How Water Balance Improves ETP Design and ZLD Feasibility

An industrial water balance is one of the most important inputs for designing, reviewing or augmenting an Effluent Treatment Plant.

It maps where water enters a facility, where it is consumed, how much becomes wastewater, which streams can be reused and what quantity must finally be treated, recovered, evaporated or discharged.

Without a reliable water balance, an ETP may be designed for the wrong flow, unsuitable wastewater characteristics or unrealistic reuse assumptions.

The same problem becomes more serious when an industry is considering Zero Liquid Discharge.

ZLD feasibility is not decided only by installing an RO system, Multiple-Effect Evaporator or another advanced treatment unit. It depends on whether the plant has correctly identified and segregated all water and wastewater streams before selecting the treatment route.

A good water balance can therefore help an industry:

• Select the correct ETP capacity

• Identify peak and average wastewater flow

• Separate high-TDS and low-TDS streams

• Reduce hydraulic load on the ETP

• Estimate realistic reuse potential

• Determine RO recovery requirements

• Calculate reject quantity

• Assess evaporator load

• Verify freshwater demand

• Compare normal discharge and ZLD options

• Detect inconsistent logbooks and flow records

• Prepare a more defensible consent and compliance submission

For industries planning a new ETP, plant expansion or wastewater-treatment upgrade, the water balance should be developed before the treatment flow sheet is finalised.

SARK Engineers & Consultants supports industries through industrial water audits, ETP design review, wastewater characterisation, process mapping and Zero Liquid Discharge consulting.

What Is an Industrial Water Balance?

An industrial water balance is a quantified representation of all major water flows within a facility.

At its simplest:

Water entering the facility = Water consumed, reused, discharged, evaporated, stored or lost

A detailed water balance should account for:

Water entering the facility

• Groundwater

• Municipal water

• Tanker water

• Surface water

• Recycled water

• Condensate return

• Rainwater

• Product or raw-material moisture

Water used within the facility

• Process operations

• Washing and rinsing

• Cooling towers

• Boilers

• Domestic use

• Gardening

• Floor cleaning

• Laboratory use

• Equipment cleaning

• Scrubbers

• Product preparation

• Fire-water makeup

Water leaving or changing form

• Trade effluent

• Domestic sewage

• Cooling-tower blowdown

• Boiler blowdown

• RO reject

• Softener or DM-plant regeneration wastewater

• Evaporation

• Moisture retained in product

• Sludge moisture

• Gardening consumption

• Recycled water

• Condensate

• Leakage and unaccounted losses

A useful water balance must be based on measurements, production data and operating patterns rather than only assumed percentages.

Why ETP Design Should Begin with Water Balance

ETP design is often started with one number:

“The factory generates 20 KLD of wastewater.”

That single figure is rarely enough.

The designer must know:

• Is 20 KLD the average flow or maximum daily flow?

• Does the flow remain constant throughout the day?

• Is it generated continuously or batch-wise?

• Does it include domestic sewage?

• Does it include cooling-tower or boiler blowdown?

• Are high-strength streams mixed with dilute wastewater?

• Are oily streams entering the same drain?

• Does floor washing create sudden hydraulic peaks?

• Are regeneration chemicals discharged in batches?

• Is the stated quantity supported by flow measurement?

• Is some wastewater being reused before reaching the ETP?

• Does rainwater enter the wastewater network?

A 20 KLD ETP receiving stable, segregated wastewater is very different from a 20 KLD ETP receiving shock loads, chemical-cleaning batches, oily runoff and high-TDS reject.

The water balance gives the ETP designer the hydraulic structure required to interpret that flow correctly.

Water Balance Helps Determine the Correct ETP Capacity

An ETP should not be sized only by multiplying freshwater consumption by an assumed wastewater-generation percentage.

The treatment capacity should be derived from actual wastewater-producing operations.

