Journal of Environmental Engineering

A new kind of acid red 138 (AR138)–calcium fluoride nanosized ${\mathrm{CaF}}_2/\mathrm{AR138}$ hybrid adsorbent (CFAR) was prepared. The microstructure of the hybrid adsorbent was characterized and its adsorption capacity to two cationic dyes, methyl blue (MB) and ethyl violet (EV), from aqueous solutions was examined using a batch sorption technique. The adsorption behavior of the MB and EV on CFAR is in good agreement with the Langmiur isotherms. The maximum adsorption capacity ($Q_m$) of CFAR for MB and EV are 370.4 and $131.6\mathrm{mg}/\mathrm{g}$, respectively. The effects of pH, ionic strength, temperature, and time have been investigated in detail. The CFAR adsorbent was used to treat two dye wastewaters with satisfactory results. In synthesis of the materials, all of the reactants are easily available and harmless to environment as well because AR138 may use a concentrated AR138-producing wastewater instead. Therefore, this paper has developed a simple, eco-friendly and waste treat waste method for large-scale production of a cost-effective sorbent.

The lateral flow sand filter (LFSF) is an on-site wastewater technology widely used to treat septic tank effluent (STE) in Nova Scotia, Canada. In this study, linear and nonlinear isotherm models (accounting for both sorption and precipitation processes) were developed and evaluated to simulate cumulative phosphorus (P) treatment in eight LFSFs that operated from September 2004 to October 2011. The LFSFs varied in design based on slope (5, 30%), sand grain size (fine, medium, coarse), and filter length (5.5, 8 m). The HYDRUS two-dimensional (2D) model was used to estimate the mass of sand involved in active P treatment to normalize the isotherm influent P loads for each LFSF. The isotherm equations tested were linear, Langmuir, Freundlich, and 2-part piecewise linear. Linear, Freundlich, and 2-part piecewise linear functions were also combined with batch sorption experiment derived Langmuir equations and subsequently tested. For the six 8-m long LFSFs, the individual 2-part piecewise linear isotherms had the best model performance. The P removal processes in the lower STE-loaded medium sand, 5.5-m-long LFSFs 7 and 8 were adequately modeled by both Langmuir and Freundlich isotherms, but all seven isotherms had satisfactory model performance. Phosphorus treatment isotherms were also developed by averaging input parameters from the individual filter isotherms on the basis of filter length and sand grain size. The average P treatment isotherms had poor model performance results for the 8-m-long LFSFs, possibly caused by different P removal rates related to filter slope and residence time. All of the eight LFSF designs were not effective at long-term P treatment with effluent concentrations exceeding $1{\mathrm{mg}\mathrm{P}\mathrm{L}}^{-1}$ at the end of the study period; however, the fine- and medium-grained sand 8-m-long designs for both slope classes had the best observed P reduction rates. The results of this study will be used to develop disposal field input parameters for watershed-scale models.

Adequate biocide addition is the key to control biological growth-related problems in recirculating cooling systems of thermoelectric power plants. The use of monochloramine (MCA) as the primary biocide is as effective as the use of free-chlorine in cooling systems using secondary-treated municipal wastewater (MWW) as the sole makeup water source. However, severe scaling caused by the secondary effluent necessitates incorporation of an additional treatment of secondary effluent (i.e., tertiary treatment) prior to use as makeup water for recirculating cooling systems. In the research reported in this paper, the effectiveness of MCA as a cooling-system biocide was evaluated for three types of tertiary-treated MWW, as follows: (1) acidification, (2) nitrification and sand filtration, and (3) nitrification, sand filtration, and granular activated-carbon adsorption. The impact of these tertiary treatment processes on chloramination was studied in both laboratory and pilot-scale experiments. For the third type of MWW treatment, reducing the total organic carbon (TOC) content in MWW exerted a 37% decrease in biological growth potential but less than a 5% decrease in biological growth rate. A MCA residual of $2–3\mathrm{mg}/\mathrm{L}$ was required to achieve biological-growth control objectives with respect to planktonic and sessile heterotrophic bacteria in cooling systems regardless of the tertiary treatment employed. Legionella analyses indicated that chloramination was effective in controlling proliferation of these species for all tertiary-treated wastewaters. Overall, preformed MCA was effective as a primary biocide in all tertiary-treated MWW evaluated in the research reported in this paper. Nitrification followed by sand filtration was the optimal tertiary treatment among the three investigated MWW because the biological-control objectives could be achieved with lower doses. The use of granular activated-carbon adsorption revealed no additional benefit compared to nitrification and sand filtration.

