In recent years, the rapid swift increase in world biodiesel production has caused an oversupply of its by-product, glycerol. Therefore, extensive research is done worldwide to convert glycerol into numerous high added-value chemicals i.e., glyceric acid, 1,2-propanediol, acrolein, glycerol carbonate, dihydroxyacetone, etc. Hydroxyl acids, glycolic acid and lactic acid, which comprise of carboxyl and alcohol functional groups, are the focus of this study. They are chemicals that are commonly found in the cosmetic industry as an antioxidant or exfoliator and a chemical source of emulsifier in the food industry, respectively. The aim of this study is to selectively convert glycerol into these acids in a single compartment electrochemical cell. For the first time, electrochemical conversion was performed on the mixed carbon-black activated carbon composite (CBAC) with Amberlyst-15 as acid catalyst. To the best of our knowledge, conversion of glycerol to glycolic and lactic acids via electrochemical studies using this electrode has not been reported yet. Two operating parameters i.e., catalyst dosage (6.4-12.8% w/v) and reaction temperature [room temperature (300 K) to 353 K] were tested. At 353 K, the selectivity of glycolic acid can reach up to 72% (with a yield of 66%), using 9.6% w/v catalyst. Under the same temperature, lactic acid achieved its highest selectivity (20.7%) and yield (18.6%) at low catalyst dosage, 6.4% w/v.
In this study the removal of Chromium (III) and Chromium (VI) ions are investigated via polymer enhanced ultrafiltration under important process parameters. This study proposes the use of unmodified starch as a novel polymer in the ultrafiltration process and its performance on the removal of chromium ions was compared with a commonly used polymer, polyethylene glycol.
In this study, a twin-chamber upflow bio-electrochemical reactor packed with palm shell granular activated carbon as biocarrier and third electrode was used for sequential nitrification and denitrification of nitrogen-rich wastewater under different operating conditions. The experiments were performed at a constant pH value for the denitrification compartment. The effect of variables, namely, electric current (I) and hydraulic retention time (HRT), on the pH was considered in the nitrification chamber. The response surface methodology was used based on three levels to develop empirical models for the study on the effects of HRT and current values as independent operating variables on NH(4)(+)-N removal. The results showed that ammonium was reduced within the function of an extensive operational range of electric intensity (20-50 mA) and HRT (6-24h). The optimum condition for ammonium oxidation (90%) was determined with an I of 32 mA and HRT of 19.2h.
Accumulation of nitrite intermediate in autohydrogenotrophic denitrification process has been a challenging difficulty to tackle. This study showed that further growth of "true denitrifying" bacteria and adaptation to nitrite led to a faster reduction of nitrite than nitrate as a solution to circumvent nitrite accumulation. Moreover, two effective parameters namely pH and bicarbonate dose were optimized in order to achieve a better reduction rate. Sodium bicarbonate dose ranging from 20 to 2000 mg/L and pH in the range of 6.5-8.5 was selected to be examined employing 0.2 g MLVSS/L of reacclimatized denitrifying bacteria. Eleven runs of experiments were designed considering the interactive effect of these two operative parameters. A fairly close reduction time less than 4.5 h (>22.22 mg NO2(-)-N/g MLVSS/h) was gained for the pH range between 7 and 8. The highest specific nitrite reduction rate at 25 mg NO2(-)-N/g MLVSS/h was achieved applying 1000 mg NaHCO3/L at pH 7.5 and 8. The pH was found to be the leading parameter and bicarbonate as the less effective parameter on nitrite reduction removal. Central composite design (CCD) and response surface design (RSM) were employed to develop a model as well as define the optimum condition. Using the experimental data, the developed quadratic model predicted optimum condition at pH 7.8 and sodium bicarbonate dose 1070 mg/L upon which denitrifiers managed to accomplish reduction within 3.5 h and attained the specific degradation rate of 28.57 mg NO2(-)-N/g MLVSS/h.
