Nanofiltration treatment for pesticides removal

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Date
2007
Authors
Tan, Lian See
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Abstract
This thesis focuses on the removal of pesticide from aqueous solution using nanofiltration membrane. Two pesticides, atrazine and dimethoate, were selected for study in this research. Four nanofiltration membranes (NF90, NF200, NF270 and DK) were subjected to a stirred dead-end filtration of the pesticide solution. It was found that NF90 showed the best rejection performance, followed by NF200 and DK. Meanwhile, although NF270 showed the highest permeate flux out of the four membranes tested, it showed the poorest rejection. In overall, for the four membranes tested, atrazine was consistently better rejected than dimethoate. The rejection performance was further enhanced by approximately 10% when filtration was done with the pesticide being dissolved in tap water or river water. This observation showed that in actual case of filtration in water treatment plant, better pesticide rejection performance could be expected. However, this was obtained at the expense of flux performance since lower permeate flux was observed for filtration of tap water and river water. Increasing operating pressure and stirring rate posed positive effects on both rejection and flux performance of nanofiltration membranes. However, increasing the feed pesticide concentration reduced the rejection and flux performance. Increasing initial pH of solution increased the rejection performance of NF200, NF270 and DK. Nevertheless, this was accompanied with reduced permeate flux. Exceptional case was observed for NF90 whereby it showed somewhat consistent performance regardless of the initial pH of solution. The effect of atrazine-dimethoate binary solutes on the rejection was also studied and it was found that the presence of binary solutes slightly reduced the rejection performance of the nanofiltration membranes. Nevertheless, the flux performance was observed not to be affected by the binary system. ANOVA (analysis of variance) results from general factorial design showed that generally, feed pesticides concentration did not play significant roles in rejection and flux performance of pesticides in the system. It was found to be significant only in the case of rejection performance of atrazine. Other factors such as type of membrane, operating pressure and stirring rate were found to play significant role in the rejection and flux performance of pesticides. Verification of experimental data for the best-performed membrane, NF90, using Spiegler-Kedem model showed that the model provided a good estimation of experimental data. The coefficient of determination (R2) obtained for the fitted data was 0.9871 and 0.9692 for atrazine and dimethoate, respectively.
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Master
Keywords
Chemical engineering , Nanofiltration treatment , Pesticides removal , Atrazine , Dimethoate
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