonne of water evaporated (vs 500 to 700 kWh per tonne for single-effect steam evaporation). GEA, SUEZ, IDE Technologies, Aquatech International, Veolia WTS are leading MVR/MEE brine concentrator suppliers. Multiple effect evaporation (MEE): steam drives first effect, vapour from first effect drives second effect, etc.; for 3-effect MEE: steam consumption 0.33 to 0.35 kg steam per kg water evaporated (vs 1.0 for single-effect); useful where waste steam or heat is available. Brine concentrators typically operate at 90 to 98 percent recovery (produce 2 to 10 percent of feed volume as concentrated brine for crystalliser). Scaling control: antiscalant dosing (specialised formulations for high-TDS, high-temperature brine, e.g. Veolia Hydrex, King Lee Technologies); acid addition to prevent carbonate and hydroxide scaling; softening pretreatment to remove calcium before concentrating sulphate-rich brine (prevents gypsum scaling).
Crystallisation for ZLD final stage: evaporative crystallisation in forced circulation crystallisers precipitates dissolved salts as solid crystals. Process: concentrated brine from BC/evaporator fed to crystalliser vessel; steam or vapour heating evaporates remaining water; salt crystals grow on seed particles; crystal slurry withdrawn and separated by centrifuge (producing salt cake at 95 to 99 percent TS); salt cake may be NaCl (sodium chloride), Na2SO4 (sodium sulphate, Glauber's salt), or mixed salt depending on feed chemistry. NaCl crystal quality: pharmaceutical grade (USP, BP) requires less than 10 ppm heavy metals; food grade NaCl greater than 99 percent purity; industrial grade for road salt; mixed salts (from complex industrial effluent) typically require landfill disposal as non-hazardous or hazardous waste. ZLD economics: CAPEX USD 2 to 10 million/1,000 m3/day treated; OPEX USD 5 to 20 per m3 treated (energy dominant - MVR electricity cost USD 3 to 12 per m3); justified where: discharge permit requires ZLD; fresh water cost exceeds USD 2 to 5 per m3 (high water scarcity); regulatory fines for non-compliance exceed ZLD operating cost. Life cycle analysis shows ZLD reduces freshwater consumption by 95 to 99 percent vs conventional once-through discharge.
Frequently Asked Questions
What is zero liquid discharge (ZLD) and when is it required?
Zero liquid discharge (ZLD) is a wastewater management approach where all process liquid effluent is treated, recovered, and recirculated within the facility, with no liquid discharge to the environment. The only output is solid waste (salt, sludge) and recovered clean water for reuse. ZLD is required when: (1) Regulatory mandate: India's Central Pollution Control Board (CPCB) mandates ZLD for textile, tannery, pharmaceutical, and large paper mills since 2016; Rajasthan, Gujarat, and Tamil Nadu state governments enforce ZLD for industries in water-stressed areas; (2) Environmental permit conditions: some EU/UK environmental permits for high-TDS, toxic effluent (pharmaceutical, chemical) require ZLD or near-ZLD (less than 5 percent discharge); (3) Water scarcity: industries in arid regions (Middle East, western US, Australia) adopt ZLD to maximise water recovery; (4) Hazardous effluent: produced water from oil and gas wells may require ZLD where surface or groundwater disposal is prohibited; (5) Economics: where water is expensive (greater than USD 3 to 5 per m3) and wastewater can be fully recovered, ZLD may be cost-effective. ZLD is expensive (OPEX USD 5 to 20 per m3) and energy-intensive; it is a last resort where regulatory or water scarcity drivers justify the cost. Near-ZLD (greater than 95 percent recovery) is often more cost-effective.
What is the cost of a zero liquid discharge system?
ZLD system costs depend on feed volume, TDS, and salt chemistry: CAPEX: RO brine concentrator + MVR evaporator + crystalliser for 500 m3/day feed at 50,000 mg/L TDS: approximately USD 5 to 15 million (USD 10,000 to 30,000 per m3/day); smaller systems (100 m3/day): higher CAPEX per unit volume due to lack of scale economics (USD 20,000 to 50,000 per m3/day); larger systems (5,000 m3/day): lower unit CAPEX (USD 5,000 to 15,000 per m3/day). OPEX components: energy (dominant): MVR electricity 15 to 35 kWh/tonne water evaporated; at USD 0.10/kWh: USD 1.50 to 3.50 per m3 evaporated; for 90 percent recovery, processing 500 m3/day produces 450 m3 recovered water plus 50 m3 that goes to crystalliser; chemicals (antiscalants, acid): USD 0.50 to 2.00 per m3; labour and maintenance: USD 0.50 to 2.00 per m3; salt/solid waste disposal: USD 0.20 to 2.00 per tonne (road salt can be revenue-neutral; hazardous mixed salt disposal USD 50 to 200 per tonne); total OPEX: USD 5 to 20 per m3 treated. Financial justification: fresh water savings at USD 2 to 5 per m3 supply cost + ZLD water value = USD 2.00 to 5.00 per m3; OPEX exceeds savings for most applications; ZLD is justified by regulatory compliance, water scarcity severity, or brand/sustainability commitments.
