Mesoporous Activated Biochar for As(III) Adsorption: A New Utilization Approach for Biogas Residue

Sequential carbonization of pig manure biogas residue into engineered biochar for diethyl phthalate removal toward environmental sustainability

Manure biogas residue has attracted increasing attention in waste recycling but faces substantial challenges because of its low carbon content, high ash content, and high heavy metal content. A novel sequential carbonization approach was proposed for recycling biogas residue; this approach consisted of pre-pyrolysis, activation with Ca(OH)2, and then activation with KOH. Pig manure-derived biogas residue was upcycled into engineered biochar (EB) with a high yield (26 %) and showed excellent performance in removing a typical plasticizer, diethyl phthalate (DEP). The proportion of carbon content greatly increased from 18 % (biogas residue) to 67 % (EB); however, the ash content decreased from 50 % (biogas residue) to 24 % (EB). The concentration of heavy metals decreased, and Zn had the largest decrease from 713 mg kg-1 to 61 mg kg-1 (p < 0.001). The sorption of DEP onto EB was rapid and reached equilibrium within 20 h. The developed specific surface area of EB was 1247 m2/g and provided abundant sorption sites for DEP; additionally, the sorption quantity reached 309 mg/g. The sorption capacity was dominated by surface adsorption. The oxygen-containing functional groups, graphene structure, porous structure, and hydrophobicity of EB contributed to the pore filling, hydrogen bonding, π-π stacking, and partitioning processes. Furthermore, the EB showed excellent practical application potential and great cycling stability. A sequential carbonization strategy was proposed to upcycle manure biogas residue into the EB for DEP removal; moreover, this strategy can aid in the attainment of environmental sustainability, including sustainable waste management and environmental pollution mitigation.

Effect of water-washing pretreatment on the enhancement of tetracycline adsorption by biogas residue biochar

Biochar preparation was a feasible strategy for realizing the reduction, harmlessness, and resource utilization of biogas residue (BR) simultaneously. How to enhance the adsorption performance of biogas residue biochar through simple, friendly, and effective way still needs to be investigated. In this study, water-washing pretreatment of BR was adopted before biochar preparation (BRBC-W), and pristine biochar (BRBC) was also produced to serve as control. The adsorption behavior and possible adsorption mechanisms of tetracycline (TC) onto biochars were comprehensively studied. The results showed that water-washing pretreatment could increase the surface area and mesoporous volume of biochar from 358.63 to 391.98 cm³∙g^-1, and 0.459 to 0.488 cm³∙g^-1, respectively. More graphitic structure was observed in BRBC-W. In addition, the surface morphology, element content, minerals composition, and surface functional groups also changed in biochar after water-washing pretreatment. The pseudo-second-order and Redlich-Peterson models better descried the adsorption behavior of TC on BCRBC-W. The maximum adsorption capacity of BRBC and BRBC-W for TC based on Langmuir isotherm was 224.93 and 306.94 mg·g^-1, respectively. The adsorption affinity of BRBC-W toward TC was greater than that of BRBC. BRBC and BRBC-W can effectively remove TC in water within a wide pH range and under the interference of co-existing ions. The adsorption mechanism of TC onto BRBC and BRBC-W included ore filling, π-π interaction, and hydrogen bonding. The enhancement of TC on BRBC-W by water-washing pretreatment was attributable to the strengthening of pore diffusion and π-π interaction. Therefore, water-washing pretreatment effectively enhanced the adsorption performance of BRB, and BRBC-W was an effective eco-friendly adsorbent for the removal of TC from aquatic environment.

Preparation of Mesoporous Biochar from Cornstalk for the Chromium (VI) Elimination by Using One-Step Hydrothermal Carbonation

Hydrothermal carbon (HTC) was prepared by the one-step hydrothermal method for Cr (VI) removal from wastewater, which was considered a "green chemistry" method. The specific surface area (SBET) of HTC was 85 m2/g with the pore size in range of 2.0-24.0 nm. FT-IR spectra analysis showed that the HTC had abundant chemical surface functional groups. The influence of adsorption parameters such as pH, HTC dosage, Cr (VI) concentration, and contact time on the removal efficiency of Cr (VI) had been investigated. When the initial concentration was 50 mg/L, pH = 6, amount of adsorbent was 0.2 g/50 ml, and adsorption time was 90 min; the Cr (VI) absorbed rate of HTC reached 98%. Batch adsorption experiments indicated that Cr (VI) adsorption data of HTC fitted the Freundlich isothermal and pseudo-second-order kinetic models. Overall, our findings provide a promising material in treatment of Cr (VI)-rich wastewater and give a clear picture of its application, which is worthy of further study.

Potassium hydroxide-modified algae-based biochar for the removal of sulfamethoxazole: Sorption performance and mechanisms

Biochar has been deemed one of the most promising sorbents for the removal of organic pollutants from aqueous solution. In this study, potassium hydroxide-modified Enteromorpha prolifera biochars (PEBCs) were prepared for the first time and applied for efficient sorption of a typical antibiotic, sulfamethoxazole (SMX). The characteristics of PEBCs, including morphology, pore structure, graphitization degree, surface functional groups, and surface element composition, were investigated. Moreover, sorption kinetic and isotherm experiments were carried out to explore the sorption process, performance, and mechanisms. The maximum sorption capacity for SMX can reach 744 mg g^-1, which is much higher than that reported for sorbents. The sorption of SMX onto PEBCs was controlled by both physical and chemical processes. Moreover, pore filling, hydrogen bonding, partitioning, π-π stacking, and electrostatic interactions were possible sorption mechanisms. This study indicated that the structure and properties of algal biochar can be further improved by potassium hydroxide modification at high temperature and applied as an excellent sorbent for the removal of antibiotics from aqueous solution.

Green catalytic process for in situ oxidation of Arsenic(III) in concentrated streams using activated carbon and oxygen gas

Arsenic(III) oxidation is a critical pre-treatment step for overall arsenic immobilization in concentrated industrial arsenic streams. Activated carbon (AC) catalysis is a green, economical and efficient method to oxidize As(III) from waters with high arsenic concentration prior to its removal through precipitation or adsorption. This research investigates AC-catalyzed oxidation process for oxidizing aqueous solutions of As(III) and proposed the possible reaction pathway. Batch tests were performed and efficient oxidation of 2.0 g/L acidic As(III) solution have been induced on AC surfaces in the presence of oxygen. The in-situ formation of reactive oxygen species on carbon surfaces and arsenic adsorption onto AC play important roles in As(III) oxidation. The kinetics of adsorption and catalyzed oxidation has been studied and the samples were characterized using ICP-OES, Zeta potential, TEM coupled with EDX and XPS techniques. A systematic reaction pathway was proposed, and reusability of AC has confirmed the economic viability of the proposed green process. This study offers a promising and facile solution for As(III) oxidation from waste water, mining and metal industrial waste streams under ambient conditions for arsenic immobilization.