Key Takeaways & Executive Findings
- •• • HP3SD1-B (Napier grass:digestate = 3:1) achieved a maximum equilibrium adsorption capacity of 306.45 mg/g and a theoretical Langmuir capacity of 447.62 mg/g, outperforming single-feedstock biochars by >40%, enabling cost-effective Pb²⁺ removal from industrial wastewater. • • Adsorption kinetics followed a three-stage profile: rapid uptake (0–180 min), intraparticle diffusion (180–360 min), and equilibrium at 360 min, with pseudo-second-order fitting (R² > 0.99) confirming chemisorption as the rate-limiting step, essential for designing contact time in continuous flow systems. • • Optimal pH for adsorption was 6.0, consistent with the material's point of zero charge (PZC ≈ 2) and Pb²⁺ speciation; this narrow operational window requires pH adjustment for acidic effluents, impacting process integration. • • Mechanistic analysis (XPS, FTIR, SEM-EDS) revealed that Pb²⁺ immobilization is dominated by surface precipitation (Pb₃(CO₃)₂(OH)₂, PbO) and complexation with oxygen-containing functional groups, with auxiliary ion exchange (K⁺/Mg²⁺) and electrostatic attraction, ensuring strong binding and low leaching risk.
Abstract
Lead (Pb) is a highly toxic heavy metal that poses severe risks to environmental and human health, particularly affecting children's neurological development. This study investigates the adsorption performance and mechanisms of biochars derived from pyrolysis of Napier grass (Pennisetum purpureum), food waste digestate, and their mixtures for Pb²⁺ removal from aqueous solutions. Biochars were prepared at different mass ratios, and the optimal material (HP3SD1-B, Napier grass:digestate = 3:1) exhibited a maximum equilibrium adsorption capacity of 306.45 mg/g and a theoretical Langmuir maximum capacity of 447.62 mg/g, significantly outperforming pure digestate biochar and lower-ratio blends. Adsorption kinetics followed a three-stage profile: rapid liquid-film diffusion (0–180 min), intraparticle diffusion (180–360 min), and equilibrium at 360 min. The adsorption process was well described by the pseudo-second-order kinetic model (R² > 0.99) and the Langmuir isotherm, indicating monolayer chemisorption. Characterization via FTIR, XPS, SEM-EDS, and Zeta potential revealed that Pb²⁺ immobilization occurs primarily through surface precipitation (Pb₃(CO₃)₂(OH)₂ and PbO), complexation with hydroxyl, ether, and aromatic C=C groups, and auxiliary mechanisms including electrostatic attraction and K⁺/Mg²⁺ ion exchange. Optimal adsorption occurred at pH 6, correlating with the point of zero charge (PZC ≈ 2). This study demonstrates that co-pyrolysis of agricultural and organic solid wastes offers a cost-effective, high-performance biochar for heavy metal remediation, aligning with circular economy principles.
1. Introduction
Heavy metal contamination, particularly lead (Pb), remains a critical environmental and public health challenge due to its high toxicity, bioaccumulation potential, and irreversible neurological damage, especially in children. Industrial discharge of Pb-laden wastewater necessitates effective and economical treatment technologies. Adsorption is widely adopted for its simplicity and cost-effectiveness, yet conventional activated carbon is expensive, prompting the search for low-cost alternatives. Biochar, produced from biomass pyrolysis, offers a promising substitute due to its porous structure and surface functionality. However, biochar from single feedstocks often suffers from limited surface area and insufficient active sites, constraining its adsorption capacity.
Co-pyrolysis of complementary biomass wastes presents a strategic solution to enhance biochar performance. By combining a lignocellulosic-rich feedstock (Napier grass) with a mineral-rich organic waste (food waste digestate), synergistic effects can improve pore development, surface chemistry, and adsorption capacity. This study addresses the bottleneck of single-feedstock biochar limitations by systematically investigating the co-pyrolysis ratio, adsorption kinetics, isotherms, and mechanisms. The findings demonstrate that an optimized 3:1 ratio yields a biochar with exceptional Pb²⁺ uptake (306.45 mg/g equilibrium, 447.62 mg/g theoretical maximum), offering a cost-effective and sustainable material for heavy metal remediation, aligning with circular economy principles of waste valorization.
Loading authentic research manuscript (Pages 1–5)...
