Application of particle-size analysis in coagulation/flocculation for reclamation of a secondary effluent.

Reclaimed secondary effluent is an important alternative water resource for urban areas; the particle-size distribution approach was applied in this study for purpose of screening and evaluating treatment processes for reclamation of a secondary effluent. Two particle-size analysing technologies namely (1) the laser light scattering technology and (2) the sequential membrane filtration technology were used in this study; particulate characteristics of the secondary effluent, of the reclaimed water by coagulation and of the reclaimed water by combined coagulation/flocculation were investigated. Optimisation of coagulation and/or combined coagulation/flocculation technologies were carried out with the help of particulate analysis of priority pollutants, following which studies on turbidity removing mechanisms of both processes were discussed. Comparison studies indicated that increase of turbidity removal efficiency by flocculation happened mainly in the particulate range of 0.2-0.3 microm and 5-8 microm; flocculation did not help or even slightly deteriorated turbidity removal of particles whose sizes are smaller than 0.2 microm and/or in the range of 0.3-5 microm.