Techno-economic evaluation of simultaneous arsenic and fluoride removal from synthetic groundwater by electrocoagulation process: optimization through response surface methodology

<p>In the present work, electrocoagulation process has been used to treat arsenic and fluoride containing synthetic water using aluminium electrode. Box–Behnken design, a subnet of response surface methodology, was employed to fix the experimental conditions and Design Expert software was used to evaluate the interaction and effects of different process parameters such as initial pH, current density and run time on removal of arsenic and fluoride as well as the operating cost. Initial concentration of arsenic and fluoride was fixed at 550 μg/l and 12 mg/l, respectively, for all the experiments. High <i>R</i>² values of three responses (arsenic removal: 0.998, fluoride removal: 0.984 and operating cost: 0.996) ensures a satisfactory adjustment of developed quadratic model with the experimental data. Under the optimum conditions, initial pH: 7, current density: 10 A/m² and run time: 95 min, the predicted arsenic and fluoride removal is found to be 98.64 and 84.80%, respectively, whereas the operating cost is found to be 0.354 USD/m³. Further, the experimental values of arsenic removal (98.51%), fluoride removal (88.33%) and operating cost (0.343 USD/m³) are found to be in good agreement with the predicted values. The present electrocoagulation process is able to reduce the arsenic and fluoride concentration below 10 μg/l and 1.5 mg/l, respectively, which are maximum contaminant level of these elements in drinking water according to WHO. EDX analysis of sludge confirms the occurrence of arsenic and fluoride in produced sludge and FTIR spectra suggest that arsenic is also removed in the form of As(III). Real groundwater sample collected from Kaudikasa Village, Rajnandgaon District, Chhattisgarh, India and having As: 512 μg/l, F: 6.3 mg/l was also treated under optimum conditions of the present study and the concentration of arsenic and fluoride became below WHO drinking water norms.</p

Life Cycle Assessment (LCA) of Greywater Treatment Using ZnCl₂ Impregnated Activated Carbon and Electrocoagulation Processes: A Comparative Study

The growing worldwide population, climate change, and decaying water infrastructure have all contributed to a need for a sustainable greywater treatment technology. The adsorption and electrocoagulation processes have shown potential to contribute to this vision; however, its burden to the environment and economy is also a necessary aspect to study. The life cycle assessment of both processes is conducted in this study. The obtained results for the adsorption system demonstrate that the adsorbent production stage highly impacts the environment. The use of ZnCl2 in the impregnation of sawdust has an enormous influence on the environmental indicators, namely ADPE (99.9%), FAETP (79.5%), and ODP (76.5%). The coproducts formed during the adsorbent production stage are recycled, and the recovered energy has been utilized in its subprocesses to reduce the burden on the total energy requirement. On the other hand, the energy and raw material requirement in the electrocoagulation process are significantly less; hence, it shows an eight times lower global warming potential (GWP) toward the environment. The scenario analysis indicates that the environmental impact (for instance, ADPE, AP, EP, FAETP, HTP, POCP, and TETP) while using electricity from natural gas is comparatively lesser than other energy sources. The sensitivity analysis of both the adsorption and electrocoagulation processes was investigated by taking a ±20% difference in the values of process parameters. The cost analysis shows that the electrocoagulation process is more cost-effective than the adsorption process

Environmental Footprints of the Catalytic Pyrolysis of Pine Needles through Integration of a Nickel-Decorated Chemically Modified Biochar Catalyst

The current study presents the life cycle analysis (LCA) of a biochar-catalyzed pyrolysis-based biorefinery system. Noncondensable gases (NCGs), produced as a coproduct, have been recycled back to the system, while biochar produced was employed for catalyst preparation, to visualize a biorefinery model. Results showed the considerable environmental impact of the process, in particular of the catalyst and energy sources utilized during the process. Matching up with the LCA metrics, both single parameter and Monte Carlo uncertainty analyses also revealed the high sensitivity of the obtained impacts for the impregnating chemical (i.e., ZnCl2, H3PO4, and NaOH) employed during catalyst preparation. Among different processes, the Ni/BC-H3PO4 catalyzed process with NCG recycling has emerged as the best possible case with the lowest environmental emissions (GWP ≈ 0.109 kg CO2 equivalent) and low cumulative energy demand (∼2.47 MJ) together with high process efficacy and productivity. Furthermore, sustaining process energy needs with varieties of different sources advocates for renewable sources (more specifically hydropower) over nonrenewable sources of energy. The study highlights the hotspots of the current technology, envisaging ways of reducing emissions through clean/renewable energy sources as well as utilizing less impact-causing intermediate materials, and thus, acting like a building stone in creating a base toward the vision of achieving net zero emissions

