An evaporator for receiving waste fluid stream and producing separate streams of an evaporated fluid and a condensate liquid for use in industrial waste treatment has a curved pathway bounded by a casing having an inlet port through which the waste fluid enters the casing. The casing defines a pathway having a flow direction therein through which the waste fluid stream flows, and within which casing the evaporated fluid is produced. The casing has a drain beneath the pathway through which the condensate passes, and an outlet through which the evaporated fluid is drawn. A series of fins of elongate aerofoil cross-section are located in and extend across the pathway in the flow direction of the waste fluid stream flowing along the pathway. The casing is curved and the fins are arranged parallel to a tangent of the curve.