Preparation Of Fruit-skin Coagulant And Its Coagulation Performance In Water Treatment

In this paper,banana peel(OBP and BBP)coagulants were prepared by orthogonal experiments using banana peel as the main raw material.The microstructures of banana peel coagulants were characterized by scanning electron microscopy(SEM),energy dispersive spectrometer(EDS)and Fourier transform infrared(FT-IR)spectrometer.Besides,storage stability and coagulation stability of banana peel coagulants were also researched,as well as coagulation mechanism preliminarily.At last,the optimal hydraulic condition of banana peel coagulants was analysed.According to the experimental results of the preparation process,the preparation conditions of OBP and BBP were as follows: 0.1mL alkaline,10 minutes water bath at 40?,4 hours of alkali extraction,and dosage of stabilizer I(for OBP)and II(for BBP)were 6ml and 0.005 m L,respectively.Color of OBP and BBP deepened and precipitation of some solid matter occurred with the extension of storage time.The surface and superficial area of OBP were roughness and large,while those of BBP were smooth and small.The main components of these coagulants included saccharides,cellulose,lignin,protein,fatty acids and another organic matters.Compared with the PAC,the removal efficiency of turbidity and color by banana peel coagulants was investigated using coagulation tests,in which dosage,coagulation pH,raw water turbidity and raw water color were considered,respectively.For turbidity,the removal rate of turbidity by OBP and BBP at the optimal dosage can reach 92.3% and 97%,respectively.The turbidity removal rate of OBP and BBP was 89.3% and 96.6% at the optimal conditions of pH value of 7 and 9,respectively.The suitable pH range of BBP and OBP was from 5 to 13 and from 5 to 9,respectively.For raw water with high turbidity,the removal rate of turbidity by OBP and BBP was less than that of PAC by 10% and 3%,respectively.For color,the removal rate of color can reach 91.9% and 87.2% at the optimal dosages,respectively.The color removal rate of OBP and BBP was 91.4% and 87.2% at the optimal conditions of pH value of 11 and 5,respectively.The suitable pH range of BBP and OBP was from 5 to 13 and from 5 to 9,respectively.Compared with PAC,OBP and BBP were slightly worse on removal rate of the color.Flocs was formed due to action of destabilization and agglomeration which occurred between colloidal pollutants in water and banana peel coagulants by hydrogen bond and neutralization,and then larger flocs was further formed due to bridging,thus leading to settlement of pollutants.The optimum hydraulic condition was obtained by Box-Behnken Design experiment with BBP as coagulant and simulated humic acid water as raw water sample.The times for mixing and flocculation were 70 s and 25 min,respectively,and the speeds for mixing and flocculation were 210r/min and 85r/min,respectively.The relative deviation between the experimental value and predicted value is as follows: the turbidity was 3.06% and the color was 0.54%.