Waste shrimp shell-derived hydrochar as an emergent material for methyl orange removal in aqueous solutions

Revolutionizing waste: Harnessing agro-food hydrochar for potent adsorption of organic and inorganic contaminants in water

Constant pollution from a wide range of human activities has a negative impact on the quantity and quality of the planet's water resources. On the other hand, agro-food waste can impact climate change and other forms of life, in addition to having social, economic, and environmental consequences. However, as a result of their inherent physicochemical properties and lignocellulosic composition, these residues are becoming increasingly recognized as valuable products in line with government policies advocating zero waste and circular economies. An advantageous way to convert these wastes into energy and chemicals is hydrothermal carbonization (HTC). This review highlights the valorization of agro-food waste into hydrochar-based adsorbents for the elimination of organic and inorganic contaminants from aqueous environments. An overview of the toxicity of pollutants in aqueous environments, food waste management, as well as HTC technology was initially proposed. Then, a discussion on the conversion of major agro-food wastes into contaminant adsorbents was given in detail. Adsorption mechanisms as well as the possibility of reuse of adsorbents were also discussed. Enhanced properties of the produced materials enable them to provide competent solutions to various ecological contexts, including removing pollutants from wastewater with cost-effectiveness and satisfactory results. Besides addressing environmental concerns, this sustainable approach opens the door for more environmentally-friendly and resource-efficient applications in the future, making it an exciting prospect.

Biochar-based adsorption for heavy metal removal in water: a sustainable and cost-effective approach

The increasing contamination of aquatic bodies by heavy metals poses a significant threat to environment and human health, necessitates innovative, sustainable and cost-effective remediation strategies. Due to their persistence and toxicity, heavy metals like copper (Cu), lead (Pb), mercury (Hg), and cadmium (Cd) pose severe threats, even in trace amounts. Traditional removal methods of these heavy metals, like chemical precipitation, oxidation/reduction, filtration, ion exchange, membrane separation, and adsorption, are costly, inefficient, and have drawbacks. As an efficient and low-cost adsorbent, biochar has the potential for heavy metal remediation from water. Biochar is a versatile carbonaceous material produced through pyrolysis of organic wastes, emerged as a powerful adsorbent for heavy metal removal from contaminated water. The unique property of biochar makes it an effective medium immobilizing and capturing of heavy metals like Pb, Cd, As and Hg. Various factors affect its adsorption potential and capacity. Feedstocks type, composition, activation methods, and production processes including the pyrolysis temperature, temperature rate and residence time significantly impact the efficacy of biochar. Therefore, this review has assessed, compared, and contrasted different forms of biochar along with their production methods, modification techniques and mechanisms for their potential use as an adsorbent for heavy metal removal from the contaminated water. Modified biochar offers an environmentally friendly and cost-effective solution for water purification and remediation of toxic heavy metals from water. This review highlights the biochar potential as a crucial component for future research projects focusing on water treatment technologies, providing avenues for safer and cleaner water resources.

Solid shrimp waste derived nanoporous carbon as an alternative bio-sorbent for oxytetracycline removal from aquaculture wastewater

Recently, it has been critical to effectively remove oxytetracycline (OTC) from aquaculture wastewater before releasing into the environment. The adsorption process is recognized as an efficient pathway for removing OTC since it is a simple, stable, and cost-effective method. This study aims to develop nanoporous carbon entirely from shrimp waste (SW) via hydrothermal carbonization assisted with KOH activation. Existing KOH significantly increases the porosity of SW nanoporous carbon. The optimal SW porous carbon was obtained using 5 wt%KOH for activation, which had the largest surface area of 679.51 m2/g with the total pore volume of 0.458 cm3/g. Moreover, the SW porous carbon with the highest porosity was selected for the OTC adsorption. The Langmuir isotherm model and the pseudo-second-order kinetic model match the experimental data, implying that the adsorption mechanism is mono-layered adsorption due to micropores by chemisorption interaction. The adsorption capacity significantly improved by increasing the dosage of SW nanoporous carbon. The SW nanoporous carbon adsorption for OTC is primarily regulated by pore filling affected by hydrogen bonding, and π-π* interaction also plays a significant role. The SW nanoporous carbon showed an efficient OTC adsorption after 5 regeneration cycles. This work demonstrates biomass waste recycling and emphasizes the potential of aquatic food processing waste-derived nanoporous carbon for antibiotic adsorption.

Seafood waste derived carbon nanomaterials for removal and detection of food safety hazards

Nanobiotechnology and the engineering of nanomaterials are currently the main focus of many researches. Seafood waste carbon nanomaterials (SWCNs) are a renewable resource with large surface area, porous structure, high reactivity, and abundant active sites. They efficiently adsorb food contaminants through π-π conjugated, ion exchange, and electrostatic interaction. Furthermore, SWCNs prepared from seafood waste are rich in N and O functional groups. They have high quantum yield (QY) and excellent fluorescence properties, making them promising materials for the removal and detection of pollutants. It provides an opportunity by which solutions to the long-term challenges of the food industry in assessing food safety, maintaining food quality, detecting contaminants and pretreating samples can be found. In addition, carbon nanomaterials can be used as adsorbents to reduce environmental pollutants and prevent food safety problems from the source. In this paper, the types of SWCNs are reviewed; the synthesis, properties and applications of SWCNs are reviewed and the raw material selection, preparation methods, reaction conditions and formation mechanisms of biomass-based carbon materials are studied in depth. Finally, the advantages of seafood waste carbon and its composite materials in pollutant removal and detection were discussed, and existing problems were pointed out, which provided ideas for the future development and research directions of this interesting and versatile material. Based on the concept of waste pricing and a recycling economy, the aim of this paper is to outline current trends and the future potential to transform residues from the seafood waste sector into valuable biological (nano) materials, and to apply them to food safety.

