ABSTRACT Harvesting is a critical step in microalgal biomass production process for many reasons. Among the existing techniques available for harvesting and dewatering microalgal biomass, recovery from aqueous medium by coagulation-flocculation has been the most economically viable process, althoughit is highly dependent on pH. This study aims to assess alternative coagulants compared to the standard coagulant aluminum sulfate for microalgal biomass recovery from anaerobic effluent of domestic sewage treatment. The effluent quality was also analyzed after biomass recovery. Coagulants represented by modified tannin, cationic starch and aluminum sulfate recovered more than 90% of algae biomass, at concentrations greater than 80 mg/L, in the pH range 7-10. Cationic starch promoted higher microalgal biomass recovery with a wider pH range. Powdered seeds of Moringa oleifera and Hibiscus esculentus(okra) gum promoted biomass removal of 50%, only in the acidic range of pH. After sedimentation of the microalgal biomass, the effluents showed a removal of >80% for phosphorus and nitrogen values and >50% for BOD and COD when using aluminum sulfate, cationic starch and modified tannin as coagulants. Natural organic coagulants in a wide pH range can replace aluminum sulfate, a reference coagulant in microalgal biomass recovery, without decreasing microalgal biomass harvesting efficiency and the quality of the final effluent.

Blooms of cyanobacteria represent a public health risk due to their cyanotoxins such as microcystins. Liquid chromatography techniques to separate and quantify microcystins invariably use acetonitrile as the organic component of the mobile phase. The price and availability of acetonitrile together with its elevated toxicity encourage the validation of acetonitrile-free methods of microcystin analysis. In this work, methanol was employed as the organic solvent of the mobile phase and the validation method was performed with different environmental water samples. The method showed limits of detection between 0.17 and 0.25 µg/L and of quantification between 0.55 and 0.82 µg/L for the microcystin variants: -RR, -YR, -LR, -LA.