Characteristics of Chlorella sp.-chitosan flocs in coagulation and dissolved air flotation

Abstract

Microalgae, photosynthetic microorganisms, thrive in nutrient-rich environments such as wastewater; however, their efficient separation from water requires effective and time-efficient harvesting techniques. This study considers the dynamic nature of microalgae and describes the interplay between the chitosan coagulant dosage and the microalgae's growth phase (cells and algal organic matter (AOM)) in coagulation and dissolved air flotation for the green freshwater microalgae Chlorella sp., focusing on floc characteristics. In the exponential phase, the absence of the AOM resulted in the growth of very large (>> 1000 mu m), strong (breakage rate similar to 80 mu m min-1), and recoverable flocs (similar to 75%) compared to the AOM-rich scenarios and the stationary phase. In the stationary phase, the flocs were smaller (223-230 mu m), also moderately strong (similar to 100 mu m min-1), but unable to reconnect (<= 60%). Overdosing chitosan had different effects; overall, the flocs grew bigger, and in the presence of AOM, the flocs maintained more than 70% of their size, which eroded over time. The findings underscore the impact of both chitosan dosage and growth phase on the floc's properties, revealing distinct behaviours in the absence and presence of the AOM. This study provides valuable insights allowing the design of effective coagulant dosing strategies for microalgae biomass separation and downstream utilization.