Recent advances in environmental and agricultural applications of hydrochars: A review

Hydrochar is a carbonaceous material that is generated through the process of hydrothermal carbonization (HTC) from biomass, which has garnered considerable attention in recent years owing to its potential applications in a diverse range of fields, such as environmental remediation and agriculture. Hydrochar is produced from a diverse range of biomass waste materials and retains exceptional properties, including high carbon content, stability, and surface area, making it an optimal candidate for various enviro-agricultural applications. Moreover, it delves into the production process of hydrochar, with explicit emphasis on the optimization of certain properties during the production of hydrochar from bio-waste. Furthermore, the potential of hydrochar as an adsorbent and catalyst support for heavy metals and dyes was extensively explored, along with a soil remediation potential that can improve the physical, chemical and biological properties of soil. This comprehensive review aims to provide a thorough overview of hydrochar with a particular focus on its production, properties, and prospective applications. The significance of hydrochar is accentuated and the growing need for alternative sources of energy and materials that are environmentally sustainable is highlighted in this paper. Besides, the consequence of hydrochar on soil properties such as water-holding capacity, nutrient retention, and total soil porosity, as well as its influence on soil chemical properties such as cation exchange capacity, electrical conductivity, and surface functionality is scrutinized.

Preparation of composites with MgAl-LDH-modified commercial activated carbon for the quick removal of Cr(VI) from aqueous solutions

The problem of soil and water contamination caused by Cr(VI) discharged from the dyeing, electroplating, and metallurgical industries is becoming increasingly serious, posing a potentially great threat to the environment and public health. Therefore, it is crucial to develop a fast, efficient, and cost-effective adsorbent for remediating Cr-contaminated wastewater. In this work, MgAl-LDH/commercial-activated carbon nanocomposites (LDH-CACs) are prepared with hydrothermal. The effects of preparation and reaction conditions on the composite properties are first investigated, and then its adsorption behavior is thoroughly explored. Finally, a potential adsorption mechanism is proposed by several characterizations like SEM-EDS, XRD, FTIR, and XPS. The removal of Cr(VI) reaches 72.47% at optimal conditions, and the adsorption study demonstrates that LDH-CAC@1 has an extremely rapid adsorption rate and a maximum adsorption capacity of 116.7 mg/g. The primary removal mechanisms include adsorption-coupled reduction, ion exchange, surface precipitation, and electrostatic attraction. The reusability experiment illustrates that LDH-CAC@1 exhibits promising reusability. This study provides an effective adsorbent with a remarkably fast reaction, which has positive environmental significance for the treatment of Cr(VI) wastewater.

A review: Hydrochar as potential adsorbents for wastewater treatment and CO2 adsorption

To valorize the biomass and organic waste, hydrothermal carbonization (HTC) stands out as a highly efficient and promising pathway given its intrinsic advantages over other thermochemical processes. Hydrochar, as the main product obtained from HTC, is widely applied as a fuel source and soil conditioner. Aside from these applications, hydrochar can be either directly used or modified as bio-adsorbents for environmental remediation. This potential arises from its tunable surface chemistry and its suitability to act as a precursor for activated or engineered carbon. In view of the importance of this topic, this review offers a thorough examination of the research progress for using hydrochar and its modified forms to remove organic dyes (cationic and anionic dyes), heavy metals, herbicides/pesticides, pharmaceuticals, and CO2. The review also sheds light on the fundamental chemistry involved in HTC of biomass and the major analytical techniques applied for understanding surface chemistry of hydrochar and modified hydrochar. The knowledge gaps and potential hurdles are identified to highlight the challenges and prospects of this research field with a summary of the key findings from this review. Overall, this article provides valuable insights and directives and pinpoints the areas meriting further investigation in the application potential of hydrochar in wastewater management and CO2 capture.

Utilization of biochar for remediation of heavy metals in aqueous environments: A review and bibliometric analysis

Biochar usage for removing heavy metals from aqueous environments has emerged as a promising research area with significant environmental and economic benefits. Using the PICO approach, the research question aimed to explore using biochar to remove heavy metals from aqueous media. We merged the data from Scopus and the Web of Science Core Collection databases to acquire a comprehensive perspective of the subject. The PRISMA guidelines were applied to establish the search parameters, identify the appropriate articles, and collect the bibliographic information from the publications between 2010 and 2022. The bibliometric analysis showed that biochar-based heavy metal remediation is a research field with increasing scholarly attention. The removal of Cr(VI), Pb(II), Cd(II), and Cu(II) was the most studied among the heavy metals. We identified five main clusters centered on adsorption, water treatment, adsorption models, analytical techniques, and hydrothermal carbonization by performing keyword co-occurrence analysis. Trending topics include biochar reusability, modification, acid mine drainage (AMD), wastewater treatment, and hydrochar. The reutilization of heavy metal-loaded spent biochar includes transforming it into electrodes for supercapacitors or stable catalyst materials. This study provides a comprehensive overview of biochar-based heavy metal remediation in aquatic environments and highlights knowledge gaps and future research directions.

Elimination of hazardous Se(IV) through adsorption-coupled reduction by iron nanoparticles embedded on mesopores of chitin obtained from waste shrimp shells

Selenium is an essential nutrient for biological function. However, there is a detrimental effect on the aquatic environment associated with higher concentrations of > 40 µg/L. The utilization of waste shrimp shells for the removal of high-concentrated selenium from wastewater is a commendable strategy in both the pollution control and waste management sectors. In the present study, a chitin-iron polymer complex hybrid material (Fe@SHC) was prepared from shrimp shell-derived hydrochar (SHC), and the synthesized composite was successfully employed to uptake selenium from wastewater. The highest removal performance of 79.18 mg/g was attained by Fe@SHC, whereas the capacity of SHC was 15.30 mg/g. It was found that the calcium content of Fe@SHC (1.98%) was lower than that of SHC (25.20%) and pHzpc of Fe@SHC was extended to 7.78 compared with that of SHC (2.00). The abundance of protonated hydroxyl (-OH2+) and amine (-NH3+) functional groups that developed through the iron co-precipitations resulted in the improved adsorption performance of Fe@SHC. XPS analysis demonstrated that the captured Se(IV) species were converted into less hazardous Se(0), which is accompanied by the electron transfer with both N-C = O (acetyl amine) and -NH2 (amine) functional groups. Adsorption kinetics disclosed that the adsorption process was governed by chemical sorption, and the Sips isotherm model provided the most accurate description of the isotherm equilibrium. This study proposed an inexpensive and environmentally friendly method for effective decontamination of Se from wastewater.