For example:

Water-consuming activity	Water use	Wastewater generated
Process washing	12 KLD	10 KLD
Equipment cleaning	4 KLD	3.5 KLD
Cooling-tower blowdown	5 KLD	5 KLD
Boiler blowdown	1 KLD	1 KLD
RO reject	3 KLD	3 KLD
Domestic use	8 KLD	6.5 KLD
Gardening	4 KLD	Nil
Product moisture	2 KLD	Nil

The total freshwater use may be 39 KLD, but the industrial ETP flow may be 22.5 KLD and the domestic sewage flow may be 6.5 KLD.

If all wastewater is assumed to be one stream, the plant may receive an oversized common treatment system or an unsuitable combined ETP-STP design.

A proper water balance clarifies whether separate systems are required.

Average Flow, Peak Flow and Batch Discharge

Two industries may both report 25 KLD wastewater generation but require very different equalisation systems.

Facility A

Wastewater is generated evenly over 20 operating hours.

Average flow:

25 ÷ 20 = 1.25 m³/hour

Facility B

Most wastewater is generated during two cleaning cycles of two hours each.

Batch-period flow:

25 ÷ 4 = 6.25 m³/hour

Both facilities generate 25 KLD, but Facility B needs much more attention to:

• Equalisation capacity

• Pump sizing

• Shock-load control

• pH variation

• Chemical dosing

• Flow balancing

• Downstream treatment stability

The daily total alone cannot reveal this difference.

Water Balance Identifies Hidden Wastewater Streams

One of the most valuable outcomes of a water audit is the discovery of streams that were not included in the original ETP design.

Common examples include:

• Compressor condensate

• Scrubber bleed

• Floor washing

• Coolant leakage

• Tank-cleaning water

• Filter backwash

• Softener regeneration

• RO reject

• Cooling-tower blowdown

• Boiler blowdown

• Laboratory wastewater

• Chemical-container washing

• Stormwater entering process drains

• Oily water from maintenance areas

These streams may appear small individually but can materially change:

• ETP hydraulic load

• COD

• Oil and grease

• TDS

• Chlorides

• Sulphates

• Heavy metals

• pH

• Sludge generation

• RO recovery

• MEE load

A facility experiencing repeated ETP failure should therefore review its full water balance before assuming that the treatment equipment is undersized.

SARK’s ETP troubleshooting and pollution-control consulting examines both treatment performance and the upstream water-generation pattern.

Water Balance Supports Wastewater Segregation

Segregation can reduce treatment cost more effectively than simply increasing ETP capacity.

An industrial facility may generate:

Low-TDS biodegradable wastewater

Examples:

• Process wash water

• Food-processing wastewater

• Paper-machine white water

• Biodegradable cleaning water

High-TDS wastewater

Examples:

• RO reject

• DM-plant regeneration wastewater

• Pickling rinse

• Chemical-treatment reject

• Cooling-tower blowdown

Oily wastewater

Examples:

• Machine washing

• Component cleaning

• Coolant leaks

• Maintenance-area runoff

High-COD concentrated streams

Examples:

• Mother liquor

• Product spills

• Concentrated washings

• Batch residues

• Chemical-cleaning waste

Domestic sewage

Examples:

• Toilets

• Washrooms

• Canteen sewage

Mixing all these streams may create a technically difficult and unnecessarily expensive treatment problem.

A water balance helps identify which streams should be:

• Treated biologically

• Treated chemically

• Sent through oil separation

• Recovered separately

• Reused directly

• Routed to RO

• Routed to an evaporator

• Sent to an authorised disposal facility

How Water Balance Improves ETP Process Selection

A treatment technology should be selected after confirming both wastewater quantity and quality.

The water balance supports this process by showing where each pollutant enters the treatment system.

Wastewater characteristic	Possible treatment implication
High suspended solids	Screening, settling, clarification or filtration
High oil and grease	Oil trap, skimmer, DAF or coalescing separator
High biodegradable COD	Biological treatment
High toxic or refractory COD	Segregation, oxidation or specialised treatment
High TDS	Membrane treatment, recovery or evaporation
Variable pH	Equalisation and controlled neutralisation
Heavy metals	Chemical precipitation and sludge management
High-temperature wastewater	Cooling or heat recovery before treatment
Intermittent batch discharge	Larger equalisation and controlled feeding

Without source-wise flow information, the ETP designer may know that COD is high but not know which operation is responsible.

