INDUSTRIES / PEA AND VEGETABLE PROCESSING
Pea processing effluent treatment
sized for the season, not the average.
Shelling, washing, blanching and cooling lines send strong, starch-rich wastewater to the drain in a short harvest campaign. We design effluent treatment plants that take that peak, turn much of the load into biogas, and start up reliably after months of standing idle.
In short
How pea processing wastewater is treated.
Pea and vegetable processing wastewater comes from washing, flotation grading, blanching, cooling and cleaning. It is warm, rich in starch, sugars and fine solids, and very strong: BOD is often 1,500 to 4,000 mg/L, many times stronger than sewage. Because it arrives in a short harvest season, the plant is sized for peak-season flow. The usual scheme is screening, equalisation and cooling, DAF or settling, an anaerobic reactor (UASB) that turns most of the load into biogas, then aerobic polishing (MBBR, SBR or extended aeration) and filtration. Under India's general standards, effluent discharged to surface water must have BOD below 30 mg/L and COD below 250 mg/L.
- 1,500–4,000mg/L
- Typical BOD of raw pea processing effluent
- 70–90%
- COD removal in a well-run UASB reactor
- 30mg/L
- BOD limit for discharge into inland surface water
- NABL
- Accredited laboratory that tests your effluent through the season
Where it comes from
Where the wastewater in a pea plant comes from.
Green peas (matar) for freezing are harvested in the winter months in North India, so frozen pea plants run an intense campaign of a few months and then either stop or switch to other vegetables such as sweet corn, carrots or mixed vegetables. The effluent plant has to handle a sudden jump from almost nothing to full load, day and night, and then sit idle.
Process by process
- Receiving and shelling: pods are shelled in viners or shellers. The hulls are mostly a solid waste, but wash-down water carries juice, fines and broken peas.
- Washing, destoning and flotation grading: large flows of water remove soil, stones and leaves. Peas are often graded in brine, so mature, starchy peas sink; this adds salt (TDS) and starch.
- Blanching: peas are heated briefly in hot water or steam to stop enzyme activity. Blancher overflow is the strongest stream, hot and loaded with dissolved sugars, starch and protein.
- Cooling and chilling: high flow, lower strength, often reusable for washing.
- Sorting and inspection: fines and rejected peas washed down to drain.
- Cleaning in place (CIP) and floor washing: caustic, acid and sanitiser in short slugs at the end of shifts, which swing pH sharply.
Why it is hard to treat
The sugars ferment within hours. Effluent left standing in a drain or an unmixed tank turns sour, its pH drops, it smells, and it can upset a biological plant downstream. Fine starch particles do not settle easily, and the load changes with every shift and blanching batch.
| Parameter | Typical raw range | Usual treated target | Why it matters |
|---|---|---|---|
| pH | 6.0 to 7.5 (falls as it sours) | 6.5 to 8.5 | Acid effluent upsets anaerobic and aerobic bacteria |
| BOD | 1,500 to 4,000 mg/L | Below 30 mg/L | Sets the size of the biological plant and the biogas yield |
| COD | 2,500 to 6,000 mg/L | Below 100 to 250 mg/L | Total organic load; decides whether anaerobic treatment pays |
| Total suspended solids | 800 to 2,500 mg/L | Below 50 to 100 mg/L | Skins, pulp and starch; too much washes out UASB sludge |
| Oil and grease | 20 to 60 mg/L | Below 10 mg/L | Low in peas, higher if fried products share the drain |
| TDS | 1,000 to 2,500 mg/L | As per consent, often 2,100 mg/L | Brine grading and CIP chemicals; matters for irrigation reuse |
| Temperature | 40 to 55 °C at the blancher outfall | Near ambient before biology | Hot water kills or slows bacteria; needs cooling or mixing |
Standards
Which discharge standards apply to a pea processing plant?
