Biochemical Methane Potential of Beef Feedlot Manure: Impact of Manure Age and Storage

Abstract

Methane capture and use from intensive livestock industries is relatively new, and there is limited chemical and kinetic degradation information available for beef feedlot manure in Australia or internationally. This paper evaluates the biochemical methane (CH) potential, apparent first-order hydrolysis rate coefficient, and losses in organic content of manure as it ages on feedlot pads and in stockpiles. Chemical characterization of fresh, pad, and stockpiled manure is assessed. Biochemical CH potential on volatile solids (VS) almost always decreased significantly from fresh to pad and from pad to stockpile, ranging (in mL CH g VS) from 230 to 360 in fresh manure, from 70 to 280 in pads, and from 60 to 200 in stockpiles. Kinetics of degradation also varied with manure age (fresh: 0.12 ± 0.01 d; pad: 0.06 ± 0.02 d; and stockpiled: 0.05 ± 0.04 d). At least 50%, and up to 80%, of the original biochemical CH potential of the manure (i.e., degradable material) was lost on drying in pads, and the loss after stockpiling was much greater (>85%). The loss of N was 15 to 60% as manure dried on pads and was much greater after stockpiling (40-90%). Phosphorus loss, though lower than nitrogenous losses, was still significant (25-65% on pads and 35-85% in stockpiles). Although digestion of stockpiled manure is still feasible to generate energy, collection of fresh manure is important to maximize outcomes, with a possible order of magnitude increase in CH production achievable.