Modified Anaerobic Digestion Model No.1 for dry and semi-dry anaerobic digestion of solid organic waste.

The role of total solids (TS) content in anaerobic digestion of selected complex organic matter, e.g. rice straw and food waste, was investigated. A range of TS from wet (4.5%) to dry (23%) was evaluated. A modified version of the Anaerobic Digestion Model No.1 for a complex organic substrate is proposed to take into account the effect of the TS content on anaerobic digestion. A linear function that correlates the kinetic constants of three specific processes (i.e. disintegration, acetate and propionate up-take) was included in the model. Results of biomethanation and volatile fatty acids production tests were used to calibrate the proposed model. Model simulations showed a good agreement between numerical and observed data.

Effect of moisture on disintegration kinetics during anaerobic digestion of complex organic substrates.

The role of the moisture content and particle size (PS) on the disintegration of complex organic matter during the wet anaerobic digestion (AD) process was investigated. A range of total solids (TS) from 5% to 11.3% and PS from 0.25 to 15 mm was evaluated using carrot waste as model complex organic matter. The experimental results showed that the methane production rate decreased with higher TS and PS. A modified version of the AD model no.1 for complex organic substrates was used to model the experimental data. The simulations showed a decrease of the disintegration rate constants with increasing TS and PS. The results of the biomethanation tests were used to calibrate and validate the applied model. In particular, the values of the disintegration constant for various TS and PS were determined. The simulations showed good agreement between the numerical and observed data.

Effect of total solids content on methane and volatile fatty acid production in anaerobic digestion of food waste.

This work investigates the role of the moisture content on anaerobic digestion of food waste, as representative of rapidly biodegradable substrates, analysing the role of volatile fatty acid production on process kinetics. A range of total solids from 4.5% to 19.2% is considered in order to compare methane yields and kinetics of reactors operated under wet to dry conditions. The experimental results show a reduction of the specific final methane yield of 4.3% and 40.8% in semi-dry and dry conditions compared with wet conditions. A decreasing trend of the specific initial methane production rate is observed when increasing the total solids concentration. Because of lack of water, volatile fatty acids accumulation occurs during the first step of the process at semi-dry and dry conditions, which is considered to be responsible for the reduction of process kinetic rates. The total volatile fatty acids concentration and speciation are proposed as indicators of process development at different total solids content.

Influence of transport from urban sources and domestic biomass combustion on the air quality of a mountain area.

The environmental influence of biomass burning for civil uses was investigated through the determination of several air toxicants in the town of Leonessa and its surroundings, in the mountain region of central Italy. Attention was focussed on PM10, polycyclic aromatic hydrocarbons (PAHs) and regulated gaseous pollutants (nitrogen dioxide, ozone and benzene). Two in-field campaigns were carried out during the summer 2012 and the winter 2013. Contemporarily, air quality was monitored in Rome and other localities of Lazio region. In the summer, all pollutants, with the exception of ozone, were more abundant in Rome. On the other hand, in the winter, PAH concentration was higher in Leonessa (15.8 vs. 7.0 ng/m3), while PM10 was less concentrated (22 vs. 34 µg/m3). Due to lack of other important sources and to limited impact of vehicle traffic, biomass burning was identified as the major PAH source in Leonessa during the winter. This hypothesis was confirmed by PAH molecular signature of PM10 (i.e. concentration diagnostic ratios and 206 ion mass trace in the chromatograms). A similar phenomenon (i.e. airborne particulate levels similar to those of the capital city but higher PAH loads) was observed in other locations of the province, suggesting that uncontrolled biomass burning contributed to pollution across the Rome metropolitan area.

Methane and VFA production in anaerobic digestion of rice straw under dry, semi-dry and wet conditions during start-up phase.

This work investigates the start-up phase of anaerobic digestion in wet, semi-dry and dry conditions of rice straw analysing the role of volatile fatty acid (VFA) production on process kinetics. Methane production yields and biodegradation kinetics in reactors operated under wet semi-dry and dry conditions were investigated. The experimental results showed a reduction in the specific final methane production yield of 57% and 63% in, respectively, semi-dry (TS = 14.8%) and dry (TS = 23.4%) conditions compared to wet (TS = 4.8%) conditions. The total VFA concentration and speciation are proposed as indicators of process development at different total solids content. High VFA concentrations were found in dry conditions, with a maximum total VFA concentration of 2110 mg/kg in dry conditions, 930 mg/kg in semi-dry conditions and 180 mg/kg in wet conditions.