Impact of alum pretreatment on biosand filter performance: reply to Dorea's commentary on Curry et al. (2020) article

Dear Editor,

Dorea's commentary on our paper (Curry et al. 2020), on how a common alum pretreatment technique reduces turbidities of biosand filter (BSF) source water but still results in significantly lower flow rates, is extremely helpful and gives further insight into why the flow rates decreased. Though our study focused on water from a construction borrow pit pond used by the community and a local river, the phenomenon is also observed by users of BSFs on the large Tonle Sap Lake, which has regular seasonal fluctuations in turbidity and nutrients (Campbell et al. 2006). The explanations and additional resources cited by Dorea in the commentary help explain why the flow reductions observed from alum pretreatment can vary depending on the type of source water. We appreciate these helpful insights and complementary information to our findings.

Sincerely,

Kevin D. Curry

Christopher P. Bloch