Journal of Environmental Engineering

Control strategies for storm water that combine unit operations and processes can offer distinct advantages for many in situ applications in the built environment. Examples include a variety of control strategies that utilize engineered buoyant media to provide filtration and adsorption for heavy metals transported by storm water. With the goal of producing such media, methods were developed to coat iron and manganese oxide onto the surface of common polymeric media. Surface characteristics of coating media were determined by powder X-ray diffraction, infrared spectroscopy, and scanning electron microscopy analyses. Results indicated that oxide coatings ranged from 20 to 200 μm in depth, and surface areas were increased from 0.05 m²/g for uncoated spherical polymeric media to 27 m²/g for the same media after oxide coating. All manganese oxide coated media generated a net negative surface charge in the typical storm water pH range of 6–8. Media specific gravity (ρ_s) remained less than 0.93 even with oxide coatings. A multiple-layer oxide coating provided surface characteristics that enhance filtration and adsorption of heavy metals using coated buoyant polymeric spherical media in storm water treatment systems such as sorptive buoyant media clarifiers.

Most current control strategies for storm water treatment utilize fixed or filter-bed media with specific gravity (ρ_s) greater than 1.0. In contrast to Part I, Part II focuses on such higher density (ρ_s > 1.0) manganese-oxide-coated media that can be used in combined unit operations and processes for in-situ treatment of storm water. Methods were developed to coat manganese oxides onto sand and cementitious media for storm water treatment. With respect to manganese, coatings of ramsdellite produced a point of zero charge (PZC) of 5.2, while mixtures of birnessite and cryptomelane produced a PZC of 2.6 Manganese oxide increased the specific surface area (SSA) of sand and cementitious media. Manganese-oxide-coated sand (MOCS) produced a larger SSA (2.48-m²/g), as compared with birnessite-coated media (BCM) (1.51 m²/g), while the two have a similar surface charge (PZC = 6.4). Manganese-oxide-coated cementitious media (MOCM) produced a significantly larger SSA (19.49 m²/g), as compared with coated sand, and SEM analyses indicated the surface contained manganese oxide and calcite of thickness 10–30 μm. Based on the results, coated cementitious media provided surface characteristics that can significantly enhance filtration and adsorption of heavy metal in storm water, in comparison to sand.

The adsorption of organic compounds onto an activated carbon cloth is studied in a dynamic reactor. An experimental design is carried out to investigate the influence of operating conditions (initial concentration C₀, flow velocity U₀, and bed thickness Z) and adsorbate's characteristics. A slow intraparticular diffusion is shown by flattened breakthrough curves, and adsorption capacities are high and range between 50 and 250 mg g⁻¹. The transfer zone Z₀, assessed by the Adams and Bohart equation, is low (3 mm). All experimental results are modeled by a neural network to take into account the specific diffusion of cloths. Parameters related to the adsorbate-adsorbent affinity in a batch reactor are consequently introduced in the input layer of the neural network (intraparticular coefficient K_w and Freundlich parameters K_f and l/n), added to operating conditions whose influence was shown (C₀, U₀, and Z) and time t. The statistical quality of the neural network modeling is high (r² = 0.956). Furthermore, the Garson connection weight method allows the relative influence of input neurons to be determined. This analysis confirms the influence of parameters relative to adsorbant-adsorbate affinity.

Adsorption of sulfur dioxide (SO₂) onto activated carbons prepared from oil-palm shells was investigated in this paper. Experimental results showed that the adsorption temperature and SO₂ concentration significantly determined the amount of SO₂ adsorbed and the equilibrium time. However, sample particle size had minimum effect on the equilibrium time. For a fixed SO₂ concentration, the adsorption rate and adsorption kinetic parameters (activation energy and frequency factor) were obtained. A linearly proportional relationship between the Brunauer-Emmett-Teller surface area and the adsorptive capacity of the activated carbon from oil-palm shells was observed. An intraparticle Knudsen diffusion model based on a Freundlich isotherm was developed for predicting the amount of SO₂ adsorbed and the SO₂ concentration profile within the particle. Based on the estimated isotherm parameters and diffusion coefficients by experimental data fitting, this model could predict the amount adsorbed under different concentrations very well. However, this model was unsuitable for the activated carbon prepared from oil-palm shells by chemical activation because of the occurrence of chemisorption, which was related to the nature of the sample surface functional groups.