In this study the kinetics of autohydrogenotrophic denitrification was studied under optimum solution pH and bicarbonate concentration. The optimal pH and bicarbonate concentration were firstly obtained using a design of experiment (DOE) methodology. For this purpose a total of 11 experiments were carried out. Sodium bicarbonate concentrations ranging of 20-2000 mg/L and pH values from 6.5 to 8.5 were used in the optimization runs. It was found that the pH has a more pronounced effect on the denitrification process as compared to the bicarbonate dose. The developed quadratic model predicted the optimum conditions at pH 8 and 1100 mg NaHCO(3)/L. Using these optimal conditions, the kinetics of denitrification for nitrate and nitrite degradation were investigated in separate experiments. Both processes were found to follow a zero order kinetic model. The ultimate specific degradation rates for nitrate and nitrite remediation were 29.60 mg NO(3)(-)-N/g MLVSS/L and 34.85 mg NO(3)(-)-N/g MLVSS/L respectively, when hydrogen was supplied every 0.5h.
Acclimation of autohydrogenotrophic denitrifying bacteria using inorganic carbon source (CO(2) and bicarbonate) and hydrogen gas as electron donor was performed in this study. In this regard, activated sludge was used as the seed source and sequencing batch reactor (SBR) technique was applied for accomplishing the acclimatization. Three distinct strategies in feeding of carbon sources were applied: (I) continuous sparging of CO(2), (II) bicarbonate plus continuous sparging of CO(2), and (III) only bicarbonate. The pH-reducing nature of CO(2) showed an unfavorable impact on denitrification rate; however bicarbonate resulted in a buffered environment in the mixed liquor and provided a suitable mean to maintain the pH in the desirable range of 7-8.2. As a result, bicarbonate as the only carbon source showed a faster adaptation, while carbon dioxide as the only carbon source as well as a complementary carbon source added to bicarbonate resulted in longer acclimation period. Adapted hydrogenotrophic denitrifying bacteria, using bicarbonate and hydrogen gas in the aforementioned pH range, caused denitrification at a rate of 13.33 mg NO(3)(-)-N/g MLVSS/h for degrading 20 and 30 mg NO(3)(-)-N/L and 9.09 mg NO(3)(-)-N/g MLVSS/h for degrading 50mg NO(3)(-)-N/L.
Nitrates in different water and wastewater streams raised concerns due to severe impacts on human and animal health. Diverse methods are reported to remove nitrate from water streams which almost fail to entirely treat nitrate, except biological denitrification which is capable of reducing inorganic nitrate compounds to harmless nitrogen gas. Review of numerous studies in biological denitrification of nitrate containing water resources, aquaculture wastewaters and industrial wastewater confirmed the potential of this method and its flexibility towards the remediation of different concentrations of nitrate. The denitrifiers could be fed with organic and inorganic substrates which have different performances and subsequent advantages or disadvantages. Review of heterotrophic and autotrophic denitrifications with different food and energy sources concluded that autotrophic denitrifiers are more effective in denitrification. Autotrophs utilize carbon dioxide and hydrogen as the source of carbon substrate and electron donors, respectively. The application of this method in bio-electro reactors (BERs) has many advantages and is promising. However, this method is not so well established and documented. BERs provide proper environment for simultaneous hydrogen production on cathodes and appropriate consumption by immobilized autotrophs on these cathodes. This survey covers various designs and aspects of BERs and their performances.
Palm shell was used to prepare activated carbon using potassium carbonate (K2CO3) as activating agent. The influence of carbonization temperatures (600-1000 degrees C) and impregnation ratios (0.5-2.0) of the prepared activated carbon on the pore development and yield were investigated. Results showed that in all cases, increasing the carbonization temperature and impregnation ratio, the yield decreased, while the adsorption of CO2 increased, progressively. Specific surface area of activated carbon was maximum about 1170 m2/g at 800 degrees C with activation duration of 2 h and at an impregnation ratio of 1.0.
