Removal of Zn2+ from Electroplating Wastewater Using Modified Wood Sawdust and Sugarcane Bagasse

This paper describes the preparation of new adsorbents derived from sugarcane bagasse and wood sawdust (Manilkara sp.) to remove zinc (II) ions from electroplating wastewater. The first part deals with the chemical modification of sugarcane bagasse and wood sawdust, using succinic anhydride to introduce carboxylic acid functions into the material. The obtained materials (modified sugarcane bagasse MB2 and modified wood sawdust MS2) were then characterized by infrared spectroscopy (IR) and used in adsorption experiments. The adsorption experiments evaluates Zn2+ removal from aqueous single metal solution and real electroplating wastewater on both batch and continuous experiments using fixed-bed columns prepared in laboratorial scale with the obtained adsorbents. Adsorption isotherms were then developed using Langmuir model and the Thomas kinetic model. The calculated Zn2+ adsorption capacities were found to be 145?mg/g for MS2 and 125?mg/g for MB2 in single metal aqueous solution, whereas for the industrial wastewater these values were 61?mg/g for MS2 and 55?mg/g for MB2.     

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.     

Competitive Effects of Trichloroethylene on Cr(VI) Removal by Zero-Valent Iron

Eleven columns were set up under various groundwater geochemistry conditions to investigate the competitive effect of trichloroethylene (TCE) on hexavalent chromium [Cr(VI)] removal by zero-valent iron (Fe0). They were found to be electron competitors in the redox reactions. In the presence of TCE, the Cr(VI) removal capacities of Fe0 were decreased by about 40% when compared with their respective Cr(VI) removal capacities with identical groundwater geochemistry but without TCE. The specific reaction rate constant (kSA) of TCE was decreased by about 50% when Cr(VI) was singly applied. The kSA of TCE was further decreased by 75% in the presence of both Cr(VI) and carbonate. However, there was no apparent effect on the kSA of TCE when Cr(VI), hardness and carbonate were all present. It revealed that TCE was a stronger electron competitor of Cr(VI) and the degradation of TCE became more favorable when both hardness and carbonate were present. This suggests that the passivated precipitates formed on the Fe0 surface in the presence of both hardness and carbonate may significantly affect the Cr(VI) removal by Fe0 but has insignificant effect on the TCE removal.     

Removal of Immiscible Contaminants from Sandy Soils Monitored by Means of Dielectric Measurements

The main objective of this paper is to explore the potential application of electromagnetic waves to evaluate the effect of contaminant removal in granular soils. Thus, various specimens of saturated silica sand were prepared using paraffin oil and lubricant oil as contaminants. Four flushing fluids were used to remove the contaminants from sand columns: Deionized water, water-detergent, water-detergent-alcohol solution, and water vapor. Dielectric permittivity was measured at different stages of the removal process at the frequency from 20?MHz?to?1.3?GHz. The measured permittivity was compared with that determined for clean and fully contaminated specimens. A theoretical mixture formula was calibrated and implemented to estimate the volume fraction of contaminant present in the pore fluid. It is concluded in this work that dielectric parameters reflect the contamination level of the soil for the nonpolar organic compounds used here. Measurement of permittivity allows us to determine that the inclusion of alcohol and detergent in the displacing fluid improved the removal efficiency. However, water vapor was the most efficient removal agent.     

Removal of Heavy Metals from Automotive Wastewater by Sulfide Precipitation

The United States Environmental Protection Agency has proposed new categorical pretreatment effluent standards for the Metal Products and Machinery Industry, which are more stringent than current discharge limits in the automotive industry. Therefore, this study was conducted to evaluate metal-sulfide precipitation chemistry as an alternative to metal-hydroxide precipitation chemistry for removing Cu, Ni, Pb, and Zn. There were three aspects of this study: (1) theoretical analysis of both metal–hydroxide and metal–sulfide chemistry; (2) experimental evaluation of commercially available sulfur-containing precipitants using deionized water; and (3) experimental evaluation of the precipitants using wastewater samples from three automotive manufacturing plants (transmission, engine, and assembly plants). The primary findings are: (1) In theory, metal–hydroxide chemistry can achieve the proposed standards when no chelating agents are present. This is not true when as small as 1 mg/L of ethylenediaminetetra-acetic acid (EDTA) is present. (2) Metal–sulfide precipitation chemistry could achieve solubility limits lower than those of metal–hydroxide chemistry over a wide range of pH. However, EDTA could still inhibit precipitation of Ni, Pb, and Zn to concentrations above the proposed standards. (3) The experiments with wastewater samples showed all precipitants removed Cu well while Ni and Zn were not well removed. The sample from transmission and engine plants were more difficult to treat than from an assembly plant, suggesting that it might have had more chelating agents. The commercially available precipitants did not perform any better than sodium sulfide. (4) Costs for using the precipitants were estimated to range from <$1/1,000 gal to >$5/1,000 gal depending on the precipitant.     