This makes both treatment design and troubleshooting weaker.

Water Balance and ZLD Feasibility

Zero Liquid Discharge means that liquid wastewater is not discharged outside the facility boundary.

In practical terms, a ZLD system may involve:

• Wastewater segregation

• Primary and secondary treatment

• Filtration

• Ultrafiltration

• Reverse osmosis

• Reuse of RO permeate

• Concentration of RO reject

• Multiple-Effect Evaporation

• ATFD or crystallisation

• Condensate recovery

• Salt or sludge management

The feasibility of ZLD depends heavily on the quantity of water that reaches the advanced treatment stage.

A poorly developed water balance can send excessive dilute wastewater to the RO and MEE, making the project unnecessarily expensive.

Why Flow Reduction Matters Before ZLD

Consider two alternatives.

Scenario 1: No segregation

Total wastewater sent to ZLD:

100 KLD

Assume RO recovery:

70%

RO permeate:

70 KLD

RO reject requiring further treatment:

30 KLD

Scenario 2: Segregation and direct reuse

Through segregation and process reuse:

• 20 KLD reused directly

• 10 KLD low-risk cooling blowdown diverted to an approved reuse application

• 70 KLD sent to ZLD treatment

At 70% RO recovery:

RO permeate:

49 KLD

RO reject:

21 KLD

The reject load drops from 30 KLD to 21 KLD.

That difference can materially affect:

• MEE capacity

• Steam consumption

• Electrical demand

• Cooling-water requirement

• Condensate generation

• Capital cost

• Operating cost

• Sludge or salt generation

The least expensive litre to evaporate is the litre that was prevented from entering the evaporator.

Determining Realistic Reuse Potential

A water balance should distinguish between theoretical reuse and practical reuse.

Treated water may appear available for reuse, but the receiving application must be able to accept it consistently.

Possible reuse areas include:

• Cooling-tower makeup

• Boiler feed after suitable polishing

• Floor washing

• Gardening

• Toilet flushing

• Scrubber makeup

• Process washing

• Equipment cleaning

• Construction

• Fire-water makeup, subject to system requirements

Each reuse application should be checked for:

• Quantity required

• Daily and seasonal demand

• TDS

• Hardness

• Chlorides

• Silica

• COD

• Microbial quality

• Colour

• Oil and grease

• Storage requirement

• Distribution system

• Cross-connection risk

Gardening is often shown as a major reuse route even when the available land, seasonal demand or water quality does not support the claimed quantity.

A credible water balance should therefore match reuse supply with actual reuse demand.

Water Balance Helps Verify Whether ZLD Is Necessary

Not every industry requires the same wastewater-disposal approach.

The decision may depend on:

• Consent conditions

• Industry category

• Pollution-control-board directions

• Local discharge availability

• CETP connectivity

• Groundwater status

• Wastewater quality

• Reuse opportunity

• Land availability

• Regulatory commitments

• Project approval conditions

• Local environmental sensitivity

A ZLD feasibility review should compare:

Normal treatment and permitted discharge

• ETP treatment

• Discharge to sewer, CETP or approved receiving system

• Monitoring and compliance cost

Partial recovery

• ETP

• Filtration

• RO

• Permeate reuse

• Approved reject handling

Full ZLD

• ETP

• RO

• MEE

• ATFD or crystallisation

• Condensate recovery

• Salt and sludge disposal

The ZLD feasibility assessment should begin with the water balance, not with a vendor quotation for an MEE.

Water Balance Can Reveal Data and Logbook Mismatches

A strong water balance also acts as a compliance-verification tool.

