Palm mills churn out empty fruit bunches (EFB) by the hundred‑thousand tonnes; turning them into compost and biochar is emerging as a scale‑ready play with soil and climate upside.
In the world’s biggest palm‑oil regions, tens of millions of tonnes of fresh fruit bunches (FFB) move through mills each year, and roughly 20–25% of that mass exits as fibrous EFB residue (ResearchGate) (ResearchGate). A mill running ~60 t FFB/hour (~500 kt/year) can generate on the order of 100 kt/year of EFB, making sustainable disposal and valorization a core operating decision.
Two routes dominate the conversation: aerobic composting for nutrient return to the plantation and pyrolysis for biochar, a carbon‑rich, stable soil amendment. The opportunity is not speculative; it’s backed by field trials, reactor runs, and practical facility design guidance.
Industrial composting parameters and design
EFB composting starts with a chemistry fix. Raw EFB is high‑carbon, low‑nitrogen material; its carbon‑to‑nitrogen ratio (C/N) typically exceeds 50:1 and has been observed near ~90–100:1, which slows biodegradation unless balanced with nitrogen‑ and moisture‑rich inputs (PMC). Mills co‑process shredded EFB with thickened palm oil mill effluent (POME) solids or manures; blending EFB with ~10–30% POME solids raises nitrogen and moisture. Specialized microbial inoculants, such as Trichoderma, are sometimes added to accelerate lignocellulose breakdown (PMC), and some operators standardize inoculant addition using a dosing pump to keep rates consistent.
Design choices span open windrows and static/reactor systems. In windrows, shredded EFB (often ~10–20 cm pieces) is formed into rows ~2–3 m high and ~3–6 m wide; turning every few days—or adding a forced‑air blower—maintains oxygen and evens temperature. EPA‑style guidance puts maturation at ~8–20 weeks (epem.gr). Turning every 1–2 weeks is also common in practice for aeration and heat control.
Controlled “tower” composting underscores how fast EFB can stabilize when parameters are tight. In one study, non‑shredded EFB mixed with an activated liquid organic fertilizer was sealed in a concrete tower (0.4×0.4×3.0 m), held at ~55–65% moisture, and allowed to self‑heat thermophilically; by day 10 the material darkened, and by day 40 it matured to pH ~7.6–8.4, moisture ~41–58%, total C ~20–21%, total N ~1.0–1.25%, and C/N ≈20, meeting Indonesian compost standards (organic carbon >10–15%, N ≥0.5%, C/N ≤30, pH ~6–8) (ResearchGate) (ResearchGate).
Key controls are consistent across systems: moisture ~50–60% (fresh bunches often arrive ~60% H2O), thermophilic peaks around 50–65 °C for sanitization and speed, oxygen via turning or blowers, and pH trending from slightly acidic toward neutral/alkaline (ammonia formation and additives like dolomite can lift pH). Without inoculants or forced conditions, EFB piles can take 6+ months; with modern aids, 1–3 months is typical (PMC) (ResearchGate).
Nutrient profile and field performance
When done, EFB compost is a humus‑rich organic fertilizer. One Trichoderma‑stimulated trial reported N:P:K of 0.91:2.13:6.68 (% by weight) in the final product—potassium exceeded 6% of dry weight (PMC). Another EFB+POME compost reached ~1% N and ~0.10% available P (ResearchGate). Compared to inorganic NPK fertilizers at ~15% each, this is lower‑grade in N, but the organic matter delivers slow‑release nutrients, soil structure gains, moisture retention, micronutrients, and beneficial microbes.
Field data back the agronomy. Trials in Indonesia and Malaysia showed EFB compost—often co‑composted with POME—increased palm growth by ~15–20% versus unfertilized controls (ResearchGate). One optimization study identified ~130 kg EFB compost per palm per year (≈2.6 t/ha/year at 20×20 m spacing) plus 4.6 kg NPK palm–1·y–1 as optimal for 4‑year‑old palms (ResearchGate). Seedling work also found improved phosphorus uptake with EFB compost (PMC).
Yard layout, leachate, and emissions control
A compost yard must handle bulky, abrasive feed and tropical weather. Practical design includes heavy‑duty shredders, a concrete pad or compacted surface, drainage and leachate collection, windrow turners or blowers, and covered areas to limit rain dilution and nutrient washout. For ~100 kt/year of EFB and a 3–4 month composting cycle, expect ~25–30 kt “in process” at steady state. At ~0.5 t/m³ bulk density, that implies tens of thousands of square meters of windrow area—on the order of a ~100×300 m footprint—plus curing zones.
