Multistage milling and classification for improving both pellet quality and biogas production from hazelnut and olive pruning

Multistage milling and classification for improving both pellet quality and biogas production from hazelnut and olive pruning

Paolo Costa Pier Paolo Dell’Omo Sabatino La Froscia 

Labo, Université AR_adelec1Scienza per Amore Association – Via Monteleone Sabino, 9 - 00131 Rome, Italy

AR_adelec1Department of Astronautical, Electrical and Energy Engineering (DIAEE), University La Sapienza, Via Eudossiana 18, 00184, Rome, Italy

Corresponding Author Email:
31 December 2018
| Citation



The effects of a mechanical process were determined on the solid fuel quality and anaerobic biodegradability of hazelnut and olive pruning. Both the feedstocks did not meet the specification for industrial and residential pellets given in the European Standard EN ISO 17225-2, because of too high ash and nitrogen content. The coarser products from processing were notable for the high reduction in both the ash and nitrogen content. Therefore, as regards hazelnut, they met the requirement of the Standard for both the industrial and residential pellet, whereas those from olive processing met the requirements for the industrial pellet. The finest products showed a high concentration of nitrogenous matter and smaller C/N ratios, far better for anaerobic digestion. The best products from hazelnut and olive achieved methane yields of 118.1 and 176.5 Nm3 tVS-1, respectively, corresponding to 70.1 % and 93.5 % gains over the untreated substrates. The process was highly energy efficient, since consumption was low compared with the energy output from the residues of fuel upgrading, intended for anaerobic digestion. The investigated process could be successfully used to improve the fuel quality of pruning and to generate products suitable for anaerobic digestion and the production of advanced biofuels.


anaerobic digestion, biogas, EN ISO 17225-2, pellet, pruning

1. Introduction
2. Materials and methods
3. Results
4. Discussion
6. Conclusions

Unknown Authors. (2006). ANSI/ASABE S319.3: Method of determining and expressing fineness of feed materials by sieving. ASABE (American Society of Agricultural and Biological Engineers). In: ASABE Standards 602.

Arranz J. I., Miranda M. T., Montero I., Sepúlveda F. J., Rojas C. V. (2015). Characterization and combustion behaviour of commercial and experimental wood pellets in South West Europe. Fuel, Vol. 142, pp. 199-207.

Barakat A., De Vries H., Rouau X. (2013). Dry fractionation process as an important step in current and future lignocellulose biorefineries: A review. Bioresour Technol, Vol. 134, pp. 362-373.

Bardiya N., Gaur A. C. (1997). Effects of carbon and nitrogen ratio on rice straw biomethanation. J. Rural Energy, Vol. 4, pp. 1-16.

Bordelannea O., Monteroa M., Bravina F., Prieur-Vernata A., Oliveti-Selmia O., Pierrea H., Papadopoulob M., Mullerb T. (2011). Biomethane CNG hybrid: A reduction by more than 80% of the greenhouse gases emissions compared to gasoline. J Nat Gas Sci Eng, Vol. 3, pp. 617-624.

Calabrò P.S., Panzera M.F. (2017). Biomethane production tests on ensiled orange peel waste, International Journal of Heat and Technology, Vol. 35, Special Issue 1, pp. S130-S136.

Carvalho L., Wopienka E., Pointner C., Lundgren J., Verma V. K., Haslinger W., Schmidl C. (2013). Performance of a pellet boiler fired with agricultural fuels. Appl Energ, Vol. 104, pp. 286-296.

EN 14918 (2009). Solid biofuels. Determination of calorific value.

EN 17225-2 (2014). Solid biofuels. Fuel specifications and classes. Graded wood pellets.

EN ISO 16948 (2015). Solid biofuels. Determination of total content of carbon, hydrogen and nitrogen. 

European Commission (2007). Communication from the Commission to the Council and the European Parliament, Renewable energy road map - Renewable energies in the 21st century: Building a more sustainable future. COM/2006/0848. Available:

European Commission (2014). State of play on the sustainability of solid and gaseous biomass used for electricity, heating and cooling in the EU, [Online]. Available:

Fedrizzi M., Sperandio G., Pagano M., Pochi D., Fanigliulo R., Recchi P. (2012). A Prototype Machine for Harvesting and Chipping of Pruning Residues: first test on Hazelnut Plantation (Corylus avellana L.), presented at CIGR-AgEng 2012: Agriculture and Engineering for a Healthier Life, Valencia, Spain, Jul. 8-12, 2012.