Zero Liquid Discharge Rules: Who Must Comply?

There is no single law that puts every Indian factory on zero liquid discharge. ZLD is imposed unit by unit and sector by sector: through CPCB and State Board directions, through the conditions in a unit's consent to establish and consent to operate, through environmental clearance conditions, and sometimes through tribunal orders for a particular area. It has most often been required for highly polluting sectors such as textile dyeing, tanneries and molasses-based distilleries, and for some chemical and pharmaceutical units, but whether your unit is covered depends on your consent and your state. If your consent says ZLD, any liquid effluent leaving the premises is a breach, however clean it is.

This guide explains what zero liquid discharge means in practice, where the obligation comes from, which sectors usually face it, how to find out whether it applies to you, how boards verify it, and what can be done if a ZLD condition is unworkable. A short section covers how residents can test a unit's ZLD claim.

For the wider legal picture on factory effluent, see our page on industrial effluent and water pollution remedies.

The essentials

Who must comply with zero liquid discharge?

Any unit whose consent to establish, consent to operate or environmental clearance contains a ZLD condition, and any unit covered by a CPCB or State Board direction requiring ZLD for its sector or area. That is the legal answer, and it matters because people often look for a single notification listing ZLD industries and do not find one. The obligation sits in the unit's own papers and in the directions that fed into them.

In practice, ZLD has been required most often for sectors whose effluent is high in dissolved salts, colour or toxic content and is hard to treat to discharge standards: textile dyeing and processing, tanneries, molasses-based distilleries, and some bulk drug, pesticide and dye intermediate units. Boards have also used ZLD for units in clusters where the receiving river or groundwater is already badly affected, or where there is simply no suitable place to discharge. CEPI assessments, which identify critically polluted industrial clusters, have sometimes been the backdrop for such conditions.

It also varies by state. A dyeing unit in one state may be on ZLD through a state policy for its cluster, while a similar unit elsewhere may be allowed to discharge treated effluent to a CETP that itself discharges within standards. So the answer to 'is my industry on ZLD?' is always 'read your consent, then check your board's directions for your sector and area'.

What zero liquid discharge actually requires

ZLD means that no liquid effluent leaves the premises. Wastewater is treated, most of it is recovered and reused in the process, and what remains is evaporated so that only solids are left. The solids, which are mostly salts and sludge, are then stored and disposed of as solid or hazardous waste. Water still leaves the site as vapour; what may not leave is liquid.

A typical ZLD system has three layers. First, conventional treatment: equalisation, neutralisation, biological treatment and filtration, much like an ordinary ETP. Second, recovery, usually reverse osmosis, which produces clean permeate for reuse and a concentrated reject. Third, the reject goes to a multiple effect evaporator and often a dryer, producing condensate (which is reused) and salt or sludge. The evaporator is the expensive part to run, because it needs steam or a lot of power.

Whether ZLD covers every stream of water depends on how the condition is written. Domestic sewage from toilets and canteens, cooling tower blowdown, boiler blowdown and stormwater are sometimes treated differently from process effluent. Some consents allow treated domestic sewage to be used for gardening on site; some say nothing, which leaves room for dispute. When Advocate B.K. Singh reads a ZLD consent for a unit, he checks first which streams the condition covers, because units are often found in breach over a cooling tower drain they never thought of as effluent.

Where a ZLD obligation can come from

The timing point is important. A consent condition is easiest to contest when it is first imposed, within the 30-day appeal window. Units that accept a ZLD condition without question and challenge it years later, after being caught in breach, rarely get anywhere.

Sectors where ZLD comes up most

This table is a general guide only. The actual position depends on your consent, your state and the date of the relevant direction.

Our guides on textile dyeing unit pollution, tannery chromium contamination and distillery and sugar mill effluent cover those sectors in more depth.

How to find out whether ZLD applies to your unit

Do this before buying a unit, before expansion, and whenever your consent is renewed.

How boards check that a unit is really ZLD

By looking for an outlet and by checking the arithmetic. Inspectors walk the boundary and nearby drains for any pipe, channel or wet patch. They look at whether the evaporator is actually running, which shows up in the boiler's fuel consumption or the electricity drawn. And they do a water balance: how much fresh water the unit draws from borewells or supply, how much goes into products and evaporation, how much is recycled, and how much salt and sludge comes out. If the numbers do not close, the board assumes the difference went out as liquid.

Flow meters at the inlet of the ETP, the RO, the evaporator and the recycle line are the backbone of this check. Many ZLD consents require them, and some sectors have to install online monitoring linked to the board. Salt is the other tell. An evaporator handling a given volume of reject should produce a predictable quantity of salt. A unit claiming full ZLD but producing very little salt, or storing none, has some explaining to do.

Boards also sample groundwater from wells and handpumps around ZLD units, because RO reject stored in unlined pits or lagoons tends to seep down. A ZLD unit with a salty, coloured handpump next door is under suspicion whatever its paperwork says.

