Enhanced ammonium removal on biochar from a new forestry waste by ultrasonic activation: Characteristics, mechanisms and evaluation

Efficient Adsorption of Nitrogen and Phosphorus in Wastewater by Biochar

Nitrogen and phosphorus play essential roles in ecosystems and organisms. However, with the development of industry and agriculture in recent years, excessive N and P have flowed into water bodies, leading to eutrophication, algal proliferation, and red tides, which are harmful to aquatic organisms. Biochar has a high specific surface area, abundant functional groups, and porous structure, which can effectively adsorb nitrogen and phosphorus in water, thus reducing environmental pollution, achieving the reusability of elements. This article provides an overview of the preparation of biochar, modification methods of biochar, advancements in the adsorption of nitrogen and phosphorus by biochar, factors influencing the adsorption of nitrogen and phosphorus in water by biochar, as well as reusability and adsorption mechanisms. Furthermore, the difficulties encountered and future research directions regarding the adsorption of nitrogen and phosphorus by biochar were proposed, providing references for the future application of biochar in nitrogen and phosphorus adsorption.

Adsorption characteristics and mechanism of ammonia nitrogen and phosphate from biogas slurry by Ca2+-modified soybean straw biochar

The utilization of biogas slurry is critical for the sustainable development of animal husbandry. Biomass carbon adsorption is a feasible method for the recycling of nutrients from biogas slurry. However, research on the co-adsorption of ammonia nitrogen and phosphate is scarce. Herein, soybean straw was utilized as the raw material to prepare Ca2+-modified biochar (CaSSB), which was investigated for its ammonia nitrogen and phosphate adsorption mechanisms. Compared with natural biochar (SSB), CaSSB possesses a high H/C ratio, larger surface area, high porosity and various functional groups. Ca2+-modified soybean straw biochar exhibited excellent adsorption performance for NH4+-N (103.18 mg/g) and PO43--P (9.75 mg/g) at pH = 6, using an adsorbent dosage of 2 g/L. The experimental adsorption data of ammonia nitrogen by CaSSB corresponded to pseudo-second-order kinetics and the Langmuir isotherm model, suggesting that the adsorption process was homogeneous and that electrostatic attraction might be the primary adsorption mechanism. Meanwhile, the adsorption of phosphate conformed to pseudo-second-order kinetics and the Langmuir-Freundlich model, whose mechanism might be attributed to ligand exchange and chemical precipitation. These results reveal the potential of CaSSBs as a cost-effective, efficient adsorbent for the recovery of ammonium and phosphate from biogas slurry.

Adsorptive removal of acid red 18 dye from aqueous solution using hexadecyl-trimethyl ammonium chloride modified nano-pumice

Discharging untreated dye-containing wastewater gives rise to environmental pollution. The present study investigated the removal efficiency and adsorption mechanism of Acid Red 18 (AR18) utilizing hexadecyl-trimethyl ammonium chloride (HDTMA.Cl) modified Nano-pumice (HMNP), which is a novel adsorbent for AR18 removal. The HDTMA.Cl is characterized by XRD, XRF, FESEM, TEM, BET and FTIR analysis. pH, contact time, initial concentration of dye and adsorbent dose were the four different parameters for investigating their effects on the adsorption process. Response surface methodology-central composite design was used to model and improve the study to reduce expenses and the number of experiments. According to the findings, at the ideal conditions (pH = 4.5, sorbent dosage = 2.375 g/l, AR18 concentration = 25 mg/l, and contact time = 70 min), the maximum removal effectiveness was 99%. The Langmuir (R2 = 0.996) and pseudo-second-order (R2 = 0.999) models were obeyed by the adsorption isotherm and kinetic, respectively. The nature of HMNP was discovered to be spontaneous, and thermodynamic investigations revealed that the AR18 adsorption process is endothermic. By tracking the adsorption capacity of the adsorbent for five cycles under ideal conditions, the reusability of HMNP was examined, which showed a reduction in HMNP's adsorption effectiveness from 99 to 85% after five consecutive recycles.

