Empty fruit bunch piles can leach a “POME‑strength” runoff. A sealed concrete pad with dedicated drainage and a biological treatment train is the difference between compliance and contamination.
Oil palm mills generate empty fruit bunch (EFB) waste at industrial scale — typically 25–30% of the processed fresh fruit bunch (FFB) by weight (studylib.net). For a 3,000‑ton‑per‑day mill, that’s roughly 750–900 tonnes of EFB every day.
When EFB are piled outdoors, rainfall and the juice from decaying fiber can create high‑strength runoff. Studies of EFB processing report wash‑water chemical oxygen demand (COD, a measure of total oxidizable organics) up to ~75,000 mg/L and biological oxygen demand (BOD, the oxygen required by microbes to break down organics) ≈31,300 mg/L (www.mdpi.com) — comparable to untreated palm oil mill effluent (POME), which typically has COD >20,000 mg/L and BOD ≈30,000 mg/L (www.mdpi.com).
Such leachate can deplete oxygen in receiving waters and breach discharge limits. Capturing and treating EFB runoff is therefore critical.
EFB generation and leachate risk
The mass balance alone explains the urgency: large EFB pads see both high organic loads and tropical downpours. The runoff’s strength and volume mean unmanaged flow can overwhelm on‑site drainage and nearby waterways, pushing COD/BOD toward untreated POME levels (www.mdpi.com).
Impermeable concrete pad specification
An EFB storage pad is constructed on a sealed, non‑porous surface (reinforced concrete) to prevent nutrient‑rich leachate from percolating into soil or groundwater. An impermeable surface also allows visual inspection and easier cleaning.
Design practice grades the pad ≈1–2% to direct runoff toward drains or sump pits, with all cracks or joints sealed to avoid leakage. Capacity planning accounts for peak rainfall and normal EFB loading; Southeast Asian storms can exceed 100–200 mm/day, so bunds or kerbs are used to contain heavy downpours.
Guidelines require separate drainage for process effluent and stormwater; wastewater channels must not intermingle with stormwater channels (id.scribd.com), and the pad’s storm drains do not overflow into the waste collection system.
Durability comes from concrete in the C30/C35 class, with thickness ≥15–20 cm and reinforcement to withstand heavy equipment loads and erosion. The surface is troweled or broom‑finished for traction and sealed to limit wear, with extended curing to prevent cracking. Where oil or chemical spills are possible, surface coatings such as epoxy or sealants are used to resist deterioration.
Dedicated drainage and collection
An independent drainage network under or around the pad collects all liquid runoff. Drainlines (PVC/HDPE) slope to a central collection tank or sump, sized for worst‑case rainfall plus runoff from saturated EFB stacks. Covers or grates prevent solids from clogging, and metals or oil traps are added if EFB contain residual oil. The separation of wastewater and stormwater channels is explicit in Indonesian guidelines (id.scribd.com).
Collected runoff flows into a sealed sump or settling pond for primary sedimentation, allowing EFB fibers and suspended solids (TSS, total suspended solids) to settle and any floating oils or scum to be skimmed. The clarified water then moves by pump or gravity into the main treatment facility. Sumps and tanks are lined or concrete to avoid seepage, and overflow or emergency relief routes return safely to the treatment system or balanced storage without flooding the pad.
For primary sedimentation, many mills deploy a clarifier as part of this front end. See clarifier applications for removing suspended solids in industrial wastewater.
Multi‑stage runoff treatment train
Captured EFB leachate is extremely high in organics and requires a staged approach to meet discharge standards (www.mdpi.com; id.scribd.com).
Sedimentation/clarification typically removes 50–70% of TSS. Settled detritus is scraped out and either composted or sent for anaerobic digestion.
Anaerobic digestion (oxygen‑free biological treatment) using an upflow anaerobic sludge blanket (UASB, a granular‑sludge reactor) or lagoons is applied for high‑strength leachate. Conventional anaerobic ponds run ≥30–60 days hydraulic retention time (HRT, the average time wastewater remains in a reactor). Experience from POME shows that long anaerobic retention (60–75 days) can cut BOD by ~80–90% (e.g., from ~27,000 to 3,500–5,000 mg/L; pustakapetani.blogspot.com). The biogas produced is a useful energy source. Because EFB leachate may be toxic if overloaded, co‑digestion with the main POME flow balances nutrients (www.mdpi.com).
