Wastewater treatment is becoming increasingly important, as the effect of soluble contaminants on sensitive ecosystems becomes clearer, and the availability of fresh water becomes more scarce.

Removing soluble contaminants from wastewater is increasingly important, especially when the treated water is returned to sensitive ecosystems. Nitrogen (N)-containing compounds from human waste and other sources cause nutrient overload, algal blooms, the creation of anoxic ‘dead zones’ and subsequent fish kills. Sensitive ecosystems like the Great Barrier Reef are particularly at risk from added nitrogen, as it disrupts the symbiotic relationship between nitrogen-fixing bacteria and algae in the coral polyps, killing the coral.

As a result, the expectations for wastewater treatment are becoming increasingly stringent. From accepting <10 mg/L N in treated effluent in the 1990s, most Australian treatment plant license conditions now specify <5 mg/L N, and in some cases as low as <3 mg/L N. In sensitive ecosystems, like the Great Barrier Reef, complete removal of N from waste water is the ultimate goal.

Conventional wastewater treatment cannot routinely achieve zero N concentrations without adding extra treatment steps at significant additional cost.

Dr Ralf Cord-Ruwisch and his team at Murdoch have a long history in wastewater treatment research, collaborating with companies in the industry since 2001. They have studied the individual biological steps required to convert nitrogen-containing compounds through to nitrite and nitrate and its eventual removal as nitrogen gas. By separating out these aerobic and anaerobic processes they demonstrated how each could be optimised, giving the potential for improved performance compared to conventional wastewater treatment processes.

They developed a process of Parallel Nitrification and Denitrification (PND), which reliably achieves faster and more complete nitrogen removal than existing wastewater systems by sidelining nitrate production. This also uses less oxygen and subsequently requires less energy for aeration than conventional treatment plants.

After the team piloted the underlying technology at the WA Water Corporation’s Woodman Point wastewater treatment plant in 2003, they developed PND from concept to a reliable long-term process ready to be up-scaled. The PND process was licensed in Australia to the Downer Group, the team’s long-term industry collaborator.

In 2016, Downer installed PND as part of the upgrade to a 1 ML/day wastewater treatment plant in Proserpine, Queensland. In a newly built 3.5 ML/day wastewater treatment plant in Mareeba, Queensland, the company incorporated PND into one of its two parallel bioreactors. Each plant discharges waste water into highly sensitive ecosystems, including the Great Barrier Reef (Proserpine). Both plants are currently undertaking benchmarking trials to quantify the effectiveness of PND operation compared to normal operation. By demonstrating the potential of the technology, the Downer group and the Murdoch team are de-risking the broader uptake of PND in the wastewater industry.