Effects of sludge thermal-alkaline pretreatment on cationic red X-GRL adsorption onto pyrolysis biochar of sewage sludge

Biochar Applications for Efficient Removal of Energetic Compound Contaminants

Military activities and the production or disposal of ammunition often lead to soil contamination with energetic compounds (ECs) such as dinitrotoluene, trinitrotoluene, and hexogen, posing significant threats to human health and the ecosystem. Biochar has emerged as a cost-effective and widely available solution for remediating contaminated sites characterized by its capacity for pollutant removal through adsorption and conversion process, along with minimal secondary pollution. This paper provides a comprehensive review of relevant literature on biochar's efficacy in eliminating ECs, including an analysis of the underlying mechanisms. The discussion addresses challenges and opportunities associated with biochar application in ECs remediation, offering insights for future research directions. In summary, the use of biochar for ECs removal presents a promising and eco-friendly approach, facilitating the remediation of contaminated sites while promoting soil function and ecosystem recovery.

Iron-based materials functionalized with carbon and phosphorus recovered from sludge enhanced the formation of stable minerals to passivate lead and chromium in wastewater and soil

The bioaccumulation and toxicity of heavy metals are serious threats to human activities and ecological health. The exploitation of environmentally friendly passivated materials is major importance for the remediation of heavy metal contaminated soil. This research developed a new type of environmental functional material with a core-shell structure, which is an iron-based material functionalized with phosphorus and carbon from sludge for heavy metal pollution remediation. The results indicated that the C/P@Fe exhibits excellent heavy metal removal ability, and the maximum removal rates of the two heavy metals in simulated wastewater could reach 100% under optimum reaction conditions. It also effectively converts the labile Cr/Pb into the stable fraction after 28 days of incubation, which increased the maximum residual fraction percentage of Cr and Pb by 32.43% and 160% in soil. Further analysis found that the carbon layer wrapped around the iron base could improve the electron transport efficiency of reducing iron, phosphorus and ferrum could react with heavy metal ions to form stable minerals, such as FeCr2O4, FeO·Cr2O3, Pb5(PO4)3OH, PbCO3, 2PbCO3·Pb(OH)2 and PbS, after reacting with C/P@Fe. The study demonstrated that the Iron-based materials functionalized with carbon and phosphorus from sludge provided a more efficient way to remove heavy metals.

Optimizing adsorption performance of sludge-derived biochar via inherent moisture-regulated physicochemical properties

Understanding the impact of abundant inherent moisture in sewage sludge on the physicochemical properties and adsorption applications of sludge-derived biochar (SDB) contributed significantly to promoting economical sludge reuse. The moisture (0-80%) contributed to the development of micropore and mesopore in SDB at 400 °C, resulting in a maximum increase in specific surface area (SSA) and total pore volume (TPV) of SDB by 38.47% (84.811-117.437 m2/g) and 92.60% (0.0905-0.1743 m3/g), respectively. At 600/800 °C, moisture only facilitated mesopore formation, while was exacerbated with increasing moisture content. Despite reduction in SSA during this stage, TPV increased by a maximum of 20.47% (0.1700-0.2048 m3/g). The presence of moisture during pyrolysis led to an increase in the formation of 3-5 thickened benzene rings and defective structures in SDB, along with more C=O, O-C=O/-OH, pyrrole N, pyridine N, and thiophene. As a result, moisture (40%/80%) increased the maximum adsorption capacity (76.2694-88.0448/90.1190 mg/g) of SDB (600 °C) for tetracycline, mainly due to enhanced pore filling effect and hydrogen bonding induced by improved physicochemical properties. This study offered a novel approach for optimizing the performance of SDB adsorption applications by manipulating the sludge moisture, which is critical for practical sludge management.

All-in-one strategy to prepare molded biochar with magnetism from sewage sludge for high-efficiency removal of Cd(Ⅱ)

Biochar in powder could lead to the separation difficulties after using and easy dispersion by wind with non-necessary consumption during the practical application. The current method for preparing molded biochar is multi-step, tedious, and required exogenous reagents. Moreover, the dehydration of sewage sludge with high water content (>85%) causes expensive production cost, limiting its secondary utilization. Therefore, an "all-in-one" strategy was developed to prepare molded biochar with magnetism by using sewage sludge as endogenetic binder, water source, carbon source, as well as magnetic source, and biomass wastes as water moderator and pore-forming agent. The molded biochar showed high removal capacity towards Cd(Ⅱ) of 456.2 mg/g, which was 6 times higher than the commercial activated carbon in powder (69.1 mg/g). The excellent removal performance of the molded biochar was in linear correlation the O/C ratio (R² =0.855), resulting in the complexation with Cd(Ⅱ). DFT calculations indicated the amounts and species of oxygen changed the electron distribution and electron-donation properties of biochar for Cd(Ⅱ). Moreover, the Na⁺ exchanges with Cd(Ⅱ) were also an important removal mechanism. This study provided a novel synthesis strategy for the molded biochar with both high particle density and high adsorption capability.

