SOLUTIONS / CIRCULAR ECONOMY AND PROCESS DESIGN
Process design for water reuse
and resource recovery.
We find out where every litre of water and every kilogram of salt in your plant comes from and goes to, then design the cheapest way to reuse the water, recover what has value and stay compliant. It is the step that makes ETP, RO and ZLD investments smaller and pay back faster.
In short
What process design for circularity means.
Process design for water reuse is the engineering study that maps every water and waste stream in a plant, measures its flow and quality, and works out the lowest-cost way to reuse water and recover materials before anything is treated or thrown away. It works by combining a water audit, a mass balance of water, salts and organic load, and a water pinch analysis that matches clean-enough streams to uses that can accept them. The result is a reuse plan, right-sized ETP, RO or ZLD equipment and, where it pays, recovery of salt, biogas, metals or heat. In India the same data supports CGWA water audits, consent renewals and environmental clearance under the EIA Notification, 2006.
- 30–55%
- Freshwater reduction we target through water pinch reuse cascades
- >99%
- Purity target for sodium sulphate from fractional crystallisation
- 10–14weeks
- Typical full engagement, from site data to regulatory submission
- NABL
- Accredited laboratory that tests every stream we model
The basics
Why design the process before you buy the plant?
Most factories size treatment plants on the total effluent flow. That means clean rinse water, cooling tower blowdown, salty process liquor and toilet waste are all mixed together and then treated to the standard of the worst stream. You pay to clean water that was nearly clean, and you pay again to evaporate salt that could have been kept separate.
Water, salts and heat that leave a plant as waste were all bought as inputs. Industrial water demand in India is expected to rise sharply by 2050, groundwater permits are tighter, and tanker water is expensive. Designing the process around recovery turns a cost into savings and sometimes into revenue.
What is a water audit?
A water audit measures how much water enters the site, where it is used, and where it leaves: through effluent, evaporation, product, leaks or losses. It produces a water balance: a diagram where every input equals every output. A plain audit usually finds savings of around 10 to 15% from leaks, overflows and wasteful practice.
What is water pinch analysis?
Water pinch analysis goes further. It lists every water source (with its quality, for example TDS or COD) and every water demand (with the worst quality it can accept), then works out the minimum fresh water the site needs if each source is sent to the right demand. Typical moves: final rinse water reused as first rinse; RO permeate to boiler feed; cooling tower blowdown to floor washing; condensate back to the boiler. Pinch analysis typically targets 30 to 55% less fresh water, often with little or no new treatment equipment.
What is a mass balance?
A mass balance tracks not just water but what it carries: salts (TDS, chloride, sulphate, hardness, silica), organic load (COD, BOD) and heat. It tells you how salt concentrates as water is reused, where scaling will start, and how big the RO, evaporator and dryer must be. Without it, ZLD plants are routinely mis-sized.
Our method
Four stages from linear waste to a closed loop.
We pair water pinch analysis with a full mass balance, then decide what is worth recovering and prepare the documents regulators expect.
- 1
Site data and stream characterisation
We sample every process stream and measure flows, TDS profiles, COD loads, temperature and thermal energy data. Our laboratory tests each sample. Weeks 1 to 2.
- 2
Water pinch and mass balance
Graphical pinch analysis finds the minimum achievable freshwater intake and produces a direct water cascade blueprint. A hydraulic and ionic mass balance, built with CAD and ASPEN simulation, gives the process flow diagram (PFD), scaling indices (LSI and Stiff-Davis) and the sizing data for capital and operating cost. Weeks 3 to 4.
- 3
Resource and salt recovery feasibility
Solubility phase diagram analysis, crystalliser configuration, crystal purity targets and identification of buyers or internal uses for recovered salt, biogas, metals or heat. Weeks 5 to 6.
- 4
ZLD roadmap, EIA and clearance
Technology selection and treatability study for a phased ZLD plan, EIA baseline studies, detailed project report (DPR), and submission to the SPCB or MoEF&CC. Weeks 7 to 14.
| Data | Why we need it |
|---|---|
| Water meter readings for each process unit (m³/day or m³/h) | To build the water balance; we install temporary meters where none exist |
| TDS, COD, BOD, TSS, pH and temperature of each stream | To match sources to demands and model salt build-up |
| Quality limits for each water use | The worst water each use can accept defines the reuse options |
| Plant layout or P&ID showing water connections | Reuse only works if pipes can reach |
| ETP and STP outlet reports for the last 12 months | To see how the existing plant really performs |
We measure your flows and test every stream in our NABL-accredited laboratory, then show you where the quickest water and cost savings are.
