Lead Removal from Acidic Solutions by Sorption on Cocoa Shells: Effect of Some Parameters

The objectives of this work were to evaluate the effects of different parameters (Pb concentration, solution pH, Ca/Mg/Na/K salt concentrations) on Pb uptake by cocoa shells and to study the mechanisms of Pb removal in very acidic conditions. Sorption tests were conducted in shaken flasks with synthetic Pb solutions and 15 g/L cocoa shells. A lead uptake value of 161 mmol/kg was measured during the assay with [Pb]i = 3.66?mmol/L in solution at pHi = 2.0 and T = 22°C. Results show that Pb uptake is very similar (14.5–16.0 mmol/kg) for an initial pH between 2.0 and 4.0, but a moderate decrease (10.8 mmol/kg) occurred when the initial pH=1.5 and the [Pb]i = 0.25?mmol/L. High Ca and Mg concentrations (2.35 mol/L) in solution induced a significant decrease in Pb removal by cocoa shells, whereas high K and Na concentrations did not affect Pb uptake by this sorbent. This suggests that Pb uptake by cocoa shells is controlled by ion-exchange reactions with Ca/Mg ions and protons. Finally, chemical tests have shown that carboxyl and amine functional groups play a dominant role in Pb uptake by cocoa shells.     

Laboratory Study of Successive Soil Saline Leaching and Electrochemical Lead Recovery

This research is related to a laboratory study on the performance of a successive soil saline leaching and electrochemical lead recovery process for soil decontamination. Erlenmeyer leaching assays showed that the addition of 5.5 mol NaCl/L in 25% (w/w) of soil pulp density maintained at pH 3.0 was found the most effective condition for Pb leaching. Under these conditions, 65% of Pb was leached from soil. Electrochemical treatment using an iron–monopolar electrode system operated at a current intensity of 3.0 A was able to reduce Pb content in soil leachate from 650 to 0.15 mg/L and this without production of metallic residue. Then, a leaching tank reactor and electrolytic cell coupled in a closed loop showed that the Pb mass balance of extrants/intrants ratio indicated 99.0±1.6% of Pb was recovered. Likewise, 94.1% of chloride ions were reused in the leaching tank reactor after electrochemical treatment.     

Modeling Substrate Interactions during Aerobic Biodegradation of Mixtures of Vinyl Chloride and Ethene

Ethene (ETH) is often associated with vinyl chloride (VC) in contaminated groundwater, as it is formed along with vinyl chloride during reductive dechlorination of higher chloroethenes (e.g., perchloroethylene and trichloroethylene). In the present study the interaction between VC and ETH during their aerobic biodegradation by enrichment cultures was investigated. The cultures were able to use both compounds as growth substrates. In mixture experiments, the degradation rate of one substrate was affected by the presence of the other. A biokinetic model based on competitive inhibition described well the observed substrate interactions over a range of initial VC (0–144 μmol?L?1) and ETH (0–37.5 μmol?L?1) concentrations, using parameters estimated from single-substrate experiments. Notably, half-velocity coefficients could be used as competitive inhibition coefficients. This finding shows the importance of obtaining accurate measurements of half-velocity coefficients in order model competitive inhibition processes. Simulation results showed that when the initial ETH concentration was raised from 0 to 30 μmol?L?1, the apparent half-velocity coefficient for VC (KVCAPP) increased by nearly three times, from 12.9 to 35.4 μmol?L?1. This finding has strong environmental implications because a low half-velocity coefficient for VC is regarded as the major prerequisite for achieving efficient and complete VC degradation. Moreover, the effect of ETH on the efficiency of VC removal is strongly dependent on the KVC/KETH ratio, consequently determination of KETH for VC-degrading microbes is important when biodegradation (or bioaugmentation) is considered for clean up of VC-contaminated sites. Additional model simulations, using the ratio of KVC to KETH for previously characterized VC- and ETH-utilizing microorganisms (values ranged from 0.06 to 1.2) showed that their ability to degrade VC in the presence of ETH may differ significantly.     

