An alternative arrangement of gravel medium in tidal flow reed beds treating pig farm wastewater

The effect of using coarse grain in the upper layer of a gravel-based reed bed is investigated. The aim for testing the “anti-sized” arrangement of gravel media is to seek a solution for the practical problem of medium clogging in reed beds that frequently takes place during the treatment of high strength wastewaters. Results from parallel operations of an anti-sized and a conventional “monosized” reed bed reveal that the former has the advantage of greater pollutant removal efficiencies. A specific clogging tendency rate is defined to quantitatively describe the clogging behaviour. Calculation of the clogging tendency rate reveals that the anti-sized reed bed has a clear advantage over the mono-sized bed because of improved ability to counteract clogging. Greater pore space in the upper layer of the anti-sized bed allows the suspended solids to be filtered and penetrate farther into the bed matrix, thereby allowing the solid-storage capacity of the matrix to be used more effectively and prolonging the operational life time of the bed. As such, the anti-sized arrangement of reed bed media may provide a viable solution for the problem of clogging.