Nitrate green removal by fixed-bed columns packed with waste biomass: Modelling and friction parameter estimation

Micro-electrolysis based nitrate reduction from aqueous solution by CNTs-Al-Cu composite under alkaline environment

CNTs-Al was prepared by ball milling combined with sintering process and then used for CNTs-Al-Cu synthesis with chemical deposition method. The obtained CNTs-Al-Cu composite was systematically characterized and its NO₃^--N reduction performance under alkaline condition was also evaluated. As indicated by the reduction batch experiment, 80.2% of NO₃^--N removal efficiency was obtained in 90 min at pH of 9. The product of the reduction process was dominated by NO₂^--N, which was further reduced to harmless N₂. The reusability of CNTs-Al-Cu composite was evaluated, and the experiment results showed that 68.1% of NO₃^--N removal efficiency was maintained after 3 cycles of regeneration. Finally, based on the characterization results and kinetic analysis, it was concluded that micro-electrolysis was mainly responsible for the removal of NO₃^--N by CNTs-Al-Cu.

Enhancing nitrate removal efficiency of micro-sized zero-valent iron by chitosan gel balls encapsulating

The activity of micro-sized zero-valent iron (MZVI) material for nitrate removal in neutral pH and low C/N ratios water needs to be improved. In this study, micro-sized zero-valent iron@chitosan (MZVI@CS) material was synthesized through embedding MZVI particles into chitosan (CS) gel by sol-gel method, and was used for deep removal of NO₃^--N in the absence of organic carbon sources and neutral pH. The NO₃^--N removal rate of MZVI@CS was 0.37 mg-N·L^-1·d^-1 (dosage of 1%, initial pH = 7, 25 °C, initial nitrate concentration = 15 mg-N·L^-1), which was 11.33 times higher than that of MZVI. The apparent activation energy (E_a) of MZVI@CS with nitrate was 38.23 kJ·mol^-1. MZVI@CS can remove nitrate effectively at a low concentration (15 mg-N·L^-1). A stable denitration rate (0.37-2.28 mg-N·L^-1·d^-1) could be maintained under weak acidic, neutral and alkaline conditions (pH = 5-9). More than 80% of reduced nitrate was converted to N₂, and only a small amount was converted to NH₄⁺ or NO₂^-. The gel structure of MZVI@CS eliminated the agglomeration between MZVI particles while the forming of Fe-CS chelates reduced the formation of iron oxide and solved the problems of passivation, hence successfully strengthened the NO₃^--N removal efficiency of MZVI. Therefore MZVI@CS has great application potential in NO₃^--N deep removal of water bodies with neutral pH and low C/N ratios.

Removal of inorganic toxic contaminants from wastewater using sustainable biomass: A review

Lignocellulosic biomass is most abundant, ecofriendly and sustainable material on this green planet which has received great attention due to exhaustion of petroleum reserves and various environmental complications. Due to its abundance and sustainability, it has been opted in number of advanced applications i.e. synthesis of green chemicals, biofuels, paper, packaging, biocomposite and for discharge of toxic contaminants from wastewaters. Utilization of sustainable biomass for removal of toxic pollutants from wastewater is robust technique due to its low-cost and easy availability. In this review, we have summarized removal of inorganic pollutants by sustainable lignocellulosic biomass in their natural as well as in chemically functionalized form. Various techniques for modification of sustainable biomass have been discussed and it was found that modified biomass showed better biosorption ability as compared to natural biomass. We conclude that modified biomass biosorbents are useful for removal of toxic inorganic pollutants to deficient levels. Several modification strategies can improve the qualities of biosorbent, however grafting is the most successful among them, as demonstrated in this work. The numerous grafting methods using a free radical grafting process are also summarized in this review article. This review also gathers studies comparing sorption capabilities with and without modification using modified and unmodified biosorbents. Chemically modified cellulosic biomass is favoured over untreated biomass because it has a higher adsorption efficiency, which is favoured by a large number of reactive binding sites, improved ion-exchange characteristics, and more functional groups available after modification.

