# Thermogravimetry Applicability in Compost and Composing Research: A Review
## 3 Results and Discussion
### Thermogravimetry in Compost Combustion  
Compost treatments generally result in variations not only in the water content but also, and more importantly, in the fuel characteristics of the starting materials [65]. During composing, the overall energy content of the composted waste is reduced as a result of the partial decomposition of the initial organic matter and a concomitant detrimental effect is also observed due to the increase in ash content [66]. However, compost still preserves most of its calorific power, which makes it possible to produce energetic compost either for direct combustion, gasification or pyrolysis. For this reason, and from an energy point of view, compost can be considered a potential biomass fuel [67]. General changes that occur during the thermal behavior of composting have been evidenced by TGA: (a) enrichment of non-volatile high molecular weight compounds, (b) synthesis of microbial biomass and (c) chemical transformations such as humic substances formation. Microbes convert 60% to 70% of carbon to CO\({}_{2}\) and utilize the remaining 30% to 40% in their body as cellular components [68]. During degradation of organic compounds, losses in calorific value are observed due to the bio oxidation of organic substances  
[PERSON] et al. [69] experimentally determined the energy potential of briquettes prepared from an oversized fraction of wasted wood compost and the theoretical combustion characteristics compared to conventional fuel: wood logs. The most decisive parameter for energy use of selected samples of compost briquettes and spruce logs is the net calorific value (NCV). NCV greatly depends on water and ash contents in the fuel, both with a negative impact on the final NCV [70]. The authors analyzed non-combustible substances in that compost, total water content and volatile matter by TGA. These results, together with others obtained (stoichiometric calculations of individual samples, elemental analysis and gross calorific value > 16.0 MJ kg\({}^{-1}\)), demonstrated that the compost under study possessed suitable properties for further use as an energy source. However, TGA results showed several times higher ash content in the samples of compost briquettes in comparison with woody biomass. Moreover, [PERSON] et al. [71] investigated about energy utilization of another type of untreated compost as a fuel (material inputs: cattle manure, sewage sludge and plant-based wastes such as leaves, wood chips, straw, hay, sawdust, and spoiled vegetables and fruits). Water and non-volatile components (i.e., ash content) were determined using thermogravimetric methods. The low calorific figures associated with this compost (<9.0 MJ kg\({}^{-1}\) on dry basis) were due in part to the enormous percentage of ash found (>60% on dry basis) and, therefore, this material could not be used as fuel without a pretreatment to reduce the incombustible content. To consider this biomass as energy compost biomass, whether for direct combustion or for its thermochemical conversion (pyrolysis), it was necessary to mix it with wood biomass (it was mixed with spruce chips in a 1 to 1 ratio). The most relevant experimental difference found between the combustion of compost briquettes and that of the prepared mixture was the flue gas temperature, which experienced an increase of almost 100 \({}^{\circ}\)C due to the net calorific value of the added wood biomass. However, with increasing excess air coefficients, the CO and NO\({}_{x}\) emission levels have found increased [69]. Another main raw material for composting is municipal solid waste (MSW). MSW is the result of human activity and, therefore, is made up of various types of waste materials that behave differently during thermal degradation processes (pyrolysis or combustion). In general terms, the thermal degradation of its individual components has been studied separately, which has masked the synergies that may take place during combustion and pyrolysis.