Question Difficulty Estimation from Text (QDET) is the application of Natural Language Processing techniques to the estimation of a value, either numerical or categorical, which represents the difficulty of questions in educational settings. We give an introduction to the field, build a taxonomy based on question characteristics, and present the various approaches that have been proposed in recent years, outlining opportunities for further research. This survey provides an introduction for researchers and practitioners into the domain of question difficulty estimation from text, and acts as a point of reference about recent research in this topic to date.
European and Italian incentive schemes promote small-scale biogas plant distribution using different types of biological and agricultural wastes as feedstock. A feed in tariff system is used in most of the European Union countries, and the incentive is paid on top of the market price capped at a maximum amount sold.\ud
The proposed study explores the feasibility of two-stage biogas plants for small-scale CHP, based on a two-phase bio-film process partially tested during the Biowalk4Biofuels (B4B) FP7 project implementing an Anaerobic Digestion (AD) based on a rotating biological contactor thus able to combine significant yields and reduced volume. The project developed a small pre-industrial biogas plant implementing a recovered 45 kWel CHP unit with 95 kWth thermal power. In the two-stage process, a high-temperature hydrolysis phase was followed by a continuously stirred methanogenesis bioreactor equipped with a rotating biological contactor. Main process performances were related to Organic Load Rate (OLR) up to 15 kg VS/m3; the overall reactor volume was 70 m3 for expected biogas production of 25 Nm3/h.\ud
Specifically, the aim of the present article is to address the use of the results and outcomes from some laboratory tests verified by the B4B system to model an overall feasibility evaluation. This allows to explore theoretical and economic feasibility of two ideal plants characterized by a 50 and 150 Nm3/h biogas production based on the overall system performances implementing a fixed biofilm for enhancing methanogenesis process. The feasibility study for the 50 Nm3/h biogas plants (equivalent to 100 kWel) shows profitable results, as well as evaluation of the 150 Nm3/h plants (300 kWe), that represent the biggest size for Italian incentives aimed at “small size” biogas plants
Life cycle assessment (LCA) is a fundamental tool for evaluating the environmental and energy load of a production cycle. Its application to renewable energy production systems offers the possibility of identifying the environmental benefits of such processes—especially those related to the by-products of production processes (i.e., digestion or biochar). Biochar has received worldwide interest because of its potential uses in bioenergy production, due to its coproducts (bio-oil and syngas), as well as in global warming mitigation, sustainable agriculture, pollutant removal, and other uses. Biochar production and use of soil is a strategy for carbon sequestration that could contribute to the reduction of emissions, providing simultaneous benefits to soil and opportunities for bioenergy generation. However, to confirm all of biochar’s benefits, it is necessary to characterize the environmental and energy loads of the production cycle. In this work, soil carbon sequestration, nitrous oxide emissions, use of fertilizers, and use of water for irrigation have been considered in the biochar’s LCA, where the latter is used as a soil conditioner. Primary data taken from experiments and prior studies, as well as open-source available databases, were combined to evaluate the environmental impacts of energy production from biomass, as well as the biochar life cycle, including pre- and post-conversion processes. From the found results, it can be deduced that the use of gasification production of energy and biochar is an attractive strategy for mitigating the environmental impacts analyzed here—especially climate change, with a net decrease of about −8.3 × 103 kg CO2 eq. Finally, this study highlighted strategic research developments that combine the specific characteristics of biochar and soil that need to be amended.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.