Critical Factors Affecting the Level of Dissolved Manganese in Different Raw Water and its Removal at Water Treatment Plants

Dissolved Mn concentration fluctuates a lot in source water, which presents a challenge for water treatment. It is crucial to identify the critical factors affecting the dissolved Mn level in source water and select appropriate treatment strategies for dissolved Mn removal. This study investigated four groups of water sources and water treatment plants (WTPs) and tracked Mn from water sources to WTPs. Results showed that the bottom sediments and porewater of both reservoirs and rivers all contained plentiful Mn in reductive form. However, Mn content and speciation in sediments and porewater could not explain the difference of dissolved Mn concentration in WTP raw water. Instead, dissolved organic carbon (DOC), dissolved oxygen, and pH were identified as critical factors controlling Mn transformation and dissolved Mn levels in bulk source water. Chemical oxidation with chlorine and chlorine dioxide effectively removed Mn from low-DOC water (DOC < 3.0 mg/L) but failed when applied to high-DOC water (DOC > 7.0 mg/L). Under this case, biological pretreatment showed advantages in treating Mn in high-DOC water. This study highlighted the importance of considering significant water quality parameters when predicting the Mn level in WTP influent water and choosing suitable techniques for effective Mn removal.