A thesis submitted in partial fulfillment of the requirements for the degree of Master of Engineering

Thesis (M.Eng.) - Asian Institute of Technology, 1992

The study of the application of polyaluminum c hl oride (PAC) as a coagu lant for water treatment at Bangkhen water treatment plant was investigated. The results of the experiments indi cated that PAC was an effective coagulant using approximately ha lf the dose normally required with alum. PAC can remove turbidity and co lour of raw water better than alum does. Furthermore, it can perform in a wide range of water pH between 3 and 10. Water treated by PAC has lower aluminum conce ntrati on than water treated by a lum. Bei ng less acidic than alum, PAC is cost effective in pH correction as illustrated by the higher pH and a lka linity of the s upernatant when PAC is used for coagu l ation. The use of polymer additive is not required with PAC. Therefore, the operation of water treatment plants can be simplified, the dosage control is s impl e and easy leading to rational facilities and efficient operation. Although PAC has been s hown to be an effective coagulant for the removal of turbidity and colour of raw water, PAC is still. not pr act i ca 1 i n t er ms of econ om i c . The cost of us i n g PA c at t he present time i s higher than the cost of using alum coagulant. The t"'egu l ar alum coagu lation at Bangkhen water treatment sti ll gives s atisfactory water quality, meeting the Thai standards for drinking water. For economic reasons, the use of a 1 um coagu 1 at ion at Bangk hen water treatment plant i s stil l practising and the app li cation of PAC i s not economica lly attractive at present.