Carboxyl and hydroxyl groups enhance ammonium adsorption capacity of iron (III) chloride and hydrochloric acid modified biochars

Enhance PD/A biofilm formation via a novel biochar/tourmaline modified-biocarriers to treat low-strength contaminated surface water: Initial adhesion and high-substrate microenvironment

In this work, a novel polyurethane carrier modified with biochar and tourmaline/zeolite powder at ratio of 1:1 and 1:2 was developed to promote the formation of biofilms and the synergy of overall bacterial activity for Partial Denitrification/Anammox to treat low-nitrogen contaminated surface water. Based on the batch experiment, the modified biocarrier, BTP2 (biochar: tourmaline = 2: 1), exhibited the highest total nitrogen removal efficiency (83.63%) under influent total nitrogen of 15 mg/L and COD/NO3- of 3. The dense biofilm was formed in inner side of biocarrier owing to the increased surface roughness and various functional groups suggested by scanning electron microscopy and Fourier-transform infrared analysis. The EPS content increased from 200.15 to 220.26 mg/g VSS in BTP2 system. Besides, the rapid NH4+ capture and organics release of the modified carrier fueled the growth of anammox and denitrification bacteria, with the activity of 2.13 ± 0.52 mg N/gVSS/h and 6.70 ± 0.52 mg N/gVSS/h (BTP2). High-throughput sequencing unraveled the increased abundances of Candidatus_Competibacter (0.82%), Thauera (0.60%) and Candidatus_Brocadia (0.55%) which was responsible for the synergy of incomplete reduction of NO3- to NO2- and NH4+ oxidation. Overall, this study provided a valid and simple-control guide for biofilm formation towards rapid enrichment and great collaboration of Anammox and denitrification bacteria.

Insight into the wheat residues-derived adsorbents for the remediation of organic and inorganic aquatic contaminants: A review

Wheat is a major grain crop of the world that provides a stable food for human consumption. Large amounts of by-products/waste materials are produced after the harvesting and processing of wheat crop. Such materials can cause an environmental issue if not disposed of properly. Several studies have shown that wheat residues can be efficient precursors for adsorbents because of their availability, renewability, lignocellulosic composition, and surface active groups enriched structure. In the literature, there are few review articles that address wheat residues-based adsorbents. However, these reviews were specific in terms of adsorbate or adsorbent and did not provide detailed information about the modification, properties, and regeneration of these adsorbents. This article extensively reviews the utilization of wheat biomass/waste including straw, bran, husk, and stalk as precursors for raw or untreated, chemically treated, carbonaceous, and composite adsorbents against various environmental pollutants. The influences of inlet pollutant amount, adsorbent dose, pH, temperature, and time on the performance of adsorbents against pollutants were considered. The maximum uptakes, equilibrium time, and adsorption nature were identified from isotherms, kinetic, and thermodynamic studies. The highest adsorbed amounts of most tested contaminants were 448.20, 322.58, and 578.13 mg/g for lead, chromium, and copper, 1374.6 and 1449.4 mg/g for methylene blue and malachite green, and 854.75, 179.21, and 107.77 mg/g for tetracycline, phosphate, and nitrate, respectively. For the studied adsorbate/adsorbent systems the adsorption mechanism and regeneration were also discussed. Significant results and future directions are finally presented.

Properties and Possibilities of Using Biochar Composites Made on the Basis of Biomass and Waste Residues Ferryferrohydrosol Sorbent

Biochar enriched with metals has an increased potential for sorption of organic and inorganic pollutants. The aim of the research was to identify the possibility of using biochar composites produced on the basis of waste plant biomass and waste FFH (ferryferrohydrosol) containing iron atoms, after CO2 capture. The composites were produced in a one-stage or two-stage pyrolysis process. Their selected properties were determined as follows: pH, ash content, C, H, N, O, specific surface area, microstructure and the presence of surface functional groups. The produced biochar and composites had different properties resulting from the production method and the additive used. The results of experiments on the removal of methylene blue (MB) from solutions allowed us to rank the adsorbents used according to the maximum dye removal value achieved as follows: BC1 (94.99%), B (84.61%), BC2 (84.09%), BC3 (83.23%) and BC4 (83.23%). In terms of maximum amoxicillin removal efficiency, the ranking is as follows: BC1 (55.49%), BC3 (23.51%), BC2 (18.13%), B (13.50%) and BC4 (5.98%). The maximum efficiency of diclofenac removal was demonstrated by adsorbents BC1 (98.71), BC3 (87.08%), BC4 (74.20%), B (36.70%) and BC2 (30.40%). The most effective removal of metals Zn, Pb and Cd from the solution was demonstrated by BC1 and BC3 composites. The final concentration of the tested metals after sorption using these composites was less than 1% of the initial concentration. The highest increase in biomass on prepared substrates was recorded for the BC5 composite. It was higher by 90% and 54% (for doses of 30 g and 15 g, respectively) in relation to the biomass growth in the soil without additives. The BC1 composite can be used in pollutant sorption processes. However, BC5 has great potential as a soil additive in crop yield and plant growth.

