Sub-Pilot-Scale Autocatalytic Pyrolysis of Wastewater Biosolids for Enhanced Energy Recovery

Abstract

Improving onsite energy generation and recovering value-added products are common goals for sustainable used water reclamation. A new process called autocatalytic pyrolysis was developed at bench scale in our previous work by using biochar produced from the biosolids pyrolysis process itself as the catalyst to enhance energy recovery from wastewater biosolids. The large-scale investigation of this process was used to increase the technical readiness level. A sub-pilot-scale catalytic pyrolytic system was constructed for this scaled-up study. The effects of configuration changes in both pyrolytic and catalytic reactors were investigated as well as the effect of vapor-catalyst contact types (i.e., downstream, in-situ) on product yield and quality. The sub-pilot-scale test with downstream catalysis resulted in higher py-gas yields and lower bio-oil yields when compared to results from a previous batch, bench-scale process. In particular, the py-gas yields increased 2.5-fold and the energy contained in the py-gas approximately quadrupled compared to the control test without autocatalysis. Biochar addition to the feed biosolids before pyrolysis (in-situ catalysis) resulted in increased py-gas production, but the increase was limited. It was expected that using a higher input pyrolyzer with a better mixing condition would further improve the py-gas yield.

Keywords

• wastewater sludge
• bio-oil
• tar cracking
• py-gas
• biochar
• auger reactor
• catalyst
• in-situ catalysis
• downstream catalysis