Application of roughing filter to pre-treat 1,000 NTU raw water for slow sand filter

Abstract

It was confirmed experimentally that a Roughing Filter (RF) is effective as a pre-treatment system for Slow Sand Filter (SSF) with coagulant dosing and mixing with raw water. This RF system can pre-treat high turbidity raw water (1,000 NTU) to generate low turbidity (10 NTU) pre-treated water for SSF treatment. In the experiment, the types of filter media, height of the filter media, filtration rate and coagulant dosing were varied and the characteristics of each item were evaluated and the design guidelines were formulated. Water Treatment Plants (WTPs) consisting of pre-treatment with RF followed by SSF to treat river water were designed and constructed in Myanmar based on the design guidelines, and the operational performance was confirmed as effective to generate treated water with a turbidity under 5 NTU, which is in compliance with the WHO guideline despite the rather short working period of about one year. Sand scraping of SSF at a frequency of about once in every one to two months was implemented to maintain the design filtration rate.