Application of biochar to anaerobic digestion versus digestate: Effects on N emissions and C stability

Research attention is growing for biochar as amendment for anaerobic digestion (AD), as it may improve both the AD process and digestate properties. In this study, two biochars (from insect frass or the woody fraction of green waste, both pyrolyzed at 450 °C) were added (5 % w/w) during semi-continuous AD of organic kitchen waste and chicken manure. Biochar was mixed either during the AD process or to the digestate post-treatment. The impact of biochar addition on the AD process, NH3 and greenhouse gas emissions, as well as C and N mineralization following soil application, was examined. Biochar did not affect the biogas yield, but did lead to a reduction in NH3 levels in the biogas and NH4+-N sorption onto the biochars, reducing the risk of AD inhibition. N sorbed as NH4+-N onto the biochar was more available for mineralization than N sorbed as NH3. N sorption on biochar-amended digestates did not result in trade-offs when these digestates were applied to soil: the sorbed N was not released as NH3 or N2O after soil application and was not released as mineral N in either the short or medium term. The C-rich biochars increased the OC content of the digestate, which enhanced its value as soil improver. Additionally, mixing biochar with digestate decreased the soil CO2 emissions up to 33 % when it was added after AD; no priming effects were observed. These findings highlight the potential benefits of incorporating biochar into AD systems and the subsequent application of biochar-amended digestate in agricultural practices.

A new attempt to control volatile organic compounds (VOCs) pollution - Modification technology of biomass for adsorption of VOCs gas

The detrimental impact of volatile organic compounds on the surroundings is widely acknowledged, and effective solutions must be sought to mitigate their pollution. Adsorption treatment is a cost-effective, energy-saving, and flexible solution that has gained popularity. Biomass is an inexpensive, naturally porous material with exceptional adsorbent properties. This article examines current research on volatile organic compounds adsorption using biomass, including the composition of these compounds and the physical (van der Waals) and chemical mechanisms (Chemical bonding) by which porous materials adsorb them. Specifically, the strategic modification of the surface chemical functional groups and pore structure is explored to facilitate optimal adsorption, including pyrolysis, activation, heteroatom doping and other methods. It is worth noting that biomass adsorbents are emerging as a highly promising strategy for green treatment of volatile organic compounds pollution in the future. Overall, the findings signify that biomass modification represents a viable and competent approach for eliminating volatile organic compounds from the environment.

Synthesis and characterization of cost-effective and high-efficiency biochar for the adsorption of Pb2+ from wastewater

This study aimed to investigate the adsorption mechanism of Pb2+ in wastewater using activated carbon derived from inexpensive materials, specifically avocado, bitter orange, and walnut leaves, through a single-step chemical activation process. The activated carbon was prepared using sulfuric acid as an activator, with a particle size of 1 mm. The pyrolysis reactor (slow-pyrolysis) operated at 600 °C for 90 min with a nitrogen flow rate of 5 L/min. Batch experiments were conducted under various conditions to determine the optimal dosage (1.5 g/L), equilibrium contact time (180 min), and pH (6.5). The study focused on employing cost-effective and highly efficient adsorbents, namely biochar produced from tree leaves, for the adsorption process. The results indicated that the pseudo-second-order kinetic model accurately described the adsorption process, while the Freundlich isotherm model best fit the experimental data. These findings suggest that tree leaves can serve as cost-effective and efficient adsorbents for a wide range of applications. Furthermore, multiple adsorption factors were evaluated in batch mode, including contact duration, pH, adsorbent dosage, concentration of the Pb2+ solution, and temperature. The maximum adsorption capacities for the activated carbon derived from avocado, bitter orange, and walnut leaves were found to be 60.46, 59.42, and 58.48 mg/g, respectively. Thus, this study highlights the effectiveness and economic feasibility of using pyrolysis-derived activated carbon from low-cost materials for the removal of Pb2+ from wastewater.

A comprehensive review of coconut-based porous materials for wastewater treatment and CO2 capture

For several decades, water pollution has become a major threat to aquatic and non-aquatic species, including humans. Different treatment techniques have already been proposed and implemented depending on wastewater characteristics. But many of these treatment techniques are expensive and inefficient. Adsorption-based techniques have shown impressive performances as an inexpensive treatment method previously. Coconut-based resources have been considered as adsorbents for wastewater treatment because of their abundance, low cost, and favorable surface properties. However, over the last decade, no comprehensive study has been published regarding biochar from coconut-based materials for wastewater treatment and CO2 capture. This review discusses biochar production technology for coconut-based materials, its modification and characterization, its utilization as an adsorbent for removing metals and organics from wastewater, and the associated removal mechanisms and the economic aspects of coconut-based biochar. Coconut-based materials are cheap and effective for removing various organic compounds such as pesticides, hormones, phenol, and phenolic compounds from solutions and capturing CO2 from air mainly through the pore-filling mechanism. Utilizing coconut-based biochars in a hybrid system that combines adsorption and other techniques, such as biotechnology or chemical coagulation is a promising way to increase their performance as an adsorbent in wastewater treatment.

Surface modification of quartz sand: A review of its progress and its effect on heavy metal adsorption

Quartz sand (SiO₂) is a prevalent filtration medium, boasting wide accessibility, superior stability, and cost-effectiveness. However, its utility is often curtailed by its sleek surface, limited active sites, and swift saturation of adsorption sites. This review outlines the prevalent strategies and agents for quartz sand surface modification and provides a comprehensive analysis of the various modification reagents and their operative mechanisms. It delves into the mechanism and utility of surface-modified quartz sand for adsorbing heavy metal ions (HMIs). It is found that the reported modifiers usually form connections with the surface of quartz sand through electrostatic forces, van der Waals forces, pore filling, chemical bonding, and/or molecular entanglement. The literature suggests that these modifications effectively address issues inherent to natural quartz sand, such as its low superficial coarseness, rapid adsorption site saturation, and limited adsorption capacity. Regrettably, comprehensive investigations into the particle size, regenerative capabilities, and application costs of surface-modified quartz sand and the critical factors for its wider adoption are lacking in most reports. The adsorption mechanisms indicate that surface-modified quartz sand primarily removes HMIs from aqueous solutions through surface complexation, ion exchange, and electrostatic and gravitational forces. However, these findings were derived under controlled laboratory conditions, and practical applications for treating real wastewater necessitate overcoming further laboratory-scale obstacles. Finally, this review outlines the limitations of partially surface modified quartz sand and suggests potential venues for future developments, providing a valuable reference for the advancement of cost-effective, HMI-absorbing, surface-modified quartz sand filter media.