Catalytic Pyrolysis Using a Nickel-Functionalized Chemically Activated Biochar Catalyst: Insight into Process Kinetics, Products, and Mechanism

The present study highlighted the impact of biochar (BC)-based catalysts on catalytic pyrolysis of pine needle biomass. Thermogravimetric plots showed positive influence of catalysts by indicating reduction in the temperature requirement of the process. The same had also been stated through process kinetics by demonstrating reduction in the process’s activation energy (Ea). Ea had been reduced from 25.95 kJ/mol in noncatalytic pyrolysis to 20.79, 15.20, 10.52, 13.99, and 9.69 kJ/mol for BC, Ni/BC, Ni/BC-ZnCl2, Ni/BC-H3PO4, and Ni/BC-NaOH catalytic pyrolysis, respectively. Physicochemical characteristics of bio-oil indicated improvement in its high heating value and % deoxygenation achieved during the process. Catalyst incorporation in the process increased the production of phenols as well as aliphatic and aromatic hydrocarbons. The presence of surface acidic functionalities coupled with metallic sites in Ni/BC-ZnCl2, Ni/BC-H3PO4, and Ni/BC-NaOH increased the aromatics selectivity to 35.18, 36.47, and 35.64%, respectively. Similarly, aliphatics were also enhanced to 9.61, 10.12, and 11.68% using Ni/BC-ZnCl2, Ni/BC-H3PO4, and Ni/BC-NaOH, respectively. Also, chemically activated catalysts showed high stability toward deactivation. Thus, low-cost BC-based catalysts can be effectively employed in place of currently utilized high-cost catalysts in the catalytic pyrolysis process, which will help to make the process more integrated and closed-loop

Life Cycle Analysis and Operating Cost Assessment of a Carbon Negative Catalytic Pyrolysis Technique Using a Spent Aluminum Hydroxide Nanoparticle Adsorbent-Derived Catalyst: Insights into Coproduct Utilization and Sustainability

The current research is intended toward the life cycle analysis (LCA) and operating cost assessment of catalytic and noncatalytic pyrolysis. The study assessed the impact of waste material-based catalysts (spent aluminum hydroxide nanoparticle (AHNP) adsorbent-derived catalysts) on the process’ overall environmental load and operating cost. Incorporating the utilization of process coproducts through recycling both noncondensable gases (NCGs) and biochar in the pyrolysis process, as well as exporting biochar as a coal substitute, reduced the values of the environmental impact and operating cost. Results revealed that biochar market export as coal replacement (for earning coal credits) is comparatively more beneficial than its back-recycling in the pyrolysis process (for offsetting natural gas requirements) from the environmental perspective. However, the reverse is true from the economic viewpoint in terms of operating cost. Among different considered processes, nickel-doped AHNP (Ni/Al)-catalyzed pyrolysis with scenario 2 (wherein all the produced biochar was coal-credited and all the NCGs were back-recycled) portrayed the highest environmental benefits owing to the maximum negative emissions (∼0.031 kg CO2 equivalent GHG emission saving). Low standard deviations (<10%), as obtained through Monte Carlo uncertainty analysis, indicated toward the reliability and robustness of the obtained LCA impacts. The present study exemplified the renewability and environmental friendliness of the AHNP-catalyzed pyrolytic biofuel over conventional petroleum-derived diesel and gasoline fuels

The Electron-Rich {Ru(acac)₂} Directed Varying Configuration of the Deprotonated Indigo and Evidence for Its Bidirectional Noninnocence

This article highlights the hitherto unexplored varying binding modes of the deprotonated natural dye indigo (H₂L) and its bidirectional noninnocent potential. The reaction of H₂L with the selective metal precursor Ru^II(acac)₂(CH₃CN)₂ (acac^– = acetylacetonate) leads to the simultaneous formation of paramagnetic Ru^III(acac)₂(HL^–) (<b>1</b>; blue solid) and diamagnetic Ru^II(acac)₂(L) (<b>2</b>; red solid), which have been characterized by standard analytical, spectroscopic, and structural analysis. Crystal structures establish that the usual <i>trans</i> configurated and twisted monodeprotonated HL^– and unprecedented <i>cis</i> configurated nearly planar dehydroindigo (L) bind to the {Ru­(acac)₂} metal fragment via the N^–,O and N,N donors, forming six- and five-membered chelates, respectively. It also reveals the existence of intramolecular N–H···O hydrogen-bonding interaction between the NH proton and CO group at the back face of the coordinated HL^–, in addition to an intermolecular N–H···O hydrogen bonding between the NH proton of HL^– of Molecule B and oxygen atom of the nearby acac of the second molecule (Molecule A) in the asymmetric unit of <b>1</b>. The specific role of the electron-rich {Ru­(acac)₂} metal fragment in stabilizing the <i>cis</i>-configuration of the electron-deficient L in <b>2</b> has been pointed out. Both <b>1</b> and <b>2</b> exhibit reversible one-electron oxidation and successive three reductions with varying <i>K</i>_c (comproportionation constant) values in the range of 10¹⁸–10⁶. The potentials for the redox processes of <b>2</b> are positively shifted with respect to those of <b>1</b>. The involvement of the metal or HL^–/L or mixed metal-HL^–/L-based orbitals in the accessible redox processes of <b>1</b>^<i>n</i> and <b>2</b>^<i>n</i> has been analyzed by spectroelectrochemistry, EPR at the paramagnetic states, and DFT calculated MO compositions/spin density distributions. The collective consideration of the experimental results and DFT/TD-DFT data has ascertained the participation of both the metal fragment {Ru­(acac)₂} and the HL^–/L in the redox processes, which in effect result in mixed electronic structural forms of <b>1</b>^<i>n</i> and <b>2</b>^<i>n</i> (<i>n</i> = +1, 0, −1, −2, −3)

