Macerator housing has a flange at each end and a flow channel therebetween so that the macerator can be connected into a sewage line for flow therethrough. A pair of power-driven shafts are mounted transversely to the flow direction and each carries a plurality of inter-engaging spaced macerator cutters thereon. The macerator cutters do not reach the outer housing walls, but there is a bypass flow space therearound. Screens are positioned on the inlet side of the housing to direct flow into the macerator cutters, but the screens permit fluid flow through the bypass space around the macerator cutters.