Resource recovery
What can be recovered from wastewater?
Circular economy in wastewater means treating effluent as a mix of water and raw materials. These are the recovery routes we assess most often.
| Resource | Where it comes from | How it is recovered | Best for | Watch-outs |
|---|---|---|---|---|
| Water | Rinses, blowdown, treated effluent, condensate | Direct reuse, UF and RO, evaporator condensate | Every plant, especially where tanker or groundwater cost is high | Salt builds up as you reuse; needs a mass balance |
| Salts (sodium sulphate, sodium chloride) | Dye baths, chemical processes, RO reject | Nanofiltration, evaporation, fractional crystallisation | Textile dyeing, chemical manufacturing | Organics spoil purity; needs a buyer or internal use |
| Biogas | High-COD organic effluent and sludge | Anaerobic digesters (UASB and others) | Dairy, food, distillery, sugar | Needs steady load and temperature; H₂S must be scrubbed |
| Sludge as fuel or compost | Biological and food-processing sludge | Dewatering, drying, co-processing or composting | Non-hazardous organic sludge | Hazardous sludge needs authorisation; heavy metals rule out land use |
| Metals (chromium, nickel, copper, zinc) | Electroplating, metal finishing | Precipitation, ion exchange, electro-recovery | Plating and chemical units | Segregation at source is essential |
| Heat | Hot effluent, condensate, chiller and boiler losses | Heat exchangers, waste-heat drying and evaporation | Pharma, food, textiles | Fouling of exchangers; heat must match a nearby use |
| Fats, fibre and whey | Dairy, food and paper effluent | Fat traps, DAF, save-alls, membrane concentration | Dairy, pulp and paper | Product quality and hygiene rules |
Related research solutions: heavy metal recovery, dairy whey water recovery, waste-heat drying and waste-to-energy and biogas.
Salt recovery
Salt recovery from effluent: from brine to saleable salt.
Textile dyeing and chemical manufacturing produce brines rich in sodium sulphate (Na₂SO₄) and sodium chloride (NaCl). In a ZLD plant, these usually end up as mixed salt that has to be stored and sent for disposal. Fractional crystallisation separates them instead, so that sodium sulphate of more than 99% purity can go back to the dye house or be sold as an industrial raw material.
Which route works depends on the ratio of the ions, temperature, concentration and what the buyer needs. We analyse the solubility phase diagram for your brine before recommending any configuration, because a crystalliser designed for the wrong ratio produces mixed, unsaleable salt.
How it links to ZLD cost
Evaporation is the most expensive part of zero liquid discharge, taking about 50 to 65% of the cost. Every stream kept out of the evaporator by segregation, and every tonne of salt sold instead of sent to a disposal facility, cuts that cost directly. Process design is the cheapest ZLD equipment you can buy. See our ZLD plants and non-thermal evaporators.
Where it is limited
Organics and colour reduce purity; a purge stream always remains for drying; and recovered salt needs a buyer and, where it was classed as waste, the board's agreement for reuse. We include a market check in the feasibility study.
Rules and standards
The regulations a process design must satisfy.
Every design and report is prepared against the rules your auditors and regulators check.
| Rule or standard | What it covers | What we deliver |
|---|---|---|
| EIA Notification, 2006 | Prior environmental clearance for new and expanding projects in listed categories | Form 1, baseline studies, EIA report, Environmental Management Plan (EMP) |
| Water Act, 1974 and Air Act, 1981 | Consent to establish and to operate from the SPCB | Water balance, treatment design basis, CTO renewals and amendments |
| CPCB ZLD guidelines, 2015 | Feasibility and expectations for ZLD in water-polluting industries | Phased ZLD roadmap and ZLD compliance verification reports |
| CGWA guidelines, 2020 | Groundwater NOC, metering and water audits for industry | Water audit and water balance in the format the NOC needs |
| Hazardous and Other Wastes Rules, 2016 | Storage, disposal and authorised utilisation of hazardous waste such as ZLD salt and sludge | Waste inventory and options to reduce or reuse waste |
| National Framework on Safe Reuse of Treated Water, 2022 | National direction on reuse of treated wastewater | Reuse plan aligned with state reuse policies |
| SEBI BRSR | Water, waste and energy disclosures for listed companies | Water footprint and intensity data ready for reporting |
| ISO 14046 | Method for water footprint assessment | Blue, green and grey water footprint; data for CDP water questionnaires and SBTi targets |
We prepare baseline air, water, soil and noise studies, Form 1, the EMP and the DPR, and support you before SPCB technical committees.
