Adsorption of ammonium in aqueous solutions by pine sawdust and wheat straw biochars

Pistia stratiotes L. Biochar for Sorptive Removal of Aqueous Inorganic Nitrogen

Biochar has proven effective in the remediation of excess nitrogen from soil and water. Excess nitrogen from agricultural fields ends up in aquatic systems and leads to reduced water quality and the proliferation of invasive species. This study aimed to assess the efficiency of chemically surface-modified biochar produced from invasive Pistia stratiotes L. for the adsorption of inorganic nitrogen (NH4+ and NO3-). Biochar structure was investigated using scanning electron microscopy, energy-dispersive X-ray analysis, X-ray photoelectron spectroscopy, Fourier-transform infrared spectroscopy, and inductively coupled plasma mass spectrometry. The results from adsorption experiments indicate that NH4+ removal was optimal (0.8-1.3 mg N g-1) at near-neutral pH levels (6.0-7.5), while NO3- removal was optimal (0.4-0.8 mg N g-1) under acidic pH conditions (4.8-6.5) using the modified biochar. These findings highlight the significance of solution pH, biochar morphology, and surface chemistry in influencing the adsorption of NH4+ and NO3-. However, further studies are necessary to assess the potential oxidative transformation of NH4+ to NO3- by biochar, which might have contributed to the reduction in NH4+ in the aqueous phase.

Nutrients recovery from livestock wastewater by batch and gas bubble-column studies with biochar, nano-composite material, and ammonium magnesium phosphate hydrate

The breeding of livestock raises substantial environmental concerns, especially the efficient management of nutrients and pollution. This research is designed to assess the potency of char and modified char in diluting nutrient concentrations in livestock wastewater. The characteristics of graphene oxide, struvite, and calcium-modified char were inspected, defining their efficacy in both batch and bed-column investigations of nutrient sorption. Various factors, including sorption capacity, time of contact, ion levels, a decrease in ion levels over time, and sorption kinetics, have been considered, along with their appropriateness for respective models. The first evaluation of the options concluded that 600 °C char was better since it exhibited higher removal efficiency. Modified char sorption data at 600 °C was used to adjust the models "PSOM, Langmuir", and "Thomas". The models were applied to both batch and bed-column experiments. The maximum phosphate sorption was 110.8 mg/g, 85.73 mg/g, and 82.46 mg/g for B-GO, B-S, and B-C modified chars respectively, in the batch experiments. The highest phosphate sorption in column experiments, at a flow rate of 400 μl/min, was 51.23 mg per 10 g of sorbent. This corresponds to a sorption rate of 5.123 mg/g. B-GO and B-S modified chars showed higher sorption capacities; this was observed in both the batch and bed-column studies. This displayed the capability of graphene oxide and struvite-modified chars for efficient ion and nutrient uptake, whether in single or multi-ion environments, making them a very good candidate for nutrient filtration in livestock wastewater treatment. Additionally, B-GO char enhanced the sorption of phosphate, resulting in augmented seed germination and seedling growth. These results reveal that B-GO char can be used as a possible substitute for chemical fertilizers.

Selective adsorption of antibiotics from human urine using biochar modified by dimethyl sulfoxide, deep eutectic solvent, and ionic liquid

Antibiotics present in human urine pose significant challenges for the use of urine-based fertilizers in agriculture. This study introduces a novel two-stage approach utilizing distinct biochar types to mitigate this concern. Initially, a modified biochar selectively adsorbed azithromycin (AZ), ciprofloxacin (CPX), sulfamethoxazole (SMX), trimethoprim (TMP), and tetracycline (TC) from human urine. Subsequently, a separate pristine biochar was employed to capture nutrients. Biochar, derived from sewage sludge and pyrolyzed at 550 and 700 °C, was modified using dimethyl sulfoxide, deep eutectic solvent, and ionic liquid to enhance antibiotic removal in the first stage. The modifications introduced hydrophilic functional groups (-OH/-COOH), which favor antibiotic adsorption. Adsorption kinetics followed the pseudo-second-order model, with the Langmuir isotherm model best describing the adsorption data. The maximum adsorption capacities for AZ, CPX, SMX, TMP, and TC after the modification were 196.08, 263.16, 81.30, 370.37, and 833.33 μg/g, respectively. Pristine biochar exhibited a superior ammonia adsorption capacity compared to the modified biochar. Hydrogen bonding, electrostatic attraction, and chemisorption drove antibiotic adsorption on the modified biochar. Regeneration efficiency declined due to solvent accumulation and potential byproduct formation on the biochar surface (<30% removal capacity after three cycles). This study presents innovative biochar modification strategies for selective antibiotic adsorption, laying the groundwork for environmentally friendly urine-based fertilizers in agriculture.

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

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

Feasibility study of Aesculus turbinata fruit shell-derived biochar for ammonia removal in wastewater and its subsequent use as nitrogen fertilizer

In the face of increasing nitrogen demand for crop cultivation driven by population growth, this study presents a sustainable solution to address both the heightened demand and the energy-intensive process of nitrogen removal from wastewater. Our approach involves the removal of nitrogen from wastewater and its subsequent return to the soil as a fertilizer. Using biochar derived from Aesculus turbinata fruit shells (ATFS), a by-product of post-medical use, we investigated the effect of pyrolysis temperature on the NH4-N adsorption capacity of ATFS biochar (ATFS-BC). Notably, the ATFS-BC pyrolyzed at 300 °C (ATFS-BC300) exhibited the highest NH4-N adsorption capacity of 15.61 mg/g. The superior performance of ATFS-BC300 was attributed to its higher number of oxygen functional groups and more negatively charged surface, which contributed to the enhanced NH4-N adsorption. The removal of NH4-N by ATFS-BC300 involved both physical diffusion and chemisorption, with NH4-N forming a robust multilayer adsorption on the biochar. Alkaline conditions favored NH4-N adsorption by ATFS-BC300; however, the presence of trivalent and divalent ions hindered this process. Rice plants were cultivated to assess the potential of NH4-N adsorbed ATFS-BC300 (NH4-ATFS-BC300) as a nitrogen fertilizer. Remarkably, medium doses of NH4-ATFS-BC300 (594.5 kg/ha) exhibited key agronomic traits similar to those of the commercial nitrogen fertilizer in rice seedlings. Furthermore, high doses of NH4-ATFS-BC300 demonstrated superior agronomic traits compared to the commercial fertilizer. This study establishes the viability of utilizing ATFS-BC300 as a dual-purpose solution for wastewater treatment and nitrogen fertilizer supply, presenting a promising avenue for addressing environmental challenges.

