A rotating biological contactor apparatus (25, 29) comprising one or more stages (26, 27, 28), each stage comprising, in combination: (a) a plurality of trough defining sections (30, 31, 32), each said trough defining section having a trough that extends longitudinally therethrough, that has transversely curved inside wall portions, and that has open opposed end portions, and each said trough defining section is unitarily formed and includes flange portions defined along said opposed end portions for joining to adjacent members, each of the plurality of trough defining sections having a similar cross-sectional trough internal surface configuration, and each trough defining section being engaged to an adjacent trough defining section in an end to end longitudinally adjacent relationship by way of a joining means joining together said flange portions so as to define a longitudinally extending trough between an adjacent pair of trough defining sections, whereby each stage includes said troughs longitudinally aligned along a common longitudinal axis; (b) two bulkhead members, one of said bulkhead members being disposed across each opposite end of said stage and including means (42, 43) for engaging each of said so disposed bulkhead members within each adjacent said flanged portion; (c) shaft means extending longitudinally through said troughs and including both bearing means for rotatably supporting said shaft means and support means for supporting said bearing means at each of said so engaged bulkhead members, wherein the length of the shaft means is defined by one or more shaft sections being connected together so that the length of the shaft means corresponds to the length of the trough sections; (d) at least one contactor drum having an axial portion and a circumferentially extending peripheral portion, said axial portion being mounted about said shaft means so as to rotate therewith in said troughs, said contactor drum comprising a core portion and a plate portion along at least one side of said core portion, said core portion including a plurality of corrugated sheet members that cooperate to define a plurality of passageways that extend generally transversely through said core portion, said core portion and said plate portion being interconnected by a plurality of longitudinally extending, peripherally located, circumferentially spaced bracket members; and (e) power means for rotating said shaft means. (a) a plurality of trough defining sections (30, 31, 32), each said trough defining section having a trough that extends longitudinally therethrough, that has transversely curved inside wall portions, and that has open opposed end portions, and each said trough defining section is unitarily formed and includes flange portions defined along said opposed end portions for joining to adjacent members, each of the plurality of trough defining sections having a similar cross-sectional trough internal surface configuration, and each trough defining section being engaged to an adjacent trough defining section in an end to end longitudinally adjacent relationship by way of a joining means joining together said flange portions so as to define a longitudinally extending trough between an adjacent pair of trough defining sections, whereby each stage includes said troughs longitudinally aligned along a common longitudinal axis; (b) two bulkhead members, one of said bulkhead members being disposed across each opposite end of said stage and including means (42, 43) for engaging each of said so disposed bulkhead members within each adjacent said flanged portion; (c) shaft means extending longitudinally through said troughs and including both bearing means for rotatably supporting said shaft means and support means for supporting said bearing means at each of said so engaged bulkhead members, wherein the length of the shaft means is defined by one or more shaft sections being connected together so that the length of the shaft means corresponds to the length of the trough sections; (d) at least one contactor drum having an axial portion and a circumferentially extending peripheral portion, said axial portion being mounted about said shaft means so as to rotate therewith in said troughs, said contactor drum comprising a core portion and a plate portion along at least one side of said core portion, said core portion including a plurality of corrugated sheet members that cooperate to define a plurality of passageways that extend generally transversely through said core portion, said core portion and said plate portion being interconnected by a plurality of longitudinally extending, peripherally located, circumferentially spaced bracket members; and (e) power means for rotating said shaft means.