Where ZLD goes wrong in practice

The commonest failure is cost. Evaporators are expensive to run, so some units run the RO, store the reject in a pond and run the evaporator only occasionally, or not at all. The reject accumulates, the pond overflows in the monsoon, or a tanker quietly takes it away. Another is undersizing: a ZLD system designed for one production level, never upgraded as output grew.

Salt disposal is the next weak point. Mixed salts from evaporators are often hazardous waste and need authorisation, storage within limits, and transport under a manifest to an authorised facility. Units without a proper disposal route stockpile salt in sheds or open yards, where rain dissolves it back into the ground. Our guide on hazardous waste manifests and transport explains the rules that apply.

Last, there is ZLD on paper: a unit that has the equipment, shows it to inspectors, and discharges anyway at night or into a borewell. These cases usually come to light through residents' complaints and groundwater samples, not through scheduled inspections.

What happens if a ZLD unit discharges effluent?

It is in breach of its consent, and the quality of the discharge does not save it. A unit permitted to discharge within standards can argue that its effluent met those standards; a ZLD unit cannot, because its permission is zero. The board can issue a show-cause notice and direct closure and disconnection of electricity and water under section 33A of the Water Act, and levy environmental compensation using the CPCB method, which counts the days of violation.

If the discharge has affected groundwater or a water body, the cost goes beyond the compensation the board assesses. Affected residents can approach the NGT under section 15 within 5 years for relief, compensation and restoration, and the tribunal applies the polluter pays principle. Cleaning up contaminated groundwater is slow and expensive, which is why these orders can be heavy.

A unit that discovers a ZLD failure itself, for example an evaporator breakdown, should treat it like any other treatment failure: stop the effluent, store it, inform the board, repair and document. Our guide on what happens when an ETP stops working sets out those steps.

Can a ZLD condition be relaxed or removed?

Sometimes, but it is hard, and the timing matters. A condition in a consent order can be appealed to the state appellate authority under section 28 of the Water Act within 30 days, and from there to the NGT under section 16. An EC condition can be challenged before the NGT within 30 days of communication. After those windows, the route is an application to the board or the ministry to amend the condition, supported by a technical case.

A technical case means more than 'ZLD is expensive'. It means showing that the unit's effluent can be treated to discharge standards, that there is a suitable sewer, CETP or receiving body, that the receiving body is not already overloaded, and that the area is not one where a ZLD direction applies to the whole cluster. Boards apply the precautionary principle, and in critically polluted areas relaxation is unlikely.

A more realistic option for small units is often a shared solution. A CETP built for ZLD can make the economics work where an individual evaporator cannot. Our guide on CETP compliance explains the obligations of members and operators. For appeals against consent conditions, see our page on the pollution appellate authority.

Planning for ZLD when setting up, expanding or buying a unit

The cheapest time to deal with ZLD is before the first brick. At the consent to establish stage, find out from the board whether your sector and location attract ZLD, and design for it: a treatability study of your expected effluent, an evaporator sized with headroom for growth, storage for salts, and a disposal tie-up with an authorised facility. The difference between a CTE and a CTO matters here, because a design weakness that slips through at CTE tends to surface at the CTO inspection, when the plant is already built. Our guide on CTE and CTO explains the two stages.

Expansion is the second danger point. Adding production without enlarging the ZLD system means the evaporator falls behind and reject piles up. An expansion that increases effluent usually needs fresh consent, and the board will look at whether your ZLD capacity has kept pace. See our page on consent for expansion.

If you are buying an existing unit, check its ZLD record as part of due diligence: inspection reports, notices, evaporator running hours, salt disposal records and groundwater results around the site. Contamination left by an earlier owner's ZLD failures can become the new owner's problem under the polluter pays principle, depending on how the deal is structured.

How residents can test a unit's ZLD claim

Start with an RTI to the State Board for the unit's consent orders and recent inspection reports. If the consent says ZLD, then any pipe, tanker or wet patch carrying effluent from the unit is a breach, and you do not need to prove the effluent was dirty. That makes your complaint much simpler: photographs of the discharge point, dates and times, and a request to inspect and check the water balance and evaporator operation.

Watch for the signs of ZLD on paper: a lagoon or pond inside the unit that is always full, tankers leaving regularly, a handpump nearby that has turned salty or coloured, white salt crust on nearby land, and an evaporator chimney that seldom shows steam. Ask the board, in your complaint, to sample groundwater from named handpumps and wells. Our guide on complaining about untreated effluent covers how to word it.

Mistakes units make with ZLD

Assuming ZLD means process effluent only, and letting blowdown, washing water or sewage go out. Running the evaporator only before inspections, which the fuel and power records reveal. Storing RO reject in unlined pits, which turns a consent breach into groundwater contamination and a far bigger claim. Treating salt as ordinary waste and selling or dumping it.

On the paperwork side, the common mistake is not keeping a daily water balance. When a complaint comes in, a unit that can show meter readings for every stage, evaporator hours and salt dispatches under manifests can answer it in a page. A unit that cannot is left arguing that it 'always runs the system', which convinces nobody. And units often miss the 30-day window to appeal a new or tightened ZLD condition, then spend years asking for relaxation that would have been easier to argue at the start.

ZLD compliance checks for units