As previously reported, there are two probable mechanisms of metal ion removal by microalgal cells [62,65,66]. The first is by the assimilation of metal ions by microalgae cells during metabolic processes and these are used for the synthesis of vitamins, enzymes and proteins. Some metals are also assimilated to function as coenzymes or activators of enzymes in the microalgae cells. The other mechanism hinges concept that microalgae extracellular/intracellular polysaccharides or other biochemicals may bind metal ions for absorption into the cells.