Effective adsorption of ammonium nitrogen by sulfonic-humic acid char and assessment of its recovery for application as nitrogen fertilizer

Ammonium nitrogen (NH₄⁺-N) is a form of N that is non-negligible in eutrophication water as well as an essential nutrient for plants growing. Carbon materials are considered superior for the adsorption recovery of excess NH₄⁺-N in water bodies. The sulfonic-humic acid char (SHAC) was prepared from humic acid (HA) by pyrolysis and hydrothermal grafting with sodium allyl sulfonate. SEM-mapping, FTIR and XPS results indicated that sulfonic groups (-SO₃H) were successfully grafted onto SHAC. The adsorption kinetic fitting displayed that the adsorption of NH₄⁺-N by SHAC conformed to the pseudo-second-order kinetics and could reach equilibrium in about 100 min. The maximum adsorption of NH₄⁺-N by SHAC was 77.24 mg/g, it was mainly contributed by electrostatic attraction, hydrogen bonding and pore volume sites. SHAC adsorption of NH₄⁺-N resulted in the material SHAC-N, which desorption rate was considerably slower than that of commercially available ammonium chloride (NH₄Cl) fertilizer and in accordance with the first order model. Wheat growth experiments revealed that the quality of wheat treated with SHAC-N (higher 100-grain weight and lower nitrate content) was better than that of NH₄Cl fertilizer. In addition, the higher residual NH₄⁺-N in the SHAC-N treatment soil facilitated subsequent crop planting. These results indicated that SHAC has excellent adsorption and slow release of NH₄⁺-N, and has great potential application for N management in environment and agriculture.

Integrated microbiological and metabolomics analyses to understand the mechanism that allows modified biochar to affect the alkalinity of saline soil and winter wheat growth

In order to understand the mechanism that allows modified biochar (BC) to enhance the salt tolerance and growth of crops in saline-alkali soil, we tested the effects of ordinary BC, nanoparticle-size BC, acidified BC (HBC), and acidified nanoparticle-size BC on winter wheat growth and the soil properties by combining microbiological and metabolomics analyses. The results showed that compared with the control with no BC, the plant height increased by 17.33 % under HBC and the proportion of large soil aggregates increased by 1.25-2.83 times. HBC increased the relative abundances of some dominant genera of bacteria (e.g., Streptococcus) and fungi (e.g., Mycothermus), as well as functions such as bacterial metabolic genetic information processing and cellular processes, and reduced the abundance of pathotrophic fungi. Metabolomics analysis showed that HBC upregulated various metabolites (including amino acids and their derivatives, lipids, flavonoids, and organic acids) and five main metabolic pathways. Among the KEGG pathways, the pyrimidine metabolism pathway was significantly upregulated, as well as crop leaf metabolism, β-alanine metabolism, and valine, leucine, and isoleucine metabolism, and the antioxidant levels and resistance to salt-alkali stress were enhanced in winter wheat leaves. Partial least squares-path modeling suggested that HBC affected the growth of winter wheat by significantly changing the soil physicochemical properties and microbial structure (path coefficients of 0.566 and 0.512, respectively).

Enhanced adsorption capacity of tetracycline on porous graphitic biochar with an ultra-large surface area†

Excessive tetracycline in the water environment may lead to the harming of human and ecosystem health. Removing tetracycline antibiotics from aqueous solution is currently a most urgent issue. Porous graphitic biochar with an ultra-large surface area was successfully prepared by a one-step method. The effects of activation temperature, activation time, and activator dosage on the structural changes of biochar were investigated by scanning electron microscopy, Brunauer–Emmett–Teller, X-ray powder diffraction, and Raman spectroscopy. The effect of the structure change, adsorption time, temperature, initial pH, and co-existing ions on the tetracycline removal efficiency was also investigated. The results show that temperature had the most potent effect on the specific surface area, pore structure, and extent of graphitization. The ultra-large surface area and pore structure of biochar are critical to the removal of tetracycline. The q_e of porous graphitic biochar could reach 1122.2 mg g⁻¹ at room temperature. The calculations of density functional theory indicate that π–π stacking interaction and p–π stacking interaction can enhance the tetracycline adsorption on the ultra-large surface area of graphitic biochar.

1. A ultra-large surface area of porous graphitic biochar was successfully using corn starch and ZnCl₂ by a one-step method. 2. The adsorption capacity of tetracycline on the biochar could get 1122.2 mg g⁻¹ at room temperature.

In situ formed CaSO4 on waste dander biochar to inhibit the mineralization of soil organic carbon

In order to reduce CO2 emissions, as well as realize the resource utilization of waste dander (WD) and the goal of international "peak carbon dioxide emissions" and "carbon neutrality", Biochar was prepared with WD via pyrolysis technology, achieving CaSO4 in situ generated on its surface, which could be used to inhibit soil organic carbon (SOC) from mineralizing and enhance soil carbon sequestration ability. The characterization results showed that the unstable carbon (C) structures as well as more conjugated structures were generated on Ca-BC, obtaining an increased C sequestration of Ca-BC to 21.70 %. With the application of Ca-BC, the mineralization rate of SOC was reduced to 0.451 mg CO2/(g·d), and the soil moisture content, pH and TOC content were increased to 45.48 %, 7.96 and 47.19 %. In addition, the bioinformatics analysis and redundancy analysis revealed that the application of Ca-BC promoted bacteria to convert into the stable C-dominant phyla (Firmicutes).

