Daniel Dianchen Gang

As(iii) removal using an iron-impregnated chitosan sorbent.

An iron-impregnated chitosan granular adsorbent was newly developed to evaluate its ability to remove arsenic from water. Since most existing arsenic removal technologies are effective in removing As(V) (arsenate), this study focused on As(III). The adsorption behavior of As(III) onto the iron-impregnated chitosan absorbent was examined by conducting batch and column studies. Maximum adsorption capacity reached 6.48 mg g(-1) at pH=8 with initial As(III) concentration of 1007 microg L(-1). The adsorption isotherm data fit well with the Freundlich model. Seven hundred and sixty eight (768) empty bed volumes (EBV) of 308 microg L(-1) of As(III) solution were treated in column experiments. These are higher than the empty bed volumes (EBV) treated using iron-chitosan composites as reported by previous researchers. The investigation has indicated that the iron-impregnated chitosan is a very promising material for As(III) removal from water.

Equilibrium, kinetic and thermodynamic studies for adsorption of BTEX onto Ordered Mesoporous Carbon (OMC)

Chemical and petrochemical industries produce substantial amounts of wastewater everyday. This wastewater contains organic pollutants such as benzene, toluene, ethylbenzene and xylenes (BTEX) that are toxic to human and aquatic life. Ordered Mesoporous Carbon (OMC), the adsorbent that possesses the characteristics of an ideal adsorbent was investigated to understand its properties and suitability for BTEX removal. Adsorption isotherms, adsorption kinetics, the effects of initial BTEX concentrations and temperatures on the adsorption process were studied. The OMCs were characterized using surface area and pore size analyzer, transmission electron microscopy (TEM), elemental analysis, thermogravimetric analysis (TGA) and fourier transform infrared spectroscopy (FTIR). The results suggested that the Langmuir Isotherm and Pseudo-Second-Order Models described the experimental data well. The thermodynamic parameters, Gibbs free energy (ΔG°), the enthalpy change (ΔH°) and the entropy change (ΔS°) of adsorption indicated that the adsorption processes were physical, endothermic, and spontaneous. In addition, OMC had 27% higher overall adsorption capacities compared to granular activated carbon (GAC).

Modeling nitrate-nitrogen removal process in first-flush reactor for stormwater treatment

Stormwater runoff is one of the most common non-point sources of water pollution to rivers, lakes, estuaries, and coastal beaches. While most pollutants and nutrients, including nitrate-nitrogen, in stormwater are discharged into receiving waters during the first-flush period, no existing best management practices (BMPs) are specifically designed to capture and treat the first-flush portion of urban stormwater runoff. This paper presents a novel BMP device for highway and urban stormwater treatment with emphasis on numerical modeling of the new BMP, called first-flush reactor (FFR). A new model, called VART-DN model, for simulation of denitrification process in the designed first-flush reactor was developed using the variable residence time (VART) model. The VART-DN model is capable of simulating various processes and mechanisms responsible for denitrification in the FFR. Based on sensitivity analysis results of model parameters, the denitrification process is sensitive to the temperature correction factor (b), maximum nitrate-nitrogen decay rate (Kmax), actual varying residence time (Tv), the constant decay rate of denitrifiying bacteria (vdec), temperature (T), biomass inhibition constant (Kb), maximum growth rate of denitrifiying bacteria (vmax), denitrifying bacteria concentration (X), longitudinal dispersion coefficient (Ks), and half-saturation constant of dissolved carbon for biomass (KCar-X); a 10% increase in the model parameter values causes a change in model root mean square error (RMSE) of −28.02, −16.16, −12.35, 11.44, −9.68, 10.61, −16.30, −9.27, 6.58 and 3.89%, respectively. The VART-DN model was tested using the data from laboratory experiments conducted using highway stormwater and secondary wastewater. Model results for the denitrification process of highway stormwater showed a good agreement with observed data and the simulation error was less than 9.0%. The RMSE and the coefficient of determination for simulating denitrification process of wastewater were 0.5167 and 0.6912, respectively, demonstrating the efficacy of the VART-DN model.

