Anaerobic digestion of selected Italian agricultural and industrial residues (grape seeds and leather dust): combined methane production and digestate characterization

Abstract

A combined experimental evaluation of methane production (obtained by anaerobic digestion) and detailed digestate characterization (with physical-chemical, thermo-gravimetric and mineralogical approaches) was conducted on two organic substrates, which are specific to Italy (at regional and national levels). One of the substrates was grape seeds, which have an agricultural origin, whereas the other substrate was vegetable-tanned leather dust, which has an industrial origin. Under the assumed experimental conditions of the performed lab-scale test series, the grape seed substrate exhibited a resulting net methane production of 175.0 NmL g volatile solids (VS)⁻¹; hence, it can be considered as a potential energy source via anaerobic digestion. Conversely, the net methane production obtained from the anaerobic digestion of the vegetable-tanned leather dust substrate was limited to 16.1 NmL gVS⁻¹. A detailed characterization of the obtained digestates showed that there were both nitrogen-containing compounds and complex organic compounds present in the digestate that was obtained from the mixture of leather dust and inoculum. As a general perspective of this experimental study, the application of diversified characterization analyzes could facilitate (1) a better understanding of the main properties of the obtained digestates to evaluate their potential valorization, and (2) a combination of the digestate characteristics with the corresponding methane productions to comprehensively evaluate the bioconversion process.

Keywords:

• anaerobic digestion
• digestate characterization
• grape seeds
• methane production
• vegetable-tanned leather dust

Acknowledgements

The authors thank: (1) the firm BIOTEC snc (Fermo, Marche Region, Italy) for providing the vegetable-tanned leather dust; (2) Dr M. Di Domenico and Dr S. Pretelli at Hera Rimini SpA multi-utility group (Rimini, Emilia-Romagna Region, Italy) for providing the anaerobic sludge (inoculum). Dr A. Berloni, Mr O. Rusciadelli and Dr J. Arduini, all at the University of Urbino ‘Carlo Bo’, are mentioned for their technical support. Part of this experimental work, regarding the digestate characterization phase, was supported by the ENVIREN project of the Hi-Tech Network funded by the Emilia-Romagna Region.