Integration of pyrolysis and anaerobic digestion - Use of aqueous liquor from digestate pyrolysis for biogas production

Anaerobic digestion of aqueous pyrolysis liquor derived from pyrolysis of solid digestate was tested in batch mode using an un-adapted inoculum. Three pyrolysis liquors produced at 330 degrees C, 430 degrees C and 530 degrees C in four COD-based concentrations of 3, 6, 12 and 30 g L-1 were investigated. The three lower concentrations showed considerable biogas production, whereas the 30 g L-1 dosage caused process inhibition. The highest methane yield of 199.1 +/- 18.5 mL g(COD)(1) (COD removal: 56.9 +/- 5.3%) was observed for the 330 degrees C pyrolysis liquor, followed by the 430 degrees C sample with only slightly lower values. The 530 degrees C sample dropped to a yield of 129.3 +/- 19.7 mL g(COD)(1) (COD removal: 36.9 +/- 5.6%). Most VOCs contained in the pyrolysis liquor (i.e. furfural, phenol, catechol, guaiacol, and levoglucosan) were reduced below detection limit (cresol by 10-60%). Consequently, integrated pyrolysis and anaerobic digestion in addition to thermochemical conversion of digestate also promises bioconversion of pyrolysis liquors. (C) 2015 Elsevier Ltd. All rights reserved.