Nitrogen-rich carbon composite fabricated from waste shrimp shells for highly efficient oxo-vanadate adsorption-coupled reduction

Protein, calcium carbonate, and chitin are abundant in shrimp shells. In this study, chemical treatment followed by hydrothermal carbonization was used to synthesize the nitrogen-rich hydrochar (HSHC) from shrimp shells. The untreated hydrochar exhibited a higher amount of calcium (25.37%) and less amount of nitrogen (2.68%) with alkaline pH (9.1). Interestingly chemical pre-treatment on shrimp shells boosted the nitrogen content to 6.81% and eliminated the calcium while controlling the pH to 6.4, which was beneficial for oxo-vanadate removal. The HSHC achieved vanadium(V) adsorption capacity of 21.20 mg/g at an optimal solution pH of 3.0, whereas the pristine hydrochar performed poorly (0.66 mg/g). The abundance of oxygen and nitrogen-based functional groups that developed through the chemical treatment resulted in improved adsorption coupled reduction performance of HSHC. This study proposed an inexpensive and environmentally friendly method for converting waste shrimp shells into value-added adsorbent.

From Waste to Resource: Valorization of Lignocellulosic Agri-Food Residues through Engineered Hydrochar and Biochar for Environmental and Clean Energy Applications-A Comprehensive Review

Agri-food residues or by-products have increased their contribution to the global tally of unsustainably generated waste. These residues, characterized by their inherent physicochemical properties and rich in lignocellulosic composition, are progressively being recognized as valuable products that align with the principles of zero waste and circular economy advocated for by different government entities. Consequently, they are utilized as raw materials in other industrial sectors, such as the notable case of environmental remediation. This review highlights the substantial potential of thermochemical valorized agri-food residues, transformed into biochar and hydrochar, as versatile adsorbents in wastewater treatment and as promising alternatives in various environmental and energy-related applications. These materials, with their enhanced properties achieved through tailored engineering techniques, offer competent solutions with cost-effective and satisfactory results in applications in various environmental contexts such as removing pollutants from wastewater or green energy generation. This sustainable approach not only addresses environmental concerns but also paves the way for a more eco-friendly and resource-efficient future, making it an exciting prospect for diverse applications.

Removal of Fluoride from Aqueous Solution Using Shrimp Shell Residue as a Biosorbent after Astaxanthin Recovery

Natural astaxanthin has been widely used in the food, cosmetic, and medicine industries due to its exceptional biological activity. Shrimp shell is one of the primary natural biological sources of astaxanthin. However, after astaxanthin recovery, there is still a lot of chitin contained in the residues. In this study, the residue from shrimp (Penaeus vannamei) shells after astaxanthin extraction using ionic liquid (IL) 1-ethyl-3-methyl-imidazolium acetate ([Emim]Ac) was used as a bioadsorbent to remove fluoride from the aqueous solution. The results show the IL extraction conditions, including the solid/liquid ratio, temperature, time, and particle size, all played important roles in the removal of fluoride by the shrimp shell residue. The shrimp shells treated using [Emim]Ac at 100 °C for 2 h exhibited an obvious porous structure, and the porosity showed a positive linear correlation with defluorination (DF, %). Moreover, the adsorption process of fluoride was nonspontaneous and endothermic, which fits well with both the pseudo-second-order and Langmuir models. The maximum adsorption capacity calculated according to the Langmuir model is 3.29 mg/g, which is better than most bioadsorbents. This study provides a low-cost and efficient method for the preparation of adsorbents from shrimp processing waste to remove fluoride from wastewater.

Efficient removal of Tris(2-chloroethyl) phosphate by biochar derived from shrimp shell: Adsorption performance and mechanism study

Tris(2-chloroethyl) phosphate (TCEP) has been detected all over the world as a typical refractory organic phosphate, especially in groundwater. This work applied a calcium-rich biochar derived from shrimp shell as a low-cost adsorbent for TCEP removal. Based on the kinetics and isotherm studies, the adsorption of TCEP on biochar was monolayer adsorbed on a uniform surface, with SS1000 (the biochar was prepared at the carbonization temperature of 1000 °C) achieving the maximum adsorption capacity of 264.11 mg·g^-1. The prepared biochar demonstrated stable TCEP removal ability throughout a wide pH range, in the presence of co-existing anions, and in diverse water bodies. A rapid removal rate of TCEP was observed during the adsorption process. When the dosage of SS1000 was 0.2 g·L^-1, 95% of TCEP could be removed within the first 30 min. The mechanism analysis indicated that the calcium species and basic functional groups on the SS1000 surface were highly involved in the TCEP adsorption process.

Mechanochemical modified nitrogen-rich biochar derived from shrimp shell: Dominant mechanism in pyridinic-N for aquatic methylene blue removal

N-doping for the preparation of functional carbon materials is a trending research topic. In this study, N-rich biochar (BC) was prepared by calcining naturally N rich shrimp shells under oxygen-limiting environment, and the calcining temperatures were controlled. BC were activated with 5% hydrochloric acid solutions and then post-modified with ball-milling to obtain a series of novel adsorbents (MBCs). All samples were characterized by SEM, BET, FT-IR, XRD, XPS, TG, and element analysis. Surface area, pore volume, and other surface functional groups were significantly improved after acidizing and ball-milling. The adsorption capacities for MB were MBC350 > MBC500 > MBC650 >BC350 > BC650 > BC500, and the equilibrium adsorption capacities were 575.01 mg/g, 506.52 mg/g, 424.59 mg/g, 113.31 mg/g, 93.53 mg/g and 86.25 mg/g, respectively. The excellent adsorption performance of MBCs for MB was ascribed to Lewis acid-base interaction, π-π interaction, electrostatic interaction and van der Waals, and the quinone group and pyridinic-N on the surface of the MBCs are identified as the major active sites. Taken together, ball-milled shrimp shell biochar is a promising material for cation dye adsorption.

