Role of moderately hydrophobic chitosan flocculants in the removal of trace antibiotics from water and membrane fouling control
Yang, Z (Yang, Zhen)[ 1 ]*（杨朕）; Hou, TY (Hou, Tianyang)[ 1 ] ; Ma, JY (Ma, Jiangya)[ 3 ] ; Yuan, B (Yuan, Bo)[ 4 ] ; Tian, ZQ (Tian, Ziqi)[ 5 ] ; Yang, WB (Yang, Weiben)[ 1 ]*（杨维本）; Graham, NJD (Graham, Nigel J. D.)[ 2 ]
[ 1 ] Nanjing Normal Univ, Sch Chem & Mat Sci, Jiangsu Prov Key Lab Mat Cycling & Pollut Control, Nanjing 210023, Peoples R China
[ 2 ] Imperial Coll London, Dept Civil & Environm Engn, South Kensington Campus, London SW7 2AZ, England
[ 3 ] Anhui Univ Technol, Sch Civil Engn & Architecture, Maanshan 243002, Anhui, Peoples R China
[ 4 ] Jiangsu Sinog Testing Co Ltd, Nanjing 210061, Peoples R China
[ 5 ] Chinese Acad Sci, Ningbo Inst Mat Technol & Engn, Ningbo 315000, Peoples R China
In this paper we describe the preparation and testing of a new class of chitosan-based flocculants for the treatment of surface waters containing antibiotic compounds. Three forms of moderately hydrophobic chitosan flocculants (MHCs) were prepared by chemically grafting hydrophobic branches with different lengths onto hydrophilic chitosan and these were evaluated by jar tests and a bench-scale continuous flow ultrafiltration (UF) membrane process with coagulation/sedimentation pre-treatment. Tests were conducted using both synthetic and real surface water in which norfloxacin and tylosin were added as representative antibiotics at an initial concentration of 0.1 mu g/L. In jar tests, the MHCs achieved similar high removal efficiencies (REs) of turbidity and UV254 absorbance, but much higher REs of the two antibiotics (71.7-84.7% and 68.7-76.6% for synthetic and river waters, respectively), compared to several commercial flocculants; the superior performance was attributed to an enhanced hydrophobic interaction and H-bonding between the flocculants and antibiotics. The presence of suspended kaolin particles and humic acid enhanced the antibiotic removal, speculated to be through MHC bridging of the kaolin/humic acid and antibiotic molecules. In the continuous flow tests involving flocculation/sedimentationUF for 40 days, an optimal MHC achieved a much greater performance than polyaluminium chloride in terms of the overall removal of antibiotics (RE (norfloxacin) of similar to 90% and RE (tylosin) of similar to 80%) and a greatly reduced rate of membrane fouling; the latter resulting from a more porous and looser structure of cake layer, caused by a surface-modification-like effect of residual MHC on the hydrophobic PVDF membrane. The results of this study have shown that MHCs offer a significant advance over the use of existing flocculants for the treatment of surface water.