Abstract
A novel process is proposed whereby wood wastes from forest tree mortalities and improved forest management are co-digested with high in nitrogen content animal manures to yield bio-methane along with nitrogen, phosphorous, and potassium bio-fertilizers. The process mimics the well-known wood conversion to methane process in lower termites but relies on thermophilic fungi, bacteria, and archaea instead. It is based on the modified state-of-the art two-step, hyperthermophilic (70 °C) hydrolysis and thermophilic (55 °C) fermentation, dry (30% TS), anaerobic digestion technology with a high organic loading and shortened retention time. The process is augmented with the thermophilic fermentation of carbon dioxide in the biogas into secondary bio-methane by employing hydrogen produced via wind-powered electrolysis. The entire process comprised of five distinct steps is designated as “Wood to Methane 3 + 2”. An industrial type, standardized plant unit has been developed that can be employed in a modular fashion. The implementation of these plant units across the US, utilizing the estimated waste wood potential along with 3/4 of the produced poultry and pig manure, would generate the equivalent of 2/3 of transportation fuel consumption and would supply about 11% of current US energy use per annum. The produced bio-methane can be cost-competitive only if it is employed as a transportation fuel to replace fossil gasoline and diesel fuels. The required annual investment over a 20-year period is well within the means of the US economy in a public–private development partnership.
Highlights
Wood is a fibrous but porous structural organic material found in the stems and roots of trees and other woody plants [1]
The US potential of biomass to be derived from wood wastes of forested lands is quite large, if proper forested land management practices are put in place over a period of 20 years
This wood wastes source can be converted to bio-methane in combination with about three-quarters of the current annual generation of rich in nitrogen animal manures from hogs and poultry via anaerobic digestion by emulating the steps involved in the naturally occurring wood decomposition by lower termites
Summary
Wood is a fibrous but porous structural organic material found in the stems and roots of trees and other woody plants [1]. The composition of wood, or of woody biomass as it is known, consists of six major components: cellulose, hemicellulose, lignin, mineral components, extractives, and water. In deciduous trees to near 30% in conifers, both on a dry matter basis, consists mainly of five-carbon sugars that are linked in an irregular, i.e., amorphous, manner. Up to 5% by dry weight, a number of low molecular weight organic compounds called extractives. These compounds comprise fatty acids, resins, waxes, and terpenes and their extraction provides valuable chemicals, among others tannin, tall oil, turpentine, and rosin [4,5]. The employment of a microbial-based process to extract the energy in wood as a gaseous fuel, i.e., bio-methane, is possible as presented
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