Optimising Chlorella vulgaris bioflocculation by Aspergillus Niger pellets and their application in wastewater treatment and lipid production

Abstract

Background: Co-culturing filamentous fungi with microalgae is thought to be a viable method for effective microalgae bioflocculation. Using filamentous fungus makes it possible to produce big, flocculated pellets without adding extra chemicals, which facilitates a variety of uses for the collected biomass. This strategy is popular since it is economical and ecologically beneficial. Most studies examine the two main bio-flocculation strategies to collect microalgae, which are assisted by fungi’s spores or pellets, and their importance in wastewater treatment. Results: Fungal pellet formation for algal harvesting and wastewater treatment is critically influenced by temperature, glucose concentration, pH, spore suspension concentration, and their interaction, resulting in large pellets (5–28 mm diameter) and achieving 100% algal flocculation efficiency within 18 h under optimized conditions at 26 °C,110 rpm. Depending on the fungal pellets’ biovolume cm3/L relative to the algal culture, the algae’s starting density, and the glucose availability. The process demonstrated dual-stage wastewater treatment efficacy: At stage one, biovolume of 107.17 cm³/L achieved 91.88% ammonium and 91.5% phosphate removal (glucose-enhanced phosphate binding), while for blanks 49.1% ammonium, 22.3% phosphate at Stage two (cost-focused), which extends for only 24 h, reduced ammonium by 21.85% and phosphate by 57.18%. In contrast, the blank group only achieved a decrease of 1.5% and 15.9%. However, excessive biovolume counterproductively pollutes water, emphasizing the need for balanced optimization. Conclusions: Fungal preformed pellets may have a better chance of forming into an efficient bio-flocculation method to harvest microalgae than the fungal spore-assisted approach, which takes a long time, produces a small number of pellets or loose pellets that lack shape or structure, and sometimes growth appears as deposits, also turning algal growth into a yellow color. The pellet-assisted technique shows excellent ability to remove phosphate and ammonium from wastewater. A suitable biovolume must be considered to achieve ideal treatment in wastewater remediation, and adding glucose can improve overall effectiveness.