Storm Water Detention Ponds: Modeling Heavy Metal Removal by Plant Species and Sediments

Laboratory and field studies were conducted to elucidate heavy metal removal by three wetland grasses and sediments in storm water detention pond. The removal of heavy metals including Cd, Cu, Pb, and Zn was mediated by fluid-flow intensity in the reactors. The growth of plants and the removal rates of contaminants were plant species dependent. All three wetland grasses removed contaminants from the spiked nutrient solutions. A first-order kinetic model adequately represented the removal of contaminants by plants. The analyses of undisturbed sediment cores in detention pond revealed strong stratification of heavy metal concentrations at the sediment–water interface. A simple model that integrates heavy metal removal by aquatic plants and sediments in storm water detention ponds is proposed. The model provides an estimate of contaminant residence time which can be related to hydraulic residence time in storm water detention ponds.     

Modeling the Removal of Arsenic by Iron Oxide Coated Sand

An arsenic filtration experiment using iron oxide coated sand was modeled using the USGS geochemical program PHREEQC. Despite some uncertainty regarding the initial conditions of the groundwater and the simplicity of the model, it replicated the experimental results within 10%. The original experiment filtered 165 bed volumes to concentrations less than 0.01 mg/L As and approximately 210 bed volumes to 0.05 mg/L As. The model filtered 168 bed volumes to 0.01 mg/L As and 228 bed volumes to 0.05 mg/L.     

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.     

Removal of Nonbiodegradable Chemicals from Mixtures during Granular Activated Carbon Bioregeneration

The purpose of this research was to better understand the interactions between biodegradable and nonbiodegradable synthetic organic chemicals (SOCs) during bioregeneration of biologically active granular activated carbon (GAC) columns. Continuous-flow GAC bioregeneration experiments were conducted at different empty-bed contact times (EBCTs) using mixtures of a biodegradable (benzene or toluene) and a nonbiodegradable (perchloroethylene or carbon tetrachloride) SOC. The GAC was pre-equilibrated with respect to each combination of SOCs to facilitate the study of bioregeneration. If no dissolved oxygen limitations occurred in the bioregeneration experiments, the effluent biodegradable SOC concentration decreased over time and then remained low, after which the effluent nonbiodegradable SOC concentration also decreased because of the increased availability of adsorption sites on the GAC. Pre- and postexperimental GAC loadings show a marked decrease in the biodegradable SOC loading as well as an increase in the nonbiodegradable SOC loading. Greater degrees of bioregeneration were found for higher SOC equilibrium concentrations and longer EBCTs. Bioregeneration ranged from 28.8 to 45.5% of the initial biodegradable SOC loading after 13–17?days. These results illustrate an increase in GAC adsorption capacity for nonbiodegradable SOCs through bioregeneration of GAC containing biodegradable SOCs.     

Enhanced Biological Phosphorus Removal Performance and Microbial Population Changes at High Organic Loading Rates

A laboratory-scale sequencing batch reactor was operated and the dynamics of Rhodocyclus-related phosphorus-accumulating organisms (PAOs) population was monitored. After the system reached a steady state and showed a stable enhanced biological phosphorus removal status, the organic loading rate was increased from 160 to 1,020?g?COD?m?3?cycle?1 in five steps. When the P storage capacity reached maximum at 330?g?COD?m?3?cycle?1, the system lost the stability and the effluent phosphorus concentration fluctuated. As the organic loading rate increased from 160 to 1,020?g?COD?m?3?cycle?1, the PAO population decreased from 83.8±4.9 to 32.2±16.2% and internal polyphosphate content decreased from 0.20 to 0.03?mg?P?mg?VSS?1. Phosphate-accumulating metabolism was weakened as the organic loading rate increased and PAO population decreased concomitantly, whereas glycogen-accumulating metabolism increased at high organic loading rates as supported by the increased intracellular glycogen content and production of a higher fraction of intracellular poly-β-hydroxyl valerate.     