Hydrothermal synthesis of sewage sludge biochar for activation of persulfate for antibiotic removal: Efficiency, stability and mechanism

The use of biochar materials as catalysts to activate persulfate (PS) for the degradation of antibiotics has attracted much attention. In this study, a carbonaceous material (Cu/Zn-SBC) was prepared from sewage sludge by hydrothermal modification. The efficiency of PS activation by Cu/Zn-SBC was investigated using tetracycline (TC) as the model antibiotic. In the Cu/Zn-SBC + PS system, the TC removal rate reached 90.13% at 10 min and exceeded 99% within 4 h. This not only met the requirement of removing large amounts of pollutants in a short time but also achieved the complete removal of pollutants in the subsequent time. Additionally, the Cu/Zn-SBC + PS system was found to be dominated by radical and nonradical pathways. Cu, hydroxyl and carboxyl groups on the surface of Cu/Zn-SBC promoted the production of free radicals and non-free radicals. Under several changes in reaction conditions and water environment factors, the TC removal rate remained above 85% within 10 min. Furthermore, the removal rate of TC was still 85.79% when Cu/Zn-SBC combined with PS was reused twice and 77.14% when reused four times. This study provides an ideal solution for the treatment of sewage sludge, and offers a stable and efficient material for removing antibiotics from wastewater.

A critical review on utilization of sewage sludge as environmental functional materials

Sewage sludge (SS) is increasingly used as an environment functional material to reduce or control pollution and improve plant growth because of the large amounts of carbon and essential plant nutrients in it. To achieve the best application results, it is essential to comprehensively review recent progress in SS utilization. This review aims to fill the gaps in knowledge by describing the properties of SS, and its usage as adsorbents, catalysts and fertilizers, and certain application mechanisms. Although SS generates several benefits for the environment and humans, many challenges still exist to limit the application, including the risks posed by potentially toxic substances (e.g., heavy metals) in SS. Therefore, future research directions are discussed and how to make SS applications more feasible in terms of technology and economy.

A sustainable reuse strategy of converting waste activated sludge into biochar for contaminants removal from water: Modifications, applications and perspectives

Conversion of sewage sludge to biochar for contaminants removal from water achieves the dual purpose of solid waste reuse and pollution elimination, in line with the concept of circular economy and carbon neutrality. However, the current understanding of sludge-derived biochar (SDB) for wastewater treatment is still limited, with a lack of summary regarding the effect of modification on the mechanism of SDB adsorption/catalytic removal aqueous contaminants. To advance knowledge in this aspect, this paper systematically reviews the recent studies on the use of (modified) SDB as adsorbents and in persulfate-based advanced oxidation processes (PS-AOPs) as catalysts for the contaminants removal from water over the past five years. Unmodified SDB not only exhibits stronger cation exchange and surface precipitation for heavy metals due to its nitrogen/mineral-rich properties, but also can provide abundant catalytic active sites for PS. An emphatic summary of how certain adsorption removal mechanisms of SDB or its catalytic performance in PS-AOPs can be enhanced by targeted regulation/modification such as increasing the specific surface area, functional groups, graphitization degree, N-doping or transition metal loading is presented. The interference of inorganic ions/natural organic matter is one of the unavoidable challenges that SDB is used for adsorption/catalytic removal of contaminants in real wastewater. Finally, this paper presents the future perspectives of SDB in the field of wastewater treatment. This review can contribute forefront knowledge and new ideas for advancing sludge treatment toward sustainable green circular economy.

Conversion of Industrial Sludge into Activated Biochar for Effective Cationic Dye Removal: Characterization and Adsorption Properties Assessment

This paper presents an in-depth characterization of a raw industrial sludge (IS-R) and its KOH-activated biochar pyrolyzed at 750 °C (IS-KOH-B) followed by their application to remove a cationic dye from aqueous solution. Materials characterization shows that compared to the IS-R, the IS-KOH-B has improved structural, textural, and surface chemical properties. In particular, the IS-KOH-B’s BET surface area and total pore volume are about 78 and 6 times higher than those found for the IS-R, respectively. The activated biochar efficiently retained the cationic dye under wide experimental conditions. Indeed, for an initial dye concentration of 50 mg L−1, removal yields were assessed to be more than 92.5%, 93.5%, and 97.8% for a large pH range (4–10), in the presence of high contents of competing cations (3000 mg L−1 of Ca2+, Mg2+, Na+, and K+), and a low used adsorbent dose (1 g L−1), respectively. The Langmuir’s adsorption capacities were 48.5 and 65.9 mg g−1 for of IS-R and IS-KOH-B, respectively, which are higher than those reported for various adsorbents in the literature. The dye removal was found to be monolayer, spontaneous, and endothermic for both the adsorbents. Moreover, this removal process seems to be controlled by chemical reactions for IS-KOH-B whereas by both physico–chemical reactions for IS-R. This study demonstrates that the raw industrial sludge and especially its KOH-activated derived biochar could be considered as promising adsorbents for the removal of dyes from aqueous solutions.

Recent advances in biochar technology for textile dyes wastewater remediation: A review

With the continuous rise of industrialization and agriculture, the concentration of organic contaminants such as dyes in the ecosystem has increased in subsequent years, causing major environmental contamination. Adsorption has been revealed to be a reliable and cost-effective way of eliminating organic pollutants. Biochar technology has the potential of converting trash into treasure when utilized for environmental remediation since it has numerous benefits such as the availability of diverse types of raw materials, low cost, and reusability. The potential of biochar as an adsorbent, support for catalysis, and a composite catalyst for dye degradation and mineralization is summarized in this research. It discusses its current research status in the adsorption and degradation of various dyes, incorporates the pertinent adsorption variables, encapsulates its regeneration techniques, investigates its engineering applications, and finally analyses limitations and discusses future development prospects.