This study examined the effects of pH, dosage, and stirring time on the removal of oil and Cr(VI) from simulated wastewater by pectin obtained from citrus byproducts. After pectin modification by etherification and polyaluminum chloride (PAC) impregnation, the extract removed highly concentrated oil and Cr(VI) from wastewater. Fourier transform infrared spectroscopy, scanning electron microscopy, and X-ray diffraction were used to characterize the flocculants and confirm modification of the pectin. An orthogonal factorial experiment with factors of stirring time, dosage, and pH was used to optimize the conditions for contaminant removal by the modified pectin. The average removal rates were 79 and 77% for oil and Cr(VI), respectively. A central composite design with factors of PAC, zinc sulfate (${\mathrm{ZnSO}}_4$), pH, and microwave irradiation time showed that PAC and ${\mathrm{ZnSO}}_4$ intensified the flocculation effect. The actual optimum removal rates for oil and Cr(VI) were 95.0 and 98.4%, respectively. Binomial regression adequately predicted the experimental results.

The effect of media packing on the performance of anaerobic hybrid reactors (combining upflow anaerobic sludge blanket reactors and anaerobic filters) was examined for the treatment of simulated coal wastewater at four hydraulic retention times (HRTs) under mesophilic ($27\pm 5°\mathrm{C}$) conditions. PVC rings were used as filter media; they were maintained at varying packing densities in three experimental reactors (R1, R2, and R3) at 34.29, 24.29, and $14.13\mathrm{kg}{\mathrm{m}}^{-3}$. Synthetic coal wastewater with an average chemical oxygen demand of $\mathrm{2,240}\mathrm{mg}{\mathrm{L}}^{-1}$ and concentration of phenolics of $752\mathrm{mg}{\mathrm{L}}^{-1}$ was used as substrate. During the four-month operation, the HRT was shortened from 0.66 to 0.33 days. The removal of phenolics was favored in Reactors R1 ($98-92\%$) and R2 ($96–86\%$) more than R3 ($94-82\%$) with the reduction of HRT. Biomass concentration of Reactors R1 and R2 increased from 42 to 69.7 and 64.7 g $\mathrm{VSS}{\mathrm{L}}^{-1}$ with an increase in the density of the packing media. Microbial biomass distribution revealed the lowest number of methanogens in Reactor R3 as a result of rapid washout of biomass.

At present, there are no good methods for disposing of hyperaccumulator plants that have accumulated heavy metals from soil. However, carbon and the metals that can replace some of the nonrenewable mineral products in hyperaccumulator plants are also resources. In this paper, carbon nanotubes (CNTs), ZnO nanoparticles, and $\mathrm{CNTs}/\mathrm{ZnO}$ nanocomposites were synthesized using Physalis alkekengi L. (Zn hyperaccumulator) as raw materials. It was found that the synthesized ZnO nanoparticles were agglomerated, with a mean size of 55.3 nm. The synthesized CNTs were middle-hollow, with an outer diameter of 70 nm. The outer diameter of $\mathrm{CNTs}/\mathrm{ZnO}$ nanocomposites was approximately 120 nm. The effects of removal of bisphenol A (BPA) in water by synthesized nanomaterials were significantly enhanced. With ultraviolet (Uv) light irradiation for 90 min alone, the photodegradation efficiency of BPA ($15\mathrm{mg}/\mathrm{L}$) was approximately 4.8%. The combinations of Uv light irradiation (90 min) with 10 mg $\mathrm{CNTs}/\mathrm{ZnO}$, ZnO nanoparticles, and CNTs increased the removal efficiencies of BPA to 86.5, 74.3, and 45.7%, respectively. The methods of synthesis of nanomaterials using a hyperaccumulator have positive effects not only on solving the recycling of the hyperaccumulator but also on decreasing the cost to prepare the photocatalyst.

