Quick answer: POME arrives hot, oily and extremely strong — commonly 40,000 to 60,000 mg/L COD, which is roughly a hundred times domestic sewage. That strength is why anaerobic digestion, not aeration, is the core of every viable POME plant: aerating that load would be prohibitively expensive and would produce enormous volumes of sludge.
What makes POME difficult
Palm oil mill effluent is one of the strongest industrial effluents routinely treated. Three properties drive the whole design:
| Property | Typical character | Design consequence |
|---|---|---|
| Organic strength | Very high COD, commonly tens of thousands of mg/L | Anaerobic treatment is the only economic first stage |
| Temperature | Hot on discharge from sterilisation | Must be cooled before biological treatment |
| Oil and grease | Significant residual oil | Oil recovery and removal ahead of biology |
| Solids | High suspended and colloidal solids | Large sludge volumes to handle |
| pH | Acidic on discharge | Correction before anaerobic digestion |
| Seasonality | Flow follows the harvest | Plant must cope with a variable load, not a constant one |
The seasonality point is underrated. A plant sized on peak-season throughput sits underloaded in the low season, and anaerobic biomass does not tolerate long starvation well. Ask any supplier how their design handles the low season before you compare prices.
The process chain
1. Oil recovery and cooling
Residual oil is recovered ahead of treatment — it has value, and it would otherwise inhibit the biology and foul every downstream surface. Cooling is mandatory: anaerobic digestion has a temperature range, and effluent leaving sterilisation is well above it.
2. pH correction and equalisation
Raw POME is acidic, and anaerobic digestion is sensitive to pH. Equalisation also buffers the batch character of mill discharge into something the digester can accept steadily.
3. Anaerobic digestion — the core stage
This is where the bulk of the organic load is removed. It is chosen for POME not out of preference but out of arithmetic: aerobic treatment of this load would demand an enormous amount of aeration energy and would generate surplus sludge in volumes that are impractical to handle. Anaerobic digestion removes the load at a fraction of the energy cost, produces far less sludge, and generates biogas that can be captured and used.
4. Aerobic polishing
Anaerobic treatment alone will not reach a discharge standard. An aerobic stage — activated sludge, MBBR or SBR depending on the limit and the site — polishes the remaining COD and handles ammonia.
5. Solids separation and sludge dewatering
Every stage above produces sludge, and POME produces a lot of it. This is the stage most often under-built. See how the five stages of a complete wastewater treatment system size against each other.
Ponds or tanks?
Many mills have historically used open lagoon systems. They work, they are cheap to build, and they have three real costs that are increasingly decisive:
- Land. Lagoon systems need a great deal of it, and retention times are long.
- Methane release. Open anaerobic lagoons release biogas to atmosphere. Where emissions are regulated or where the mill wants the energy, this is a direct loss.
- Control. A lagoon cannot be tuned. When the discharge limit tightens, there is little to adjust.
Closed tank-based digestion costs more to build, occupies far less land, allows biogas capture, and can be controlled. The right answer depends on land availability, the discharge standard, and whether biogas has value at your site — but the trend in tightening-permit jurisdictions runs toward closed systems.
Sludge: the part that decides your running cost
POME plants generate substantial sludge from oil separation, from anaerobic digestion and from the aerobic stage. What you do with it splits into two paths:
| Land application | Off-site disposal | |
|---|---|---|
| Cake dryness needed | Lower — wetter cake acceptable | As dry as practical |
| Equipment that fits | Multi-disc screw press — continuous, unattended | Chamber or membrane filter press — much drier cake |
| Cost driver | Transport volume | Disposal weight |
Where cake leaves the site and is charged by weight, the moisture difference between a screw press cake and a membrane filter press cake is a permanent monthly saving, and it is straightforward to model before you buy. Where sludge is applied to the plantation, the screw press’s continuous unattended operation usually wins. Our comparison of filter press versus screw press for sludge dewatering works through the decision in detail.
What to send when asking for a proposal
- Mill throughput in tonnes of fresh fruit bunch per hour, and operating hours
- POME volume per day, and how it varies between peak and low season
- Effluent analysis: COD, BOD, suspended solids, oil and grease, pH, temperature, ammonia nitrogen
- The discharge standard you must meet, or whether effluent is land-applied
- Whether biogas capture is wanted, and whether there is a use for the energy on site
- Available land, and whether an existing lagoon system is being upgraded or replaced
- How sludge currently leaves the site and how it is charged
Item 2 is the one most often given as a single number. Give the range, because a plant that performs in peak season and starves in the low season is a plant that will fail its limit twice a year.
Upgrading an existing lagoon system
Most POME projects are upgrades rather than new builds. The usual sequence, in order of return:
- Fix oil removal and cooling first. They are cheap and they protect everything downstream.
- Add or improve the polishing stage if the gap to the limit is modest.
- Convert anaerobic lagoons to closed digestion where land, emissions or biogas value justify it.
- Add mechanical dewatering where sludge handling has become the bottleneck — which it usually has by this point.
Working in that order avoids the common mistake of buying a large new biological stage while the real constraint is upstream oil carryover or downstream sludge backlog.
Frequently asked questions
Why is anaerobic treatment used for POME instead of aeration?
Because of the organic strength. POME carries an extremely high COD load, and aerating that much load would demand an enormous amount of energy and produce surplus sludge in volumes that are impractical to handle. Anaerobic digestion removes the bulk of the load at a fraction of the energy cost, produces far less sludge, and generates biogas that can be captured and used.
Does POME need to be cooled before treatment?
Yes. Effluent leaving sterilisation is well above the temperature range anaerobic digestion operates in, so cooling is mandatory rather than optional. Feeding hot POME directly to a digester inhibits the biomass and destabilises the process.
Can anaerobic treatment alone meet a discharge standard?
No. Anaerobic digestion removes the bulk of the organic load but leaves residual COD and ammonia above typical discharge limits. An aerobic polishing stage — activated sludge, MBBR or SBR depending on the limit and the site — is required after it.
Should we replace our lagoon system with closed tanks?
It depends on three things: how much land you have, how strict your discharge standard is, and whether biogas has value at your site. Lagoons are cheap to build but need a lot of land, release methane to atmosphere, and cannot be tuned when limits tighten. Closed digestion costs more, uses far less land, allows biogas capture and can be controlled.
What dewatering equipment suits POME sludge?
It depends on where the sludge goes. If it is applied to the plantation, a multi-disc screw press usually wins because it runs continuously and unattended and copes well with oily sludge. If cake leaves the site and disposal is charged by weight, a chamber or membrane filter press produces a much drier cake and the moisture difference becomes a permanent monthly saving.
How does seasonality affect the plant design?
POME flow follows the harvest, so load varies considerably through the year. A plant sized only on peak-season throughput will sit underloaded in the low season, and anaerobic biomass does not tolerate prolonged starvation well. Give your supplier the seasonal range rather than a single average figure, and ask specifically how the design handles the low season.
Send your mill throughput, effluent analysis and discharge or land-application requirement and we will propose the process chain and equipment: request a POME treatment proposal.