Boosting Energy Production Through Co- Digestion

Many wastewater treatment plants (WWTPs) are seizing the opportunity to become an energy production facility as well as a treatment facility. Glenelg WWTP in Adelaide (South Australia) is an example of this and has been working towards becoming energy neutral. Three combustion engines are located at Glenelg WWTP which utilise either biogas (from the anaerobic digesters) or natural gas for electricity production. Historically the digesters were only fed with primary sludge and thickened secondary sludge drawn from the wastewater treatment process, and produced enough biogas to provide approximately 55% of the power used onsite.

Ways to boost the biogas production were investigated including adding liquid waste with a high organic load from industry to the anaerobic digesters (referred to as co-digestion). This has the advantages of not only generating more energy, but it also avoids overloading the sewer and secondary treatment systems with trade waste, preventing sewer corrosion and reducing the energy required to treat wastewater.

Following the success of a co-digestion research program, the construction of a fully automated co-digestion plant was undertaken at Glenelg WWTP. A customer base of appropriate trade wastes (or substrates) was established and rigorous testing methodologies of the substrates established. The amount of energy generated with biogas has remained above 65% of onsite electricity usage, reaching as high as 85%, since the co-digestion plant was commissioned, and the stability of the digesters has not been impacted.

Optimisation of the co-digestion process is an ongoing process to continue to increase the biogas production as more knowledge of the biogas dynamics is obtained. This paper provides an overview of the co-digestion journey and the technical and operational lessons learnt from going through this process, in addition to the innovative tools that can be utilised to boost biogas production.