AWWA WQTC64093

Floc breakage during particle-liquid separation can lead to significant operational problems, such as reduced clarification rates and filter run times. For natural organic matter (NOM) removal using conventional coagulation, previous research has shown that improved floc properties may be seen when the ratio of organics to coagulant is reduced. However, that implies the addition of higher coagulant doses leading to increased sludge production. Water pretreatment with a magnetic ion exchange resin (MIEX®) followed by conventional coagulation can reduce the coagulant dose by up to 80 % without negatively affecting the level of NOM removal. However, the impact of MIEX® pretreatment and reduced coagulant dose on floc particles has not yet been fully investigated. Results have shown that MIEX is able to significantly reduce the charge concentration in organic rich waters. Logically this reduction, was thought to be the reason, for the potential coagulant dose reduction. It is known that the charge of the anionic organics has to be neutralized in order to remove it effectively by precipitation. Further on it was shown in this study that NOM character was important in determining how the floc physical properties were affected by MIEX® pretreatment. A significant increase in floc size, strength and settling velocity was measured for coagulated NOM after MIEX® pretreatment, in comparison to conventional coagulation for waters dominated by hydrophobic compounds. Treatment of hydrophilic waters did not result in such significant improvement of floc physical properties. Considering these results, MIEX® looks capable of engineering robust downstream floc particles for selected waters, while also reducing potential sludge production by applying very low coagulant doses. Includes 38 references, table, figures.