Pyrolysis recycling of pig manure biochar adsorption material for decreasing ammonia nitrogen in biogas slurry

Biochar adsorption materials have a good removal effect on ammonia nitrogen in piggery biogas slurry. However, the cost of biochar adsorption material is still high. If these materials can be recycled several times, the cost can be significantly reduced. Therefore, this paper investigated a new process of biochar adsorption material (C@Mg-P) pyrolysis cycle for reducing ammonia nitrogen in piggery biogas slurry. The effects of pyrolysis process conditions (pyrolysis temperature and pyrolysis time) and number of recycling times on reducing ammonia nitrogen in biogas slurry by C@Mg-P were studied, a preliminary investigation on the reaction mechanism of C@Mg-P for reducing ammonia nitrogen in biogas slurry was conducted, and the economic feasibility of the pyrolysis recycling process was analyzed. It was found that the NH₃-N elimination efficiency by C@Mg-P was 79.16 % under the optimal conditions of 0.5 h and 100 °C. Second, C@Mg-P removed 70.31 % NH₃-N after recycling 10 times. Chemical precipitation, ion exchange, physical adsorption and electrostatic attraction were the potential reaction mechanisms for NH₃-N reduction by C@Mg-P. Moreover, C@Mg-P had a good decolorization effect on piggery biogas slurry with a 72.56 % decolorization rate. Compared with the non-pyrolyzed recycling process, the proposed process saved 80 % of the cost, thus representing an economically possible approach for pig manure biochar application in wastewater denitrification treatment.

Detection and removal technologies for ammonium and antibiotics in agricultural wastewater: Recent advances and prospective

With the extensive development of industrial livestock and poultry production, a considerable part of agricultural wastewater containing tremendous ammonium and antibiotics have been indiscriminately released into the aquatic systems, causing serious harms to ecosystem and human health. In this review, ammonium detection technologies, including spectroscopy and fluorescence methods, and sensors were systematically summarized. Antibiotics analysis methodologies were critically reviewed, including chromatographic methods coupled with mass spectrometry, electrochemical sensors, fluorescence sensors, and biosensors. Current progress in remediation methods for ammonium removal were discussed and analyzed, including chemical precipitation, breakpoint chlorination, air stripping, reverse osmosis, adsorption, advanced oxidation processes (AOPs), and biological methods. Antibiotics removal approaches were comprehensively reviewed, including physical, AOPs, and biological processes. Furthermore, the simultaneous removal strategies for ammonium and antibiotics were reviewed and discussed, including physical adsorption processes, AOPs, biological processes. Finally, research gaps and the future perspectives were discussed. Through conducting comprehensive review, future research priorities include: (1) to improve the stabilities and adaptabilities of detection and analysis techniques for ammonium and antibiotics, (2) to develop innovative, efficient, and low cost approaches for simultaneous removal of ammonium and antibiotics, and (3) to explore the underlying mechanisms that governs the simultaneous removal of ammonium and antibiotics. This review could facilitate the evolution of innovative and efficient technologies for ammonium and antibiotics treatment in agricultural wastewater.

The adsorption mechanism of sludge-based biochar toward highly concentrated organic membrane concentrates from landfill leachate

In this study, the sludge-based biochar (BC) was prepared by dewatered sludge from a membrane bioreactor to treat the membrane concentrate. Then, the adsorbed and saturated BC was regenerated (RBC) by pyrolysis and deashing treatment to further treat the membrane concentrate. Afterward, the composition of membrane concentrate before and after BC or RBC treatment was detected, and the biochars' surface characteristics were characterized. The results showed that RBC outperformed BC in the abatement of chemical oxygen demand (COD_Cr), ammonia nitrogen (NH₃-N), and total nitrogen (TN), with their removal rates of 60.07%, 51.55%, and 66.00%, respectively, an improvement of 9.49%, 9.00% and 16.50% of the removal rate compare to BC. The specific surface area of BC and RBC was about 109 times as much as the original dewatered sludge, and the pore size of BC and RBC belonged to mesopore which was a benefit for removing small and mediate size pollutants. The increase of the oxygen-containing functional group in RBC and the ash abatement contributed much to the improvement of RBC adsorption performance. In addition, cost analysis showed that BC+RBC had a cost of 0.76$/kg for COD removal, which was a lower cost than other common membrane concentrate treatment technologies.

