From open ponds to sealed digesters, mills are racing to trap biogas from palm oil mill effluent and spin it into electricity — for themselves and nearby villages — after scrubbing it clean.
Industry: Palm_Oil | Process: Palm_Oil_Mill_Effluent_(POME)_Treatment
Palm oil mills use roughly 5–7.5 tonnes of water per tonne of crude palm oil (CPO), and about half becomes Palm Oil Mill Effluent (POME) (www.mdpi.com) (www.mdpi.com). That waste stream — ~95–96% water with 4–5% total solids (including 2–4% suspended solids) and sky‑high organic load (BOD, a biochemical oxygen demand indicator of organic load, ~8,200–35,400 mg/L; COD, chemical oxygen demand, ~15,100–65,100 mg/L) — is a methane rocket waiting to be captured (www.mdpi.com) (www.mdpi.com).
Unmanaged open ponds vent an estimated ~12.36 kg of methane (CH₄) per tonne of POME (www.mdpi.com). Seal that biology inside a digester, though, and yields jump: anaerobic digestion (AD) can produce ~0.014–0.035 m³ CH₄ per liter of POME; studies report 1 m³ POME producing ~28 m³ biogas at ~65% CH₄, and CH₄ content >50% is typical (www.mdpi.com). Linear modeling predicted ~909.8 m³ POME could generate ~34,490 m³ biogas (www.mdpi.com).
In practical terms, a mid-size mill (60 t FFB/hour) generating ~234,000 m³ POME/year could produce ~33,150 MWh of electricity, with a payback of ~4.3 years (www.mdpi.com). Indonesia’s plantation base (≥12.8 million hectares, >850 mills) means POME biogas potential far exceeds current use: 2012 production could have yielded ~3.3 million MWh/year, displacing ~1.3 million kL of diesel (prestasisawit.mpob.gov.my). Yet by 2021, only ~28.4 million m³ of POME biogas were used — 5.9% of the 2025 goal (489.8 million m³) (britcham.or.id). Fully harnessed, POME biogas could cut ~42.6 MtCO₂e/year (methane abatement plus diesel avoidance) (britcham.or.id) (prestasisawit.mpob.gov.my).
Covered lagoon retrofits
An economical move is to retrofit existing anaerobic ponds with gas‑tight covers — essentially turning them into digesters. A covered lagoon typically uses an HDPE or fabric membrane to seal an existing pond bottom and/or surface, creating a near‑anaerobic digester (www.solmax.com) (www.solmax.com). One Malaysian project lined and covered ~9,290 m² of lagoon to capture methane (www.solmax.com) (www.solmax.com).
Covered lagoons benefit from long hydraulic retention time (HRT, how long wastewater stays in the reactor) and low per‑volume capital cost, but they need land. Performance can be strong: a closed‑lagoon plant cut POME COD by ~91% and produced ~325,000 m³ biogas/month (55% CH₄) (www.mdpi.com). In Malaysia, a comparative analysis of four in‑ground lagoons found COD removal of 67–85% and CH₄ yields of 0.135–0.364 Nm³ per kg COD removed (www.researchgate.net).
Durability and mixing are the pain points. Simple covers (non‑UV stabilized black HDPE) can crack and leak within a few years (www.en-aqualimpia.com). Modern designs use thick UV‑resistant liners (e.g., 2 mm EPDM rated ≥20 years) and floating covers (www.en-aqualimpia.com). Gas is commonly collected via perimeter trenches. Because sludge accumulates, periodic removal or slaker agitation is needed (www.en-aqualimpia.com). Mechanical agitation improves uniformity and biogas output and prevents float layers (www.en-aqualimpia.com). Where plants add mixers or ancillary devices, mills lean on wastewater ancillaries to standardize equipment across lagoons.
Figure: Typical covered POME lagoon with HDPE liner and floating cover for biogas capture (www.solmax.com) (www.solmax.com). (Source: Solmax/SYS, Malaysia case)
Megawatts from pond covers
In Malaysia, covered lagoons frequently power 1–3 MW generators; one project’s POME lagoon (~100,000 ft²) is sized to supply ~1.6 MW to the grid (www.solmax.com). In Indonesia, less than 10% of mills have any biogas plant (www.mdpi.com), and many still run four‑stage open ponds that vent methane (www.en-aqualimpia.com).
