Seyed Sadr

24 Aug 2012

Seyed started his PhD at the University of Surrey in Water and Chemical Process Engineering in April 2011. The title of his research is: “Application of Membrane Assisted Technologies in Water Reuse Scenarios”. He completed his master in Water Sciences Engineering at Azad University of Shoushtar, Iran in 2009 and his B.Sc. in the same subject at Azad university of Ahvaz, Iran in 2006. He worked for a civil and environmental company in Iran for four years (part-time) before he came to undertake his PhD.


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Abstract


Modelling the removal of organics in nanofiltration for water reuse

Nanofiltration (NF) is an effectual and ecologically convenient technology for decontamination and water reuse. NF in a large number of studies has shown the capability of removing different emerging organic micro-pollutants such as endocrine disrupting compounds (EDCs) and pharmaceutical active compounds (PhACs). The major problems involved in nanofiltration application and during the filtration are rejection decline and increase in fouling which might not be completely predictable. There are some models to assess and predict the rejection of organics. However, they are generally either statistic models or more related to the material science of the membranes. Therefore, the study aims to represent a mechanism-based model which can evaluate the behaviour of organics in nanofiltration rejection. The mechanisms to be considered in the model can be divided into three different assortments:

1) Steric hindrance: Steric hindrance plays a major role when the large size of groups within a molecule and/or the spatial structure of a molecule prevent chemical reactions that can be observed in some other molecules with smaller groups or sizes. Steric hindrance is mainly correlated to the ratio of the size of the solute to the size of the membrane pores.

2) Hydrophobic-hydrophobic adsorption: Van der Waals interaction is defined as the sum of the attractive or repulsive forces between molecules. Hydrophobic-hydrophobic (Van der Waals) interactions between the solutes and the membranes are likely to affect organic rejection.

3) Electrostatic repulsion: This arises if two molecules carry the same charge approach each other. Electrostatic repulsion between charged molecules and the charged membrane surface might positively affect the rejection of micropollutants.

The description of the model is made up of the parameters, such as Molecular weight, flux, time, and hydrophobicity, which are correlated to the organic rejection mechanisms. The organic rejection has been modelled as:

R (%) = f (Steric hindrance) + f (Adsorption) + f (Electrostatic repulsion)

Where R is rejection efficiency.

After understanding the mechanisms and considering the parameters, parameter estimation, calibration and validation of the model should be conducted. The software AQUASIM has been used for parameter estimation, calibration and validation.

The results show that this model is able to correctly assess and model the organics rejection in nanofiltration. It has been concluded that a classification of compounds into four major assortments is needed.

Presumably, the validation of the model with more sets of data will lead to having better results. In addition, combination of this new model with statistical models would be worthwhile in order to undertake further research.

Keywords: Nanofiltration; Pharmaceuticals; Endocrine disruptors; Modelling; Rejection mechanism