NOVELTY - System comprises: an aquatic plant cultivator (120); an anaerobic digester (140) operatively coupled to the aquatic plant cultivator to receive aquatic plants and produce biogas; a biogas converter (160) coupled to the anaerobic digester to receive the biogas and produce liquefied methane and thermal energy (142), where at least a portion of the thermal energy results from a methane liquefaction process; a thermal path between the biogas converter and the aquatic plant cultivator and the anaerobic digester; and a controller coupled to the converter, the cultivator and the digester.    USE - The systems and the methods are useful for processing methane, preferably for converting aquatic plants (microalgae or duckweed) to liquid methane (all claimed).    ADVANTAGE - The system: utilizes a unified facility that simultaneously captures carbon dioxide, processes multiple organic waste streams, and produces high quality, low cost liquefied bio-methane for vehicular fuel; and provides a sustainable, renewable source of fuel, thus reducing the impact of global warming and the need for importing fuels from other countries.    DETAILED DESCRIPTION - System comprises: an aquatic plant cultivator (120); an anaerobic digester (140) operatively coupled to the aquatic plant cultivator to receive aquatic plants and municipal solid waste, and produce biogas; a biogas converter (160) coupled to the anaerobic digester to receive the biogas and produce liquefied methane, thermal energy (142) and carbon dioxide at a temperature different than a temperature at the aquatic plant cultivator, where at least a portion of the thermal energy results from a methane liquefaction process; a thermal path between the biogas converter and at least one of the aquatic plant cultivator and the anaerobic digester; and a controller coupled to the biogas converter and the aquatic plant cultivator and the anaerobic digester, where the controller is programmed with instructions that, when executed, direct the portion of thermal energy between the biogas converter, the aquatic plant cultivator and the anaerobic digester. INDEPENDENT CLAIMS are also included for:    (1) a system-2, comprising: an aquatic plant cultivator; a pre-treatment device (153) operatively coupled to the aquatic plant cultivator and a source of municipal solid waste (MSW), where the pre-treatment device has a heat exchanger positioned to heat aquatic plants and the MSW; an anaerobic digester vessel operatively coupled to the pre-treatment device to receive the aquatic plants and MSW and produce biogas; a biogas converter coupled to the anaerobic digester vessel to receive the biogas and produce liquefied methane and thermal energy, where at least part of the thermal energy is produced by a refrigeration cycle, and the thermal energy includes thermal energy stored in carbon dioxide; an anaerobic digester return path coupled between the anaerobic digester vessel and the aquatic plant cultivator to direct output from the anaerobic digester vessel to the aquatic plant cultivator; a biogas path coupled between the anaerobic digester vessel and the biogas converter to direct biogas to the biogas converter; a first biogas converter return path coupled between the biogas converter and at least one of the pre-treatment device and the anaerobic digester vessel to direct a first thermal output from the biogas converter to the pre-treatment device and the anaerobic digester vessel; a second biogas converter return path coupled between the biogas converter and the aquatic plant cultivator to direct a second thermal output from biogas converter to the aquatic plant cultivator, where the second thermal output includes the carbon dioxide; and a controller coupled to the aquatic plant cultivator, the pretreatment device, the anaerobic digester vessel, and the biogas converter, where the controller is programmed with instructions that, when executed, directs flow of energy and constituents among the aquatic plant cultivator, the pretreatment device, the anaerobic digester vessel, and the biogas converter;    (2) method-1 for processing methane, comprising: growing aquatic plants at an aquatic plant cultivator; receiving the aquatic plants at an anaerobic digester; producing biogas at the anaerobic digester; receiving the biogas at a biogas converter; liquefying methane from the biogas at the biogas converter; producing at least a portion of thermal energy at the biogas converter as a result of liquefying the methane; and transferring the portion of thermal energy to at least one of the anaerobic digester and the aquatic plant cultivator;    (3) method-2 for processing methane, comprising: growing a first portion of aquatic plants at an aquatic plant cultivator; directing the first portion of the aquatic plants and a first portion of MSW to a pre-treatment device; heating the first portion of the aquatic plants and the first portion of the MSW at the pre-treatment device to kill the first portion of the aquatic plants and pathogens carried by at least one of the first portion of the aquatic plants and the first portion of the MSW; directing the first portion of the aquatic plants and the first portion of the MSW to an anaerobic digester vessel to produce biogas; directing the biogas from the anaerobic digester vessel to a biogas converter to produce liquefied methane and thermal energy; and directing at least a portion of the thermal energy from the biogas converter to the pre-treatment device to kill a second portion of the aquatic plants and pathogens carried by at least one of the second portion of the aquatic plants and a second portion of the MSW; and    (4) a method-3 for processing methane.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic block diagram of the system and method for converting algae and/or other aquatic plants to liquid methane.    Aquatic plant cultivator (120)    Anaerobic digester (140)    Thermal energy (142)    Pretreatment device (153)    Biogas converter (160)