Construction of activated biochar/Bi2WO6 and /Bi2MoO6 composites to enhance adsorption and photocatalysis performance for efficient application in the removal of pollutants and disinfection

To synergistically enhance the adsorption and photocatalytic performance of Bi2WO6 and Bi2MoO6, using activated biochar (ACB) as substrate, ACB-Bi2WO6 and ACB-Bi2MoO6 composites were facilely prepared by hydrothermal synthesis. Their adsorption-photocatalytic degradation effects on rhodamine B (RhB), tetracycline (TC), and norfloxacin (NOR) were comparatively investigated. Additionally, the effects of environmental factors, wastewater treatment tests, and disinfection were systematically studied, and the enhancement mechanisms and reasons for the degradation differences were highlighted. The results showed that ACB-Bi2WO6 and ACB-Bi2MoO6 were confirmed to form intimately contacted heterojunctions by various advanced characterization techniques. The introduction of ACB narrowed the band-gap energy of Bi2WO6 and Bi2MoO6, and improved the visible light absorption range and specific surface area. The optimal loading ratios of ACB-Bi2WO6 and ACB-Bi2MoO6 were 1:1.06 and 1:0.58, respectively. The removal rate of ACB-Bi2WO6 for high concentrations of RhB (200 mg·L-1), TC and NOR (50 mg·L-1) were 89.15%, 87.27%, and 72.17%, respectively, which were higher than those of ACB-Bi2MoO6 and significantly stronger than those of Bi2WO6 and Bi2MoO6. This was attributed to the more effective inhibition of photogenerated carrier recombination, higher absorbance, and uniform morphology via ACB-Bi2WO6. ·OH and holes were dominant active species in photocatalysis, and the possible photogenerated carrier transfer path is type II heterojunction. Furthermore, ACB-Bi2WO6 possessed good reusability, and the removal of RhB and TC from the actual wastewater exceeded 80.63% and 58.54%, respectively. The sterilization rates of ACB-Bi2WO6 reached 99% and 95% for E. coli and S. aureus within 24 h, respectively. Therefore, ACB-Bi2WO6 was more recommended for environmental applications.

Study on the Mechanism and Experiment of Styrene Butadiene Rubber Reinforcement by Spent Fluid Catalytic Cracking Catalyst

Spent Fluid Catalytic Cracking (FCC) Catalyst is a major waste in the field of the petroleum processing field, with a large output and serious pollution. The treatment cost of these waste catalysts is high, and how to achieve their efficient reuse has become a key topic of research at home and abroad. To this end, this paper conducted a mechanistic and experimental study on the replacement of some carbon blacks by spent FCC catalysts for the preparation of rubber products and explored the synergistic reinforcing effect of spent catalysts and carbon blacks, in order to extend the reuse methods of spent catalysts and reduce the pollution caused by them to the environment. The experimental results demonstrated that the filler dispersion and distribution in the compound are more uniform after replacing the carbon black with modified spent FCC catalysts. The crosslinking density of rubber increases, the Payne effect is decreased, and the dynamic mechanical properties and aging resistance are improved. When the number of replacement parts reached 15, the comprehensive performance of the rubber composites remained the same as that of the control group. In this paper, the spent FCC catalysts modified by the physical method instead of the carbon-black-filled SBR can not only improve the performance of rubber products, but also can provide basic technical and theoretical support to realize the recycling of spent FCC catalysts and reduce the environmental pressure. The feasibility of preparing rubber composites by spent catalysts is also verified.

