Microalgae for municipal wastewater nutrient remediation: mechanisms, reactors and outlook for tertiary treatment

The first use of microalgae by humans dates back 2000 years to the Chinese, who used Nostoc to survive during famine. However, microalgal biotechnology only really began to develop in the middle of the last century. Nowadays, there are numerous commercial applications of microalgae. For example, (i) microalgae can be used to enhance the nutritional value of food and animal feed owing to their chemical composition, (ii) they play a crucial role in aquaculture and (iii) they can be incorporated into cosmetics. Moreover, they are cultivated as a source of highly valuable molecules. For example, polyunsaturated fatty acid oils are added to infant formulas and nutritional supplements and pigments are important as natural dyes. Stable isotope biochemicals help in structural determination and metabolic studies. Future research should focus on the improvement of production systems and the genetic modification of strains. Microalgal products would in that way become even more diversified and economically competitive.

The integration of microalgae-based biofuel and bioproducts production with wastewater treatment has major advantages for both industries. However, major challenges to the implementation of an integrated system include the large-scale production of algae and the harvesting of microalgae in a way that allows for downstream processing to produce biofuels and other bioproducts of value. Although the majority of algal production systems use suspended cultures in either open ponds or closed reactors, the use of attached cultures may offer several advantages. With regard to harvesting methods, better understanding and control of autoflocculation and bioflocculation could improve performance and reduce chemical addition requirements for conventional mechanical methods that include centrifugation, tangential filtration, gravity sedimentation, and dissolved air flotation. There are many approaches currently used by companies and industries using clean water at laboratory, bench, and pilot scale; however, large-scale systems for controlled algae production and/or harvesting for wastewater treatment and subsequent processing for bioproducts are lacking. Further investigation and development of large-scale production and harvesting methods for biofuels and bioproducts are necessary, particularly with less studied but promising approaches such as those involving attached algal biofilm cultures. Copyright © 2011 Elsevier Inc. All rights reserved.