Pomegranate husk as an adsorbent in the removal of toxic chromium from wastewater

The use of a new sorbent developed from the husk of pomegranate, a famous fruit in Egypt, for the removal of toxic chromium from aqueous solution has been investigated. The batch experiment was conducted to determine the adsorption capacity of the pomegranate husk. The effects of initial metal concentration (25 and 50 mg l^?1), pH, contact time, and sorbent concentration (2–6 g l^?1) have been studied at room temperature. A strong dependence of the adsorption capacity on pH was observed, the capacity increased as the pH decreased, and the optimum pH value was pH 1.0. Adsorption equilibrium and kinetics were studied with different sorbent and metal concentrations. The adsorption process was fast, and equilibrium was reached within 3 h. The maximum removal was 100% for 25 mg l^?1 of Cr⁶⁺ concentration on 5 g l^?1 pomegranate husk concentration, and the maximum adsorption capacity was 10.59 mg g^?1. The kinetic data were analysed using various kinetic models—pseudo-first-order, pseudo-second-order, Elovich, and intraparticle diffusion equations—and the equilibrium data were tested using several isotherm models, Langmuir, Freundlich, Tempkin, Dubinin–Radushkevich, and Generalized isotherm equations. The Elovich and pseudo-second-order equations provided the greatest accuracy for the kinetic data, while Langmuir and Generalized isotherm models were the closest fit for the equilibrium data. The activation energy of sorption has also been evaluated as 0.236 and 0.707 kJ mol^?1 for 25 and 50 mg l^?1 chromium concentration, respectively.     

Potential of rice husk ash in atrazine removal

An experimental study was carried out to explore the possibility of using a prepared microporous material, Rice Husk Ash (RHA) as an alternative to the commercial Powdered Activated Carbon (PAC), to remove atrazine (ATZ) pesticide from aqueous solution. The effects of contact time and pH on the adsorption were studied using the batch technique. Based on Hückel model calculations, the zwitterion behaviour of atrazine molecule was proved to be related to the pH of zero charge point of adsorbents (6.8 for RHA and 8.2 for PAC). The results showed that the Pseudo Second Order model is applicable to both adsorbents, suggesting that chemisorption is the rate-limiting step. The equilibrium data fitted well with the Langmuir model in the case of RHA, whereas the Freundlich model better fitted the equilibrium data in the PAC case, suggesting the existence of multi-layer adsorption of atrazine. The adsorption for RHA was found to be feasible and spontaneous, with a removal capacity of atrazine of more than 7?mg?g^?1. With regard to the BET surface, this removal capacity (50.5?µg_ATZ / m²_RHA) was 25% better than that PAC (37.75µg_ATZ / m²_PAC).     

Magnetic particles precipitated onto wheat husk for removal of methyl blue from aqueous solution

Magnetic particles prepared via co-precipitation and impregnated onto wheat husk (MN-WH) were used for the removal of methyl blue (MB) from aqueous solution. Experiments were conducted in a batch mode for optimization regarding pH, contact time, adsorbent dose, initial dye concentrations, and temperature. Maximum adsorption (98%) was achieved at pH 5. The adsorption data were fitted into pseudo-first, pseudo-second, intraparticle diffusion, and Elovich equation revealing that adsorption followed pseudo-second-order kinetics. The four most common isotherm models, i.e. the Langmuir, Freundlich, Tempkin, and Dubinin–Radushkevich (D–R), were used to evaluate the data, with the best fit to a Langmuir isotherm (R² = 0.996), followed by a Freundlich isotherm (R² = 0.995), indicating monolayer adsorption of MB on the surface of MN-WH. Thermodynamic parameters calculated from the Van't Hoff equation revealed that the adsorption is exothermic (ΔHº = ?19.7 kJ mol^?1).     

Removal of Cr(VI) from aqueous solution using waste weed, Salvinia cucullata

Biosorption studies of Cr(VI) were carried out using waste weed, Salvinia cucullata. Various adsorption parameters were studied, such as agitation speed, contact time, pH, particle size, and concentrations of adsorbent and adsorbate. The equilibrium was achieved in 12 h. A lower pH favoured adsorption of Cr(VI). The kinetics followed pseudo-second-order rate equations. The adsorption isotherm obeyed both the Langmuir and Freundlich models. The calculated activation energy (1.1 kJ mol^-1) suggested that the adsorption followed a diffusion-controlled mechanism. Various thermodynamic parameters such as Δ G^°, Δ H^°, and Δ S^° were also calculated. The positive values of enthalpy indicated the endothermic nature of the reaction, and Δ S^° showed the increasing randomness at the solid liquid interface of Cr(VI) on the adsorbent, which revealed the ease of adsorption reaction. These thermo-dynamic parameters showed the spontaneity of the reaction. The maximum adsorption of uptake (232 mg g^-1) compared well with reported values of similar adsorbents. The rate-determining step was observed to follow an intra-particle diffusion model.     

