Palm oil mill effluent is a highly polluting material, due to its high biological oxygen demand (BOD), low pH and colloidal nature. It was estimated that a processing plant with a capacity of 10 tons fresh fruit per hour would need a water treatment plant comparable to that required by a population of half a million inhabitants (Brezing, 1986). While considerable progress has been made since the time when oil palm wastewater was simply discarded in nearby waterways, liquid oil palm wastes still affect the environment and the quality of life in rural areas. Palm oil mills now employ conventional biological treatment systems, such as anaerobic and facultative ponds in series, anaerobic and aerobic lagoons in series, or anaerobic digestion tanks and facultative ponds in series. However, some mills are still not able to treat their wastewater in ways that meet effluent standards. In the rainy season, overflow from the wastewater treatment plants causes heavy water pollution to nearby waterways. Another issue is that anaerobic ponds release greenhouse gases (methane and carbon dioxide) that contribute to global warming. Communities located near oil mills may also suffer from odour emissions caused by poorly managed effluent treatment systems (Chavalparit, 2006).
Increasing the consumption of palm oil effluent by livestock, if possible near the production site to avoid wastage, palatability issues and transportation, has been proposed as a means to minimize pollution (Devendra, 1985). However, using palm oil effluent for livestock feeding could only be a partial solution to effluent management, as it was estimated that a 40 t/h oil mill would require around 44,000 pigs or 43,000 cattle for the entire effluent to be utilized (Agamuthu, 1995).