Nutrient release pattern and mitigation of N2O emissions under the application of activated poultry manure compost biochar with organic resources

Biochar was generally used to reduce the macronutrient releases and to mitigate N2O gas emissions in cropland. This experiment evaluated the trend of major plant nutrient releases using the modified Hyperbola model and the greenhouse gas emissions by incorporating different poultry manure compost biochar with organic resources. The treatments consisted of the control as the organic fertilizer materials, the incorporated poultry manure compost biochar with organic fertilizer materials (PMCBF), and the incorporated plasma-activated poultry manure compost biochar with organic fertilizer materials (PAMBF) under redox conditions. The results showed that the cumulated highest concentrations of NH4-N and NO3-N were 2168.6 mg L-1 and 21.7 mg L-1 in the control, respectively. Compared with the control, the predicted reduction rates of NH4-N release from the PMCBF and PAMBF were 26.2% and 15.4%, respectively. In the control, the cumulated highest concentrations of PO4-P and K in leachate were 681.04 mg L-1 and 120.5 mg L-1, respectively. The predicted reduction rates of PO4-P and K were 55.1% and 15.5%, respectively, under the PAMBF compared to the control. The modified Hyperbola model with cumulated NH4-N, PO4-P, and K-releases under the treatments was a good fit (p < 0.0001). For greenhouse gas (GHG) emissions, the lowest cumulative N2O was 59.59 mg m-2 in the soil incorporated with PMCBF, and its reduction rate was 23.5% compared with the control. The findings of this study will contribute to more profound insights into the potential application of PAMBF and PMCBF as bio-fertilizers adapted to mitigate NH4-N, PO4-P, and K releases and N2O emissions, offering scientific evidence for organic farming strategies.

New insights into biochar ammoniacal nitrogen adsorption and its correlation to aerobic degradation ammonia emissions

One of the technical barriers to the wider use of biochar in the composting practices is the lack of accurate quantification linking biochar properties to application outcomes. To address this issue, this paper investigates the use of ammonia nitrogen adsorption capacity by biochar as a predictor of ammonia emission during composting in the presence of biochar. With this in mind, this work investigated the use of ammonia nitrogen adsorption capacity of biochar when mixed with solid digestate, and the reduction in ammonia emissions resulting from the addition of biochar during aerobic degradation of solid digestate. A biochar synthesized at 900 °C, another synthesized at 450 °C, and two derivatives of the latter biochar, one chemically modified with nitric acid and the other with potassium hydroxide, were tested. This study concluded that the chemical characteristics of the biochar, including pH and oxygen/carbon atomic ratio, had a greater influence on the adsorption of ammonia nitrogen than physical attributes such as specific surface area. In this regard, nitric acid modification had superior performance compared to hydroxide potassium modification to increase biochar chemical attributes and reduce ammonia emissions when applied to aerobic degradation. Finally, a significant linear correlation (p-value < 0.05, r2 = 0.79) was found between biochar ammonia nitrogen adsorption capacity and ammonia emissions along composting, showing the potential of this variable as a predictive parameter. This study provides insights for future explorations aiming to develop predictive tests for biochar performance.

Effects of different aging methods on the ability of biochar to adsorb heavy metal cadmium and its physical and chemical properties

The aging process can affect the physical and chemical properties as well as adsorption capacity of biochar. This study focuses on the heavy metal cadmium (Cd) as the research object, and artificially ages biochar prepared from rice straw and corn straw through accelerated freeze-thaw cycles, alternating dry wet cycles, and ultraviolet light treatment, in order to evaluate the effects of different aging conditions on the physical and chemical properties of the two different types of biochar and on their adsorption capacities for Cd. After aging, the pH of rice and corn biochar decreased to varying degrees, respectively. The surface structure was ruptured, the average pore diameter was decreased, and the specific surface area was increased by 27.3%, 21.9%, and 9.8% (rice) and 95.4%, 27.7%, and 13.4% (corn). Ultraviolet light aging has the most significant impact on the elemental content of biochar, and the C content was decreased by 12.4% (rice) and 9.3% (corn). The O content was increased by 11.2% (rice) and 44.1% (corn), and the numbers of O/C, H/C, (O + N)/C, and oxygen-containing functional groups were increased. These results demonstrate that the aging process reduces the degree of aromatization of biochar, while enhancing its polarity and Cd adsorption capacity. Rice straw biochar (RSB) has a greater ability to adsorb Cd than corn straw biochar (CSB). In addition, ultraviolet light aging is particularly effective in increasing heavy metal adsorption.

Effects of biochar-amended soils as intermediate covers on the physical, mechanical and biochemical behaviour of municipal solid wastes

The effects of biochar-amended soils as landfill covers have been extensively studied in terms of liquid and gas permeability. However, the influences of biochar-amended soils on the performance of municipal solid wastes (MSWs) in bioreactor landfills have not been well understood. This paper investigates the potential application of biochar-amended soils as final and intermediate covers in landfills. The MSWs with biochar-amended soils as final and intermediate covers were recirculated with mature leachate in laboratory-scale bioreactors. The pH, chemical oxygen demand, ammonia and volatile fatty acids (VFAs) concentrations of leachates, mass reduction rates, settlement, methane, and total gas generations of MSWs were investigated. The results indicate that biochar-amended soils as intermediate landfill covers can provide pH-buffer capacity, increase the pH of leachate and decrease the accumulation of VFAs in the early stage of decomposition. The concentration of ammonia in the leachate with biochar-amended soils as intermediate cover is lower than that with natural soils. The application of biochar-amended soils as intermediate and/or final covers increases the biocompression ratios and settlement of MSWs. The application of biochar-amended soils as final cover slightly decreases the methane generation potential (L0). Biochar-amended soils as intermediate covers increase L0 by 10%, and biochar-amended soils as both intermediate and final covers enhance L0 by 25%. The increase in the ammonia removal, settlement, and methane yield indicates the viability of biochar-amended soils as intermediate landfill covers. Further studies can focus on the long-term behaviour of MSWs with soil covers with different biochar amendment rates and particle sizes.

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.

Quantitative analysis of the current status and research trends of biochar research - A scientific bibliometric analysis based on global research achievements from 2003 to 2023

Biochar has excellent physical and chemical properties such as porosity, high carbon content, high cation exchange capacity, and rich surface functional groups and has been widely used in environmental remediation. Over the past 20 years, although various reviews have described the application of biochar as an environmentally friendly multifunctional material in environmental remediation, no comprehensive summary and analysis of the research trends in this field exists. To promote the rapid and stable development of the field of biochar, the current state of research on biochar is clarified using the bibliometric method in this report, and potential development directions and challenges for the future are identified. All relevant biochar literature from 2003-2023 was collected from the Chinese National Knowledge Infrastructure and Web of Science Core Collection. A total of 6,119 published Chinese papers and 25,174 English papers were selected for the quantitative analysis. CiteSpace, VOSviewer, and Scimago graphics software was used to summarize the numbers of papers published over the years, as well as the countries, institutions, and authors that published the most articles. Secondly, using keyword co-occurrence and emergence analysis, the recognized research hotspots in different areas such as adsorbents, soil remediation, catalytic oxidation, supercapacitors, and "biochar-microbial" synergy were analyzed. Finally, the prospects and challenges of biochar were assessed to provide new perspectives for further promoting its development in technological, economic, environmental, and other aspects.

