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Complex journey for sewage 
When the flush button is pushed, it is a long and complicated journey for the sewage. Each day 140 million litres of sewage are treated at Christchurch City Council’s wastewater treatment plant at Bromley and each day 30 tonnes of solids are removed from the flow. Every resident uses an average 250 litres of water daily, all of which are taken through the treatment plant to remove pollutants and produce an effluent that is as near as possible to fresh water. At present the plant is undergoing a $33.7 million upgrade to increase its capacity and provide operational flexibility. In the first stage of treatment, screens remove rags and the first set of tanks remove grit. Four tonnes a day are buried at the Burwood landfill but a trial is to be conducted soon to see if the rags and grit can be composted. No part of the plant’s operation is simple and a description of the preaeration and grit removal tanks says “Air is injected along one side of the tank above the hoppers that the settled grit is pumped from. The injected air provides oxygen to the flow and assists in removing fat and grease and induces a spiral flow pattern that allows the grit and sand- sized particles to settle out and be removed while maintaining the organic matter in suspension. pic: Shift engineer John Miles in the control room, during his shift monitoring the round- the- clock wastewater treatment process. |