A daily forecast system of marine beach water quality (WATERMAN) has been developed for Hong Kong. Individual multiple linear regression (MLR) models were developed to forecast daily water quality (lnEC concentration) at each of the 41 beaches. The forecast system was developed through data assimilation with the most recent water quality data, and supported by field studies and deterministic hydrological, hydrodynamic, and water quality models. Model input parameters included three rainfall variables (daily rainfall in the previous three days): the previous day’s solar radiation, onshore wind speed, and water temperature; tide level and predicted salinity at sampling time; and the geometric mean of the five most recent E. coli measurements. The forecasts were disseminated through the Internet and smart phone apps. The operational performance of the beach water quality forecast system during 2010–2011 is presented for 16 representative beaches. An overall accuracy of 78–100% in forecasting compliance or exceedance of the water quality objective (WQO) can be obtained, with correct positives (exceedances) of approximately 30–70%. A parameter analysis reveals beaches with different characteristics: (1) beaches dominated by nonpoint pollution sources; (2) beaches affected by nearby point source pollution; and (3) clean beaches that are relatively free of pollution. As compared with the current beach advisory based entirely on sparsely sampled data, the number of incorrect forecasts of WQO exceedances (beach incorrectly open) can be significantly reduced by 25% using the forecast system. The corresponding reduction of excess illnesses attributable to the incorrect open forecasts can be estimated to be approximately 30%. The forecast system is able to enhance protection of public health while allowing maximum beach access.

An image-analysis technique was applied for noninvasive measurements of settling rate of polystyrene latex spheres of 6, 10, 20, 50, 100, and 160 μm diameters in a quiescent environment. A CCD (charged couple device) camera and strobe light were used to capture in situ images of the particles, which were analyzed using image-analysis software. To overcome the challenge of noninvasive measurement of very slow-moving particles, variable pixel resolutions were chosen depending on settling speed so that the separation of the particle images in a given camera exposure time was sufficient to determine the temporal displacements of the particles with precision. Particle-settling behavior was not disrupted for any kind of sample handling, and measurements were made without hindering particle settling and allowing particle movement under gravity alone. Measurements were compared with settling rates calculated with Stokes’ law, and the validity of Stokes’ law under low particle Reynolds number ($\mathsf{R}<0.1$) was investigated for solid and spherical particles. While the smaller particles settled at a rate closely predicted by Stokes’ law, the larger particles settled slightly more slowly than was predicted. This effect is likely due to an increase in the drag coefficient with relatively larger-particle Reynolds number, compared to the value used in Stokes’ law.

Stoichiometry of hydrogen sulfide–induced corrosion of concrete sewers was quantified in a bench-scale experimental setup consisting of six concrete pipe reactors. The setup was installed in an underground sewer research and monitoring station with access to fresh municipal wastewater. Hydrogen sulfide gas was injected intermittently into the headspace of the pipe reactors in peak concentrations of approximately $\mathrm{1,000}{\mathrm{ppm}}_v$. Mass balance calculations on total injected amounts of hydrogen sulfide gas and observed corrosion depths demonstrated that only a fraction of the hydrogen sulfide gas caused corrosion. The stoichiometry of the corrosion process was found to depend on both duration and level of hydrogen sulfide exposure. The highest fraction of sulfide-causing corrosion was found after extended exposure and low injection frequencies. When sulfide exposure was terminated, a significant potential for sustained corrosion was observed. This was most likely the result of sulfuric acid production from oxidation of reaction intermediates accumulated during sulfide exposure such as elemental sulfur.

Specific ultraviolet absorbance (SUVA) is the ratio of ultraviolet absorbance (UVA) to dissolved organic carbon (DOC) or UVA per unit of DOC. The octanol water partition coefficient ($K_{OW}$) is the ratio of the concentration of the organic compound in octanol to that in water. Both of these parameters depend on the nature of the organic substance or the functional groups present in the organic compound. Two very different compounds may have the same $K_{OW}$ or SUVA, the ratio of $K_{OW}$ to SUVA of these will be different. Therefore, these two parameters for a particular category or nature of compounds are likely to be correlated. The present project aims at preliminary investigations to establish the correlation between $K_{OW}$ and SUVA for four categories of organic compounds. Keeping this objective in view, 41 synthetic samples containing a single organic compound of known concentration were prepared and analyzed for SUVA and $K_{OW}$. UVA was measured at 254 nm and at maximum absorption (${\lambda }_{\max }$). The $K_{OW}$, ${\mathrm{SUVA}}_{254}$, and ${\mathrm{SUVA}}_{\lambda \max }$ of a particular group of organics other than the aromatic compounds are found to be linearly correlated. The slope of the line is characteristic of the nature of the organic or functional groups in the organic compounds. The slopes (ratios) between $K_{OW}$ and ${\mathrm{SUVA}}_{\lambda \max }$ for carbohydrates, alcohols, and acids are 0.2, 17.4, and 11.2, respectively. The correlation is more sensitive at ${\lambda }_{\max }$ than at 254 nm. Regarding aromatic organic compounds, $\log K_{OW}$ is linearly correlated to SUVA and logSUVA.