Chitin-Based Magnesium Oxide Biocomposite for the Removal of Methyl Orange from Water

In this work, a cost-effective chitin-based magnesium oxide (CHt@MgO) biocomposite with excellent anionic methyl orange (MO) dye removal efficiency from water was developed. The CHt@MgO biocomposite was characterized by FT-IR, XRD, SEM-EDX, and TGA/DTG. Results proved the successful synthesis of CHt@MgO biocomposite. Adsorption of MO on the CHt@MgO biocomposite was optimized by varying experimental conditions such as pH, amount of adsorbent (m), contact time (t), temperature (T), and initial MO concentration (C_o). The optimized parameters for MO removal by CHt@MgO biocomposite were as follows: pH, 6; m, 2 g/L; t, 120 min. Two common isotherm models (Langmuir and Freundlich) and three kinetic models (pseudo-first-order (PFO), pseudo-second-order (PSO), and intraparticle diffusion (IPD)) were tested for experimental data fitting. Results showed that Langmuir and PFO were the most suitable to respectively describe equilibrium and kinetic results on the adsorption of MO adsorption on CHt@MgO biocomposite. The maximum Langmuir monolayer adsorption capacity (q_m) on CHt@MgO biocomposite toward MO dye was 252 mg/g at 60 °C. The reusability tests revealed that CHt@MgO biocomposite possessed high (90.7%) removal efficiency after the fifth regeneration cycle.

Selenium Oxoanions Removal from Wastewater by MoS42− Intercalated FeMgAl LDH: Catalytic Roles of Fe and Mechanism Insights

FeMgAl−MoS4 LDH was successfully synthesized by a one-pot hydrothermal process followed by ion-exchange methods, and this novel adsorbent was first conducted for aqueous selenite and selenate elimination. The Fe as a component for metal cation layers of LDHs could modulate the layer charge density, leading to more functional groups inserted into layers, and more importantly, this heterogeneous Fe can catalyze the surface reactions between Se(IV) or Se(VI) with S(-II) for oxoanions sequestration. The mechanisms are ion exchange between functional groups with HSeO3− and SeO32− for Se(IV) or SeO42− for Se(VI), followed by reduction by S(-II) from MoS42− groups. The existence of Fe in LDH cation layers, obviously enhanced the reactions (almost two times more for Se(IV) and three times more for Se(VI), respectively), resulting in satisfying adsorption capacities of 483.9 mg/g and 167.2 mg/g for Se(IV) and Se(VI), respectively. Mechanisms were further revealed by elementary analysis, XRD, FT−IR, SEM−EDX, and XPS, as well as the quantitative study. For sorption kinetics, the calculated values of capacities from the pseudo-second-order model are much closer to the experimental values. For sorption isotherms, Langmuir is better than the Freundlich isotherms model for closer capacities (505 mg/g for selenite and 172 mg/g for selenate). All these results demonstrated that the presence of heterogeneous Fe could catalyze the reduction of Se (IV/VI) for the aqueous system, and maybe other high oxidative states hazardous ions. So FeMgAl−MoS4 is a kind of novel adsorbent that offers a promising multi-functional and highly efficient solution for water selenium purification.

Shrimp waste-derived porous carbon adsorbent: Performance, mechanism, and application of machine learning

Aquaculture generates significant amount of processing wastes (more than 500 million pounds annually in the United States), the bulk of which ends up in the environment or is used in animal feed. Proper utilization of shrimp waste can increase their economic value and divert them from landfills. In this study, shrimp waste was converted to a porous carbon (named SPC) via direct pyrolysis and activation. SPC was characterized, and its performance for adsorbing ciprofloxacin from simulated water, natural waters, and wastewater was benchmarked against a commercial powdered activated carbon (PAC). The surface area of SPC (2262 m²/g) exceeded that of PAC (984 m²/g) due to abundance of micropores and mesopores. The adsorption of ciprofloxacin by SPC was thermodynamically spontaneous (ΔG = -19 kJ/mol) and fast (k₁ = 1.05/min) at 25 °C. The capacity of SPC for ciprofloxacin (442 mg/g) was higher than that of PAC (181 mg/g). SPC also efficiently and simultaneously removed low concentrations (200 µg/L) of ciprofloxacin, long-chain per- and polyfluoroalkyl substances (PFAS), and Cu ions from water. An artificial neural network function was derived to predict ciprofloxacin adsorption and identify the relative contribution of each input parameter. This study demonstrates a sustainable and commercially viable pathway to reuse shrimp processing wastes.

Adsorption of Methyl Orange from an Aqueous Solution onto a BPPO-Based Anion Exchange Membrane

In this research, the development of a novel brominated poly(2,6-dimethyl-1,4-phenylene oxide) (BPPO)-based homogeneous anion exchange membrane (AEM) via the solution casting method was reported. Fourier transform infrared spectroscopy was used to confirm the successful development of the BPPO-based AEM. The prepared AEM showed excellent thermal stability. It exhibited an ion exchange capacity of 2.66 mg/g, a water uptake (W _R) of 68%, and a linear swelling ratio of 31%. Methyl orange (MO), an anionic dye, was used as a model pollutant to evaluate the ion exchange ability of the membrane. The adsorption capacity of MO increased with the increase in contact time, membrane dosage (adsorbent), temperature, and pH while declined with the increase in initial concentration of MO in an aqueous solution and molarity of NaCl. Adsorption isotherm study showed that adsorption of MO was fitted well to the Freundlich adsorption isotherm because the value of the correlation coefficient (R ² = 0.974) was close to unity. Adsorption kinetics study showed that adsorption of MO fitted well to the pseudo-second-order kinetic model. Adsorption thermodynamics evaluation represented that adsorption of MO was an endothermic (ΔH° = 18.72 kJ/mol) and spontaneous process. The AEM presented a maximum adsorption capacity of 18 mg/g. Moreover, the regeneration of the prepared membrane confirmed its ability to be utilized for three consecutive cycles. The developed BPPO-based AEM was an outstanding candidate for adsorption of MO from an aqueous solution.

