An Integrated Chemical, Thermal, and Microbiological Approach to Compost Stability Evaluation

Abstract

The evaluation of compost stability is of the utmost importance for the reliability of composting as a recycling strategy. To date there is no single parameter that can give a sure indication of the stability of composts from different starting materials. This paper investigates different methods of evaluating the dynamics of transformation of materials and the stability level of the end products in a composting process. The following parameters were determined on compost samples of different ages from cotton (Gossypium herbaceum L.) cardings and yard wastes: humification index (HI), degree of humification (DH), thermogravimetry (TG) microbial biomass C (B(C)), and ninhydrin-reactive N (B(NIN)). Finally, from TG, derivative thermogravimetry (DTG) and differential scanning calorimetry (DSC) thermal stability parameters were deduced. Humification parameters in the end products (0.2 and 81% for HI and DH, respectively) showed the effective stability reached by the organic matter (OM). Thermal analysis evidenced the presence of two main organic pools with different thermal stability. During composting a relative increase in the more stable organic pool was indicated by the variation of the thermostability index R1 from 0.41 to 0.74. The parameter R1 was significantly correlated with both HI (r = -0.94; P < 0.05) and DH (r = 0.97; P < 0.05). Microbial biomass content dynamics reflected the availability of readily decomposable substrates. The ratio between B(NIN) and total N in the end product was 0.96%, indicating a good stability level. The simultaneous application of different approaches, considering different properties of composting materials, provides a more complete description of the stability and quality reached by the organic materials.

Quality of Vermicompost Obtained from Residues of Forestry and Livestock

“…These findings coincide with Castillo (2002) who obtained 29.72% of organic-C content when using cattle and bovine manures. Such a behavior has been published by several researchers (Mondini et al, 2003) stating that the increase of organic-C concentration can be a result of the C usage from the initial organic residues by microorganisms in order to build new cellular materials, which can be re-used in the vermicomposting process later on, although such an increase do not coincide with Nogales et al (2005) and Santamaría-Romero et al (2001) who observed a decrease in organic-C content due to losses in the form of CO 2 in the process.…”

Characterization of Maturity Level in Laying Hen Manure by Chemical and Thermogravimetric Analysis

“…The first transition, at approx. 124°C, is attributed to residual water removal (free and bound water) from the samples [1,26] . The three transitions in the range 180-600°C, approx.…”

“…275, 381 and 475°C, are due to different organic pools. Mass loss at 731°C is due to the CaCO 3 decarboxylation [1,16] . The presence of CaCO 3 is typical of these samples because is a part of animal Table 4: TG in air flow (100 ml/min): main thermogravimetric weight loss (% of initial sample) and temperature ranges in which they occurred T range (°C) 1 : M mass variation as % of initial sample mass, *: Represent 5% significant level feed.…”

“…Such techniques would allow assessing their level of stabilization and maturity, in order to improve agronomic performance and reduce environmental impact. In fact, the application of unstable organic materials on soil could damage both crops and the soil itself because of (they introduce) phyto-toxic compounds and could sometimes lead to competition for N between microbial biomass and crops [1,2] . Poultry manures (PM), both the litter and caged laying hen varieties, need bio-stabilisation and maturation in order to be used safely.…”

“…Some of these methods can be applied to composted PM [15] . Physical techniques such as thermogravimetric analysis have also been applied to assess compost biostabilisation; for this technique a small sample is sufficient, it does not require chemical extraction and is easy to reproduce [1,16] . Fewer studies are available on methods to assess PM stabilization or maturity, particularly of caged laying hen manure which has not undergone "conventional" composting processes.…”