Abstract
This paper highlights the correlation between constant rate and constant pressure microfiltration characteristics of secondary effluent emanating from a sewage treatment plant that treats municipal wastewater. As filtration proceeded, cake formation and pore blocking occurred causing an increase in pressure drop in the case of constant rate filtration or flux decline in the case of constant pressure filtration. To rejuvenate the membrane, in situ periodic backwashing was introduced in such a way that it was triggered when the pressure drop or flux reached a pre-set value. Backwashing is effective in recovering of the flux and the increase in pressure drop resulted from the formation of the filter cake. However, after each backwashing, the initial pressure drop seemed to increase or the initial flux seemed to decrease due to the irreversible pore blocking of the membrane. Mathematical model has been developed to describe the pore blocking behavior in both operations. Constant pressure microfiltration characteristics are estimated using the experimental data of constant rate filtration along with the models that represent cake formation and pore blocking. The evaluated results well coincided with the experimental data and it was found that constant pressure filtration characteristics can be predicted from the constant rate filtration experiments. Further analysis of data suggests that the constant pressure filtration with cyclic backwashing is also favourable in industrial applications because it can be operated under almost constant rate condition. The filtrate is found to be free from pathogens, hence it can be reused as reclaimed water for urban reuse.