Removal of Ammonium Ions from Aqueous Solutions Using Alkali-Activated Analcime as Sorbent

Five alkali-activated analcime (ANA) sorbents (ANA-MK 1, ANA 2, ANA 3, ANA-MK 4, and ANA-MK 5) were developed for ammonium (NH4+) ion removal. Acid treatment and calcination were used as pre-treatments for analcime, and metakaolin (MK) was used as a blending agent in three sorbents. Sorption experiments were performed to evaluate the effects of sorbent dosage (1–20 g L−1), initial NH4+ ion concentration (5–1000 g L−1), and contact time (1 min–24 h). ANA-MK 1, ANA 2, and ANA-MK 4 were the most efficient sorbents for NH4+ ion removal, with a maximum experimental sorption uptake of 29.79, 26.00, and 22.24 mg g−1, respectively. ANA 3 and ANA-MK 5 demonstrated lower sorption capacities at 7.18 and 12.65 mg g−1, respectively. The results for the sorption of NH4+ ions onto the alkali-activated analcime surfaces were modeled using several isotherms. The Langmuir, Freundlich, Sips, and Bi-Langmuir isotherms were the best isotherm models to represent the studied systems. The results of the kinetic studies showed the maximum NH4+ ion removal percentage of the sorbents was ~80%, except for ANA-MK 5, which had a ~70% removal. Moreover, the pseudo-first-order, pseudo-second-order, and Elovich models were applied to the experimental data. The results showed that the sorption process for ANA-MK 1, ANA 2, ANA 3, and ANA-MK 4 followed the Elovich model, whereas the pseudo-second-order model provided the best correlation for ANA-MK 5.

Novel synthesis of multicomponent porous nano-hybrid composite, theoretical investigation using DFT and dye adsorption applications: disposing of waste with waste

Extensive studies have shown that doping can enhance the properties of graphene, but the application to real industrial wastewater treatment and theoretical calculations are limited. In this study, the hybrid nanoadsorbent Cu, N co-doped graphene (Cu@NG) was successfully synthesized via green route using carbon rods from waste dry batteries, human urine and copper nitrate, then multiple characterizations, detailed density functional theory (DFT) theoretical calculations and comprehensive actual wastewater tests are performed in environmental applications to investigate the adsorption properties and mechanism. The results showed that Cu@NG surface is mesoporous, decorated with CuO crystals and doped with N atoms. The isotherms and kinetics were simulated by Langmuir and pseudo-second-order models, respectively. The theoretical maximum sorption for MB and CV on Cu@NG is 116.28 mg·g^-1 and CV is 86.96 mg·g^-1, respectively. Pilot tests with Cu@NG on real textile wastewater showed that COD, BOD and color were removed by 54.2%, 55.2% and 86.4%, respectively. The desorption rate of Cu@NG is approximately above 90% for both MB and CV on Cu@NG after six cycles of treatment. The DFT calculations confirmed the experimental results as MB is more reactive than CV molecules. Besides, interactions have been systematically investigated via topology and natural bond orbital (NBO) analyses. The process mechanism involved mainly electrostatic adsorption, π-π stacking interactions and H-bonding interactions and ion exchange.

Production of biochar from crop residues and its application for anaerobic digestion

Anaerobic digestion (AD) is a viable and cost-effective method for converting organic waste into usable renewable energy. The efficiency of organic waste digestion, nonetheless, is limited due to inhibition and instability. Accordingly, biochar is an effective method for improving the efficiency of AD by adsorbing inhibitors, promoting biogas generation and methane concentration, maintaining process stability, colonizing microorganisms selectively, and mitigating the inhibition of volatile fatty acids and ammonia. This paper reviews the features of crop waste-derived biochar and its application in AD systems. Four critical roles of biochar in AD systems were identified: maintaining pH stability, promoting hydrolysis, enhancing the direct interspecies electron transfer pathway, and supporting microbial development. This work also highlights that the interaction between biochar dose, amount of organic component in the substrate, and inoculum-to-substrate ratio should be the focus of future research before deploying commercial applications.

