Biological-Based Systems for Waste Processing

Inedible plant materials are a valuable resource in a controlled ecological life support system (CELSS). These plant “wastes” yield the sugars which facilitate the microbial-based recycle of C, H, O, and N. Conversion of these wastes to carbon dioxide and heat while also generating nutritious foodstuffs requires that: 1) the recalcitrance of cellulose in these materials be understood, and 2) ways be found to efficiently overcome the protective effect of lignin and other components closely associated with the cellulose. Means must be found to cost effectively increase the bioavailability of the cellulose which are intrinsically safe and environmentally compatible.

The pretreatment of cellulosic materials in liquid water at temperatures above 200°C can give a hydrated, swollen cellulose. The resulting enhancements in surface area increase the rate of enzyme hydrolysis. However, this pretreatment involves complex phenomena due to auto-catalytic degradation of cellulose which occurs at pH levels below 5. A model is currently being developed to aid in selection of conditions which minimize chemical degradation of cellulose while maximizing disruption of its physical structure. The goal is to maximize cellulose surface area. Pretreatment studies are being coupled with measurements and modeling of changes in cellulose properties in order to relate the effect of pretreatments on hydrolysis (using various cellulolytic enzymes) and microbial use of lignocellulosics. The fundamental modeling and experimental studies are being complemented by analyses of lignocellulosic materials which may be grown in a CELSS including rapeseed, cowpea, and rice.