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Zero Liquid Discharge (ZLD) Systems

Every drop recovered, only salt leaves the plant — membrane concentration, evaporation and crystallisation engineered for the lowest life-cycle cost.

What zero liquid discharge means

A zero liquid discharge system treats industrial effluent so that no liquid waste leaves the site: water is recovered for reuse and dissolved salts are converted to a solid that can be sold, reused or landfilled. ZLD is mandated for many textile, dyeing, tannery, distillery, pharmaceutical and chemical units in India where no receiving water body or CETP is available, and is adopted voluntarily where fresh water is scarce or expensive.

ZLD is expensive if designed badly and manageable if designed well. The whole game is minimising the volume that reaches the evaporator — every cubic metre concentrated by membranes instead of steam saves money for the life of the plant. Segregating streams, recovering salts of value and choosing the right evaporator type decide whether a ZLD plant is a burden or an asset.

KK Enviro Engineers designs and builds complete ZLD trains — from pre-treatment through high-recovery RO, evaporation, crystallisation and salt handling — and retrofits evaporators onto existing ETPs.

Stages of a ZLD train

Process flow — typical sequence
Streamsegregation andpre-treatment01Biological andtertiarytreatment02Primary RO03High-recoverybrineconcentration04Evaporation05Crystallisationand saltrecovery06Condensaterecovery07Salt and residuehandling08
  1. Stream segregation and pre-treatmentHigh-TDS and low-TDS streams kept apart; oil, colour, hardness and silica removed so membranes and evaporators stay clean.
  2. Biological and tertiary treatmentConventional ETP stages bring COD and TSS down before membranes.
  3. Primary RORecovers 70–80 % as permeate for reuse in process, cooling or boiler make-up.
  4. High-recovery brine concentrationSecond-stage high-pressure RO, disc-tube RO or forward osmosis pushes recovery to 90–95 %, shrinking the evaporator to a fraction of its size.
  5. Evaporation — MEE or MVRMultiple-effect (steam) or mechanical-vapour-recompression (electric) falling-film or forced-circulation evaporators concentrate brine to near saturation.
  6. Crystallisation and salt recoveryForced-circulation crystalliser or ATFD (agitated thin-film dryer) produces dry salt; sodium sulphate or chloride recovered for reuse where quality permits.
  7. Condensate recoveryEvaporator condensate polished and returned as high-quality process water.
  8. Salt and residue handlingBagging, storage and disposal to authorised TSDF, or sale as by-product.

Technologies we select from

High-pressure / DTRO

Brine concentration to 80,000–120,000 mg/L TDS before evaporation.

MEE (steam)

Multiple-effect evaporators where steam is available and cheap.

MVR (electric)

Mechanical vapour recompression — 30–50 kWh/m³, no steam boiler needed.

Forced-circulation crystalliser

For scaling salts and mixed brines at the tail end of the train.

ATFD

Agitated thin-film dryer to convert mother liquor to dry powder.

Forward osmosis

Low-fouling concentration for difficult, oily or high-organic brines.

Softening + silica removal

Lime-soda or ion exchange so evaporators do not scale.

Salt purification

Selective crystallisation to recover saleable sodium sulphate or NaCl.

Industries where ZLD applies

Textile dyeing and processing
Dye-bath and wash water with high TDS and colour; ZLD mandated across major Indian clusters; glauber salt recovery offsets cost.
Pharmaceutical and API
Solvent-laden, high-COD, high-TDS mother liquors; stripping and MEE with condensate reuse.
Chemicals, dyes and intermediates
Mixed inorganic salts, ammonia and refractory COD; segregation and salt-specific crystallisation.
Distilleries and breweries
Spent wash concentration by MEE followed by incineration or bio-composting.
Tanneries
Chloride-heavy soak liquor and chrome-bearing streams; salt recovery for reuse in soaking.
Power, refineries and steel
Cooling-tower blowdown, RO reject and coke-oven wastewater concentrated to solids.

How KK Enviro Engineers delivers a ZLD plant

Inlet characterisation and sampling plan → process selection and mass balance → PFD, P&ID, hydraulic and equipment sizing → civil and mechanical drawings → BOQ, vendor RFQs and procurement → erection supervision → commissioning, performance guarantee test and operator training → operation & maintenance. Delivered as a containerised or skid-mounted package for small and remote sites, or as a site-built turnkey plant for large capacities. Documentation to refinery-grade standards: datasheets, interlock lists, cause-and-effect matrices and O&M manuals your team can actually run the plant from.

Frequently asked questions

What does zero liquid discharge mean?

No liquid effluent leaves the site. Water is recovered for reuse by membranes and evaporation; dissolved salts are converted to a solid that is sold, reused or landfilled.

Which industries need ZLD?

Textile dyeing, tanneries, distilleries, pharmaceuticals and chemical units in India where no receiving water or CETP is available, and any industry where fresh water is scarce or expensive.

Why is ZLD so expensive to run?

Because evaporation is energy-intensive. The key to affordable ZLD is minimising the volume that reaches the evaporator — stream segregation, high-recovery RO and salt recovery. See our article on cutting ZLD OPEX.

MEE or MVR evaporator?

Multiple-effect (MEE) where steam is cheap or available as waste heat; mechanical vapour recompression (MVR) where only electricity is available — it needs no boiler and usually has lower life-cycle cost.

Facing a ZLD requirement?

Send your effluent analysis, flows per stream and utility availability — we reply with a recovery scheme, evaporator sizing and budget range within one working day.