Adsorption characteristics of ammonium ion onto hydrous biochars in dilute aqueous solutions

Organic particles and high pH in food waste anaerobic digestate enhanced NH4+ adsorption on wood-derived biochar

Biogas residues (i.e., digestate) are rich in NH4+ that has great agricultural value but environmental risk if not recycled. Biochar can be an effective adsorbent retaining NH4+ from digestate. However, it remains unclear how the unique composition of digestate affects the capacity and mechanisms of NH4+ adsorption on biochar. This study examined the mechanisms and driving factors of NH4+ recovery from digestate containing different molecular-weight organic particles by using wood-derived biochar with or without H2O2 modification. Four solutions were prepared, including pure NH4+, synthetic NH4+ with multiple cations mimicking digestate solution, supernatant of digestate with small organic particles and dissolved organic matter, and digestate mixture containing supernatant and large organic particles. The results showed that compared with pure NH4+ solution, the adsorbed NH4+ was 42% lower in the synthetic NH4+ solution with multiple cations but was 2.2 time higher in the supernatant of digestate on two biochars following 48-h adsorption. Modified biochar did not change NH4+ adsorption in pure NH4+ solution despite higher specific surface area than raw biochar, but it increased the adsorption of NH4+ in digestate solutions with high pH (e.g., 4.03 vs. 3.37 mg N g-1 for modified and raw biochar, respectively, in the supernatant of digestate). Compared with the supernatant, the large organic particles in digestate mixture significantly but slightly decreased NH4+ adsorption on modified but not raw biochar. The desorption rate of NH4+ on the biochar was up to 74%-100%, and it was not supressed by the adsorption of organic particles in digestate. The findings here demonstrate the dominant role of electrostatic attraction in NH4+ adsorption, the important role of high pH and organic particles in digestate in facilitating NH4+ adsorption on biochar, and the suitability of the wood-derived biochar in recovering NH4+ from digestate and releasing N for agricultural application.

Game changer for anaerobic fermentation of paper mulberry: Sucrose-loaded biochar enhancing microbial communities and lactic acid fermentation

This study investigated biochar effects, either alone or combined with sucrose, on fermentation quality, microbial communities, and in vitro rumen digestion of anaerobic fermented paper mulberry. The biochar alkaline functional groups bind to lactic acid, reducing acid inhibition and promoting Lactiplantibacillus proliferation. Owing to the low sugar content of paper mulberry, lactic acid bacteria in the biochar group primarily underwent heterofermentation, resulting in the lowest lactic and highest acetic acid contents. Treated with sucrose-loaded biochar, the increased substrate supported homofermentation, leading to the highest lactic and lowest acetic acid contents, with a 15.0 % increase in lactic acid and a 22.2 % decrease in ammoniacal nitrogen compared with the control after 75 days. In vitro rumen tests showed that the biochar-sucrose group had the highest dry matter degradation rate (45.9 %) and a 24.2 % reduction in methane emissions. Concludingly, sucrose-loaded biochar is recommended as effective for lactic acid production under anaerobic conditions.

Biochar as ammonia exchange biofilm carrier for enhanced aerobic nitrification in activated sludge

The effects of biochar on aerobic nitrification in activated sludge were investigated in sequencing batch reactors. Biochar amended reactors exhibited 87-94 % lower ammonia in effluent and 16-71 % greater removal of total Kjeldahl nitrogen compared to control reactors. Quantitative qPCR analyses revealed that the relative abundance of ammonia oxidizing bacteria (AOB, amoA/16S rRNA genes) was greater in biochar than in control reactors. AOB were enriched on biochar surfaces, with biochar particles having up to 12.1 times greater relative abundance of AOB compared to suspended biomass. Biochar's maximum ammonia sorption capacity of 4.4 mg N/g at pH 7 decreased with decreasing pH, however a pH-sensitive fluorescent probe was used to show that biofilms growing on biochar surfaces maintain a median pH of > 6.7 despite reactor acidification by nitrification. Microbial colonization of biochar in activated sludge creates a pH-sheltered environment that sustains biochar's ammonia sorption capacity, resulting in enrichment of AOB on biochar particles and improved nitrification.