Effects of temperature and total solid content on biohydrogen production from dark fermentation of rice straw: Performance and microbial community characteristics

Semi-continuous experiments were carried out in lab-scale continuous stirred tank reactors to evaluate the effects of fermentation temperature (37 ± 1 °C and 55 ± 1 °C) and total solids (TS) contents (3 %, 6 %, and 12 %) on biohydrogen production from the dark fermentations (DF) of rice straw (RS) and the total operation duration was 105 days. The experimental results show that biohydrogen production (0.46-63.60 mL/g VS_added) from the thermophilic (55 ± 1 °C) DF (TDF) was higher than the mesophilic (37 ± 1 °C) DF (MDF) (0.19-2.13 mL/g VS_added) at the three TS contents, and achieved the highest of 63.60 ± 2.98 mL/g VS_added at TS = 6 % in TDF. The pH, NH₄⁺-N and total volatile fatty acid of fermentation liquids in the TDF were all higher than those in the MDF. The high abundance of lactic acid-producing bacteria resulted in low biohydrogen produced at TS = 3 %. Under the TDF with TS = 6 %, the highest abundance of hydrolytic bacteria (Ruminiclostridium 54.24 %) led to the highest biohydrogen production. The increase of TS content from 6 % to 12 % induced degradation pathway changes from biohydrogen production to methane production. This study demonstrated that butyric acid fermentation was the main pathway to produce biohydrogen from RS in both DFs.

Novel insights into the adsorption of organic contaminants by biochar: A review

With rising concerns in the practical application of biochar for the remediation of environment influenced by various organic contaminants, a critical review to facilitate insights the crucial role that biochar has played in wastewater and polluted soil decontamination is urgently needed. This research therefore aimed to describe different intriguing dimensions of biochar interactions with organic contaminants, which including: (i) an introduction of biochar preparation and the related physicochemical properties, (ii) an overview of mechanisms and factors controlling the adsorption of organic contaminants onto biochar, and (iii) a summary of the challenges and an outlook of the further research needs in this issue. In the light of the survey consequences, the appearance of biochar indicates the potential in substituting the existing costly adsorbents, and it has been proved that biochar is one promising adsorbent for organic pollutants adsorption removal from water and soil. However, some research gaps, such as dynamic adsorption, potential environmental risks, interactions between biochar and soil microbes, novel modification techniques, need to be further investigated to facilitate its practical application. This research will be conductive to better understanding the adsorption removal of organic contaminants by biochar.

Application of layered double hydroxide-biochar composites in wastewater treatment: Recent trends, modification strategies, and outlook

In recent years, layered double hydroxide-biochar (LDH-BC) composites as adsorbents and catalysts for contaminants removal (inorganic anions, heavy metals, and organics) have received increasing attention and became a new research point. It is because of the good chemical stability, abundant surface functional groups, excellent anion exchange ability, and good electronic properties of LDH-BC composites. Hence, we offer an overall review on the developments and processes in the synthesis of LDH-BC composites as adsorbents and catalysts. Special attention is devoted to the strategies for enhancing the properties of LDH-BC composites, including (1) magnetic treatment, (2) acid treatment, (3) alkali treatment, (4) controlling metal ion ratios, (5) LDHs intercalation, and (6) calcination. In addition, further studies are called for LDH-BC composites and potential areas for future application of LDH-BC composites are also proposed.

(Im)mobilization of arsenic, chromium, and nickel in soils via biochar: A meta-analysis

Biochar is a promising immobilizing agent of trace elements (TEs) in contaminated soils. However, several contradictory results have been reported regarding the potential of biochar to immobilize arsenic (As), chromium (Cr), and nickel (Ni) in contaminated soils. We conducted a meta-analysis on the published papers since 2006 until 2019 to examine the effects of biochar on the chemical (im)mobilization of As, Cr, and Ni in contaminated soils and to elucidate the major factors that control their interactions with biochar in soil. We synthesized 48 individual papers comprised of a total of 9351 pairwise comparisons and used the statistical tool of Cohen's d as an appropriate effect size for the comparison between means. We found that the application of biochar often increased the As mobilization in soils. Important variables that modulated the biochar effects on As mobilization in soil were pyrolysis temperature and time (ranging between 8 and 16 times when T > 450 °C and t > 1hr), organic matter (7-16 times when SOM<3%) and further site conditions. In contrast to As, biochar efficiently immobilized Cr and Ni in contaminated soils. The extent of the Cr and Ni immobilization was determined by the feedstock (Cr: 7-18 times for agricultural residue-derived biochar; Ni: 13-32 times for woody biomass-derived biochar). Our meta-analysis provides a compilation on the potential of different types of biochar to reduce/increase the mobilization of As, Cr, and Ni in various soils and under different experimental conditions. This study provides important insights on factors that affect biochar's efficiency for the (im)mobilization of As, Cr, and Ni in contaminated soils. While biochar effectively immobilizes Cr and Ni, a proper management of As-polluted soils with pristine biochar is still challenging. This limitation might be overcome by modification of biochar surfaces to exhibit higher surface area and functionality and active sites for surface complexation with TEs.

