Spectral and microscopic analysis of fulvic acids isolated from marine fish waste and sugarcane bagasse co-compost

Fulvic acids are highly beneficial molecules promoting several soil functions such as nutrient absorption, metal transportation and improving soil structure. These activities are assisted by their molecular structure upon interaction with soil medium. The present study describes the isolation of fulvic acids (FA) from mature marine fish waste and sugarcane bagasse co-compost using alkaline extraction method and studying its molecular and structural characteristics using spectroscopic and microscopic techniques. UV–visible spectroscopic analysis of fulvic acids revealed presence of absorption peak at 264 nm due to characteristics of double bonds of aromatic or unsaturated compounds. Fluorescence spectroscopic analysis of fulvic acids showed emission (455 nm) and excitation (395 nm) spectrum respectively. The photometric ratio (E4/E6) and fluorescence index (FI) confirmed high humification degree of FA. The low color co-ordinate values (L* and b*) measured by CIELAB ensured good maturity of the FAs present in the co-compost. Especially, Proton NMR spectroscopy detected resonance signals of aliphatic protons (0.82–2.0 ppm) and aromatic proton (7.5 ppm) in the molecular structure of FA. FTIR spectrum identified functional groups such as hydroxyl; aliphatic, amide I and polysaccharide and classified the FA as type II. Stereo microscopic examination visualized presence of light brown crystalline particles. Further, SEM analysis of the FA particles revealed presence of various shapes such as spherical; cubical; flakes and micro-aggregate structures. Therefore, it is concluded that spectroscopic and microscopic tools are reliable techniques to reveal the molecular and structural characteristics of FA isolated from co-compost for usage as an organic fertilizer. •Fulvic acids (FA) isolated from marine fish waste and sugarcane bagasse co-compost.•Spectroscopic and microscopic tools revealed molecular composition and shape of FA.•Proton NMR spectra revealed aliphatic (0.82–2.0 ppm) and aromatic protons (7.5 ppm).•Stereo microscopy displayed brown crystals with size ranging 0.70–0.80 mm.•SEM showed aggregate morphology of FA particles with no pores.