Preparation and post-treatments of ordered mesoporous carbons (OMC) for resorcinol removal

In this investigation, acrylic acid was used as a carbon precursor and SBA-15 as a mesoporous template to synthesize the ordered mesoporous carbons (OMC). Different ratios of SBA-15 to acrylic acid were evaluated to improve the OMCs adsorption capacity. It was found that the optimal ratio of SBA-15 to acrylic acid is 3:1. In the post-treatment study, four methods (NaOH, urea, NH3H2O, and AlCl3) were explored to investigate their influences on resorcinol removal. Results showed the ammonium hydroxide-treated OMC had the highest adsorption capacity of 40.6xa0mg/g for resorcinol removal. The nano-structures of the OMC and post-treated OMCs were characterized and confirmed. FTIR analysis indicated that the surface functional groups were changed after post-treatments. XRD patterns and TEM images suggested that the ordered structure was well maintained during the post-treatment processes, although the erosion effect was observed.

Response of estuarine phytoplankton to nutrient and spatio-temporal pattern of physico-chemical water quality parameters in Little Vermilion Bay, Louisiana

Abstract We studied the response pattern of phytoplankton to nutrient concentrations in Little Vermilion Bay, Louisiana in July and November 2013. It is important to understand the response of phytoplankton to nutrient concentrations in order to find impacts of eutrophication and improve the water quality for survival of fish and other aquatic life. Total Nitrogen and Total Phosphorus were measured in Little Vermillion Bay at several sampling locations along with some other water quality parameters and response of phytoplankton biomass was evaluated. The spatial–temporal pattern of water quality parameters in the study area was assessed using a spatial interpolation method. Phytoplankton biomass was positively correlated with nutrient enrichment in Little Vermillion Bay. Chlorophyll a concentrations were found to be strongly dependent on Total Nitrogen and Total Phosphorus in the water column. Nutrient concentration in the water column has a strong control over phytoplankton biomass and primary production. The TN:TP ratio was evaluated to establish the limiting nutrient for eutrophication in the study area. Both nitrogen and phosphorus were found to have strong relationships with phytoplankton growth and a growth limiting nutrient was not established for Little Vermilion Bay.

Adsorptive Selenite Removal Using Iron-Coated GAC: Modeling Selenite Breakthrough with the Pore Surface Diffusion Model

Iron-coated granular activated carbon (Fe-GAC) was proven to be effective for removing selenite from aqueous solution in batch studies. Design and use of the adsorbent in column settings requires understanding the key mass transfer characteristics for full-scale applications. In this study, rapid small-scale column tests (RSSCTs) were conducted at various empty bed contact times (EBCTs). A pore and surface diffusion model (PSDM) was introduced to predict selenite breakthrough curves of continuous flow packed columns containing Fe-GAC. Effluent Se(IV) breakthrough occurred immediately in the experiment with 0.055-min EBCT. The column reactor was found to treat approximately 780 bed volumes of water containing 1.0 mg=L Se(IV) when EBCTwas increased to 0.447 min before breakthrough occurred. The adsorption capacity was estimated to be 3.06 mg=g. The adsorption results showed that the PSDM could provide satisfactory predictions for the column performance with the external mass transport coefficient (kf )o f8.55 × 10 −3 cm=s. Full-scale column design criteria, such as hydraulic loading rate (HLR), carbon usage rate (CUR), and degree of column utilization (DoCU) were calculated and recommended. DOI: 10.1061/(ASCE)EE.1943-7870.0000633.

Adsorptive removal of resorcinol on a novel ordered mesoporous carbon (OMC) employing COK-19 silica scaffold: Kinetics and equilibrium study

Phenolic compounds and their derivatives have been found in industrial wastewater, which pose threats to the natural environment. Ordered mesoporous carbon (OMC) has been identified as an ideal adsorbent possessing high specific surface area and large pore volume to alleviate these pollutants. A novel ordered mesoporous carbon was prepared using COK-19 template with the cubic Fm3m structure for the first time. Ordered mesoporous silica COK-19 was synthesized and reported in 2015. Sucrose as the carbon precursor was impregnated into the mesopores of silica and converted to carbon through carbonization process using sulfuric acid as a catalyst. Ordered mesoporous carbon was obtained after the removal of silica framework using hydrofluoric acid. Boric acid was employed for the preparation of OMCs with tunable pore sizes in the range of 6.9-16.6u202fnm. Several characterization techniques such as nitrogen adsorption-desorption isotherms, transmission electron microscope (TEM), Fourier transform infrared spectroscopy, Boehm titration and elemental analysis were employed to characterize the OMCs. The pore size analysis and TEM images confirmed that OMC has replicated the mesostructure of the COK-19. Results obtained from adsorption kinetics and isotherms suggest that the Pseudo-second-order model and Langmuir isotherm well described the experimental data.