Preparation of ultrahigh-surface-area sludge biopolymers-based carbon using alkali treatment for organic matters recovery coupled to catalytic pyrolysis

In this work, we employed waste activated sludge (WAS) as carbon source to prepare ultrahigh specific surface area (SSA) biopolymers-based carbons (BBCs) through alkali (KOH) treatment coupled to pyrolysis strategy. Before the pyrolysis process, the involvement of KOH made a great recovery of soluble biopolymers from WAS, resulting in highly-efficient catalytic pyrolysis. The Brunner-Emmett-Teller and pore volume of BBCs prepared at 800°C (BBC₈₀₀) reached the maximum at 2633.89 m²·g^-1 and 2.919 m³·g^-1, respectively. X-ray photoelectron spectroscopy suggested that aromatic carbon in the form of C=C was the dominant fraction of C element in BBCs. The N element in BBCs were composed of pyrrolic nitrogen and pyridinic nitrogen at 700°C, while a new graphitic nitrogen appeared over 800°C. As a refractory pollutant of wastewater treatment plants, tetracycline (TC) was selected to evaluate adsorption performance of BBCs. The adsorption behavior of BBCs towards TC was conformed to the pseudo-second-order kinetic and the Langmuir models, signifying that chemisorption of monolayers was dominant in TC adsorption. The adsorption capacity of BBC₈₀₀ reached the maximum at 877.19 mg·g^-1 for 90 min at 298 K. Thermodynamic analysis indicated that the adsorption process was endothermic and spontaneous. Hydrogen bonding and π-π stacking interaction were mainly responsible for TC adsorption, and interfacial diffusion was the main rate-control step in adsorption process. The presence of soluble microbial products (SMPs) enhanced TC removal. This work provided a novel strategy to prepare bio-carbon with ultrahigh SSA using WAS for highly-efficient removal of organic pollutants.

A novel, efficient and sustainable magnetic sludge biochar modified by graphene oxide for environmental concentration imidacloprid removal

Environmental concentration imidacloprid (IMI) has become a potential risk to ecological safety and human health, therefore an efficient, sustainable and environment friendly approach was urgently needed for its removal. In this study, a novel graphene oxide supported magnetic sludge biochar composite (GO/CoFe₂O₄-SBC) was first time synthesized and assessed for IMI removal at environmental concentration level. The maximum adsorption capacity of GO/CoFe₂O₄-SBC for IMI was 8.64 × 10³ μg g^-1. Physicochemical characteristics, kinetics (pseudo-second-order), isotherms (Freundlich and Temkin), thermodynamics and environmental factors analysis suggested that its outstanding adsorption performance was mainly attributed to pore filling, π-π conjugation and functional groups interaction. The mechanisms analysis indicated that intraparticle diffusion was the main rate-limiting step and its adsorption was a spontaneous, endothermic and randomness increased process. The magnetic sensitivity enabled it to be easily separated from water. The sustainable adsorption capacity (>90% of the initial adsorption capacity) of GO/CoFe₂O₄-SBC was well maintained by ethanol extraction even after five reuse cycles. GO/CoFe₂O₄-SBC also exhibited environmental security with its leaching concentrations of Fe and Co were below 0.5 mg L^-1 in a wide pH range. The performance of GO/CoFe₂O₄-SBC suggested that it could be served as a promising adsorbent for environmental concentration IMI removal.

Biochar produced from the co-pyrolysis of sewage sludge and waste tires for cadmium and tetracycline adsorption from water

Application of sewage sludge biochar as an adsorbent for pollutant removal has obtained special attention due to their low cost and surface functionality. In this research, sludge-tire composite biochar (STB) was successfully prepared through co-pyrolysis at 300, 500 and 700 °C, respectively. Cadmium (Cd) and tetracycline (TC) were selected as the target pollutant. The results indicated that STB has the highest surface area (49.71 m²/g), more inorganic minerals (Kaolinite) as well as relatively stable physicochemical properties with 10% tire particles (TP) at 700 °C. The adsorption results indicated that the pseudo-second-order equation and Langmuir isotherm model could better describe the adsorption of Cd²⁺ and TC by STB. The maximum adsorption capacity of Cd²⁺ and TC was 50.25 mg/g and 90.09 mg/g, respectively. The main mechanism of the adsorption process of STB for Cd mainly involves anion binding adsorption and ion exchange. The main mechanism of the adsorption process of STB for TC mainly involves complexation and cation exchange. The present study could set a scientific foundation for further research on the recycle of sewage sludge and tires.