Efficient removal of Sb(III) from water using β-FeOOH-modified biochar:Synthesis, performance and mechanism

Since the toxicity of Sb(III) is 10 times as high as that of Sb(V) in the environment, it is urgent to find a way to cut down Sb(III). β-FeOOH-modified biochar (β-FeOOH/BC) was prepared and used to remove Sb(III). The characterization results suggested that oxygen-containing functional groups formed on β-FeOOH/BC, which increased the Sb(III) removal efficiency. Even under complex water matrix conditions, the outstanding adsorption performance of β-FeOOH/BC for Sb(III) was obtained. The adsorption reaction rapidly reached a high removal efficiency within 5 min and approached adsorption equilibrium in about 6 h. The adsorption process was fitted to pseudo-second-order kinetics. Amount of maximum adsorption was 202.53 mg g^-1 at 308 K according to Langmuir model. β-FeOOH/BC removed Sb(III) mainly through pore-filling complexation, cation-π and coordination exchange. The CO sites and persistent free radicals (PFRs) acted as electron acceptors, facilitating the electron transfer. In brief, β-FeOOH/BC adsorbent material could adsorb and oxidize Sb(III), which showed excellent prospects for reducing the risk of Sb(III).

Evaluation of digestate-derived biochar to alleviate ammonia inhibition during long-term anaerobic digestion of food waste

The feasibility of using food waste anaerobic digestate-derived biochar (FWDB) to mitigate ammonia toxicity in an anaerobic digester was evaluated. The optimal conditions for preparing and adding the activated FWDB were explored using response surface experiments, and the long-term effects of adding activated FWDB on digester performance under optimum conditions were verified in semi-continuous experiments. The results showed that the optimal preparation and addition conditions for activated FWDB were pyrolysis temperature of 565 °C, particle size of 0-0.30 mm, and dosage of 15.52 g·L-1. During the long-term operation of the digesters, when the total ammonia nitrogen (TAN) concentration was higher than 2000 mg·L-1, the control and experimental digesters showed deteriorated reactor performance. Volatile fatty acids in the control digester accumulated to 20,306 mg·L-1 after the TAN concentration increased to 3391 mg·L-1, the methane yield decreased to 31 mL·g VS-1, and the digester experienced process failure. In contrast, the experimental digester with added activated FWDB only suffered a slight short-term accumulation of acetate and a slight decline in methane yield. This may be attributed to the adsorption of NH4+/NH3 by activated FWDB, which reduced the TAN concentration in the anaerobic digestion (AD) system and mitigated ammonia toxicity. Microbial analysis and metagenome predictions demonstrated that the community richness, diversity, and evenness, as well as the abundance of acetogens and related key genes (ACSM1, paaF, and acdA) were higher in the experimental digester than in the control digester. This study provides a closed-loop AD enhancement strategy by pyrolysis of digestate and in-situ supplementation into the digester.

Recirculation of activated sludge for coagulant synthesis under hydrothermal conditions

A hypothesis was proposed that the activated sludge was converted into hydrochar full of phenolic hydroxyl and then was made into coagulant by graft copolymerization. The results show that under the addition of HCl, the content of phenolic hydroxyl on the surface of hydrochar (SBC) under hydrothermal conditions increased sharply, up to 1.586 mmol/g, showing that HCl dosage of 0.10 g/g _{dry sludge} and holding time of 4 h was recommended. Under graft copolymerization with the addition of DMC, the coagulant was synthesized. Based on the analysis by FTIR, XPS, zeta potential, etc., the possible synthesis route of coagulant from SBC was that phenolic hydroxyl on SBC was activated by the initiator and then the polymerization between SBC and DMC was triggered. The optimal grafting conditions are gotten. It was named as SBC_{HCl0.10 g, 4 h}-g-DMC_0.7. The removal by SBC_{HCl0.10 g, 4 h}-g-DMC_0.7 on COD and turbidity in domestic wastewater is up to 69% and 93%, respectively. The component of COD indicated that almost all particulate COD and most of colloidal COD are removed. On the contrary, the removal on dissolved COD can be neglected. Most of NH₃-N and P is kept in the wastewater. This is in favor of subsequent reuse and biological treatment.

Synthesis of acidified magnetic sludge-biochar and its role in ammonium nitrogen removal: Perception on effect and mechanism

An acidified magnetic sludge-biochar (MSB) was prepared to enhance ammonium nitrogen (AN) removal efficiency in eutrophic water, and MSB was obtained by secondary pyrolysis of sludge biochar powder. A series of MSB were prepared under 300, 400, 500, 600 °C and different valence states of iron ions by impregnation pyrolysis, which is based on the deposition of unstable iron minerals on biochar matrix. Physicochemical properties of pristine biochar and MSB were revealed through characterization analysis, suggesting that MSB prepared by ferric chloride at 400 °C presented the largest adsorption capacity, and the acid-modification enhanced the ammonium adsorption capacity by 10.7%. Electrostatic attraction and ion-exchange processes were identified as the main adsorption mechanisms of MSB on AN. As the most dominant mechanism, ion exchange of AN with functional groups containing -OH and CO on the surface of MSB resulted in the relative content of -OH (61.3%) and CO (11.5%) bonds reduced to 34.2% and 7.0% respectively. The novel magnetic sludge-biochar with acid-modification possessed enhanced electron transfer capacity, revealing a removal pathway of ammonium by nitrification. The findings above demonstrated that MSB is a promising adsorbent for ammonium removal and can be applied to the natural nitrogen-rich water regulation.