Collected leachate or co‑mixed POME can be routed through the mill’s wastewater line as needed—for example via an automatic screen for debris management, a DAF unit for primary solids separation, and a biological digestion stage—before reuse or discharge. Ventilation and simple gas monitoring are common good practice: aerobic composting emits CO₂, water vapor, and some ammonia; excessive CH₄ is unlikely in well‑aerated piles. Open burning of EFB is discouraged or regulated, and optimized composting shortens time and cuts CH₄/CO₂ versus stockpiling or burning (Winrock).
Pyrolysis and biochar yields
Thermal conversion offers a second pathway. Pyrolysis—heating biomass in low oxygen—splits EFB into a solid char (biochar), syngas, and bio‑oil; “slow” pyrolysis favors higher char yield with more volatile components, while “fast” pyrolysis gives less char but higher fixed carbon. In one fluidized‑bed experiment, 300 °C produced a maximum char yield of ~41.6% of dry feed; yields fell below 30% at 600–700 °C. The resulting char’s higher heating value as fuel was ~24–26 MJ/kg (ResearchGate).
Feed preparation matters. A microwave‑assisted case study densified EFB into ~100 g pellets and applied 850 W for ~30 minutes, producing biochar with 64.6% fixed carbon (67.4% C by weight) and a heating value of 26.7 MJ/kg; ash content was ~22% (ScienceDirect). While microwave pyrolysis is novel and not yet standard at scale, proven options include batch kilns, rotary drum reactors, metal retorts, and continuous screw pyrolyzers. Designed well, syngas byproducts can be combusted for process heat or electricity, including mill boiler integration.
Soil amendment effects and rates
As a soil amendment, EFB biochar is typically alkaline and porous, with high cation exchange capacity—traits that raise pH on acidic soils, retain nutrients, and improve water holding. On peat soils, adding OPEFB (oil palm EFB) biochar with dolomite significantly elevated soil pH and electrical conductivity; a field protocol applying 2.5 kg per palm of OPEFB‑biochar with half‑rate dolomite improved peat pH and palm growth, suggesting partial substitution for agricultural lime (ResearchGate).
Nutrient retention and yield results vary by soil. In a Malaysian acidic‑soil trial, adding 15–30 t/ha (wet basis) of slow‑pyrolysis EFB biochar increased available NPK and boosted sweet corn biomass; 30 t/ha gave the largest growth response. Rice‑husk char improved porosity and hydraulic conductivity but did not increase yield in that study, whereas EFB char’s net effect was more beneficial for crop growth (ResearchGate). Typical application guidelines in trials are ~1–5% w/w (10–50 t/ha), though local needs vary; an Indonesian peatland study used only a few kilograms per plant and still observed improvements (ResearchGate).
Beyond agronomy, biochar locks carbon into soil for hundreds to thousands of years, positioning EFB pyrolysis for carbon sequestration value in addition to nutrient cycling.
Integrated approach and quality benchmarks
Composting and pyrolysis can run in tandem. Well‑managed composting yields a neutral to slightly alkaline organic fertilizer; mature EFB composts typically contain ~20–25% organic carbon, ~1% total nitrogen, and a few percent of P and K, with process targets of C/N ~15–25, moisture 40–60%, and thermophilic peaks around ~60 °C—parameters controllable to meet Indonesian quality standards (ResearchGate) (PMC). Facility investment—land, shredder, turner, covered pads—is significant but offsets disposal costs and generates product.
At the same time, low‑temperature EFB pyrolysis can yield up to ~40% biochar by dry feed, with soil trials showing pH increases, higher K/P availability, and growth gains in palms and sweet corn at sufficient rates (ResearchGate) (ResearchGate) (ResearchGate). Char production can integrate energy recovery from syngas or bio‑oil, while composting can shrink methane emissions compared with stockpiling or burning (Winrock).
Pilot results are actionable: EFB + POME with cellulolytic microbes reached maturity in ~6 weeks in a tower setup (ResearchGate), and EFB biochar at 30 t/ha boosted sweet corn yield by ≈20–30% in an acidic soil study (ResearchGate). For mill managers, that points to integrated EFB management—compost for near‑term nutrient returns and biochar for long‑term carbon and soil function—as a credible, data‑driven strategy.
