Biomethane Production and Utilization Pathways: an MDCA-based Impact Assessment in Sardinia, Italy

Biogas from the anaerobic digestion of organic substrates represents a renewable and sustainable fuel widely deployed in Sardinia, supported by the high share of rural areas and the generation of agro-industrial residues and by-products. On the wave of new economic incentives, interest is gradually shifting to biomethane. Nonetheless, the possible uses of biomethane are compelled by the local energy system, which defects in the implementation of the natural gas grid and gas fuelling stations. This is the reason why heat and power production may still be considered one of the most plausible biomethane utilization. Multiple options for upgrading biogas into biomethane exist. Chemical absorption represents an established and reliable upgrading solution. However, innovative alternatives such as biological methanation have emerged characterized by high sustainability and versatility. In the present paper, six scenarios for biomethane generation and utilization are presented and analysed to determine an integrated impact benchmark for each of them. The impact assessment is structured in criteria that depict the environmental, economic, technological and social dimensions. It is carried out using the Multi-criteria Decision Analysis. An in-depth literature review allowed to identify quantitative and qualitative indicators for each dimension according to a rationale described in the paper. The results describe the processes and technologies involved and determine the integrated impacts for the considered scenarios. The method adopted emphasizes the regional worth of the assessment process, and the critical importance of collecting technological data at the pilot or commercial scale, given the distinctiveness of the experiences developed at the laboratory-scale

A MCDA-Based Assessment of Biomethane Generation and Use in Sardinia

The selection of a local and sustainable use of biogas, and biogas feedstocks, towards the upgrading process to biomethane, is a key aspect towards more consistent energy planning within the frame of the EU Green Deal and Sustainable Development Goals. In this paper, four biomethane production and utilization pathways were assessed in the view of economic, environmental, technological, and social dimensions compared to a reference scenario in which direct biogas use in a cogeneration unit is assumed. The technologies analyzed included membrane systems, amine scrubbing, water scrubbing, and biological methanation, regarding the Sardinian context. The impact assessment was carried out using the TOPSIS method. As an output, thirteen consistent indicators reflecting the holistic aspect of sustainability were designed and proposed based on an in-depth literature review and the authors’ technological knowledge. The results show that the reference scenario was the preferable one. In terms of environmental and social considerations, biological methanation emerged as the most environmentally and socially responsible alternative. From the economic perspective, all the upgrading options depicted similar results. The technological-oriented weighting showed that the two most widespread upgrading options highlighted the optimal results

Opportunities for Green Energy through Emerging Crops: Biogas Valorization of Cannabis sativa L. Residues

The present work shows the experimental evidence carried out on a pilot scale and demonstrating the potential of Cannabis sativa L. by-products for biogas production through anaerobic digestion. While the current state-of-the-art tests on anaerobic digestion feasibility are carried out at the laboratory scale, the here described tests were carried out at a pilot-to-large scale. An experimental campaign was carried out on hemp straw residues to assess the effective performance of this feedstock in biogas production by reproducing the real operating conditions of an industrial plant. An organic loading rate was applied according to two different amounts of hemp straw residues (3% wt/wt and 5% wt/wt). Also, specific bioenhancers were used to maximize biogas production. When an enzymatic treatment was not applied, a higher amount of hemp straw residues determined an increase of the median values of the gas production rate of biogas of 92.1%. This reached 116.6% when bioenhancers were applied. The increase of the specific gas production of biogas due to an increment of the organic loading rate (5% wt/wt) was +77.9% without enzymatic treatment and it was +129.8% when enzymes were used. The best management of the biodigester was found in the combination of higher values of hemp straw residues coupled with the enzymatic treatment, reaching 0.248 Nm3·kgvolatile solids−1 of specific biogas production. Comparisons were made between the biogas performance obtained within the present study and those found in the literature review coming from studies on a laboratory scale, as well as those related to the most common energy crops. The hemp straw performance was similar to those provided by previous studies on a laboratory scale. Values reported in the literature for other lignocellulosic crops are close to those of this work. Based on the findings, biogas production can be improved by using bioenhancers. Results suggest an integration of industrial hemp straw residues as complementary biomass for cleaner production and to contribute to the fight against climate change

Biogas from anaerobic digestion of fruit and vegetable wastes: experimental results on pilot-scale and preliminary performance evaluation of a full-scale power plant

This paper presents the experimental results obtained through an anaerobic digestion pilot plant by using fruit and vegetable wastes as single substrate. The substrate materials were sampled from the wastes produced by the Fruit and Vegetable Wholesale Market of Sardinia (Italy). The experimental study was carried out over a period of about six months to evaluate the most suitable operating parameters of the process depending on the availability of different kinds of fruit and vegetable wastes over the different periods of the year. Overall, the optimum daily loading rate of wastes was 35 kg/d, with a corresponding hydraulic residence time of 27 days. The optimum organic loading rate ranged from 2.5 to 3.0 kgVS/m3d and the average specific biogas production was about 0.78 Nm3/kgVS, with a specific methane yield of about 0.43 Nm3/kgVS. The results of the experimental investigation were used for a preliminary performance evaluation of a full-scale anaerobic digestion power plant for treating all the fruit and vegetable wastes produced by the Wholesale Market of Sardinia (9 t/d). The estimate of daily methane production (290 Nm3/d) leads to a CHP unit with a power output of about 42 kW and an annual electrical production of about 300 MWh/y (about 25% of the wholesale market electrical consumption). The AD power plant also shows interesting economic features, since its energy production cost (about 150 €/MWh) is slightly lower than the energy purchase cost of the wholesale market (about 200 €/MWh) and a pay-back time of about 7.25 years can be achieved in the case of dispatching the electrical energy to the national grid. The PBT decreases to about 5.4 years if 50% of the available thermal energy is used to substitute heat production from fossil fuel boilers. Keywords Anaerobic digestion; fruit and vegetable waste; biogas production; mesophilic digestion

Biomass ash reutilisation as an additive in the composting process of organic fraction of municipal solid waste

In this work the effects of selected types of biomass ash on the composting process and final product quality were studied by conducting a 96-day long experiment where the source separated organic fraction of municipal waste, mixed with wood prunings that served as bulking agent, was added with 0%, 2%, 4% and 8% wt/wt of biomass ash. The evolution over time of the main process parameters was observed, and the final composts were characterised. On the basis of the results, both the composting process and the quality of the final product were improved by ash addition. Enhanced volatile solids reduction and biological stability (up to 32% and 52%, respectively, as compared to the unamended product) were attained when ash was added, since ash favored the aerobic degradation by acting as a physical conditioner. In the final products, higher humification of organic matter (expressed in terms of the humification index, that was 2.25 times higher in the most-enriched compost than in the unamended one) and total Ca, K, Mg and P content were observed when ash was used. The latter aspect may influence the composts marketability positively, particularly with regards to potassium and phosphorus. The heavy metals content, that is regarded as the main environmental disadvantage when using ash as a composting additive, did not negatively affect the final composts quality. However, some other controversial effects of ash, related to the moisture and temperature values attained during the process, pH (8.8–9.2 as compared to 8.2 of the unamended compost) and electrical conductivity levels (up to 53% higher as compared to the unamended compost) in the final composts, were also observed