Optimized Coagulation of High Alkalinity, Low Temperature and Particle Water: pH Adjustment and Polyelectrolytes as Coagulant Aids

Abstract

The Yellow River in winter as source water is characterized as high alkalinity, low temperature and low particle concentrations, which have brought many difficulties to water treatment plants. This study fully examines the optimized coagulation process of the Yellow River by conventional and pre-polymerized metal coagulants, pH adjustment and polyelectrolytes as the primary coagulants or coagulant aids. For all the metal coagulants, polyaluminum chlorides are superior to traditional metal coagulants due to their stable polymeric species and low consumption of alkalinity. The removal of natural organic matter by monomeric metal coagulants can be improved through pH adjustment, which is in accordance with the higher concentration of polymeric species formed at corresponding pH value. With the addition of polyelectrolytes as coagulant aids, the coagulation performance is significantly improved. The effective removal of dissolved organic matter is consistent with high charge density, while molecular weight is relatively important for removing particles, which is consistent with polyelectrolytes as primary coagulants. These results suggest that the coagulation mechanisms in the removal of dissolved organic matter and particles are different, which may be exploited for optimized coagulation for the typical source water in practice.

Enhanced coagulation for high alkalinity and micro-polluted water: The third way through coagulant optimization

“…Generally, aqueous NOM is negatively charged and the coagulant demand for neutralizing the negative charge is much higher than that for neutralizing the charge of mineral particles. Therefore, PDAD-MAC with the highest positive charge was found to be the most efficient coagulant aid in terms of NOM removal (Chang et al, 2005;Yu et al, 2007). Due to the different mechanisms in mineral particles and OMr removal, it is difficult to simultaneously achieve optimal removal for both particles and NOM.…”

Coagulation behavior of polyaluminum chloride: Effects of pH and coagulant dosage

“…As a pre-hydrolyzed coagulant, PACl is becoming increasingly popular in the coagulation-flocculation process. PACl has many benefits over conventional hydrolyzing aluminum or iron salts, such as better performance at low temperature [17,18], less aluminum residuals [19], less sludge volume [20], less effect on the pH value of raw water [8,21], and more rapid flocculation [21]. Furthermore, there are large differences between alum and PACl in morphology and precipitates in water [17,22].…”

Organic removal assessment at full-scale treatment facilities using advanced organic characterization tools

“…In previous studies, water alkalinity of the north has been proven to be higher than that of the south. 6,24,25 Therefore, the variation of pH might be attributed to the alkalinity differences. SUVA as an important parameter has been used to determine the conjugation and aromaticity of DOM by many researchers.…”