A council wastewater plant met its E. coli consent with no chemical dosing at all using the Supercritical UV™ disinfection system, saving an estimated $1,600 per day during irrigation season.
A council wastewater treatment plant receives a large volume of industrial trade waste. The treatment process consists of screening, anaerobic pond, aerated lagoon, settlement, and chemical dosing, followed by conventional submerged lamp ultraviolet disinfection.
Chemical dosing is used to remove phosphorus and raise UVT so the conventional UV system can treat effectively. For much of the year the council irrigates wastewater to land, where the key consent requirement is E. coli <1,000 MPN/100mL. During irrigation season, phosphorus removal is not required but chemical dosing continues regardless, purely to keep UVT high enough for the conventional system to function.
NovoLabs™ was invited to demonstrate that the Supercritical UV™ system could achieve the same level of disinfection without any chemical pre-treatment. A mobile testing unit was installed immediately upstream of the chemical dosing point and operated from December 2020 to January 2021. During this period, UVT before chemical dosing ranged from 12% to 42%.
Performance was compared directly: the conventional system with chemical dosing averaged 70% UVT; the Supercritical UV™ system operated without chemical dosing at an average UVT of 30%.
Both systems reduced E. coli to well below the consent requirement of 1,000 MPN/100mL. The Supercritical UV™ system achieved this without any chemical dosing, even when UVT was as low as 12%.
Avoiding chemical dosing during irrigation is estimated to save over $1,600/day in chemical costs alone, with further savings from eliminating chemical sludge disposal. An additional environmental benefit: without chemical dosing, valuable nutrients are recycled back to land rather than locked up in sludge - the equivalent of over 100 tonnes of superphosphate per year returned to land.
"The NovoLabs™ containerised Supercritical UV™ disinfection system would save approximately $1,600/day when irrigating and provide a more holistic and sustainable solution in line with the aspirations of local iwi."
— Council Project Engineer
