Digesters are one part of the answer perhaps. Another useful part could be the use of pyrolysis to convert the remaining biomass into gasses. These gases could be burned directly (like old fashioned town gas from coal) or converted into liquid fuel. There would still be the problem of disposing of the ash from this process but the volume would be considerably smaller than the volume of landfill. Such a two-pronged attack on the situation would yield more biofuel than simply digesting and would reduce volume.