ANAEROBIC-DIGESTION OF PRINT PASTES - A PRELIMINARY SCREENING OF INHIBITION BY DYES AND BIODEGRADABILITY OF THICKENERS

The paper reports the results of a screening laboratory- and pilot-sca le investigation into the anaerobic inhibition/toxicity of dyes and an aerobic biodegradability of fertile print-paste thickeners. Removal an d anaerobic toxicity of six dyes, belonging to different classes (azo, anthraquinone, cyanine, etc.) were evaluated at different concentrati ons (250-2400 mg/l), in tests spanning 72 or 96 h. The anaerobic biode gradability of a mixture of thickeners was evaluated in an up-flow fil ter adding milk whey as co-substrate, during a test spanning 70 days. A low degradation was found, in the order of 30-35% on COD (chemical o xygen demand). Moreover increasing the thickener load to the filter (t hickener/milk whey > 0.5 on a COD basis) caused failure of the process . Possible reasons for the malfunction were thought to be inhibition o f the methanogenesis due to chemicals present in the thickeners (e.g. surfactants, chelating agents, etc.) and the high ammonia concentratio n reached in the filter, derived from hydrolysis of urea in the thicke ners. (C) 1998 Published by Elsevier Science Ltd.