Process and apparatus for the biological purification of wastewater

Claim 1

A process for the biological purification of wastewater in at least two immediately successive gas treatment stages which comprises: gasifying the wastewater in the presence of activated sludge to conduct biological degradation of organic substrate, withdrawing resultant wastewater activated sludge mixture from the treatment stages and dividing said mixture in a post-clarification stage, into purified water and said activated sludge, and partially recycling the activated sludge into the treatment stages, and further comprising conducting primarily nitrification in the last of said at least two immediately successive treatment stages in the presence of a macroporous carrier material consisting essentially of open-cell polyurethane foam particles having a particle size diameter of 2-50 mm, a specific gravity of 20-200 kg/m 3 and open pore size of 0.1-5 mm, with the macroporous carrier material carrying nitrifying bacteria thereon with the bacteria in a concentration on the carrier material of 10-30 g/l, and with primarily organic carbon compound degradation having been conducted in the at least one upstream stage of said at least two immediately successive treatment stages with a feed stream of gas containing a greater proportion of oxygen than air and conducting the organic carbon compound degradation in the at least one upstream stage to an extent such that the BOD 5 of the wastewater being passed to the last treatment stage to conduct nitrification therein is at a level of organic pollutants of 10-30 mg/l, treating the wastewater in the nitrification stage with a feed stream of air, and separating the carrier material for nitrifying bacteria from the wastewater-activated sludge mixture exiting from the nitrification stage, and retaining said carrier material in the nitrification stage whereby loss of nitrifying bacteria is avoided by retaining said nitrifying bacteria on said particles.