Raw Wool Scouring Wastewater Treatment: Grease Recovery, Lanolin and High COD

A fleece leaving a sheep is anywhere from 30 to 70 percent impurity by weight — wool grease, dried sweat, sand, dirt, vegetable matter and dung. The scouring line exists to strip all of it off with hot water and detergent, and everything stripped ends up in the water. The result is a hot, alkaline, dark brown effluent with a grease content measured in grams per litre and COD that can exceed 50,000 mg/L in the first bowl. It is also one of the few industrial effluents where the most valuable material in the stream is the pollutant.

The Bowl Train and Why the First Bowl Dominates

A conventional scour is four to six bowls in series with counter-current water flow. Raw wool enters the first bowl, clean water enters the last, and the liquor moves the other way. Bowls run at 60 to 70 °C with non-ionic detergent and soda ash at pH 9 to 10, because wool grease emulsifies and suint dissolves under those conditions and neither happens well in cold water.

Load distribution across the train is extremely uneven. The first bowl, sometimes called the crack bowl, removes the bulk of the dirt and suint and can carry 40,000 to 100,000 mg/L COD with 10,000 to 30,000 mg/L grease. By the last rinse bowl the water is comparatively clean. Treating all bowls as one combined stream throws away the only thing that makes the problem tractable — the fact that most of the load is concentrated in one place where it can be recovered rather than destroyed.

Suint deserves a mention because it is the reason this effluent has unusually high potassium. Dried sheep sweat is largely potassium salts of organic acids; it dissolves instantly and contributes both COD and alkalinity. Historically it was evaporated and sold as potash. In a few plants it still is.

Wool grease — lanolin once it is refined — is a saleable product used in cosmetics and pharmaceutical ointments. Recovering it is standard practice and it is the single most effective COD reduction step available, cutting 40 to 70 percent of the load before any biological treatment sees the water.

The centrifugal route recovers grease from the warm first-bowl liquor directly, usually with a heated disc stack centrifuge running at 80 to 95 °C. It is clean, continuous and preserves grease quality. The alternative is acid cracking: acidify the liquor to pH 3.5 to 4 with sulphuric acid to break the emulsion, separate the greasy sludge, then neutralise before further treatment. Acid cracking recovers more grease but degrades its quality and adds a chemical cost and a neutralisation step.

Whichever route is used, the recovered grease has to be removed quickly. Lanolin solidifies near body temperature and the emulsion re-stabilises if the liquor cools and sits, which is why grease recovery works best when the centrifuge is fed directly from the bowl rather than from a buffer tank.

Dewatering, DAF and the Residual Emulsion

After grease recovery there is still 1,000 to 5,000 mg/L of emulsified grease and a lot of suspended dirt. Dissolved air flotation with ferric or aluminium coagulation handles this well and produces a float that can be combined with the recovered grease stream or sent to sludge handling. The same selection criteria reappear in surface treatment pickling line wastewater, which is worth opening alongside this one.

Chemical coagulation alone is cheaper to install and usually less effective on the emulsified fraction, which is stabilised by the detergent still present in the water. If the plant can shift to a low-foaming, readily split detergent, downstream performance improves noticeably. That is a purchasing decision, not a treatment decision, and it is often the cheapest upgrade available. If your site also runs this kind of duty, Chemical Fertiliser Plant Wastewater Treatment system covers the cost side of the decision in more depth.

Sand and grit from the first bowl are genuinely abrasive. Screens and grit removal ahead of pumps and centrifuges are not optional on this stream — wear rates on unscreened scouring liquor are severe.

What This Looks Like in Practice

One reference point: a 6 m³/day installation we delivered in Wenshui, Shanxi (2021) was treating feed at roughly 172,000 mg/L COD and holding discharge near 5,000 mg/L, about 97.1% removal. The train was hydrolysis acidification + DAF + oil separation + ultrafiltration.

Figures are site-measured values from commissioned plants, not modelled estimates.

Biological Treatment and Its Failure Modes

Anaerobic treatment of the high-strength first-bowl stream is attractive for energy recovery and works in UASB or contact reactors, but grease is the enemy. Long-chain fatty acids adsorb onto biomass, cause floatation and washout, and are inhibitory at moderate concentrations. Thermophilic operation helps by keeping the grease liquid. Most plants that succeed here either pre-treat aggressively or co-digest with a dilute stream. For the reuse angle specifically, power plant flue gas desulphurisation wastewater treatment goes further than we can here.

