Instrumental characterization of organic wastes for evaluation of vermicompost maturity

Instrumental analysis of vermicompost with the help of modern technologies provides essential information on its maturity, before it can be used for agricultural application. Nowadays, vermicompost is considered as a promising organic alternative to chemical fertilizers in agriculture and horticulture. The objectives of this review are to summarize the sophisticated instrumental techniques such as scanning electron microscopy (SEM), fourier transform infrared (FT-IR) spectroscopy, thermogravimetry (TG), ultraviolet-visible (UV-vis) spectroscopy techniques, physico-chemical parameters (pH, electrical conductivity, organic carbon content, C:N ratio, nitrogen, phosphorus, potassium, sodium, calcium) and biological indicator (germination index) to determine the maturity of vermicompost produced from organic wastes. These techniques are reliable, fast and are capable of tracking organic waste degradation during the bioconversion process and fertilizing ability of the final product. SEM analysis provides essential information on surface morphology of vermicompost samples. The SEM micrograph of final vermicompost reveals disaggregation. In contrast, the initial SEM micrograph reflects robust and relatively contiguous structures. FT-IR spectroscopy technique is used to confirm the decomposition of polypeptides, polysaccharides, aliphatic, aromatic, carboxylic, phenolic groups and lignin during vermicomposting of organic wastes. TG method is used to characterize organic waste mineralization where progressive reduction in the mass loss of vermicompost indicates net mineralization and degradation. UV-vis spectroscopy is used to assess the degree of humification. The sharp fall in humification index during vermicomposting process indicates high level of organic material humification. Changes in physico-chemical and biological parameters are also an indicative parameter for organic waste mineralization as well as vermicompost stability and maturity.