Wood Biochar Enhances the Valorisation of the Anaerobic Digestion of Chicken Manure

In this study, the efficacy of biochar to mitigate ammonia stress and improve methane production is investigated. Chicken manure (CM) was subjected to high-solid mesophilic anaerobic digestion (15% total solid content) with wood biochar (BC). Wood biochar was further treated using HNO3 and NaOH to produce acid–alkali-treated wood biochar (TBC), with an improvement in its overall ammonium adsorption capacity and porosity. Three treatments were loaded in triplicate into the digesters, without biochar, with biochar and with acid–alkali-treated biochar and maintained at 37 °C for 110 days. The study found a significant improvement in CH4 formation kinetics via enhanced substrate degradation, leading to CH4 production of 74.7 mL g−1 VS and 70.1 mL g−1 VS by BC and TBC treatments, compared to 39.5 mL g−1 VS by control treatments on the 28th day, respectively. However, only the use of TBC was able to prolong methane production during the semi-inhibition phase. The use of TBC also resulted in the highest removal of total ammonia nitrogen (TAN) of 86.3%. In addition, the treatment with TBC preserved the highest microbial biomass at day 110. The presence of TBC also resulted in an increase in electrical conductivity, possibly promoting DIET-mediated methanogenesis. Overall, the acid–alkali treatment of biochar can be a novel approach to improve biochar’s existing characteristics for its utilisation as an additive in anaerobic digestion.

Improvement in the physicochemical characteristics of biochar derived from solid digestate of food waste with different moisture contents

The management of digestate from food waste (DFW) has become a worldwide challenge. Pyrolysis is a promising technology to generate biochar from the DFW. However, unlike other biomass, DFW usually has high salt and moisture content, which affects the properties of biochar generated from pyrolysis. The characteristics of biochar derived from DFW with different MCs (5%, 20%, 40%, and 60%) were investigated in the present study. It was found that more micropore and mesopore structures were generated in the biochar with the increase of MC from 5% to 60%, resulting in the Brunauer-Emmett-Teller surface area of the biochar increased from 89.23 m² g^-1 to 117.75 m² g^-1. The MC could also promote the variation of oxygen-containing functional groups and the generation of amorphous carbon structures, which are beneficial for the adsorption property of the biochar. Pyrolysis could stabilize the metals in the biochar, while MC has little effect on the metal speciations. These results provide fundamental information on the impact of MC on the properties of biochar derived from DFW and are important for the optimization of the pre-drying process.

Biodegradation of Congo red dye using polyurethane foam-based biocarrier combined with activated carbon and sodium alginate: Batch and continuous study

Dyes are an important class of organic pollutants and are well known for their adverse effects on aquatic life and human beings. In this work, an effort has been made to treat the dye-containing wastewater using modified biocarriers in packed bed bioreactors (PBBRs). Lysinibacillus sp. immobilized polyurethane foam combined with activated carbon and sodium alginate was used for the biodegradation of Congo red dye. The optimum values of process time, glucose concentration, and dye concentration were obtained to be 4.0 days, 2.0 g/L, and 50 mg/L, respectively. The maximum dye removal efficiency (RE) of 92.63 % was obtained at the optimized conditions. The continuous PBBR offered a maximum RE and elimination capacity of 90.73% and 10.89 mg/L. d, respectively, at an inlet loading rate of 12 mg/L. d. Moreover, the growth kinetic of Lysinibacillus sp. was well predicted by the Andrew-Haldane model with a regression coefficient of 0.98.

Zero waste multistage utilization of Ginkgo biloba branches

Zero waste multistage utilization of biomass from Ginkgo biloba branches (GBBs) was achieved through extraction of bioactive components, analysis of antioxidant and antibacterial activities, preparation and composition of pyrolyzate, adsorption and reuse of modified biochar. The results showed that GBBs had abundant bioactive components for potential application in the industry of food, chemical raw materials and biomedicine. Especially, the bioactive compounds in acetone extract (10 mg/mL) of GBBs identified by DPPH and ABTS had free radical scavenging abilities of 92.28% and 98.18%, respectively, which are equivalent to Vitamin C used as an antioxidant in food additives. Fourier Transform Infrared and X-Ray Diffraction analysis showed that carboxymethyl cellulose (CMC) and magnetic Fe₃O₄ were successfully incorporated into raw biochar (RB) to form CMC-Fe₃O₄-RB nanomaterial. Scanning electron microscopy and X-Ray Diffraction spectroscopy displayed Fe, C, and O existed on the surface of CMC-Fe₃O₄-RB. Compared with RB, CMC-Fe₃O₄-RB had a larger specific surface area, pore volume and pore size. Meanwhile, nanomagnetic CMC-Fe₃O₄-RB solved the problem of agglomeration in traditional magnetized biochar production, and improved the adsorption capacity of Pb²⁺, which was 29.90% higher than that of RB by ICP-OES. Further, the Pb²⁺ (10 mg/L) adsorption capacity of CMC-Fe₃O₄-RB reached the highest level in 2 h at the dosage of 0.01 g/L, and remained stable at 52.987 mg/g after five cycles of adsorption and desorption. This research aided in the creation of a strategy for GBBs zero waste multistage usage and a circular economic model for GBBs industry development, which can be promoted and applied to the fields of food industry and environment improvement.

