Biogas, which typically consists of about 50–70% of methane gas, is produced by anaerobic digestion of organic waste and wastewater. Biogas is considered an important energy resource with much potential; however, its application is low due to its low quality. In this regard, upgrading it to natural gas quality (above 90% methane) will broaden its application. In this research, a novel ex-situ immobilized biomethanation bioreactor (IBBR) was developed for biologically upgrading biogas by reducing CO2 to CH4 using hydrogen gas as an electron donor. The developed process is based on immobilized microorganisms within a polymeric matrix enabling the application of high recirculation to increase the hydrogen bioavailability. This generates an increase in the consumption rate of hydrogen and the production rate of methane. This process was successfully demonstrated at laboratory-scale system, where the developed process led to a production of 80–89% methane with consumption of more than 93% of the fed hydrogen. However, a lower methane content was achieved in the bench-scale system, likely as a result of lower hydrogen consumption (63–90%). To conclude, the IBBRs show promising results with a potential for simple and effective biogas upgrading.

Municipal solid waste management is considered one of the major environmental challenges. Organic waste, especially food waste, usually accounts for over 50 wt% of municipal solid waste, yet, in most countries, it is the least recovered material. Decentralized composting aims to develop a new framework of waste management, building a closed-loop system for the composting of home, community, and commercial organic waste in urban environments. However, in some cases, decentralized composting is not economically and/or environmentally viable. Even when it is viable, various barriers and challenges need to be addressed in many cases. Different models in the literature address certain aspects of organic waste management, such as food waste treatment technology, recovery of energy, site selection, or environmental impact. The objective of this study is to provide guidelines and a methodological framework to quantify economic, social, operational, environmental, and regulatory aspects, in order to examine the viability and feasibility of decentralized composting projects at any given location. The decentralized composting analysis model proposed in this study has been developed with an innovative approach to decentralized composting project planning and design, an approach that is both holistic and very practical. The innovative model incorporates various aspects to examine the viability of decentralized composting projects based on benefit/cost criteria. In this respect, a result obtained through another model that examines a specific aspect of decentralized composting can be used as input for the model presented here. The decentralized composting analysis model provides a powerful tool for decision makers, based on the quantification of the decentralized composting project characteristics, and a benefit/cost index that takes into account the various impact variables. The decentralized composting analysis model allows examining the viability of the decentralized composting project in different scenarios, locations and options, and can help indicate the most viable alternative. In this paper, we describe the decentralized composting analysis model and its methodological framework, along with numerical examples to demonstrate its implementation.

For systems of sediments, soils, and subsurface solids that involve aggregations of fine-grained materials and zones of immobile water, the desorption of organic contaminants is often controlled by aqueous diffusion within the immobile water of a sorption domain. Accurate modeling in such systems requires not only a rational conceptual model for rates, but also good understanding of the equilibrium condition and of the initial conditions that existed at the onset of desorption. In this work, numerical modeling was used to obtain synthetic experimental results with a hypothetical (yet realistic) system in which rates were controlled by sorption-retarded diffusion. Batch sorption and desorption experiments are simulated at a variety of time scales and the results interpreted through modeling. Results show that even 50 days can be far too short to obtain equilibrium isotherms, and that the associated isotherm interpretations cause incorrect kinetic interpretations and predictions. In particular, 4- week batch sorption/desorption rate experiments could be well described using any of the presumed isotherms, but these results lead to greatly overpredicted rates of desorption under longer term conditions more relevant to field remediation. Additional results were also generated to quantitatively illustrate how misunderstanding of sorption equilibrium and diffusion rate will lead to incorrect suppositions of desorption hysteresis.