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Spent tire rubber-derived chars and their corresponding H 3 PO 4 and CO 2 -activated chars were used as adsorbents in the recovery of Pb(II) ion and (W(VI)) oxyanion from synthetic solutions. The developed chars (both raw and activated) were thoroughly characterized to have insight about their textural and surface chemistry properties. H 3 PO 4 -activated chars presented lower surface areas than the raw chars and an acidic surface chemistry which affected the performance of these samples as they showed the lowest removals of the metallic ions. On the other hand, CO 2 -activated chars presented increased surface areas and increased mineral content compared to the raw chars, having presented higher uptake capacities for both Pb(II) (103-116 mg/g) and W(VI) (27-31 mg/g) ions. Cation exchange with Ca, Mg and Zn ions was appointed as a mechanism for Pb removal, as well as surface precipitation in the form of hydrocerussite (Pb 3 (CO 3 ) 2 (OH) 2 ). W(VI) adsorption might have been ruled by strong electrostatic attractions between the negatively charged tungstate species and the highly positively charged carbons' surface.The results shown in this work allow concluding that the valorisation of spent tire rubber through pyrolysis and the subsequent activation of the obtained chars is an alternative and a feasible option to generate adsorbent materials with a high uptake capacity of critical metallic elements., (© 2023. The Author(s).)

Highly efficient simultaneous removal of paracetamol and Cu 2+ ions from aqueous solutions was accomplished by using bovine bone char (BC). The adsorption behaviour was determined by kinetic and equilibrium studies of both single and binary system solutions. BC is a predominantly mesoporous material with a surface area of 103 m 2  g -1 . The influence of the initial pH on Cu 2+ removal was tested, suggesting that the optimal pH was 3.0. The removal of paracetamol from single and binary systems was 9.45 and 12.7%, respectively. On the other hand, the Cu 2+ removal was 36.2% for a single system, suggesting a higher affinity for BC. Moreover, in the case of binary mixtures, the presence of paracetamol led to an enhanced affinity of Cu 2+ due to a synergistic/cooperative mechanism, which led to a copper removal of 97.3%. The cooperative model was successfully adjusted to the equilibrium data of the binary systems. The modelling results indicated the formation of a first adsorption layer where paracetamol and copper are retained, and a second layer with a great affinity for copper ions after the formation of a Cu-paracetamol complex, leading to higher removal of Cu 2+ .

Deep eutectic solvents (DES), a new class of alternative solvents, have recently been used in the pre-treatment of lignocellulosic biomass. Due to the ability to dissolve phenolic compounds, they have been efficiently applied as delignification agents. However, to extend DES application to bioprocesses, such as Anaerobic Digestion (AD), their toxicity to microbial consortia must be evaluated. In this work, an effective delignifying DES, composed of choline chloride (ChCl) and oxalic acid (OA) (1:1) was prepared and its effect evaluated, for the first time, in biogas production. Results show that the presence of DES had both beneficial and detrimental effects on the anaerobic consortium, depending on its concentration. In the concentration range of 0.3-12.5 g/L, the presence of DES led to a lag-phase of 1 to 8 d as the DES concentration increased. However, after the lag-phase has been surpassed, DES up to a concentration of 12.5 g/L improved the biogas production, reaching an accumulated biogas volume three times higher than the control assay for the concentration of 12.5 g/L. For the highest DES concentrations (19.8-78.1 g/L), the biogas production was inhibited. The assays performed with DES components alone have indicated that OA at 3.2 g/L was the main responsible for the inhibition of biogas production (50% less biogas produced than the control). ChCl at 4.9 g/L has not presented a lag-phase and produced an accumulated biogas volume like the control assay (1200 mL for 30 d incubation). This work points out that ChCl:OA DES may be used in the delignification of biomass further submitted to AD, provided the inhibitory concentrations of OA are not achieved., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

Pyrolysis chars derived from rice wastes were chemically activated and used in W(VI) oxyanion adsorption assays in synthetic and mining wastewaters. For comparison purposes, a commercial activated carbon (CAC) was also used. Different experimental conditions were tested in the adsorption assays: solid/liquid ratio (S/L), initial pH, contact time, and initial W concentration. The porous carbon P2C+KOH presented the overall best performance in both media, due to its high surface area (2610 m 2 g -1 ), mesopore volume (1.14 cm 3 g -1 ), and neutral pH pzc (6.92). In the synthetic wastewater, the highest uptake capacity of P2C+KOH (854 mg g -1 ) was found in the assays with an S/L 0.1 g L -1 , an initial pH 2, and an initial W concentration of 150 mg L -1 , for 24 h. This value was almost 8 times higher than the one obtained for CAC (113 mg g -1 ). In the mining wastewater, P2C+KOH showed an even higher uptake capacity (1561 mg g -1 ) in the assay with the same experimental conditions, which was almost 3 times higher than for CAC (561 mg g -1 ). These results suggest that P2C+KOH seems to be an efficient alternative to CAC in the W(VI) adsorption from liquid effluents., (Copyright © 2021 Elsevier B.V. All rights reserved.)