Closed‑tank digester control
Compact sealed reactors — sequencing batch, upflow, or continuous stirred‑tank reactors (CSTR, a fully mixed anaerobic vessel) — trade land footprint for process control and gas yields per volume. In these systems, POME (often cooled) is fed into a sealed reactor (lined concrete or steel) with mechanical mixing and biogas capture. CSTRs typically operate mesophilic (∼35–40 °C; “mesophilic” is moderate temperature biology); thermophilic (higher‑temperature) reactors can edge up gas but need extra heat, so Indonesian practice favors mesophilic operation (organicsbali.com). Continuous stirring preserves even conditions and avoids dead zones; many designs recirculate effluent to dilute scum and stabilize pH (www.mdpi.com). Mills implementing AD deploy anaerobic digestion systems to match throughput and stability goals.
Conversion rates can be high. At a Bangka Island site, a sealed lagoon (essentially a large CSTR) treating all POME from a 30 t/h mill achieved ~91% COD removal and generated 325,292 m³ biogas/month (55% CH₄) (www.mdpi.com). One estimate suggests a 45 t/h mill could support ~0.95–1.52 MW of cogeneration using combined POME+EFB gas (www.mdpi.com). A developer notes a 60 t/h mill with a CSTR plant could yield ~2–4 MWe (megawatts electrical) depending on efficiency and POME quality (organicsbali.com).
Closed tanks cost more per cubic meter than lagoons but need far less land. One study notes ~US$2.5–3 million for a 1 MW POME digester in Indonesia (prestasisawit.mpob.gov.my). Economics vary: an Indonesian techno‑economic case in Bangka reported IRR ~6.8% (10.8‑year payback) (www.researchgate.net), while a Malaysian analysis of a 60 t/h mill found payback ~4.3 years (www.mdpi.com). With free feedstock and large scale, projects often bank on feed‑in tariffs (FITs, policy price supports) or carbon credits; during high CDM (Clean Development Mechanism) prices, IRRs rose above 20% (prestasisawit.mpob.gov.my).
Some operations merge approaches — an “in‑ground lagoon” fully covered but with mixers — to combine low cost and better kinetics (www.researchgate.net). The common denominator is methane capture: any sealed anaerobic chamber outperforms open ponds. Experts warn Indonesia needs a “technological shift from closed lagoons to more efficient bioreactors” to boost yields and economics (www.researchgate.net).
Biogas cleaning and upgrading
Raw POME biogas typically carries ~50–70% CH₄, 30–45% CO₂, and traces of hydrogen sulfide (H₂S), water vapor, oxygen, ammonia, and siloxanes (silicon‑containing compounds that foul engines) (www.mdpi.com) (ohioline.osu.edu). For on‑site power, the priority is removing corrosives: H₂S must be scrubbed (via iron chloride dosing, bio‑scrubbers, or activated carbon) to protect engines (ohioline.osu.edu). Mills dosing iron salts standardize delivery with an accurate dosing pump, and many designs include activated carbon beds to polish H₂S or siloxanes. Moisture is removed by cooling (chillers) or condensation to avoid rust and reduce flammability risk (organicsbali.com) (ohioline.osu.edu). Low‑level siloxanes are captured with activated carbon or silica gel prior to combustion turbines (organicsbali.com) (ohioline.osu.edu). A typical POME plant routes raw gas through a bioscrubber, then a chiller and particulate/siloxane filters before the generator (organicsbali.com).