Most pea and vegetable processing consents use the general standards under Schedule VI of the Environment (Protection) Rules, 1986, set according to where the treated water goes. Your State Pollution Control Board's consent to operate decides what applies at your site.
| Parameter | Inland surface water | Land for irrigation | IFC / World Bank guideline (fruit and vegetable processing) |
|---|---|---|---|
| pH | 5.5 to 9.0 | 5.5 to 9.0 | 6 to 9 |
| BOD (3 days at 27 °C) | 30 | 100 | 50 |
| COD | 250 | Not specified | 250 |
| Total suspended solids | 100 | 200 | 50 |
| Oil and grease | 10 | 10 | 10 |
| Temperature | Not more than 5 °C above the receiving water | Not specified | Not specified here |
Discharge into a public sewer that ends in a sewage treatment plant is allowed a higher BOD (350 mg/L) where the local body accepts it. The IFC guideline is not an Indian legal standard but is used by export buyers and lenders.
Treatment
Why anaerobic first, then aerobic?
Treating effluent of 4,000 mg/L COD with aeration alone means buying a lot of blower power to supply oxygen. An anaerobic stage removes most of the load without air and gives you fuel in return, leaving a smaller aerobic stage to polish the water to discharge limits.
| Stage | What happens | Design point for pea effluent |
|---|---|---|
| 1. Screening | Rotary drum or vibrating screen removes skins, pods, broken peas and pulp. | Fine screen close to the source; screenings go to cattle feed or compost, not the drain |
| 2. Equalisation and cooling | A mixed tank evens out flow and strength between batches and shifts, and brings hot blancher water down in temperature. | At least a full day of peak-season flow; mixed or aerated to stop souring; pH correction for CIP slugs |
| 3. DAF or primary settling | Dissolved air flotation or a settling tank removes fine solids and starch colloids. | Protects the UASB from solids that would wash out its sludge blanket |
| 4. Anaerobic reactor (UASB) | In an upflow anaerobic sludge blanket reactor, a bed of granular sludge converts organic matter into biogas without oxygen. | Organic loading of roughly 2.5 to 7 kg COD per m³ per day; 70 to 90% COD removal when well run |
| 5. Aerobic polishing | MBBR, SBR or extended aeration removes the remaining BOD and oxidises ammonia from protein breakdown. | Sized on the load leaving the UASB, with standby capacity for the peak of the campaign |
| 6. Clarification and sludge dewatering | Biomass settles; excess sludge is dewatered on a filter press or screw press. | Organic, non-hazardous sludge that composts well where norms allow |
| 7. Filtration and disinfection | Sand and carbon filters and chlorination or UV. | Needed for reuse in washing yards, gardens and cooling tower make-up |
| Option | Best for | Footprint | Watch-outs |
|---|---|---|---|
| UASB + MBBR or SBR | Medium and large plants, biogas use, limited land | Medium | Needs good solids removal ahead; granules must be preserved between seasons |
| Covered anaerobic lagoon + aerated lagoon | Plants with plenty of land and low capital budgets | Very large | Odour if uncovered; sludge builds up; slower response to load changes |
| Aerobic only (extended aeration or MBBR) | Small plants or weaker effluent (COD below about 1,500 mg/L) | Medium to large | High power bill at full season load; more sludge |
| High-rate anaerobic (EGSB / IC reactor) | Large, steady flows with high COD | Small | Higher capital; less forgiving of solids and start-stop operation |
Published trials on starch-heavy wastewater have shown 81 to 99% COD removal at well-chosen loading, and over two dozen full-scale UASB plants run in the closely related potato processing sector. A published food-industry MBBR ahead of an SBR cut BOD by more than 75% before the SBR stage started. High-rate MBBR designs on food effluent are loaded at up to about 6 to 10 kg BOD per m³ per day in roughing duty.
Our NABL-accredited laboratory tests composite samples for BOD, COD, TSS, TDS, nitrogen and oil and grease at the start, peak and end of your campaign, so the plant is designed on your real load.
