Biorefinery Paradigm in Wastewater Management: Opportunities for Resource Recovery from Aerobic Granular Sludge Systems

Aerobic granules, with a size range of 0.2-5 mm, are a dense colony of different strains of microorganisms held together by extracellular polymeric substances (EPS) secreted by the bacterial cells under special operational conditions. These granules are the principal components of the aerobic granular sludge (AGS) biotechnology. AGS has been widely and successfully applied for the treatment of municipal and different industrial wastewater streams in the past two decades and has the potential for successful application in cold regions. Moreover, in addition to efficient wastewater treatment, AGS also offers great opportunity for high-value resource recovery. AGS granules contain high phosphorus and high EPS contents. The high EPS content presents an opportunity to recover numerous high-value resources including xanthan and curdlan from AGS biosolids. Xanthan is widely used in the food, biomedical, and oil industries, as well as for soil strengthening in geotechnical applications. Curdlan is used in biomedical and pharmaceutical, food, cosmetic, as well as construction industries. These resources are currently in high demand globally and research efforts geared towards their recovery would be imperative to achieving the biorefinery concept in wastewater. Literature search shows that research is needed on the optimization of the biosynthesis of xanthan and curdlan in AGS bioreactors while maintaining the wastewater treatment capability of the granules. In addition, the market potentials of xanthan and curdlan needs to be determined in order to make their recovery from waste aerobic granules lucrative. This paper provides an overview of resources recoverable from waste aerobic granules.