Novel technology for improving the treatability of turbidizing substances by coagulation and sedimentation

Treatability in the coagulation and sedimentation of turbidizing substances varies greatly depending on the rapid stirring strength G_R. It is demonstrated that when PACl coagulant is used, the optimum treatability is achieved at G_R values of 450 for turbidity and 1,000 sec⁻¹ for STR, a newly introduced evaluation parameter. These values are much higher than the values typical of many water purification plants where the G_R values are set at 100~200 sec⁻¹. The remarkable improvement of coagulation and sedimentation treatment is found to be related to the formation of denser, smaller-diameter microfloc with increasing G_R, and an increase in the incorporation of coagulant-derived aluminium in the microfloc and zeta-potential of the microfloc, among other flock properties.