Recycling phosphorus and calcium from aquaculture waste as a precursor for hydroxyapatite (HAp) production: a review

Water contaminated with phosphorus needs to be managed efficiently to ensure that clean water sources will be preserved. Aquaculture plays an essential role in supplying food and generating high revenue. However, the quantity of phosphorus released from aquaculture effluents is among the major concerns for the environment. Phosphorus is a non-renewable, spatially concentrated material essential for global food production. Phosphorus is also known as a primary source of eutrophication. Hence, phosphorus recovery and separation from different wastewater streams are mandatory. This paper reviews the source of phosphorus in the environment, focusing on aquaculture wastewater as a precursor for hydroxyapatite formation evaluates the research progress on maximizing phosphorus removal from aquaculture wastewater effluents and converting it into a conversion. Shrimp shell waste appears to be an essential resource for manufacturing high-value chemicals, given current trends in wealth creation from waste. Shrimp shell waste is the richest source of calcium carbonate and has been used to produce hydroxyapatite after proper treatment is reviewed. There have been significant attempts to create safe and long-term solutions for the disposal of shrimp shell debris. Through the discussion, the optimum condition of the method, the source of phosphorus, and the calcium are the factors that influence the formation of hydroxyapatite as a pioneer in zero-waste management for sustainability and profitable approach. This review will provide comprehensive documentation on resource utilization and product development from aquaculture wastewater and waste to achieve a zero-waste approach.

Adsorption-enhanced photocatalytic property of Ag-doped biochar/g-C3N4/TiO2 composite by incorporating cotton-based biochar

In this study, the biochar obtained from waste cotton fibers was introduced into the Ag-doped g-C3N4/TiO2 hybrid composite through a facile one-step hydrothermal process. The morphology, elemental composition, crystal structure, microstructure, specific surface area, chemical bonding state, energy band structure, and separation efficiency of photoinduced charge carriers of the resultant composite were examined using scanning electron microscope, energy dispersive X-ray spectrometer, X-ray diffractometer, transmission electron microscope, surface area analyzer, X-ray photoelectron spectroscope, Ultraviolet-visible spectrophotometer, ultraviolet photoelectron spectroscope, and photoluminescence spectroscope. The adsorption isotherms, kinetics and thermodynamics of the biochar, Ag-doped g-C3N4/TiO2 and Ag-doped biochar/g-C3N4/TiO2 were evaluated using the model methyl orange dye. The photoacatalytic degradation of the model pollutants including methyl orange, methylene blue, congo red, and tetracycline hydrochloride and the photocatalytic reduction of Cr(VI) ions were also assessed under visible light. Experimental results indicated that the photocatalytic property of the Ag-doped biochar/g-C3N4/TiO2 was significantly enhanced through the adsorption enhancement compared with the Ag-doped g-C3N4/TiO2. This was due to the uniform doping of multi-scale porous biochar with g-C3N4 nanosheet, Ag and TiO2 nanoparticles. The adsorptive enhancement induced by the biochar resulted in the narrowed band gap, suitable electronic energy band structure, and fast separation of photoinduced charge carriers of the Ag-doped biochar/g-C3N4/TiO2, which was probably due to the coexistence of multi-valence Ti+4/+3 and Ag0/+1 species and oxygen-containing groups of biochar. The major reactive species of the Ag-doped biochar/g-C3N4/TiO2 were 1O2 and h+. The MO dye adsorption onto the Ag-doped biochar/g-C3N4/TiO2 followed the Langmuir isotherm model, pseudo-first-order and pseudo-second-order kinetic models, and the adsorption process was an endothermic reaction with entropy reduction effects. As such, the Ag-doped biochar/g-C3N4/TiO2 exhibited a promising application for the treatment of wastewater containing multi-pollutants especially organic dyes and heavy metal ions.

Nitrogen-doped hydrochars from shrimp waste as visible-light photocatalysts: Roles of nitrogen species

The increasing shrimp waste production has caused severe environmental problems. In this study, nitrogen-doped hydrochars (NDHCs) were facilely synthesized from shrimp waste and glucose by one-pot hydrothermal carbonization (HTC). The characterizations showed that NDHCs had large surface areas of up to 30.5 m² g^-1 with numerous functional groups on their porous surfaces. The nitrogen content (1.3-2.8%) and species distribution in NDHCs were associated with the amount of added glucose. These NDHCs were applied as visible-light-induced photocatalysts, and their photocatalytic performances were evaluated by methylene blue (MB) degradation. The removal rate of MB reached 88.9% after 1 h of visible light radiation by NDHC-1, which was 2.3 times higher than that of glucose-derived hydrochar (GHC). The mechanism study showed that the improved photoactivity of NDHCs was attributed to the increased adsorption capacity by porous surface and the promoted formation of hydroxyl radicals by synergistic effects of quaternary N and pyrrolic N during photocatalysis. This study offered a green approach to preparing tunable, efficient, and low-cost photocatalyst from waste biomass and insight into the photocatalytic mechanism of hydrochar materials.

