Energy-efficient wastewater treatment for dairy effluent using passive aeration biofilm technology

Cheesemaking, while a value-adding process for dairy farms, generates large volumes of nutrient-rich wastewater, particularly from whey and wash water. This effluent has high levels of organic pollutants, measured as chemical and biological oxygen demand (COD/BOD), which, if not treated properly, can significantly harm surrounding ecosystems. Traditional wastewater treatment methods are energy-intensive due to the need to pump compressed air into large tanks to supply oxygen, making them costly and environmentally taxing—especially for smaller agricultural producers like Melville Park in Western Australia. For farms and food processors, especially those in regional areas, there has been a pressing need for a more efficient, scalable, and cost-effective wastewater solution.

To address this challenge, Dr. Ralf Cord-Ruwisch and his team at Murdoch University developed a prototype wastewater treatment process known as Passive Aeration Simultaneous Nitrification and Denitrification (PASND). The system uses biofilms embedded with glycogen-accumulating organisms (GAOs) capable of rapidly absorbing organic material from cheese effluent and storing it for later processing. Rather than relying on energy-intensive aeration, the PASND method exposes these biofilms to atmospheric oxygen, mimicking the efficiency of oxygen transfer in lungs. This simple, passive approach allows oxygen uptake without mechanical input, significantly reducing energy demands.

The results of the trial demonstrate that PASND is a viable, low-energy alternative to conventional wastewater treatment systems—especially for high-COD effluents like cheese wastewater. Compared to traditional systems, PASND reduces operational costs significantly by eliminating the need for compressed air and minimising excess sludge production. Its compact design and simple operation make it ideal for small and medium-sized food processors seeking sustainable waste management options.

Moreover, this innovation opens up new opportunities for water recycling in agriculture and food production, helping industries meet environmental regulations and reduce their carbon footprint. With successful field deployment at Melville Park, the system provides a replicable model for other dairy operations and food manufacturers across Australia.

The next phase of development for the PASND system involves refining process monitoring, improving reliability, and broadening application. Priorities include integrating automated shutdown systems to protect biofilms during downtime, incorporating phosphate removal steps for more sensitive environments, and exploring hybrid systems that combine PASND with anaerobic digestion for high-strength waste streams.

The system also shows promise beyond dairy wastewater. Adaptations could support hydroponic and protected cropping systems, where controlled recycling of cleaning water and nutrient solutions is essential. PASND’s structural similarity to flood-and-drain systems makes it particularly relevant for greenhouse operations looking to reduce environmental impact and enhance sustainability.

Continued research will focus on managing potential challenges like biocide contamination, acid buildup, and salt accumulation—critical for widespread adoption. With its strong performance and minimal energy requirements, PASND stands to revolutionise waste treatment for food and agriculture, transforming an environmental challenge into an opportunity for innovation and resource recovery.