Selective reduction of nitrate to nitrogen by Fe0-Cu0-CuFe2O4 composite coupled with carbon dioxide anion radical under UV irradiation

Zero-valent iron (Fe⁰) has been widely used for the reduction of nitrate, but the end reduction product is mainly ammonium. Here, a novel strategy for selective reduction of nitrate (NO₃^-) to nitrogen gas (N₂) with high efficiency and N₂ selectivity was investigated using Fe-based material (Fe⁰-Cu⁰-CuFe₂O₄) combined with citric acid (CA) and ultraviolet (UV) irradiation. In this strategy, the nitrate was firstly reduced to nitrite (NO₂^-) by Fe⁰-Cu⁰-CuFe₂O₄/UV process, and then the produced NO₂^- could be further reduced to N₂ by carbon dioxide anion radicals (CO₂^•-) which was generated from CA that was added later. In this process, the selective reduction of NO₃^- to NO₂^- was a key step. For this purpose, we synthesized Fe⁰-Cu⁰-CuFe₂O₄ composite by simple chemical replacement and in-situ growth process, which made it have a delicate structure with good contact between Cu and Fe and CuFe₂O₄. The selective reduction of NO₃^- to NO₂^- in Fe⁰-Cu⁰-CuFe₂O₄/UV process was due to that the Cu⁰ was the electron enrichment center and the photo-generated hole could suppress the NO₃^- reduction to NH₄⁺ by Fe²⁺. In this proposed strategy, 100% NO₃^- removal efficiency and 96.3% N₂ selectivity were achieved when the initial NO₃^- concentration was 30 mg N/L and the reduction time was 60 min. The denitrification mechanism of the Fe⁰-Cu⁰-CuFe₂O₄/UV/CA system was proposed.

Enhanced phosphate removal and potential recovery from wastewater by thermo-chemically calcinated shell adsorbents

Shell from the seafood processing industry is an under-utilised waste resource worldwide. Calcite, the major component of shell is commonly used in wastewater treatment for the removal of phosphorus (P). Here, mussel and oyster shell-based adsorbents (MSB and OSB) were used for removal of P as phosphate (PO₄^3-) from aqueous solution and secondary wastewater, following preparation through chemical calcination at 700 °C. Batch adsorption experiments were carried out to identify the effects of various operating parameters (e.g., pH, dosage, contact time, initial concentration of P ions, co-existing ions), while a desorption study helped to understand the availability of the bonded P. The optimal contact time for PO₄^3- removal was 120 min using both adsorbents with the dose at 200 mg. Characterisation of the adsorbent was performed using SEM-EDX, pH_pzc, BET, FTIR and XRD. The XRD analysis showed that both calcite and lime were present on the surface of the shell particles. P was adsorbed effectively through inner-sphere complexation and surface microprecipitation mechanisms, while an enhanced maximum P adsorption capacity of 12.44 mg/g for MSB and 8.25 mg/g for OSB was reached. The Redlich-Peterson isotherm model fitted well with the equilibrium isotherm data (R² ≥ 0.97) which also suggested a heterogenic surface. The desorption study (on the saturated adsorbent) found that ~97% of bonded P could be plant available in soil. These results suggest that a shell-based adsorbent can serve as a promising material for P removal from real wastewater effluent and subsequently could be used as a soil conditioner.