Adsorption behavior and performance of ammonium onto sorghum straw biochar from water

Sorghum has been widely used for liquor production and brewing, but how to make efficiently utilize sorghum straw (SS) has become an urgent problem. Meanwhile, the wastewater produced by winemaking is typical organic wastewater with a high ammonium concentration. To solve the problem of resource utilization of SS and remove ammonium from water, SS was used to prepare biochar as an adsorbent for ammonium adsorption. Batch adsorption experiments were carried out to study the influencing factors and adsorption mechanisms of ammonium onto sorghum straw biochar (SSB). The results showed that the adsorption capacity of SSB was much higher than that of SS. The SSB pyrolyzed at 300 °C had the highest adsorption capacity. The favorable pH was 6–10, and the optimal dosage was 2.5 g/L. The adsorption process and behavior conformed to the pseudo-second-order kinetic and Langmuir isotherm adsorption models. The maximum ammonium adsorption capacity of SSB at 45 °C was 7.09 mg/g, which was equivalent to 7.60 times of SS. The ammonium adsorption of SS and SSB was mainly chemical adsorption. The regeneration test indicated that SSB had good regeneration performance after three adsorption-regeneration cycles. This work suggests that SSB could be potentially applied to sewage treatment containing ammonium to achieve the purpose of resource recycling.

Removal of emerging contaminants (bisphenol A and antibiotics) from kitchen wastewater by alkali-modified biochar

Using current wastewater treatment technologies, it can be challenging to remove the emerging contaminants (ECs) present in kitchen wastewater (KW) of complex compositions and high organic content. In this study, biochar, derived from straw, was modified as an adsorbent to remove ECs such as bisphenol A (BPA), tetracycline (TC) and ofloxacin (OFL) from a complex KW system. An alkali-modified biochar, having larger specific surface areas and stronger hydrophobicity, was found to exhibit a higher adsorption capacity, with more than 95% of the target ECs being removed. Indeed, in a static operation mode, the alkali-modified biochar had maximum adsorption capacities of 71.43, 101.01 and 54.05 mg/g for BPA, TC, and OFL, respectively. The adsorption kinetics and isotherms models indicated that the adsorption process was controlled by chemisorption, as well as the monolayer adsorption of contaminants onto the external and internal surfaces of the alkali-modified biochar. The adsorption of TC and OFL was significantly affected by the initial pH values of KW. However, the presence of different environmental factors (COD, NH₄⁺ and PO₄^3-) had little effects on the adsorption of the contaminants. The alkali-modified biochar was further tested in a fixed-bed column where the maximum dynamic adsorption capacities for BPA and OFL were 55 and 45 mg/g, representing about 75% and 83% of the static saturated adsorption capacities. These findings can be of major significance for the application of alkali-modified biochar in the removal of ECs from complex KW systems.

Pyrolysis of Solid Digestate from Sewage Sludge and Lignocellulosic Biomass: Kinetic and Thermodynamic Analysis, Characterization of Biochar

This study investigates the pyrolysis behavior and reaction kinetics of two different types of solid digestates from: (i) sewage sludge and (ii) a mixture of sewage sludge and lignocellulosic biomass—Typha latifolia plant. Thermogravimetric data in the temperature range 25–800 °C were analyzed using Flynn–Wall–Ozawa and Kissinger–Akahira–Sunose kinetic methods, and the thermodynamic parameters (ΔH, ΔG, and ΔS) were also determined. Biochars were characterized using different chemical methods (FTIR, SEM–EDS, XRD, heavy metal, and nutrient analysis) and tested as soil enhancers using a germination test. Finally, their potential for biosorption of NH4+, PO43−, Cu2+, and Cd2+ ions was studied. Kinetic and thermodynamic parameters revealed a complex degradation mechanism of digestates, as they showed higher activation energies than undigested materials. Values for sewage sludge digestate were between 57 and 351 kJ/mol, and for digestate composed of sewage sludge and T. latifolia between 62 and 401 kJ/mol. Characterizations of biochars revealed high nutrient content and promising potential for further use. The advantage of biochar obtained from a digestate mixture of sewage sludge and lignocellulosic biomass is the lower content of heavy metals. Biosorption tests showed low biosorption capacity of digestate-derived biochars and their modifications for NH4+ and PO43− ions, but high biosorption capacity for Cu2+ and Cd2+ ions. Modification with KOH was more efficient than modification with HCl. The digestate-derived biochars exhibited excellent performance in germination tests, especially at concentrations between 6 and 10 wt.%.

Engineered biochars for recovering phosphate and ammonium from wastewater: A review

Biochar has gained great scientific attention as a promising agent for agricultural and environmental applications. A variety of biochars with excellent properties such as high porosity, surface area and functional groups have been developed for nutrients recovery from wastewater. Compared to pristine biochar, engineered biochar with enlarged surface area and abundant functional groups has been prepared which shows a new type of carbon-based material with enhanced adsorption potential for nutrients in wastewater. To date, a few reviews have been specifically focused on several important aspects of engineered biochar, such as its application to recover phosphate and ammonium from wastewater and subsequent use as a slow-release fertilizer. In this work, novel modification/treatment methods including activation with acid/alkali, functionalization with amides, thiols and oxidizing agents, metal salt impregnation, loading with various minerals and carbon-based materials are reviewed for preparing engineered biochar with improved adsorption capacity. Various sources of biomass for producing biochars were estimated, and the intrinsic characteristics and potential of biochar products for simultaneous recovery/removal of phosphate and ammonium from wastewater were evaluated. Relevant interaction mechanisms of phosphate and ammonium adsorption on engineered biochars have been discussed in details. Finally, important future prospects as well as industrial/commercial-scale application of engineered biochars for phosphate and ammonium recovery from wastewater have been emphasized. We believe that this review will provide broad scientific opportunities for thorough understanding of applying engineered biochar as a low-cost and environmentally sustainable material for nutrients recovery from wastewater.