Resource recovery
Biogas, feed and water: what a pea plant can recover.
Biogas
Each kilogram of COD removed in the UASB gives roughly 0.25 to 0.29 m³ of methane in practice. A worked example: a plant treating 300 KLD at 4,000 mg/L COD carries 1,200 kg of COD a day. At 80% removal and 0.27 m³ per kg, that is about 260 m³ of methane, or roughly 400 m³ of biogas a day. That is about as much energy as 250 litres of diesel, enough to make a real dent in boiler fuel during the season. Whether it is worth capturing depends on flow and season length, which we work out at design stage. See biogas and waste-to-energy.
Hulls, rejects and screenings
Pea hulls and pods are a large share of the weight received. Fresh, they are good cattle feed; they can also be ensiled, composted or co-digested for biogas. Keeping them out of the drain is the cheapest treatment step there is.
Water
Chiller and cooling water is often clean enough to reuse counter-current for first washing. Treated effluent, after filtration and disinfection, suits floor and yard washing, crate washing, gardens and cooling towers. Irrigation of nearby fields is possible where the consent allows it and TDS is controlled.
Cost
What does a pea processing ETP cost?
Because the effluent is ten or more times stronger than sewage, cost follows the organic load (kg COD per day) more than the flow. These ranges help you budget before we see your data.
| Peak-season flow | Typical plant | Indicative ETP cost* |
|---|---|---|
| 50 to 100 KLD | Small processor; aerobic only or compact anaerobic stage | ₹30 to 70 lakh |
| 200 to 300 KLD | Medium frozen pea and vegetable plant, UASB plus MBBR | ₹80 lakh to ₹1.8 crore |
| 500 KLD and above | Large multi-line plant with biogas use | ₹1.5 crore upwards |
*Indicative 2026 ranges for equipment, electricals and installation of a screening, equalisation, DAF, anaerobic and aerobic plant, excluding land, civil works, taxes, biogas use equipment and any RO stage. Lagoon-based systems cost less to build but need much more land. We give a firm price after testing your effluent through a campaign and seeing the site.
What drives capital cost
- Peak-season COD load, not annual average flow
- How well solids are kept out at source
- UASB vs lagoon vs aerobic only
- Discharge route: surface water, sewer or irrigation
- Biogas use: flare only, boiler burner or engine
What drives running cost
- Aeration power for the polishing stage
- pH correction and nutrients during start-up
- DAF chemicals and sludge handling
- Seasonal operators and start-up support
- Biogas savings, which offset part of the cost
We audit seasonal plants, add anaerobic pre-treatment or DAF ahead of overloaded aeration tanks, supply tested coagulants and polymers, and run the start-up and campaign under contract.
Troubleshooting
Common problems in pea processing ETPs, and fixes.
- 01The problem
The plant is overloaded in the first weeks of the season.
What we doSize on peak-season COD, start the biology before the campaign and ramp the load, using equalisation as a buffer.
- 02The problem
Effluent sours in the equalisation tank and the UASB turns acid.
What we doMix or aerate the tank, limit holding time, dose alkalinity and track VFA and alkalinity daily.
- 03The problem
UASB sludge washes out and outlet TSS rises.
What we doImprove screening and add DAF to stop starch and fines, and correct the upflow velocity.
- 04The problem
Hot blancher water kills the biology.
What we doRecover heat or cool the blancher overflow, and blend it in equalisation before treatment.
- 05The problem
Odour complaints from neighbours.
What we doCover anaerobic tanks, capture and burn the biogas, and remove hulls and screenings from site daily.
What we offer
What Rispri offers vegetable processors.
Effluent treatment plants
Screening, DAF, UASB and aerobic ETPs designed for seasonal load.
ETP solutions →Effluent testing
NABL-accredited tests through the campaign, plus monthly compliance reports.
Testing →Biogas recovery
Biogas capture and use from anaerobic stages and organic solid waste.
