Establishing the nexus between the coagulant for microalgae harvesting and the biomass nutrient assemblage

Abstract

Microalgae biomass is being studied as a potential resource for the production of renewable biofertilizer, but transforming the highly dispersed miniscule microalgae cells into harvestable biomass is challenging. Amongst the strategies for harvesting microalgae biomass, the coagulation–flocculation method is expedient. However, this method requires the use of coagulants that can interfere with the chemical composition and functionality of the biomass. Therefore, the need to establish the nexus between the harvesting coagulant and the biomass nutrient assemblage is germane. The physicochemical characteristics and the nutrient speciation of biomass harvested with either synthetic (AlCl₃ and FeCl₃) or naturally sourced (Moringa oleifera, gastropod shell and MargaritarIa discoidea) coagulants were evaluated. The influence of the different coagulants on the forms and patterns of nutrients (i.e., phosphorus, nitrogen and potassium) in the harvested biomass was evaluated. The physicochemical characteristics of the biomass, which influence nutrient availability, were impacted to various degrees by the different coagulants studied. The different coagulants used had no effect on the total phosphorus fraction of the harvested biomass, but impacted the available phosphorus fraction. All the coagulants investigated enhanced the available nitrogen in the biomass, as the percentage of the available nitrogen that constitute the total nitrogen fraction was >90% in all the harvested biomass samples, but less than 80% in the non-coagulant-biomass. None of the coagulants studied impacted the species of potassium in the biomass.