Biomass based biochar production approaches and its applications in wastewater treatment, machine learning and microbial sensors

Biochar is a stable carbonaceous material derived from various biomass and can be utilized as adsorbents, catalysts and precursors in various environmental applications. This review discusses various feedstock materials and methods of biochar production via traditional as well as modern approaches. Additionally, the biochar characteristics, HTC process, and its modification by employing steam and gas purging, acidic, basic / alkaline and organo-solvent, electro- and magnetic fields have been discussed. The recent biochar applications for real water, wastewater and industrial wastewater for the abstraction of environmental contaminants also reviewed. Moreover, applications in machine learning and microbial sensors were discussed. In the meantime, analyses on commercial and environmental profit, current ecological concerns and the future directions of biochar application have been well presented.

Screening the optimal modified biochar for nitrogen retention in black soil

Reducing the environmental problems caused by nitrogen loss and nitrogen pollution is of great significance. The addition of biochar to soil is a new method for increasing nitrogen interception due to the special structural and physicochemical properties of biochar. The optimal modified biochar was screened out after acid-base modification and batch adsorption test in this paper. And then the effects of different soil and biochar mixing methods on soil physicochemical properties and nitrogen adsorption and retention were explored through soil column leaching test. The results showed that the biochar with a pyrolysis temperature of 700 °C had the best adsorption effect on nitrogen after being modified by 0.1 mol/L HCI, and the adsorption capacity of nitrate nitrogen reached 121.46 mg/g. The adsorption process of ammonia nitrogen and nitrate nitrogen conformed to the Langmuir model and was mainly homogeneous monolayer. After mixing the selected modified biochar with black soil, the pH increased by 4.77%, the content of ammonia nitrogen increased by 4.89%, and the nitrate content increased by 16.62%. In this study, the adsorption effect of biochar on nitrogen in black soil was discussed, so as to explore the optimal use of biochar in soil, which provided some reference basis for the relevant research.

Efficient Adsorption of Ammonia by Surface-Modified Activated Carbon Fiber Mesh

In view of the characteristics and risks of ammonia, its removal is important for industrial production and environmental safety. In this study, viscose-based activated carbon fiber (ACF) was used as a substrate and chemically modified by nitric acid impregnation to enhance the adsorption capacity of the adsorbent for ammonia. A series of modified ACF-based adsorbents were prepared and characterized using BET, FTIR, XPS, and Boehm titration. Isotherm tests (293.15 K, 303.15 K, 313.15 K) and dynamic adsorption experiments were performed. The characterization results showed that impregnation with low concentrations of nitric acid not only increased the surface acidic functional group content but also increased the specific surface area, while impregnation with high concentrations of nitric acid could be able to decrease the specific surface area. ACF-N-6 significantly increased the surface functional group content without destroying the physical structure of the activated carbon fibers. The experimental results showed that the highest adsorption of ammonia by ACFs was 14.08 mmol-L-1 (ACF-N-6) at 293 K, and the adsorption capacity was increased by 165% compared with that of ACF-raw; by fitting the adsorption isotherm and calculating the equivalent heat of adsorption and thermodynamic parameters using the Langmuir-Freundlich model, the adsorption process could be found to exist simultaneously. Regarding physical adsorption and chemical adsorption, the results of the correlation analysis showed that the ammonia adsorption performance was strongly correlated with the carboxyl group content and positively correlated with the relative humidity (RH) of the inlet gas. This study contributes to the development of an efficient ammonia adsorption system with important applications in industrial production and environmental safety.

Reduction of Odor-causing Compounds in Wastewater using Biochar: A Review

Wastewater contains chemical compounds that cause malodors, such as ammonium cation, dimethyl sulfide, and volatile organic compounds. Biochar-based reduction in the odorants has been proposed as an effective approach along with maintaining environmental neutrality as biochar is a sustainable material made from biomass and biowaste. Biochar can have high specific surface area and microporous structure with proper activation, appropriate for sorption purposes. Recently, various research directions have been proposed to determine the removal efficiency of biochar for different odorants contained in wastewater. This article is aimed at providing the most updated review of biochar-based removal of odor-causing compounds in wastewater while highlighting the current advances. It was distinguished that the odorant removal performance of biochar is highly associated with the raw material and modification method of biochar, and the kind of odorants. Further research should be required for more practical use of biochar for the reduction of odorants in wastewater.

