A method of supplementing the metabolic reactions that take place within landfill waste matter by deploying a supplement for the metabolic reactions into the waste matter in a gaseous or airborne state. The method can be applied to improve landfill gas yield and/or reduce the production of undesirable chemical species at a landfill site. The supplement may comprise microorganisms or microbiological material and nutrients. The supplement may be atomised to make it gaseous and mixed with a carrier gas before being added to the ground. The carrier gas may be recycled landfill gas such as carbon dioxide. The gaseous supplement may be added via an existing pipe work which is normally used to extract land fill gas such as methane. Ideally the invention is used to increase the yield of methane gas.
