Pilot scale high solids anaerobic digestion of steam autoclaved municipal solid waste (MSW) pulp

Authors: Holtman, Kevin; Bozzi, David; Franquivillanueva, Diana; Offeman, Richard; Orts, William

Submitted to: Renewable Energy
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/16/2017
Publication Date: 3/31/2017
Citation: Holtman, K.M., Bozzi, D.V., Franquivillanueva, D.M., Offeman, R.D., Orts, W.J. 2017. Pilot scale high solids anaerobic digestion of steam autoclaved municipal solid waste (MSW) pulp. Renewable Energy. 113(113):257-265.

Interpretive Summary: Estimates from the USDA reveal that as much as 30% of the U.S. food supply is wasted, either pre- or post-consumer. This represents losses well over one hundred billion dollars and adds costs in waste disposal. Unfortunately, food waste streams are a complex mix of ingredients that also generally includes an array of packaging materials. Researchers at the ARS-USDA have been working with the waste-handling industry to find ways to isolate relatively uniform output streams from solid waste and for conversion into biofuels or bioproducts. This manuscript provides demonstration of engineering hypotheses and biogas yields and solids reductions for a pilot scale high solids, USDA-designed anaerobic digester that is specifically suited to accommodate lignocellulosic-rich substrates. This digester completely reduces municipal solid waste (MSW) into its non-biodegradable, elemental components. In this report, a lignocellulosic-rich stream was isolated from MSW via steam autoclaving which the digester successfully converted into biomethane at near theoretical yields. This result adds value to food-derived wastes, reduces the amount of solid waste going to landfill and thus reduces the level of greenhouse gases emitted.

Technical Abstract: Steam autoclaving is an efficient method for the separation and recovery of nearly all organics from MSW, yet a reliable alternative outlet for the large volume of organics produced has not yet been successfully demonstrated. The material produced by the autoclave contains a high concentration of solubilized food waste absorbed onto a lignocellulosic matrix, making it a unique substrate. This manuscript details the experience of operating a 1500 gal high solids anaerobic digester on this feedstock. Solids reductions were high; 55 % total solids reduction; and 63 % and 79 % on a volatile solids (VS) and a biodegradable volatile solids (BVS) basis. Gas yields were also high, for instance, 248 L CH4/kg VSfed or 393 L CH4/kg VSdestroyed and methane content was steady at 60 %. Unique design elements such as hydraulic conveyance of material, in situ classification, and in-place buffering to maintain pH stability were tested and confirmed. The digestate passed all criteria for land application of biosolids in the US, but exceeded the EU limits for Cu, Ni, and Zn.