Rashca™: A new robust process for the conversion of digested sewage sludge and sludge screenings to liquid biofuel
Sirovski, F. and Sharpe, D., Industrial Chemicals Ltd, UK
(free)
Sewage sludge (SS), also known as biosolids, is the residual organic matter from waste water
treatment. In 2012, the UK produced 1,136, 000 of tonnes dry solids of SS (DEFRA). To obtain a total
amount of sewage sludge produced this figure should be increased by at least 5 fold. The sludge is a
valuable resource for the production of biofuel, recovery of nutrients and precious metals.
ICL have developed and patented a novel robust continuous process for the conversion of SS and
sludge screenings to a liquid biofuel that can be combusted in reciprocating engines and steam
boilers. This process is called RASHCA™ (Rapid Subcritical HydroCarbonification). The process
comprises continuous conversion of digested or undigested dewatered sewage sludge filter cake at
circa 300 C and 100 barg in the presence of NaOH catalyst. The efficient and uniform heating of
sewage sludge cake is attained by using novel ohmic heating technology.
The liquid biofuel obtained has HHV of around 40-42 MJ/Kg and is suitable for combustion in
proprietary stationary diesel gen-sets after their minor mechanical modification.
Process side products include nutrients, environmentally friendly molluscicide and gold. No actual
waste is formed as the result.
Keywords
Biofuels, hydrothermal processing, ohmic heating, sewage sludge (SS).
