Recuperação de microalgas cultivadas em efluente de tratamento anaeróbio de esgoto por processo de coagulação-floculação

Abstract

Harvesting is a critical step in microalgae biomass production process for many purposes. Among the existing techniques available for harvesting and dewatering microalgae biomass, recovery from aqueous medium by coagulation-flocculation has been the most economically viable process, although highly dependent on pH. This study aims to assess alternative coagulants for microalgae biomass recovery as compared with the standard coagulant aluminium sulphate from anaerobic effluent of domestic sewage treatment. The effluent quality was also analysed after biomass recovery. Coagulants represented by modified tannin, cationic starch and aluminium sulphate recovered more than 90% of algae biomass, at concentrations greater than 80 mg/L, in the pH range 7-10. Cationicstarch promoted higher microalgae biomass recovery with the wider pH range. Seeds of Moringa Oleiferaand Hibiscus esculentus(okra) gum promoted biomass removal of 50%, only in the acidic range of pH. The effluents after sedimentation of the microalgae biomass showed removal >80% for phosphorus and nitrogen and >50% for BOD and COD, using aluminium sulphate, cationic starch and modified tannin. MBM recovered from aluminum sulphate (AS-BMA) presentedhigher EC50values, while MBMrecovered from natural organic polymers resulted in EC50values 50% lower thenBMA-AS.Natural organic coagulants in a wide pH range can replace aluminium sulphate, which is a reference in microalgae biomass recovery, without decreasing microalgae biomass harvesting efficiency and the quality of the final effluent.