A rapid method for fungal assisted algal flocculation: Critical parameters & mechanism insights

•Rapid flocculation (99%) of C. pyrenoidosa with pregrown A. fumigatus biomass in 3 h•Fungal age/viability, flocculation temperature & agitation are critical parameters.•Involvement of specific surface groups in algal fungal interaction•Increased lipid content in AF pellets•Process repeatable with native and waste water grown algae in 4 h

A method for rapid flocculation of Chlorella pyrenoidosa cells with Aspergillus fumigatus pellets was developed. The process could flocculate 99% algal cells within 3 h. In order to identify the critical parameters, apart from the flocculation conditions (different fungal-algal ratios, flocculation temperature and agitation), the effect of cultivation time and various pretreatments (autoclaving, Cycloheximide exposure) for A. fumigatus was also investigated. Results revealed that 24 h old fungal pellets flocculated at 38 °C and 1:5 fungal-algal ratio showed the best flocculation efficiency. The cell viability assay showed that a viable and metabolically active fungal pellet is a prerequisite for flocculation. Scanning Electron Microscopy (SEM) studies confirmed that in addition to viability, an intact and undamaged hyphae is also required for algal attachment. Fourier transform infrared spectroscopy (FTIR) data of the algal-fungal pellets compared to that of algae and fungi showed the involvement of specific groups in the interaction. Sharp decrease in peak intensity at 1024 cm− 1 for the algal-fungal pellets indicated the role of C-N groups in the flocculation process. The lipid content of the harvested algal fungal pellet was similar to the algal and fungal partners. Finally, this method was tested on wastewater grown algae, where 95% flocculation was achieved within 3.5 h. The algal-fungal pellets (1650 μm diameter) could be easily separated from the treated water. Hence, this process could serve as an alternative for concentrating microalgal cultures for biofuel production in a cost effective way. This report reveals critical parameters and new insights on algal-fungal flocculation apart from providing a rapid and feasible algal harvesting technique.

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