Waste-to-energy →ETP and boiler chemicals
Coagulants, polymers and boiler treatment, tested on your water.
Chemicals →Solid waste management
Plans for hulls, rejects and sludge: feed, compost or digestion.
Waste management →Buying guide
What to ask before you buy a food processing ETP.
Use this list with any supplier, including us.
- Is the design based on in-season samples? Composite samples at peak, not one grab sample.
- Is it sized on peak-season COD load? Ask for the kg COD per day used.
- How will the anaerobic sludge survive the off-season?
- What is the start-up plan, and who runs it?
- How much biogas, and what will it replace?
- Which outlet values are guaranteed in writing?
- Where do hulls, screenings and sludge go?
- Who tests the outlet? A NABL-accredited report carries weight with the board.
Why Rispri
One team from sample to running plant.
Our own NABL lab
We test your effluent through the season and certify the outlet, so the designer and the tester work together.
Engineering since 1999
1,498+ plants and turnkey projects for industries, hotels, hospitals and cities.
Chemicals in house
Coagulants, polymers and boiler chemicals from our own catalogue keep running costs predictable.
Operate and maintain
Seasonal O&M with start-up support, lab reports and help with your board.
Questions
Pea and vegetable processing effluent FAQs.
What is in pea processing wastewater?
Mostly dissolved sugars, starch and protein from blanching, plus skins, pulp and soil from washing, and cleaning chemicals from CIP. It is warm, strongly organic (BOD often 1,500 to 4,000 mg/L) and ferments quickly if left standing.
Why use anaerobic treatment first?
Aerobic treatment of very strong effluent needs a lot of aeration power. A UASB reactor removes most of the COD without air and produces biogas, leaving a much smaller aerobic stage to polish the water.
What discharge standards apply to vegetable processing effluent?
Most consents use the general standards: for inland surface water, pH 5.5 to 9.0, BOD 30 mg/L, COD 250 mg/L, TSS 100 mg/L and oil and grease 10 mg/L. For land irrigation the BOD limit is 100 mg/L. Your consent may set tighter values.
How do you handle the seasonal nature of pea processing?
By sizing for peak-season load, with a large equalisation tank, and by planning the off-season: preserving the anaerobic sludge, servicing equipment and ramping the load up before the harvest peak.
Will the plant work after being idle for months?
Yes, if planned for. Granular UASB sludge kept cool and covered stays active for months, and the aerobic stage can be reseeded. Start up two to four weeks before the campaign and check pH, VFA and alkalinity daily.
How much biogas can a pea plant produce?
Roughly 0.25 to 0.29 m³ of methane per kg of COD removed. A plant treating 300 KLD at 4,000 mg/L COD might produce around 400 m³ of biogas a day in season, about the energy of 250 litres of diesel.
What can be done with pea hulls and pods?
Fresh hulls are good cattle feed and can also be ensiled, composted or digested for biogas. Keeping them out of the drain greatly reduces the load on the ETP.
How much does a food processing ETP cost?
As an indication, a 200 to 300 KLD plant with UASB and MBBR costs about ₹80 lakh to ₹1.8 crore for equipment and installation, excluding civil work and land. Cost follows the COD load, so we price after testing your effluent.
Can treated effluent be reused in the plant?
Yes, for floor and crate washing, gardens, cooling towers and, where allowed, irrigation. It must not touch the product; water in contact with food must be of potable quality.
Can we use a lagoon instead of a UASB?
Yes, if you have plenty of land. Covered anaerobic lagoons are cheaper to build but take far more space, need cover to control odour and respond more slowly to load changes.
Why does our ETP smell during the season?
Usually because effluent sours in drains, equalisation or open anaerobic tanks. Mixing, shorter holding times, covering anaerobic tanks and burning the biogas usually solve it.
Do you operate seasonal ETPs?
Yes. We run start-up, campaign operation and shutdown under O&M contracts, with trained operators, chemicals and NABL-accredited test reports for your board.
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