The wastewater industry continues to lead the way in the adoption of anaerobic digestion as a sustainable treatment technology for sewage sludge. However, John O’Regan says few plants are making the most of the clear advantages that co-digestion has to offer.
IN the face of social and political pressure to reduce the environmental impact of waste disposal, anaerobic digestion (AD) is becoming an increasingly popular solution in the wastewater sector. What’s more, with the government continuing its drive to implement legislation and incentives for renewable energy production, it provides a greener and more financially lucrative way forward.
With such clear economical and environmental benefits, the question remains: why are professionals not making the most of unused capacity in their digesters by adding domestic waste and/or farmyard slurry to the mix? Co-digestion not only opens to the door to wider financial returns and an additional gate fee, it produces increased volumes of biogas. This extra biogas can be used to generate renewable electricity and heat, reducing a plant’s dependence on fossil fuel and has potential to be fed back into the National Grid. It also offers an alternative to food waste disposal in landfill, which is not only expensive but can potentially generate undesired, harmful methane as the waste decomposes underground.
So it would seem co-digestion does genuinely present an attractive commercial growth opportunity for individual wastewater treatment plants, whilst helping contribute towards the UK’s legally binding carbon reduction targets. However, the marked level of apprehension amongst industry professionals remains and this is due to a widely disputed problem – how do you securely manage the increased levels of digestate?
With the burden of liability falling to the sludge producer, these concerns are heightened by a backdrop of obstacles surrounding current disposal methods. The increasing expense of practices such as landfill and land application is matched with diminishing availability of useable land. There is also growing public and legal opposition and other liability implications associated with spreading solids that contain unknown and potentially toxic contaminants on agricultural land. These issues have meant that industry is still seeking an injection of confidence to help drive widespread uptake.
John O’Regan is chief executive officer at SCFI.