For example:

• Freshwater meter records show 80 KLD

• Production consumption accounts for 30 KLD

• Cooling and boiler makeup account for 15 KLD

• Domestic use accounts for 10 KLD

• Gardening accounts for 5 KLD

• Recorded wastewater is only 8 KLD

The accounted water is:

30 + 15 + 10 + 5 + 8 = 68 KLD

Unaccounted water:

80 - 68 = 12 KLD

That missing 12 KLD may indicate:

• Leakage

• Unmetered use

• Incorrect logbooks

• Underreported wastewater

• Unrecorded tanker supply

• Hidden discharge

• Evaporation not properly estimated

• Process retention

• Meter error

A water balance does not automatically prove misconduct, but it identifies where further verification is required.

Data Required to Prepare a Reliable Water Balance

Industries should collect:

Water-source data

• Groundwater meter readings

• Municipal bills

• Tanker receipts

• Recycled-water flow

• Borewell operating hours

• Pump capacity

• Telemetry records

Production data

• Daily production

• Product mix

• Batch frequency

• Shift pattern

• Seasonal variation

• Shutdown periods

Process data

• Water use by operation

• Washing frequency

• Tank volumes

• Equipment-cleaning cycles

• Chemical preparation

• Product moisture

Utility data

• Cooling-tower makeup

• Cooling-tower blowdown

• Boiler makeup

• Boiler blowdown

• Condensate return

• RO feed

• RO permeate

• RO reject

• Softener regeneration

• DM-plant regeneration

Wastewater data

• ETP inlet flow

• STP inlet flow

• Individual stream flow

• Batch discharge

• Treated-water reuse

• Sludge quantity

• Tanker disposal

• CETP discharge

• MEE feed and condensate

Supporting documents

• Consent to Establish

• Consent to Operate

• Groundwater permission

• ETP and STP drawings

• Flow diagrams

• Water bills

• Meter calibration records

• Laboratory reports

• Daily logbooks

• Production records

Common Water-Balance Mistakes

Using consent quantity as actual flow

Consent values represent an approved basis. They may not reflect current operations.

Assuming a fixed percentage of freshwater becomes wastewater

Different processes retain, evaporate or reuse water differently.

Combining sewage and trade effluent

This can distort both STP and ETP design.

Ignoring peak flow

Daily average flow may conceal short-duration hydraulic shocks.

Ignoring high-TDS streams

Small reject flows can dominate ZLD cost.

Treating gardening as unlimited reuse

Gardening demand varies with land area, season and rainfall.

Ignoring rainwater ingress

Stormwater can overload treatment systems and dilute laboratory results.

Relying entirely on logbooks

Logbooks should be verified using meters, pump hours, tank levels and production data.

Assuming installed ETP capacity equals effective capacity

Hydraulic capacity alone does not confirm adequate COD, TDS or pollutant-removal capacity.

Selecting ZLD equipment before reducing wastewater flow

This often results in oversized RO, MEE and utility systems.

Water-Balance Diagnostic Matrix

Observation	Possible concern	Recommended verification
ETP flow exceeds design	Hidden streams or stormwater ingress	Drain mapping and flow measurement
ETP flow is much lower than freshwater use	Underreporting, reuse or unaccounted loss	Source-wise reconciliation
RO reject is sent to gardening	TDS and consent incompatibility	Water-quality and approval review
Sewage flow appears too low	Manpower or logbook mismatch	Domestic demand calculation
MEE load is high	Excess dilute wastewater	Segregation and reuse study
Treated water storage remains full	Reuse demand is inadequate	Reuse-demand mapping
COD varies sharply	Batch or concentrated discharge	Source sampling
TDS rises despite stable production	Regeneration or blowdown contribution	Utility-stream analysis
ETP overflows during rain	Stormwater connection	Drain survey
Freshwater use exceeds permission	Metering or process-demand issue	Water audit and conservation plan

How Water Balance Supports ETP Augmentation

When an ETP fails, the immediate response is often to add:

• A larger tank

• Another blower

• More chemicals

• Additional filters

• A larger RO

• A new biological stage

These additions may not solve the actual problem.