Thermal Removal of Mercury in Spent Powdered Activated Carbon from TOXECON Process

This research developed and demonstrated a technology to liberate Hg adsorbed onto powdered activated carbon (PAC) by the TOXECON process using pilot-scale high temperature air slide (HTAS) and bench-scale thermogravimetric analyzer (TGA). The HTAS removed 65, 83, and 92% of Hg captured with PAC when ran at 900°F, 1,000°F, and 1,200°F, respectively, while the TGA removed 46 and 100% of Hg at 800°F and 900°F, respectively. However, addition of CuO–Fe2O3 mixture and CuCl catalysts enhanced Hg removal and PAC regeneration at lower temperatures. CuO–Fe2O3 mixture performed better than CuCl in PAC regeneration. Scanning electron microscopy images and energy dispersive X-ray analysis show no change in PAC particle aggregation or chemical composition. Thermally treated sorbents had higher surface area and pore volume than the untreated samples indicating regeneration. The optimum temperature for PAC regeneration in the HTAS was 1,000°F. At this temperature, the regenerated sorbent had sufficient adsorption capacity similar to its virgin counterpart at 33.9% loss on ignition. Consequently, the regenerated PAC may be recycled back into the system by blending it with virgin PAC.     

Simultaneous Removal of Carbon and Nitrogen from Swine Wastewater Using an Immobilized-Cell Reactor

A single-stage phosphorylated polyvinyl alcohol immobilized-cell reactor with three operation modes was employed to investigate the efficiency of simultaneous carbon/nitrogen removal from raw swine wastewater. In continuous aeration mode, the removal efficiency of chemical oxygen demand (COD) and total nitrogen (T-N) exceeded 70 and 8%, respectively, at hydraulic retention time of 10?days. In intermittent aeration (IA) mode, the removal efficiency of COD and T-N was more than 85 and 46%, respectively, when the reactor was set at 50% aeration duration to cycle time to operate at three aerobic-anoxic cycles per day. When oxidation-reduction-potential control was adopted to control the duration of the anoxic period in the real-time controlled (RTC) IA mode for a 4?h aeration period, the total cycle time was reduced by about 20% with a slight increase in removal efficiency of COD (87%) and T-N (47%). The system with no extra chambers required is efficient in simultaneous carbon/nitrogen removal.     

Removal of Contaminants from Underground Spaces by Induced Ventilation

The present paper introduces induced airflow as an effective means for removal of contaminants from underground enclosed spaces. The airflow is caused by natural convection in a vertical duct which absorbs solar irradiation outside the building. Experimental studies and three-dimensional numerical simulations have been performed in a scaled-down laboratory model. The experiments included temperature and velocity measurements and flow visualization. The results obtained from the simulations are fully supported by the experimental results, indicating that effective ventilation by the proposed method is achievable. For real-size structures, three-dimensional computer simulations have been performed using a standard k-ε turbulence model. The results yield a detailed flow field inside the enclosure for various configurations of the ducts and partitions. Rate of air change is calculated both for the whole enclosure, and for the regions above the floor where contaminants like radon tend to accumulate. By adjustment of openings in the basement, the ceiling may be cleared of contaminants as well. It is shown that a properly designed structure, even at low solar fluxes, can provide adequate ventilation of a real-size underground enclosure.     

Cation Effects on Chromium Removal in Permeable Reactive Walls

Permeable reactive walls have proven to be successful in laboratory and pilot-scale field applications. However, the long-term efficacy of reactive permeable walls has not been established due to the novelty of the technology. Also, the impact of common groundwater ions such as calcium and magnesium (i.e., hardness) on permeable reactive walls is unknown. In theory, the ions may react competitively with chromium in solution and/or other materials on the surface of the zero-valent iron. The ions may also form precipitates that could clog the reactive zone over time, resulting in decreased contaminant removal and a shorter wall lifetime. The purpose of this research was to determine the effects of common groundwater ions on permeable reactive walls. A range of calcium and magnesium concentrations was tested in laboratory columns to determine the effect of these ions on removal of a constant chromium concentration (100 mg/L). Results from the laboratory tests indicated that calcium and magnesium had a significant impact on chromium removal. The most dramatic effects were witnessed at hardness levels up to 140 mg/L as CaCO3 where zero-valent iron capacity was reduced by 45%.     