Optimization of pig manure-derived biochar for ammonium and phosphate simultaneous recovery from livestock wastewater

Livestock wastewater has led to serious eco-environmental issues. To effectively treat livestock wastewater and realize the resource utilization of livestock solid waste, manure waste has been widely used to prepare biochar for the recovery of nitrogen and phosphorus. However, fresh biochar has a poor ability to adsorb phosphate due to its negative charge. To overcome the defect, the proportion of biochar samples prepared at 400 °C and 700 °C was optimized under a mass ratio of 2:3 to obtain mixed biochar PM 4-7, achieving the purpose of enhanced ammonium and phosphate recovery in livestock wastewater simultaneously without any modification. The effects of pyrolysis temperature, dosage, and pH were studied, different adsorption models were used to explore the adsorption mechanism, and the effect of biochar loaded with nutrient elements on seed was verified through a seed germination experiment. It was revealed that the maximum removal rates of phosphate and ammonium were 33.88 % and 41.50 %, respectively, endorsing that mixed biochar PM 4-7 can recover nutrients from livestock wastewater, and could be used as a slow-release fertilizer to promote seed germination and growth. This method provides a new potential way for the efficient resource utilization of pig manure and the recovery of nutrients from breeding wastewater.

Hydrochar synthesis from waste corncob using subcritical water and microwave-assisted carbonization methods and ammonium enrichment of synthesized hydrochars

Corncob (CC) is an industrial biological waste that is generated in significant quantities, and converting such biological wastes into value-added hydrochars through a viable process such as hydrothermal carbonization can provide significant benefits. It is of great importance to ensure eco-friendly and appropriate methods that are suitable for the area where the hydrochar will be used. This study aimed to synthesize hydrochars from a solid food waste, CC, using two different hydrothermal carbonization methods based on microwave-assisted (MHC) and subcritical water (SHC) using them as a biosorbent for NH₄⁺ adsorption from water and characterizing their specific features. Hydrochars were synthesized in 1 h at 180 °C and 240 °C by MHC and SHC methods, respectively. Hydrochars synthesized by MHC and SHC methods were characterized by SEM-EDX, N₂ adsorption-desorption isotherms, and FT-IR analyses. According to the EDX results, the C/O ratio (atomic %) in MHC and SHC was determined to be 0.55 and 0.35, respectively. Nitrogen adsorption-desorption isotherms revealed that hydrochars obtained by both methods have three distinct pore types, namely, micro, meso, and macro. In the energy consumption per unit adsorbent, a lower value was obtained for MHC than SHC. NH₄⁺ adsorption using MHC and SHC was found to be compatible with the Langmuir isotherm model and the NH₄⁺ adsorption capacities were 13.09 and 10.54 mg/g, respectively. pH was the most effective variable on hydrochars in the NH₄⁺ adsorption based on the response surface method (RSM), and the highest adsorption occurred at pH 6.5 and 40 mg/L of initial NH₄⁺ concentration, using 1.5 g/L of adsorbent at 35 °C. The results revealed that MHC is a unique method that can be used for hydrochars derived from CC in NH₄⁺ adsorption, and MHC is more cost-effective than SHC in hydrochar production.

Biochar application can mitigate NH3 volatilization in acidic forest and upland soils but stimulates gaseous N losses in flooded acidic paddy soil

Biochar (BC) has attracted attention for carbon sequestration, a strategy to mitigate climate change and alleviate soil acidification. Most meta-analyses have insufficiently elaborated the effects of BC on soil N transformation so the practical importance of BC could not be assessed. In this study, a ¹⁵N tracing study was conducted to investigate the effects of BC amendment on soil gross N transformations in acidic soils with different land-use types. The results show that the BC amendment accelerated the soil gross mineralization rate of labile organic N to NH₄⁺ (M_Nlab) (3 %-128 %) which was associated with an increase in total nitrogen. BC mitigated NH₃ volatilization (V_NH3) (52 %-99 %) in upland and forest soils due to NH₄⁺/NH₃ adsorption, while it caused higher gaseous N losses (NH₃ and N₂O) in flooded paddy soils. An important function was the effect of BC addition on NH₄⁺ oxidation (O_NH4). While O_NH4 increased (4 %-19 %) in upland soils, it was inhibited (34 %-71 %) in paddy soils and did not show a response in forest soils. Overall, the BC amendment reduced the potential risk of N loss (P_RL), especially in forest soils (82 %-98 %). This study also shows that the BC effect on soil N cycling is land-use specific. The suitability of practices including BC hinges on the effects on gaseous N losses.

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.

Screening tests for N sorption allow to select and engineer biochars for N mitigation during biomass processing

Biochar amendment during biomass processing can improve those processes and products, and reduce the emissions of greenhouse gases and NH₃, resulting in ecologic and economic benefits. The potential positive effects of biochar are related to NH₄⁺-N and NH₃ sorption, which in turn are depending on different biochar characteristics. By knowing the relationship between biochar characteristics and NH₄⁺-N and NH₃ sorption, biochar production can be steered towards a higher N sorption or existing biochars can be selected for targeted applications for high N sorption. Therefore, this study aims to develop fast screening tests to estimate the potential for both NH₄⁺-N and NH₃ sorption of biochar, before application in biomass processing. Further, the effects of feedstock, pyrolysis temperature, biochar characteristics and biochar treatments on N sorption are studied. The results show that NH₄⁺-N sorption varied between 0 and 1.54 mg NH₄⁺-N/g fresh biochar and was highest for manure-based biochars with a high nutrient content and cation exchange capacity, produced at lower temperatures (300-450 °C). For some biochars, the feedstock itself had a higher NH₄⁺-N sorption than the biochar. Grinding and washing increased the NH₄⁺-N sorption. In addition, a general linear model was proposed to predict the NH₄⁺-N sorption based on three chemical characteristics_· NH₃ sorption varied between 0 and 100 % of the negative control and showed a linear positive relationship with the NH₄⁺-N sorption, moisture retention factor and cation exchange capacity. Pyrolysis temperature and feedstock type did not significantly affect NH₃ sorption. NH₄⁺-N and NH₃ desorption varied amongst biochar type.

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.

Simulated adsorption of iodine by an amino-metal-organic framework modified with covalent bonds

Radioactive iodine in nuclear waste is increasingly harmful to the human body and the environment because of its strong radioactivity, high fluidity, easy solubility in water, and long half-life. It is very important to find clean and economical materials to recover and fix radioactive iodine. In this paper, the amino-metal-organic framework was covalently modified to obtain composite materials to improve the recycling of iodine in the environment. These adsorbents are used to adsorb iodine in water, showing outstanding adsorption performance. The adsorption data are in good agreement with the Langmuir isothermal adsorption model and pseudo-second-order kinetic model, indicating that the adsorption process is mainly monolayer adsorption and chemical adsorption. The two materials showed selective adsorption capacity for iodine in the solution containing multiple competing ions. The adsorption capacity of the covalently modified composite increased from 949.52 to 2157.44 mg/g. Compared with the amino-metal-organic framework, the modified composite contains more electron-rich groups as active sites, and forms charge transfer compounds with iodine to realize chemical adsorption. Through the simulated adsorption of ultra-high-pressure micro-jet, the material has certain working ability under high pressure, which provides a theoretical basis for the future recovery and utilization of iodine under high pressure.