A water balance may show that the better solution is:

• Segregating oily wastewater

• Removing RO reject from the biological ETP

• Installing a separate high-TDS collection tank

• Correcting batch-discharge timing

• Preventing stormwater ingress

• Increasing equalisation

• Reusing a clean stream directly

• Reducing floor-washing water

• Controlling coolant losses

• Correcting domestic sewage estimates

The decision between ETP augmentation and a new ETP should therefore be supported by measured water-flow data.

How SARK Engineers & Consultants Can Help

SARK Engineers & Consultants undertakes integrated water, wastewater and process assessments for new and operating industrial facilities.

The scope may include:

• Industrial water audit

• Source-wise water mapping

• Process water balance

• Wastewater-flow measurement

• ETP and STP capacity review

• Wastewater segregation study

• ETP feasibility assessment

• ZLD feasibility assessment

• RO and MEE load estimation

• Treated-water reuse planning

• Consent-condition reconciliation

• Groundwater-compliance review

• ETP augmentation planning

• Vendor proposal review

• Technical BOQ review

• Corrective-action planning

For a new treatment project, SARK can review the proposed water balance, ETP flow sheet, equipment capacities, reuse assumptions and vendor BOQ before procurement.

For an operating facility, the assessment can compare actual flow, water consumption, treatment capacity and statutory records to identify the cause of repeated non-compliance.

Explore SARK’s industrial process-consulting services and project-assessment services for broader plant-level technical review.

Frequently Asked Questions

Why is a water balance necessary for ETP design?

A water balance identifies the actual quantity, source, timing and type of wastewater generated by a facility. This helps determine ETP capacity, equalisation requirement, segregation strategy and suitable treatment technology.

Can an ETP be designed only from freshwater-consumption data?

Freshwater consumption is useful, but it is not sufficient by itself. Some water is evaporated, retained in product, reused or consumed domestically, while additional wastewater may arise from regeneration, blowdown and cleaning operations.

How does water balance reduce ZLD cost?

It identifies streams that can be reused, segregated or prevented from entering the advanced treatment system. Lower RO feed and reject flow can substantially reduce MEE capacity, steam consumption and operating cost.

Should domestic sewage be included in the ETP water balance?

Domestic sewage should be included in the overall site water balance but normally shown separately from industrial trade effluent. Whether it can be combined depends on wastewater characteristics, treatment design and consent conditions.

What is the difference between a water audit and a water balance?

A water balance quantifies where water enters, moves and leaves the facility. A water audit is broader and may also assess efficiency, leakage, reuse, conservation, metering, compliance and improvement opportunities.

Can treated ETP water always be reused for gardening?

No. Gardening reuse depends on water quality, available green area, seasonal demand, soil conditions and regulatory approval. It should not be used as an assumed disposal route without verification.

How is MEE capacity estimated for a ZLD plant?

MEE capacity is influenced by RO reject flow, dissolved solids, recovery target, operating hours and upstream treatment performance. A source-wise water balance is essential before finalising the evaporator load.

When should an industry revise its water balance?

The water balance should be revised when production changes, machinery is added, water sources change, ETP or STP is modified, reuse increases, consent is renewed or actual meter data differs materially from approved quantities.

Final Conclusion

An ETP should not be designed as an isolated treatment unit.

Its performance depends on the complete water system that feeds it.

A reliable industrial water balance connects:

• Freshwater abstraction

• Production

• Utilities

• Domestic use

• Wastewater generation

• Treatment

• Reuse

• Reject handling

• Sludge

• Final disposal

For ZLD projects, the same balance determines whether the proposed recovery system is technically practical and commercially justified.

The best time to prepare the water balance is before the ETP, RO or MEE is purchased.

The next best time is before repeated treatment failure becomes a regulatory problem.

Planning a new ETP, plant expansion or ZLD system?

Share the process flow, water-source data, production details, utility consumption, wastewater streams, laboratory reports and proposed vendor design for an independent technical review by SARK Engineers & Consultants.