Functionalized Activated Carbon Derived from Palm Kernel Shells for the Treatment of Simulated Heavy Metal-Contaminated Water

Heavy metal contamination in water poses a great risk to human health as well as to the lives of other creatures. Activated carbon is a useful material to be applied for the treatment of heavy metal-contaminated water. In this study, functionalized activated carbon (FAC) was produced by the induction of nitro groups onto activated carbon using nitric acid. The resulting material was characterized in detail using the XRD, Raman, BET, FTIR, and FESEM techniques. The FAC was used for the treatment of heavy metal-contaminated water using different adsorption parameters, i.e., solution pH, contact time, adsorbent dosage and heavy metal ion concentrations, and these parameters were systematically optimized. It was found that FAC requires 90 min for the maximum adsorption of the heavy metal ions; Cr6+, Pb2+, Zn2+ and Cd2+. The kinetic study revealed that the metal ion adsorption follows the pseudo-second-order. The Freundlich and Langmuir isotherms were applied to determine the best fitting adsorption isotherm models. The adsorption capacities were also determined for each metal ion.

A Life Cycle Assessment of an Energy-Biochar Chain Involving a Gasification Plant in Italy

Life cycle assessment (LCA) is a fundamental tool for evaluating the environmental and energy load of a production cycle. Its application to renewable energy production systems offers the possibility of identifying the environmental benefits of such processes—especially those related to the by-products of production processes (i.e., digestion or biochar). Biochar has received worldwide interest because of its potential uses in bioenergy production, due to its coproducts (bio-oil and syngas), as well as in global warming mitigation, sustainable agriculture, pollutant removal, and other uses. Biochar production and use of soil is a strategy for carbon sequestration that could contribute to the reduction of emissions, providing simultaneous benefits to soil and opportunities for bioenergy generation. However, to confirm all of biochar’s benefits, it is necessary to characterize the environmental and energy loads of the production cycle. In this work, soil carbon sequestration, nitrous oxide emissions, use of fertilizers, and use of water for irrigation have been considered in the biochar’s LCA, where the latter is used as a soil conditioner. Primary data taken from experiments and prior studies, as well as open-source available databases, were combined to evaluate the environmental impacts of energy production from biomass, as well as the biochar life cycle, including pre- and post-conversion processes. From the found results, it can be deduced that the use of gasification production of energy and biochar is an attractive strategy for mitigating the environmental impacts analyzed here—especially climate change, with a net decrease of about −8.3 × 103 kg CO2 eq. Finally, this study highlighted strategic research developments that combine the specific characteristics of biochar and soil that need to be amended.

Online monitoring of polysaccharide solution concentration by electromagnetic field, electrical conductivity and spectrophotometry measurements

Online control of industrial processes by lean principle increases productivity and yields higher product quality. Polysaccharides are dissolved in liquids, such as water, in many industrial products, like paints, cosmetics and culinary products. In these products, it is important to control viscosity or create thixotropy and yield stress for product functionality. Electromagnetic field and electrical conductivity techniques were applied to a meter polysaccharide dissolution process online up to a 0.5 wt% concentration, and the resultant solution was also further tested by UV–Vis spectrophotometry. The electromagnetic field technique measures changes in the local electrical permittivity of the liquid and the interest in this research were to find out whether the changes correlate to the concentration changes during the dissolution of polymer polysaccharide. The results that were obtained showed good consistency, suggesting the feasibility of the electromagnetic field technique in online monitoring of a polysaccharide suspension concentration. Moreover, this technique gives the advantage of instant monitoring of a polysaccharide dissolution for improved process control.

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A Review on the Removal of Carbamazepine from Aqueous Solution by Using Activated Carbon and Biochar