Background: The awareness of environmental and socio-economic impacts caused by greenhouse gas emissions from the livestock sector leverages the adoption of strategies to counteract it. Feed supplements can play an important role in the reduction of the main greenhouse gas produced by ruminants-methane (CH 4 ). In this context, this study aims to assess the effect of two biochar sources and inclusion levels on rumen fermentation parameters in vitro ., Methods: Two sources of biochar (agro-forestry residues, AFB, and potato peel, PPB) were added at two levels (5 and 10%, dry matter (DM) basis) to two basal substrates (haylage and corn silage) and incubated 24-h with rumen inocula to assess the effects on CH 4 production and main rumen fermentation parameters in vitro ., Results: AFB and PPB were obtained at different carbonization conditions resulting in different apparent surface areas, ash content, pH at the point of zero charge (pHpzc), and elemental analysis. Relative to control (0% biochar), biochar supplementation kept unaffected total gas production and yield (mL and mL/g DM, p  = 0.140 and p  = 0.240, respectively) and fermentation pH ( p  = 0.666), increased CH 4 production and yield (mL and mL/g DM, respectively, p  = 0.001) and ammonia-N (NH 3 -N, p  = 0.040), and decreased total volatile fatty acids (VFA) production ( p  < 0.001) and H 2 generated and consumed ( p  ≤ 0.001). Biochar sources and inclusion levels had no negative effect on most of the fermentation parameters and efficiency. Acetic:propionic acid ratio ( p  = 0.048) and H 2 consumed ( p  = 0.019) were lower with AFB inclusion when compared to PPB. Biochar inclusion at 10% reduced H 2 consumed ( p  < 0.001) and tended to reduce total gas production ( p  = 0.055). Total VFA production ( p  = 0.019), acetic acid proportion ( p  = 0.011) and H 2 generated ( p  = 0.048) were the lowest with AFB supplemented at 10%, no differences being observed among the other treatments. The basal substrate affected most fermentation parameters independently of biochar source and level used., Discussion: Biochar supplementation increased NH 3 -N content, iso -butyric, iso -valeric and valeric acid proportions, and decreased VFA production suggesting a reduced energy supply for microbial growth, higher proteolysis and deamination of substrate N, and a decrease of NH 3 -N incorporation into microbial protein. No interaction was found between substrate and biochar source or level on any of the parameters measured. Although AFB and PPB had different textural and compositional characteristics, their effects on the rumen fermentation parameters were similar, the only observed effects being due to AFB included at 10%. Biochar supplementation promoted CH 4 production regardless of the source and inclusion level, suggesting that there may be other effects beyond biomass and temperature of production of biochar, highlighting the need to consider other characteristics to better identify the mechanism by which biochar may influence CH 4 production., Competing Interests: The authors declare there are no competing interests., (©2020 Rodrigues et al.)

Porous carbons from digestate-derived hydrochar were produced, characterized and their performance to reclaim phosphate from water was evaluated as a preliminary approach to demonstrate their practical application. In a first step, the digestate was converted into hydrochars through hydrothermal carbonization by using two different pH conditions: 8.3 (native conditions) and 3.0 (addition of H 2 SO 4 ). The resulting hydrochars did not present significant differences. Consecutively, the hydrochars were activated with KOH to produce activated carbons with enhanced textural properties. The resulting porous carbons presented marked differences: the AC native presented a lower ash content (20.3 wt%) and a higher surface area (S BET  = 1106 m 2 /g) when compared with the AC-H 2 SO 4 (ash content = 43.7 wt% S BET  = 503 m 2 /g). Phosphorus, as phosphate, is a resource present in significative amount in wastewater, causing serious problems of eutrophication. Therefore, the performance of the porous carbons samples to recover phosphate - P(PO 4 3- ) - from water was evaluated through exploitation assays that included kinetic studies. The lumped model presented a good fitting to the kinetic data and the obtained uptake capacities were the same for both carbons, 12 mg P(PO 4 3- )/g carbon. Despite the poorer textural properties of AC-H 2 SO 4 , this carbon was richer in Ca, Al, Fe, K, and Mg cations which promoted the formation of mineral complexes with phosphate anions. The results obtained in this work are promising for the future development of P(PO 4 3- ) enriched carbons that can be used thereafter as biofertilizers in soil amendment applications., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

Twelve biochars from forest and agri-food wastes (pruning of Quercus ilex, Eucalyptus grandis, Pinus pinaster, Quercus suber, Malus pumila, Prunus spinosa, Cydonia oblonga, Eriobotrya japonica, Juglans regia, Actinidia deliciosa, Citrus sinensis and Vitis vinifera) were investigated as potential low-cost and renewable adsorbents for removal of a commonly used pharmaceutical, fluoxetine. Preliminary adsorption experiments allowed to select the most promising adsorbents, Quercus ilex, Cydonia oblonga, Eucalyptus, Juglans regia and Vitis vinifera pruning material. They were characterized by proximate, elemental and mineral analysis, thermogravimetric analysis, Fourier transform infrared spectroscopy, determination of specific surface area and pH at the point of zero charge. Batch and equilibrium studies were performed, and the influence of pH was evaluated. The equilibrium was reached in less than 15 min in all systems. The maximum adsorption capacity obtained was 6.41 mg/g for the Eucalyptus biochar, which also demonstrated a good behavior in continuous mode (packed column)., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