Synthetic wastewater was used for the investigation of main factors affecting F⁻ removal performance. The existence of ${\mathrm{SiF}}^{\mathit{2}{\mathit{-}}_{\mathit{6}}}$ or ${\mathrm{PO}}^{\mathit{3}{\mathit{-}}_{\mathit{4}}}$, and a low initial F⁻ concentration were the main causes of low and unstable F⁻ removal. Lowering the pH reduced the adverse effects of ${\mathrm{SiF}}^{\mathit{2}{\mathit{-}}_{\mathit{6}}}$ and ${\mathrm{PO}}^{\mathit{3}{\mathit{-}}_{\mathit{4}}}$, and adding over 4 mg/L⁻¹ of freshly formed CaF₂ precipitates as seed greatly enhanced F⁻ removal during treatment of low concentration wastewater (50 mg/L⁻¹ F⁻). The seed-generation method, in which a small portion of wastewater was first mixed with the whole dose of Ca²⁺ and then mixed with the remaining portion of wastewater, greatly improved F⁻ removal performance and could be used instead of the method of adding seed. The conclusions obtained from the treatment of synthetic wastewater were verified by using several kinds of actual electronics wastewater. The pH should be lower than 9 for efficiently removing F⁻ from wastewater having a high ratio of SiO₂ to F⁻, and an even lower pH was needed for treating wastewater with a relatively high ${\mathrm{PO}}^{\mathit{3}{\mathit{-}}_{\mathit{4}}}$ concentration. The seed-generation method was also found to be effective for such wastewater with high concentrations of ${\mathrm{PO}}^{\mathit{3}{\mathit{-}}_{\mathit{4}}}$.

The kinetics of the ozonation of polyethylene glycol (PEG) with ultraviolet (UV) radiation in the acid-based electroplating solution of the printed wiring board industry is studied. The substrate prescription of a typical electroplating solution is with pH of 0.18–0.42, [CuSO₄⋅5H₂O] of 200 g/L, [H₂SO₄] of 60 g/L, and [Cl⁻] of 0.03 g/L. Certainly, the discarded electroplating solution is hard to treat with the common chemical and biological processes because of its acidic and metallic compositions. In addition, it contains valuable substances suitable for recovery and reutilization. One of the most important processes for reviving it is to remove the aged organic additives such as PEG. A two-step reaction mechanism in terms of ozone A and total organic carbon is proposed to express the reaction kinetics of PEG ozonation with UV radiation with intensity [I_uv]. The initial concentration of PEG is 30 mg/L, according to the recipe of a typical electroplating solution, which is equivalent to total organic carbon of 16.3 mg/L. The reaction rate r expressions of the concentrations of the liquid phase ozone C_ALb, PEG C_BLb, and intermediates C_ILb are r_A (=dC_ALb/dt) = −(k_Am + k_I[I_uv])C_ALb − (k_R1 + k_RI1[I_uv])C_ALbC_BLb − (k_R2 + k_RI2[I_uv])C_ALbC_ILb, r_B (=dC_BLb/dt) = −(k_R1 + k_RI1[I_uv])C_ALbC_BLb, r_int (=dC_ILb/dt) = (k_R1 + k_RI1[I_uv])C_ALbC_BLb − (k_R2 + k_RI2[I_uv])C_ALbC_ILb, with k_Am = 0.0036 s⁻¹, k_I = 4.654 × 10⁻⁵s⁻¹/(Wm⁻²), k_R1 = 13.525 M⁻¹s⁻¹, k_R2 = 0.751 M⁻¹s⁻¹, k_RI1 = 0.683 M⁻¹s⁻¹/(Wm⁻²), and k_RI2 = 0.042 M⁻¹s⁻¹/(Wm⁻²). These reaction kinetic expressions are useful and referable for the proper design of an ozonation system with UV radiation for the treatment of PEG in the printed wiring board electroplating solution.

This paper presents the results of an investigation on the treatment of two industrial solid wastes produced by oil refineries in Singapore, namely Ni/Mo/γAl₂O₃ and Co/Mo/γAl₂O₃. Calcination at 500°C was effective in removing carbon and sulfur in both wastes followed by generation of heavy metal oxides. A two-stage leaching process was successful in removing 44% nickel, 77% cobalt, and 83% molybdenum. However, toxicity characteristic leaching procedure leaching tests for spent catalyst residues of Co/Mo/γAl₂O₃ and Ni/Mo/γAl₂O₃ after the two-stage leaching process showed that the concentration of Mo, Co, and Ni in the leachate exceeded the allowable limits. Finally, the residues, when subjected to an enhanced binder stabilization treatment with marine clay, produced a commercial-value brick made of up to 30% by weight spent catalysts. It is believed that stabilization can be achieved through either encapsulation whereby the clay forms a matrix around the heavy metals to prevent leaching or incorporation in which the heavy metals actually become part of the stabilizing matrix.