From waste to fertilizer: Nutrient recovery from wastewater by pristine and engineered biochars

Biochar application for the recovery of nutrients from wastewater is a sustainable method based on a circular economy. Wastewater, food wastewater, and stormwater are valuable sources of nutrients (i.e., PO₄^3-, NO₃^-, and NH₄⁺). The unique properties of biochar, such as its large specific surface area, pH buffering capacity, and ion-exchange ability, make it a cost-effective and environmentally friendly adsorbent. Biochar engineering improves biochar properties and provide targeted adsorbents. The biochar-based fertilizers can be a sustainable alternative to traditional fertilization. The aim of the study was to compare the potential of pristine and engineered biochars to recover nutrients from wastewater and to determine the factors which may affect this process. Engineered biochar can be used as a selective adsorbent from multicomponent solutions. Adsorption on engineered biochar can be also regulated by additional mechanisms: surface precipitation and ligand/ion exchange. Metal modification (e.g. Mg, Fe) enhances PO₄^3- and NO₃^- adsorption capacity, and thus may provide the extra plant macro-/micronutrients. The desorption mechanism, which is the basis for nutrient release are strongly pH depended. The use of biochar-based fertilizer can have economic and agricultural benefits when using waste materials and reducing pyrolysis energy costs.

Emerging nanotechnology based advanced techniques for wastewater treatment

The increasing trend of industrialization leads to tremendous release of industrial effluents. Waste water treatment is one of the important sectors to focus in order to overcome the most threatening issue of waste disposal and to ensure sustainability. Sustainable and energy efficient treatment methods are the attractive technologies for their current implementation of waste management. Even though the existing technologies are effective, unsustainability makes them unfit for their extended applications. Conventional and advanced technologies have been extensively implemented for the treatment of wide spectrum of effluents. Hybrid technologies including chemical and biological methods also emerging as promising technologies but secondary sludge generation is still unaddressed. Even though effectiveness of biochar varies over type of contaminants, cost-effectiveness and eco-friendly nature extended their applications in waste management. Nanotechnology and membrane technology are the promising and emerging areas of interest due to their widespread applications in waste water treatment. Carbon nano structures, nano filters, graphene, nano magnets modified with activated carbon are the potential candidates for the treatment. The present review demonstrates the emerging treatment technologies with special focus to nano based waste water treatment methods.

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

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

Ball milling sulfur-doped nano zero-valent iron @biochar composite for the efficient removal of phosphorus from water: Performance and mechanisms

This study successfully prepared a novel sulfur-doped nano zero-valent iron @biochar (BM-SnZVI@BC) by modifying corn stover biochar with Fe⁰ and S⁰ using a mechanical ball milling method for effective phosphorus (P) adsorption in the waterbody. Batch experiments revealed that BM-SnZVI@BC (BC/S⁰/Fe⁰ = 3:1:1) reached a Q_max of 25.00 mg P/g and followed PFO and Langmuir models. This work had shown that electrostatic attraction, surface chemical precipitation, hydrogen bonding, and ligand effects all contributed to P removal. Since the FeS layer mitigated the oxidation-induced surface passivation of nZVI, sulfidation significantly extended the lifetime of BM-SnZVI@BC, removing 84.4% of P even after 60 d aging in air. The regeneration experiments of composites showed that re-ball milling destroyed the surface iron oxide layer to improve the properties of the recovered material. This is an essential step in the design of P-removal agents to implement anti-aging and commercialization of adsorbents for engineering applications.

Unintentional release of antibiotics associated with nutrients recovery from source-separated human urine by biochar

The use of biochar to recover nitrogen and phosphorus from wastewater especially source-separated human urine is attractive from both economic and environmental standpoints. The widespread use of pharmaceuticals has raised concerns as they are not fully metabolized and ended up in human urine. The objective of this study is to examine adsorption of antibiotics (azithromycin, ciprofloxacin, sulfamethoxazole, trimethoprim, and tetracycline) and nutrients (ammonium and phosphate) in source-separated human urine by biochar and subsequent desorption. Batch adsorption experiments were conducted using biochar prepared from oak wood (OW) and paper mill sludge (PMS) to elucidate the effects of adsorption time, pH, and adsorbent dose. The desorption of adsorbed nutrients and antibiotics was also investigated. While the nutrient adsorption was more favorable by the PMS biochar, antibiotic adsorption was more prolific by the OW biochar. Hydrogen bonding and π-π interaction were identified as potential adsorption mechanisms. Experimental results agree with the Freundlich isotherm and pseudo-second order models (except the OW biochar for the kinetics). The findings suggest that biochar can adsorb both nutrients (43.30-266.67 mg g^-1) and antibiotics (246.70-389.0 μg g^-1) simultaneously. Lower solution pH (<5) was better for antibiotic adsorption, while higher solution pH (≥5) favored nutrient recovery. Also, desorption of the antibiotics (maximum of 92.6% for trimethoprim) was observed and might arise in the environment with the applications of biochar for nutrient recovery from human urine and subsequently for soil quality improvement. The findings serve as a foundation for future research on adsorption-based methods for separating nutrients and antibiotics in aqueous solutions, particularly urine.

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.

Chitosan-modified biochar: Preparation, modifications, mechanisms and applications

The chitosan-modified biochar composite, as a carbohydrate polymer, has received increasing attention and becomes a research hotspot. It is a promising impurity adsorption material, which has potential application value in the agricultural environment fields such as soil improvement and sewage purification. The composite can combine the advantages of biochar with chitosan, and the resulting composite usually exhibits a great improvement in its surface functional groups, adsorption sites, stability, and adsorption properties. In addition, compared to other adsorbents, the composite truly achieves the concept of "waste control by waste". In this paper, the preparation method, composite classification, adsorption mechanism, and models of biochar modified by chitosan are introduced, meanwhile, we also review and summarize their effects on the decontamination of wastewater and soil. In addition to common heavy metal ions, we also review the adsorption and removal of some other organic/inorganic pollutants, including (1) drug residues; (2) dyes; (3) phosphates; (4) radionuclides; (5) perfluorochemicals, etc. Moreover, challenges and prospects for the composite are presented and further studies are called for the chitosan-biochar composite. We believe that the composite will lead to further achievements in the field of environmental remediation.