Maize Cob Waste (MCW) is available worldwide in high amounts, as maize is the most produced cereal in the world. MCW is generally left in the crop fields, but due to its low biodegradability it has a negligible impact in soil fertility. Moreover, MCW can be used as substrate to balance the C/N ratio during the Anaerobic co-Digestion (AcoD) with other biodegradable substrates, and is an excellent precursor for the production of Activated Carbons (ACs). In this context, a biorefinery is theoretically discussed in the present review, based on the idea that MCW, after proper pre-treatment is valorised as precursor of ACs and as co-substrate in AcoD for biomethane generation. This paper provides an overview on different scientific and technological aspects that can be involved in the development of the proposed biorefinery; the major topics considered in this work are the following ones: (i) the most suitable pre-treatments of MCW prior to AcoD; (ii) AcoD process with regard to the critical parameters resulting from MCW pre-treatments; (iii) production of ACs using MCW as precursor, with the aim to use these ACs in biogas conditioning (H 2 S removal) and upgrading (biomethane production), and (iv) an overview on biogas upgrading technologies., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

The aim of the present work was to assess the efficiency of biochars obtained from the co-gasification of blends of rice husk + corn cob (biochar 50CC) and rice husk + eucalyptus stumps (biochar 50ES), as potential renewable low-cost adsorbents for Cr(III) recovery from wastewaters. The two gasification biochars presented a weak porous structure (A BET  = 63-144 m 2  g -1 ), but a strong alkaline character, promoted by a high content of mineral matter (59.8% w/w of ashes for 50CC biochar and 81.9% w/w for 50ES biochar). The biochars were used for Cr(III) recovery from synthetic solutions by varying the initial pH value (3, 4, and 5), liquid/solid (L/S) ratio (100-500 mL g -1 ), contact time (1-120 h), and initial Cr(III) concentration (10-150 mg L -1 ). High Cr(III) removal percentages (around 100%) were obtained for both biochars, due to Cr precipitation, at low L/S ratios (100 and 200 mL g -1 ), for the initial pH 5 and initial Cr concentration of 50 mg L -1 . Under the experimental conditions in which other removal mechanisms rather than precipitation occurred, a higher removal percentage (49.9%) and the highest uptake capacity (6.87 mg g -1 ) were registered for 50CC biochar. In the equilibrium, 50ES biochar presented a Cr(III) removal percentage of 27% with a maximum uptake capacity of 2.58 mg g -1 . The better performance on Cr(III) recovery for the biochar 50CC was attributed to its better textural properties, as well as its higher cation exchange capacity.

Two activated carbons (ACs) were prepared by physical activation of Maize Cob Waste (MCW) with CO 2 , during 2 and 3 h (MCW(PA)2h and MCW(PA)3h, respectively). Two other ACs were prepared by chemical activation: a) MCW(LD) - MCW was impregnated with anaerobic liquid digestate (LD) and carbonized under N 2 atmosphere; and b) CAR-MCW(LD) - previously carbonized MCW was impregnated with LD and carbonized under N 2 atmosphere. All ACs were fully characterized for textural and chemical properties, and then used in dynamic H 2 S removal assays from real biogas samples. Regarding H 2 S removal, the ACs that were physically activated behaved much better than the impregnated ones: MCW(PA)3h and MCW(PA)2h showed H 2 S uptake capacities of 15.5 and 0.65 mg g -1 , respectively, while MCW(LD) and CAR-MCW(LD) showed values of 0.47 and 0.25 mg g -1 , respectively. This may indicate that textural properties (surface area and microporosity) are more important than mineral content in H 2 S removal. Effectively, both surface area and micropore volume were much higher for the samples of MCW(PA)3h (S BET  = 820 m 2  g -1 and V micro  = 0.32 cm 3  g -1 ) and MCW(PA)2h (S BET  = 630 m 2  g -1 and V micro  = 0.21 cm 3  g -1 ) than for the ACs that were chemically activated (S BET  = 38.0 m 2  g -1 and V micro  = 0.01 cm 3  g -1 for MCW(LD); S BET  = 8.0 m 2  g -1 and V micro  = 0.01 cm 3  g -1 for CAR-MCW(LD)). High oxygen content in MCW(PA)3h favoured the catalytic oxidation reaction of H 2 S, promoting its removal. The use of MCW as precursor and LD as activating agent of the ACs may contribute for the integrated management of maize wastes and to diversify the applications of anaerobic digestate., (Copyright © 2019 Elsevier Ltd. All rights reserved.)