The economic of advanced digestion
Jolly, M. and Gillard, J. Black & Veatch, UK
(free)
The process of digestion of sewage sludge reduces the solids remaining for disposal, produces biogas and if dewatered generates a liquor for treatment. In recent years a number of advanced digestion processes have become available which can be added to the conventional digestion process. Some of these processes are well proven with numerous sites around the world whilst others are only just tested at full scale. Traditionally advanced treatment of sludge was more associated with bacterial quality and not economics, however recently the focus has shifted.
The advanced treatment processes affect the digestion process by improving the conversion of organic matter to biogas. This is carried out using different methods such as high pressure steam injection, increased heating, physical and electrical rupturing of cells. Each process has an associated consequences that change the economics of the treatment of sludge.
This paper looks at a number of different advanced digestion techniques including
- Thermal hydrolysis
- Enzyme hydrolysis
- Microsludge
- Open Cell
- Cell Rupture.
An assessment is made of the economics of increased biogas production and improved dewaterability against of the potential increased cost of treating the liquors. The costs associated with liquor treatment is affected by the change in concentration of recycled material particularly ammonia.
