Impact of alum pretreatment on biosand filter performance: a commentary on Curry et al. (2020)

In a recent contribution by Curry and colleagues, a field-derived assessment of a reportedly common pretreatment technique to reduce turbidities of biosand filter (BSF) feed water was reported. Their results demonstrated that despite alum pretreatment achieving lower settled turbidity values relative to control filters, such intervention led to significantly lower flow rates in the alum-dosed BSFs. However, their study stopped short of providing a more meaningful interpretation to what may initially seem like a counterintuitive finding, which is presented here.