Bamboo-derived adsorbents for environmental remediation: A review of recent progress

The bamboo family of plants is one of the fastest-growing species in the world. As such, there is an abundance of bamboo residues available for exploitation, especially in southeast Asian, central African and south American regions. The preparation of efficient adsorbents from bamboo residues is an emerging exploitation pathway. Biochars, activated carbons or raw bamboo fibers embedded with nanoparticles, each class of materials has been shown to be highly efficient in adsorption processes. This review aims to summarize recent findings in the application of bamboo-based adsorbents in the removal of organic, inorganic, or gaseous pollutants. Therefore, this review first discusses the preparation methods and surface modification methodologies and their effects on the adsorbent elemental content and other basic properties. The following sections assess the recent progress in the adsorption of heavy metals, organics, and gaseous substances by bamboo-based adsorbents, focusing on the optimum adsorption capacities, adsorption mechanisms and the optimum-fitting kinetic models and isotherms. Finally, research gaps were identified and directions for future research are proposed.

The Study of Optimal Adsorption Conditions of Phosphate on Fe-Modified Biochar by Response Surface Methodology

A batch of Fe-modified biochars MS (for soybean straw), MR (for rape straw), and MP (for peanut shell) were prepared by impregnating biochars pyrolyzed from three different raw biomass materials, i.e., peanut shell, soybean straw, and rape straw, with FeCl₃ solution in different Fe/C impregnation ratios (0, 0.112, 0.224, 0.448, 0.560, 0.672, and 0.896) in this research. Their characteristics (pH, porosities, surface morphologies, crystal structures, and interfacial chemical behaviors) and phosphate adsorption capacities and mechanisms were evaluated. The optimization of their phosphate removal efficiency (Y%) was analyzed using the response surface method. Our results indicated that MR, MP, and MS showed their best phosphate adsorption capacity at Fe/C ratios of 0.672, 0.672, and 0.560, respectively. Rapid phosphate removal was observed within the first few minutes and the equilibrium was attained by 12 h in all treatment. The optimal conditions for phosphorus removal were pH = 7.0, initial phosphate concentration = 132.64 mg L^-1, and ambient temperature = 25 °C, where the Y% values were 97.76, 90.23, and 86.23% of MS, MP, and MR, respectively. Among the three biochars, the maximum phosphate removal efficiency determined was 97.80%. The phosphate adsorption process of three modified biochars followed a pseudo-second-order adsorption kinetic model, indicating monolayer adsorption based on electrostatic adsorption or ion exchange. Thus, this study clarified the mechanism of phosphate adsorption by three Fe-modified biochar composites, which present as low-cost soil conditioners for rapid and sustainable phosphate removal.

Recovery of nitrogen and phosphorus in wastewater by red mud-modified biochar and its potential application

A large amount of wastewater containing nitrogen, phosphorus, and fluorine produces in the production of phosphate fertilizer. In this study, to simultaneously recover nitrogen and phosphorus from phosphorus-containing wastewater and realize the resource utilization of red mud and rape straw, red mud-modified rape straw biochar (RM/RSBC) was prepared by facile one step, and the physicochemical properties were characterized by Zeta potential, SEM-EDS, BET specific surface area (SSA), FTIR, XRD, and XPS. The adsorption performance and mechanisms of ammonium and phosphate onto RM/RSBC were explored through static, fixed-bed column adsorption, and practical wastewater experiments. The results showed that pH = 3.0 and 8.0 were favorable for the removal of phosphate and ammonium, respectively. The main adsorption mechanisms of ammonium and phosphate were the interaction between ammonium and surface functional groups and surface precipitation, respectively. The removal efficiencies of ammonium and phosphate by fixed-bed column adsorption mainly depended on the addition amount of RM/RSBC, the concentration of ammonium and phosphate, and the flow rate. The results of the germination experiment showed that adding > 0.5 wt% of RM/RSBC loaded with ammonium and phosphate promoted the growth of mung beans. This study shows that RM/RSBC can not only recover ammonium and phosphate in wastewater, but also realize the resource utilization of red mud and rape straw.

