Treatment of low-turbidity source water by permanganate pre-oxidation: In situ formed hydrous manganese dioxide as filter aid

•KMnO4 dosing improves the treatability of sedimentation and filtration towards particles.•δMnO2 acts as nuclei to enhance particles removal coagulation and sedimentation.•δMnO2 aids filtration to decrease particles levels in effluents of anthracite filters.•The better water quality is achieved at the expenses of more significant WHL.