Experimental Investigation of the Interaction of Soil Air Permeability and Soil Vapor Extraction

Soil vapor extraction column experiments were performed to investigate contaminant removal and its interaction with soil air permeability. Water, TCE, and PCE, and a mixture of TCE and PCE were used as contaminants. Three gradations of Ottawa sand were used at relative densities of 0.60 and 1.0:?medium, fine, and uniform. Soil air permeability was found to increase linearly with time by 25–150?% to a maximum value when the contaminant was completely removed. The largest increase in soil air permeability was found for fine and/or dense samples. The experimental data were used in a previously developed model by Farhan in 1998 and Farhan et al. in 2001 to predict column behavior. In general, the model predictions were in good agreement with the experimental results. They revealed that the assumption of local equilibrium between the pore air and contaminants is valid for a wide range of pore velocities (2.0–9.2 cm/s).     

Heavy Metals Removal from Acidic and Saline Soil Leachate Using Either Electrochemical Coagulation or Chemical Precipitation

This study compares electrocoagulation and chemical precipitation for heavy metals removal from acidic soil saline leachate (SSL) at the laboratory pilot scale. The electrocoagulation process was evaluated via an electrolytic cell [12 cm (width)×12 cm (length)×19 cm (depth)] using mild steel electrodes (10 cm width×11 cm high), whereas chemical precipitation was evaluated using either calcium hydroxide [Ca(OH)2] or sodium hydroxide (NaOH). By comparison with chemical precipitation at a pH varying between 7 and 8, electrocoagulation was more effective in removing metals from SSL having a relatively low contamination level (124?mg?Pb/L and 38?mg?Zn/L). For SSL enriched with different heavy metals (each concentration of metals was initially adjusted to 100 mg/L) and treated at a pH lower than 8.5, with the exception of Cd, the residual metal concentrations at the end of the experiments were below the acceptable level recommended for effluent discharge in urban sewage works (less than 4 mg/L of each residual metal concentration was recorded) using electrocoagulation, contrary to chemical precipitation using NaOH (more than 15 mg/L of each residual metal concentration was recorded). By comparison, chemical precipitation using Ca(OH)2 was effective in reducing Cr, Cu, Ni, and Zn under the permissive level, but not for Cd and Pb. However, both chemical precipitation processes needed to be operated at higher pH values (around 10.0) to be more effective in reducing metals from SSL and, therefore, required a pH adjustment of the effluent before discharge, whereas electrochemical treatment had a practical advantage of producing an effluent having a pH close to the neutral value and suitable for stream discharge in the receiving water. On the other hand, electrocoagulation was also found to be very efficient for removing Pb from very contaminated solutions (250–2,000 mg?Pb/L). At least 94% of Pb was removed regardless of the initial Pb concentration in the SSL. Electrochemical coagulation involves a total cost varying from 8.67 to 13.00 $/tds, whereas 0.84 to 16.73 $/tds is recorded using chemical precipitation. The cost included only energy consumption, chemicals consumption, and metallic sludge disposal.     

Effect of Metallic Iron Concentration on End-Product Distribution during Metallic Iron-Assisted Autotrophic Denitrification

The main objective of this study was to determine the optimum composition of a reactive porous medium containing sand and metallic iron, to be used for Fe(0)-assisted hydrogenotrophic denitrification. This determination is important to ensure that the end-product distribution after such treatment is acceptable, i.e., ammonia formation due to abiotic nitrate reduction by metallic iron in such media is minimized, while a reasonable rate of biological denitrification is maintained. Based on a previous study it was established that steel wool, with its relatively low specific surface area, exhibited the least propensity to abiotically reduce nitrate. It was also established that to achieve acceptable end-product distribution, the steel wool concentration in the reactive porous media has to be lowered even below the lowest value, i.e., 4.0?g steel wool/m3 of sand, used during that study. It was further hypothesized that to counter any detrimental effect of lower steel wool concentration on biological nitrate removal rate, increase of the retention time in porous media to values higher than 13 days, the maximum value investigated in that study, may be necessary. In the present study, experiments were conducted in batch reactors containing denitrifying microorganisms and various concentrations of steel wool and in semibatch reactors containing sand seeded with denitrifying microorganisms and various concentrations of steel wool. Based on the results of the semibatch experiments, it appears that to achieve acceptable end-product distribution, the steel wool concentration in the reactive porous media has to be maintained around 2.0?g steel wool/m3 sand and the corresponding retention time in the reactive media must be around 26 days.     