Brick manufactured from incinerated sewage sludge ash and clay is investigated. The results of Atterberg limits tests of molded ash-clay mixtures indicated that both plastic index and dry shrinkage decrease with an increasing amount of ash in the mixture. Results of tests indicated that the ash proportion and firing temperature were the two key factors determining the quality of brick. Increasing the firing temperature and decreasing the amount of ash in the brick resulted in a decrease of water absorption. The appropriate percentage of ash content for producing quality bricks was in the range of 20 to 40% by weight with a 13 to 15% optimum moisture content prepared in the molded mixture and firing at 1,000°C for 6 h. With 10% ash content, the ash-clay bricks exhibited higher compressive strength than normal clay bricks. This study showed that the pulverized sludge ash could be used as brick material. The bonding strength can be further enhanced by controlling operating conditions.

A 3D multilevel eutrophication model has been developed and applied to the tropical coastal waters of Singapore. The model considers the nitrogen, phosphorus, and carbon cycles; phytoplankton and zooplankton dynamics; and dissolved oxygen balance in the water column coupled to benthic processes and is driven by a 3D multilevel hydrodynamic model. The eutrophication model was calibrated with field data obtained from the Southwest Monsoon in August 1998 and subsequently validated using data from the Northeast Monsoon in December 1998. Predictions of nutrient and phytoplankton concentrations from the model simulation agreed well with the observed data. The model results show that the coastal waters of Singapore are relatively well-mixed and differences in concentration with depth for all state variables are generally <20%. In the Singapore Strait, horizontal spatial differences for all the variables are generally <40%. In the Southwest Monsoon, slightly larger values for phytoplankton and dissolved oxygen but smaller nutrient values are found in the eastern region of Singapore, compared to the west. The reverse trend is found in the Northeast Monsoon.

In engineering design and analysis, mathematical models that generally involve a number of uncertain parameters are frequently employed for decision making. Over the years, a number of techniques have been developed to quantify model output uncertainty contributed by uncertain input parameters. Typically, the methods that are easy to apply may give inaccurate estimates of model output uncertainty. Other methods that reliably produce very accurate results are either difficult to apply or require intensive computational effort. This paper describes the development of generic expectation functions as a function of means and coefficients of variation of input random variables. The generic expectation functions are straightforward to develop, and apply to problems related to reliability, risk, and uncertainty analysis. Several expectation functions based on commonly used probability distributions have been developed. Using them, any order of moment can be estimated exactly. It is found that if exact moments of the model output are available, one can find a good estimate of reliability, risk, and uncertainty of a system without knowing its model output distribution exactly. This technique is applicable when an output variable is a function of several independent random variables in multiplicative, additive, or combined (multiplicative and additive) forms. A practical example is presented to demonstrate the application of generic expectation functions.

The trickle-bed air biofilter performance for treating mixtures of ethylacetate (EA), toluene (T), and xylene (X) volatile organic compounds (VOCs) was evaluated under different influent VOC loadings. The EA removal efficiencies were significantly higher than those for T and X, indicating that EA is a preferred substrate in the EATX waste gas. More than 80% removal efficiencies could be achieved under influent loadings below 77 g EA/m³/h, 8 g T/m³/h, and 10 g X/m³/h. The trickle-bed air biofilter appears efficient for controlling EATX emission with medium EA loadings and low TX loadings. The elimination capacities of EA, T, and X for a pure VOC feed were higher than for a mixed VOC feed and the differences increased with increased influent VOC loading.

The migration of the dicarboximide fungicide vinclozolin and its principal degradation products through porous media was experimentally determined by simulating pesticide applications to a 23–30 mesh Ottawa sand and a North Carolina Piedmont aquic hapludult soil in laboratory columns. The mass of vinclozolin and its degradates were measured in the porous media 24, 168, and 504 h after fungicide application, varying pore fluid pH and size of simulated rain events. Degradation in the soil was near detection limits under all experimental scenarios. In sand at pH 8.8, vinclozolin degraded along two pathways. The degradation to the butenoic acid degradate was faster than the degradation to vinclozolin's enanilide degradate. The presence of the enanilide pathway had not previously been observed in solutions with pH > 7, indicating that the presence of particles plays a role in the rate and pathway of vinclozolin degradation. Thus, the direct extrapolation of dicarboximide chemistry from solution studies to agricultural field conditions is not possible without consideration of the soil matrix characteristics.

A rotating-perforated-tubes biofilm reactor was used for treatment of synthetic wastewater at different operating conditions. The biofilm reactor consisted of two sections each having 25 perforated tubes mounted on three perforated discs. The battery of the tubes was rotated with the aid of a shaft and a motor. Effects of major process variables such as feed wastewater flow rate and COD concentration on the system performance were investigated. Kinetics of COD removal was investigated and kinetic constants determined by using the experimental data. An empirical design equation was developed to quantify the system's performance as a function of major process variables.