Ricerc@Sapienza

This paper evaluates the effects of ultrasonication (US) applied, individually or in combination with a mechanical treatment, to the effluent of anaerobic digestion (AD) of lignocellulosic waste, on methane (CH4) production. US of the substrate downstream of AD is a relatively novel concept aimed at improving the degradation of recalcitrant components in order to enhance the overall energy efficiency of the process. US tests were carried out on real digestate samples at different energies (500−50,000 kJ/kg total solids (TS), corresponding to sonication densities of 0.08−0.45 W/ml).

Anaerobic digestion (AD) of organic waste, although widely practiced, may require suitable accompanying treatments to enhance the degradability of complex materials. Since these may require significant efforts in terms of energy and chemical demand, careful assessment of their overall environmental sustainability is mandatory to evaluate their full-scale feasibility. The study aims to represent the environmental profile of ultrasonication (US) applied as a post-treatment of anaerobic digestion of agro-industrial organic residues.

The effects of a mechanical pretreatment, carried out by a two stages mill followed by fractionation into two different products, were determined on the biodegradability and methane yield of wheat straw. Straw was chopped in a knife mill to an average length of about 30 mm, and a portion was used as reference material. Pretreatment reduced the size of the processed straw, whose median particle size was 300μm and 1200μm for the fine and the coarse fractions, respectively.

The effects of an industrial scale, mechanical pretreatment were determined on the methane yield of Giant reed stems. The feedstock was pretreated using a two stages dry milling process and the experiments were performed for two different mass flow rates (600 and 900 kg h-1). Untreated and pretreated stems were both anaerobically digested in batch reactors under mesophilic conditions for 28 days. The cumulative biogas production from the pretreated materials exceeded 212 Nm3t-1of volatile solids, showing a 137% gain compared to the raw material.

The aim of this work was to provide a complete exergy and energy analysis of a biogas upgrading technology: pressure swing adsorption. This technology has going to be widely used in Europe, because allowed to reach very high methane recovery (93.4%) and Wobbe Index (50.81 MJ/m3 STP) values. In this study, the upgrading process has been implemented in Aspen Plus and Aspen Adsorption dynamics simulation environment and the biogas was upgraded to biomethane, meeting the UNIT/TS 11537:2019 standards for Biogas to be injected in the gas grid.