This work is focused to find a viable alternative for a sustainable onion residues
treatment and recycling, by anaerobic digestion with biogas generation and bio-fertilizers
reuse. Onion residues were treated by anaerobic digestion using as seed inoculum
anaerobic sludge from treatment of wastewater barley malting process. Preliminary results at
mesophylic temperature range, based on the exploratory results were: a) the biogas yield
and anaerobic biodegradability of onion wastes were low, with potential higher delay bulbs
than peels, due to acidification, b) two stages anaerobic digestion system should be tested,
c) co-digestion should be tried, due to the high onion wastes C/N, d) lime pretreatment of
onion wastes could improve alkalinity supply, e) type and amount of buffering agents need to
be considered in the anaerobic digestion treatment of this wastes , because concerns about
anaerobic bio-solid recycling to soil as organic fertilizer (salt effects on crops and water), f)
disease fungal control must be verified with bio-solid obtained from anaerobic treatment of
onion wastes.
Keywords: anaerobic