Packaged anaerobic systems are commonly grouped under biological digestion offerings; see waste‑water biological digestion options for lagoon and reactor configurations.
An aerobic polishing stage (oxygenated biological treatment) follows, whether after anaerobic or directly. Aerated lagoons, oxidation ditches, or Sequencing Batch Reactors (SBR, time‑sequenced fill‑and‑draw reactors) are used. A well‑designed aerobic pond with 10–20+ days HRT can bring BOD down near the required ≤100 mg/L under Indonesian standards (id.scribd.com).
Where land is available, a constructed wetland or green belt provides tertiary polishing. Laboratory studies show a reed‑wetland (Scirpus grossus) can remove ~96–97% of COD and ~98% of TSS in POME polishing over ~30 days (www.researchgate.net), and similar plant/microbe systems (water lettuce, duckweed, algae) also reduce nutrients (N, P).
Many mills standardize aerobic polishing with time‑sequenced reactors; see sequence batch reactor (SBR) configurations for flexible, high‑rate operation.
Final filtration and disinfection can follow biological treatment if required to meet residual turbidity or pathogen targets before discharge or reuse. Sand filtration is a common step; see sand/silica media for capturing 5–10 micron particles.
Activated carbon is used when organics and taste/odor need polishing; see activated carbon for adsorption applications in industrial water.
Non‑chemical disinfection is often specified for low‑operating‑cost polishing; see ultraviolet (UV) systems for 99.99% pathogen kill.
Regulatory benchmarks and retention time
By combining these stages, typical effluent can meet or beat Indonesian discharge limits. KepMenLH No.51/1995 for CPO mills specifies BOD ≤100 mg/L, COD ≤350 mg/L, TSS ≤250 mg/L, oil/grease ≤25 mg/L, total N ≤50 mg/L, and pH 6–9 (id.scribd.com). Properly sized anaerobic/aerobic ponds with ≥30–90 days total retention time and vegetated polishing have been shown to reduce COD/BOD by >90% (www.researchgate.net; pustakapetani.blogspot.com).
As design anchors, 30–60 days of anaerobic retention followed by 10–20 days of aerobic polishing can achieve >95% BOD removal, while wetlands (if applied) often run ~20–30 days of contact time for remaining organics and nutrients (www.researchgate.net).
Design loads and monitoring metrics
Runoff volume scales with pad area and storm intensity. If pad area is A and rainfall intensity is R (mm/day), max daily runoff is 0.001·A·R (m³). Sumps and pumps are sized for this peak plus any base discharge from EFB flushing.
For load‑of‑organics planning, a design‑strength EFB leachate COD ~50,000 mg/L (BOD ~30,000 mg/L) is a practical basis (www.mdpi.com). At 1,000 m³/day, untreated organic load is ~50,000 kg COD/day. A multi‑stage treatment (e.g., ~80% anaerobic + ~90% aerobic) must cut this by ≥99.5% to reach <350 mg/L COD.
Other parameters trend as follows: EFB runoff pH is typically ≈5–7 (mildly acidic from organic acids), and aeration/wetlands tend to neutralize pH. Nutrients (N, P) released during EFB decomposition are mostly captured in biomass or denitrified in anaerobic zones; care is taken not to discharge excess ammonia.
Periodic monitoring — at least monthly — of BOD, COD, TSS, oil & grease, NH₃‑N, and pH is mandated for palm mills (id.scribd.com).
Why the pad-to-polishing chain matters
A sealed pad, segregated drains, contained sumps, and staged biological treatment convert a high‑BOD/COD leachate into compliant effluent. Captured leachate from EFB stacks — essentially a concentrated “juice” — is best handled as engineered wastewater: sedimentation, anaerobic digestion, aerobic polishing, and, where needed, filtration and disinfection.
The same measures required by regulation (id.scribd.com; id.scribd.com) also enable resource recovery: primary solids for composting and biogas from anaerobic stages (www.mdpi.com; www.researchgate.net; pustakapetani.blogspot.com).