Simultaneous adsorption of ammonia and phosphate using ferric sulfate modified carbon/zeolite composite from coal gasification slag

Removal of nutrients in water is crucial to control eutrophication. Fly ash has been increasingly used to synthesize zeolite to remove nutrients, but it is still poorly understood about the removal capacity of zeolite synthesized from coal gasification slag (CGS), which has not been well recycled in many countries. In this study, the CGS was acid leached, alkali dissolved, and synthesized to carbon/zeolite composite (C/ZC) under induction by medical stone. After being modified by ferric sulfate, the composite was analyzed for the adsorption of NH₄⁺ and PO₄^3-. Results showed that the maximum adsorption capacity by C/ZC is 5.17 mg/g, but C/ZC has no adsorption capacity of PO₄^3-. The ferric sulfate was used to modify C/ZC to obtain carbon/zeolite composite modified by iron (M-C/ZC). M-C/ZC has a higher specific surface area (348.3 m²/g), and the negatively charge of M-C/ZC can adsorb NH₄⁺ and form Fe-O-P between PO₄^3- and Fe-OH bonds. The maximum adsorption capacity of NH₄⁺ and PO₄^3- by M-C/ZC are 7.44 mg/g and 6.94 mg/g, respectively. The removal efficiency of NH₄⁺ and PO₄^3- are up to 88% and 99% under initial NH₄⁺ (5 mg/L) and PO₄^3- (10 mg/L) concentration. The regeneration capacity of M-C/ZC of NH₄⁺ was stronger than that of PO₄^3-. After three cycles, the regeneration rate of M-C/ZC of NH₄⁺ was still up to 76.96%. Our findings suggest the good application potential of M-C/ZC for removing NH₄⁺ and PO₄^3- from wastewater.

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.

Biochar application in biofiltration systems to remove nutrients, pathogens, and pharmaceutical and personal care products from wastewater

Although conventional on-site wastewater treatment systems (OWTSs) provide only primary treatment of domestic wastewater, removal of a limited level of nutrients (N, P), pathogens, and pharmaceuticals and personal care products (PPCPs) could be achieved by such a treatment process. Biochar has the capacity to remove various contaminants and has been widely used as an ideal soil amendment in agriculture due to its persistence, superior nutrient-retention properties, low cost, and ready availability. However, few applications on the use of biochar in onsite wastewater treatment have been explored. In this review, we systematically reviewed the applications of biochar in filtration-based OWTSs for nutrient (N, P) removal and recovery as well as pathogen and PPCP removal. Although adsorption was the main mechanism for P, pathogen, and PPCP removal, biochar can also serve as the growth media for enhanced biological degradation, improves available alkalinity, and increases water holding capacity in the OWTSs. The biochar source, surface modification methods, and preparation procedures (e.g., pyrolysis temperature change) have significant effects on contaminant removal performance in biochar-amended OWTSs. Specifically, contradictory results have been reported on the effect of pyrolysis temperature change on biochar removal performance (i.e., increased, decreased, or no change) of N, P, and PPCPs. Wastewater composition and environmental pH also play important roles in the removal of nutrients, pathogens, and PPCPs. Overall, biochar holds great potential to serve as an alternative filtration material or to be amended to the current OWTS to improve system performance in removing a variety of contaminants at low cost.

Characterisation, adsorption and desorption of ammonium and nitrate of biochar derived from different feedstocks

Biochar is known to be a highly adsorptive material, especially when the biochar is altered by activation to further increase its sorption ability. Little information, however, is available on the potential reversibility of both ammonium (NH4+) and nitrate (NO3-) sorption on the inherent biochar pH. The objective of our study was to characterise biochars made using different pyrolysis conditions from five various plant materials and rubber tyre, and to use them to investigate the biochar properties responsible for NH4+ and NO3- adsorption and desorption. The rubber tyre, maize stover and sugarcane pith were the weakest adsorbing biochars (5.7-7.8 mg g^-1) and best described by the Freundlich adsorption isotherm. The grape pip, grape skin and pine wood biochars had adsorption capacities in the range 8.3-9.4 mg NH4+ g^-1 and best described by a linear adsorption isotherm at 100 mg L^-1. The NH4+ adsorption results were associated with physisorption which implies that they can act as slow release NH4+ fertilisers if NH4+ is bioavailable. The six biochars had NO3- adsorption capacities in the range 15.2-15.9 mg g^-1 and were well fitted to the linear adsorption isotherm at 100 mg L^-1. All six biochars had a stronger NO3- removal affinity (82-89%) compared to NH4+ (33-39%). Adsorbed nitrate was not desorbable (0.01-0.23%) compared to adsorbed NH4+ which was 53-60% desorbable. The desorption result was possibly due to NO3- competing redox reactions or NO3- being too strongly adsorbed for extraction. Desorption of NH4+ was associated with biochar net negative pH values and volatilisation of ammonia.

Synthesis of zeolite/geopolymer composite for enhanced sequestration of phosphate (PO43-) and ammonium (NH4+) ions; equilibrium properties and realistic study

Zeolite impeded geopolymer (Z/G) was synthesized from natural kaolinite and diatomite. The structure (Z/G) was characterized as an enhanced adsorbent for PO₄^3- and NH₄⁺ ions from aqueous solutions, groundwater, and sewage water. The synthetic Z/G structure exhibits sequestration capacities of 206 mg/g and 140 mg/g for PO₄^3- and NH₄⁺, respectively which are higher values than the recognized results for the geopolymer and other adsorbents in literature. The sequestration reactions of PO₄^3- and NH₄⁺ by Z/G are of Pseudo-Second order kinetic behavior considering both the Chi-squared (χ²) and correlation coefficient (R²) values. The sequestration reactions occur in homogenous and monolayer forms considering their agreement with Langmuir behavior. The Gaussian energies (12.4 kJ/mol (PO₄^3-) and 10.47 kJ/mol (NH₄⁺)) demonstrate the operation of a chemical sequestration mechanism that might be involved zeolitic ion exchange process and chemical complexation. Additionally, these reactions are exothermic processes of spontaneous and favorable properties based on thermodynamic studies. The Z/G structure is of significant affinity for both PO₄^3- and NH₄⁺ even in the existence of other anions as Cl^-, HCO₃^-, SO₄^2-, and NO₃^-. Finally, the structure used effectively in the purification of groundwater and sewage water from PO₄^3- and NH₄⁺ in addition to nitrate, sulfate, and some metal ions.

Circular economy-driven ammonium recovery from municipal wastewater: State of the art, challenges and solutions forward

In current biological nitrogen removal (BNR) processes, most of ammonium in municipal wastewater is biologically transformed to nitrogen gas, making ammonium recovery impossible. Thus, this article aims to provide a holistic review with in-depth discussions on (i) current BNR processes for municipal wastewater treatment, (ii) environmental and economic costs behind ammonium in municipal wastewater, (iii) state of the art of ammonium recovery from municipal wastewater including anaerobic membrane bioreactor turning municipal wastewater to a liquid fertilizer, capturing ammonium in phototrophic biomass, waste activated sludge for land application, bioelectrochemical systems, biological conversion of ammonium to nitrous oxide as a fuel oxidizer, and adsorption, (iv) feasibility and challenge of adsorption for ammonium recovery from municipal wastewater and (v) innovative municipal wastewater reclamation processes coupled with ammonium recovery. Moving forward, municipal wastewater reclamation and resource recovery should be addressed under the framework of circular economy.