Aerobic polishing is more forgiving. Extended aeration, sequencing batch reactors and MBRs all handle scouring effluent once the grease is down to a few hundred mg/L. Nutrient balance matters: this effluent is carbon-rich and comparatively short of nitrogen and phosphorus, so urea and phosphoric acid dosing is normally needed to hold a BOD:N:P ratio near 100:5:1.

Foaming and filamentous bulking are the two chronic problems. Both trace back to grease and low nutrient conditions, and both are usually treated with antifoam and chlorine dosing rather than fixed — which works for a week and then comes back. Fixing grease removal upstream is the durable answer.

Other Streams on the Same Site

Scouring is not the only wastewater a wool mill produces. Carbonising — treating wool with sulphuric acid and baking to destroy vegetable matter — generates a strongly acidic effluent with dissolved organic matter and requires neutralisation and usually separate handling. Dyeing and finishing lines contribute the familiar textile problems of colour, salt and residual auxiliaries.

Keeping these segregated is worth the extra pipework. Acidic carbonising effluent neutralises scouring alkalinity for free if it is metered in, but it needs flow balancing and pH control to do that safely. Mixing everything into one sewer produces a larger, more variable and harder-to-treat stream than any of the parts.

Integrated Treatment Strategies

Where several streams need joint treatment, Designing Zero Liquid Discharge is the more detailed reference. Most facilities do not run a single clean stream, and a shared equalisation and biological stage is usually the economical answer once the streams are chemically compatible.

Why Choose Baihuipu as Your Manufacturer

Picking a supplier for this kind of plant is mostly about who carries the risk when something goes wrong. We have built this equipment for more than twenty years, and we are the ones who fabricated it, programmed the controls and will still answer the phone three years from now.

Own Factory, Real Capacity

Tanks, skids, control panels and membrane housings are built in our own Guangdong facility. Nothing critical is subcontracted, which is why we can commit to delivery dates and hold quality across a batch instead of hoping the shop floor gets it right.

20+ Years Across Dozens of Industries

Experience matters most when your waste stream behaves nothing like the textbook example. We have dealt with toxic organics, heavy metals, extreme salinity and refractory COD in food processing, chemical manufacturing, electroplating, mining and municipal projects.

Certification and Export Practice

CE marking is standard and we work to ISO 9001 procedures. Where a project calls for specific material grades, pressure vessel certification or ATEX-rated equipment, we build to that standard and ship the full documentation pack.

We Engineer the Whole Train

Screening, equalisation, biological or chemical treatment, membranes, evaporation, brine handling — the complete line comes from one organisation. Process design, mechanical, electrical and PLC programming sit under the same roof, so there is no gap for finger-pointing at handover.

After the Handover

Spares for everything we install are held in stock. Remote telemetry is available on most systems, and our service engineers commission, train your operators and turn out for emergencies.

Documentation You Can Actually Audit

Each system ships with as-built drawings, material certificates, welding records and a functional specification. If a client's own consultant wants to review the process calculation basis, we hand it over rather than treating it as proprietary.

Twenty-Plus Export Markets

We have shipped to the United States, Canada, Russia, Indonesia, India, Nigeria and Vietnam among others. Crating, export documentation and certificates are handled in-house, which keeps customs surprises to a minimum.

Getting Started

Send us a water analysis and your production profile and we will tell you honestly what the process should look like and roughly what it costs to build and run. Reach our engineering team on WhatsApp: +86 13631765076 or via hkbhp.com.

WhatsApp: +86 13631765076

Frequently Asked Questions

What spare parts should we hold on site?

Critical spares are pumps, dosing valves, instrumentation sensors and any specialty media. We ship a recommended spares kit with the plant and hold stock for everything we supply, so lead times on replacements stay short.

What information do you need to quote?

Water analysis for your worst-case stream, peak and average flows, discharge limits, available footprint and utilities. If you do not have a full analysis yet, we can start from a partial one and flag the gaps.

Do you handle installation and operator training?

Every unit we supply is commissioned by our own engineers. Training happens on site with your actual operators, and the O&M manual covers routine work plus troubleshooting. Remote diagnostics through the control system are included for the first year.

What happens if the incoming wool scouring load exceeds the design figure?

Load swings are the most common reason plants underperform. We set the design envelope from your worst-case samples, not your average ones, and specify enough buffer in the biological stage to ride out shocks. If your process genuinely shifts up permanently, we can usually add capacity in stages.

What does it cost to run, per cubic metre?

Energy dominates, then chemicals, then sludge disposal. We give you a per-cubic-metre breakdown during proposal so you can compare it against your sewer charge — treating too aggressively is a common and expensive mistake.