Determination of maturity in the vermicompost produced from palm oil mill effluent using spectroscopy, structural characterization and thermogravimetric analysis

• Vermicompost could be characterized by FT-IR, UV–vis, SEM, BET and TG analysis.
• FT-IR, UV–vis and TG showed reduction in readily degradable matters in vermicompost.
• SEM and BET revealed that the vermicompost was smaller and had larger surface area.

Vermicompost produced from palm oil mill effluent was evaluated for its maturity using: (i) spectroscopic analysis (Fourier transform infrared spectroscopy (FT-IR) and ultraviolet visible (UV–vis) spectroscopy); (ii) structural characterization (scanning electron microscope (SEM) and Brunauer, Emmett and Teller (BET) surface area) and (iii) thermogravimetric (TG) analysis. The FT-IR showed increased mineralization of polysaccharides, carbohydrates and aliphatic methylene compounds in the vermicompost as compared to the control (without earthworms). A slight increase of aromatic compounds was observed and proven by UV–vis spectroscopy analysis for vermicompost. Structural characterization (SEM micrographs) of the vermicompost was revealed to be more fragmented than initial wastes and control. The vermicompost also showed larger surface area by using BET method. Finally, the TG analysis showed lower mass loss in the vermicompost in comparison with the initial wastes and control, suggesting higher stability in feedstock which had undergone vermicomposting process. The first derivative curve from TG analysis also showed degradation of various compounds, which was consistent with the spectroscopic characterization.