Renewable Energy Generation Through Co-digestion with non-sewage Wastes

Conventionally biogas production and renewable energy generation utilising digestion at wastewater treatment plants (WWTPs) has only been considered cost effective at a large scale, unless the facilities have pre-existing digesters and primary sedimentation tanks. The perception is that small WWTPs (less than 20 MLD) - are limited in opportunities for beneficial biogas and renewable energy generation. This view has arisen from two key factors: Small facilities have limited sludge volume which typically means low gas production, and; the capital cost associated with installation of new infrastructure is proportionally high, meaning these facilities are not cost-effective at a small scale.

Recent global experience has shown that smaller WWTPs can produce biogas cost-effectively. The key to success is the introduction of non-sewage high-strength waste streams (HSWs). These HSWs can be codigested with sewage sludge to boost biogas production and generate electricity to offset consumption, and in some cases, export power to the grid. The increased biogas yield, coupled with the income generation obtained through “tipping fees” for accepting the HSWs, improves the business case for these facilities. Other advantages include a significant reduction in landfill waste and reduced greenhouse gas (GHG) emissions.