# Thermogravimetry Applicability in Compost and Composing Research: A Review
## 3 Results and Discussion  
### Composting Evolution Research by Using a Variety of Techniques  
#### 3.1.1 Composting Evolution Research by Thermogravimetry  
Various authors have published results derived from the use of thermogravimetric techniques in the analysis of compost and its evolution. These techniques have been also used to check the process of maturation or stabilization of the compost (Section 3.2). Thermal studies in compost are directly related to the degradation of hemicelluloses, cellulose and lignin, since composts are mainly formed by these compounds, or to the humic and fulvic acids formed during composting.  
Different researchers [18; 19; 20; 21; 22; 23; 24] exposed three main phases in the thermal degradation of compost: (i) the first phase is between an initial and final temperature of 25 and 120 \({}^{\circ}\)C; (ii) the second phase is between 200 \({}^{\circ}\)C and 350 \({}^{\circ}\)C; (iii) the third phase is between 350 \({}^{\circ}\)C and 700 \({}^{\circ}\)C (Figure 1).  
In the first phase, first peak at DTG (<200 \({}^{\circ}\)C), this water content reduction is due to a thermal dehydration process of the compost samples [25]. Other authors also indicate a decarboxylation in labile compounds [26].  
In the second phase (200 to 350 \({}^{\circ}\)C) the thermal decomposition of the organic components already takes place. In this sense, between 200-300 \({}^{\circ}\)C (second peak at the DTG) the thermal degradation of simple organic matter and semi-volatile compounds such as hemicelluloses, cellulose, degradation of aliphatic structures and microbial cell walls can be associated [27]. It has been proven that as composting time increases, weight losses in the range of thermal degradation of carbohydrates are constantly decreasing [5; 11; 13; 28; 29; 30; 31; 32]. Moreover, [PERSON] et al. [34] identified the breakage of polysaccharide and cellulose fibers in this interval. As composting progresses, lower peaks of DTG in this area, due to the decreased concentration of easily degradable compounds, are noted. Conversely, [PERSON] and [PERSON] [35] indicated that carbohydrates were probably responsible for some of the peaks found between 300-315 \({}^{\circ}\)C.  
In the third phase, under higher temperatures (350-700 \({}^{\circ}\)C, third peak in the DTG) degradation of aromatic structures and organic polymers such as lignin, or others synthesized during the compost stabilization process have been associated [36]. [PERSON] et al. [23] found that dietary fibers and lignin break down over a wide range of temperatures and that they are the main components that break down beyond 400 \({}^{\circ}\)C. DTG peaks at this area increase with the days of composting. This trend towards a progressive transformation of readily biodegradable compounds into macromolecules is being suggested. These formed compounds are known as humic-type substances [5; 26; 37] also indicated a shift towards higher temperature, more thermally stable, the DTG peaks in the 350-700 \({}^{\circ}\)C zone as composting time increases [13; 38; 39; 40]. This shift to higher molecular complexity and aromaticity during the composting process is attributed [9]. Conversely, [PERSON] et al. [27], by combining TGA and FTIR, proved that between 380-460 \({}^{\circ}\)C the decarboxylation phase is lower for gray humic acid compared to brown humic acid. Furthermore, [PERSON] et al. [23] showed peaks of DTG after 600 \({}^{\circ}\)C attributed to the volatilization of carbon in the compost.  
Figure 1: TGA [weight and DTG (derivative weight)] corresponding to the Municipal Solid Waste (MSW) evolution in composting (figures shown are from the authors).