BACKGROUNDRecently, a virtuous material cycle has been reported where soluble bio-based substances (SBO) obtained by anaerobic digestion, composting and chemical hydrolysis of urban wastes are recycled at 0.05-2% concentration to the anaerobic bioreactor to reduce the ammonia content in the fermentation digestate, with no adverse effect on biogas yield and composition. The aim of the present work was to assess whether the same SBO effect was real also for the anaerobic fermentation of farm manure. RESULTSManure fermentations were carried out at 35 degrees C for 40 days in the absence (control) and in the presence of 0.2% SBO using a 115 L reactor, yielding over 1000 biogas NL. No SBO effect on biogas production and composition was evident. The control fermentation produced 18% ammonia at the expense of the pristine organic N. In contrast, fermentation in the presence of SBO produced no ammonia and no reduction of the pristine organic N. CONCLUSIONSThe SBO assisted anaerobic fermentation for reducing digestate ammonia content can be applied to farm manure as well as to urban biowastes. This finding gives the prospect of more benefits from a wider material cycle including both urban and agriculture wastes processed by integrated chemical and biochemical technology. (c) 2016 Society of Chemical Industry