Effective removal of Cd2+ and Pb2+ pollutants from wastewater by dielectrophoresis-assisted adsorption

Dielectrophoresis (DEP) process could enhance the removal the Cd²⁺ and Pb²⁺ with less absorbent. The removal rates of both Cd²⁺ and Pb²⁺ increased with the increase of voltage. The overall removal rate of Cd²⁺ and Pb²⁺ in the binary system is higher than that of Cd²⁺ or Pb²⁺ in the single system. DEP could cause considerable changes of the bentonite particles in both surface morphology and microstructure. Dielectrophoresis (DEP) was combined with adsorption (ADS) to simultaneously and effectively remove Cd²⁺ and Pb²⁺ species from aqueous solution. To implement the process, bentonite particles of submicro-meter size were used to first adsorb the heavy metal ions. These particles were subsequently trapped and removed by DEP. The effects of the adsorbent dosage, DEP cell voltage and the capture pool numbers on the removal rate were investigated in batch processes, which allowed us to determine the optimal experimental conditions. The high removal efficiency, 97.3% and 99.9% for Cd²⁺ and Pb²⁺, respectively, were achieved when the ions are coexisting in the system. The microstructure of bentonite particles before and after ADS/DEP was examined by scanning electron microscopy. Our results suggest that the dielectrophoresis-assisted adsorption method has a high capability to remove the heavy metals from wastewater.     

1,3,5-triazine-triethylenetetramine polymer: an efficient adsorbent for removal of Cr(VI) ions from aqueous solution

The synthesis of 1,3,5-triazine-triethylenetetramine (TATETA), its characterization by infrared spectroscopy and elemental analysis, and its application for removal of Cr(VI) ions from aqueous solution is reported. The effects of pH, contact time, initial concentration of Cr(VI), sorbent dose, and temperature on adsorption were investigated and optimized by batch adsorption experiments. Adsorption was highest at acidic conditions with an equilibration time of 25 min. The adsorption followed a Langmuir model, with an adsorption capacity of 303 mg g^?1, was second order in its kinetics, and exothermic and thus spontaneous.     

污灌湿地系统土壤-植物中铬的赋存形态研究

采取逐级提取法对江苏盐城某污水灌溉湿地土壤中的铬的赋存形态以及其上生长的丰要植物芦苇的不同组织部位中的总铬进行了分析测定，并研究其生物有效性。结果表明：与对照点相比，污灌土壤中铬质最分数明显升高而受到不同程度的污染，其赋存形态质量分数由高到低顺序为残渣态（RES-）→铁锰态（（OFeMn-））→碳酸态（CARB-）→有机态（OM-）和交换态（EX-）之和。芦苇不同组织部位中铬分布研究表明根部质量分数远大于茎和叶，说明根系吸收为主要作用，而后迁移至其它易积累部位。对各种形态的铬与植物中的铬总量之间的相关性进行了分析，相关系数表明，植物中的生物富集量与各种赋存形态都有一定的线性关系，其中强有机质结合态与生物富集量具有最好的线性相关性。     

Concurrent adsorption and reduction of chromium(VI) to chromium(III) using nitrogen-doped porous carbon adsorbent derived from loofah sponge

• A high-efficiency N-doped porous carbon adsorbent for Cr(VI) was synthesized. • The maximum adsorption capacity of Cr(VI) reached up to 285.71 mg/g at 318K. • The potential mechanism for Cr(VI) adsorption by NHPC was put forward. • DFT analyzed the adsorption energy and interaction between NHPC and Cr(VI). To develop highly effective adsorbents for chromium removal, a nitrogen-doped biomass-derived carbon (NHPC) was synthesized via direct carbonation of loofah sponge followed by alkali activation and doping modification. NHPC possessed a hierarchical micro-/mesoporous lamellar structure with nitrogen-containing functional groups (1.33 at%), specific surface area (1792.47 m²/g), and pore volume (1.18 cm³/g). NHPC exhibited a higher Cr(VI) adsorption affinity than the HPC (without nitrogen doping) or the pristine loofah sponge carbon (LSC) did. The influence of process parameters, including pH, dosage, time, temperature, and Cr(VI) concentration, on Cr(VI) adsorption by NHPC were evaluated. The Cr(VI) adsorption kinetics matched with the pseudo-second-order model (R²≥0.9983). The Cr(VI) adsorption isotherm was fitted with the Langmuir isotherm model, which indicated the maximum Cr(VI) adsorption capacities: 227.27, 238.10, and 285.71 mg/g at 298K, 308K, and 318K, respectively. The model analysis also indicated that adsorption of Cr(VI) on NHPC was a spontaneous, endothermal, and entropy-increasing process. The Cr(VI) adsorption process potentially involved mixed reductive and adsorbed mechanism. Furthermore, computational chemistry calculations revealed that the adsorption energy between NHPC and Cr(VI) (−0.84 eV) was lower than that of HPC (−0.51 eV), suggesting that nitrogen doping could greatly enhance the interaction between NHPC and Cr(VI).     