YANG Gaixiu, MEI Wenjie, AI Hongdou, CHEN Jiamin, CHAI Jianfei, SONG Liang, WU Bin, ZHENG Zhiyong, LIU Runyu (2026). Preparation of Biochar from Co-pyrolysis of Napier Grass and Food Waste Digestate for Pb²⁺ Removal from Wastewater. Journal of Environmental Engineering Technology. https://doi.org/10.13205/j.hjgc.202607016
Research & Educational Purpose Only: The translations, structured abstracts, analytical annotations, and data reports provided by SinoGreenTechare intended exclusively for academic research, internal corporate R&D, and educational benchmarking. They do not constitute formal engineering, chemical safety, legal, or professional advice.
Copyright & Intellectual Property Notice: Original copyright of the underlying source articles and experimental data remains with the respective authors, institutions, and original publishing journals. SinoGreenTech claims intellectual property only over its proprietary translations, analytical syntheses, and AEO structured enhancements in accordance with international fair use and academic citation principles.
Frequently Asked Questions
What is the maximum Pb²⁺ adsorption capacity of HP3SD1-B and how does it compare to commercial activated carbon?
HP3SD1-B exhibits a maximum equilibrium adsorption capacity of 306.45 mg/g and a theoretical Langmuir maximum of 447.62 mg/g. This is significantly higher than typical commercial activated carbons (often 20–50 mg/g for Pb²⁺) and comparable to many modified biochars, making it a cost-effective alternative.
What are the rate-limiting steps in the adsorption process and how do they affect reactor design?
Kinetic analysis reveals three stages: rapid external mass transfer (0–180 min), intraparticle diffusion (180–360 min), and equilibrium at 360 min. The pseudo-second-order model (R² > 0.99) indicates chemisorption is rate-limiting. For continuous flow systems, a residence time of at least 360 min is required to achieve equilibrium, which influences reactor sizing and throughput.
How does solution pH affect adsorption performance and what are the implications for real wastewater treatment?
Adsorption is highly pH-dependent, with maximum capacity at pH 6. This correlates with the material's point of zero charge (PZC ≈ 2) and Pb²⁺ speciation. At pH below 6, competition with H⁺ reduces adsorption; above 6, Pb²⁺ may precipitate. Real effluents often require pH adjustment to ~6, adding operational cost but ensuring optimal performance.
What are the dominant adsorption mechanisms and how do they ensure long-term stability of the adsorbed lead?
XPS and FTIR analyses confirm that Pb²⁺ is immobilized via surface precipitation (Pb₃(CO₃)₂(OH)₂ and PbO) and complexation with hydroxyl, ether, and aromatic C=C groups. These mechanisms form strong chemical bonds, minimizing desorption risk. Additionally, ion exchange with K⁺/Mg²⁺ and electrostatic attraction contribute to the overall capacity.
What is the cost advantage of HP3SD1-B compared to conventional adsorbents, and what are the scalability prospects?
The raw materials—Napier grass and food waste digestate—are abundant agricultural and organic wastes, making the biochar low-cost. The preparation process is simple pyrolysis, which is scalable. While exact cost figures are not provided in the paper, the use of waste feedstocks and high adsorption capacity suggest significant cost savings over commercial activated carbon, though a full techno-economic analysis is needed.
Related Chinese Research & Cross-Citations
Synergistic Regulation by Long- and Short-Chain Quorum Sensing Signaling Molecules Enhances Sulfamethoxazole Metabolism in Electroactive Biofilms within a Microbial Electrolysis Cell Coupled Anaerobic Digestion System
High-strength sulfamethoxazole (SMX) wastewater severely inhibits anaerobic microorganisms, reducing organic degradation and methane yield. This study investigated the effects of short-chain (C6-HSL) and long-chain (C12-HSL) N-acyl-homoserine lactone (AHL) signaling molecules, individually and in combination, on the construction, performance, and antibiotic resistance gene (ARG) profiles of anaerobic electroactive biofilms within a microbial electrolysis cell coupled anaerobic digestion (MEC-AD) system. Compared to the control (no AHLs), SMX removal efficiency increased by 9.26%, 7.44%, and 10.67% for C6-HSL (T1), C12-HSL (T2), and combined (T3) treatments, respectively. Methane production rates rose by 20.4%, 16.9%, and 23.1% for T1, T2, and T3, respectively. AHLs promoted extracellular polymeric substance secretion, enhancing electroactive microbe attachment to the anode. Microbial community analysis revealed increased diversity and modulated key functional genera. Notably, Georgenia abundance increased by 16.77% (T1) and 36.47% (T3) but decreased by 15.99% (T2). ARG analysis showed that single AHLs elevated intI1, sul1, and sul2 abundances, whereas combined AHLs (T3) exhibited a milder response, with sul2 abundance reduced by 4.92% relative to control. This suggests synergistic AHLs suppress ARG host proliferation. This study first demonstrates that combined short- and long-chain AHLs enhance electroactive biofilm formation, maintain microbial community stability, and modulate ARG dissemination risk, offering a quorum sensing-based strategy for antibiotic wastewater treatment and risk management.