Molecular simulation and experimental validation of resorcinol adsorption on Ordered Mesoporous Carbon (OMC)

Numerous research works have been devoted in the adsorption area using experimental approaches. All these approaches are based on trial and error process and extremely time consuming. Molecular simulation technique is a new tool that can be used to design and predict the performance of an adsorbent. This research proposed a simulation technique that can greatly reduce the time in designing the adsorbent. In this study, a new Rhombic ordered mesoporous carbon (OMC) model is proposed and constructed with various pore sizes and oxygen contents using Materials Visualizer Module to optimize the structure of OMC for resorcinol adsorption. The specific surface area, pore volume, small angle X-ray diffraction pattern, and resorcinol adsorption capacity were calculated by Forcite and Sorption module in Materials Studio Package. The simulation results were validated experimentally through synthesizing OMC with different pore sizes and oxygen contents prepared via hard template method employing SBA-15 silica scaffold. Boric acid was used as the pore expanding reagent to synthesize OMC with different pore sizes (from 4.6 to 11.3u202fnm) and varying oxygen contents (from 11.9% to 17.8%). Based on the simulation and experimental validation, the optimal pore size was found to be 6u202fnm for maximum adsorption of resorcinol.

Background electrolytes and pH effects on selenate adsorption using iron-impregnated granular activated carbon and surface binding mechanisms

Iron-impregnated granular activated carbon (Fe-GAC) has been shown effective for selenite adsorptive removal from aqueous solutions, but similar effectiveness was not observed with selenate. This study examined the effects of background electrolytes and pH on selenate adsorption on to Fe-GAC, and surface bindings to elucidate the selenate adsorption mechanisms. The decrease magnitude of selenate adsorption capacity under three background electrolytes followed the order: LiClxa0>xa0NaClxa0>xa0KCl, as ionic strength increased from 0.01 to 0.1xa0M. Larger adsorption capacity differences among the three electrolytes were observed under the higher ionic strengths (0.05 and 0.1xa0M) than those under 0.01xa0M. Multiplet peak fittings of high resolution X-ray photoelectron spectra for O1s and Fe2p3/2 indicated the presence of iron (III) on adsorbent surface. pH variations during the adsorbent preparation within 3-8 in NaCl solutions did not cause appreciable changes in the iron redox state and composition. Raman spectra showed the formation of both monodentate and bidentate inner sphere complexes under pHs <7 and a mixture of outer sphere and inner sphere complexes at pH 8. These results explained the lower selenate adsorption under alkaline conditions. Mechanisms for monodentate and bidentate formations and a stable six-member ring structure were proposed. Two strategies were recommended for modifying Fe-GAC preparation procedure to enhance the selenate adsorption: (1) mixed-metal oxide coatings to increase the point of zero charge (pHzpc); and (2) ferrous iron coating to initially reduce selenate followed by selenite adsorption.

Development and Evaluation of Functional Open Graded Friction Courses (FOGFC) Mixtures for In Situ Highway Runoff Treatment

The use of Open Graded Friction Course (OGFC) pavements as road surfacing materials has grown considerably over the past decades. Acknowledged benefits include reduced splash and spray, better visibility, better traction, and less noise. Moreover, the installation of OGFC shows noticeable improvements of runoff water quality, which might be due to the retention of pollutants by internal pores. However, the traditional OGFC has little or no effects on the dissolved constituents, such as dissolved organic matter, dissolved copper and zinc in the stormwater. This study was conducted to correct this problem by adding additives into the OGFC mixtures to produce Functional OGFC (FOGFC), which has adsorption functions for dissolved constituents, such as organic matters and dissolved heavy metals commonly found in highway stormwater runoffs. The characteristics and environmental applications of this novel FOGFC were evaluated. Results indicated that FOGFC not only preserves OGFC’s advantages in the removal of particulate pollutants, but also significantly extends its ability to remove non-particulates or dissolved pollutants, thus eliminating the needs of external treatment facilities to a certain extent.