The material left over from a process that no longer has an economic value nor has potential as a valuable resource. Its lack of value may be the result of difficulties in recovery that may be otherwise uneconomic, expensive to transport, or possess hazardous properties. Process waste is waste generated from within a process such as from by-products in reactors or loss of solvents from separations and recycle systems, whereas utility waste is (p. 407) waste generated through the provision utility services to the main process such as waste from steam boiler blowdown or heat loss from a heat exchanger network.