Preparation Of Biosorbent By Harvesting Microalgae Using Electrolytic Air Flotation

With high growth rate,high protein and oil content,and high added value,microalgae have great potential in food,feed,energy,pharmaceutical and environmental fields.Reducing the cost of harvesting microalgae and improving the recovery and reuse of microalgae extraction residues are hot spots of current research.In this paper,Chlorella vulgaris was harvested by non-sacrificial anode electrolytic air flotation using Chlorella vulgaris as the experimental algae species.The effects of electrode size and process parameters on the harvesting rate were investigated,and the Chlorella vulgaris extract residues were prepared as adsorbent to adsorb pollutant wastewater to realize the dual utilization of microalgae residue resources and wastewater resources.In this study,the limiting factors and harvesting mechanism of the harvesting process and the adsorption mechanism of microalgae biosorbent on dye pollutants were analyzed in depth,which provided new ideas and technologies to solve the problems of high harvesting cost of industrial production and resource utilization of microalgae waste.The main research contents and conclusions are as follows:The bubble behavior during the harvesting of microalgae by electrolytic air flotation was investigated.With an inert electrode as the anode and stainless steel wires(0.8 mm,0.2 mm,and 0.05 mm in diameter)as the cathode,hydrogen bubbles were generated at the cathode during electrolysis,and the detachment diameter of the bubbles was related to the diameter of the electrode wires.At a fixed voltage of 20 V,the bubble size increases with the diameter of the electrode wire and the time required for the bubble to reach a steady state increases.The effects of current and algal solution height on the harvesting rate were investigated.Within the set experimental parameters,both higher algal solution height and higher current had a positive effect on the harvesting rate of microalgae,with the harvesting efficiency reaching more than 90% within 50 min at 6 cm algal solution height and 3A current.Higher currents shortened the time for the harvesting rate to reach its maximum.The reasons for stable harvesting of Chlorella were analyzed,comparing the bubble accumulation in the actual algal solution and the centrifuged supernatant at the same height,where the trend of bubble accumulation was almost the same,and the extracellular polymer produced by microalgae was the main reason for avoiding bubble rupture.KOH activation of microalgae residues was investigated to prepare modified microalgae biosorbents at different pyrolysis temperatures to compare the physicochemical properties and adsorption performance with methyl orange(MO)and methylene blue(MB)as the target pollutants.The results showed that the best adsorption capacity and removal rate were achieved for the adsorbent prepared at750 °C(KCBC750),respectively.The effect of the adsorbent dosage and pH of the dye solution on the adsorption performance of KCBC750 was investigated.3 mg of adsorbent was added to remove the dye MO(150 mg/L,10 ml),and 4 mg of adsorbent was added to remove the dye MB(300 mg/L,10 ml).The best adsorption effect of the adsorbent on MB was achieved when the solution pH was 2;and the solution pH was 12.The strong specific surface area and negative electrical properties of the material are the main reasons for this phenomenon.The adsorption kinetic model and adsorption isotherm model of KCBC750 adsorbent on dyes MO and MB were analyzed,and the results showed that the adsorption of dyes by KCBC750 were in accordance with the quasi-secondary kinetic model,intraparticle diffusion model and Langmuir isotherm model.Based on the changes of the IR spectra before and after adsorption,it was shown that there was a bond interaction between this adsorbent material and the dyes.