Appraising the performance of oil palm fibre biochar for low concentration ammoniacal nitrogen recovery from aquaculture wastewater

Oil palm fibre is a type of solid waste generated from palm oil processing plant. At present, there is no proper utilization of this abundant waste. Ammoniacal nitrogen (NH3-N) has received a lot of attention as a water pollutant due to its toxicity, which has an impact on both the environment and human health. In aquaculture wastewater (AQW), NH3-N is present in low concentrations (<10 ppm), and removing low concentrations of NH3-N is tedious. Thus, this study focuses on the potential of oil palm fibre biochar (OPFB) for sustainable low concentration NH3-N recovery from AQW and the recovered spent adsorbent to be used as a bio-fertilizer. The Physico-chemical properties of OPFB show a positive correlation with NH3-N recovery. A significant reduction of value-added metals in OPFB has confirmed the recovery of NH3-N through the ion exchange process. The adsorption isotherms and kinetics of NH3-N recovery had good correlation coefficients under the Freundlich and pseudo-second-order kinetic model confirming a multilayer heterogeneous and chemical adsorption respectively. Thermodynamic parameters indicated that the recovery process via adsorption was exothermic and had a Physio-chemical mechanism. At optimum conditions, OPFB could recover up to 66% of NH3-N actual AQW. The properties of spent OPFB showed potential reutilization as a soil amendment agent or biofertilizer which could be easily degraded.

A re-analysis of NH4+ sorption on biochar: Have expectations been too high?

Sorption of nutrients such as NH₄⁺ is often quoted as a critical property of biochar, explaining its value as a soil amendment and a filter material. However, published values for NH₄⁺ sorption to biochar vary by more than 3 orders of magnitude, without consensus as to the source of this variability. This lack of understanding greatly limits our ability to use quantitative sorption measurements towards product design. Here, our objective was to conduct a quantitative analysis of the sources of variability, and infer which biochar traits are more favourable to high sorption capacity. To do so, we conducted a standardized remodelling exercise of published batch sorption studies using Langmuir sorption isotherm. We excluded studies presenting datasets that either could not be reconciled with the standard Langmuir sorption isotherm or generated clear outliers. Our analysis indicates that the magnitude of sorption capacity of unmodified biochar for NH₄⁺ is lower than previously reported, with a median of 4.2 mg NH₄⁺ g^-1 and a maximum reported sorption capacity of 22.8 mg NH₄⁺ g^-1. Activation resulted in a significant relative improvement in sorption capacity, but absolute improvements remain modest, with a maximum reported sorption of 27.56 mg NH₄⁺ g^-1 for an activated biochar. Methodology appeared to substantially impact sorption estimates, especially practices such as pH control of batch sorption solution and ash removal. Our results highlight some significant challenges in the quantification of NH₄⁺ sorption by biochar and our curated data set provides a potentially valuable scale against which future estimates can be assessed.

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

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

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.

A Review on Bamboo as an Adsorbent for Removal of Pollutants for Wastewater Treatment

Water and wastewater treatment are very important for obtaining clean and sanitary water as well as protecting the environment from toxic pollutants. Not only enriched with cellulose and carbon but the abundant resources of bamboo also make it suitable to be utilized as an adsorbent. With the right processing technologies and improvements, the potential of bamboo is unlimited. This study review provides knowledge on the use of bamboo-based adsorbents for the removal of contaminants and pollutants in wastewater in the form of activated carbon, biochar, and aerogel. This review highlighted bamboo utilization and its relevance as an adsorbent for wastewater treatment. The technologies for the processing and improvement of bamboo as well as the performance of the bamboo-based adsorbents are also discussed in this study. The adsorption capacity of bamboo has shown improvement with modification and good adsorption capacity achieved with some of the adsorbent being able to be recycled and reused.

Enhanced removal of ammonium from water using sulfonated reed waste biochar-A lab-scale investigation

The removal of excessive ammonium from water is vital for preventing eutrophication of surface water and ensuring drinking water safety. Several studies have explored the use of biochar for removing ammonium from water. However, the efficacy of pristine biochar is generally weak, and various biochar modification approaches have been proposed to enhance adsorption capacity. In this study, biochar obtained from giant reed stalks (300, 500, 700 °C) was modified by sulfonation, and the ammonium adsorption capabilities of both giant reed biochars (RBCs) and sulfonated reed biochars (SRBCs) were assessed. The ammonium adsorption rates of SRBCs were much faster than RBCs, with equilibrium times of ∼2 h and ∼8 h for SRBCs and RBCs, respectively. The Langmuir maximum adsorption capacities of SRBCs were 4.20-5.19 mg N/g for SRBCs, significantly greater than RBCs (1.09-1.92 mg N/g). Physical-chemical characterization methods confirmed the increased levels of carboxylic and sulfonic groups on sulfonated biochar. The reaction of ammonium with these O-containing functional groups was the primary mechanism for the enhancement of ammonium adsorption by SRBCs. To conclude, sulfonation significantly improved the adsorption performance of biochar, suggesting its potential application for ammonium mitigation in water.