Simultaneous removal of nitrate and diethyl phthalate using a novel sponge-based biocarrier combined modified walnut shell biochar with Fe3O4 in the immobilized bioreactor

A novel biological carrier combining sponge and modified walnut shell biochar with Fe₃O₄ (MWSB@Fe₃O₄) was fabricated to achieve simultaneous removal of nitrate and diethyl phthalate (DEP). The optimal reaction conditions of the immobilized bioreactor were: carbon to nitrogen (C/N) ratio of 1.5, Fe²⁺ concentration of 20 mg L^-1, and hydraulic retention time (HRT) of 8 h. Under the optimal conditions and DEP concentration of 800 μg L^-1, the highest removal efficiency of DEP and nitrate in the immobilized bioreactor with the novel biological carrier were 67.87% and 83.97% (68.43 μg L^-1 h^-1 and 1.71 mg L^-1 h^-1), respectively. Scanning electron microscopy (SEM) showed that the novel biological carrier in this study carried more bio-sediments which is closely related to the denitrification efficiency. The gas chromatography (GC) data showed that the nitrogen production of the immobilized bioreactor (99.85%) was higher than that of another experimental group (97.84%). Fluorescence excitation-emission matrix (EEM) and Fourier transform infrared spectrometer (FTIR) indicated the immobilized bioreactor emerged more extracellular polymeric substances (EPS) which was related to favourable biological stability under the DEP environment. Moreover, according to high-throughput sequencing data, the Zoogloea sp. L2 responsible for iron-reduction and denitrification was the main strain in this immobilized bioreactor.

Temperature-dependent magnesium citrate modified formation of MgO nanoparticles biochar composites with efficient phosphate removal

Nano-MgO biochar composites (nMBCs) have been considered as potential adsorbents for phosphate removal from aqueous solution. It is an effective strategy to improve P removal efficiency that adjustment of the size, distribution and crystallinity of MgO particles embedded into the carbon matrix. Herein, we prepared a highly efficient phosphate adsorbent by co-pyrolysis of lotus seedpod and magnesium citrate and studied its adsorption mechanisms. Results showed that the uniformly dispersed MgO nanoparticle was formed on the surface of nMBCs with the temperature increasing, with the particles size ranging from 3 to 10 nm. Furthermore, high temperature promoted the formation of a large amount of reactive lattice oxygen, which was demonstrated to be the main active adsorption site, thus the phosphate immobilization capacity of nMBCs was greatly improved with the pyrolysis temperature increasing from 450 °C to 750 °C. Besides, some stable CO bonds were formed due to the catalysis of Mg²⁺, which could bond to HPO₄^2-/H₂PO₄^- by hydrogen bond, enhancing the adsorption performance. The isotherm adsorption experiment showed that MBC-750 achieved an excellent phosphorus adsorption amount of 452.752 mg-P/g. The effectiveness of nMBCs is enhanced and a method for producing an effective nanocomposite adsorbent material for removing phosphate from wastewater is provided.

Preparation of magnetic biochar and its application in catalytic degradation of organic pollutants: A review

In recent years, magnetic biochar (MBC) has been greatly concerned because of its magnetic separation characteristics, and has been successfully used as a catalyst in the catalytic degradation of organic pollutants. However, there is currently a lack of a more systematic summary of MBC preparation methods, and no detailed overview of the catalytic mechanism of MBC catalysts for the degradation of organic pollutants. Therefore, we carry out this work to fill the above gaps. At first, we summarize the raw materials, preparation methods, and types of MBC in detail, and emphasize the MBC prepared by iron-containing sludge. Then, the catalytic mechanisms of MBC in peroxydisulfate, peroxymonosulfate, Fenton-like, photocatalysis, and NaBH₄ systems are carefully summarized, highlighting the contribution of various parts of MBC in catalysis. The degradation efficiency of organic pollutants in the above systems is evaluated. Finally, the stability and reusability of MBC catalysts are evaluated. In conclusion, this review contributes a meager force to the future development of MBC.

Coexistence of polyethylene microplastics and biochar increases ammonium sorption in an aqueous solution

Biochar is used to remove ammonium (NH₄⁺) from wastewater, where microplastics are emerging pollutants. However, whether microplastics can adsorb NH₄⁺ or how they will affect the sorption of NH₄⁺ by biochars have not been studied. Here, batch sorption kinetics and isotherm experiments were conducted to elucidate the sorption of NH₄⁺ on a manure biochar (MBC), a straw biochar (SBC), a wood sawdust biochar (WBC), a polyethylene microplastic (PE), and their combination. The results showed that PE had a smaller sorption capacity (Q_max = 3.29 mg g^-1) but a faster adsorption rate (k_s = 0.08 g (mg min)^-1) for NH₄⁺ than biochars (Q_max = 5.67 ~ 20.54 mg g^-1; k_s = 0.02 ~ 0.04 g (mg min)^-1). When PE and biochars coexisted in an aqueous solution, the NH₄⁺ sorption capacity was increased by 17.0% in PE+SBC, 7.1% in PE+MBC, and 8.6% in PE+WBC, which likely due to the deprotonation of functional groups and the decreases in small molecular-size dissolved organic carbon. We conclude that microplastics can adsorb NH₄⁺; moreover, they can enhance the NH₄⁺ sorption capacity of biochars. Therefore, when biochar is used for NH₄⁺ removal from wastewater, the interaction of biochar and microplastics needs to be considered.

