CAVITATION AND BACKWASH: THE WAY IT IS OR FIXABLE PROBLEM?

The City of Northglenn, Colorado owns and operates a conventional surface water treatment plant (WTP) that was constructed in 1980. Since the opening of the plant, operations staff has observed loud noise and vibration made by the filter backwash control valve and air bubbles in the filters. The noise and vibration of the flow control valve was caused by valve cavitation. Pipe deformation and leaks caused by the cavitation were repaired by periodically welding patches to the pipe downstream of the control valve. Air bubbles in the filter during backwashing decreased the effectiveness of the backwash. To account for the decreased effectiveness of the backwash due to the bubbles, the backwash cycle time was increased.The goals of this study were to identify the cause of the flow control valve cavitation and the source of the air bubbles in the filters, and to develop alternatives that will either reduce or eliminate both issues.