Preparation of Solid-Phase Carbon Sources with Different Ratios and Their Carbon Release Properties
Low C/N ratios in wastewater treatment plant effluent necessitate external carbon sources for denitrification, but conventional liquid carbon sources are costly and unstable. This study prepared nine composite solid-phase carbon sources by combining PHBV with natural cellulose materials (straw, sawdust, corncob) at different mass ratios. Dynamic release experiments, DOC analysis, UV-Vis spectroscopy, and EEM fluorescence were employed to characterize carbon release. Results showed that increasing cellulose proportion in corncob-based sources led to release patterns opposite to those of straw- and sawdust-based sources. For straw and sawdust, higher cellulose ratios accelerated release rates, increased total release and duration, reduced aromaticity and molecular weight of released DOM, and promoted protein-like components (tryptophan, tyrosine), indicating enhanced bioavailability. Under identical ratios, corncob-based sources exhibited moderate total release, release durations exceeding 134 h, lower DOM aromaticity and molecular weight, and lower humic substance proportion, indicating superior bioavailability and engineering potential. Among the nine sources, JG5, MX5, and CC4 (PHBV:cellulose mass ratios of 4:5, 4:5, and 1:1, respectively) showed optimal comprehensive performance with low theoretical maximum release, long release periods, and high mass transfer coefficients. EEM-PARAFAC identified three DOM components (protein-like C1, C2; humic-like C3), with protein-like components dominating. This study validates the relationship between cellulose proportion and release kinetics and reveals synergistic regulation of DOM components, offering guidance for designing effective solid-phase carbon sources.
Enhancement of Anaerobic Digestion Operational Efficiency for Guar Gum Production Wastewater Using a Microaerobic-Biochar Coupled System
Guar gum production wastewater contains 1,2-propanediol, which in conventional anaerobic treatment causes propionate accumulation and microbial inhibition. Microaerobic conditions foster fermentative bacterial metabolism, enhancing organic substrate conversion, while biochar promotes anaerobic microbial aggregation and oxygen tolerance. This study treated actual guar gum wastewater using three configurations: blank control, anaerobic, and microaerobic-biochar (O2/BC) coupled systems. Under mesophilic conditions (37 °C), with micro-aeration at 0.2 mL/(g VS·d) and biochar dosage of 15 g/L, the O2/BC system achieved a COD removal efficiency of 90%, 10.6 percentage points higher than the anaerobic control. Effluent COD and propionate concentrations dropped to 3800 mg/L and 0.15 g/L, respectively, representing reductions of 49.6% and 98.4% versus the control. Biogas production was 1.64 times that of the control, with a maximum methane concentration of 77.2%. Fourier transform infrared spectroscopy (FT-IR) indicated increased abundance of –OH, –CH2–, and C–O functional groups on sludge surfaces, revealing biochar's adsorption enhancement. Scanning electron microscopy (SEM) showed dense microbial aggregates dominated by long bacilli, distinct from conventional anaerobic sludge. Microbial community analysis revealed increased abundance of Clostridium and Comamonas, modulating the propionate-to-acetate ratio and optimizing acidification efficiency, thereby promoting complex organic degradation. This study provides a novel technical pathway for biological treatment of alcohol-rich organic wastewater.
