Algal softening followed by ozonation: The fate of persistent micropollutants and natural organic matter in groundwater

•Softening followed by ozonation were applied to remove carbamazepine and diclofenac.•The oxidation of those chemicals with O3 was enhanced at elevated pH values.•This study used microalgae to soften groundwater via photosynthesis in the light.•The softening of groundwater greatly removed radical-scavenging carbonate species.•The softening also mitigated the quenching of OH radicals by natural organic matter.