The biofiltration of waste water makes it possible to use microorganisms to clean waste water of contaminants. In large-scale purification plants in particular, the Liaperl expanded clay spheres provide an ideal substrate for colonization by microbes, which filter the waste water and liberate it from nitrogen and phosphates. With Liaqua, Liapor provides the optimum solution for exhaust air purification. In biofilters, bio-scrubbers and percolating filters, microorganisms are able to reproduce on the expanded clay spheres. They absorb and break down contaminants, cleaning the exhaust air as they do so.