Removal of ammonia nitrogen and phosphorus by biochar prepared from sludge residue after rusty scrap iron and reduced iron powder enhanced fermentation

The rusty scrap iron (RSI) or a mixture of rusty scrap iron and reduced iron powder (RSI-RIP) can be used as an exogenous additive to enhance the anaerobic fermentation of sewage sludge. In order to make rational use of the fermentation residue, the sludge after intensified fermentation was pyrolyzed to produce biochar in this study, which was used in the adsorption of ammonia and phosphorus from the anaerobic fermentation broth. The experimental results demonstrated that the pore structure of the sludge biochar was greatly improved after enhanced fermentation with RSI and RIP. Meanwhile, there was an increase in the proportion of metallic elements such as Ca, Fe and Mg. On the other hand, the RSI-RIP co-enhanced fermented biochar (ES600) prepared at 600 °C showed a higher adsorption capacity, which was comparable to the commercially activated carbon. Neutral or weakly alkaline environments were preferred during the adsorption process. At a suitable pH condition, the maximum removal efficiency of ammonia nitrogen (NH₄⁺-N) and total phosphorus (TP) on ES600 reached 91.3% and 98.6%, respectively. In addition, the saturated ES600 was regenerated by simple washing with ammonia-free water. After three cycles, the removal efficiency of NH₄⁺-N and TP remained at 71.3% and 83.2%, respectively. As a result, the biochar prepared from RSI-RIP enhanced fermented sludge can be used as a promising low-cost adsorbent.

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

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

Characteristics and mechanisms of phosphorous adsorption by rape straw-derived biochar functionalized with calcium from eggshell

Biochar modified with calcium source is acted as an effective adsorbent for phosphorous recovery. In this research, eggshell is used as a low-cost and environmentally friendly calcium source to replace chemical reagents such as CaCO₃, Ca(OH)₂ and CaCl₂ used in the modified biochar production. Biochar derived from rape straw and modified with eggshell shows prominent phosphorous adsorption performance (e.g., equilibrium adsorption amount, 109.7 mg/g). The kinetic and isotherm analysis demonstrate that chemical adsorption process is performed as the main controlled step for the modified biochar adsorption, and the phosphate adsorption process is composed of both monolayer adsorption and multi-layer adsorption. Moreover, it is found from the physicochemical structures comparison before and after phosphate adsorption that Ca-P precipitation, hydrogen bonding and electrostatic attraction are identified as main adsorption mechanisms. In addition, the adsorbed phosphates are mainly distributed inside the space with pore sizes of 15-50 nm.

Promoting the decontamination of different types of water pollutants (Cd2+, safranin dye, and phosphate) using a novel structure of exfoliated bentonite admixed with cellulose nanofiber

Exfoliated bentonite sheets admixed with nano-cellulose fibers (EXB/CF) were prepared as advanced bio-composite of enhanced decontamination properties for different species of water pollutants (Cd²⁺, safranin dye, and phosphate). The composite achieved promising adsorption capacities with experimental values of 206.8 mg/g (Cd²⁺), 336 mg/g (safranin), and 296 mg/g (phosphate); and predicted maximum capacities of 212.9 mg/g (Cd²⁺), 341 mg/g (safranin), and 305 mg/g (phosphate). The adsorption systems for the three species follow the Freundlich isotherm model and Pseudo-First order as kinetic model considering both the linear and nonlinear fitting demonstrating heterogeneous and multilayer uptake properties of physisorption type. The operation of physisorption mechanisms was supported by the obtained adsorption energies from D-R model that are less than 8 kJ/mol as well as the calculated free energies and enthalpies. The thermodynamic investigation revealed the nature of the adsorption reactions of the three pollutants by EXB/CF as exothermic, favorable, and spontaneous reactions. The EXB/CF composite also is of significant recyclability value and applied in five decontamination reusing runs for Cd²⁺, safranin dye, and phosphate achieving promising removal percentages.

Preparation of biochar by mango peel and its adsorption characteristics of Cd(ii) in solution

Biochars were prepared by pyrolyzing mango peel waste at 300, 400, 500, 600 and 700 °C. Various characterizations were carried out to explore the effect of pyrolysis temperature on the biochars. The data indicated that the physical and chemical properties of biochar such as pH, element ratio, specific surface area and functional groups changed with the increase of pyrolysis temperature. The yield and contents of hydrogen, nitrogen and oxygen decreased, while contents of the ash and carbon, pH and specific surface area of the biochars increased. In addition, the molar ratios of H/C, O/C and (O + N)/C decreased. In this study, batch adsorption experiments for Cd(ii) adsorption were performed with initial Cd(ii) concentrations of 10-300 mg L-1, contact times of 0-2880 min, various pH (2-8) and biochar dose (1-20 g L-1). Langmuir isotherm and pseudo-second-order kinetics models were better fits than other models, suggesting the dominant adsorption of mango peel biochars is via monolayer adsorption. Biochar derived at 500 °C was found to have the highest adsorption capacity of 13.28 mg g-1 among all biochars and the adsorption efficiency was still 67.7% of the initial adsorption capacity after desorption for 4 times. Based on adsorption kinetics and isotherm analysis in combination with EDS, FTIR and XRD analysis, it was concluded that cation exchange, complexation with surface functional groups and precipitation with minerals were the dominant mechanisms responsible for Cd adsorption by mango peel biochar. The study suggested that mango peel can be recycled to biochars and can be used as a low-cost adsorbent for Cd(ii) removal from wastewater.

Enhanced removal of ammonium from water by ball-milled biochar

Novel biochar was prepared by ball milling using bamboo as raw material. The aim of this study was to find a good alternative way to improve the potentials of biochar for ammonium adsorption from aqueous solution. The sorption performance of ball-milled bamboo biochar (BMBB) was compared with that of bamboo biochar (BB) using batch adsorption experiments. Different adsorption kinetics models proved that the pseudo-second order was the best kinetic model for explanation of the adsorption kinetics characteristics, indicative of the energetically heterogeneous solid surface of the biochar. The Langmuir model could fit the isothermal adsorption data of BMBB well. The maximum adsorption capacity of BMBB (22.9 mg g^-1) was much higher than that of BB (7.0 mg g^-1). This study offers a relatively cost-effective and efficient methodology for the improvement in the adsorption capacity of biochar for ammonium nitrogen.

