In contrast with other wastewater treatment plants where the sludge is treated anaerobically to produce methane and electricity, Wetalla reclamation plant in Toowoomba is applying aerobic digestion to stabilize the sludge. Aerobic digestion is essentially a biological process where aerobic and facultative bacteria degrade further the organic matter in the final sludge to reduce the final volume and also obtain a mature humus-like compost that can be used as fertilizer in agriculture. It can also be used as soil cover or landfill cover depending on its quality. One way to measure its quality is to measure the CO2 emission rate. A high CO2 production will indicate an unstable product with high content of easily biodegradable material promoting bacterial growth. This could badly affect plant growth if the material was used as compost. It is therefore important to monitor the CO2 production rate to ensure that the aerobic digestion process is working properly. Typical residence times are 2-3 weeks and the biosolids should be overturned regularly to ensure good oxygen mass transfer.

USQ has recently acquired an online CO2/CH4 analyzer to measure emission rate from soils. The monitoring of Wetalla’s biosolids is important for several reasons:
- Gather data from the process and ensure that the design residence time is sufficient to obtain a stabilized final residue suitable for further applications
- Estimate the volatile solids destruction in the process and the overall kinetic.
- Fine-tune the overturning/mixing regime: if the CO2 emission rate from the final residue was found to be lower than the required standard, it would mean that fewer turnings could be applied which could save electricity.
- Ensure that the aerobic process is operating properly by measuring methane emissions. If Methane was found it would mean that aeration is not sufficient and that anaerobic bacteria are growing. Methane emissions should be avoided as methane has a strong greenhouse gas potential.
USQ researchers have already obtain some data from the process and need a student to analyze them and possibly go to the plant to obtain further data.

Dr Antoine Trzcinski

• School of Engineering and Built Environment

• Agricultural Biotechnology
• Agriculture, Land and Farm Management
• Analytical Chemistry
• Atmospheric Sciences
• Biochemistry and Cell Biology
• Chemical Engineering
• Civil Engineering
• Environmental Biotechnology
• Environmental Engineering
• Environmental Science and Management

• Master of Research (MRES)
• Master of Research (MRES)