Municipal wastewater treatment plants generate sludge as a by-product of the physical, chemical and biological processes used in the treatment of wastewater. Generally, this sludge must be subject to some form of treatment in order to alter its character. By using anaerobic digestion in the treatment of wastewater sludge, methane gas is produced and it is known as biogas. It must not only be seen as a renewable energy source, but even more as one of the promising solutions to the large environmental problem concerning waste handling, water pollution, CO2 emission, etc
Biodiesel has gained widespread importance in recent years as an alternative, renewable liquid transportation fuel. It is derived from natural triglycerides in the presence of an alcohol and an alkali catalyst via a transesterification reaction. To date, transesterification based on the use of chemical catalysts has been predominant for biodiesel production at the industrial scale due to its high conversion efficiency at reasonable cost. Recently, biocatalytic transesterification has received considerable attention due to its favorable conversion rate and relatively simple downstream processing demands for the recovery of by‐products and purification of biodiesel. Biocatalysis of the transesterification reaction using commercially purified lipase represents a major cost constraint.
However, more cost‐effective techniques based on the immobilization of both extracellular and intracellular lipases on support materials facilitate the reusability of the catalyst. Other variables, including the presence of alcohol, glycerol and the activity of water can profoundly affect lipase activity and stability during the reaction. This review evaluates the current status for lipase biocatalyst‐mediated production of biodiesel, and identifies the key parameters affecting lipase activity and stability. Pioneer studies on reactor‐based lipase conversion of triglycerides are presented