Journal of Environmental Engineering

This paper reports the results of a study on the equilibrium behavior of cadmium adsorption by a tropical, indigenous single-cell algal species, identified as Oocystis sp., in a static reactor. An exponential equation, in the form of $C_e/C_0=\alpha \exp (\beta M/C_0)\text{,}$ was found to be statistically significant in expressing the relationship between the ratio of equilibrium cadmium (Cd) concentration in solution $\left(C_e\right)$ to the initial cadmium concentration $\left(C_0\right)$ and the ratio of algal biomass (M) to initial cadmium concentration $\left(C_0\right)$ for both living and dead algal biomass. Based on the above equation and the mass balance of cadmium in the system, another two equations were developed and verified by a series of batch experiments. One equation, in the form of $x/m=[1-\alpha \exp (\beta M/C_0\left)\right]/(M/C_0)\text{,}$ describes the relationship between the cadmium content per unit algal biomass $(x/m)$ and the ratio $M/C_0\text{.}$ The other equation takes the form of $x/m=\beta (1-C_e/C_0)/\ln (C_e/\alpha C_0)$ and describes the relationship between the ratio of equilibrium cadmium concentration to initial cadmium concentration and cadmium content per unit algal biomass. The above models for Cd adsorption were found to be applicable over a $pH$ range of 4.5–10.5 even though it was found that $pH$ affects the Cd adsorption potential significantly.

A series of plant scale low temperature regenerative thermal oxidizers (LTRTOs) equipped with heating wires were constructed to treat volatile organic compounds (VOCs) laden gas streams. All regenerative beds were packed with gravel (approximate particle size 1.25 cm, specific area 205 m²/m³, and specific heat capacity 840 J/kg °C) and equipped with K-type thermocouples for measuring gas temperatures. Test gas streams were extracted from manufacturing sections of varnishing, semiconductor packing, and petrochemical plants, representing a variety of gas-phase pollutants, including several commercial solvents. Experimental results indicate that 98% or greater treatment of VOCs with concentrations between 100 and 7,000 ppm as methane. Analysis of gas temperature variation with time at various bed depths confirm that VOC degradation occurs at temperatures ranging from 300 to 440°C, which are much lower than autoignition points of tested compounds. A 1.0 s gas residence time in the oxidation zone of regenerative beds is required for successful LTRTO operation.

Crude oil spills have far-reaching consequences not only from the point of view of economic considerations but also from the point of view of environmental pollution. This is particularly important in oil-producing countries like Saudi Arabia. In an attempt to study this phenomenon further, an analytical and experimental study was undertaken. In this study analytical estimation of crude oil spills in layered sandy soils was performed by vertically integrating the oil content function. This function exhibits discontinuities at the interfaces of different soil layers. The influence of layering on the estimation process was examined by comparing the analytical results with and without the layering. An experimental setup was used to assess the predictions of the analytical model formulated. The experimental results, for homogeneous soils, were compared with predictions of previous analytical and empirical models. This study shows that analytical as well as empirical models consistently underestimate the actual spill volume in soils. Furthermore, analytical predictions were shown to depend on how close the system was to hydrostatic equilibrium. It also shows that soil layering is a very significant factor that should be incorporated in quantifying the extent of aquifer contamination.

The transport of permanganate in low permeability media (LPM) and its ability to degrade trichloroethylene (TCE) in situ were studied through diffusive transport experiments with intact soil cores. A transport cell was developed to measure the effective diffusion coefficient $\left(D_{\mathrm{eff}}\right)$ of a ${\mathrm{Br}}^{-}$ tracer through intact cores of silty clay LPM obtained from a field site and enable calculation of the apparent tortuosity $\left({\tau }_a\right)$ of the medium. Then, 5000 mg L⁻¹ of ${\mathrm{KMnO}}_4$ was added to the cell and diffusive transport and soil matrix interactions were observed. After three months, the soil cores were dissected for morphologic examination and characterization of matrix ions, total organic carbon, ${\mathrm{MnO}}_4^{-}\text{,}$ and manganese oxides $\left({\mathrm{MnO}}_2\right)\text{.}$ The experiment was then repeated after 2 μL of pure phase TCE were delivered into the center of each of two intact cores. Permanganate transport was observed for one month and then an extraction of the entire soil core was made to determine the extent of TCE degradation. This research demonstrated that permanganate can migrate by diffusion and yield reactive zones that can be predicted based on the properties of the LPM and the oxidant source. Under the experimental conditions examined, permanganate had little effect on the LPM’s pore structure or continuity, and appreciable soil organic matter remained even after 40–60 days of exposure to the oxidant. ${\mathrm{MnO}}_2$ solids, an oxidation by-product, were observed in the LPM, but not at levels sufficient to cause pore filling or alter the apparent matrix tortuosity, even when TCE was present. During diffusive transport of permanganate, TCE in the silty clay LPM was degraded by 97%.

In the process of crossflow microfiltration, a deposit of cake layer tends to form on the membrane, which usually controls the performance of filtration. However it is found that there exists a condition under which no deposit of cake layer is made. This condition is called the subcritical flux condition and the maximum flux in the condition here is called the critical flux. Which means, it is a flux below which a decline of flux with time due to the deposit of cake layer does not occur. This study develops a concentration polarization model to predict the critical flux condition and to study about its characteristics. The model is verified with experimental results. For the model, the concept of effective particle diameter is introduced to find a representative size of various particles in relation to diffusive properties of particles. The modeling and the experimental results include that the critical flux condition can be determined by the use of effective particle diameter and the ratio of initial permeate flux to crossflow velocity. This study also finds that the (sub)critical flux operation is limited for the real world application because of the limitation to increasing crossflow velocity and its sensitivity to the change of feed composition.

