Palm oil mills, starch and ethanol plants produce huge amounts of highly organic loaded effluent. The waste water is treated in a series of lagoons (up to 15) to degrade the organic content of the waste water by anaerobic bacteria. The waste water of the last lagoon can be used to irrigate the surrounding plantations. This process produces methane gas which emits into the atmosphere. Methane contributes tremendously to global warming.

Its GWP (global warming potential) is 21 times higher than the GWP of CO2 that means that the reduction of one tonne of methane is equivalent to the reduction of 21 tonnes of CO2.