Deliverables and cost
What you get, how long it takes, and what it saves.
Each study can be bought on its own or as part of a full engagement.
| Scope | Method | Main deliverable | Typical time | Expected outcome |
|---|---|---|---|---|
| Water pinch audit | Stream synthesis and graphical pinch analysis | Direct water cascade blueprint | 3 to 4 weeks | Target of 30–50% lower water bills |
| Mass balance modelling | ASPEN and CAD simulation | Ionic and hydraulic flow diagram (PFD) | 2 to 3 weeks | Accurate capital and operating cost sizing |
| Salt recovery design | Fractional crystallisation simulation | Salt purity and recovery feasibility study | 4 weeks | Waste turned into a saleable raw material |
| EIA and environmental clearance | Baseline studies and SPCB guidelines | DPR and EIA report, with support at hearings | 6 to 8 weeks | A complete, defensible submission |
| Zero discharge roadmap | Technology selection and treatability study | Phased ZLD implementation plan | 4 to 6 weeks | A closed loop built in affordable stages |
Times are typical and depend on site size and data available. Study fees depend on the number of streams and samples; we quote after a short call. Savings are targets, not guarantees, and are confirmed by the study. On circular water and salt recovery investments, we typically see capital payback of under 14 months where water or disposal costs are high.
What drives the study scope
- Number of process streams and units
- Whether meters exist or must be installed
- Number of laboratory samples
- Need for EIA or clearance documents
- Single site or multi-tenant industrial park
Where the savings come from
- Lower fresh water and tanker purchases
- Smaller ETP, RO and evaporator
- Less steam for evaporation
- Lower hazardous waste disposal fees
- Revenue from salt, biogas or metals
A simple example
- A plant sends 100 KLD to ZLD
- Pinch study reuses 30 KLD directly
- Only 70 KLD reaches RO
- RO reject and evaporator shrink by about 30%
- So does the steam bill
Challenges
Common problems, and how process design solves them.
- 01The problem
Water bills and tanker costs rise every year.
What we doWater pinch and mass balance studies find every stream that can be reused before new capacity is bought.
- 02The problem
Mixed salts from RO reject are costly to store and dispose of.
What we doSegregate salty streams and use fractional crystallisation to separate sodium sulphate and sodium chloride into saleable grades.
- 03The problem
The ZLD plant was sized on total flow and the evaporator is overloaded.
What we doRebuild the salt balance from measured data, take weak streams out of the evaporator feed and add lower-cost evaporation.
- 04The problem
Environmental clearance and consent renewals take too long.
What we doPrepare EIA reports, water balance data and compliance files in the form regulators expect.
- 05The problem
Investors and buyers ask for water and ESG disclosures.
What we doQuantify your water footprint and intensity so it goes straight into BRSR, CDP and customer reports.
Where it fits
Sector applications.
ZLD and sodium sulphate recovery
ZLD with fractional Na₂SO₄ crystallisation, returning salt to dye house operations.
Textile guide →High-COD ZLD roadmap
ZLD architecture for API synthesis wastewater with solvents, metals and variable pH.
Pharma guide →Heavy metal and high-TDS closed loop
Metal precipitation, high-recovery RO, MVR evaporation and centrifuge salt recovery for chromium and nickel plating.
Metal recovery →Multi-tenant water pinch audit
Cross-factory cascades that find reuse between neighbouring plants and CETPs.
Chemical guide →Organic load and heat recovery
Biogas optimisation, fat recovery and cascading CIP wash water to cooling tower make-up.
Dairy guide →Water footprint assessment
ISO 14046 assessment for ESG reporting, CDP water disclosures and green finance documents.