Hematite/selenium disulfide hybrid catalyst for enhanced Fe(III)/Fe(II) redox cycling in advanced oxidation processes

Regeneration of Fe(II) is a key issue for heterogeneous advanced oxidation processes (AOPs) using iron-based catalysts. Herein, a hybrid catalyst was developed from α-Fe₂O₃ and SeS₂ to enhance the Fe(III)/Fe(II) redox cycling in both hydrogen peroxide (H₂O₂) system and persulfate (PS) system. The regeneration of Fe(II) was evidenced by the increased Fe(II)/Fe(III) ratio in the used catalyst (205.8% in the H₂O₂ system or 125.4% in the PS system), compared to 68.4% in the fresh hybrid catalyst Fe/Se-3. Methyl orange was used as a model pollutant to evaluate the degradation performance of the hybrid catalyst. Owing to the promotion of Fe(II) regeneration, Fe/Se-3 achieved a pollutant removal efficiency of 100.0% in 12 min in both systems, significantly higher than that with pure α-Fe₂O₃ (33.9 ± 3.6% in the H₂O₂ system or 30.7 ± 2.8% in the PS system). The dominant active species were identified as hydroxyl radicals in the H₂O₂ system and sulfate radicals in the PS system. In the proposed mechanism, soluble and surface-bound Fe species are provided by α-Fe₂O₃ to activate H₂O₂ or PS to radicals, and SeS₂ participates in the reactions via Se(IV) reducing Fe(III) to Fe(II) and S atoms being released through protonation to expose more active Se sites.

A state-of-the-art review on producing engineered biochar from shellfish waste and its application in aquaculture wastewater treatment

Global production of shellfish aquaculture is steadily increasing owing to the growing market demands for shellfish. The intensification of shellfish aquaculture to maximize production rate has led to increased generation of aquaculture waste streams, particularly the effluents and shellfish wastes. If not effectively managed, these wastes could pose serious threats to human health and the ecosystem while compromising the overall sustainability of the industry. The present work comprehensively reviews the source, composition, and environmental implications of shellfish wastes and aquaculture wastewater. Moreover, recent advancements in the valorization of shellfish wastes into value-added biochar via emerging thermochemical and modification techniques are scrutinized. The utilization of the produced biochar in removing emerging pollutants from aquaculture wastewater is also discussed. It was revealed that shellfish waste-derived biochar exhibits relatively higher adsorption capacities (300-1500 mg/g) compared to lignocellulose biochar (<200 mg/g). The shellfish waste-derived biochar can be effectively employed for the removal of various contaminants such as antibiotics, heavy metals, and excessive nutrients from aquaculture wastewater. Finally, future research priorities and challenges faced to improve the sustainability of the shellfish aquaculture industry to effectively support global food security are elaborated. This review envisages that future studies should focus on the biorefinery concept to extract more useful compounds (e.g., carotenoid, chitin) from shellfish wastes for promoting environmental-friendly aquaculture.

The impact of the different types of acid solution on the extraction and adsorption performance of chitin from shrimp shell waste

The properties of chitin-based adsorbents varied among studies since they are influenced by different factors, such as the types of base and acid used to extract the chitin. Therefore, this works aimed to investigate the impact of four different acid solutions on the extraction and properties of chitin from shrimp shell waste, and to evaluate the adsorption performance of the obtained chitin on removing dye from an aqueous solution. The result showed that H₂SO₄, HCl, and HNO₃ could remove high minerals from the shrimp shell, while the effect of CH₃COOH was inferior. The Fourier Transform Infrared (FTIR) and X-ray diffraction (XRD) indicated that the extracted chitin was α-amorphous structure, regardless of the type of acid solution. However, the type of acid solution influenced the crystallinity index of the extracted chitin. The Scanning Electron Microscope (SEM) showed both fibrillar material and porous structures. In addition, the chitin extracted through demineralization using H₂SO₄ was more effective in removing RBBR dye from aqueous solution, followed by HCl, HNO_3, and the last, CH₃COOH treatment. The performances of chitin-based adsorbent could be attributed to the strength of acid solution used to remove mineral during the extraction process and the obtained pore structures.

Preparation of chitosan crosslinked with metal-organic framework (MOF-199)@aminated graphene oxide aerogel for the adsorption of formaldehyde gas and methyl orange

Chitosan crosslinked with metal-organic framework (MOF-199)@aminated graphene oxide aerogel (MOF-199@AFGO/CS) were prepared to adsorb formaldehyde and methyl orange. The prepared MOF-199@AFGO/CS aerogel was well characterized via SEM, EDX, FT-IR, XRD and XPS to reveal the microstructure and composition. Besides, the mechanical property and the stability of MOF-199@AFGO/CS aerogel were investigated. The results showed that MOF-199@AFGO/CS aerogel had good stability in water, compression resilience and thermostability. The study on the ability to adsorb formaldehyde gas and methyl orange showed that the adsorption capacity of MOF-199@AFGO/CS aerogel was related to the pore size and the surface functional groups of MOF-199@AFGO/CS aerogel. When the pore size is moderate, as the amino group and MOF-199 on the aerogel increased, the adsorption capacity of formaldehyde gas (197.89 mg/g) and methyl orange (412 mg/g) can reach the maximum. Furthermore, the adsorption process at equilibrium followed the Freundlich isotherm model. The kinetic behavior was well fitted by the pseudo-second-order model, indicating chemisorption as the rate-determining step. This work can provide a reliable basis for the adsorbent to remove pollutants in different forms at the same time, and has potential application in simultaneously adsorbing liquid pollutants and gas pollutants.