How does a brine concentrator work in ZLD?
A brine concentrator (BC) in a ZLD system is typically a mechanical vapour recompression (MVR) or multiple-effect evaporation (MEE) unit that concentrates high-TDS wastewater (RO reject, blowdown) before final crystallisation. MVR brine concentrator operation: (1) Feed pretreatment: softening (lime/soda, IX) removes Ca2+ and Mg2+ to prevent CaCO3 and CaSO4 scaling on heat transfer surfaces; pH adjustment; deaeration to remove CO2; (2) Feed enters the evaporator vessel (forced circulation or falling film design); feed is heated in tube-and-shell heat exchanger by compressed vapour; (3) Feed partially flashes and evaporates in the vessel; vapour leaves overhead and is compressed by centrifugal compressor (GEA Wiegand, Sulzer, Pilling Turbines) at pressure ratio 1.1 to 1.3, raising condensing temperature by 5 to 15 degrees C; (4) Compressed vapour condenses inside heat exchanger tubes, releasing latent heat to evaporate more feed; condensate (clean water) recovered for reuse; (5) Concentrated brine (15 to 25 percent TDS) is withdrawn from circulation and sent to final crystalliser; (6) Crystal slurry from crystalliser is centrifuged to produce salt cake (95 to 99 percent TS); liquor returns to BC. Energy input: only compression work (10 to 25 kWh/tonne water evaporated); very efficient vs steam evaporation (500 to 700 kWh/tonne). Leading suppliers: IDE Technologies, GEA, SUEZ WTS, Veolia, Aquatech.
Can ZLD systems recover usable salt?
Yes, ZLD crystallisers can produce saleable salt if the feed wastewater chemistry produces a recoverable pure salt. Salt recovery scenarios: (1) NaCl (sodium chloride): from seawater desalination brine (37 to 50 g/L NaCl), coal mine drainage, or industrial sodium chloride-dominated effluent; crystalliser produces greater than 99 percent NaCl dry salt; potential markets: de-icing road salt (lower-grade, less than 97 percent), industrial process salt (chlor-alkali plants, less than 99 percent), water softener salt (less than 99.5 percent), food grade (less than 99.9 percent, USP specification); NaCl market price USD 30 to 80 per tonne; can partially offset ZLD OPEX; (2) Na2SO4 (sodium sulphate, Glauber's salt): from mining, textile, and chemical effluent high in sulphate; produces anhydrous Na2SO4 (less than 99 percent) used in glass manufacturing, detergent, and pulp; market price USD 50 to 150 per tonne; (3) Mixed salt (from complex industrial wastewater): mixture of NaCl, Na2SO4, NaNO3, and other salts; difficult to sell; typically requires landfill disposal as non-hazardous waste (if below RCRA/EU hazardous waste thresholds) or hazardous waste incineration. Salt revenue: at best partially offsets disposal costs; rarely generates significant positive revenue. For salt to be commercially viable: feed water must be predominantly one salt type; purity greater than 99 percent required for most markets; heavy metals and organic contamination must be below food-grade or industrial limits.
A specialty chemicals plant near Warrington generated 180 m3/day of high-TDS effluent (TDS 42,000 mg/L, predominantly sodium sulphate and sodium chloride) from its reaction process. An Environmental Permit tightening required virtual zero discharge of this brine stream; the previous practice of discharging 140 m3/day to estuary under a Marine Licence was terminated by the EA following WFD quality objective concerns.
A ZLD train was designed: feed went through a high-recovery BWRO (85 percent recovery) reducing volume to 27 m3/day of concentrate at 280,000 mg/L TDS. The RO concentrate entered a single-effect MVR evaporator (GEA NIRO-type), producing a 25 percent solids slurry. A forced-circulation crystalliser then produced a mixed NaCl/Na2SO4 salt cake at 96 percent DS, dewatered by a Flottweg centrifuge. The 27 m3/day of MVR condensate (TDS less than 10 mg/L) was returned to the process, and the 6 to 7 tonne/day salt cake was disposed of as non-hazardous solid waste at GBP 48 per tonne.
