Hydrochar (HC) serves as a promising adsorbent to remove the cadmium from aqueous solution due to porous structure. The chemical aging method is an efficient and easy-operated approach to improve the adsorption capacity of HC. In this study, four chemical aging hydrochars (CAHCs) were obtained by using nitric acid (HNO₃) with mass fractions of 5% (N5-HC), 10% (N10-HC), and 15% (N15-HC) to age the pristine HC (N0-HC) and remove the Cd²⁺ from the aqueous solution. The results displayed that the N15-HC adsorption capacity was 19.99 mg g⁻¹ (initial Cd²⁺ concentration was 50 mg L⁻¹), which increased by 7.4 folds compared to N0-HC. After chemical aging, the specific surface area and oxygen-containing functional groups of CAHCs were increased, which contributed to combination with Cd²⁺ by physical adsorption and surface complexation. Moreover, ion exchange also occurred during the adsorption process of Cd²⁺. These findings have important implications for wastewater treatment to transform the forestry waste into a valuable adsorbent for Cd²⁺ removal from water.

Pollutants in wastewater and exhaust gas bring out serious concerns to public health and the environment. Biochar can be developed as a sustainable adsorbent originating from abundant bio-wastes, such as agricultural waste, forestry residue, food waste and human waste. Here we highlight the state-of-the-art research progress on pyrochar and hydrochar for the sorption of pollutants (heavy metal, organics, gas, etc) in wastewater and exhaust gases. The adsorption performance of pyrochar and hydrochar are compared and discussed in-depth, including preparation procedures (carbonization and activation), sorption possible mechanisms, and physiochemical properties. Challenges and perspective for designing efficient and environmental benign biochar-based adsorbents are finally addressed.

MSW landfill releases a lot of harmful pollutants such as H₂S, NH₃, and VOCs. In this study, two laboratory-scale biocovers such as biochar (BC) derived from agricultural & forestry wastes (AFW) pyrolysis, and sludge modified the biochar (SBC) were designed and used to remove the harmful pollutants. In order to understand in-situ biodegradation mechanism of the harmful pollutants by the SBC, the removal performances of the harmful pollutants together with the bacterial community in the BC and SBC were investigated in simulated landfill systems for 60 days comparing with the contrast experiment of a landfill cover soil (LCS). Meanwhile, the adsorption capacities of representative harmful pollutants (hydrogen sulfide, toluene, acetone and chlorobenzene) in the LCS, BC, and SBC were also tested in a fixed bed reactor. The removal efficiencies of the harmful pollutants by the SBC ranged from 95.43% to 100.00%, which was much higher than that of the LCS. The adsorption capacities of the harmful pollutants in the SBC were 4 times higher than that of the LCS since the SBC exhibited higher BET surface and N-containing functional groups. Meanwhile, the biodegradation rates of the harmful pollutants in the SBC were also much higher than that of the LCS since the populations of the bacterial community in the SBC were more abundant due to its facilitating the growth and activity of microorganisms in the porous structure of the SBC. In addition, a synergistic combination of adsorption and biodegradation in the SBC that enhanced the reproduction rate of microorganisms by consuming the absorbed-pollutants as carbon sources, which also contributed to enhance the biodegradation rates of the harmful pollutants.

Cadmium (Cd) contamination of the soil is one of the most serious environmental problems of agricultural production. Phytoremediation has attracted increasing attention because it can safely remove the soil contaminates via plant uptake, accumulations and plant harvesting. However, the high Cd toxicity to plant tissues and treatment of the large amount of hazardous plant residues from phytoremediation have limited its commercial implementation. Here we show that the leaves of the tall fescue (Festuca arundinacea) can excrete Cd out to avoid Cd toxicity in plant tissues. Cd specific fluorescence spectroscopy with laser confocal scanning microscope, screening electron microscope with energy dispersive spectroscopy and guttation fluids analysis confirmed that leaf hydathodes were the pathway of Cd excretion in tall fescue. Element analysis showed that Cd was preferentially excreted out when compared to the ion nutrients. The amount of leaf Cd excretion was linearly increased in response to the Cd stress period. The phytoremediation efficiency was evaluated to remove 14.4% of soil Cd annually by the leaf Cd excretion in our experimental system. These findings indicate that a novel strategy of Cd phytoexcretion based on washing-off and collection of leaf surface Cd is feasible to avoid Cd toxic in plant tissues and the high treatment cost of hazardous plant residues.