Removal of toxic chromium(VI) from aqueous solution by activated carbon using Casuarina equisetifolia

Highly activated carbon from the seed husk of Casuarina Casuarinas equisetifolia, a worldwide famous plant, have been prepared and tested for the removal of toxic Cr(VI) from its aqueous solution. The adsorbent was investigated for influences of initial chromium concentration (75, 100, 125, and 150 mg l^-1), pH, contact time, and quantity of carbon on removal of Cr(VI) from aqueous solution at room temperature (25±2 °C). The adsorption kinetic of Cr(VI) was studied, and the rates of sorption were found to conform to pseudo-second-order kinetics with a good correlation (R²≥0.99). The Langmuir and Freundlich models fit the isotherm data well. Furthermore, the Gibbs free energy was obtained for each system and was found to be-5.29 kJ mol^-1 for removal of Cr(IV). The negative value of Δ G° indicates the feasibility and spontaneous nature of adsorption. The results indicate that acidic pH (1.05) supported the adsorption of Cr(IV) on activated carbon. The maximum adsorption capacity of Cr(VI) on activated carbon was about 172.4 mg g^-1 at pH 1.05.     

Effects of reducing agent and approaching anodes on chromium removal in electrokinetic soil remediation

A soil remediation method combining in situ reduction of Cr(VI) with approaching anodes electrokinetic (AAs-EK) remediation is proposed. EK experiments were conducted to compare the effect of approaching anodes (AAs) and fixed electrodes (FEs) with and without sodium bisulfite (NaHSO₃) as a reducing agent. When NaHSO₃ was added to the soil before EK treatment, 90.3% of the Cr(VI) was reduced to Cr(III). EK experiments showed that the adverse effect of contrasting migration of Cr(III) and Cr(VI) species, which limits the practical application of this technique, was eliminated in the presence of the reducing agent. Furthermore, Tessier fractionation analysis indicated that the reducing agent changed the distribution of the chemical forms of Cr. The AAs-EK method was shown to acidize the soil as the anode moved toward the cathode and this acid front pushed the “focusing” region toward the cathode. After remediation, the pH of the soil was between 1.8 and 5.0 in AAs-EK experiments. The total Cr removal efficiency was 64.4% (except in the “focusing” region) when the reduction reaction was combined with AAs-EK method. We conclude that AAs-EK remediation in the presence of NaHSO₃ is an appropriate method for Cr-contaminated soil.     

Predicting the migration of dissolved toxic substances from catchments by a collective model

In the present paper a collective model for predicting the migration of dissolved toxic substances through drainage areas is described. The model has been validated using data for ¹³⁷Cs and ⁹⁰Sr concentrations in water of some European contaminated rivers following the atmospheric fall-out from the accident at the Chernobyl power plant. It has been demonstrated that the migration rate λ (s⁻¹) of a dissolved toxic substance from a catchment may be evaluated by the following approximate formula: λ=(c ln t+d)/t, where t is the time from a pulse deposition event and the coefficients c and d depend on the characteristics of the substance. It has been shown that the mathematical form of the transfer function (flux of dissolved substance at time t following a single pulse deposition of a pollutant onto the catchment) of a toxic substance from a drainage area is very simple. Moreover, the values of the transfer function parameters are slightly variable despite the large range of characteristics of the catchments here examined. Indeed, the statistical aggregation of competing migration processes can lead to ‘stable’ collective behaviours that are less variable than each single process.     

