The second Water Quality Report for the Bundamba Advanced Water Treatment Plant in Queensland, Australia, has confirmed the excellent quality of the purified water it produces and proved that the water is safe to add to the drinking supply, says government agency WaterSecure
More than 47,800 water quality tests were conducted in the period from December 2008 to June 2010, taking the total amount of tests now performed to more than 64,000. The tests showed the treatment process was 100% effective in removing contaminants present in the inflowing water as prescribed by the relevant guidelines.
The Independent International Expert Scientific Advisory Panel reviewed the results, and panel chair, University of Queensland vice chancellor Professor Paul Greenfield said that the panel had “concluded the treatment process barriers are able to control any water quality hazards and produce purified recycled water suitable to augment a drinking water supply”.
The three barriers employed at Bundamba AWTP – microfiltration, reverse osmosis and advanced oxidation, plus the final chlorine disinfection – are treating all contaminants in feedwater from the WWTPs effectively. As would be expected in the commissioning and initial operations period of a plant such as Bundamba, processes will need to be refined to consistently achieve optimum results, says WaterSecure.
During the testing period there were only four early warning triggers; each was a byproduct of the disinfection processes used at the plant rather than as a result of a contaminant present in the inflowing water. Each was resolved satisfactorily and none constituted a health risk based on the fact that potential exposure would have been for a very short time, even if water was used to augment drinking water supplies.
On one occasion, a result was returned showing NDMA (N‑nitrosodimethylamine) at levels above the Australian Guidelines for Water Recycling. It is believed the occurrence could have been due to factors specific to the day it occurred.The Bundamba plant was restarting after maintenance work had been completed and feedwater had been stored for 2 weeks rather than the normal 24 h, allowing extra time for disinfection byproducts to form.
Changes to the chloramine system implemented in June 2009 have resulted in a dramatic decrease in NDMA formation. It is also believed that a contributing factor could have been high NDMA levels in the feedwater. Changes made by Queensland Urban Utilities to the way it adds chlorine to water supplied from its plants should control any future formation of NDMA in feedwater supplied to the Bundamba plant.
Similarly, following warnings about bromodichloromethane concentrations, corrective action on the pretreatment chloramination dosing system to move the sodium hypochlorite dosing point, reducing the retention time, was implemented in June 2009. While this action resulted in a reduction in the average concentration of bromodichloromethane and the frequency of early warning triggers, one more early warning occurred in February 2010.
The cause is believed to be a combination of conditions created by the circulation of reverse osmosis permeate during testing (since ceased and processes put in place to prevent this situation) and an increased monochloramine concentration set point which has since been reduced. No early warning triggers have occurred since this time.
WaterSecure emphasizes that because this water would always be added to an environmental barrier, in this case Lake Wivenhoe, the natural processes would also treat these chemicals and reduce their concentration.