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

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

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

The adsorption treatment of ammonium-containing wastewater has attracted significant global attention. Most enhanced adsorption methods employ chemical modification, and there are few reports on physical activation. We present a physical activation to explore whether physical ultrasound may enhance the adsorption performance and comprehensive utilisation of a new forestry waste, Caragana korshinskii was used as a feedstock to prepare activated biochar (ACB) by controlling the pyrolysis temperatures and ultrasound parameters. The optimal parameters were determined via batch adsorption of NH₄⁺, and the adsorption characteristics were assessed by 8 kinds of models and influence experiments. Moreover, the physicochemical properties of ACB during the pyrolysis process were investigated, and the ultrasonic activation and adsorption mechanisms were discussed using multiple characterisation techniques. Additionally, the cost analysis, the safety of the ultrasonic process and disposal method also were evaluated. The results showed that the ultrasonic activation significantly enhanced the NH₄⁺ adsorption efficiency of biochar by approximately 5 times. ACB exhibited the best performance at 500 °C with an ultrasonic activation time of 480 min, frequency of 45 kHz, and power of 700 W. The ultrasonic activation reduced the biochar ash and induced pore formation, which increased the specific surface area through cavitation corrosion and micro-acoustic flow mechanism. The NH₄⁺ adsorption mechanisms comprised physicochemical processes, of which physical adsorption was dominant. The preparation cost of 1 kg ACB was about 0.42 US dollar, and no secondary pollution occurred in the activation process. The findings prove that ultrasonic technology is efficient and convenient for enhancing biochar adsorption performance, and thus is suitable for industrial applications and promotion.

Capture and recover dissolved phosphorous from aqueous solutions by a designer biochar: Mechanism and performance insights

Excessive phosphorus (P) in marine and freshwater systems has been identified as a primary perpetrator for the harmful and nuisance algal blooms. In this study, a novel designer biochar was produced from sawdust biomass treated with lime sludge prior to pyrolysis. The adsorption of dissolved P on the designer biochar was comprehensively evaluated under different experimental conditions. It revealed that the removal of dissolved P by the designer biochar was more efficient than unmodified biochar, lime sludge, and their post-combination, suggesting that the pretreatment of biomass with lime sludge for the designer biochar production has a significantly synergic effect on enhancing P removal. Post-adsorption characterization and mathematical modeling analyses indicated that the adsorption of dissolved P on the designer biochar could be controlled by multiple mechanisms including physical and chemical adsorption. The precipitation reaction between P anions and metal ions on the surface of the designer biochar was identified as a predominant mechanism. The X-ray diffraction showed that the precipitation reaction generated a series of P fertilizer forms depositing onto the designer biochar. In addition, batch adsorption experiments showed that both initial solution pH and coexisting anions had a lesser effect on the P removal by the designer biochar. This study proposed that the designer biochar could be a promising sorbent to remove dissolved P, and the nutrient-captured biochar could be used as a fertilizer to recover nutrients.

Modified Exfoliated Carbon Nanoplatelets as Sorbents for Ammonium from Natural Mineral Waters

In this manuscript an improved sorbent based on modified exfoliated carbon nanoplatelets, applied in the removal of ammonium from aqueous samples, is presented. This sorbent showed better efficiency in comparison with the previous one obtained in our group for ammonium removal, the values of the maximum sorption capacity being improved from 10 to 12.04 mg/g. In terms of kinetics and sorption characteristic parameters, their values were also improved. Based on these results, a sorption mechanism was proposed, taking into account ion-exchange and chemisorption processes at the surface of the oxidized exfoliated carbon nanoplatelets. Future applications for simultaneous removal of other positive charged contaminants from natural waters might be possible.