Simultaneous Removal of Cd and Cr(VI) Using Fe-Loaded Zeolite

Current research focuses on the simultaneous removal of Cd and Cr(VI) in water by a newly developed material having both abilities of sorption and electrochemical reduction. The material was derived from the zeolite modified by Fe(II) chloride followed by sodium borohydride reduction. The Fe-loaded zeolite simultaneously removed Cd and Cr(VI) to below the detection limit at a fairly rapid rate within 1?h for Cd and within 20?h for Cr(VI), under the pH ranging from slightly acid to around neutral. At high concentration of coexisting Cr(VI), the removal efficiency of Fe-loaded zeolite for Cd slightly decreased due to surface fouling by Cr(III) hydroxide precipitations. On the contrary, the coexisting Cd was found to increase the removal rate of Cr(VI) by Fe-loaded zeolite. From the test results, the Fe-loaded zeolite was found to be a possible alternative in simultaneous removal of Cd and Cr(VI) in the aqueous phase.     

Escherichia coli Removal Efficacy of a Marshland Upwelling System

The Marshland Upwelling System (MUS), a decentralized wastewater treatment strategy for coastal dwellings, was examined to assess its ability to remove Escherichia coli from raw sewage as a step towards total treatment. Wastewater was intermittently injected down a 4.6-m injection well into the surrounding salt marsh at 0.9, 1.9, and 3.8 lpm over the 13-month evaluation period. Optimal E. coli removal and hydraulic performance was achieved at the 1.9-lpm flow rate with influent concentrations of 260,000±370,000 E. coli/100 mL reduced to a mean effluent count of 0.4±10.6 E. coli/100 mL. Escherichia coli concentrations declined exponentially with only 0.9-m travel distance needed to reduce influent concentrations by 1 order of magnitude. Predicted surface concentrations were less than 1 E. coli/100 mL. The probability of effluent counts exceeding the U.S. Environmental Protection Agency standard of 126 E. coli/100 mL for recreational waters was 5.5×10?12%. Increasing flows to 3.8 lpm initiated localized hydraulic dysfunction as indicated by elevated injection pressures and transient increases in bacterial counts. Based on these findings, the MUS can provide an effluent of acceptable bacterial quality under specified operating parameters and the site-specific hydrogeological conditions analyzed.     

Effect of Nonsteady state H2O2 Tests on Oxygen Transfer Rate in Enhanced Biological Phosphorus Removal Process

A laboratory scale enhanced biological phosphorus removal process was operated in the University of Cape Town configuration to study the variations in alpha and oxygen transfer efficiency (OTEf) under different process conditions. As part of this investigation, process oxygen transfer parameters were determined using the steady state oxygen uptake rate (OUR) and the nonsteady state hydrogen peroxide addition (HPA) methods, as per the American Society of Civil Engineers guidelines. The results indicated that the oxygen transfer parameters [volumetric mass transfer coefficient (KLaf), oxygen transfer rate (OTRf), α and OTEf)] were higher when both methods were applied on the same day, compared to the subsequent period, when only the steady state OUR method was employed, under similar operating conditions. The difference in the oxygen transfer parameters appears to be due to the addition of H2O2 that generates reactive oxygen species in the nonsteady state HPA test. Based on the findings, it was concluded that the HPA test was not a suitable technique to measure oxygen transfer under process conditions. Further, a conceptual model hypothesizing the impacts of H2O2 addition on activated sludge process is presented.     

电解质的组成对铝电解中电渗的影响

通过试验考察了氧化铝浓度、分子比及氟化镁含量对铝电解电渗的影响 ,并通过电子探针和 X-射线衍射分析了电渗的物质 ,电渗的深度。结果表明 :电渗的主要物质是钠氟化合物 ,随着氧化铝浓度及氟化镁含量的增加 ,电渗的深度及电渗的物质量增加 ;当冰晶石分子比达到 2 .0时 ,电渗的深度急剧增加     

Comparison of Oxygen Transfer Parameters Determined from the Steady State Oxygen Uptake Rate and the Non-Steady-State Changing Power Level Methods

In this study, a laboratory scale Univ. of Cape Town enhanced biological phosphorus removal process was operated under controlled conditions at a solids retention time of 15 days. Results are presented for the process performance and oxygen transfer parameters determined by applying the steady state oxygen uptake rate (OUR) and the changing power level (CPL) techniques, as per ASCE standard guidelines. The testing periods were temporally separated to eliminate interference of the tests. During the application of the CPL method, the sludge volume index gradually increased and higher values of the oxygen transfer rate and alpha were measured, in comparison to the data from the steady state OUR method, under similar process performance. Furthermore, the mass transfer rate decreased as the CPL method of testing continued. In contrast, the oxygen transfer parameters remained uniform during the time when the OUR method was applied. The data indicated that the CPL method resulted in higher and variable oxygen transfer parameters, even though the process performance remained unchanged. Therefore, a more rigorous evaluation of the CPL method is recommended to clarify the validity of the test.     

