Lead-lag series and staged parallel operational strategies improve the performance and cost-effectiveness of bonechar for control of fluoride in groundwater

Affordable, locally managed, decentralized treatment technologies are needed to protect health in resource-poor regions where communities consume groundwater containing elevated levels of fluoride (F). Bonechar is a promising low-cost sorbent for F that can be produced using local materials and simple pyrolysis technology. However, the sorption capacity of bonechar is low relative to the quantities of F that must be removed to meet health criteria (typically several mg/L), especially at pH typical of groundwaters containing high levels of geogenic F. This necessitates large bonechar contactors and/or frequent sorbent replacement, which could be prohibitively costly in materials and labor. One strategy for improving the feasibility of bonechar water treatment is to utilize lead-lag series or staged parallel configurations of two or more contactors. This study used column testing to quantify potential benefits to bonechar use rate, replacement frequency, and long-run average F concentration in treated water of lead-lag series and staged parallel operational modes compared with single contactor mode. Lead-lag series operation exhibited the largest reduction in bonechar use rate (46% reduction over single contactor mode compared with 29% reduction for staged parallel) and lowest long-run average F levels when treating central Mexican groundwater at pH 8.2 containing 8.5 mg/L F.