Visible-light-driven photocatalytic degradation of dye and antibiotics by activated biochar composited with K+ doped g-C3N4: Effects, mechanisms, actual wastewater treatment and disinfection

To improve the performance of graphitic carbon nitride (g-C₃N₄), a hotly researched metal-free photocatalyst, for better application in the efficient removal of organic pollutants, adsorption synergistically enhanced photocatalysis mechanism was thoroughly explored. Based on KOH pore-forming activated biochar (ACB) and K⁺ doped g-C₃N₄ (K-gC₃N₄), the novel activated biochar-based K-gC₃N₄ composite (ACB-K-gC₃N₄) was synthesized via the innovative ultrasonic-milling method. Rhodamine B (RhB), tetracycline (TC), norfloxacin (NOR), and chloramphenicol (CAP) were selected as target pollutants, and the effects of environmental factors, recycling and actual wastewater tests, disinfection effects, and various enhancement strategies were investigated. The results showed that K-gC₃N₄ was successfully composited with ACB by various characterizations, where the loading mass ratio of 1:2 exhibited the best performance. ACB-K-gC₃N₄ possessed a larger specific surface area, richer functional groups, suitable band gap (2.29 eV), and broader visible light absorption (~716 nm) than K-gC₃N₄. ACB-K-gC₃N₄ presented effective removal efficiency over K-gC₃N₄ for four pollutants, in which the removal efficiency of RhB reached 93.26%, and the degradation rate constant of 0.0119 min^-1 was four times higher than K-gC₃N₄ (0.0029 min^-1). Moreover, ACB-K-gC₃N₄ was superior to K-gC₃N₄ in disinfecting S. aureus and E. coli, with a sterilization rate of exceeding 90% for 12 h. The photodegradation activity was dominated by ·O₂^-, h⁺, and ·OH, and the mechanisms involved in the three stages. This was attributed to the unique structure and surface properties (defects and persistent free radicals) of ACB, as evidenced by improved adsorption stage and transfer of degradation intermediates, facilitated the generation of active species, accelerated migration of photogenerated electrons, and inhibited photogenerated carriers recombination by the heterojunction. The good reusability and stability, enhancement strategies (blowing air and heating), and satisfactory feasibility for actual wastewater allow ACB-K-gC₃N₄ possible to promote high-concentration wastewater treatment and disinfection.

Ultrasonic Activated Biochar and Its Removal of Harmful Substances in Environment

Biochar has been widely used in the fields of environment and energy, and green preparation can make biochar-based materials more environmentally friendly. Particularly, in the low-temperature pyrolysis of biochar, labile C with low biological toxicity is the main influencing factor of bacteria in soil. Therefore, it is worth studying to develop the fabrication technology of low-temperature pyrolysis biochar with rich pore structure. The mechanical effect of ultrasonic cavitation is considered to be an effective strategy for the preparation of biochar. However, the sonochemical effects on biochar remain to be studied. In this review, ultrasonic modification and ultrasonic-chemical modification on biochar has been reviewed. Metal oxide/biochar composites can also be obtained by an ultrasonic-chemical method. It is worth mentioning that there have been some reports on the regeneration of biochar by ultrasound. In addition to ultrasonic preparation of biochar, ultrasound can also trigger the sonocatalytic performance and promote the adsorption ability of biochar for the removal of harmful substances. The catalytic mechanism of ultrasound/biochar needs to be further investigated. For application, biochar prepared by ultrasound has been used for the removal of heavy metals in water, the adsorption of carbon dioxide, and soil remediation.

A Review on Production and Surface Modifications of Biochar Materials via Biomass Pyrolysis Process for Supercapacitor Applications

Biochar (BC) based materials are solid carbon enriched materials produced via different thermochemical techniques such as pyrolysis. However, the non-modified/non-activated BC-based materials obtained from the low-temperature pyrolysis of biomass cannot perform well in energy storage applications due to the mismatched physicochemical and electrical properties such as low surface area, poor pore features, and low density and conductivity. Therefore, to improve the surface features and structure of the BC and surface functionalities, surface modifications and activations are introduced to improve its properties to achieve enhanced electrochemical performance. The surface modifications use various activation methods to modify the surface properties of BC to achieve enhanced performance for supercapacitors in energy storage applications. This article provides a detailed review of surface modification methods and the application of modified BC to be used for the synthesis of electrodes for supercapacitors. The effect of those activation methods on physicochemical and electrical properties is critically presented. Finally, the research gap and future prospects are also elucidated.

