Vinasse is a sulfate-rich liquid substrate, from which high levels of hydrogen sulfide in biogas can be obtained due to the sulfate reduction process under anaerobic conditions. Hydrogen sulfide is corrosive and toxic and must be removed for any utilization of the biogas. Mathematical models have been developed to study separately sulfate reduction in anaerobic digestion and sulfide removal from biogas streams. However, the levels of hydrogen sulfide produced in the anaerobic digestion stage have an effect on the sulfide removal processes in the next stage. As a method to study both processes and their interaction, a new approach is introduced and reviewed in the present article: the sulfur chain in biogas production. The necessity of studying the sulfate reduction processes in vinasse as a typical sulfate-rich substrate to predict hydrogen sulfide concentrations in the gas phase, as well as the best model approach to that aim are established here. In addition, the approaches to model sulfide removal based on direct conversion processes, the models' capability to predict the removal of hydrogen sulfide from the biogas (at levels between 20 000 and 30 000 ppm v ) as well as the concentration profile of the reactants in this removal processes are discussed.•Equilibrium Equation (9) (m 3 kmol −1 ) •Equilibrium Equation (10) (−) K 100 Concentration of H 2 S or pH at which the uptake rate is decreased 100 times (kmol m −3 ) K 2 Concentration of H 2 S or pH at which the uptake rate is decreased twice (kmol m −3 ) K a, acid Acid-base equilibrium coefficient (kmol m −3 ) K A/B Acid-base kinetic parameter (m 3 kmol −1 d −1 ) K H Henry's law coefficient (kmol m −3 bar −1 ) K I Inhibition coefficient by undissociated H 2 S (kmol m −3 ) K P2 Competitive product inhibition coefficient in Equation (30) (kg m −3 ) K S Half saturation value (kg COD_S i · m −3 ) K S * Half saturation value in absence of inhibitor in Equation (30) kg m −3 K SO4 Half saturation value for sulfates (kmol m −3 ) EL Barrera et al. K W Water equilibrium constant (kmol m −3 ) L n− Organic ligand (−) p H2S Hydrogen sulfide partial pressure (bar) pH LL Lower pH limits where the groups of microorganism are 50% inhibited (−) pH UL Upper pH limits where the groups of microorganism are 50% inhibited (−) pH 0 pH of the maximum growth rate of Thiobacillus ferrooxidans (−) r Reaction rate (kmol m −3 s −1 ) S Concentration of soluble components (for hydrogen ions, sulfates, sulfides and its ionized forms units are in kmol m −3 ) (kg COD_S i m −3 ) S I Inhibitor concentration (undissociated H 2 S) (kmol m −3 ) T Temperature ( • C) t Time (s) X Particulate component (kg VSS m −3 ) x Distance from gas-liquid interface (m) Y Yield of biomass on the substrate (kg VSS kg COD_S i −1 ) Greek letters α LL-α UL Positive values which affect the steepness of the curve (−) ρ A Acid-base kinetic rate (kmol m −3 d −1 ) ρ uptake Kinetic rate of substrate uptake (kg COD_S i m −3 d −1 ) ρ growth Kinetic rate of bacterial growth (kg VSS m −3 d −1 ) ρ decay Kinetic rate of bacterial ...
Abstract:A solid oxide fuel cell (SOFC) system integrated with an ethanol steam reforming stage is evaluated considering the first and second laws of thermodynamics. The irreversibility losses distribution and the plant energy and exergy efficiencies are studied under different process conditions (823
The kinetics of organic matter and nutrient removal in a pilot vertical subsurface wetland with red ferralitic soil as substrate were evaluated. The wetland (20 m(2)) was planted with Cyperus alternifolius. The domestic wastewater that was treated in the wetland had undergone a primary treatment consisting of a septic moat and a buffer tank. From the sixth week of operation, the performance of the wetland stabilized, and a significant reduction in pollutant concentration of the effluent wastewater was obtained. Also a significant increase of dissolved oxygen (5 mg/l) was obtained. The organic matter removal efficiency was greater than 85% and the nutrient removal efficiency was greater than 75% in the vertical subsurface wetland. Nitrogen and biochemical oxygen demand (BOD) removal could be described by a first-order model. The kinetic constants were 3.64 and 3.27 d(-1) for BOD and for total nitrogen, respectively. Data on the removal of phosphorus were adapted to a second-order model. The kinetic constant was 0.96 (mg/l)(-1) d(-1). The results demonstrated the potential of vertical flow constructed wetlands to clean treated domestic wastewater before discharge into the environment.
The search of sustainability is a need for human activities in general. Particularly, cement sector as a significant contributor to climate change has to implement strategies to reduce its environmental impacts. But, effective strategies have to be complemented by adequate methodological techniques to assess, guide and certificate sustainability. Amongst all the techniques developed by the scientific community in recent years, life cycle techniques highlight as one of the most used one due to its integrated and holistic philosophy. In Cuba, a new cement based on a combination of calcined clay and limestone to reduce clinker to 50% (Low Carbon Cement, LC3) is been developed as part of an international collaboration project. The main goal of this research is to assess sustainability of cement sector in Cuba using life cycle techniques such as: Life cycle assessment (environmental-LCA), Social Life Cycle Assessment (S-LCA), Life Cycle Costing (LCC), Economic Life Cycle Assessment (EcLCA). As part of the assessment LC3 is compared with traditional produced cements in Cuba OPC and PPC. Results show that LC3 introduction allows increasing sustainability in cement sector by reducing carbon emissions, energy consumption, costs and reporting positive effects on society.
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