Carbamazepine (CBZ), one of the most used pharmaceuticals worldwide and a Contaminant of Emerging Concern, represents a potential risk for the environment and human health. Wastewater treatment plants (WWTPs) are a significant source of CBZ to the environment, polluting the whole water cycle. In this review, the CBZ presence and fate in the urban water cycle are addressed, with a focus on adsorption as a possible solution for its removal. Specifically, the scientific literature on CBZ removal by activated carbon and its possible substitute Biochar, is comprehensively scanned and summed up, in view of increasing the circularity in water treatments. CBZ adsorption onto activated carbon and biochar is analyzed considering several aspects, such as physicochemical characteristics of the adsorbents, operational conditions of the adsorption processes and adsorption kinetics and isotherms models. WWTPs usually show almost no removal of CBZ (even negative), whereas removal is witnessed in drinking water treatment plants through advanced treatments (even >90%). Among these, adsorption is considered one of the preferable methods, being economical and easier to operate. Adsorption capacity of CBZ is influenced by the characteristics of the adsorbent precursors, pyrolysis temperature and modification or activation processes. Among operational conditions, pH shows low influence on the process, as CBZ has no charge in most pH ranges. Differently, increasing temperature and rotational speed favor the adsorption of CBZ. The presence of other micro-contaminants and organic matter decreases the CBZ adsorption due to competition effects. These results, however, concern mainly laboratory-scale studies, hence, full-scale investigations are recommended to take into account the complexity of the real conditions.

Recycling of Brewer's Spent Grain as a Biosorbent by Nitro-Oxidation for Uranyl Ion Removal from Wastewater

Developing biosorbents derived from agro-industrial biomass is considered as an economic and sustainable method for dealing with uranium-contaminated wastewater. The present study explores the feasibility of oxidizing a representative protein-rich biomass, brewer's spent grain (BSG), to an effective and reusable uranyl ion adsorbent to reduce the cost and waste generation during water treatment. The unique composition of BSG favors the oxidation process and yields in a high carboxyl group content (1.3 mmol/g) of the biosorbent. This makes BSG a cheap, sustainable, and suitable raw material independent from pre-treatment. The oxidized brewer's spent grain (OBSG) presents a high adsorption capacity of U(VI) of 297.3 mg/g (c 0(U) = 900 mg/L, pH = 4.7) and fast adsorption kinetics (1 h) compared with other biosorbents reported in the literature. Infrared spectra (Fourier transform infrared), 13C solid-state nuclear magnetic resonance spectra, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and thermogravimetric analysis were employed to characterize the biosorbents and reveal the adsorption mechanisms. The desorption and reusability of OBSG were tested for five cycles, resulting in a remaining adsorption of U(VI) of 100.3 mg/g and a desorption ratio of 89%. This study offers a viable and sustainable approach to convert agro-industrial waste into effective and reusable biosorbents for uranium removal from wastewater.

Nanoparticles-EPS corona increases the accumulation of heavy metals and biotoxicity of nanoparticles

Microbial extracellular polymeric substances (EPS) coating nanoparticles (NPs) surface can form NPs-EPS corona, which significantly affect the adsorption of NPs to toxic substances and alter the ecotoxicological effect of NPs. In this work, the EPS coronas on TiO₂ NPs (TNPs) and CeO₂ NPs (CNPs) were characterized and the adsorption characteristics of NPs with and without EPS corona to five heavy metals were investigated in single-metal and multiple-metal systems. The results of spectral analysis showed that NPs-EPS corona exhibited new crystalline phases and abundant functional groups. Moreover, 42 and 13 proteins were identified in the TNPs-EPS and CNPs-EPS coronas, respectively. The rates of Cd²⁺, Pb²⁺, Cu²⁺, Ni²⁺ and Ag⁺ adsorption by NPs-EPS corona increased to values that were 6.7-7.6, 4.4-5.1, 4.2-5.5, 3.9-4.9 and 8.5-8.8 times those of NPs without EPS corona, respectively, in single-metal system. NPs-EPS coronas are effective in absorbing Ag⁺, Pb²⁺ and Cu²⁺ compared with Cd²⁺and Ni²⁺ in multiple metal adsorption. These results indicated that NPs-EPS corona effectively adsorb and remove heavy metals by forming NPs-EPS-metal complexes and inducing precipitation. However, NPs-EPS corona can enhance the toxicity of NPs by accumulating highly-toxic heavy metals in aquatic environments.