Development of biogenic bimetallic Pd/Fe nanoparticle-impregnated aerobic microbial granules with potential for dye removal

The objective of this study was to develop bimetallic core-shell Pd/Fe nanoparticles on the surface of aerobic microbial granules (Bio-Pd/Fe) and to evaluate their dye removal potential using a representative dye, methyl orange (MO). The aerobic microbial granules (1.5 ± 0.32 mm) were grown for 70 days in a 3-L glass sequencing batch reactor (SBR) with a 12-h cycle time. The Bio-Pd/Fe formation was catalyzed by the Bio-H₂ gas produced by the granules. The developed Bio-Pd/Fe was further used for MO removal from aqueous solutions, and the reaction parameters were optimized by response surface methodology (RSM). The XRD, SEM, EDAX, elemental mapping, and XPS studies confirmed the formation of Bio-Pd/Fe. Under the optimized removal conditions, 99.33% MO could be removed by Bio-Pd/Fe, whereas removal by Bio-Pd, Bio-Fe, aerobic microbial granules, and heat-killed granules were found to be quite low (68.91 ± 0.2%, 76.8 ± 0.3%, 19.8 ± 0.6%, and 6.59 ± 0.2%, respectively). The mechanism of removal was investigated by UV-visible spectroscopy, redox potential analysis, HR-LCMS analyses of the solution phase, and XRD and XPS analyses of the solid sorbent. The degradation products of MO exhibited m/z values corresponding to 292, 212, and 160 m/z. The remnant toxicity of the intermediate degradation products was analysed using freshwater algae, Scenedesmus sp. And Allium cepa, as indicator organisms. These assays suggested that after the treatment with Bio-Pd/Fe, MO was transformed to a lesser toxic form.

Efficient Adsorption of Anionic Dyes by Ammoniated Waste Polyacrylonitrile Fiber: Mechanism and Practicability

Adsorption is one of the commonly used methods in wastewater treatment, but it has the problem of high cost and a complicated production process. In this paper, a low-cost and efficient decolorizing adsorbent was successfully prepared based on waste polyacrylonitrile fiber (PANF). The waste PANF was ammoniated by propylene diamine derivates (PANAMF), and benzylamine (PANABMF) and quaternary ammonium ions (PANQMF) were introduced for PANAMF to regulate hydrophilicity and hydrophobicity. With acidic red 249 as the model anionic dye, influences of the adsorption center structure, the degree of modification, the concentration of acid, the dye structure, and the auxiliary agent in the solution on the dye adsorption performance were studied. Isothermal models, kinetic models, reusability, and continuous application ability of the fiber adsorbent were discussed. PANAMF, PANABMF, and PANAQF exhibit excellent adsorption performance compared to the common adsorbent. After protonation, the saturation adsorption value can reach 2051.3 mg/g for PANAMF. PANAMF also exhibited excellent reusability, and the adsorption capacity after being reused eight times still can keep 72.7% of that for the first time. The adsorption of the anionic dye for PANAMF is a chemisorption process, and the rate-determining step is changed from the diffuse step to the adsorption on the surface with the adsorption time. PANAMF can also be used in the continuous flow process, and the absorption amount is similar to that in the batch adsorption, which shows excellent commercial application potential.

Chitosan-derived hydrothermally carbonized materials and its applications: A review of recent literature

Chitosan (CS) is a linear polysaccharide biopolymer, one of the most abundant biowastes in the environment. This makes chitosan a potential material for a wide range of applications. To improve CS's properties, chitosan has to be chemically modified. Hydrothermal carbonization (HTC) is a sustainable process for converting chitosan to solid carbonized material. This article presents a review on the applications of hydrothermally treated chitosan in different fields such as water treatment, heavy metals adsorption, carbon dioxide capturing, solar cells, energy storage, biosensing, supercapacitors, and catalysis. Moreover, this review covers the impact of HTC process parameters on the properties of the produced carbon material. The diversity of applications indicates the great possibilities and multifunctionality of hydrothermally carbonized chitosan and its derivatives. The utilization of HTC-CS is expected to further expand as a result of the movement toward sustainable, environmentally-friendly resources. Thus, this review also recommends a few suggestions to improve the properties of HTC chitosan and its comprehensive applications.

Optimize the preparation of Fe3O4-modified magnetic mesoporous biochar and its removal of methyl orange in wastewater

In this paper, Eichhornia Crassipes stems were used as biomass feedstock, and Fe²⁺ was used as the precursor solution to prepare Fe₃O₄-modified magnetic mesoporous biochar (Fe₃O₄@BC). By using Box-Behnken design (BBD) response surface methodology, the influences of three preparation parameters (X₁ = Fe²⁺ concentration, X₂ = pyrolysis temperature and X₃ = pyrolysis time) on the adsorption of methyl orange (MO) by Fe₃O₄@BC were investigated, and a reliable response surface model was constructed. The results show that X₁X₂ and X₁X₃ have a significant influence on the adsorption of MO by Fe₃O₄@BC. The surface area and pore volume of Fe₃O₄@BC are controlled by all preparation parameters. The increase of pyrolysis time will significantly reduce the -OH on the surface of Fe₃O₄@BC and weaken its MO adsorption capacity. Through the numerical optimization of the constructed model, the optimal preparation parameters of Fe₃O₄@BC can be obtained as follows: Fe²⁺ concentration = 0.27 mol/L, pyrolysis temperature = 405 °C, and pyrolysis time = 3.2 h. The adsorption experiment shows that the adsorption of Fe₃O₄@BC to MO is a spontaneous exothermic process, and the adsorption capacity is maximum when pH = 4. The adsorption kinetics and adsorption isotherms of Fe₃O₄@BC to MO conform to the pseudo-second-order kinetics and Sips model, respectively. Mechanism analysis shows that electrostatic interaction and H bond formation are the main forces for Fe₃O₄@BC to adsorb MO. This research not only realizes a new way of resource utilization of Eichhornia Crassipes biomass but also enriches the preparation research of magnetic biochar.