The Electron-Rich {Ru(acac)₂} Directed Varying Configuration of the Deprotonated Indigo and Evidence for Its Bidirectional Noninnocence

This article highlights the hitherto unexplored varying binding modes of the deprotonated natural dye indigo (H₂L) and its bidirectional noninnocent potential. The reaction of H₂L with the selective metal precursor Ru^II(acac)₂(CH₃CN)₂ (acac^– = acetylacetonate) leads to the simultaneous formation of paramagnetic Ru^III(acac)₂(HL^–) (<b>1</b>; blue solid) and diamagnetic Ru^II(acac)₂(L) (<b>2</b>; red solid), which have been characterized by standard analytical, spectroscopic, and structural analysis. Crystal structures establish that the usual <i>trans</i> configurated and twisted monodeprotonated HL^– and unprecedented <i>cis</i> configurated nearly planar dehydroindigo (L) bind to the {Ru­(acac)₂} metal fragment via the N^–,O and N,N donors, forming six- and five-membered chelates, respectively. It also reveals the existence of intramolecular N–H···O hydrogen-bonding interaction between the NH proton and CO group at the back face of the coordinated HL^–, in addition to an intermolecular N–H···O hydrogen bonding between the NH proton of HL^– of Molecule B and oxygen atom of the nearby acac of the second molecule (Molecule A) in the asymmetric unit of <b>1</b>. The specific role of the electron-rich {Ru­(acac)₂} metal fragment in stabilizing the <i>cis</i>-configuration of the electron-deficient L in <b>2</b> has been pointed out. Both <b>1</b> and <b>2</b> exhibit reversible one-electron oxidation and successive three reductions with varying <i>K</i>_c (comproportionation constant) values in the range of 10¹⁸–10⁶. The potentials for the redox processes of <b>2</b> are positively shifted with respect to those of <b>1</b>. The involvement of the metal or HL^–/L or mixed metal-HL^–/L-based orbitals in the accessible redox processes of <b>1</b>^<i>n</i> and <b>2</b>^<i>n</i> has been analyzed by spectroelectrochemistry, EPR at the paramagnetic states, and DFT calculated MO compositions/spin density distributions. The collective consideration of the experimental results and DFT/TD-DFT data has ascertained the participation of both the metal fragment {Ru­(acac)₂} and the HL^–/L in the redox processes, which in effect result in mixed electronic structural forms of <b>1</b>^<i>n</i> and <b>2</b>^<i>n</i> (<i>n</i> = +1, 0, −1, −2, −3)

The Electron-Rich {Ru(acac)₂} Directed Varying Configuration of the Deprotonated Indigo and Evidence for Its Bidirectional Noninnocence

