Wasting the Nation.indd - Groundwork

Chapter 5: Modernising municipal wasteWriter Joseph Jenkins [2005] describes them as “giant diapers”. Inside these municipalnappies, the liberally mixed waste goes through a cycle of chemical and physical changeas organic wastes biodegrade. More than 60% of the waste is organic, including foodand garden wastes, paper, cardboard and some woods and textiles, so the effects ofdecomposition are dramatic. Williams describes a five-stage process of what happensinside a regular landfill in Britain [1998: 197-201]:Stage 1: Decomposition takes place in the presence of air. Micro-organisms use oxygento break the fresh waste down into simpler hydrocarbons and the process producescarbon dioxide, water and heat. The CO 2moves into the atmosphere or into thewater leachate, making it slightly acidic. This stage does not last more than a fewweeks as more waste is piled on top and oxygen is excluded by the daily coverage andcompaction of waste.Stage 2: Hydrolysis and fermentation become the main processes as the oxygen runsout and different micro-organisms start breaking down the waste. The carbohydrates,proteins and fats in organic matter are broken down to sugars and then to hydrogen,ammonia and organic acids. The leachate as a result contains high nitrogen in ammoniaform. Temperatures drop and gas composed of 80% carbon dioxide and 20% hydrogenis produced.Stage 3: The waste body now turns very acid and so increases the solubility of metalsand flushes them into the leachate. Methane-generating micro-organisms play anincreasing role and smelly hydrogen sulphide is produced as part of the gas.Stage 4: This is the main landfill gas generation stage. Acid levels drop while the lackof oxygen maintains the anaerobic conditions required to produce gas composed ofaround 60% methane and 40% carbon dioxide. This process starts around 6 monthsafter the fresh waste has been incorporated and gas formation will continue for between15 and 30 years after the last waste is deposited. Some landfill gas will still be generatedup to 100 years later.Stage 5: The waste body slowly returns to aerobic (oxygen rich) conditions as the acidsin the mix are used up in the production of methane and carbon dioxide. At this stage,residual methane is converted to carbon dioxide and water by a new lot of aerobicmicro-organisms.Wasting the Nation - groundWork - 131 -