The wastewater treatment in the biodiesel production with alkali-catalyzed transesterification

Abstract

Abstract Biodiesel has been studied in last few decades because of limited energy resources and a huge increase of the energy demand. The basic feedstocks for the production of biodiesel are vegetable oils and animal fats that contain primarily triacylglycerols while the main reaction is transesterification. This reaction is most frequently conducted at commercial scale in the presence of the homogeneous alkali catalyst. Previous studies on biodiesel were mainly focused on its production and fuel properties, while its environmental management is rarely considered. The present work is a review of the previous studies on treating wastewaters generated by the biodiesel production processes involving alkali-catalyzed transesterification. The attention is focused on physical, chemical, physico-chemical, electrochemical, biological and integrated treatment processes of biodiesel wastewaters. Both advantages and disadvantages of different biodiesel wastewater treatment processes are discussed. Since different input biodiesel wastewaters are employed in different studies, it is difficult to compare different treatments with respect to their contaminant removal efficiencies. Proper acidification and chemical coagulation/flocculation or electrocoagulation remove grease and oil successfully but they are unsuccessful in removing COD. The combinations of acidification, coagulation and the electrochemical treatment improve the removal efficiencies of COD and BOD. Advanced oxidation technologies appear not to be effective in removing the contaminants from raw biodiesel wastewaters. The performance of biological processes is improved by the pretreatment of biodiesel wastewater with acidification, chemical coagulation, electrocoagulation or photo-Fenton. When selecting a treatment process, it should be evaluated with respect to its treatment efficiency and operational requirements. The right choice is probably an integration treatment involving acidification, coagulation/flocculation or electrocoagulation and a biological process. The reuse of the pretreated wastewater is also an interesting alternative.