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Anaerobic digestion (AD) is a process in which microorganisms, under oxygen-free conditions, convert organic matter into biogas and digestate. Normally, only 40–70% of biomass is converted into biogas; therefore, digestate still contains significant amounts of degradable organic matter and biogas potential. The recovery of this residual biogas potential could optimize substrate utilization and lower methane emissions during digestate storage and handling. Post-treatment methods have been studied with the aim of enhancing the recovery of biogas from digestate. This review summarizes the studies in which these methods have been applied to agricultural and wastewater digestate and gives a detailed overview of the existing scientific knowledge in the field. The current studies have shown large variation in outcomes, which reflects differences in treatment conditions and digestate compositions. While studies involving biological post-treatment of digestate are still limited, mechanical methods have been relatively more explored. In some cases, they could increase methane yields of digestate; however, the extra gain in methane has often not covered treatment energy inputs. Thermal and chemical methods have been studied the most and have yielded some promising results. Despite all the research conducted in the area, several knowledge gaps still should be addressed. For a more thorough insight of the pros and cons within post-treatment, more research where the effects of the treatments are tested in continuous AD systems, along with detailed economic analysis, should be performed.

Thermocouples are temperature sensors widely used, but the reliability of the values indicated by them must be constantly checked. When the tolerable error limits are exceeded or when one wishes to increase the reliability of results, calibration should be performed. This text will address what are the main sources of errors in thermocouples and what are the ways to calibrate them. By a calibration, it was performed an improvement in LDA Arduino software, which now includes the Equation of a fitting curve in your source code, sending information to the system Lorscheiter Viewer correlated with a measuring instrument calibrated by a certified laboratory.

Controlled release of carbon dioxide (CO2) into the soil and atmosphere is performed to test detection and monitoring tools, for which several field laboratories were established by a number of institutions worldwide. Numerical simulations of CO2 behavior in the shallow subsurface region are other forms of validation and verification of the leakage pathways and destinations. These studies aim to improve monitoring and verification of CO2 in case of unexpected leakages for public assurance. In this work, we present the results of a numerical modeling study conducted to simulate the injection of CO2 as carried out during a field test in Viamão, southern Brazil, where 20 kg day–1 of CO2 was pumped for 30 days through a vertical well 3 m below ground in an altered granitic soil. Multiphase flow simulations were performed with the TOUGH2/EOS7CA software for unsaturated porous media, using field data and injection parameters, including sensitivity tests to permeability direction, diffusivity, and boundary conditions. Results with increased horizontal permeabilities are in better agreement with the field observations. In this condition, mass balance calculations indicate approximately 90% of injected CO2 (20 kg day–1 during 30 days) remains in the soil after 180 days from injection start, consistent with the measured flow through the soil–atmosphere interface. © 2019 Society of Chemical Industry and John Wiley & Sons, Ltd.

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