This article highlights the hitherto unexplored varying binding modes of the deprotonated natural dye indigo (H₂L) and its bidirectional noninnocent potential. The reaction of H₂L with the selective metal precursor Ru^II(acac)₂(CH₃CN)₂ (acac^– = acetylacetonate) leads to the simultaneous formation of paramagnetic Ru^III(acac)₂(HL^–) (<b>1</b>; blue solid) and diamagnetic Ru^II(acac)₂(L) (<b>2</b>; red solid), which have been characterized by standard analytical, spectroscopic, and structural analysis. Crystal structures establish that the usual <i>trans</i> configurated and twisted monodeprotonated HL^– and unprecedented <i>cis</i> configurated nearly planar dehydroindigo (L) bind to the {Ru­(acac)₂} metal fragment via the N^–,O and N,N donors, forming six- and five-membered chelates, respectively. It also reveals the existence of intramolecular N–H···O hydrogen-bonding interaction between the NH proton and CO group at the back face of the coordinated HL^–, in addition to an intermolecular N–H···O hydrogen bonding between the NH proton of HL^– of Molecule B and oxygen atom of the nearby acac of the second molecule (Molecule A) in the asymmetric unit of <b>1</b>. The specific role of the electron-rich {Ru­(acac)₂} metal fragment in stabilizing the <i>cis</i>-configuration of the electron-deficient L in <b>2</b> has been pointed out. Both <b>1</b> and <b>2</b> exhibit reversible one-electron oxidation and successive three reductions with varying <i>K</i>_c (comproportionation constant) values in the range of 10¹⁸–10⁶. The potentials for the redox processes of <b>2</b> are positively shifted with respect to those of <b>1</b>. The involvement of the metal or HL^–/L or mixed metal-HL^–/L-based orbitals in the accessible redox processes of <b>1</b>^<i>n</i> and <b>2</b>^<i>n</i> has been analyzed by spectroelectrochemistry, EPR at the paramagnetic states, and DFT calculated MO compositions/spin density distributions. The collective consideration of the experimental results and DFT/TD-DFT data has ascertained the participation of both the metal fragment {Ru­(acac)₂} and the HL^–/L in the redox processes, which in effect result in mixed electronic structural forms of <b>1</b>^<i>n</i> and <b>2</b>^<i>n</i> (<i>n</i> = +1, 0, −1, −2, −3)

Revelation of Varying Bonding Motif of Alloxazine, a Flavin Analogue, in Selected Ruthenium(II/III) Frameworks

The reaction of alloxazine (L) and Ru^II(acac)₂(CH₃CN)₂ (acac^– = acetylacetonate) in refluxing methanol leads to the simultaneous formation of Ru^II(acac)₂(L) (<b>1</b> = bluish-green) and Ru^III(acac)₂(L^–) (<b>2</b> = red) encompassing a usual neutral α-iminoketo chelating form of L and an unprecedented monodeprotonated α-iminoenolato chelating form of L^–, respectively. The crystal structure of <b>2</b> establishes that N5,O4^– donors of L^– result in a nearly planar five-membered chelate with the {Ru^III(acac)₂⁺} metal fragment. The packing diagram of <b>2</b> further reveals its hydrogen-bonded dimeric form as well as π–π interactions between the nearly planar tricyclic rings of coordinated alloxazine ligands in nearby molecules. The paramagnetic <b>2</b> and one-electron-oxidized <b>1</b>⁺ display ruthenium­(III)-based anisotropic axial EPR in CH₃CN at 77 K with ⟨<i>g</i>⟩/Δ<i>g</i> of 2.136/0.488 and 2.084/0.364, respectively (⟨<i>g</i>⟩ = {1/3­(<i>g</i>₁² + <i>g</i>₂² + <i>g</i>₃²)}^1/2 and Δ<i>g</i> = <i>g</i>₁ – <i>g</i>₃). The multiple electron-transfer processes of <b>1</b> and <b>2</b> in CH₃CN have been analyzed by DFT-calculated MO compositions and Mulliken spin density distributions at the paramagnetic states, which suggest successive two-electron uptake by the π-system of the heterocyclic ring of L (L → L^•– → L^2–) or L^– (L^– → L^•2– → L^3–) besides metal-based (Ru^II/Ru^III) redox process. The origin of the ligand as well as mixed metal–ligand-based multiple electronic transitions of <b>1</b>^<i>n</i> (<i>n</i> = +1, 0, −1, −2) and <b>2</b>^<i>n</i> (<i>n</i> = 0, −1, −2) in the UV and visible regions, respectively, has been assessed by TD-DFT calculations in each redox state. The p<i>K</i>_a values of <b>1</b> and <b>2</b> incorporating two and one NH protons of 6.5 (N3H, p<i>K</i>_a1)/8.16 (N1H, p<i>K</i>_a2) and 8.43 (N1H, p<i>K</i>_a1), respectively, are estimated by monitoring their spectral changes as a function of pH in CH₃CN–H₂O (1:1). <b>1</b> and <b>2</b> in CH₃CN also participate in proton-driven internal reorganizations involving the coordinated alloxazine moiety, i.e., transformation of an α-iminoketo chelating form to an α-iminoenolato chelating form and the reverse process without any electron-transfer step: Ru^II(acac)₂(L) (<b>1</b>) → Ru^II(acac)₂(L^–) (<b>2</b>^–) and Ru^III(acac)₂(L^–) (<b>2</b>) → Ru^III(acac)₂(L) (<b>1</b>⁺)