Camphor leaf (CL) was widely used to extract camphor oil and thus led to abundant forestry waste. In order to reduce pollution, the waste CL was used to prepare bio-adsorbent for Pb(II) removal after alkali treatment and functional modification. The effects of solution pH, initial Pb(II) concentration, contact time and solution temperature were investigated on adsorption process to evaluate the potential application in heavy metal ions’ removal. It was found that the massive hydroxyl groups released and plenty of micro-pores formed after the alkali treatment of CL bio-adsorbent, which obviously increased the Pb(II) adsorption. And the adsorption performance promoted continually after further functional modification by ionized 1,2,3,4-butanetetracarboxylic acid (BTCA). The increase of pH was favourable for the adsorption even though the precipitation effect was deducted. Linear fitting method was more suitable to describe the adsorption process than nonlinear fitting method, including adsorption isotherms and adsorption kinetics research. The adsorption thermodynamics was better to be described by nonlinear fitting method due to its lower root mean square error (RMSE) value and higher R² value. Among which, the adsorption isotherm and adsorption kinetics were fitted well to Langmuir model and pseudo-second-order model, respectively. The adsorption thermodynamics was exothermic in nature and the process was spontaneous at low solution temperature. The adsorption mechanism was revealed as the combination of dominant chemical adsorption and assistant physical adsorption.

Sorption and desorption of heavy metals (Cd, Cu, Pb, and Zn) was evaluated in biochars derived from sugarcane bagasse (SB), eucalyptus forest residues (CE), castor meal (CM), green coconut pericarp (PC), and water hyacinth (WH) as candidate materials for the treatment of contaminated waters and soils. Solid–liquid distribution coefficients depended strongly on the initial metal concentration, with K d,ₘₐₓ values mostly within the range 10³–10⁴ L kg⁻¹. For all biochars, up to 95 % removal of all the target metals from water was achieved. The WH biochar showed the highest K d,ₘₐₓ values for all the metals, especially Cd and Zn, followed by CE (for Cd and Pb) and PC (for Cd, Pb, and Zn). Sorption data were fitted satisfactorily with Freundlich and linear models (in the latter case, for the low concentration range). The sorption appeared to be controlled by cationic exchange, together with specific surface complexation at low metal concentrations. The low desorption yields, generally less than 5 %, confirmed that the sorption process was largely irreversible and that the biochars could potentially be used in decontamination applications.

The efficiency of low-cost, abundantly available local forestry waste, oak (Quercus robur) acorn peel (OP), to remove toxic Cr(VI) from aqueous solutions was studied in a batch system as a function of contact time, adsorbate concentration, adsorbent dosage, and pH. In an equilibrium time of 420 min, the maximum Cr removal by OP at pH 2 and 10 was 100 and 97 %, respectively. The sorption data fitted well with Langmuir adsorption model. Evaluation using Langmuir expression presented a monolayer sorption capacity of 47.39 mg g⁻¹ with an equilibrium sorbent dose of 5 g L⁻¹ and pH 7. Uptake of Cr by OP was described by pseudo-second-order chemisorption model. ICP-OES, LC-ICPMS analysis of the aqueous and solid phases revealed that the mechanism of Cr(VI) removal is by ‘integrated adsorption and reduction’ mechanism. ESEM-EDX and XRD analysis of OP before and after adsorption also confirmed that both adsorption and reduction of Cr(VI) to less toxic Cr³⁺ forms followed by complexation onto the adsorbent surface contributed to the removal of Cr(VI). Consistent with batch studies, OP effectively removed (>95 %) Cr from the real water samples collected from lake and sea. The results of this study illustrate that OP could be an economical, green, and effective biomaterial for Cr(VI) removal from natural aquatic ecosystems and industrial effluents.