Nanostructured photoanodes were prepared via a novel combination of titanium dioxide (TiO2) nanoparticles and mesoporous carbon (C). Four different photoanodes were synthesized by sol-gel spin coating onto a glassy substrate of fluorine-doped tin oxide. The photocatalytic activities of TiO2, TiO2/C/TiO2, TiO2/C/C/TiO2, and TiO2/C/TiO2/C/TiO2 photoanodes were evaluated by exposing the synthesized photoanodes to UV-visible light. The photocurrent density observed in these photoanodes confirmed that an additional layer of mesoporous carbon could successfully increase the photocurrent density. The highest photocurrent density of ~1.022 mA cm(-2) at 1 V/saturated calomel electrode was achieved with TiO2/C/C/TiO2 under an illumination intensity of 100 mW cm(-2) from a solar simulator. The highest value of surface roughness was measured for a TiO2/C/C/TiO2 combination owing to the presence of two continuous layers of mesoporous carbon. The resulting films had a thickness ranging from 1.605 µm to 5.165 µm after the calcination process. The presence of double-layer mesoporous carbon resulted in a 20% increase in the photocurrent density compared with the TiO2/C/TiO2 combination when only a single mesoporous carbon layer was employed. The improved performance of these photoanodes can be attributed to the enhanced porosity and increased void space due to the presence of mesoporous carbon. For the first time, it has been demonstrated here that the photoelectrochemical performance of TiO2 can be improved by integrating several layers of mesoporous carbon. Comparison of the rate of removal of humic acid by the prepared photoanodes showed that the highest performance from TiO2/C/C/TiO2 was due to the highest photocurrent density generated. Therefore, this study showed that optimizing the sequence of mesoporous carbon layers can be a viable and inexpensive method for enhanced humic acid removal.
The extensive amount of available information on global warming suggests that this issue has become prevalent worldwide. Majority of countries have issued laws and policies in response to this concern by requiring their industrial sectors to reduce greenhouse gas emissions, such as CO2. Thus, introducing new and more effective treatment methods, such as biological techniques, is crucial to control the emission of greenhouse gases. Many studies have demonstrated CO2 fixation using photo-bioreactors and raceway ponds, but a comprehensive review is yet to be published on biological CO2 fixation. A comprehensive review of CO2 fixation through biological process is presented in this paper as biological processes are ideal to control both organic and inorganic pollutants. This process can also cover the classification of methods, functional mechanisms, designs, and their operational parameters, which are crucial for efficient CO2 fixation. This review also suggests the bio-trickling filter process as an appropriate approach in CO2 fixation to assist in creating a pollution-free environment. Finally, this paper introduces optimum designs, growth rate models, and CO2 fixation of microalgae, functions, and operations in biological CO2 fixation.
Catalytic esterification of glycerol with oleic acid (OA) was optimized over hydrophobic mesoporous zirconia-silica heterogeneous acid catalyst (ZrO2-SiO2-Me&Et-PhSO3H) and benchmarked with commercial catalysts (Aquivion and Amberlyst 15) in order to examine the effect of catalyst acidity on conversion, yield and product selectivity. The process optimisation results showed an 80% conversion with a 59.4% glycerol mono-oleate (GMO) and 34.6% glycerol dioleate (GDO) selectivities corresponding to a combined GMO and GDO selectivity of 94.8% at equimolar OA-to-glycerol ratio, 160°C reaction temperature, 5 wt% catalyst concentration with respect to the OA weight and 4 h reaction time. This work reveals that the hydrophobic and mild acidic ZrO2-SiO2-Me&Et-PhSO3H catalyst outperformed Amberlyst 15 and Aquivion with a yield of 82% and GMO selectivity of 60%. It is found that catalyst acidity is a key parameter for catalytic activity and conversion rate. Nevertheless, high acidity/acid strength reduced the product yield in the glycerol esterification of OA.
The emission of waste anaesthetic gas is a growing contributor to global warming and remains a factor in atmospheric ozone depletion. Volatile anaesthetics in medical waste gases could be removed via adsorption using suitable activated carbon materials possessing an enhanced affinity to anaesthetic molecules. In this work, the effects of surface physical and chemical properties on sevoflurane adsorption were investigated by oxidative hydrothermal surface modification of a commercial activated carbon using only distilled water. The hydrothermal surface modification was carried out at different treatment temperatures (150-300 °C) for varying durations (10-30 min), and adsorption was conducted under fixed conditions (bed depth = 10 cm, inlet concentration = 528 mg/L, and flow rate = 3 L/min). The hydrothermal treatment generally increased the BET surface area of the activated carbons. At oxidation temperatures above 200 °C, the micropore volume of the samples diminished. The relative amount of surface oxygen was enriched as the treatment temperature increased. Treatment duration did not significantly affect the introduction of relative amount of surface oxygen, except at higher temperatures. There were no new types of functional groups introduced. However, disappearance and re-formation of oxygen functional groups containing C-O structures (as in hydroxyl and ether groups) occurred when treatment temperature was increased from 150 to 200 °C, and when treatments were conducted above 200 °C, respectively. The ester/acetal groups were enriched under the temperature range studied. The findings suggested that the re-formation of surface oxygen functionalities might lead to the development of functional groups that improve sevoflurane adsorption.
