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BACKGROUND The synthesis gas or hydrogen‐rich gas, at longer residence times and higher temperatures, is frequently the target of pyrolysis biomass. Biochars obtained at such conditions contain less functional groups but they are more effective for longer‐term soil C storage. The aim of this study was to elucidate the adsorption mechanisms and the effect of the ageing process on high‐temperature biochar towards lead adsorption. The biochars under study were produced from the pyrolysis of almond wood and olive tree pruning. RESULTS: The almond hardwood biochar was the most susceptible to the oxidation process. This biochar exhibited higher carbon loss than the olive biochar, 22.07% and 11.76%, respectively. The adsorption process was better described by the Langmuir model and pseudo‐second order kinetics. The maximum adsorption capacity decreased from 40.3 to 24.8 mg g–1 after the oxidation process for almond‐derived biochar and remained unchanged for the olive‐biochar. Analyses demonstrated that 67% of the adsorbed Pb2+ was removed through complexation by oxygen functionalities and phosphorous compounds. After the oxidation process, this fraction accounted for only 45% of the adsorbed Pb2+, ion exchange and cation‐π being the most prominent mechanisms for the adsorption. CONCLUSION: Biochar oxidation could cause the mobilization of 30% of the adsorbed lead under acid conditions. Special attention should be given to biochar's intrinsic properties, such as O/C and H/C ratio, for the application of these materials in the treatment of contaminated soil. High‐temperature biochars would offer the additional advantage of managing the remediation of scenarios with low pH. © 2020 Society of Chemical Industry (SCI) [ABSTRACT FROM AUTHOR]

BACKGROUND: Conductive materials, such as activated carbon (AC), graphene and biochar, have recently been applied for enhancing methane (CH4) production in anaerobic digesters. However, few efforts have been made to develop engineered conductive materials for these purposes. The aim of this work was to synthesize carbon materials from pecan nut shells and peach stones to apply them in anaerobic sludge incubations for enhancing the methanogenic activity, as well as the reduction of nitrous oxide (N2O). RESULT: Addition of conductive materials increased up to six‐fold the maximum CH4 production rate. Moreover, oxidation of these carbon materials with cold oxygen plasma enriched their surface with redox functional groups (e.g. quinones), so that their application further increased the methanogenic production rate up to 11‐fold as compared to controls lacking conductive materials. Furthermore, the reduction rate of N2O was increased several orders of magnitude in the presence of synthesized carbon materials, which constitutes the first demonstration that conductive materials can significantly increase the reduction rate of this greenhouse gas. CONCLUSION: Results indicate that there is great potential to develop engineered conductive materials to enhance both the production of CH4 and the reduction of N2O from wastewater treatment plants (WWTP), which may contribute to achieve more efficient processes. © 2019 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

BACKGROUND The aim of this study was to investigate the feasibility of utilizing a continuous-flow anaerobic granular sludge bed ( UASB) reactor for the removal of palladium ( II) from aqueous streams and the recovery of this precious metal as biogenic Pd(0). Anaerobic methanogenic granular sludge has been recently shown to reduce Pd( II) in the presence of a suitable electron donor leading to the formation of biomass-associated Pd(0). RESULTS Two laboratory-scale UASB reactors were fed with ethanol or acetate, in order to compare their performance in terms of Pd removal and reduction. Pd( II) was added in two periods of increasing concentration, 5 mg Pd( II) L−1 and then 15 mg Pd( II) L−1. Extensive removal of Pd (up to 99%), was attained in both reactors. X-ray diffraction ( XRD) and energy-dispersive X-ray spectroscopy ( EDS) analysis confirmed significant differences in the content of Pd(0) in the biomass, depending on the electron donor used. The main mechanisms of Pd( II) removal when acetate and ethanol were used as electron donor were biosorption and reduction to Pd(0) by biogenic H2 released as fermentation product, respectively. CONCLUSIONS The results obtained demonstrate that it is possible to apply a continuous process for Pd reduction and recovery using a methanogenic consortium. © 2015 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

The mining industry is the major producer of acid mine drainage (AMD). The problem of AMD concerns at active and abandoned mine sites. Acid mine drainage needs to be treated since it can contaminate surface water. Constructed wetlands (CW), a passive treatment technology, combines naturally-occurring biogeochemical, geochemical, and physical processes. This technology can be used for the long-term remediation of AMD. The challenge is to overcome some factors, for instance, chemical characteristics of AMD such a high acidity and toxic metals concentrations, to achieve efficient CW systems. Design criteria, conformational arrangements, and careful selection of each component must be considered to achieve the treatment. The main objective of this review is to summarize the current advances, applications, and the prevalent difficulties and opportunities to apply the CW technology for AMD treatment. According to the cited literature, sub-surface CW (SS-CW) systems are suggested for an efficient AMD treatment. The synergistic interactions between CW components determine heavy metal removal from water solution. The microorganism-plant interaction is considered the most important since it implies symbiosis mechanisms for heavy metal removal and tolerance. In addition, formation of litter and biofilm layers contributes to heavy metal removal by adsorption mechanisms. The addition of organic amendments to the substrate material and AMD bacterial consortium inoculation are some of the strategies to improve heavy metal removal. Adequate experimental design from laboratory to full scale systems need to be used to optimize equilibria between CW components selection and construction and operational costs. The principal limitations for CW treating AMD is the toxicity effect that heavy metals produce on CW plants and microorganisms. However, these aspects can be solved partially by choosing carefully constructed wetlands components suitable for the AMD characteristics. From the economic point of view, a variety of factors affects the cost of constructed wetlands, such as: detention time, treatment goals, media type, pretreatment type, number of cells, source, and availability of gravel media, and land requirements, among others. [ABSTRACT FROM AUTHOR]