Modeling Elution Histories of Copper and Lead from Contaminated Soil Treated by Poly(amidoamine) Dendrimers

A dynamic “two-site” model was formulated and tested for simulating the elution histories of copper (Cu2+) and lead (Pb2+) from a contaminated soil treated by poly(amidoamine) dendrimers. In the model, the metal sorption sites of the soil were divided into two compartments: one with a fast desorption rate and the other with a slow desorption rate. The model was tested for simulating and predicting Cu2+ and Pb2+ elution histories obtained from column experiments. Compared to the classical “one-site” model and the modified “gamma distribution” model, the “two-site” model not only provides much improved power for simulating the observed metal elution data, but also can more accurately predict the metal elution histories under various experimental conditions including initial metal concentration in soil, dendrimer concentration, and pH.     

Use of Phosphate Rock for the Removal of Ni2+ from Aqueous Solutions: Kinetic and Thermodynamics Studies

A study was carried out in batch conditions to examine the removal of nickel ions from an aqueous solution by phosphate rock. The effect of different sorption parameters, such as initial metal concentration, equilibration time, solution pH, and temperature on the amount of Ni2+ sorbed was studied and discussed. The sorption process followed pseudo-second-order kinetics with necessary time of 2?h to reach equilibrium. The maximum removal obtained is at initial pH around 8. Nickel uptake was quantitatively evaluated using the Langmuir and Dubinin–Kaganer–Radushkevich model. The Langmuir adsorption isotherm constant corresponding to adsorption capacity, Q0, was found to be 7.63?mg/g. The possibility of metal recovery was investigated using several eluting agents. The desorbed amount of nickel decreased continuously with increasing pH, and increased with increasing Ca2+ concentration in leaching solution.     

Calibration of a Model for Volatile Organic Compound Mass Removal by Multiphase Extraction

A number of remedial technologies are based on multiphase extraction, the simultaneous removal of contaminated liquids and vapors from soil or rock through one or more wells subjected to a high vacuum. This technical note proposes an empirical model for predicting cumulative contaminant-mass removal by multiphase extraction as a function of remedial-system run time. Model calibration employs early-time mass-removal data.     

Complicating Factors of Using Ethylenediamine Tetraacetic Acid to Enhance Electrokinetic Remediation of Multiple Heavy Metals in Clayey Soils

Batch and electrokinetic experiments were conducted to investigate the removal of three different heavy metals, chromium(VI), nickel(II), and cadmium(II), from a clayey soil by using ethylenediamine tetraacetic acid (EDTA) as a complexing agent. The batch experiments revealed that high removal of these heavy metals (62–100%) was possible by using either a 0.1?M or 0.2?M EDTA concentration over a wide range of pH conditions (2–10). However, the results of the electrokinetic experiments using EDTA at the cathode showed low heavy metal removal efficiency. Using EDTA at the cathode along with the pH control at the anode with NaOH increased the pH throughout the soil and achieved high (95%) Cr(VI) removal, but the removal of Ni(II) and Cd(II) was limited due to the precipitation of these metals near the cathode. Apparently, the low mobility of EDTA and its migration direction, which opposed electroosmotic flow, prevented EDTA complexation from occurring. Overall, this study found that many complicating factors affect EDTA-enhanced electrokinetic remediation, and further research is necessary to optimize this process to achieve high contaminant removal efficiency.     

Design and Operation of Point-of-Use Treatment System for Arsenic Removal

A point-of-use (POU) system was designed and constructed using commercially available activated alumina to remove arsenic from drinking water. Testing with City of Albuquerque chlorinated tap water containing an average of 23 ug/L arsenic found that 1 L of adsorbent would provide water for direct consumption by a family of four for 435 days. It was estimated that the POU system constructed for this study could be sold for $162, and the arsenic adsorption columns were estimated to cost $4. A monthly cost to the customer of $10/month was estimated to purchase, install, and operate this POU system, assuming annual replacement of adsorption media cartridges. The implications of relying upon POU systems to comply with a new drinking water standard for arsenic are discussed.     