Upgrading to pipeline spec or CNG requires CO₂ removal. Common options include water scrubbing, pressure‑swing adsorption (PSA), amine absorption, and membrane separation (ohioline.osu.edu) (ohioline.osu.edu). In bench tests, water scrubbing with >9.7 MPa feed achieves ~97% CH₄ (ohioline.osu.edu); PSA and amine systems can also deliver pipeline‑quality (>97%) CH₄ (ohioline.osu.edu). Amine absorption maps to proven gas‑sweetening packages such as a CO₂/H₂S amine solvent, while membrane separators (hollow‑fiber polyimers) are compact and popular; a Malaysian techno‑economic study found membrane separation delivered the shortest payback for POME bio‑CNG (www.mdpi.com). The Ohio State factsheet notes water scrubbing simultaneously removes CO₂ and H₂S (and ammonia if needed), whereas membranes mainly strip CO₂ and water (ohioline.osu.edu) (ohioline.osu.edu). Given POME biogas can contain 0–2,000+ ppm H₂S (ohioline.osu.edu) (ohioline.osu.edu), hybrid trains are common. For CO₂ polishing, mills increasingly look to compact membrane systems. Pipeline gas typically requires <3% CO₂/H₂S and methane >95–97% (ohioline.osu.edu).
Electricity and local benefits
Captured biogas is commonly burned in engines or turbines to generate electricity, often with useful heat for the mill. Gas engines convert ~30–40% of biogas energy into electricity (www.mdpi.com). One plant reported ~696,000 kWh/month from 325,000 m³ biogas (55% CH₄), implying ~39% electrical efficiency (www.mdpi.com). In well‑optimized CHP (combined heat and power), one tonne of POME yields ~10 kWh. Scale matters: a 30 t/h mill’s POME can sustain ~2 MW (~8.3 GWh/year), and a 60 t/h mill ~3–4 MW (~13.3 GWh/year) (www.mdpi.com).
Power typically first covers mill loads (sterilizers, dryers, boilers) with surplus for local grids. In rural Indonesia, POME gas slashes diesel dependence: POME power costs about Rp700–900/kWh (≈$0.05–0.06), versus Rp2,700–4,000 for diesel gensets (prestasisawit.mpob.gov.my). At 2012 output, POME‑to‑power could replace ~1.3 million kL diesel/year (~4% of national imports) (prestasisawit.mpob.gov.my). Community gains are tangible: a Malaysian project reported odor‑free clean energy for nearby villages (www.solmax.com), and a Jakarta Post analysis argued POME biogas can deliver cheap, reliable power for remote villages (prestasisawit.mpob.gov.my) (prestasisawit.mpob.gov.my).
On emissions, the Bangka plant alone could cut ~1,131 t CO₂e/month (~13.6 kt/year) (www.mdpi.com). Nationally, fully capturing POME biogas would lower emissions by tens of MtCO₂e annually (britcham.or.id) (prestasisawit.mpob.gov.my). Those gains underpin policy: Indonesia’s RUEN (national energy plan) targets 489.8 million m³ of POME biogas by 2025, and the government has promoted POME‑to‑power via FITs and cooperation with GIZ (greengrowth.bappenas.go.id) (britcham.or.id). Uptake remains low (5–10% of mills) due to capital and regulatory hurdles (www.mdpi.com) (prestasisawit.mpob.gov.my), and business cases often pencil out only with grid access or carbon credits (prestasisawit.mpob.gov.my) (www.researchgate.net).
Waste‑to‑energy conclusion
Whether via covered lagoons or closed‑tank reactors, POME AD can capture >90% of POME’s methane (www.mdpi.com) (www.researchgate.net). After scrubbing H₂S and moisture — and, where needed, CO₂ upgrading through membrane systems or an amine solvent — the biomethane runs generators that deliver affordable, lower‑carbon power for mills and nearby communities. This waste‑to‑energy route reduces costs (fuel substitution with process by‑product reuse) and emissions (methane and fossil displacement), aligning with Indonesia’s energy transition goals and climate targets (britcham.or.id) (www.mdpi.com).
Sources: Peer‑reviewed studies and industry reports on POME treatment and biogas, including Sodri et al. 2022 (Energies) (www.mdpi.com) (www.mdpi.com), Malaysian case studies (www.solmax.com) (www.mdpi.com), Indonesian government and industry data (britcham.or.id) (prestasisawit.mpob.gov.my), and technical references on biogas cleaning (ohioline.osu.edu) (www.mdpi.com).