This research investigated the treatment process of an Iranian zinc plant residue for recycling lead utilizing brine leaching and cementation with aluminum powder. Response surface modeling was employed for this purpose and accordingly, two quadratic mathematical models with R² of 0.9058 and 0.9463 were identified for relationship between process parameters. The ANOVA and 3D response surface graphs exhibited that the leaching and cementation processes were significantly depended on the interactive effects between influential parameters. The interaction effects of liquid/solid ratio with NaCl concentration, temperature and stirring rate, and quadratic effect of NaCl concentration had the largest impact on the recovery. It was also distinguished that the most impressive parameters on the cementation performance were the linear effect of Al:Pb molar ratio, cementation time and temperature, and the quadratic impact of agitation rate. Additionally, numerical optimization was carried out by desirability function approach and the maximum leaching recovery of lead (77.14%) was achieved at 400 g/L NaCl concentration, 10 mL/g liquid/solid ratio, 300 rpm stirring speed, 50 °C temperature, and 60-min leaching time. Also, the highest cementation efficiency (74.97%) was determined after 75 min at 1.5 Al:Pb molar (stoichiometry) ratio, ~ 420 rpm agitation rate, and 50 °C temperature. Furthermore, thermodynamic conclusions implied an endothermic nature and good affinity of lead toward each two processes.

The data on growth and reproduction of composting earthworms may be beneficial for large scale earthworm production. The growth and reproduction of Perionyx excavatus were assessed in limited supplies of four experimental diets-cow dung alone and its mixture with acacia (Acacia auriculiformis) leaf litter, bamboo (Bambusa polymorpha) leaf litter and terrestrial weed Mikania micrantha under laboratory conditions to select suitable diet from our locally available resource for vermiculture. Growth performance of Perionyx excavatus was significantly (P<0.05) higher in cow dung (maximum weight mg worm-1 629 and growth rate mg worm-1 day-1 22.91). The rate of reproduction (0.3 cocoons worm-1 day-1 and 3.31 juveniles adult-1 week-1) was significantly higher (P<0.05) in acacia-cow dung mixture. The cocoon production was maximum on the 30th day in all experimental diets (cow dung, acacia-cow dung, bamboo-cow dung, mikania-cow dung). All the diets showed a maximum peak of juvenile production on the 45th day. The lowest rate of biomass increase as well as the rate of reproduction were observed in mikania-cow dung mixture. Present result indicates that cow dung and acacia leaf litter can be used as vermiculture substrate for P. excavatus.

Low-cost adsorbent, pine bark biochar (PBB) from the forest residue, was produced and applied to remove tetracycline (TC) from aqueous solution via adsorption pathway. The PBB, hence obtained, was modified using aqueous ferric and ferrous ion solutions to obtain magnetic pine bark biochar (M-PBB). Batch adsorption experiments were conducted to examine the adsorption of TC by PBB and M-PBB in the variation of pH, contact time, dosage, and temperature. The adsorbents were characterized by SEM/EDX, TGA, and pHₚzc. The adsorption mechanism was evaluated by fitting Langmuir, Freundlich, Temkin, and Dubinin-Radushkevich (D-R) isotherms model. Also, the experimental data were analyzed by kinetics models (pseudo-first-order, pseudo-second-order, intra-particle diffusion, and Elovich) and thermodynamics. The maximum adsorption capacity (qₘ) of M-PBB was 15.3 mg/g from the experiment at pH 6. A high correlation coefficient (R² ≈ 0.9) of Freundlich isotherm postulated multi-layer adsorption of TC on M-PBB at pH 6. The kinetic studies showed that the pseudo-first-order was more suitable for representing the adsorption of TC molecules on the surface. The thermodynamic analysis was showed that the adsorption process is favorable, spontaneous, and endothermic at studied temperatures. M-PBB demonstrated a potential for removal of TC from water as a low-cost and convenient adsorbent.