Adsorption of copper (II) in aqueous solution using biochars derived from Ascophyllum nodosum seaweed

There has been growing research interest in exploiting biochar for cost-effective. removal of different pollutants. Heavy metals, especially copper II (Cu II) is highly toxic and nonbiodegradable pollutants, and has been major source of environmental pollution. In this study adsorption of Cu (II) on seaweed (Ascophyllum nodosum)-derived biochar was systematically examined. The removal efficiency based on surface property of biochar and type of interactions associated with biochar produced at varying pyrolysis conditions were investigated. The highest removal efficiency of Cu (II) from aqueous media was >99% with 223 mg g-1 Cu (II) adsorption capacity observed by biochar derived at 700 °C and pH 5. Langmuir adsorption isotherm described the adsorption mechanisms of Cu (II) on biochar with cationic and anionic electrostatic attractions, surface precipitation, and pore depositions. Thus, this study shows that waste biomass (seaweed) could be a valuable bioresource for heavy metal remediation from various water bodies.

Evaluating biochar and its modifications for the removal of ammonium, nitrate, and phosphate in water

Removal of nitrogen (N) and phosphorus (P) from water through the use of various sorbents is often considered an economically viable way for supplementing conventional methods. Biochar has been widely studied for its potential adsorption capabilities for soluble N and P, but the performance of different types of biochars can vary widely. In this review, we summarized the adsorption capacities of biochars in removing N (NH₄-N and NO₃-N) and P (PO₄-P) based on the reported data, and discussed the possible mechanisms and influencing factors. In general, the NH₄-N adsorption capacity of unmodified biochars is relatively low, at levels of less than 20 mg/g. This adsorption is mainly via ion exchange and/or interactions with oxygen-containing functional groups on biochar surfaces. The affinity is even lower for NO₃-N, because of electrostatic repulsion by negatively charged biochar surfaces. Precipitation of PO₄-P by metals/metal oxides in biochar is the primary mechanism for PO₄-P removal. Biochars modified by metals have a significantly higher capacity to remove NH₄-N, NO₃-N, and PO₄-P than unmodified biochar, due to the change in surface charge and the increase in metal oxides on the biochar surface. Ambient conditions in the aqueous phase, including temperature, pH, and co-existing ions, can significantly alter the adsorption of N and P by biochars, indicating the importance of optimal processing parameters for N and P removal. However, the release of endogenous N and P from biochar to water can impede its performance, and the presence of competing ions in water poses practical challenges for the use of biochar for nutrient removal. This review demonstrates that progress is needed to improve the performance of biochars and overcome challenges before the widespread field application of biochar for N and P removal is realized.

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

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

Synchronous removal of ammonium and phosphate from swine wastewater by two agricultural waste based adsorbents: Performance and mechanisms

Two agricultural wastes, Chinese medicinal herbal residue and spent Pleurotus ostreatus substrate, were developed to remove ammonium and phosphate from swine wastewater. These adsorbents were mesoporous materials with abundant smooth layered pores, and rough protuberances and grooves, respectively. Their adsorption capacities were 1131.65 and 1631.79 mg N g^-1, and 63.41 and 62.58 mg P g^-1 at pH 8.0, dosage of 0.2 g L^-1 and contact time of 360 min. And kinetics data of ammonium and phosphate fitted best with the intra-particle diffusion and pseudo-second-order models, respectively. Based on the point of zero charge, FTIR and XPS analyses, ammonium was removed mainly by electrostatic attraction, ion exchange and surface precipitation, while phosphate was by ligand exchange, surface complexation and precipitation. Therefore, the two agricultural wastes have great potential to synchronously remove ammonium and phosphate from swine wastewater.

Recent advances in biochar application for water and wastewater treatment: a review

In the past decade, researchers have carried out a massive amount of research on the application of biochar for contaminants removal from aqueous solutions. As an emerging sorbent with great potential, biochar has shown significant advantages such as the broad sources of feedstocks, easy preparation process, and favorable surface and structural properties. This review provides an overview of recent advances in biochar application in water and wastewater treatment, including a brief discussion of the involved sorption mechanisms of contaminants removal, as well as the biochar modification methods. Furthermore, environmental concerns of biochar that need to be paid attention to and future research directions are put forward to promote the further application of biochar in practical water and wastewater treatment.

