Physical, biological and chemical processes during storage and spontaneous combustion of waste fuel

Abstract

The storage of unsorted industrial waste (IND) fuel and refused-derived fuel (RDF) in piles at two different locations in Sweden was investigated. The objective was to assess the feasibility of waste storage in open areas for later energy utilization, and to study the physical, biological and chemical processes that occur during storage, by monitoring a number of parameters. One monitored IND pile showed an increase in temperature from an average of 49±10 to 73±7 °C, accompanied by considerable fluctuations in the waste mass interstitial oxygen and carbon dioxide concentrations during the first month of storage. Thereafter, steady-state conditions were registered for about 4 months, with an average pile temperature of 77±8 °C, interstitial oxygen concentration varying from below the detection limit up to 5% by volume, interstitial carbon dioxide concentrations varying from 0.2 to 18%, and interstitial methane concentrations varying from below detection limit up to 0.5%. After 6 months of storage, spontaneous combustion occurred in the monitored IND pile. This was preceded by strong winds, which ventilated the pile and increased its oxygen content. Spontaneous combustion was also observed in one RDF pile after the same storage time (about 6 months). The leachate produced as a result of the large quantity of water used in an attempt to douse the burning RDF pile showed higher concentrations of chemical oxygen demand, biochemical oxygen demand, total nitrogen, total oxidized nitrogen, total phosphorus and the heavy metals lead, cadmium and chromium than the median values in the leachate from municipal solid waste (MSW) landfill and from MSW incineration residues (50% fly ash) landfill. Baling to reduce waste fuel porosity is suggested as a safer option for the storage of waste material for energy recovery purposes.