Competitive adsorption behaviour and mechanisms of cadmium, nickel and ammonium from aqueous solution by fresh and ageing rice straw biochars

In this study, competitive adsorption behaviour and mechanisms of Cd²⁺, Ni²⁺ and NH₄⁺ by fresh and artificially ageing biochars produced from rice straw at 400 and 700 °C (RB400, RB700, HRB400 and HRB700) were investigated. Cd²⁺ competed with Ni²⁺ and NH₄⁺ for the overlapped adsorption sites on the biochars. For Cd²⁺ and Ni²⁺ adsorption, cation exchange (Q_ci) and mineral co-precipitation (Q_cp) were the primary mechanisms for the low-temperature and high-temperature biochars, respectively. However, the other potential mechanisms (Q_co) made the greatest contributions to NH₄⁺ adsorption (>60%). Cd²⁺ and Ni²⁺ competition increased the proportions of mineral co-precipitation (Q_cp) and other potential mechanisms (Q_co) but decreased that of cation exchange (Q_ci) mechanism. Biochar ageing increased the contribution of surface complexation (Q_cf) mechanism, especially for the low-temperature biochars. This study indicated that biochar aging and types and states of adsorbates should be considered when biochars were applied to remove contaminants.

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.

The Removal of Crystal Violet from Textile Wastewater Using Palm Kernel Shell-Derived Biochar

In this study, we explored the adsorption potential of biochar derived from palm kernel shell (BC-PKS) as an affordable adsorbent for the removal of crystal violet from wastewater. Kinetics, equilibrium, and thermodynamics studies were carried out to evaluate the adsorption of crystal violet onto BC-PKS. The kinetics adsorption process followed the pseudo-second-order model, indicating that the rate of adsorption is principally controlled by chemisorption. The adsorption equilibrium data were better fitted by the Langmuir isotherm model with a determination coefficient of 0.954 and a maximum adsorption of 24.45 mg/g. Thermodynamics studies found the adsorption of crystal violet by BC-PKS to be endothermic with increasing randomness at the BC-PKS/crystal violet interface. The percentage removal and adsorption capacity increased with the pH of the solution, as the negative charges on the biochar surface at high pH enhance the electrostatic attraction between crystal violet molecules and BC-PKS. Increasing the BC-PKS dosage from 0.1 to 1.0 g increased percent removal and decreased the adsorption capacity of crystal violet onto BC-PKS. Therefore, biochar from agricultural by-products, i.e., palm kernel shell, can be cost-effective adsorbents for the removal of crystal violet from textile wastewater.

Removal of ammonium ion from aqueous solutions by using unmodified and H2O2-modified zeolitic waste

In the petroleum industry during a catalytic cracking process, the used zeolitic catalyst becomes waste. This article investigated the sorption capacities of ammonium ions from aqueous solutions onto the previously mentioned zeolitic waste by batch experiments. Three types of zeolitic waste were used: unmodified zeolitic waste with two different particle size distributions and H2O2-modified zeolitic waste. Several techniques, including X-ray diffraction (XRD) analysis, Fourier transform infrared spectroscopy (FT-IR), Brunauer-Emmett-Teller (BET) multilayer adsorption theory measurements, and X-ray fluorescence analysis (XRF) were used to demonstrate experimentally that the zeolitic waste could be used as a sorbent for the water decontamination of NH4+ ions. The morphology of zeolitic waste investigated by scanning electron microscopy (SEM) revealed particles with a spherical shape. The nitrogen adsorption-desorption isotherms showed an isotherm mixture of types I (pure microporous) and IV (mesoporous). This suggested that the investigated zeolitic materials were mesoporous (4.84 nm) and microporous (0.852 nm), as well as containing slit/cylindric pores, according to a quench solid density functional theory (QSDFT) adsorption branch model. Zeolitic waste from the oil industry showed good NH4+ sorption properties (removal efficiency of 72%), thus becoming a potential adsorbent to be used in the treatment of contaminated aqueous effluents polluted with ammonium ions. Simultaneous waste and water decontamination can be achieved, providing a new tool and enhanced capabilities for environmental remediation.

High-Temperature Hay Biochar Application into Soil Increases N2O Fluxes

Biochar has been proposed as an amendment that can improve soil conditions, increase harvest yield, and reduce N losses through NO3− leaching and N2O emissions. We conducted an experiment to test the hay biochar mitigation effect on N2O emissions depending on its production temperature. The pot experiment consisted of the soil amendment with three different production temperature biochars (300 °C, 550 °C, 850 °C) alone and in combination with three different organic fertilizers (cattle slurry, slurry digestate, vinasse), in growth chamber conditions. The effects of biochar and fertilizer were both significant, but the interaction biochar:fertilizer was not. The amendment with the three fertilizer types and with the highest production temperature biochar resulted in significantly higher cumulative N2O fluxes. Biochar did not show a mitigation effect on N2O emissions when applied with organic fertilizer. Cumulative emissions were higher with biochar addition, with increasing emissions for increasing biochar production temperature. Our results support the idea that biochar cannot be considered as a universal tool for the reduction of N2O emissions.

Biochar with near-neutral pH reduces ammonia volatilization and improves plant growth in a soil-plant system: A closed chamber experiment

Ammonia (NH₃) volatilization is considered as one of the major mechanisms responsible for the loss of nitrogen (N) from soil-plant systems worldwide. This study investigated the effect of biochar amendment to a calcareous soil (pH 7.8) on NH₃ volatilization and plant N uptake. In particular, the effect of biochar's feedstock and application rate on both NH₃ volatilization and plant growth were quantified using a specially designed closed chamber system. Two well-characterized biochars prepared from poultry manure (PM-BC) and green waste compost (GW-BC) were applied to the soil (0, 0.5, 1, 1.5 and 2% w/w equivalent to 0, 7.5, 15, 22 and 30 t ha^-1) and wheat (Triticum aestivum, variety: Calingiri) was grown for 30 days. Both PM-BC and GW-BC decreased NH₃ volatilization to a similar degree (by 47 and 38%, respectively), in the soil-plant system compared to the unamended control. Higher plant biomass production of up to 70% was obtained in the closed chamber systems with the addition of biochar. The increase in plant biomass was due to the reduction in N loss as NH₃ gas, thereby increasing the N supply to the plants. Plant N uptake was improved by as much as 58% with biochar addition when additional NPK nutrients were supplied to the soil. This study demonstrates that the application of biochars can mitigate NH₃ emission from calcareous agricultural cropping soil and that the retained N is plant-available and can improve wheat biomass yield.

Agricultural waste

The management of agricultural waste has become very important because the inappropriate disposal yields negative effects on the environment. The resource recovery from agricultural waste which converts waste into available resources can reduce the waste and new resource consumption. This review summarizes the 2018 researches of over three hundred scholar papers from several aspects: agricultural waste, and, waste chemical characterization, agricultural waste material, adsorption, waste energy, composting, waste biogas, agricultural waste management, and others.

