Energy from refuse by bioconversion, fermentation and residue disposal processes

Biological conversion of organic refuse to methane by anaerobic fermentation is one mechanism by which the energy in urban waste can be reclaimed. Laboratory studies have been used to determine the rate and quantity of gas production at various operating temperatures. The dewatering characteristics of the spent fermentation slurry have been evaluated. The spent solids can be dewatered to a sufficiently low moisture content such that incineration is self-sustaining. The incineration system has been evaluated to determine the possible energy recovery from the spent cake. A process for treating the liquid blowdown from the system has been developed. A mathematical simulation of the total system has been constructed to evaluate performance under various operating conditions. The operating cost of the system can be obtained. A plant processing 908 metric tons of refuse per day will produce 3905 m/sup 3/ of methane per hour. If the methane is marketed for $3.53/100 m/sup 3/, the system will require a dump fee for refuse disposal in excess of $5.34/metric ton. Sale of recovered steam from the incineration of the spent cake can reduce the dump fee by about $3.00. Recovery of just methane provides an efficiency of energy recovery of 32.6 percent. Thismore » efficiency can be increased to 63.4 percent if the steam from the incinerator can be sold.« less