Abstract: A wastewater treatment system for use on a marine vessel comprising an aerobic fixed film biological reactor, a tubular flocculator and a dissolved air flotation (DAF) unit. The process units desirably include means for reducing erratic movement of the wastewater due to sea-induced movement of the marine vessel. The DAF unit includes a plurality of inclined baffles arranged to create a plurality of parallel inverted U-shaped flow paths that effect combined co-current and counter-current flotation separation while reducing erratic movement of the wastewater. The selection of process units and operating conditions advantageously reduces the footprint of the wastewater treatment system and reduces cost and complexity associated with the handling of wastewater treatment chemicals.