Anaerobic biodegradability of print pastes plus primary sewage sludge

The object of this research was to investigate the behaviour of the co-digestion of print pastes and primary sludge at lab-scale, in view of a possible fullscale application of this process. The research was focused upon the following aspects: performance and reliability of the co-digestion process, possible interference with the sludge stabilisation (which remained the first aim of the digestion), disappearance of the colour due to the pastes, composition of the supernatant to be sent back to the aerobic wastewater process. Three print pastes were used. Inhibition of the anaerobic process was found during the first period. After approximately 70 days of acclimation, the reactors operated regularly, with satisfactory performance. However, print pastes, that accounted for 10% of the total influent CODs were not biodegraded to a large extent. Absorbance in the visible spectra of the supernatants was modified and/or reduced with respect to the influent, depending on the dyes present in the paste.