Role of Bioflocculation on Chemical Oxygen Demand Removal in Solids Contact Chamber of Trickling Filter/Solids Contact Process

The trickling filter/solids contact (TF/SC) process was developed in the late 1970s to improve the quality of the final effluent from existing trickling filter plants, to be able to meet stricter Environmental Protection Agency effluent requirements. Although this process has successfully achieved this objective, it is still not completely understood, there is limited information regarding the flocculation phenomena occurring in the solids contact chamber (SCC), and no information could be found on the relationship between flocculation and organic matter removal kinetics. To better understand the kinetics of biological flocculation in a continuous flow SCC, a long-term experimental program was conducted using a TF/SC pilot plant constructed at the Marrero, La., wastewater treatment plant. This program started in January 1998 and has continued through date. The present article will focus on two major areas: (1) the kinetics of bioflocculation in the SCC; and (2) effect of bioflocculation on chemical oxygen demand (COD) removal. Analysis of the wastewater composition revealed that, on the average, only 18.7% of the total COD in the SCC influent is truly dissolved. Therefore, most of the total COD removal observed in the SCC must be due to a physical process, such as flocculation. The experimental data confirmed that flocculation of the particulate COD contained in the trickling filter effluent explains the high total COD removal observed at the SCC. Both total and colloidal COD removals are well explained by the first-order flocculation model.     

Experiments with a Resin-in-Pulp Process for Treating Lead-Contaminated Soil

This paper presents the results of experiments to evaluate the potential for using a resin-in-pulp process to remove lead contamination from soil. These experiments examined the kinetics and equilibrium partitioning of lead, lead carbonate, lead oxide, and lead sulfate in resin-soil-acetate buffer systems. The results show the trade-offs to be made among the amount of resin used, the number of contacting stages that may be needed to meet a target final soil concentration, the contact time, the solution pH, and the solution acetate concentration.     

Oxidative and Reductive Pathways in Manganese-Catalyzed Fenton’s Reactions

Soluble manganese (II) and amorphous and crystalline manganese (IV) oxides were investigated as catalysts for the Fenton-like decomposition of hydrogen peroxide into oxidants and reductants. 1-Hexanol was used as a hydroxyl radical probe and carbon tetrachloride (CT) was used as a reductant probe. Soluble manganese (II)-catalyzed reactions at acidic pH resulted in >99% degradation of 1-hexanol and no measurable transformation of CT, indicating that hydroxyl radicals were generated but reductants were not. However, when these reactions were conducted at near-neutral pH, an amorphous manganese oxide precipitate formed and 89% of the CT degraded in 60?min, while 1-hexanol degradation was negligible. Using an amorphous manganese oxide synthesized in a separate reactor, CT was rapidly degraded while 1-hexanol oxidation was undetectable. Reactions catalyzed by the crystalline manganese oxide pyrolusite(β-MnO2) at near-neutral pH also resulted in significant CT degradation, indicating that reductants are generated by both the crystalline and amorphous manganese oxide-catalyzed decomposition of H2O2. The presence of manganese oxides in the subsurface and their ability to catalyze the generation of reductants in modified Fenton’s reactions has important implications for hydrogen peroxide stability and contaminant transformation pathways during the in situ Fenton’s treatment of contaminated soils and groundwater.     

Evaluation of Electrokinetic Removal of Heavy Metals from Tailing Soils

Electrokinetic remediation was studied for the removal of toxic heavy metals from tailing soils. The study emphasized the dependency of removal efficiencies upon their speciations, as demonstrated by the different extraction methods used, which included sequential extraction, total digestion, and 0.1 N HCl extraction. The tailing soils examined showed different physicochemical characteristics, such as initial pH, particle size distribution, and major mineral constituents, and they contained high concentrations of target metal contaminants in various forms. The electrokinetic removal efficiencies of heavy metals were significantly influenced by their partitioning prior to treatment, and the pHs of the tailing soils. The mobile and weakly bound fractions of heavy metals, such as the exchangeable fraction, were easily removed by electrokinetic treatment (more than 90% removal efficiency), but immobile and strongly bound fractions, such as the organically bound species and residual fractions, were not significantly removed (less than 20% removal efficiencies).