An assembly for supporting biomass for treating sludge or wastewater includes a first corrugated sheet having crests and valleys, a second corrugated sheet having crests and valleys and an intermediate member mounted between the first and second corrugated sheets. The crests have peak surfaces and the valleys have trough surfaces. The first corrugated sheet has a first longitudinal axis and the second corrugated sheet has a second longitudinal axis. The corrugations of the first corrugated sheet define a first corrugation angle of about zero degrees (0.degree.) to about forty-five degrees (45.degree.) relative to the first longitudinal axis and the corrugations of the second corrugated sheet define a second corrugation angle of about zero degrees (0.degree.) to about forty-five degrees (45.degree.) relative to the second longitudinal axis. The second corrugated sheet is mounted to the first corrugated sheet and the intermediate member has openings therein.