Zero liquid discharge to estuary achieved, resolving the EA enforcement notice. Water recovery 97.8 percent. Total OPEX GBP 42 per m3 treated (energy dominant at GBP 28 per m3 for MVR electricity at GBP 0.22 per kWh). The GBP 2.4 million capital cost was fully justified by the alternative of GBP 6 million in receptor monitoring, legal costs, and potential marine licence revocation fine of up to GBP 250,000 under EPR 2016.
Questions to Ask Shortlisted Providers
- 1
What is the specific energy consumption of the brine concentrator and crystalliser at our design TDS and flow, and how was this figure validated?
MVR specific energy varies from 15 to 35 kWh per tonne water evaporated; at GBP 0.25 per kWh, a 10 kWh/tonne difference costs GBP 60,000 to 120,000 per year for a 200 m3/day system; independently verified energy data is essential.
- 2
What scaling control strategy is used for the evaporator heat transfer surfaces, and what is the maximum expected antiscalant dosing rate?
Calcium carbonate, calcium sulphate (gypsum), and silica are the principal scalants in brine concentrators; inadequate scale control leads to heat transfer fouling, reduced throughput, and expensive chemical cleaning shutdowns.
- 3
Has the crystalliser been operated on feed water with similar chemical composition to ours, and can you provide reference sites?
Mixed salt streams behave differently from single-salt systems; crystal habit, filterability, and centrifuge dewatering performance are all affected by minor feed constituents that only appear at full scale.
- 4
What is the guaranteed water recovery rate, and what are the liquidated damages provisions if it is not achieved?
ZLD contracts should specify minimum water recovery (e.g. 95 percent) with financial remedy for under-performance; ZLD economics are entirely dependent on maximising water recovered and minimising solid waste volume.
- 5
How does the system handle feed variation (TDS spikes, pH excursions, organic contamination), and what pretreatment conditioning is required?
Feed variation is the most common cause of ZLD operational failure; clarifying the pretreatment requirements and the system's operating envelope prevents costly field modifications after commissioning.
What Drives Cost in This Category
ZLD CAPEX scales approximately with feed volume to the power 0.7; a 100 m3/day system at 50,000 mg/L TDS costs approximately USD 4 to 8 million; doubling volume to 200 m3/day increases CAPEX by approximately 60 to 70 percent, not 100 percent.
MVR evaporation consumes 15 to 35 kWh per tonne water evaporated; at UK industrial electricity prices of GBP 0.15 to 0.28 per kWh, energy represents 50 to 70 percent of ZLD OPEX; on-site renewable generation or grid connection upgrades materially alter the business case.
Pure NaCl salt cake (greater than 99 percent) can achieve GBP 30 to 60 per tonne as de-icing or water softener salt; mixed or contaminated salt costs GBP 40 to 200 per tonne to dispose at landfill or incineration; the difference is GBP 70 to 260 per tonne, which is material for systems producing 5 to 30 tonne/day.
High-strength feeds with calcium, silica, or organic fouling potential require softening, pH adjustment, and antiscalant dosing before the evaporator; these pretreatment systems add GBP 200,000 to 800,000 to CAPEX and GBP 2 to 8 per m3 to OPEX.
Key Regulations & Standards
EPR 2016 (SI 2016/1154): industrial discharges to controlled waters or sewer require an Environmental Permit from the EA; tightening permit conditions or revocation of Marine Licence for brine discharge are the primary regulatory drivers for ZLD adoption in the UK.
Marine and Coastal Access Act 2009, Part 4: discharging to tidal or coastal waters requires a Marine Licence from the Marine Management Organisation (MMO); brine discharge from industrial ZLD failure scenarios can trigger licence revocation and penalties up to GBP 500,000.
UK-retained Water Framework Directive requires that industrial discharges do not prevent water bodies from achieving or maintaining good chemical and ecological status; EA's river basin management plans impose discharge reduction obligations on high-TDS industrial dischargers near sensitive watercourses.
Mixed salt crystalliser outputs are classified under EWC codes (typically 06 09 02 for non-hazardous process salt, or 06 09 99); if the salt contains listed hazardous substances above threshold concentrations, it is classified as hazardous waste under the Hazardous Waste (England and Wales) Regulations 2005, requiring licensed carrier and consignment note.
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