POME is a thick concentrated dark brownish colloidal slurry (comprising water, oil and fine cellulosic materials) which is generated as the largest amount of liquid wastes (about 95% water and 5% solids) from the palm oil industry. POME is produced in the form of condensate and clarification sludge from two main processes in the oil mill, namely, sterilisation and clarification, respectively. The sterilisation of FFB, clarifica­tion of the extracted CPO and hydrocylone separation of the cracked mixture of kernel and shells contribute about 36%, 60% and 4% of POME, respectively, in the oil mill (Sethupathi 2004). With about 1.5 m3 (or about 1.5 tonnes) of water used in process­ing 1 tonne of FFB, about half of this quantity (~0.50-0.75 tonnes water) comes out as POME (Alam et al. 2009). In 2004, for instance, about 40 million tonnes of POME was generated from about 372 palm oil mills in Malaysia (Yacob et al. 2005). This figure rose drastically to about 53.1 million tonnes in 2006. Generally, for every tonne of CPO produced, about 3.25 tonnes of POME is generated (Corley and Tinker 2003).

POME contains about 40,500 mg/l total solids (comprising cellulosic materials) and 4,000 mg/l fats, oil and grease (Ma 2000) depending on the method of oil extraction and the characteristics of the FFB. The pH of POME ranges from 4 to 5, whilst its temperature of POME may vary from 80 to 90°C (Ma 2000) due to heat production during the sterilisation and other mechanical processes within the palm oil mill. The biological oxygen demand (BOD) and chemical oxygen demand (COD) of POME are very high exceeding 25,000 mg/l and 50,000 mg/l, respec­tively; hence, they are considered more polluting than domestic sewage (Ma 2000).

POME contains dissolved substances such as protein (about 9.6% DM), carbo­hydrate, nitrogenous compounds (ammonical nitrogen of 20-40 mg/l and total nitrogen of 100-1,200 mg/l) and fats which can be converted into useful materials using microbial processes (Ma 2000). POME contains about 11% cellulose, 7% hemicellulose and 42% lignin on dry basis (O-Thong et al. 2012). The amount of minerals such as phosphorus (about 0.26%), magnesium (about 0.25%) and calcium (about 0.28%) which are found in POME is good for healthy plants’ growth. Muhrizal et al. (2006) reported that POME contains high content of aluminium as compared to that of chicken manure and composted sawdust. POME has been reported by Habib et al. (1997) to contain low concentrations of lead (about 17.5 pg/g) due to the contaminations from the paints and glazing materials used on plastic and metal pipes and tanks in the oil mill.