Biochar of distillers' grains anaerobic digestion residue: Influence of pyrolysis conditions on its characteristics and ammonium adsorptive optimization

To promote the sustainable development of the liquor/ethanol industry and environment protection, alternative ways to dispose of anaerobic digestion residue (ADR) are urgently required. This research aims at studying the effects of different residence times (RTs) (30, 60 and 120 min) and heating rates (HR) (2.5, 5.0 and 10.0°C min^-1) under 700°C on characteristics of ADR biochar as well as the optimization of ammonium (NH₄⁺) adsorption. Results showed that, with the increasing RT and HR, the aromaticity as well as the content of fixed carbon and elemental carbon of ADR biochar increased, but the pyrolysis yield, volatile matter content, elemental hydrogen, oxygen and polarity decreased. Biochar prepared at 60 min and 5.0°C min^-1 under 700°C presented the best development of orderly and honeycomb shape structures, highest specific surface area and maximal amount of NH₄⁺ adsorption (3.15 mg N g^-1). The multilayer heterogeneous adsorption process dominated the NH₄⁺ adsorption behaviour. And the maximal amount of NH₄⁺ adsorption was achieved with 4 g biochar L^-1 at pH 11.0 along with the order of the competitive effect of K⁺ > Na⁺ > Ca²⁺ > Mg²⁺. Furthermore, NH₄⁺ adsorption was exothermic. Thus, the present study demonstrated that ADR biochar has potential to adsorb NH₄⁺ from NH₄⁺ polluted water to meet environmental standards.

Removal of Ammonium from Swine Wastewater Using Synthesized Zeolite from Fly Ash

Synthetic zeolites with pretreated fly ash as a raw material were used to remove ammonium from wastewater using a hydrothermal method in this study. Two pretreatment methods of fly ash were used to compare the ammonium removal of zeolites: water-washing and pickling. In addition, the effects of several factors including the time, temperature, pH, adsorbent dosage, coexisting ions and initial concentration were investigated to gain insight into the adsorption rate, behavior and mechanism of synthetic zeolites for ammonium. N2 adsorption/desorption isotherms showed that the synthetic zeolite was a mesoporous material with a higher specific area (13.05 m2/g) than the values for raw fly ash (0.34 m2/g). The X-ray diffraction result suggested that the synthetic products mainly belonged to zeolite P and Y. The adsorption kinetic data fitted well with a pseudo-second-order model. The maximum ammonium adsorption capacity was 32.16 mg/g. The synthetic zeolites were also applied to adsorb the ammonium from real swine wastewater. The ammonium removal efficiencies in raw swine wastewater and effluent from the biochemical unit were 64.34% and 79.61%, respectively, which indicated that the synthetic zeolites have a good application for real ammonium wastewater.

Large-Scale Screening and Machine Learning to Predict the Computation-Ready, Experimental Metal-Organic Frameworks for CO2 Capture from Air

The rising level of CO2 in the atmosphere has attracted attention in recent years. The technique of capturing CO2 from higher CO2 concentrations, such as power plants, has been widely studied, but capturing lower concentrations of CO2 directly from the air remains a challenge. This study uses high-throughput computer (Monte Carlo and molecular dynamics simulation) and machine learning (ML) to study 6013 computation-ready, experimental metal-organic frameworks (CoRE-MOFs) for CO2 adsorption and diffusion properties in the air with very low concentrations of CO2. First, the law influencing CO2 adsorption and diffusion in air is obtained as a structure-performance relationship, and then the law influencing the performance of CO2 adsorption and diffusion in air is further explored by four ML algorithms. Random forest (RF) was considered the optimal algorithm for prediction of CO2 selectivity, with an R value of 0.981, and this algorithm was further applied to analyze the relative importance of each metal-organic framework (MOF) descriptor quantitatively. Finally, 14 MOFs with the best properties were successfully screened out, and it was found that a key to capturing a low concentration CO2 from the air was the diffusion performance of CO2 in MOFs. When the pore-limiting diameter (PLD) of a MOF was closer to the CO2 dynamic diameter, this MOF could possess higher CO2 diffusion separation selectivity. This study could provide valuable guidance for the synthesis of new MOFs in experiments that capture directly low concentration CO2 from the air.

