Influence of algal strain on microalgal-bacterial bioflocculation rate and floc characteristics

Abstract

Microalgal-bacterial (MaB) flocs are a promising route towards sustainable wastewater treatment, but the effects of algal species and algal abundance on MaB floc function are not yet understood. MaB flocs were created by inoculating activated sludge with several species of algae at different initial algal to bacterial biomass ratios (5:1, 2:1, 1:1, or 1:5 algae:activated sludge) to determine the effects on nutrient removal, lipid content, microalgal-bacterial bioflocculation rates, and settleability. The algal species Chlorella vulgaris, Chlorella sorokiniana, Scenedesmus dimorphus, and Neochloris oleoabundans all formed MaB flocs within 2 h of inoculation with activated sludge. Chlorella vulgaris formed MaB flocs with the highest lipid content (11.1%), followed by S. dimorphus (8.2%), and N. oleoabundans (6.4%), for MaB flocs inoculated at 1:1 algae:activated sludge (w/w) ratio. Chlorella vulgaris incorporated into activated sludge to form MaB flocs to the greatest extent, and C. sorokiniana the least. Phosphorus removal was influenced by the species of microalgae used for MaB floc inoculum, with S. dimorphus showing highest P removal of up to 92–97% at 5:1 and 2:1 algae:activated sludge (w/w) ratios.