TECHNOLOGY FOCUS - ENVIRONMENT - Preferred Method: The method comprises: mixing the plant material with the dung with to facilitate anaerobic fermentation; and using at least some of the captured gas and/or the biomethane fuel to power collection and mixing of the dung, where some of the gas is used for cooking on the farm.    TECHNOLOGY FOCUS - INSTRUMENTATION AND TESTING - Preferred Components: The vehicle comprises a barge equipped with a propulsion unit operable in the water to drive the barge, which carries: a cutter configured and arranged to be deployed under the water to cut the plants; a conveyor operable to convey the cut plant material into the barge; and a bulkhead movable aftward as the cut plant material is conveyed into the barge and forward as the cut plant material is discharged from the barge. The conveyor is reversible to discharge the cut plant material from the barge. The barge is equipped with an engine configured and arranged to be fueled with biofuel derived from the biogas. The transfer means comprises a hopper into which the cut plant material is discharged from the vehicle. The hopper is fixed and is mounted on a vessel drivable through the water to deliver the cut material from the hopper to the anaerobic digester. The transport mechanism includes: a macerator operative to macerate the cut plant material; a conduit between the hopper and the anaerobic digester; and a pump operative to pump the macerated material from the hopper to the anaerobic digester by way of the conduit. The hopper is carried by a floating platform moored in the water. The macerator comprises: many rolls configured and arranged to be driven to crush the cut plant material; and a shredder operative to shred the crushed plant material. The hopper contains a sprayer operative to spray water over the cut plant material to facilitate its passage through the hopper. The pump is a rotary positive displacement pump. The fermentation tank: has a wall shaped to facilitate circulation of the plant material; comprises a sheet curved about a horizontal axis, where the sheet is formed of synthetic plastics material; and has an outlet for residue from the fermentation connected to a separator operative in use to separate liquid from solid components of the residue. The wall has a cross section in the form of a cardioid having two lobes and a cusp between the lobes, where the cusp is directed upwards, and where some of the biogas is fed back to the fermentation tank and directed through the cusp so as to stimulate circulation of the plant material around each of the lobes. The system comprises many tanks in series. The anaerobic digester: operates on a continuous digestion process; is located in a lagoon of the water, where the water in the lagoon provides a heat transfer medium between the tanks; comprises a fermentation tank where the plant material is circulated in a continuous process; and comprises a heater for the tank. The system includes: means for treating the solid component to produce compost; means for treating the liquid component to extract usable water; and means for mixing the plant material with an additional material to accelerate anaerobic fermentation of the material, where the additional material comprises a fermentation conditioner comprising an organic material, preferably dung.