Comparative Study on the Harvesting of Marine Chlorella vulgaris Microalgae from a Dilute Slurry Using Autoflocculation-Sedimentation and Electrocoagulation-Flotation Methods

Abstract

One of the most noticeable steps in the microalgae biomass production is the harvesting of cells from a very dilute slurry culture medium, which accounts for 20–30% of the whole process operating cost. In the present study, Chlorella vulgaris microalgae of the Persian Gulf, as a type of stable colloidal particles, were initially cultivated in an f/2 culture medium. The dispersed biomass was then harvested using the methods of autoflocculation–sedimentation in the jar test setup and electrocoagulation–flotation in a laboratory-scale horizontal electrodes’ plexiglass container. In this regard, the affecting factors on their harvesting efficiency were optimized and modelled applying response surface methodology. Considering the autoflocculation–sedimentation process and design of experiments results, the maximum harvesting efficiency of 66.00% was obtained under optimum conditions of pH = 12, mixing rate of 20 rpm, and 30 min sedimentation time. In the electrocoagulation–flotation under the optimum conditions of pH = 8.00 and 4.00 v/cm, DC electric field intensity between aluminium electrodes, the harvesting efficiency of 99.55% was achieved within 6 min. However, under the same operating conditions, for the first time in this study, by replacing the aluminium electrodes with the carbon cloth covered by a thin layer of filter paper as the anode, and the stainless-steel cathode, the 98.00% flotation efficiency was attained. Compared to the aluminium electrodes, the carbon cloth/stainless-steel set exhibited the lowest pollution, due to less electrodes’ corrosion.