A green rust-coated expanded perlite particle electrode-based adsorption coupling with the three-dimensional electrokinetics that enhances hexavalent chromium removal

A green rust-coated expanded perlite (GR-coated Exp-p) microelectrode was synthesized and incorporated into a column-mode three-dimensional electrokinetic (3D-EK) platform to effectively pursue a continuous Cr(VI) removal from the aqueous solution. Brucite-like layers of GR were decorated onto the Exp-p material. The molar ratio of Fe(II) to Fe(III) played a most vital role among the three synthesis factors in influencing the performance of the particle electrode. For the equilibrium adsorption experiments, the target maximum adsorption capacity of 122 mg/g was predicted by a target optimizer and desirability function at the conditions following the pH of 4.7, the initial concentration of 172.4 mg/L, the dosage of 0.28 g/L, and the temperature of 28.96 °C, respectively. SO₄^2-, Cl^-, and NO₃^- fiercely competed with Cr(VI) anions in the acidic conditions for the locally positive sites. A low concentration and a slow flow were favored in the column-mode 3D-EK platform. The pseudo-first-order and Langmuir models were suitable for describing the kinetics and isotherms of the adsorption process, respectively. Cr(VI) anions were electrostatically attracted to the silanol groups and GR surface of the adsorbent, subsequently reduced in both heterogeneity and homogeneity, and finally immobilized by coordinating with silanediol groups and silanetriol groups.

Multi wall carbon nanotubes application for treatment of Cr(VI)-contaminated groundwater; Modeling of batch & column experiments

Multi wall carbon nanotubes (MWCNTs) are carbonaceous nanomaterials with novel adsorption properties. In this study MWCNTs were used as adsorbents for hexavalent chromium, Cr(VI), and the influence of operating parameters, on adsorption process, such as pH, MWCNTs and Cr(VI) concentration, and contact time have been investigated. Batch and column experiments were carried out in order to investigate the removal efficiency of MWCNTs for different Cr(VI) concentrations related to groundwater polluted by either anthropogenic activities or by geogenic processes. The experimental results showed that pH was the most crucial factor for adsorption efficiency. Cr(VI) adsorption was inversely proportional with pH value and more specifically adsorption was significantly decreased for pH values higher than 7. The effect of adsorbent's concentration showed the high adsorption capacity of MWCNTs. The adsorption process was very fast since was almost completed within 1 h. Different isotherm models have been adopted to interpret the experimental equilibrium data, as well as two mass-transfer based model were used to describe the dynamic behavior of Cr(VI) sorption phenomenon in column experiments.

The mechanism of nitrate-Cr(VI) reduction mediated by microbial under different initial pHs

To date, comparatively little research is known about the role of pH conditions in bioremediation of Cr(VI) contaminated aquifers. This study explored microbial Cr(VI) reduction and denitrification under different initial pHs. The underlying mechanism was also investigated. When testing 50 mg/L-N nitrate and 10 mg/L Cr(VI), complete contaminants removal was observed at initial pH 10.0 and 11.0, and only 10 %-30 % of removal achieved under other conditions, which might be ascribe to the significant up-regulation of functional genes narG (8.31 and 10.46 folds) and azoR (24.90 and 15.96 folds) at initial pH 10.0 and 11.0. Metagenomic sequencing showed that alkali tolerant bacteria played major roles in the NO₃^--Cr(VI) reduction (i.e. Pannonibacter increased by 13.08 % and 25.24 % at initial pH 10.0 and 11.0), and metabolic pathways of Degradation and Energy were found of increased abundant. Furthermore, a significative study suggested that potential interspecies cooperation existed at initial pH 11.0 to facilitating the simultaneous removal of contaminants, and Pannonibacter indicus might be an important participant in the degradation of contaminants. The results of this study will fully understand the metabolic patterns of bacteria under alkaline conditions, expand the range of available functional bacteria, and enhance the practical aspects of co-contaminants remediation.