• Energy Research

peer-reviewed Globally, governments have increased their commitment to mitigate greenhouse gas (GHG) emissions. At the same time, the compostable bioplastic market is growing rapidly as many single-use petrochemical plastics are being banned internationally. A prospective consequential life cycle assessment approach was conducted to quantify the environmental envelopes of compostable bioplastic production for the bioplastic value chains to operate within the bounds of climate neutrality. Four indicative feedstocks of (i) lignocellulosic biomass from forestry, (ii) maize biomass, (iii) food waste digestate, and (iv) food waste were evaluated for potential bioplastic production. Upstream and end-of-life emissions for these feedstocks equated to GHG balances of -16.3 to +23.5, 0.3 to 1.0, 1.0 to 4.8, and -0.1 to +0.4 kg CO2 eq. per kg bioplastic, respectively. The scenarios demonstrated that indirect land-use change could have a considerable negative impact on the environmental performance of maize-based plastic, but a positive impact, via terrestrial carbon sequestration, for lignocellulosic-derived plastic (unless increased feedstock demand drives deforestation). Appropriate use of residues and sidestreams is critical to the environmental performance of bioplastics. Efficient utilisation of residues may require decentralisation of bio-plastic production and implementation of biorefinery and circular economy concepts.

The effect of trace elements (TEs) addition and NaOH pretreatment on the anaerobic digestion of rice straw was investigated in batch tests. Co, Ni and Se were added to the raw rice straw at different dosages. The NaOH pretreatment was applied to the rice straw both alone and in combination with the addition of TEs, in order to evaluate potential synergistic effects of the pretreatment and the TEs supplementation on the biogas production yields. The results obtained showed that the alkaline pretreatment was more effective than the TEs addition in increasing the cumulative biogas production, causing a 21.4% enhancement of the final biomethane yield, whereas the increase due to TEs dosing was not statistically significant. The analysis of volatile fatty acids (VFAs) confirmed that the NaOH pretreatment resulted in a higher production of VFAs, indicating an increased hydrolysis, while TEs addition did not cause significant changes in the VFA concentrations.

The Biohydrogen Potential (BHP) of six different types of waste biomass typical for the Campania Region (Italy) was investigated. Anaerobic sludge pre-treated with the specific methanogenic inhibitor sodium 2-bromoethanesulfonic acid (BESA) was used as seed inoculum. The BESA pre-treatment yielded the highest BHP in BHP tests carried out with pre-treated anaerobic sludge using potato and pumpkin waste as the substrates, in comparison with aeration or heat shock pre-treatment. The BHP tests carried out with different complex waste biomass showed average BHP values in a decreasing order from potato and pumpkin wastes (171.1 ± 7.3 ml H2/g VS) to buffalo manure (135.6 ± 4.1 ml H2/g VS), dried blood (slaughter house waste, 87.6 ± 4.1 ml H2/g VS), fennel waste (58.1 ± 29.8 ml H2/g VS), olive pomace (54.9 ± 5.4 ml H2/g VS) and olive mill wastewater (46.0 ± 15.6 ml H2/g VS). The digestate was analyzed for major soluble metabolites to elucidate the different biochemical pathways in the BHP tests. These showed the H2 was produced via mixed type fermentation pathways.

AbstractBiological reduction of nitric oxide (NO) to di‐nitrogen (N2) gas in aqueous Fe(II)EDTA2− solutions is a key reaction in BioDeNOx, a novel process for NOx removal from flue gases. The mechanism and kinetics of the first step of NO reduction, that is, the conversion of NO to N2O, was determined in batch experiments using various types of inocula. Experiments were performed in Fe(II)EDTA2− medium (5–25 mM) under BioDeNOx reactor conditions (55°C, pH 7.2 ± 0.2) with ethanol as external electron donor. BioDeNOx reactor mixed liquor gave the highest NO reduction rates (±0.34 ${\rm nmol}\,{\rm s}^{ - 1} \,{\rm mg}_{{\rm prot}}^{ - 1} $) with an estimated Km value for NO lower than 10 nM. The specific NO (to N2O) reduction rate depended on the NO (aq) and Fe(II)EDTA2− concentration as well as the temperature. The experimental results, complemented with kinetic and thermodynamic considerations, show that Fe(II)EDTA2−, and not ethanol, is the primary electron donor for NO reduction, that is, the BioDeNOx reactor medium (the redox system Fe(II)EDTA2−/Fe(III)EDTA−) interferes with the NO reduction electron transfer chain and thus enhances the NO denitrification rate. Biotechnol. Bioeng. 2008;100: 1099–1107. © 2008 Wiley Periodicals, Inc.

Abstract A local sensitivity analysis was performed for a chemically synthesized elemental sulfur (S0)-based two-step denitrification model, accounting for nitrite (NO2−) accumulation, biomass growth and S0 hydrolysis. The sensitivity analysis was aimed at verifying the model stability, understanding the model structure and individuating the model parameters to be further optimized. The mass specific area of the sulfur particles (a*) and hydrolysis kinetic constant (k1) were identified as the dominant parameters on the model outputs, i.e. nitrate (NO3−), NO2− and sulfate (SO42−) concentrations, confirming that the microbially catalyzed S0 hydrolysis is the rate-limiting step during S0-driven denitrification. Additionally, the maximum growth rates of the denitrifying biomass on NO3− and NO2− were detected as the most sensitive kinetic parameters.

Abstract This work investigated the effect of three different chemical pretreatment methods on the biogas production from the anaerobic digestion of wheat straw. The lignocellulosic material was separately pretreated using i) the organic solvent N-methylmorpholine N-oxide (NMMO) at 120 °C for 3 h, ii) the organosolv method, employing ethanol as the organic solvent at 180 °C for 1 h and iii) using an alkaline pretreatment with NaOH at 30 °C for 24 h. All the pretreatments were effective in increasing the biomethane production yield of wheat straw. In particular, the cumulative biomethane production yield of 274 mL CH4/g VS obtained with the untreated feedstock was enhanced by 11% by the NMMO pretreatment and by 15% by both the organosolv and alkaline pretreatment. The three pretreatment methods had a different impact on the chemical composition of the straw. NMMO hardly changed the amount of carbohydrates and lignin present in the original feedstock. Organosolv had a major impact on dissolving the hemicellulose component, whereas the alkaline pretreatment was the most effective in removing the lignin fraction. In addition to the increased biogas yields, the applied pretreatments enhanced the kinetics of biomethane production.