Harvesting of Microcystis Flos-Aquae Using Dissolved Air Flotation : The Inhibitory Effect of Carboxyl Groups in Uronic Acid-Containing Carbohydrates

Harvesting algal biomass reduces nutrients loading in eutrophicated lakes and the protein rich microalgal biomass could be recycled as feedstocks of feed and fertilizer. Due to the complexity of algogenic organic matter (AOM), the key components and functional groups in AOM that inhibit coagulation based microalgal harvesting have not been disclosed thus far. This study quantitatively analyzed the responsive compositions and functional groups of AOM involved in the dissolved air flotation (DAF) harvesting of M. flos-aquae . The results showed that harvesting efficiency significantly deteriorated in the presence of AOM. Stoichiometric analysis of functional groups in carbohydrates, proteins and humic-like substances using model components revealed that carboxyl groups in uronic acids of carbohydrates were the major inhibitors. Carboxyl groups in uronic acid-containing carbohydrates accounted for 76% of the total reduction in carboxyl groups, which was much higher than that in proteins (23%) and humic-like substances (1%). A conceptual model of charge competition was proposed to explain the inhibition mechanism of carboxyl functional groups in uronic acid-containing carbohydrates on microalgal DAF. Strategies such as preventing carboxyl deprotonation by pH reduction and employment of sweeping/bridging polymeric coagulants/flocculants were proposed for the to reduce the inhibitory effect of carboxyl functional groups