Conversion of sewage sludge into biochar: A potential resource in water and wastewater treatment

Production of biochar from sewage sludge (SS) is consistent with the goal of sustainable resource recovery and promotes a wastewater-based circular economy. Thermochemical conversion of SS to biochar resolves two major issues simultaneously as it minimizes the cost of disposal and acts as a resource to eliminate the toxic contaminants from water and wastewater. The reusability and ready availability of the biochar, irrespective of the season, makes it an economically viable material for wastewater treatment. In this review, explicit insights into the production, modification and usage of SS derived biochar are provided including (i) the production yield, (ii) characteristic features such as physical, chemical, electrochemical and morphological aspects, and (iii) impact on contaminant removal through adsorption, catalytic and electrochemical processes. Particular attention is given to the use of SS derived biochar as an adsorbent for contaminants present in wastewaters, the potential use of biochar as a catalyst and support material in advanced oxidation processes and the use of biochars as an electrode material. The effect of pyrolysis conditions and co-pyrolysis with other materials on biochar properties is explored and insight is provided into the toxicity of biochar components present at different process conditions.

Effects of NaOH Activation on Adsorptive Removal of Herbicides by Biochars Prepared from Ground Coffee Residues

In this study, the adsorption of herbicides using ground coffee residue biochars without (GCRB) and with NaOH activation (GCRB-N) was compared to provide deeper insights into their adsorption behaviors and mechanisms. The physicochemical characteristics of GCRB and GCRB-N were analyzed using Brunauer–Emmett–Teller surface area, Fourier transform infrared spectroscopy, scanning electron microscopy, and X-ray diffraction and the effects of pH, temperature, ionic strength, and humic acids on the adsorption of herbicides were identified. Moreover, the adsorption kinetics and isotherms were studied. The specific surface area and total pore volume of GCRB-N (405.33 m2/g and 0.293 cm3/g) were greater than those of GCRB (3.83 m2/g and 0.014 cm3/g). The GCBR-N could more effectively remove the herbicides (Qe,exp of Alachlor = 122.71 μmol/g, Qe,exp of Diuron = 166.42 μmol/g, and Qe,exp of Simazine = 99.16 μmol/g) than GCRB (Qe,exp of Alachlor = 11.74 μmol/g, Qe,exp of Diuron = 9.95 μmol/g, and Qe,exp of Simazine = 6.53 μmol/g). These results suggested that chemical activation with NaOH might be a promising option to make the GCRB more practical and effective for removing herbicides in the aqueous solutions.

Hydrothermal synthesis of magnetic sludge biochar for tetracycline and ciprofloxacin adsorptive removal

In this study, biochar derived from municipal sludge was activated by zinc chloride, which was first time used as the precursor for hydrothermal synthesis of magnetic sludge biochar (Fe/Zn-SBC) for tetracycline (TC) and ciprofloxacin (CIP) removal. The maximum adsorption capacity of Fe/Zn-SBC for TC and CIP were 145 mg g^-1 and 74.2 mg g^-1 at 25 °C, respectively. Kinetics, isotherms, thermodynamics and characterization analysis suggested that the adsorption process was dominated by pore filling, oxygen-containing groups complexation, π-π conjugation and hydrogen bonding. Fe/Zn-SBC had the high selective adsorption capacity for TC and CIP in a wide pH range and even at the high ionic strength. The magnetic sensitivity ensured its easy separation performance. The co-processing of ultrasound and ethanol could effectively regenerate the used Fe/Zn-SBC. Also, it exhibited great environmental safety in the pH range of 3 to 12. These superiority suggested that it is a promising adsorbent for antibiotics removal.

Single and competitive adsorptions of micropollutants using pristine and alkali-modified biochars from spent coffee grounds

This study investigated the single and competitive adsorption characteristics of micropollutants using the pristine and alkali-modified spent coffee grounds (SCG) biochars. The alkali modification substantially improved the physicochemical characteristics of the SCG biochars (specific surface area and pore volume), which may have led to differences in the adsorption behaviors of the micropollutants. The pseudo second order model (R² ≥ 0.990) better described the single and competitive adsorption kinetics than the pseudo first order model (R² ≥ 0.664). It is evident that chemisorption played a key role in the removal of the micropollutants by the pristine and alkali-modified SCG biochars. The single and competitive adsorptions of the micropollutants were highly dependent on the solution pH and ionic strength since the pore-filling effects, electrostatic and hydrophobic interactions governed their removal by the pristine and alkali-modified SCG biochars. The higher removal efficiencies of the micropollutants by the alkali-modified SCG biochars (≥ 44.5%) in the presence of dissolved organic matter compared to the pristine SCG biochars (≤ 18.5%) support the assumption that alkali modification could markedly reinforce the surface structural properties of the SCG biochars related to the adsorption capacities.

Comparative Study of Cationic Dye Adsorption Using Industrial Latex Sludge with Sulfonate and Pyrolysis Treatment

Industrial latex sludge as raw material was made into sulfonated latex sludge (SLS) and latex sludge active carbon (LSC) adsorbents by sulfonate and pyrolysis treatment to remove textile dye cationic blue X-GRRL from aqueous solution. The adsorption properties of SLS and LSC for X-GRRL were studied and compared by investigating the experimental parameters such as adsorbents dosage, pH, contact time and initial concentration. The kinetics of adsorption on SLS and LSC followed the pseudo-second-order kinetic model well. The adsorption isotherm and thermodynamic studies were further used to evaluate and compare the adsorption process of X-GRRL on SLS and LSC. The maximum adsorption capacities were 1219.6 mg/g for SLS and 476.2 mg/g for LSC according to the Langmuir model, respectively. These findings not only provide a sustainable strategy to turn industrial solid waste latex sludge into useful material for environment remediation, but also develop an efficient adsorbent for the treatment of dye wastewater.

