Zeta potential distributions in particle treatment processes

Most experimental studies of particle destabilization prior to flocculation and granular media filtration characterize the surface charge of particles using the observed average zeta potential. A more complete accounting of particle–particle and particle–collector interactions can be deduced from analyzing the complete distribution of particle zeta potentials. Zeta potential distributions (ZPDs) of silica particles under chemical conditions reflective of destabilization by pH control, ionic strength adjustment, alum destabilization, and polymer destabilization were investigated. Most of the ZPDs of silica particles were broad and skewed (i.e. not normally distributed). When particle surface charge is controlled by pH control, ionic strength adjustment, and alum destabilization, the variances of the ZPDs are comparable. However, when a high-charge-density polymer is utilized as the coagulant, under-dosed and optimally dosed systems result in ZPDs that are broad and over-dosed systems result in narrow distributions.