THERMOCHEMICAL TREATMENT OF LIGNOCELLULOSIC AND NITROGENOUS RESIDUALS FOR INCREASING ANAEROBIC BIODEGRADABILITY.

The microbiological conversion of residual organic materials to methane gas has the potential of supplying a significant proportion of the current natural gas demand in the United States. Studies on the bioconversion of oranic residuals to methane have emphasized one significant problem which both adds to the cost of methane production and reduces the actual gas production by 20 to 100 percent below the potential yield. This problem is the inability of microorganisms to completely ferment all the organic matter in residuals. The objective of reported studies at Stanford University has been to increase the biodegradability and hence, methane production from residual orgnaic materials by heat treatment at elevated temperatures and pressures. The study has concentrated on increasing the biodegradability of lignocellulosic and nitrogenous proteins materials. Extensive research data are presented which demonstrate that heat treatment at temperatures of 175 degree to 200 degree C can significantly increase the convertibility of lignocellulosic and nitrogenous organic residues to methane. In addition to increased methane production, heat treatment can decrease the quantity of residue requiring subsequent disposal after methane fermentation is complete. Lignocellulosic materials require chemical addition in order to achieve a significant increase in biodegradability. The chemical costs no doubt would be high, and this would probably limit the economic viabiltiy of heat treatment for increasing methane yields from such materials. With nitrogenous organics, heat treatment can be effective for increasing biodegradability without the addition of chemicals. In addition the increased dewaterability of the digested sludge which results should make heat treatment an attractive procedure for pretreatment of sludges and other readily available nitrogen-containing residues.