Application of electrochemical reactor divided by cellulosic membrane for optimized simultaneous removal of phenols,chromium, and ammonia from tannery effluents

The post treatment of simulated tannery wastewater was evaluated in an electrochemical oxidation process under galvanostatic conditions. A continuous flow reactor divided by a cellulosic membrane consisted of Ti/SnO₂–Sb anodes and iron cathodes was used. Central composite design and response surface methodology (RSM) were applied to investigate the effects of six operational parameters, namely initial concentration of total phenols (TPh), total chromium (TCr), total ammonia nitrogen (TAN), flow rate (Q), current intensity (I), and electrode surface area (A). Effectiveness of the innovative cellulosic membrane was proven by considerable pH variations in the anolyte and catholyte chambers. A faster removal rate was observed for TPh and TAN, followed by TCr. The treatment level was very sensitive to Q and I in the studied ranges. RSM showed the removal efficiencies of 78.14%, 63.42%, and 86.09% for TPh, TCr, and TAN, respectively, are achieved under optimal conditions with consumption of only 9.03 kWh m^?3 electrical energy. Chlorinated compounds such as chloroform, 2,4-dichlorophenol, and chlorobenzene were detected as the degradation intermediates. According to the obtained results, electrolysis in the divided cell with cellulosic membrane is a practical, cost-effective method for advanced treatment of tannery effluents.     

Occurrence,removal, and environmental risks of pharmaceuticals in wastewater treatment plants in south China

Pharmaceutically active compounds in wastewater released from human consumption have received considerable attention because of their possible risks for aquatic environments. In this study, the occurrence and removal of 10 pharmaceuticals in three municipal wastewater treatment plants in southern China were investigated and the environmental risks they posed were assessed. Nifedipine, atenolol, metoprolol, valsartan and pravastatin were detected in the influent wastewater. The highest average concentration in the influents was observed for metoprolol (164.6 ng/L), followed by valsartan (120.3 ng/L) in August, while median concentrations were higher in November than in August. The total average daily mass loadings of the pharmaceuticals in the three plants were 289.52 mg/d/person, 430.46 mg/d/person and 368.67 mg/d/person, respectively. Elimination in the treatment plants studied was incomplete, with metoprolol levels increasing during biological treatment. Biological treatment was the most effective step for PhACs removal in all of the plants studied. Moreover, the removal of PhACs was observed with higher efficiencies in August than in November. The WWTP equipped with an Unitank process exhibited similar removals of most PhACs as other WWTPs equipped with an anoxic/oxic (A/O) process or various anaerobic-anoxic-oxic (A²/O) process. The environmental risk assessment concluded that all of the single PhAC in the effluents displayed a low risk (RQ<0.1) to the aquatic environments.

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Adsorption of phosphate on magnetite-enriched particles (MEP) separated from the mill scale

MEP were separated from mill scale at low magnetic intensity i.e., 300 to 500 gauss. The phosphate adsorption capacity of MEP was determined 6.41 mg/g. MEP packed-bed columns were successfully regenerated with alkaline solution. Phosphate is a major pollutant in water, causing serious environmental and health consequences. In present study, the phosphate adsorption on novel magnetite-enriched particles (MEP) was comprehensively investigated. A new method and device were introduced for the separation of MEP from the mill scale at low magnetic intensity. Particles were characterized with different techniques such as XRD, XRF, SEM and EDS. The XRD and XRF analysis of MEP identified the dominant existence of crystalline magnetite. Furthermore, the morphological analysis of MEP confirmed the agglomerate porous morphology of magnetite. Oxygen and iron, the main constituents of magnetite were acknowledged during the elemental analysis using EDS. The phosphate adsorption on MEP is well explained using various isotherm and kinetic models, exhibiting the monolayer adsorption of phosphate on the surface of MEP. The maximum adsorption capacity was determined 6.41 mg/g. Based on particle size (45–75 and 75–150 µm) and empty bed contact time (1 and 2 h), four columns were operated for 54 days. MEP were appeared successful to remove all phosphate concentration from the column influent having 2 mg/L concentration. The operated column reactors were successfully regenerated with alkaline solution. The results indicated potential for practical application of the MEP for phosphate removal.     

Optimization of methyl orange removal from aqueous solution by response surface methodology using spent tea leaves as adsorbent

The effective disposal of redundant tea waste is crucial to environmental protection and comprehensive utilization of trash resources. In this work, the removal of methyl orange （MO） from aqueous solution using spent tea leaves as the sorbent was investigated in a batch experiment. First, the effects of various parameters such as temperature, adsorption time, dose of spent tea leaves, and initial concentration of MO were investigated. Then, the response surface methodology （RSM）, based on Box- Behnken design, was employed to obtain the optimum adsorption conditions. The optimal conditions could be obtained at an initial concentration of MO of 9.75 mg·L-1, temperature of 35.3℃, contact time of 63.8 min, and an adsorbent dosage 3.90 g· L-1. Under the optimized condi- tions, the maximal removal of MO was 58.2%. The results indicate that spent tea leaves could be used as an effective and economical adsorbent in the removal of MO from aqueous solution.     