Simultaneous Organic and Nutrient Removal in a Naturally Ventilated Biotower Treating Presettled Municipal Wastewater

The performance of a down-flow hanging sponge (DHS) system was continuously evaluated for 1 year for enhancement of organic matter and nutrient removal in the treatment of presettled municipal wastewater. A pilot-scale DHS (24 L) was installed at a wastewater-treatment site and operated at an ambient temperature of 25°C. This paper reports on the results of a long-term monitoring of the system. The DHS system was operated at three different hydraulic retention times (HRTs), i.e., 6, 4, and 2 h. The available results showed that increasing the HRT significantly improved the removal of chemical oxygen demand (COD) fractions. The removal efficiencies of COD were 89, 80, and 56% at HRTs of 6, 4, and 2 h, respectively. Also, ammonia (NH4–N) concentration significantly decreased by increasing the HRT. Ammonia removal percentages of 99, 90, and 72% were achieved when the DHS system was operated at HRTs of 6, 4, and 2 h, respectively, but decreasing HRT exerted a slightly negative effect on the removal of total phosphorous. Scanning electron microscopy observation revealed no clogging of the sponge pores after 12 months of continuous operation. Accordingly, the results suggested that the proposed system may be a competitive solution for municipal wastewater treatment under variable conditions.     

Removal of Antibiotics from Surface and Distilled Water in Conventional Water Treatment Processes

Conventional drinking water treatment processes were evaluated under typical water treatment plant conditions to determine their effectiveness in the removal of seven common antibiotics: carbadox, sulfachlorpyridazine, sulfadimethoxine, sulfamerazine, sulfamethazine, sulfathiazole, and trimethoprim. Experiments were conducted using synthetic solutions prepared by spiking both distilled/deionized water and Missouri River water with the studied compounds. Sorption on Calgon WPH powdered activated carbon, reverse osmosis, and oxidation with chlorine and ozone under typical plant conditions were all shown to be effective in removing the studied antibiotics. Conversely, coagulation/flocculation/sedimentation with alum and iron salts, excess lime/soda ash softening, ultraviolet irradiation at disinfection dosages, and ion exchange were all relatively ineffective methods of antibiotic removal. This study shows that the studied antibiotics could be effectively removed using processes already in use in many water treatment plants. Additional work is needed on by-product formation and the removal of other classes of antibiotics.     

Cell Immobilized FOG-Trap System for Fat, Oil, and Grease Removal from Restaurant Wastewater

Cell immobilized lipase-producing bacteria on three different matrices were incorporated in a fat-, oil-, and grease (FOG) trap system for restaurant wastewater treatment. During a 16-day laboratory-scale experiment for the treatment of synthetic FOG wastewater containing soybean oil, no significant difference (two-tailed t test at 95% confidence interval) in the FOG removal between two systems was observed at FOG influent ≤ 1,000?mg/L. However, the typical trap showed lower FOG removal efficiency than the matrix-based system when the influent FOG concentration was increased to ≥ 5,000?mg/L. In addition, the matrix-based trap system was able to sustain a stable high FOG removal, with <100?mg/L effluent, even at 10,000 mg/L influent FOG. Based on FOG heights measured and mass balance calculations, 97.4 and 99.5% of the total FOG load for 16 days were removed in a typical trap and matrix-based system, respectively. About 93.6% of the removal in the matrix-based was accounted to biodegradation. The 30-day full-scale operations demonstrated a distinguishably better performance in the matrix-based system (92.7±9.06% of 1,044.8±537.27?mg FOG/L) than in the typical trap system (74.6±27.13% of 463.4±296.87?mg FOG/L) for the treatment of barbeque restaurant wastewater. Similarly, matrix-based system revealed higher chemical oxygen demand removal (85.9±11.99%) than the typical trap system (60.4±31.26%). Characterizations of the influent, emulsified, adsorbed and effluent FOG indicated that straight saturated fatty acids constituted the cause of clogging problems in the FOG-trap and piping system.     

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.     

Prediction of Arsenic Removal by Electrocoagulation: Model Development by Factorial Design

Model was developed by two-level five-factor full-factorial designed-experiment to predict arsenic removal from contaminated water by electrocoagulation. Five factors, namely arsenic concentration (As), solution volume (V); current (I), electrode area (A), and current processing time (t) were investigated. Among the factors, arsenic concentration (As) and volume (V) have negative effect, and area (A), time (t), and current (I) have positive effect on arsenic removal. Within the studied levels of the factors, variance analysis at 5% significance level indicated that electrode area is not significant in arsenic removal by electrocoagulation. The model predicted reasonably good arsenic removal (error<2%) from low (0.288 mg/L) and high (0.882 mg/L) initial arsenic concentrations in presence of naturally cooccurring solutes in the groundwater. For the range of operating variables studied, optimum removal of arsenic (98.56%) is obtained at higher arsenic concentration (1.18 mg/L), lower volume (1 L), higher current (3 A), and higher current processing time (120 s).     

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.