Carbon nanotube supported sludge biochar as an efficient adsorbent for low concentrations of sulfamethoxazole removal

A novel adsorbent of sludge biochar (SBC) and multi-walled carbon nanotube (CNT) composite was synthesized (CNT-SBC) to remove low concentrations of sulfamethoxazole (SMX) from water. The key factors of dose, contact time, pH and temperature were investigated. Higher dose of adsorbents provided more active sites for SMX adsorption. The effect of pH was due to the electrostatic interaction. Increasing the temperature was beneficial to SMX adsorption, which was a spontaneous endothermic process and the strength of the spontaneous increased with CNT supporting. As pseudo-second-order, Elovich, Langmuir and Freundlich models fitted the experimental data better, this suggested that both physisorption and chemisorption played vital roles during the adsorption process. In addition, liquid film diffusion was the main rate-limiting step of adsorption. Compared with SBC (5.43 × 10³ μg g^-1), CNT-SBC-1 (CNT:SBC = 1:2), CNT-SBC-2 (CNT:SBC = 1:4) and CNT-SBC-3 (CNT:SBC = 1:6) exhibited better adsorption performance with up to 2.35 × 10⁴, 1.49 × 10⁴ and 1.22 × 10⁴ μg g^-1 at 25 °C, respectively. The characterization analysis demonstrated that the stronger adsorption capacity of CNT-SBC was mainly attributed to the pore filling, functional groups complexation and π-π interaction. In summary, as an efficient and environment-friendly adsorbent, CNT-SBC has promising potential for low concentrations of SMX and other emerging contaminants removal from water.

Anaerobic treatment of glutamate-rich wastewater in a continuous UASB reactor: Effect of hydraulic retention time and methanogenic degradation pathway

To investigate the anaerobic treatment efficiency and degradation pathways of glutamate-rich wastewater under various hydraulic retention times (HRTs), a lab-scale upflow anaerobic sludge blanket (UASB) reactor was operated continuously for 180 days. Results showed that high chemical oxygen demand (COD) removal efficiencies of 95.5%-96.5% were achieved at HRTs of 4.5 h-6 h with a maximum methane yield of 0.31 L-CH₄/g-COD. When the HRT was shortened to less than 3 h, the removal performance of the reactor declined. There also was an excessive accumulation of volatile fatty acids, which implies that an appropriately small HRT is applicable to the UASB reactor treating glutamate-rich wastewater. Methanogenic degradation of glutamate in the UASB reactor depended on the HRT applied, and the typical methane-producing capability of the sludge at an HRT of 3 h, in descending order, was acetate > glutamate > butyrate > H₂/CO₂ > valerate > propionate. Clostridium and Methanosaeta were predominant in the glutamate-degrading sludge. At least three degradation pathways most likely existed in the UASB reactor, and the pathway via 3-methlaspartate by Clostridium pascui was expected to be dominant.

Correction to the calculation of Polanyi potential from Dubinnin-Rudushkevich equation

The Dubinin-Radushkevitch (D-R) adsorption isotherm model has been widely used to measure adsorption, and it can be used to value the mean free adsorption energy (E). In order to do this, the first step is to calculate the Polanyi adsorption potential (Ɛ). However, we find that the computational formula of Polanyi potential from the D-R equation has a dimensinal problem. Specifically, the units of the equilibrium concentration of solute (C_e) used in the Polanyi potential equation are in chaos. Accurate calculation is the basic characteristic of scientific papers. This comment highlighted the possible flaws related to the calculation of Polanyi potential and analyzed the evolution and application of Polanyi potential equation, and then provided the modified form of Polanyi potential equation. This note offers deeper insights into the Polanyi potential equation, and can help avoid misuse and propagation of the Polanyi potential equation in adsorption research.

A green biochar/iron oxide composite for methylene blue removal

Adsorbents that effectively remove dye substances from industrial effluents are needed for the protection of human health and the natural environment. However, adsorbent manufacture is associated with secondary environmental impacts. In this study, a green biochar/iron oxide composite was produced using a facile approach involving banana peel extract and FeSO₄. The modified biochar's capacity to adsorb methylene blue (MB) was considerably enhanced (Langmuir Q_max of 862 mg/g for MB when C₀ = 500 mg/L, pH = 6.1, T =313 K) compared to the unmodified banana peel biochar, and exhibited good performance for a wide range of pH values (pH 2.05-9.21). The Langmuir isotherm model and pseudo second-order kinetic model accurately describe the adsorption process. The material properties and corresponding adsorption mechanisms were investigated by various experimental techniques. Enhanced MB adsorption by the biochar/iron oxide composite is attributed to increased electronic attraction to MB molecules, as evidenced by XPS analysis. High adsorption capacity was retained after 5 regeneration cycles. This study suggests that biochar can be modified by a green synthesis approach to produce biochar/iron oxide composite with good MB removal capacity.