Using Recycled Concrete as an Adsorbent to Remove Phosphate from Polluted Water

Phosphate pollution remains a significant hazard to terrestrial and aquatic ecosystems. We developed an economical and efficient method for phosphate adsorption on waste construction concrete modified with seawater. Compared with raw concrete materials, the phosphate adsorption capacity of seawater-modified waste concrete was highly efficient, especially at low phosphate concentrations. The inflection point for seawater-modified concrete was 0.66 and 1.22 mg L for the raw material. The relative phosphate adsorption was 4.64 and 2.39 mg g, respectively. Phosphate removal was >90% over a pH range of 3 to 11 for the raw and modified materials. Chemical and physical analysis of the modified concrete indicated that Ca and Mg particles were uniformly sequestrated on the surface, and Ca was the determinant controlling phosphate uptake. Phosphate adsorption isotherms fit well using the Freundlich, Temkin, Elovich, Fowler-Guggenheim, and Hill-de Boer models and indicated that intermolecular forces in the concrete particles were enhanced by calcium oxides from seawater. This method can efficiently remove phosphate from polluted water and repurposes waste construction concrete.

Dataset of the aqueous solution and petrochemical wastewater treatment containing ammonia using low cost and efficient bio-adsorbents

In this dataset, the removal of ammonia from synthetic and real wastewater was studied using the Ziziphus spina-christi activated carbon (ZSAC) and the biochar of Sargassum oligocystum (BSO). Several analyses such as FTIR, SEM, EDS, XRD, and BET were used to determine the physical and surface properties of the adsorbents. The BET analysis showed a high specific surface area of 112.5 and 45.8 m²/g for ZSAC and BSO, respectively. Also, the results indicated that the highest adsorption of ammonia from synthetic wastewater using ZSAC and BSO were obtained 97.9% and 96.2%, at contact time of 80 min, 25 °C, pH 8, and adsorbent dosage of 5 g/L. In addition, the adsorption results of real wastewater from Asaluyeh Pardis Petrochemical Company demonstrated that both adsorbents had the removal efficiency of approximately 90%, which indicates high adsorption efficiency using two adsorbents. Moreover, equilibrium studies showed that the adsorption process of ammonia from wastewater using both adsorbents follows the Freundlich model and the maximum adsorption capacity using the Langmuir isotherm were calculated to be 25.77 mg/g and 7.46 mg/g for ZSAC and BSO, respectively. Furthermore, the thermodynamic study showed that the adsorption process using the bio-adsorbents was spontaneous and exothermic.

Effective decontamination of phosphate and ammonium utilizing novel muscovite/phillipsite composite; equilibrium investigation and realistic application

Novel muscovite/synthetic zeolitic phillipsite composite (Mu/Ph) was synthesized and inspected by different analytical techniques as a hybrid product of enhanced physicochemical properties and adsorption capacities for phosphate and ammonium. Mu/Ph adsorption systems for phosphate and ammonium were inspected considering the kinetic, equilibrium and thermodynamic studies as well as the controlling mechanisms. The kinetic behaviors of Mu/Ph for both phosphate and ammonium were remarkably described by Pseudo-second order model and the equilibration times were attained after 720 min and 480 min, respectively. The equilibrium curves for both ions were categorized as L-type isotherms which assigned mainly to systems of high affinity between the inspected adsorbents and the target dissolved ions. Additionally, the uptake results of both ions displayed slight preferences to be described by the Langmuir model. The thermodynamic studies revealed endothermic and exothermic nature for phosphate and ammonium, respectively. Moreover, the calculated parameters indicated physisorption of them by spontaneous reaction involved ion exchange processes controlled mainly by electrostatic interactions rather than ionic or covalent binding. The composite showed promising reusability properties to be applied in the reduction of phosphate and ammonium six times. The novel synthetic Mu/Ph exhibits higher capacities than numerous studied adsorbents and was applied in decontamination of phosphate and ammonium from real sewage water achieving exceptional results.

Nitrogen and phosphorus removal from wastewater by sand with wheat straw

Wheat straw amendment to sandy soil has the potential to remove nutrients from wastewater. This study investigated the ability of wheat straw to remove inorganic nitrogen (N) and phosphorus (P) from wastewater when mixed into sand at different rates. Wastewater from a sewage treatment plant was added to sand alone and amended with different wheat straw rates 2.5, 5, 7.5, 10, and 12.5 g wheat straw kg^-1 so that the sand was covered with about 15 cm of wastewater. Leaching was carried out after 4, 8, and 16 days and inorganic N and P were analysed after leaching in both the leachate and sand, as well as N₂O and CO₂ release. In the amended sand, nitrate was about fourfold lower throughout the experiment compared to sand alone. Ammonium was twofold higher than sand alone at 12.5 g straw kg^-1 throughout the experiment and on day 16 also at ≥ 5 g straw kg^-1. Leachate inorganic N concentration was up to 70-fold higher in sand alone than in amended soils irrespective of straw rate. On day 16, P leaching was about threefold lower and P retention was 40% higher in all amended treatments than sand alone. The redox potential in sand alone was higher than with straw amendments. With straw amendment, the release of CO₂ per day was six times higher than with sand alone and increased with straw rates, but very little N₂O and CH₄ was released throughout the experiment. It can be concluded that amendment of sand with wheat straw can remove large proportions of inorganic N and P from wastewater, even at low straw rates. Likely mechanisms for retention are dissimilatory nitrate reduction and subsequent binding of ammonium to straw for N, and binding to the straw and microbial uptake for P.

Sorption of ammonium and nitrate to biochars is electrostatic and pH-dependent

Biochars are potentially effective sorbents for NH4+ and NO3- in water treatment and soil applications. Here we compare NH4+ and NO3- sorption rates to acid-washed biochars produced from red oak (Quercus rubra) and corn stover (Zea mays) at three pyrolysis temperatures (400, 500 and 600 °C) and a range of solution pHs (3.5-7.5). Additionally, we examined sorption mechanisms by quantification of NH4+ and NO3- sorption, as well as Ca2+ and Cl- displacement for corn stover biochars. Solution pH curves showed that NH4+ sorption was maximized (0.7-0.8 mg N g-1) with low pyrolysis temperature (400 °C) biochar at near neutral pH (7.0-7.5), whereas NO3- sorption was maximized (1.4-1.5 mg N g-1) with high pyrolysis temperatures (600 °C) and low pH (3.5-4). The Langmuir (r2 = 0.90-1.00) and Freundlich (r2 = 0.81-0.97) models were good predictors for both NH4+ (pH 7) and NO3- (pH 3.7) sorption isotherms. Lastly, NH4+ and NO3- displaced Ca2+ and Cl-, respectively, from previously CaCl2-saturated corn stover biochars. Results from the pH curves, Langmuir isotherms, and cation displacement curves all support the predominance of ion exchange mechanisms. Our results demonstrate the importance of solution pH and chemical composition in influencing NH4+ and NO3- sorption capacities of biochar.