NOVELTY - A system for composting biosolids, comprises a pad for supporting pile(s) of biosolids, where the pad surface defines at least one row region having a central zone (24) and edge zone(s) (26), to receive the pile; a source (52) of heat-retaining fluid; an array of pipes (44, 46, 48, 50, 65) embedded in the pad, and in fluid communication with the source; and controller. The controller selectively controls circulation of fluid from central zone to other zones, via pipes, to transfer heat generated by aerobic decomposition of compost in central zone, to a zone in need of the generated heat.    USE - As a system for composting of biosolids (claimed), to provide compostable biosolids, which constitute a valuable resource for fertilizer and soil improvement; useful as a large-scale composting system for outdoor operation, to compost municipal wastes.    ADVANTAGE - The composting system permits heat generated by aerobic decomposition of compost within the central zone of the biosolid-receiving pad, to be transferred to the edge zone of the pad in need of the generated heat, thus thawing snow and ice built on a portion of the cover at the edge zone, to permit the user to easily remove the cover without damage. Alternatively, the generated heat may be transferred from one central zone to another central zone, to activate/initiate composting process in a fresh pile received on the other zone of the pad. The computerized controller operates the system, including circulation of fluid from selected central zones to selected edge zones, with real time data collection of temperature at critical locations, and optional serial extraction and application of heat from and to multiple regions/zones on the pad. The system permits user control fluid circulation, and provides a visual display associated with the controller. The system can be operated according a timed mode, a volume mode and/or a temperature mode, to selectively circulate the fluid according to the selected mode, serially within each selected region and zone of the pad, and optionally followed by a selected recovery period.    DETAILED DESCRIPTION - A system for composting of biosolids, comprises a pad for supporting at least one pile of biosolids, where the pad defines at least one row region having a central zone (24) and adjacent edge zone(s) (26), to receive a corresponding pile on its surface; a source (e.g. a storage tank (52)) of heat-retaining fluid for transferring heat between the zones of pad; an array of pipes (44, 46, 48, 50, 65) embedded in the pad, and in fluid communication with the source of heat-retaining fluid; and a controller for controlling operation of the system. The array of pipes includes a first sub-array located in the central zone, and a second sub-array located in the edge zone. Each sub-array is independently connected to the source of heat-retaining fluid. The controller includes elements for selectively controlling circulation of the fluid through the pipes, from the central zone to other zones of the pad, to transfer heat generated by aerobic decomposition of compost within the central zone, to a zone in need of the generated heat. The controller selectively controls circulation of the heat-retaining fluid between multiple row regions. The zone in need of heat is preferably an edge zone, or a central zone of one of the multiple row regions that is remote from heat source. The system includes valves (56, 62, 68) for selectively controlling the flow of the fluid through the array of pipes; pumps (54, 58) for circulating the fluid through the pipes and the source; at least one temperature sensor (66) in each of the central zone and edge zone, for transmitting signals in real time indicative of a temperature of the pad, fluid or biosolid pile; and signal transmission lines between the controller and the temperature sensor, pumps and valves. The system further comprises a removable cover containing a flexible membrane, for selectively covering the pile. The cover is dimensioned to extend over the central zone and at least a portion of the edge zone for contacting the pad within the edge zone. The controller further includes a visual display for displaying a graphic illustration of the row region(s) including central and edge zones, the temperatures detected by temperature sensors, the on/off status of the pumps and valves, and the enabled/disabled status of central and edge zones. The zone with enabled status includes a heat-generating actively composting pile. The zone with disabled status, indicates an absence of an actively composting pile. The temperature, on/off status and enablement status is displayed in real time; and the controller permits user control over the system in response to the real time information. An INDEPENDENT CLAIM is included for composting biosolids involving supporting at least one pile of biosolids on the central region of the pad; and selectively controlling circulation of the heat-retaining fluid in response to signal information received from the temperature sensor(s), where the fluid is selectively transferred from the central zone to another zone of pad, to transfer heat generated by aerobic decomposition of compost within the central zone, to the other zone of pad in need of the generated heat.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic view of a fluid piping and storage components of a system useful for composting of biosolids.    Central zone of pad region (24)    Edge zone of pad region (26)    Hot supply pipe (44)    Cold return pipe (46)    Cold supply pipe (48)    Hot return pipe (50)    Storage tank of heat-retaining fluid (52)    Pumps (54, 58)    Shut-off valves (56, 62)    Connector pipes (65)    Temperature sensor (66)    Control valves. 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