Request a water footprint study →Buying guide
What to ask any process design consultant.
- Will every stream be measured and tested? Or will the study rely on design figures and guesses?
- Is the laboratory accredited? NABL-accredited results carry weight with boards and auditors.
- Does the mass balance include salts and scaling, not just water?
- Are the reuse options costed? Piping, pumps and treatment, with payback for each.
- Is the consultant independent of one equipment type? Ask whether no-cost reuse options come first.
- Will the report work for the board? CGWA water audit, CTO renewal or EIA formats.
- Can the same team build and run the recommended plant? That keeps responsibility in one place.
Why Rispri
One accountable partner, from lab bench to running plant.
Lab and engineering under one roof
Our NABL-accredited laboratory tests the water, sizes the process and verifies results after start-up.
Designs proven since 1999
1,498+ plants and turnkey projects, from compact STPs to industrial ETP, RO and ZLD systems.
Compliance built in
We design to CPCB and SPCB limits with margin and plan for OCEMS, CGWA and reuse rules from the first drawing.
Research collaborations
Proven low-energy evaporation and reject recovery, in collaboration with IIT Bombay, IIT Kharagpur and ICT Mumbai.
Questions
Process design and circularity FAQs.
What is water pinch analysis, and how does it differ from a water audit?
A water audit counts how much water is used and lost. Water pinch analysis matches each water source to the uses that can accept its quality, and finds the minimum fresh water the site truly needs. An audit typically saves 10 to 15%; pinch analysis targets 30 to 55% and often allows a smaller ETP.
What is a mass balance in wastewater treatment?
A mass balance tracks the flow of water and of what it carries, such as salts, COD and heat, through every stage of a plant. It shows where salts concentrate and scale, and it is the basis for sizing RO, evaporators and dryers correctly.
What is circular economy in wastewater?
It means treating effluent as a source of water and materials rather than waste. In practice, a plant reduces water use, reuses streams directly, recycles treated water and recovers resources such as salt, biogas, metals and heat before anything is disposed of.
Can salt recovered from ZLD be sold?
Yes, if crystallisation reaches the purity the buyer needs. For textile effluent, sodium sulphate of more than 99% purity is achievable and can be reused in dyeing. Mixed salts and the purge stream still need authorised disposal, and we check the market as part of the study.
How does process design reduce ZLD cost?
Evaporation is about 50 to 65% of ZLD cost. Segregating salty streams, reusing clean streams directly and raising RO recovery all reduce the volume reaching the evaporator, which cuts both its size and its steam bill.
Is ZLD mandatory, and for which industries?
ZLD is required where the SPCB consent or a CPCB, court or NGT direction says so. It is most common for textile dyeing and processing, distilleries, tanneries, pulp and paper, and bulk drug and pharma units. Check your own consent conditions.
How long does a full engagement take?
A full engagement from data collection to DPR and regulatory submission typically takes 10 to 14 weeks: site data in weeks 1–2, pinch and mass balance in weeks 3–4, salt recovery in weeks 5–6, and EIA and submission in weeks 7–14.
What data do you need to start a water audit or pinch study?
Water meter readings for each process unit, quality data (TDS, COD, BOD, TSS, pH, temperature) for each stream, the quality limits for each water use, a plant layout or P&ID, and the last 12 months of ETP or STP outlet reports. Where data is missing, we measure and test it.
Is a water audit required under CGWA rules?
Industries drawing groundwater under the CGWA guidelines, 2020 need a no-objection certificate and are expected to meter abstraction and carry out water audits. Your NOC conditions state what is required and how often.
Do you prepare EIA reports and environmental clearance applications?
Yes. We prepare baseline environmental studies, Form 1, the Environmental Management Plan and the DPR, apply for SPCB consents and renewals, and support you before technical committees. Our laboratory provides the air, water, soil and noise data.
What is an ISO 14046 water footprint?
ISO 14046 is the international method for assessing a product's or site's water footprint, covering how much water is used and its environmental impact. We calculate blue, green and grey water footprints for BRSR, CDP and customer reports.
What is the payback on water reuse and salt recovery?
It depends on what you pay for water, steam and disposal today. Where those costs are high, we typically see capital payback of under 14 months on circular water and salt recovery investments. The study gives a payback for each option.
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