Performance and microbial community variations of a upflow anaerobic sludge blanket (UASB) reactor for treating monosodium glutamate wastewater: Effects of organic loading rate

To investigate the effect of the organic loading rate (OLR) on anaerobic treatment of monosodium glutamate (MSG) wastewater, a lab-scale up-flow anaerobic blanket (UASB) reactor was continuously operated over a 222-day period. The overall performances of COD removal and methane recovery initially exhibited an increase and subsequently decreased when the OLR was increased from 1 g-COD/L/d to 24 g-COD/L/d. At the optimal OLR of 8 g-COD/L/d, superior performance was obtained with a maximum COD removal efficiency of 97%, a methane production rate of 2.3 L/L/d, and specific methanogenic activity of 86 mg-CH₄/g-VSS/d (feeding on glutamate), with superior characteristics of sludge in VSS concentration, average diameter of granules, and settling velocity. According to the results of the specific methanogenic activity, the methanogenic pathway was more inclined to pass through acetate than through hydrogen. Methanosarcina instead of Methanosaeta, with Methanobacterium and greatly increased Firmicutes, dominated in the UASB reactor after long term operation. These results support that the OLR had a substantial effect on both the treatment and energy recovery efficiency of MSG wastewater as well as on microbial community variations in the UASB reactor.

Biochar produced from the co-pyrolysis of sewage sludge and walnut shell for ammonium and phosphate adsorption from water

Pyrolysis of sewage sludge to obtain biochar is an environmentally friendly method of sewage sludge utilization. In this study, sewage sludge and walnut shell were co-pyrolyzed to produce biochar, which was utilized in the adsorption of ammonium and phosphate from water. Brunauer-Emmett-Teller analysis, X-ray diffraction spectroscopy, scanning electron microscopy, and Fourier transform infrared techniques were applied to analyze the physical and chemical properties of the biochar. The sewage sludge-based biochar consisted of rich metal oxides and functional groups, and the addition of walnut shell was beneficial for the development of porous structure. When the mixing ratio of sewage sludge and walnut shell was 3:1, the derived biochar (MBC3-1) showed a high adsorption capacity for NH₄⁺ in neutral or weak alkaline water. Pure sewage sludge biochar (SBC) was the best option for the adsorption of PO₄^3- in a wide pH range of water. The adsorption of NH₄⁺ and v on MBC3-1 and SBC were controlled by intraparticle diffusion and pseudo-second-order kinetic models, respectively. Isothermal studies indicated that multiple adsorption processes occurred in the adsorption of NH₄⁺ and PO₄^3-, and the maximum adsorption capacity of NH₄⁺ and PO₄^3- reached 22.85 mg/g and 303.49 mg/g on MBC3-1 and SBC, respectively. Thermodynamic analysis confirmed the exothermic and endothermic nature for NH₄⁺ and PO₄^3- adsorption on biochar, respectively.

Adsorption removal of cationic dyes from aqueous solutions using ceramic adsorbents prepared from industrial waste coal gangue

Industrial solid waste coal gangue has huge utilization potential. Low-cost ceramic microsphere adsorbents were prepared from coal gangue by spray drying and sintering method and applied to remove cationic red X-5GN and cationic blue X-GRRL from aqueous solutions. The structural properties of the adsorbents were characterized. Adsorption kinetics, adsorption isotherms and effect of solution pH were studied. Adsorption mechanism and disposal of the spent adsorbents were also discussed. The results showed that the adsorption capacity of the cationic red and cationic blue onto the ceramic adsorbents was 1.044 mg g^-1 and 2.170 mg g^-1 respectively, according to the Langmuir model. The adsorption equilibrium time was quickly reached with the removal of both dyes over 90% within 1 min. The adsorbents exhibited favorable applicability with varying solution pH. Electrostatic attractions, n-π interactions and hydrogen bonding were proposed to be involved in the adsorption process based on the adsorption behavior. Using coal gangue ceramic adsorbents to treat colored wastewater could achieve the purpose of treating wastes with wastes. Therefore, the gangue adsorbent has promising application prospects for its comprehensive economic and environmental benefits.

Accelerated phosphorus recovery from aqueous solution onto decorated sewage sludge carbon

In search of efficient phosphorus resource recovery and pollution remediation should be highly concerned due to the view of phosphorus nonrenewable and eutrophication. This work presented a new insight into conversion of sewage sludge into favorable carbonaceous adsorbent for accelerated removing and recovering phosphorus from aqueous solution, what addressed the issues of phosphorus recovery and pollution remediation as well as sludge disposal. Ca and water hyacinth were evolved to decorate sludge derived carbon. Effect of mass ratio of sludge, water hyacinth and calcium carbonate on the morphologies and adsorption kinetics was investigated. The adsorbents (SW-Ca-112) resulted from sludge in the presence of water hyacinth and CaCO₃ in a mass ratio of 1:1:2 had the highest adsorption capacity of 49.50 mg/g P and adsorption rate. Decoration of Ca favored adsorption ability and the presence of water hyacinth accelerated the adsorption rate due to the enhanced porosity. Formation of acicular Ca₅(PO₄)₃OH nanoparticles contributed to the favorable adsorption process. Thus, the contribution of decorated Ca and water hyacinth to the adsorption ability and rate to phosphorus was understand, providing important information on resource utilization of sewage sludge as efficient adsorbent for immobilizing phosphorus from aqueous solution.

