The Effects and Mechanism of Phycocyanin Removal from Water by High-Frequency Ultrasound Treatment.

The effects and mechanism of phycocyanin removal from water by high-frequency ultrasound treatment were studied. The efficiency of sonication treatment in removing proteins derived from algal cells was investigated, and the factors influencing the process, including the effects of coagulation, were also studied. In addition, sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE), the three-dimensional fluorescence spectrum, and mass spectrum were used to illustrate the removal mechanism. The results indicated that phycocyanin can be degraded to the point where it is barely detectable in water samples after 180min of high-frequency sonication. While the total nitrogen (TN) concentration remained consistent during the entire sonication process (240min), about 78.9% of the dissolved organic nitrogen (DON) was oxidized into inorganic nitrogen. The sonication effect was greatly influenced by the ultrasound frequency, with 200kHz having the highest removal performance due to the large production of hydroxyl (HO) radicals. Coagulation was adversely influenced by sonication in the first 60min due to the cross-linking reaction between protein molecules caused by the sonication. The influence of sonication weakened with sonication time due to the further degradation of the proteins by ultrasound. The variation of the TN, DON, and inorganic nitrogen indicated that the main mechanism occurring during the high-frequency sonication of the phycocyanin was the direct oxidation of the radicals, which was totally different from of the mechanism occurring during ultrasound with low frequency.