Anaerobic digestion is a biological process with wide application for the treatment of high organic-containing streams. The production of biogas and the lack of oxygen requirements are the main energetic advantages of this process. However, the digested stream may not readily find a final disposal outlet under certain circumstances. The present manuscript analyzed the feasibility of valorizing digestate by the hydrothermal carbonization (HTC) process. A hypothetical plant treating cattle manure and cheese whey as co-substrate (25% v/w, wet weight) was studied. The global performance was evaluated using available data reported in the literature. The best configuration was digestion as a first stage with the subsequent treatment of digestate in an HTC unit. The treatment of manure as sole substrate reported a value of 752 m3/d of biogas which could be increased to 1076 m3/d (43% increase) when coupling an HTC unit for digestate post-treatment and the introduction of the co-substrate. However, the high energy demand of the combined configurations indicated, as the best alternative, the valorization of just a fraction (15%) of digestate to provide the benefits of enhancing biogas production. This configuration presented a much better energy performance than the thermal hydrolysis pre-treatment of manure. The increase in biogas production does not compensate for the high energy demand of the pre-treatment unit. However, several technical factors still need further research to make this alternative a reality, as it is the handling and pumping of high solid slurries that significantly affects the energy demand of the thermal treatment units and the possible toxicity of hydrochar when used in a biological process.
This study analyzes various regulatory framework mechanisms applied to prevent, minimize, and mitigate environmental accidents and disasters, within the extractive mining industry, in seven Latin American countries. The selected countries offer an ample view of the mining industry specter since each one of them is at the different development stages, such as Chile, Bolivia, Mexico, and Brazil. Nevertheless, some of the countries have similar technical characteristics, as is the case of Peru, Colombia, and Ecuador. Controls and regulations employed in each of the countries reveal particularities that should be appreciated and understood. In conclusion, the existence of mining regulations has not diminished the occurrence of environmental accidents in those countries. However, the existing environmental controls allow authorities to quantify with substantial precision the degree of impact coming from Latin America’s mining industry. Furthermore, for more than a decade, mining industries have been subjected to several global initiatives to integrate elements of corporative social responsibility into their management systems—mainly in strong cooperation with different governmental formalization programs. The key focus is, cooperation among different scales (industry and small-scale and artisanal mining) which challenged, but also improved the capacities of environmental authorities and the effectiveness of different legal frameworks.
Anaerobic digestion is a technology widely used for the stabilisation of sewage sludge in wastewater treatment plants (WWTP). This technology presents several advantages such as the production of energy and the use of this energy to cover the demand of the treatment plant. However, sludge digestion systems may not produce an enough amount of biogas to cover a great fraction of the total energy demand. In the present manuscript is evaluated the introduction of a fermentative hydrogen phase and the effect produced in the system in terms of the energy balance. Food waste were considered as carbohydrate rich co-substrate and batch fermentation of this process is evaluated. The system was modelled using SuperPro designer considering conventional waste activated sludge system for the treatment of wastewater whereas the sewage sludge line was studied under mesophilic regimens. The mass and energy balance indicated an increase between 20 - 60% in the whole valorisation process, reporting as suitable this alternative when using digestate as inoculum source for starting-up the hydrogen process.
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