Mech. shredded poly(ethylene terephthalate) and polyurethane foam wastes were used as biofilter fillings. The av. efficiency of decreasing the chem. O2 demand in domestic sewage depended on the hydraulic load and fluctuated in the range 28-89%. The use of polyurethane foam allowed to decrease the biol. O2 demand by 81-95%. The N-NH4 + ions were also removed in biofilters filled with polyurethane foam and poly(ethylene terephthalate) flakes by 55-64% or 48-69%, resp.