Highly efficient adsorption of dyes by biochar derived from pigments-extracted macroalgae pyrolyzed at different temperature

Biochar is known to efficiently adsorb dyes from wastewater. In this study, biochar was derived from macroalgae residue by pyrolysis, and the influence of varying temperature (from 400 °C to 800 °C) on biochar characteristics was investigated. Among the biochar samples tested, macroalgae-derived biochar possessing highly porous structure, special surface chemical behavior and high thermal stability was found to be efficient in removing malachite green, crystal violet and Congo red. The biochar derived by pyrolysis at 800 °C showed the highest adsorption capacity for malachite green (5306.2 mg g^-1). In this study, the transformation of microalgae residue into a highly efficient dye adsorbent is a promising procedure for economic and environmental protection.

Highly effective enhancement of waste activated sludge dewaterability by altering proteins properties using methanol solution coupled with inorganic coagulants

Proteins are the dominant organic component of extracellular polymeric substances (EPS) in waste activated sludge (WAS), and play an important role during sludge dewatering processes. Methanol is a polar hydrophilic reagent and can denature proteins, which suggested to us that the modification of protein configurations with methanol could improve sludge dewatering performance. In this study, methanol was used to precondition WAS prior to adding inorganic coagulants for dewatering enhancement. The morphology and EPS properties (especially of proteins) were investigated to analyze and explain the effects of methanol in the sludge conditioning process. The results show that methanol performed much better than traditional inorganic coagulants in improving sludge dewaterability in term of specific resistance to filtration (SRF) and cake solid content (CSC). Extractable proteins in EPS increased to a maximum when the concentration of methanol reached 40% (w/w) because cell membranes were destroyed and intracellular substances and water were released. Floc protein content was reduced with the further increase in methanol concentration due to protein precipitation. Confocal laser scanning microscopy analysis indicated that proteins precipitated and formed larger aggregates because methanol destroyed both the hydration shell and the hydrophobic clusters of proteins and expanded the protein tertiary structure to release interstitial water and bound water. The combination treatment of methanol and inorganic coagulants (PAC or FeCl₃) showed significant synergetic effects on enhancing sludge dewatering and cake drying. In practical applications, methanol from the dewatering sludge can be returned to the biochemical pool and used as the carbon source for nitrogen removal in the denitrification process. This integrated process is appropriate for sludge final disposal technologies that have high energy demands, such as incineration and pyrolysis. This paper describes a novel approach to improving sludge dewaterability through the alteration of protein properties by use of physiochemical techniques.

Dissolving organic matter from low-organic sewage sludge for shortening the anaerobic digestion time

Pretreatments have been successfully used to shorten the HRT of anaerobic digestion (AD) of sewage sludge, but they become ineffective for low-organic sewage sludge, with HRT > 10 days. Herein, a new process using alkaline hydrolysis-anaerobic digestion has been developed to solve this problem. Firstly, maximum organic matter in the sludge was dissolved by strong alkaline hydrolysis (pH > 11) in a two-stage alkaline hydrolysis system (TSAHS). Secondly, only the supernatant of the sludge that contained most of the methane potential was applied for AD. The operational conditions were optimized and the process mechanism was also analyzed. The results showed that under optimum operational conditions, above 19% of the organic matter in the sludge was released into the supernatant after alkaline hydrolysis in TSAHS, and the supernatant for AD achieved a methane production of 392 mL CH₄ per g COD. The process attained a methane production of 0.26 m³ CH₄ per kg VS and a VS reduction of 43.5%, while the HRT was only 12 h. The advantage of the mechanism was that the alkaline neutralization capacity of the sludge maintained a proper pH value for the supernatant from TSAHS, which benefited subsequent AD. It is concluded that the new process based on the dissolution of organic matter can attain a short digestion time for low-organic sludge.

Pretreatments have been successfully used to shorten the HRT of anaerobic digestion (AD) of sewage sludge, but they become ineffective for low-organic sewage sludge, with HRT > 10 days. A new process below was developed to solve this problem.

Long-term leaching behaviours of cement composites prepared by hazardous wastes

In order to evaluate the long-term environmental impact of Eco-Ordinary Portland Cement (EOPC) prepared by municipal solid wastes (MSS) and hazardous wastes (HW), consecutive leaching tests with a time span of 180 days were conducted on the EOPC composites in the compact and ground forms under deionized and saline water conditions. The results show that the heavy metals investigated can be classified into three groups according to their leaching behaviours. The concentrations of V, Pb, Ni, Ba, Cd and Zn in the leachate increase with the leaching time, which can be classified into the first group. Cu and Sn are in the second group, and their concentrations increase initially, and decline afterward. Cr and As are in the third group, and their concentrations decline firstly, followed by a clear increase. Besides, a kinetic study was also conducted in the present study, revealing that the leaching behaviours of heavy metals follow a second-order model. Furthermore, our results suggest that the EOPC is resistant to the saline water, but the application of such materials in marine conditions should be paid attention to due to the pollution of arsenic.

In order to evaluate the long-term environmental impact of Eco-Ordinary Portland Cement (EOPC) prepared by hazardous wastes, long-term leaching tests were conducted on the EOPC composites under deionized and saline water conditions.