The inhalational anaesthetic agent - sevoflurane is widely employed for the induction and maintenance of surgical anaesthesia. Sevoflurane possesses a high global warming potential that imposes negative impact to the environment. The only way to resolve the issue is to remove sevoflurane from the medical waste gas before it reaches the atmosphere. A continuous adsorption study with a fixed-bed column was conducted using two commercial granular activated carbons (E-GAC and H-GAC), to selectively remove sevoflurane. The effect of bed depth (Z, 5-15 cm), gas flow rate (Q, 0.5-6.0 L/min) and inlet sevoflurane concentration (C0, ∼55-700 mg/L) was investigated. E-GAC demonstrated ∼60% higher adsorption capacity than H-GAC under the same operating conditions. Varying the levels of Z, Q and C0 showed significant differences in the adsorption capacities of E-GAC, whereas only changing the C0 level had significant differences for H-GAC. Three breakthrough models (Adams-Bohart, Thomas, and Yoon-Nelson) and Bed-depth/service time (BDST) analysis were applied to predict the breakthrough characteristics of the adsorption tests and determine the characteristic parameters of the column. The Yoon-Nelson and Thomas model-predicted breakthrough curves were in good agreement with the experimental values. In the case of the Adams-Bohart model, a low correlation was observed. The predicted breakthrough time (tb) based on kinetic constant (kBDST) in BDST analysis showed satisfactory agreement with the measured values. The results suggest the possibility of designing, scaling up and optimising an adsorption system for removing sevoflurane with the aid of the models and BDST analysis.
Activated carbons have been reported to be useful for adsorptive removal of the volatile anaesthetic sevoflurane from a vapour stream. The surface functionalities on activated carbons could be modified through aqueous oxidation using oxidising solutions to enhance the sevoflurane adsorption. In this study, an attempt to oxidise the surface of a commercial activated carbon to improve its adsorption capacity for sevoflurane was conducted using 6 mol/L nitric acid, 2 mol/L ammonium persulfate, and 30 wt per cent (wt%) of hydrogen peroxide (H2O2). The adsorption tests at fixed conditions (bed depth: 10 cm, inlet concentration: 528 mg/L, and flow rate: 3 L/min) revealed that H2O2 oxidation gave desirable sevoflurane adsorption (0.510 ± 0.005 mg/m2). A parametric study was conducted with H2O2 to investigate the effect of oxidation conditions to the changes in surface oxygen functionalities by varying the concentration, oxidation duration, and temperature, and the Conductor-like Screening Model for Real Solvents (COSMO-RS) was applied to predict the interactions between oxygen functionalities and sevoflurane. The H2O2 oxidation incorporated varying degrees of both surface oxygen functionalities with hydrogen bond (HB) acceptor and HB donor characters under the studied conditions. Oxidised samples with enriched oxygen functionalities with HB acceptor character and fewer HB donor character exhibited better adsorption capacity for sevoflurane. The presence of a high amount of oxygen functional groups with HB donor character adversely affected the sevoflurane adsorption despite the enrichment of oxygen functional groups with HB acceptor character that have a higher tendency to adsorb sevoflurane.
The effects of polyethyleneimine (PEI) impregnation on the Pb(2+) adsorption kinetics of palm shell-activated carbon and pH profile of bulk solution were investigated. Adsorption data were fitted to four established adsorption kinetics models, namely, pseudo-first-order, pseudo-second-order, Elovich equation and intraparticle diffusion. It was found that PEI impregnation at 16.68 and 29.82 wt% PEI/AC increased the Pb(2+) uptake rate while the opposite was observed for PEI impregnation at 4.76 and 8.41 wt% PEI/AC. The increased uptake rates were due to higher concentration of PEI molecules on the surface of clogged pores as well as varying pore volumes. The adsorption kinetics data fitted the pseudo-second-order model better than the pseudo-first-order model, implying chemisorption was the rate-controlling step. The bulk solution pH generally showed an increasing trend from the use of virgin to PEI-impregnated activated carbon.
