Analyzing Solar Pyrolysis Process of Walnut Shells: Thermal Biomaterial Behavioral Outcomes

This paper presents a new experimental method for the thermal analysis of solar pyrolysis of walnut shells. The method consists of two types of thermal experiments: (A) the pyrolysis of walnut shells, and (B) the heating-cooling of the biochar obtained during experiment A. Nutshells are a waste product from the pecan nut industry. The state of Sonora, Mexico, produces large volumes of walnuts and their residue. Likewise, this region has a considerable solar resource. The motivation of this study is to obtain biochar - a bi-product of high commercial value used for soil enhancement - using solar energy and agro-industrial waste. In this experiment, biomass pyrolysis of 50g of nutshells was carried out inside a stainless-steel reactor heated with concentrated radiation from a solar simulator. Three different heat fluxes were used: 234, 482, and 725 W. The maximum reaction temperatures were: 382, 498, and 674 °C respectively. The composition of the pyrolysis gases (H2, CO, CO2, and CH4) was measured and the biochar obtained was characterized. Finally, the performance of the solar reactor allowed us to identify and differentiate between evaporation, pyrolysis of cellulosic material, and lignin degradatio

Biochar-Assisted Bioengineered Strategies for Metal Removal: Mechanisms, Key Considerations, and Perspectives for the Treatment of Solid and Liquid Matrixes

Biochar has drawn the scientific community’s attention during the last few years due to its low production value and unique physicochemical properties, which are helpful for numerous applications. The development of biotechnological processes for the remediation of heavy metal environmental pollution is one central research avenue in which biochar application has shown promising results, due to its positive effect on the bacteria that catalyze these activities. Biochar stimulates bacterial activity through adsorption, adhesion, electron transport, and ion exchange. However, before biochar implementation, a complete understanding of its potential effects is necessary, considering that those interactions between biochar and bacteria may help improve the performance of biological processes designed for the remediation of environmental pollution by metals, which has been historically characterized by limitations related to the recalcitrance and toxicity of these pollutants. In this review, the key biochar–microorganism interactions and properties of unmodified biochar with the potential to improve metal bioremediation in both solid (mine tailings, polluted soils) and liquid matrixes (metal-laden wastewaters) are summarized. Knowledge gaps regarding the mechanisms involved in remediation strategies, the effect of long-term biochar use and the development of improved biochar technologies and their combination with existent remediation technologies is summarized. Additionally, an up-to-date summary of the development of biochar-assisted bioengineered strategies for metal passivation or removal from solid and liquid matrixes is presented, along with key perspectives for the application of biochar-based biotechnologies at full scale during the treatment of mining effluents in the real scale

Analysis of the Solar Pyrolysis of a Walnut Shell: Insights into the Thermal Behavior of Biomaterials

The state of Sonora, Mexico, stands as one of the leading producers of pecan nuts in the country, which are commercialized without shells, leaving behind this unused residue. Additionally, this region has abundant solar resources, as shown by its high levels of direct normal irradiance (DNI). This study contributes to research efforts aimed at achieving a synergy between concentrated solar energy technology and biomass pyrolysis processes, with the idea of using the advantages of organic waste to reduce greenhouse gas emissions and avoiding the combustion of conventional pyrolysis through the concentration of solar thermal energy. The objective of this study is to pioneer a new experimental analysis methodology in research on solar pyrolysis reactors. The two main features of this new methodology are, firstly, the comparison of temperature profiles during the heating of inert and reactive materials and, secondly, the analysis of heating rates. This facilitated a better interpretation of the observed phenomenon. The methodology encompasses two different thermal experiments: (A) the pyrolysis of pecan shells and (B) the heating–cooling process of the biochar produced in experiment (A). Additionally, an experiment involving the heating of volcanic stone is presented, which reveals the temperature profiles of an inert material and serves as a comparative reference with experiment (B). In this experimental study, 50 g of pecan shells were subjected to pyrolysis within a cylindrical stainless-steel reactor with a volume of 156 cm3, heated by concentrated radiation from a solar simulator. Three different heat fluxes were applied (234, 482, and 725 W), resulting in maximum reaction temperatures of 382, 498, and 674 °C, respectively. Pyrolysis gas analyses (H2, CO, CO2, and CH4) and characterization of the obtained biochar were conducted. The analysis of heating rates, both for biochar heating and biomass pyrolysis, facilitated the identification, differentiation, and interpretation of processes such as moisture evaporation, tar production endpoint, cellulosic material pyrolysis, and lignin degradation. This analysis proved to be a valuable tool as it revealed heating and cooling patterns that were not previously identified. The potential implications of this tool would be associated with improvements in the design and operation protocols of solar reactors

Use of a rotating biological contactor system for treatment of septic tank effluents.

Although septic tanks is the most common wastewater treatment device used in the State of Yucatan, Mexico, it is a deficient purification process and therefore further treatment is needed. This work presents the results from a pilot-scale rotating biological contactor (RBC) process used to treat septic tank effluent. The RBC was operated with three organic loading rates (5.2, 15.9 and 17.2 g BOD5/m2·d) and two rotation velocities (15 and 30 rpm). COD, BOD5, TKN and NH3-N removal efficiencies were measured and a factorial analysis was carried out to determine the best operating conditions. The organic loading rate was shown to be the variable that had the greatest effect on the process, with lower loads and better efficiency (roughly 90% for COD and BOD5). Rotation velocity was significant for the removal nitrogenous matter. The most efficient combination was found to be 5.2 g DBO5/m2·d at 30 rpm, which is equivalent to a tangential velocity of 16.49 m/min

Magnetic Biochar Obtained by Chemical Coprecipitation and Pyrolysis of Corn Cob Residues: Characterization and Methylene Blue Adsorption

Biochar is a carbonaceous and porous material with limited adsorption capacity, which increases by modifying its surface. Many of the biochars modified with magnetic nanoparticles reported previously were obtained in two steps: first, the biomass was pyrolyzed, and then the modification was performed. In this research, a biochar with Fe3O4 particles was obtained during the pyrolysis process. Corn cob residues were used to obtain the biochar (i.e., BCM) and the magnetic one (i.e., BCMFe). The BCMFe biochar was synthesized by a chemical coprecipitation technique prior to the pyrolysis process. The biochars obtained were characterized to determine their physicochemical, surface, and structural properties. The characterization revealed a porous surface with a 1013.52 m2/g area for BCM and 903.67 m2/g for BCMFe. The pores were uniformly distributed, as observed in SEM images. BCMFe showed Fe3O4 particles on the surface with a spherical shape and a uniform distribution. According to FTIR analysis, the functional groups formed on the surface were aliphatic and carbonyl functional groups. Ash content in the biochar was 4.0% in BCM and 8.0% in BCMFe; the difference corresponded to the presence of inorganic elements. The TGA showed that BCM lost 93.8 wt% while BCMFe was more thermally stable due to the inorganic species on the biochar surface, with a weight loss of 78.6%. Both biochars were tested as adsorbent materials for methylene blue. BCM and BCMFe obtained a maximum adsorption capacity (qm) of 23.17 mg/g and 39.66 mg/g, respectively. The obtained biochars are promising materials for the efficient removal of organic pollutants