The effects of changing NOM composition and characteristics on coagulation performance, optimisation and control

A number of water utilities have been experiencing operational difficulties during specific times of the year, associated with elevated levels of organics due to heavy rainfall or snow melt. Water samples were collected from Albert treatment works (Halifax, UK) and the natural organic matter (NOM) was characterised using XAD resin adsorption techniques. The addition of a cationic polyelectrolyte was employed to determine the charge density of the fractions. Results show that NOM fraction make-up changes throughout the year, with the fulvic acid fraction (FAF) showing the greatest increase during the autumn and winter period. The charge density of the FAF fraction also increases. The coagulation conditions for traditional coagulants, such as iron, are more affected by increased levels of organics than the novel coagulant also investigated, and the zeta potential range for optimum removal is narrower. Therefore, the conditions required for zero charge during coagulation varies with both raw water source and the coagulant type.