Crayfish shell biochar for the mitigation of Pb contaminated water and soil: Characteristics, mechanisms, and applications

Biochar has been widely used in the mitigation of soil potentially toxic metals due to its high efficiency and low cost. Crayfish shell biochar (CSBC) was prepared at 300, 500, and 700 °C (referred to as CS300, CS500, and CS700, respectively) and the performance and mechanism of CSBC for mitigating Pb polluted water and soil was investigated. The results indicated that CSBC prepared at higher temperatures possessed higher pH value and ash content, more abundant pore structure, and higher stability. Pb²⁺ adsorption onto CSBC fitted well with the pseudo second order and intraparticle diffusion models. The maximum adsorption capacity of Pb²⁺ increased with the pyrolysis temperature, being 599.70, 1114.53, and 1166.44 mg·g^-1 for CS300, CS500 and CS700, respectively. Compared with the control soil samples, the content of available Pb after applying 0.05%-5% CSBC was reduced by 1.87%-16.48% in acidic soils and 1.00%-11.09% in alkaline soils. Moreover, the fractionation of exchangeable Pb was converted to stable organic matter bound, Fe-Mn oxide bound, and residue fractions. XRD, SEM-EDS, and FTIR analysis showed that ion exchange, complexation, precipitation, and C-π interaction are the dominant interaction mechanisms. Therefore, CSBC can employ as an effective immobilizing agent for the mitigation of Pb contaminated water and soil.

Increasing straw surface functionalities for enhanced adsorption property

A simple low-temperature partial-oxidation process was demonstrated as an effective technology for reed straw modification towards environmental remediation. At an optimal temperature of 180 °C, the straw materials exhibited a remarkable colour change from light yellow to dark brown, increased methylene blue (MB) uptake by 1.8 times, enhanced removal efficiency from 34.5% to 92.8%, and a high yield of 77.2%. Spectroscopic characterization and Boehm titration proved that the amount of surface oxygen (O)-containing functional groups significantly increased after modification. A strong linear correlation (R² = 0.93) existed between total amounts of O-containing functional groups and MB uptake for modification temperatures below 180 °C, whereas blockage of the pore entrances and competition with metallic cations must be taken into account for samples generated from excess heating (>180 °C). These results provided insights into designing promising technologies for sustainable environmental management through reutilization of agricultural waste.

Synthesis, Characterization, and CO2 Uptake of Adsorbents Prepared by Hydrothermal Carbonization of Chitosan

Chitosan, a heteropolysaccharide obtained from the N-deacetylation of chitin, has stood out as a raw material to produce CO2 adsorbents. In this work, we report the hydrothermal carbonization (HTC) of chitosan for different times and the potential of the materials for CO2 adsorption. Elemental analysis indicated that the carbon weight content increases, whereas the relative amount of oxygen atoms decreases upon increasing the time of HTC. The relative nitrogen content was almost constant, indicating that HTC did not lead to significant loss of nitrogenated compounds. FTIR and 13C MAS/NMR spectra suggest that the structure of the sorbents becomes more aromatic with the increase of HTC time. The thermal properties of HTC materials were similar to that of chitosan, whereas their basicity was less compared to that of the parent chitosan. SEM images did not show significant porosity, which was confirmed by the BET area of the materials, around 2 m2·g-1, similar to that of the parent chitosan. The materials were tested for CO2 capture at 25 °C and 1 bar; the HTC chitosan adsorbents showed CO2 uptakes about 4-fold higher than that of the parent chitosan. The adsorption process was better described by the Freundlich isotherm and the pseudo-second-order kinetic model.

Valorization of plastics and paper mill sludge into carbon composite and its catalytic performance for acarbon material consisted of the multi-layerzo dye oxidation

In this work, polyvinyl chloride (PVC) and paper mill sludge (PMS) were co-pyrolyzed under two environments of N₂ and CO₂. The pyrolysis process was assessed by conducting thermogravimetric analysis (TGA) and monitoring the evolution of gaseous products. The resulting solid composites were characterized using XRD, XPS, BET, and Raman analyzers, and their ability to catalytically activate persulfate (S₂O₈^2-) was tested by conducting methyl orange (MO) degradation experiments. Co-pyrolysis of PVC and PMS at the same mass ratio (1:1) in CO₂ resulted in the highest production of H₂ and CO (0.36 mol % H₂ at 480 °C & 1.53 mol % CO at 700 °C). The characterization results revealed that the composite consisted of Fe₃O₄, highly graphitic carbon, and mesoporous structure. In MO oxidation experiments, the co-pyrolyzed composite actively generated OH and SO₄^- by activating S₂O₈^2- to achieve complete removal of 5 mg L^-1 of MO during 100 min at acidic-neutral pH condition. The composite was also able to complete 3 successive cycles of MO oxidation without deactivation. Consequently, the feasibility of achieving the simultaneous production of energy resources and catalyst via industrial wastes utilization in pyrolytic process was demonstrated.

Engineered biochar with anisotropic layered double hydroxide nanosheets to simultaneously and efficiently capture Pb2+ and CrO42- from electroplating wastewater

Cationic and anionic heavy metal contaminants generally co-exist in practical industrial effluent, and simultaneously removal of these species is a bottleneck for most of the bio-adsorbents because of their contrary charge. In this work, pinewood sawdust derived engineered biochar (BC) was fabricated with MgAl layered double hydroxide (MgAl-LDH) nanosheets, which could efficiently and simultaneously capture heavy metal cations and oxyanions from wastewater. The synergetic effect between loaded MgAl-LDH and BC substantially improves its adsorption performance towards both cationic and anionic contaminants, i.e., Pb2+ and CrO42-. The adsorption capacity of MgAl-LDH/BC for Pb2+ reached 591.2 mg/g, which is 263% higher than that of BC, and in the case of CrO42-, the adsorption capacity is 330.8 mg/g, 416% higher than that of BC. The elimination of Pb2+ was mainly attributed to forming complexations with surface functional groups. While for oxyanions removal, CrO42- can be reduced to Cr3+ by functional groups, and then generated Cr3+ could replace Al3+ via morphic substitution, consequently formed an MgCr-LDH structure. Further, in the continuous fixed-bed column study, 225 bed volume of simulating electroplating wastewater co-existed with Pb2+ and CrO42- can be efficiently treated. Hence, this study sheds light on the engineered biochar design to efficiently and simultaneously capture heavy metal cations and oxyanions and its feasibility on real wastewater purification.