Potential of biologically activated carbon to improve chlorine stability from biodegradation in surface waters

We report that biological activated carbon (BAC) has the significant potential to improve chlorine stability in the drinking water and dissolved organic carbon (DOC) is not a good indicator of chlorine stability. The BAC followed by enhanced coagulation (EC) could be beneficial for improving chlorine stability. BAC granules obtained from an aged (>26,000-bed volume over a year) BAC column was incubated in the same surface water. The prolonged (58 days) incubation achieved a DOC removal (up to 47%) and improvement of chlorine stability (up to 93% of chlorine reactive agents) with time. Surprisingly, a smaller initial biological removal in DOC (12% or 0.61 mg/L) by BAC substantially improved chlorine stability (64% of chlorine reactive agents), but a further improvement per mg-DOC removal is small. BAC process removes non-coagulable compounds that are chlorine reactive, but at the same time increases the coagulable compounds that are chlorine reactive, implying coagulation after BAC (BAC/EC) is beneficial in stabilising the chlorine and DOC removal. Over the incubation period, a shift in the microbial community is less significant except for the abundance of Nitrospira increasing with the removal in biodegradable organic carbon. BAC treatment followed by coagulation is a good strategy, but the evaluation should be based on chlorine stability and disinfection by-products (DBPs) formation rather than the DOC.