Properties and Uses of POME

POMEPalm Oil processing gives rise to highly polluting waste-water, known as Palm Oil Mill Effluent (POME), which is often discarded in disposal ponds, resulting in the leaching of contaminants that pollute the groundwater and soil, and in the release of methane gas into the atmosphere. POME is an oily wastewater generated by palm oil processing mills and consists of various suspended components. This liquid waste combined with the wastes from steriliser condensate and cooling water is called palm oil mill effluent.

On average, for each ton of FFB (fresh fruit bunches) processed, a standard palm oil mill generate about 1 tonne of liquid waste with biochemical oxygen demand 27 kg, chemical oxygen demand 62 kg, suspended solids (SS) 35 kg and oil and grease 6 kg. POME has a very high BOD and COD, which is 100 times more than the municipal sewage.

POME is a non-toxic waste, as no chemical is added during the oil extraction process, but will pose environmental issues due to large oxygen depleting capability in aquatic system due to organic and nutrient contents. The high organic matter is due to the presence of different sugars such as arabinose, xylose, glucose, galactose and manose. The suspended solids in the POME are mainly oil-bearing cellulosic materials from the fruits. Since the POME is non-toxic as no chemical is added in the oil extraction process, it is a good source of nutrients for microorganisms.

Biogas Potential of POME

POME is always regarded as a highly polluting wastewater generated from palm oil mills. However, reutilization of POME to generate renewable energies in commercial scale has great potential. Anaerobic digestion is widely adopted in the industry as a primary treatment for POME. Biogas is produced in the process in the amount of 20 mper ton FFB. This effluent could be used for biogas production through anaerobic digestion. At many palm oil mills this process is already in place to meet water quality standards for industrial effluent. The gas, however, is flared off.

Palm oil mills, being one of the largest industries in Malaysia and Indonesia, effluents from these mills can be anaerobically converted into biogas which in turn can be used to generate power through CHP systems such as gas turbines or gas-fired engines. A cost effective way to recover biogas from POME is to replace the existing ponding/lagoon system with a closed digester system which can be achieved by installing floating plastic membranes on the open ponds.

As per conservative estimates, potential POME produced from all Palm Oil Mills in Indonesia and Malaysia is more than 50 million m3 each year which is equivalent to power generation capacity of more than 800 GW.

New Trends

Recovery of organic-based product is a new approach in managing POME which is aimed at getting by-products such as volatile fatty acid, biogas and poly-hydroxyalkanoates to promote sustainability of the palm oil industry.  It is envisaged that POME can be sustainably reused as a fermentation substrate in production of various metabolites through biotechnological advances. In addition, POME consists of high organic acids and is suitable to be used as a carbon source.

POME has emerged as an alternative option as a chemical remediation to grow microalgae for biomass production and simultaneously act as part of wastewater treatment process. POME contains hemicelluloses and lignocelluloses material (complex carbohydrate polymers) which result in high COD value (15,000–100,000 mg/L).

POME-Biogas

Utilizing POME as nutrients source to culture microalgae is not a new scenario, especially in Malaysia. Most palm oil millers favor the culture of microalgae as a tertiary treatment before POME is discharged due to practically low cost and high efficiency. Therefore, most of the nutrients such as nitrate and ortho-phosphate that are not removed during anaerobic digestion will be further treated in a microalgae pond. Consequently, the cultured microalgae will be used as a diet supplement for live feed culture.

In recent years, POME is also gaining prominence as a feedstock for biodiesel production, especially in the European Union. The use of POME as a feedstock in biodiesel plants requires that the plant has an esterification unit in the back-end to prepare the feedstock and to breakdown the FFA. In recent years, biomethane production from POME is also getting traction in Indonesia and Malaysia.

Palm Kernel Shells as Biomass Resource

Biomass residue from palm oil industries are attractive renewable energy fuel in Southeast Asia. The abundance of these biomass resources is increasing with the fast development of palm oil industries in Malaysia, Indonesia and Thailand. In the Palm Oil value chain there is an overall surplus of by-products and the utilisation rate of these by-products is low.

Palm kernel shells (or PKS) are the shell fractions left after the nut has been removed after crushing in the Palm Oil mill. Kernel shells are a fibrous material and can be easily handled in bulk directly from the product line to the end use. Large and small shell fractions are mixed with dust-like fractions and small fibres.

Moisture content in kernel shells is low compared to other biomass residues with different sources suggesting values between 11% and 13%. Palm kernel shells contain residues of Palm Oil, which accounts for its slightly higher heating value than average lignocellulosic biomass. Compared to other residues from the industry, it is a good quality biomass fuel with uniform size distribution, easy handling, easy crushing, and limited biological activity due to low moisture content.

Press fibre and shell generated by the palm oil mills are traditionally used as solid fuels for steam boilers. The steam generated is used to run turbines for electricity production. These two solid fuels alone are able to generate more than enough energy to meet the energy demands of a palm oil mill. Most palm oil mills in the region are self-sufficient in terms of energy by making use of kernel shells and mesocarp fibers in cogeneration. The demand for palm kernel shells has increased considerably in Malaysia, Indonesia and Thailand resulting in price close to that of coal. Nowadays, cement industries are using palm kernel shells to replace coal mainly because of CDM benefits.

The problems associated with the burning of these solid fuels are the emissions of dark smoke and the carry-over of partially carbonized fibrous particulates due to incomplete combustion of the fuels can be tackled by commercially-proven technologies in the form of high-pressure boilers. Dual-fired boilers capable of burning either diesel oil or natural gas are the most suitable for burning palm Oil waste since they could also facilitate the use of POME-derived biogas as a supplementary fuel. However, there is a great scope for introduction of high-efficiency CHP systems in the industry which will result in substantial supply of excess power to the public grid.