Fuel, thermal and surface properties of microwave-pyrolyzed biochars depend on feedstock type and pyrolysis temperature

We evaluated the fuel, thermal and surface properties of twelve biochars produced from three lignocellulosic (canola straw, sawdust, wheat straw) and one non-lignocellulosic feedstock (manure pellet) pyrolyzed at three temperatures using a microwave. Regardless of feedstock type, increasing pyrolysis temperature progressively reduced the abundance of -OH functional group and yield, but increased pH and thermal stability of biochar. Gross calorific values (GCV), carbon stability, and degree of aromaticity of biochars derived from lignocellulosic feedstocks increased with increasing temperature due to decreased elemental oxygen content. However, high ash content in the non-lignocellulosic feedstock retarded its thermal degradation, producing biochars with low GCV. The specific surface area of biochars was low, with the highest value of 43 m² g^-1 achieved for sawdust biochar produced at 500 °C. We conclude that the fuel, thermal, and surface properties of the biochars were dependent on the feedstock type and pyrolysis temperature.

Preparation of natural rubber based semi-IPNs superabsorbent and its adsorption behavior for ammonium

In this study, a natural rubber (NR) based amphiphilic semi-interpenetrating polymer network (semi-IPN) superabsorbent hydrogel was designed and synthesized with natural rubber-graft-poly (acrylic acid-co-acrylamide) [NR-g-P(AA-co-AM)] network and linear poly (diallyldimethyl ammonium chloride) (PDADMAC). Through a series of characterization and test, the structure, morphology, thermal properties, biodegradation, and swelling properties of NR-g-P(AA-co-AM)/PDADMAC were determined. Subsequently, NR-g-P(AA-co-AM)/PDADMAC was used for ammonium adsorption to remove ammonium nitrogen in aqueous solution. The adsorption behavior of the absorbent was also studied. Results showed that the maximum water absorbency of NR-g-P(AA-co-AM)/PDADMAC was 112.04 ± 6.55 g/g and water retention capacity of soil with the superabsorbent was 115.62 ± 2.08%. The NH₄⁺ adsorption quickly reached equilibrium and the maximum adsorption capacity was 13.02 mmol g^-1 calculated from Langmuir isotherm model. The results suggest that the product is efficient for ammonium removal and can be used as water-retaining agents.

Remediation of Soil Polluted with Cd in a Postmining Area Using Thiourea-Modified Biochar

Cadmium presence in soil is considered a significant threat to human health. Biochar is recognized as an effective method to immobilize Cd ions in different soils. However, obtaining effective and viable biochar to remove elevated Cd from postmining soil remains a challenge. More modifiers need to be explored to improve biochar remediation capacity. In this investigation, pot experiments were conducted to study the effects of poplar-bark biochar (PBC600) and thiourea-modified poplar-bark biochar (TPBC600) on Cd speciation and availability, as well as on soil properties. Our results showed that the addition of biochar had a significant influence on soil properties. In the presence of TPBC600, the acid-soluble and reducible Cd fractions were transformed into oxidizable and residual Cd fractions. This process effectively reduced Cd bioavailability in the soil system. Compared to PBC600, TPBC600 was more effective in improving soil pH, electrical conductivity (EC), organic matter (SOM), total nitrogen (TN), ammonium nitrogen (NH4+-N), nitrate nitrogen (NO3−-N), available potassium (AK), available phosphorus (AP), and available sulfur (AS). However, this improvement diminished as incubation time increased. Results of Pearson correlation analysis, multivariate linear regression analysis, and principal component analysis showed that soil pH and available phosphorus played key roles in reducing the available cadmium in soil. Therefore, TPBC600 was shown to be an effective modifier that could be used in the remediation of soil polluted with Cd.

Regular Biochar and Bacteria-Inoculated Biochar Alter the Composition of the Microbial Community in the Soil of a Chinese Fir Plantation

Biochar is a promising material for the improvement of soil quality. However, studies on biochar have mostly been carried out in laboratory conditions or have focused on agricultural aspects. The impacts of the application of biochar on soil characteristics and related ecological processes of the forest ecosystem have not been fully resolved. In this study, we investigated the effects of regular biochar and bacteria-loaded biochar on the microbial communities in the bulk soil and the rhizosphere soil of an annual Chinese fir plantation. In early spring (April), the two types of biochar were added to the soil at the rates of 2.22 t·ha−1, 4.44 t·ha−1, 6.67 t·ha−1, 8.89 t·ha−1, and 11.11 t·ha−1 by ring furrow application around the seedlings, and soil samples were collected at the end of autumn (November). The results showed that biochar addition increased the soil nutrient content and promoted the growth and diversity of soil microbial communities. The diversity of soil fungi was significantly increased, and the diversity of soil bacteria was significantly decreased. Principal component analysis under the different biochar types and application rates demonstrated that microbial communities differed significantly between the treatments and controls and that the effect of biochar on the microbial community of the bulk soil was more significant than that of the rhizosphere soil. Under the same dosage, the effect of bacteria-loaded biochar on soil was more significant than that of regular biochar.