Palm shell activated carbon was modified via surface impregnation with polyethyleneimine (PEI) to enhance removal of Cu(2+) from aqueous solution in this study. The effect of PEI modification on batch adsorption of Cu(2+) as well as the equilibrium behavior of adsorption of metal ions on activated carbon were investigated. PEI modification clearly increased the Cu(2+) adsorption capacities by 68% and 75.86% for initial solution pH of 3 and 5 respectively. The adsorption data of Cu(2+) on both virgin and PEI-modified AC for both initial solution pH of 3 and 5 fitted the Langmuir and Redlich-Peterson isotherms considerably better than the Freundlich isotherm.
In this study, the kinetics of adsorption of Pb(II) from aqueous solution onto palm shell-based activated carbon (PSAC) were investigated by employing ion selective electrode (ISE) for real-time Pb(II) and pH monitoring. Usage of ISE was very appropriate for real-time adsorption kinetics data collection as it facilitated recording of adsorption data at very specific and short time intervals as well as provided consistent kinetics data. Parameters studied were initial Pb(II) concentration and agitation speed. It was found that increases in initial Pb(II) concentration and agitation speed resulted in higher initial rate of adsorption. Pseudo first-order, pseudo second-order, Elovich, intraparticle diffusion and liquid film diffusion models were used to fit the adsorption kinetics data. It was suggested that chemisorption was the rate-controlling step for adsorption of Pb(II) onto PSAC since the adsorption kinetics data fitted both the pseudo second-order and Elovich models well.
Climate engineering solutions with emphasis on CO2 removal remain a global open challenge to balancing atmospheric CO2 equilibrium levels. As a result, warnings of impending climate disasters are growing every day in urgency. Beyond ordinary CO2 removal through natural CO2 sinks such as oceans and forest vegetation, direct CO2 conversion into valuable intermediaries is necessary. Here, a direct electrosynthesis of the peroxydicarbonate anion (C2O62-) was investigated by the reaction of CO2 with the superoxide ion (O2·-), electrochemically generated from O2 reduction in bis(trifluoromethylsulfonyl)imide [TFSI-] anion derived ionic liquid (IL) media. This is the first time that the IL media were employed successfully for CO2 conversion into C2O62-. Moreover, the charge transfer coefficient for the O2·- generation process in the ILs was less than 0.5, indicating that the process was irreversible. Voltammetry experiments coupled with global electrophilicity index analysis revealed that, when CO2/O2 was contacted simultaneously in the IL medium, O2·- was generated in situ first at a potential of approximately -1.0 V. Also, CO2 was more susceptible to attack by O2·- before any possible interaction with the IL except for [PMIm+][TFSI-]. This was because CO2 has a higher global electrophilicity index (ωCO2 = 0.489 eV) than those for the [EDMPAmm+][TFSI-] and [MOEMMor+][TFSI-]. By further COSMO-RS modeling, CO2 absorption was proven feasible at the COSMO-surface of the [TFSI-] IL-anion where the charge densities were σ = -1.100 and 1.1097 e/nm2. Therefore, the susceptible competitiveness of either IL cations or CO2 to the nucleophilic effects of O2·- was a function of their positive character as estimated by their electrophilicity indices. As determined by experimental attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) and DFT-FTIR computation, the reaction yielded C2O62- in the ILs. Consequently, the presence of O=O symmetric stretching FTIR vibrational mode at ∼844 cm-1 coupled with the disappearance of the oxidative cyclic voltammetry waves when sparging CO2 and O2 confirmed the presence of C2O62-. Moreover, based on DFT/B3LYP/6-31G, pure C2O62- has symmetric O=O stretching at ∼805 and ∼844 cm-1 when it is in association with the IL-cation. This was the first spectroscopic observation of C2O62- in ILs, and the O=O symmetric stretching vibration has peculiarity for identifying C2O62- in ILs. This will open new doors to utilize CO2 in industrial applications with the aid of reactive oxygen species.