37 Construction, repair, installation, management and maintenance of apparatus and installations for treatment of drinking water; Apparatus and installations for treatment of waste water; Clarification apparatus and installations; Apparatus and installations for treatment of sludge; Filtration, sterilisation and purification apparatus and installations; Apparatus and installations for producing electric energy and heat from biogas; Apparatus and installations for the treatment of organic waste and biomass through anaerobic digestion for producing biogas; Digesters; Cogenerators powered by biogas; Flotation units; Apparatus and installations for improving energy efficiency; Apparatus and installations for treating odours and washing of biogas