Background: Investigating the performance of naturally operated treatment plants may be due to the fact that they cannot be operated as desired, or that they should be modified to achieve good performance e.g. for nutrients removal. The advantage of kinetic coefficient determination is that the model can be adjusted to fit data and then used for analyzing alternatives to improve the process. This study investigates the efficiency of subsurface artificial wetland and determines its kinetic coefficients for nutrient removal. Methods: The present study investigated the kinetics of biological reactions that occurred in subsurface wetland to remove wastewater nutrient. Samples were taken from 3 locations of wetlands for 6 months. The nutrient content was determined through measuring Total Kjehldahl Nitrogen (TKN), ammonium, nitrate, and phosphate values. Results: Average levels for TKN, ammonium, nitrate, and phosphate in effluent of control wetland were 41.15, 23.59, 1.735, and 6.43 mg/L, and in wetland with reeds were 28.91, 19.99, 1.49 and 5.63 mg/L, respectively. First-order, second-order, and Stover-Kincannon models were applied and analyzed using statistical parameters obtained from the models (Umax, KB). Conclusion: The nutrients removal at Yazd wastewater treatment plant was remarkable, and the presence of reeds in wetland beds was not very efficient in improving system performance. Other more efficient plants are suggested to be evaluated in the system. Stover-Kincannon kinetic model provided predictions having the closest relationship with actual data obtained from the field.

Background: This study assessed the removal of organic material and nutrients from full-scale subsurface flow (SSF) constructed wetlands (CWs) followed by anaerobic stabilization ponds under environmental conditions. Methods: The effluents were distributed evenly in 12 reed beds. Samples were taken twice monthly for a total of 6 months from several points in the wetland. Biochemical oxygen demand (BOD), chemical oxygen demand (COD), total suspended solids (TSS), and nutrient removal from the system and the longitudinal effect of the reed beds for removal of pollutions were determined. A full-scale model of flow, BOD, and nutrients in SSF in the CWs is presented. Results: The flow rate and concentrations of parameters indicated that removal of organic matter and nutrients in the cold months decreased rather than in the hot months, as expected. The removal efficiency for BOD, COD, and TSS and the strongest biological interactions showed no uniform trends. The beds showed the highest removal rates in the first few meters of bed. The hybrid Monod-Plug flow regime and the Stover-Kincannon models showed the best fit for the kinetics of the processes. Umax in the Stover-Kincannon model was 3.64 mg/l.d for nitrogen and 0.24 mg/l.d for phosphorus. These values are very low, which indicates lower consumption and inefficiency of the system for removing nitrogen and phosphorus. Conclusion: It can be concluded that the SSF in CWs are able to treat average wastewater as effectively as common mechanical systems at lower cost.

Background: The efficacy of NH4Cl-induced activated carbon (NAC) was examined in order to adsorb RR198, an azo reactive model dye, from an aqueous solution.
Methods: The effects of pH (3 to 10), adsorbent dose (0.1 to 1.2 g/L), dye concentration and contact time on the adsorption efficiency were investigated.
Results: The results showed that the removal of dye was highest at a solution pH of 7 and a powder dose of 1.1 g/L. The 85.9%, 72.6% and 65.4% removal of RR198 was obtained for a concentration of 25, 50 and 100 mg/L, respectively, at a relatively short contact time of 30 minutes, and at optimum pH and NAC concentrations of 1 g/L. The experimental data for kinetic analysis illustrated a best fit to the pseudo-second-order model. The study data on equilibrium were modeled using Langmuir, Freundlich and Dubinin–Radushkevich models; the Langmuir equation provided the best fit for the data.
Conclusion: Therefore, the NAC appears to be an efficient and appropriate adsorbent for the removal of reactive azo dyes from waste streams.
 

Background: The presence of even a very small quantity of dye in water bodies is undesirable and affects the water bodies. Dye removal from industrial waste water is significant; hence in this study, a material that is an economical waste product was employed to test its acid dye removing capacity from aqueous solution.
Methods: In this study, batch mode experiments were performed in the sorption process of Acid Red 97 (AR 97), Acid Red 114 (AR 114) and Acid Red 151 (AR 151) onto Curcuma angustifolia scales (CS). Also, the effect of process parameters like pH and adsorbent dosage was studied. The experimental data of AR 97, AR 114 and AR 151 sorption was fitted to Langmuir, Freundlich and Temkin isotherm models. Kinetic results in AR 97, AR 114 and AR 151 sorption were fitted at various concentrations to pseudo-first order, pseudo-second order, Elovich and Intra-particle diffusion model.
Results: The monolayer sorption capacity of the acid dyes was found to be AR 97 (350.87 mg/g), AR 114 (202.42 mg/g) and AR 151 (168.91 mg/g). The Pseudo-second order model proved to be the best fit for the acid dyes. Boyd plot, confirms film diffusion in all acid dye sorption processes.
Conclusion: The results showed higher dye removal for acid dyes at pH 2. The isotherm data, demonstrated good sorption capacity with AR 97>AR 114>AR 151. Employing the CS material in this study proves to be a potential alternative to costlier adsorbents, utilized for the treatment of dye containing industrial waste water.