The role of biochar on alleviating ammonia toxicity in anaerobic digestion of nitrogen-rich wastes: A review

This paper reviewed the mechanisms of biochar in relieving ammonia inhibition. Biochar affects nitrogen-rich waste's anaerobic digestion (AD) performance through four ways: promotion of direct interspecies electron transfer (DIET) and microbial growth, adsorption, pH buffering, and provision of nutrients. Biochar enhances the DIET pathway by acting as an electron carrier. The role of DIET in relieving ammonia nitrogen may be exaggerated because many related studies don't provide definite evidence. Therefore, some bioinformatics technology should be used to assist in investigating DIET. Biochar absorbs ammonia nitrogen by chemical adsorption (electrostatic attraction, ion exchange, and complexation) and physical adsorption. The absorption efficiency, mainly affected by the properties of biochar, pH and temperature of AD, can reach 50 mg g^-1 on average. The biochar addition can buffer pH by reducing the concentrations of VFAs, alleviating ammonia inhibition. In addition, biochar can release trace elements and increase the bioavailability of trace elements.

Removal of heavy metals from wastewaters with biochar pyrolyzed from MgAl-layered double hydroxide-coated rice husk: Mechanism and application

This study reports a MgAl-LDH rice husk biochar composite (MgAl-LDH@RHB) with a regular hydrotalcite structure synthesized by a simple hydrothermal method, which was then used to remove Cd(II) and Cu(II) from water. The influencing factors on the adsorption performance were determined through batch adsorption experiments, and the adsorption characteristics and cycling capacity were evaluated with eight models and adsorption-desorption experiments. The results showed that the adsorption of Cd(II) and Cu(II) by MgAl-LDH@RHB conformed to the Langmuir-Freundlich model and PSO kinetics model, indicating single-layer chemical adsorption. In addition, the experimental maximum adsorption capacities for Cd(II) and Cu(II) were 125.34 and 104.34 mg g^-1, respectively. The adsorption of Cd(II) and Cu(II) by MgAl-LDH@RHB was dominated by surface precipitation and ion exchange. The findings reveal the mechanism for the heavy metal removal by MgAl-LDH@RHB and provide a theoretical reference for agricultural waste disposal and water pollution control.

Recent advancements on biochars enrichment with ammonium and nitrates from wastewaters: A critical review on benefits for environment and agriculture

During the last decade, biochars have been considered as attractive and eco-friendly materials with various applications including wastewater treatment, energy production and soil amendments. However, the important nitrogen losses during biochars production using the pyrolysis process have limited their potential use in agriculture as biofertilizer. Therefore, it seems necessary to enrich these biochars with nitrogen sources before their use in agricultural soils. This paper is the first comprehensive review on the assessment of biomass type and the biochars' properties effects on N recovery efficiency from aqueous solutions as well as its release and availability for plants when applying the N-enriched chars in soils. In particular, the N recovery efficiency by raw biochars versus the type of the raw feedstock is summarized. Then, correlations between the adsorption performance and the main physico-chemical properties are established. The main mechanisms involved during ammonium (NH₄-N) and nitrates (NO₃-N) recovery process are thoroughly discussed. A special attention is given to the assessment of the biochars physico-chemical modification impact on their N recovery capacities improvement. After that, the application of these N-enriched biochars in agriculture and their impacts on plants growth as well as methane and nitrous oxide greenhouse gas emissions reduction are also discussed. Finally, the main future development and challenges of biochars enrichment with N from wastewaters and their valorization as biofertilizers for plants growth and greenhouse gas (GHG) emissions reduction are provided. This systematic review is intended to promote the real application of biochars for nutrients recovery from wastewaters and their reuse as eco-friendly fertilizers.