40 Treatment of materials; decolouration, filtration and purification of waste water, water, gasses and airstreams, as well as absorption of impurities from waste water, water, gasses and airstreams; rental of installations and apparatuses for decolouration, filtration and purification of waste water, water, gasses and airstreams, as well as installations and apparatuses for the absorption of impurities from waste water, water, gasses and airstreams