Background: The rapid increase in agricultural and industrial development has made heavy metal pollution a serious environmental problem and public health threat; therefore, removal of heavy metals from water is important. The current study prepared DNPH@SDS@Fe3O4 nanoparticles as a novel and effective adsorbent for removal of Hg(II) ions from an aqueous solution.
Methods: A selective adsorbent for Hg(II) was synthesized by coating Fe3O4 nanoparticles with sodium dodecyl sulfate which was further functionalized with 2,4-dinitrophenylhydrazine (2,4-DNPH). The synthesized nanoparticles were characterized by Fourier transform infrared spectroscopy (FTIR), x-ray diffraction (XRD), scanning electron microscopy (SEM) and SEM–EDXSt. The effects of pH, dose of adsorbent and shaking time on adsorption capacity were investigated. The kinetics and equilibrium of adsorption of the metal ions were thoroughly studied.
Results: SEM showed that the size of the nanoparticles was 20 to 35 nm. The maximum adsorption capacity for Hg(II) was 164.0 mg g-1 for an adsorbent dose of 0.04 g at pH 7.0, 25°C and the initial metal concentration was 25 mg L-1,which was greater than for most adsorbents previously examined for Hg(II) adsorption. Adsorption experimental data showed good correlation with the pseudo-second-order model and Langmuir isotherm model.
Conclusion: The results indicated that the DNPH@SDS@Fe3O4 nanoparticles are an efficient adsorbent for removal of heavy metal from wastewater.
 

Background: Synthetic dyes have several harmful effects on human health as well as aquatic life. In this study, activated carbon (AV-AC), based on Aloe vera leaf shells, was used as a novel agricultural adsorbent, one that is low-cost and available for the removal of Congo red (CR) as a carcinogenic dye from aqueous solutions.

Methods: In the batch system, the influence of different parameters like contact time, pH, adsorbent dosage, and initial CR concentration were examined on the dye removal from liquid medium. The experimental data were fitted by pseudo-first-order and pseudo-second-order kinetics, and also Langmuir and Freundlich isotherms models.

Results: The optimum contact time and pH for the uptake of CR were obtained at 20 minutes and acidic pH of 2. The maximum uptake capacity of CR dye by AV-AC was 1850 mg/g. The results showed that the experimental data were well-fitted by the pseudo-second-order kinetic model (R2 > 0.99) and Freundlich isotherm model (R2 > 0.99).

Conclusion: According to the results of our study, the AV-AC is a low-cost, non-toxic, and effective adsorbent for the uptake of CR dye from aqueous media.

Background: To remove methylene blue (MB) from aqueous solutions, nanoscale zero-valent iron (nZVI) predicated on reduced expanded graphene oxide (rEGO) was used as the activator of persulfate.
Methods: Scanning electron microscope (SEM) and energy dispersive spectroscopy (EDS) analyses were used to investigate the surface morphology and to examine the surface elemental composition. X-ray diffraction (XRD) was used to determine the chemical compositions of the synthesized compound. In this study, the effects of pH (3-9), activator dose (0.4-1.6 g L-1), persulfate concentration (0.192-0.768 g L-1), and reaction time (0-60 minutes) on the removal of 10 mg L-1 MB were studied by nZVI -reduced expanded graphene oxide/persulfate (nZVI@rEGO/PS) process.
Results: The maximum removal efficiencies of MB at optimum operational conditions (pH 3, activator dose = 1.2 g L-1, persulfate concentration = 0.576 g L-1, and reaction time = 20 minutes) by nZVI@rEGO/PS process was 96%. The chemical method was used to prepare expanded graphene. The volume of natural flake graphite increased about 25 times after the process. SEM image of the nZVI@rEGO showed the presence of nZVI placed on the EGO surface in chain structure with a diameter about 100 nm. The EDS analysis of the activator indicated the existence of Fe element to an amount greater than 50%.
Conclusion: According to the results, nZVI@rEGO is considered as a promising activator of persulfate.