NOVELTY - A separator scrubber and parallel path contaminant isolation loop (10) comprises: fuel cell; fuel processing system (16); separator scrubber (22) secured in fluid communication between system and fuel reactant inlet line (40) of cell; parallel path contaminant isolation loop (50) secured in fluid communication with accumulator; and liquid ion conductivity sensor secured in communication with liquid stream passing from scrubber through parallel path contaminant isolation loop and back to scrubber for sensing conductivity of stream.    USE - As separator scrubber and parallel path contaminant isolation loop for a fuel reactant stream of a fuel cell (claimed), that are used in transportation vehicles, portable power plants, or as stationary power plants.    ADVANTAGE - The separator scrubber and parallel path contaminant isolation loop efficiently removes contaminants such as ammonia from a fuel reactant stream passing into a fuel cell. The separator scrubber and parallel path contaminant isolation loop provides for enormous flexibility to operate with substantial variations of nitrogen concentrations within the base fuel. The scrubber and loop also provide a user-adjustable warning period prior to maintenance and/or replacement of the ion exchangers by varying the operational parameters of the parallel paths.    DETAILED DESCRIPTION - A separator scrubber and parallel path contaminant isolation loop (10) for a fuel reactant stream of a fuel cell (12), comprises: at least one fuel cell for receiving the fuel reactant stream; a fuel processing system (16) for processing a base fuel into the fuel reactant stream; a separator scrubber (22) secured in fluid communication between the fuel processing system and a fuel reactant inlet line (40) of the fuel cell and configured for dissolving ammonia from the fuel reactant stream passing from the fuel processing system through the separator scrubber to the fuel cell and for directing flow of the dissolved ammonia into a separated contaminant liquid stream within an accumulator (34) secured in fluid communication with the separator scrubber; a parallel path contaminant isolation loop (50) secured in fluid communication with the accumulator and configured for directing flow of the separated contaminant liquid stream through the loop, where the parallel path contaminant isolation loop includes a loop conduit (54) for directing flow of the separated contaminant liquid stream out of the accumulator, an isolation loop pump (56) secured in pumping relationship with the loop conduit for pumping the separated contaminant liquid stream through the isolation loop, a first path (58) secured in fluid communication with the loop conduit downstream from the isolation loop pump, a second path (60) secured in fluid communication with the loop conduit downstream from the isolation loop pump and configured to be parallel with the first path, the first path and second path is configured to direct flow of the separated contaminant liquid stream through the paths and into a loop conduit return line (64) secured in fluid communication between the paths and a water discharge (32) within the separator scrubber; where first flow rate and first decontamination capacity operational parameters of the first path may only be the same as either one or none of the second flow rate and second decontamination capacity operational parameters of the second path so that the second path decontaminates the separated contaminant liquid stream for a second decontamination duration that is greater than a first decontamination duration of the first path by a predetermined duration of a warning period; and a liquid ion conductivity sensor secured in communication with a liquid stream passing from the separator scrubber through the parallel path contaminant isolation loop and back to the scrubber for sensing a conductivity of the liquid stream. An INDEPENDENT CLAIM is included for scheduling service of a separator scrubber and parallel path contaminant isolation loop for a fuel reactant stream of a fuel cell, involving: a) directing flow of a base fuel from a fuel processing system through a separator scrubber); b) removing ammonia from the base fuel into a separated contaminant liquid stream; c) directing flow of the separated contaminant liquid stream through a parallel path contamination isolation loop where first flow rate and first decontamination capacity operational parameters of a first path may only be the same as either one or none of second flow rate and second decontamination capacity operational parameters of a second path so that the second path decontaminates the separated contaminant liquid stream for a second decontamination duration that is greater than a first decontamination duration of the first path by a predetermined duration of a warning period; and d) servicing the separator scrubber and parallel path isolation loop during the warning period.    DESCRIPTION OF DRAWING(S) - The figure shows a simplified schematic representation of a separator scrubber and parallel path contaminant isolation loop for a fuel reactant stream of a fuel cell.    Parallel path contaminant isolation loop (10, 50)    Fuel cell (12)    Fuel processing system (16)    Separator scrubber (22)    Water discharge (32)    Accumulator (34)    Fuel reactant inlet line (40)    Loop conduit (54)    Isolation loop pump (56)    First path (58)    Second path (60)    loop conduit return line (64)