Introducing a dual approach to industrial wastewater reclamation and microalgae harvesting by filamentous fungus

Fungal-assisted bioflocculation offers a promising and economical method for harvesting microalgae, although there is a lack of studies on fungi and microalgae co-cultivation in real/unsterilized wastewater without additional carbon sources. In this study, the capability of fungus ( Aspergillus oryzae ) for the simultaneous purposes of microalgae ( Chlorella sorokiniana ) harvesting, purification of pretreated fish processing wastewater (FPWW) (free from oils and fats) and recycling of algal/fungus pellets was investigated. A. oryzae was successfully produced in pellet form at pH 4–5 and used first in harvesting a pure C. sorokiniana suspension. The highest harvesting efficiency (98 %) within 6 h was obtained under optimised conditions of an initial pH of 9, 150 rpm, and a fungus:algal biomass ratio of 2.5:1. SEM analysis showed that successful fungus-microalgae symbiosis was established by integrating A. oryzae hyphae with C. sorokiniana cells. The formed algal/fungus pellets were further used to purify FPWW. The results showed that both microalgae monoculture and co-culture had high total nitrogen (TN) (89.6 %, 93.4 %), total phosphorus (TP) (95.4 %, 92.9 %) and chemical oxygen demand (COD) (67.9 %, 69.4 %) removal efficiency. A. oryzae pellets showed potential for use as a bioflocculant in harvesting microalgae and FPWW suspension, with harvesting efficiency of 99 %. Also, algal/fungal pellets show potential for recycling, although more investigation is needed to assess their long-term effects. These findings suggest a possible advance in microalgae harvesting and nutrient removal with algal/fungus pellets, offering a cost-effective solution to enhance sustainability and productivity in algal-based treatment systems. • A. oryzae forms uniform pellets under optimum conditions. • A. oryzae hyphae integrated with C. sorokiniana under optimum conditions (pH 5). • Algae/fungus pellets effectively treat FPWW with removal of >90 % of nutrients. • A. oryzae can act as bioflocculant with 99 % harvesting efficiency in FPWW. • Application of algae and fungus promotes sustainability in FPWW treatment system.