Pilot-Plant Experiments on Rock-Bed Filtration for Improving Canal Water Quality

Pilot-plant experiments were conducted for on-site water treatment along a canal in Bangkok to evaluate the performance of a rock-bed filtration system under different operating conditions. Three different rock sizes with approximate equivalent diameters of 10 cm, 15 cm, and 20 cm were used as filter media in two rectangular reactor units (5.04 m long, 0.5 m wide, and 0.75 m deep). A diffuser network of 1.25 cm diameter PVC tubes was installed at the bottom along the length of each reactor to provide aeration. The reactors were fed with raw canal water by a pump through a head tank unit to vary the hydraulic retention time (HRT) from 3 to 13 h. During the 15 months operation, the HRT, filter media size, and aeration locations were changed in five test runs consisting of ten experiments to analyze the filtration mechanism and to determine the optimum operating conditions. The results showed that rock-bed filtration with aeration and a HRT of more than 6 h could successfully improve canal water quality as i...