Acidic surface functional groups control chemisorption of ammonium onto carbon materials in aqueous media

Elucidation of mechanistic insight into the interaction of carbon materials' physicochemical surface properties and ammonium (NH₄⁺) adsorption in aqueous media was made by conducting a systematic study using a wide range of carbon materials. Three types of biochars (rice husk, poultry litter, and enhanced poultry litter) and activated carbons (fresh and aged coconut shell-based and charcoal-based) were used for investigating the NH₄⁺ adsorption mechanism. Poultry litter biochar, with lowest surface area (3 m² g^-1) and largest pore diameter (29 nm), showed the highest NH₄⁺ adsorption capacity (0.34 mg NH₄⁺g^-1), while charcoal-based activated carbon, with the highest surface area (1133 m² g^-1) and small pore diameter (6 nm), had the least NH₄⁺ adsorption capacity (0.09 mg NH₄⁺g^-1). The value of Freundlich isotherm constant 'n' was >1 for all tested carbon materials indicating chemisorption as the dominant sorption mechanism. Aging of the carbon surface resulted in 30% increase in NH₄⁺ retention. Surface chemical properties that most influenced NH₄⁺ chemisorption on to carbon materials were found to be acidic surface functional groups (ASFGs), elemental composition, ash content, and pH. The optimal conditions for NH₄⁺ adsorption, regardless of type and source of carbon materials, were solution pH of 8, a high amount of ash content, and carboxyl, carbonyl, and phenolic functional groups. Evaluation of CEC and ASFGs indicated that CEC and ASFGs are not equivalent terms. Through this study, conducted on carbon adsorbents derived from different sources, with different surface physical and chemical properties, we established that ASFGs, and not CEC, play a critical role in ammonium chemisorption on carbon materials. The study showed that low cost and eco-friendly biochars, with optimal surface chemistry, can replace expensive activated carbons for NH₄⁺ remediation in aqueous media.

Enhanced adsorption of Cd (II) from aqueous solution by a shrimp bran modified Typha orientalis biochar

The biochar which was characterized with well-developed facial structure and O-/N-containing functional groups could effectively remove Cd (II) from water. In this paper, Typha orientalis-based biochar (BCS) with well-developed N containing functional groups was modified with shrimp bran which was rich in crude protein for the first time. There are more well-developed O-/N-containing functional groups in the structure of BCS than that of pure Typha orientalis-based biochar without any modification (BC), and this conclusion was depended on their comparisons of Brunauer-Emmett-Teller (BET), X-ray diffraction (XRD), scanning electron microscopy (SEM), elemental analysis (EA), Boehm titration, Fourier transform infrared (FTIR), and other characterization techniques. Moreover, according to the experiment, the phenomenon that the adsorption capacity of Cd(II) on these two adsorbents (BCs) decreased with the increase of solution ionic strength could be carried out. The Cd(II) adsorption studies combined with X-ray photoelectron spectroscopy (XPS) analysis revealed that the adsorption mechanism was mainly attributed to physical microporous filtration and chemical interaction between Cd(II) and the surface functional groups (surface complexation, ion exchange, and electrostatic attraction).

Evaluation of Removal Efficiency of Ni(II) and 2,4-DCP Using in Situ Nitrogen-Doped Biochar Modified with Aquatic Animal Waste

Currently, biochar (BC) has shown promising potential in groundwater and surface-water remediation. In this work, Trapa natans husks based biochar (TBC) was prepared and modified with aquatic animal waste (shrimp and crab) to produce shrimp-modified biochar (SBC) and crab-modified biochar (CBC), respectively. The as-prepared BCs (TBC, SBC, and CBC) were characterized by X-ray diffraction, scanning electron microscopy, elemental analysis, Boehm titration, Fourier transform infrared, and X-ray photoelectron spectroscopy. SBC and CBC had more developed nitrogen-containing functional groups than TBC, which indicates that the crude proteins in shrimp and crab have successfully achieved in situ nitrogen doping. Results of batch experiments showed that SBC and CBC had larger groundwater pollutants (2,4-dichlorophenol (2,4-DCP) and Ni(II)) adsorption capacities than TBC. According to batch adsorption experiment and characterization analysis results, the proposed adsorption mechanism of 2,4-DCP includes hydrogen bonding and π-π electron-donor-acceptor interaction, while the mechanism for Ni(II) adsorption are proposed to be surface complexation, ion exchange, and electrostatic attraction.