Effect of hydraulic conditions on flocculation performances and floc characteristics in Chinese herbal extracts by chitosan and chitosan hydrochloride

• Chitosan hydrochloride produced bigger, stronger and better recoverability flocs.
• Chitosan hydrochloride provides better flocculation performance than chitosan.
• Fast-mixing speed had greater effect on chitosan hydrochloride flocs than chitosan.
• Fast-mixing speed had slight influence on chlorogenic acid for both flocculants.

Chitosan and chitosan hydrochloride was used in the flocculation of impurities in Chinese herbals extract of Xiao’er Kechuanling Oral Liquid (XKOL) to study the effect of different fast-mixing hydraulic conditions on the flocculation performance and floc characteristics. The results showed that with the increase of fast-mixing speed chitosan floc size increased initially and then decreased, while chitosan hydrochloride floc size declined. The trends of the strength and recovery factors were contrary to that of the floc size for both flocculants. Floc fractal dimensions of both chitosan and chitosan hydrochloride increased firstly and declined latterly in response to increasing fast-stirring intensity. Fast-mixing speed had greater influence on chitosan hydrochloride flocs size than that of chitosan. Chitosan hydrochloride flocs had bigger size, higher strength and recoverability compared with chitosan flocs. In addition, compared with traditional alcohol precipitation of XKOL, both chitosan and chitosan hydrochloride presented better flocculation efficiency with high clarity, impurities removal, and retention rate of active ingredient chlorogenic acid. The lowest turbidity 14.9 NTU and 10.4 NTU was achieved at fast-stirring speed 1.31 m/s and 1.05 m/s by chitosan and chitosan hydrochloride, respectively. The removal rate of tannin and protein by chitosan hydrochloride reached to the highest value of 78.9% and 49.3% at about 1.05 m/s, respectively, which were higher than that of chitosan at optimum 1.31 m/s. The retention rate of chlorogenic acid was slightly influenced by the fast-mixing rate with above 93% in the studied speed range.

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