Verification of Wegelin\'s design criteria for horizontal flow roughing filters (HRFs) with alternative filter material

Abstract

Wegelin\'s design criteria founded on the “1/3 – 2/3” filter theory are still to date the most comprehensive models applied in design of roughing filters. This study aimed at verifying these criteria based on gravel as a filter medium and two other possible
alternative filter media, namely broken burnt bricks and charcoal maize cobs. Gravel was used as a control medium since it is one of the most commonly used roughing filter media and also because it was used in developing these criteria. The per cent reduction in raw water suspended solids (SS) concentration was compared against the expected model prediction. SS was used as a parameter of choice since the “1/3 – 2/3” filter theory is based on SS reduction. A pilot plant study was undertaken to meet this objective. The pilot plant was monitored for a continuous 85 days from commissioning till the end of the project. Results showed that in general, filters filled with charcoal maize cobs and broken burnt bricks were off model prediction by 13% compared to gravel\'s 15%. The performances also varied in both low- and high-peak periods. It is concluded that the Wegelin\'s design criteria should be used as a guideline step followed by actual field and laboratory tests to establish the actual filter design parameters in line with the filter media in use and the quality of the raw water to be treated.

Water SA Vol 32(1)pp:105-109