Winneke filters air relief. How to burp your filter Improvements possible through regular filter inspections and optimization

Figure 1 – Arial view of Winneke Water Treatment Plant Introduction Melbourne Water‘s Winneke Water Treatment plant includes 16 rapid sand filters Filter inspections and a process review was carried out in 2015 A number of issues were identified relating to deficiencies with the filter backwashing process and subsequent impact on filter performance Problem Trapped air in the plenum chamber after the backwash air scour step Issues identified Boiling and displacement of the filter media and support gravel layer due to trapped air in the plenum being forced through the filter nozzles at a high rate during the washwater step Sand media loss into the plenum chamber and backwash channel Sand blocking filter laterals and nozzles creating quiet zones

Figure 2 - Appearance of boiling and quiet areas during a filter backwash

Figure 3 - Boiling occurring as air is forced out by washwater

Figure 4 – Sand cleaned out of plenum chamber Objective Provide an alternate means to relieve trapped air from plenum chamber during the washwater step and prevent boiling Actions

� Installation and trial of manual plenum chamber air relief valve

� Once proven, install actuated valves and update the backwash system to automate the relief process

Figure 5 – Schematic of trapped air in the plenum chamber

Figure 6 – Trial plenum air release valve (manual) Once air scouring was completed as washwater entered the filter, boiling was visible (Figure 3). This indicated that there was trapped air present in plenum chamber. As a result, plenum chamber air relief valve (manual) was installed at the downstream side of air inlet valve. This valve provided an alternative pathway to relieve the trapped air allowing it to be squeezed from the plenum chamber as the washwater entered the filter rather than through the filter bed Results The manual air release valve was opened, as soon as air inlet valve was closed. Significant volume of air escaped through the air release valve. Minimal air was relieved through the filter media.

Figure 7 - No boiling on washwater cycle – post manual release valve Outcome Promising results for the manual trial Actuated valve replacement for manual trial to automate process Future Actions Rollout solution to all 16 filters and conduct further media and plenum inspections to verify if media disruption has reduced Author: - Thilini Malalasekera – Melbourne Water –Water Supply (thilini.malalasekera@melbournewater.com.au)