铬对生活污水中氮磷的植物净化效果及体内氮磷含量的影响

采用水培法,设置4个Cr6＋质量浓度（0,1,10,20mg·L-1）处理风车草（Cyperus alternifolius）和薏米（Coix aquatica Roxb）,以此研究铬对生活污水中氮磷净化效果及植物体内氮磷质量分数的影响。结果表明：（1）试验期内,铬质量浓度为1mg·L-1时促进风车草和薏米对总氮的去除,铬质量浓度为20mg·L-1时则抑制;总氮去除率因处理时间不同而不同,表现在处理17d时0mg·L-1、1mg·L-1铬处理显著高于处理7d,但20mg·L-1处理则相反;除Cr20处理外,薏米对总氮的去除率显著高于风车草。（2）风车草和薏米对生活污水中总磷的去除率随铬处理时间延长而降低,表现在处理17d时10mg·L-1、20mg·L-1铬处理显著低于处理7d;在20mg·L-1铬处理下皆显著低于对照;风车草对总磷的去除率在10mg·L-1、20mg·L-1铬处理下显著高于薏米。（3）不同质量浓度Cr6＋处理下风车草和薏米体内氮、磷质量分数的变化不同,其中20mg·L-1铬处理下风车草茎和薏米根、茎及叶片皆显著低于对照。     

Effectiveness of tertiary treatment processes in removing different classes of emerging contaminants from domestic wastewater

● Different advanced treatment processes were tested for ECs removal from wastewater. ● UV radiation showed low to moderate removal for 5 of the 38 micropollutants. ● Among tested membrane processes, nanofiltration showed the better performance. ● The use of PAC achieved high or partially removal for 31 out of the 38 compounds. ● The environmental and economical evaluation of a pilot-scale PAC unit is suggested. In this work, 38 different organic emerging contaminants (ECs), belonging to various chemical classes such as pharmaceuticals (PhCs), endocrine-disrupting chemicals (EDCs), benzotriazoles (BTRs), benzothiazoles (BTHs), and perfluorinated compounds (PFCs), were initially identified and quantified in the biologically treated wastewater collected from Athens’ (Greece) Sewage Treatment Plant (STP). Processes already used in existing STPs such as microfiltration (MF), nanofiltration (NF), ultrafiltration (UF), UV radiation, and powdered activated carbon (PAC) were assessed for ECs’ removal, under the conditions that represent their actual application for disinfection or advanced wastewater treatment. The results indicated that MF removed only one out of the 38 ECs and hence it was selected as pretreatment step for the other processes. UV radiation in the studied conditions showed low to moderate removal for 5 out of the 38 ECs. NF showed better results than UF due to the smaller pore sizes of the filtration system. However, this enhancement was observed mainly for 8 compounds originating from the classes of PhCs and PFCs, while the removal of EDCs was not statistically significant. Among the various studied technologies, PAC stands out due to its capability to sufficiently remove most ECs. In particular, removal rates higher than 70% were observed for 9 compounds, 22 were partially removed, while 7 demonstrated low removal rates. Based on our screening experiments, future research should focus on scaling-up PAC in actual conditions, combining PAC with other processes, and conduct a complete economic and environmental assessment of the treatment.     

Estimation of far-field horizontal and vertical turbulent diffusion coefficients from the concentration field of a wastewater plume near the Akashi Strait

We carried out a field study of the plume discharged by a near-shore wastewater outfall near the Akashi Strait, Japan. Using an Acoustic Doppler Current Profiler and a tow-body CTD, we measured the near-surface salinity and temperature fields in the region throughout an M₂ tidal cycle. We filtered the data in T–S space to remove water masses other than the wastewater, and then used the adiabatic mixing assumption to calculate the concentration of wastewater in the far field of this plume. Averaging the T–S fields of repeated surveys over a time period during which the tidal regime did not change substantially, allowed comparison of the time-averaged plume with the analytical solution for a plume diffusing in both the horizontal and vertical dimensions. The resulting vertical turbulent diffusion coefficients agreed well with those resulting from Thorpe scales determined via a vertically-profiling CTD, as well as with the canonical value for open channel flow of D _z = 0.067hu _*. The corresponding horizontal turbulent diffusion coefficients, however, were two orders of magnitude larger than those typically observed in straight channels, and an order of magnitude larger than those observed in meandering rivers. This is likely a result of enhanced horizontal mixing due to barotropic eddies generated by the interaction of strong tidal flow with headlands and levees, as well as due to the time-varying nature of tidal flow, and baroclinic spreading of the buoyant wastewater plume.