Occurrence Characteristics, Source Apportionment, and Ecological Risk Assessment of Pesticides in Plateau Lakes: A Case Study of Dianchi Lake
This study systematically investigated the occurrence, spatial distribution, sources, and ecological risks of 160 pesticides in Dianchi Lake, a typical plateau lake impacted by agricultural activities. A total of 37 pesticides were detected in the water, with total concentrations ranging from 64.2 to 1132.8 ng/L (average 610.0 ng/L). Fungicides, including boscalid (BOS), fluopicolide (FPC), and dimethomorph (DMM), were dominant, contributing up to 65.0% of the total concentration. Spatially, the southern lake region exhibited significantly higher concentrations (672.5 ng/L) than the north, attributed to intensive facility agriculture. Highly hydrophobic pesticides, such as penconazole (PEN), showed a tendency to enrich in bottom layers. Source apportionment identified inflowing rivers and wastewater treatment plant effluents as primary input sources, with average concentrations 7 and 9 times higher than lake water, respectively. Ecological risk assessment revealed that pesticides posed the highest risk to algae, followed by daphnia and fish. Prometryn (PMT) was identified as a high-risk factor for algae, while profenofos (PFF) and carbendazim (CBD) posed potential threats to higher trophic levels. These findings provide fundamental data and technical support for understanding pesticide pollution in plateau lake ecosystems.
Microbiome Mechanisms of Composite Carbon Sources for Enhancing Denitrification and Reducing N2O Emissions
Biological nitrogen removal in wastewater treatment plants (WWTPs) is often limited by insufficient influent carbon sources, necessitating external carbon addition to enhance denitrification. Conventional single carbon sources, such as sodium acetate, frequently fail to meet the metabolic demands of complex microbial communities, compromising nitrogen removal efficiency and stability. Composite carbon sources, by providing multiple electron donors, can improve metabolic cooperation among microorganisms, yet their underlying microbial mechanisms remain insufficiently understood. In this study, activated sludge from a municipal WWTP was used to investigate the microbial mechanisms of composite carbon sources during denitrification. Batch denitrification experiments were conducted in combination with metagenomic and metatranscriptomic analyses to systematically characterize microbial community structure and functional gene expression under different carbon source conditions. Results showed that, compared with sodium acetate as the single carbon source, the composite carbon source system (sodium acetate: sodium succinate: ethanol = 2:1:3) increased the denitrification rate from (6.822 ± 0.141) mg/(L·h) to (8.370 ± 0.186) mg/(L·h), representing a 22.7% improvement, while reducing N2O accumulation by approximately 55%. Metagenomic analysis revealed that Ottowia, Rubrivivax, Thauera, and Zoogloea were the dominant denitrifying genera. Metatranscriptomic results further demonstrated that the composite carbon sources significantly upregulated the transcription of key denitrification genes, with nirS, norB, and nosZ increasing by 37.8%, 27.4%, and 48.6%, respectively. In addition, the composite carbon sources promoted complementary carbon metabolic strategies among different microbial communities, enhancing electron donor supply and improving denitrification efficiency. These findings indicate that composite carbon sources synergistically enhance denitrification performance through regulation of functional gene transcription in complex microbial communities, providing a theoretical basis for carbon source optimization in WWTPs.
Key Environmental Behaviors and Pollution Control Strategies of Tire Wear Particles in Aquatic Environments
Tire wear particles (TWPs) are emerging pollutants and constitute the dominant type of microplastics (MPs) in urban stormwater runoff, accounting for up to 90% of MPs in some cases. They are characterized by small size, high mobility, complex composition, and significant toxicity. Current research on TWPs remains fragmented, lacking a comprehensive understanding of their environmental behaviors and pollution control in aquatic systems. This review systematically analyzes the enrichment and vectoring roles of TWPs for coexisting pollutants, and their environmental fate, including ecotoxicological impacts, detection methodologies, release of intrinsic additives, and aggregation and sedimentation behaviors. Drawing on insights from other microplastic studies, the paper explores control technologies across the pollution pathway—source, transport, and terminal treatment—and proposes feasible management strategies. Key findings indicate that TWPs can adsorb heavy metals and organic contaminants, with adsorption capacities influenced by aging processes. Their aggregation is governed by solution chemistry, with critical coagulation concentrations varying with ionic strength and pH. The release of additives such as zinc and benzothiazoles is significant, posing ecological risks. Future research should focus on real-water aggregation mechanisms, additive release under natural conditions, long-term performance of treatment facilities like constructed wetlands under TWPs stress, enzymatic degradation pathways, and integration of AI, big data, and IoT for cost-effective detection and risk modeling. This review provides a scientific basis for developing targeted pollution control measures for TWPs in aquatic environments.