Shallow water covers are often implemented over sulphide-bearing mine tailings to reduce oxygen uptake by the tailings and, consequently, acid generation. At some sites, however, wind-induced waves could resuspend the tailings and possibly impact the quality of the overlying water cover. Wind-induced resuspension was investigated for a base metal mine site using published semiempirical predictive methods, measured tailings properties, and field measurements. The results of the predictions were compared with field measurements. Tailings erosion occurred when the bed shear stress due to the wave-induced oscillatory flow and countercurrent flow exceeded the measured critical shear stress, $0.12<{\tau }_c<0.17 {\mathrm{Nm}}^{-2}\text{,}$ of the tailings. For this site and for the maximum hourly average wind speed of 10 m/s observed during the study, the critical depth for tailings resuspension was predicted to be 1.18–1.34 m. Field data suggested that tailings resuspension occurred primarily in parts of the tailings pond where the water cover depth was 1 m or less. Following erosion and resuspension, tailings were carried by surface drift current and bottom return currents to deeper locations.

The capacity of an existing model to simulate the growth (biomass) of a reed [Phragmites australis (Cav) Trin. ex Stuedel] in fresh water habitats using published field data and the incorporation of a submodel to estimate seasonal variation in reed mineral–nutrient content was investigated. This new feature also enabled one to estimate plant removal of mineral–nutrients from sediments. Model-predicted and observed shoot, rhizome, and root biomass showed concordance correlation coefficients of 0.97, 0.52, and 0.99, respectively. The nutrient analysis study showed that the annual uptakes of nitrogen and phosphorus from sediment by P. australis in the Denmark Vejlerne Nature Reserve were 143.9 and 16.1 kg ha⁻¹, respectively. The simulated results also showed that at the time of peak standing stock of minerals, shoots contained 40 and 22.5% of whole plant N and P, respectively. This suggested that the use of the common reed in wastewater treatment plants allows removal of nitrogen more easily than phosphorus, because a higher percentage of nitrogen is bound with the easily removable shoot parts.

In this paper the effect of operating parameters on biotrickling filter performance degrading chlorobenzene and o-dichlorobenzene mixture were studied. The large laboratory scale biofilter, total volume 40 L, filled with inert packing material was used. The biomass adaptation and cultivation were performed in a batch fermentor and were used to inoculate the biotrickling filter. After a starting period, the influence of the substrate load increase, liquid recirculation flow rate, and empty bed retention time on elimination capacity and removal efficiency were found. The most important recirculation liquid parameters were analyzed every day, that is: concentration of metabolites, dissolved organic carbon, nitrate, chloride, and biomass. A good correlation was found between intermediate concentration and the removal efficiency of the biotrickling filter. The measurements of the absorbance, very easy and rapid, can be used as a control parameter of the biofiltration efficiency.

Selection, acclimation, and kinetic characterization of a nitrifying microflora chosen from natural sources and capable of degrading total ammonia nitrogen (TAN) at high concentration was performed. The inocula of animal manure and of marine sediments were selected due to their nitrate production (55.8 mg N/L⋅day) and tolerance to salinity (16 g ${\mathrm{Cl}}^{-}/L)\text{.}$ An acclimation continuous culture was made using TAN up to 1,000 mg N/L and nitrogen load rate of 250 to 1,000 mg N/L⋅day. The TAN degradation rate after acclimation reached 0.16 mg N/mg VSS⋅h (VSS=volatile suspended solids) at a feed concentration of 1,000 mg N/L; the ammonia-oxidizing population increased from 60 to 77% whereas nitrite-oxidizing bacteria decreased from 40 to 23%. The following substrate-inhibition Haldane parameters were determined: $r_{\mathrm{TAN}\text{,}\max }=0.21$ and 0.19 mg N/mg VSS⋅h; $K_s=3.0$ and 4.8 mg ${\mathrm{NH}}_3-N/L;$ $K_i=22.4$ and 35.6 mg ${\mathrm{NH}}_3-N/L$ for sludge before and after acclimation, respectively. Differences between $r_{\mathrm{TAN}\text{,}\max }$ values were not statistically significant with a confidence limit of 95%, whereas $K_s$ and $K_i$ differences were significant, showing a better tolerance to higher ammonium concentrations.

Some of the highest losses of nitrate to surface waters come from drained agricultural land. This research studied, for Belgian farming conditions, (i) the effect of subsurface drainage density on nitrate losses and (ii) the economics of nitrate losses, using the nitrogen version of the program DRAINMOD-N. DRAINMOD was used to simulate the performance of the drainage system of the Hooibeekhoeve experiment, situated in the sandy region of the Kempen (Belgium) for a 14-year (1985–1998) period. A continuous cropping with maize was assumed. Daily ${\mathrm{NO}}_3-N$ losses were predicted for a range of drain spacings and depths, two drainage strategies (conventional and controlled), and three fertilizer application rates (225, 275, and 325 $\mathrm{kg} N {\mathrm{ha}}^{-1})\text{.}$ Losses of N in subsurface drainage were assumed to occur almost entirely in the ${\mathrm{NO}}_3-N$ form. Losses of organic and inorganic N in the form of ${\mathrm{NO}}_3-N$ in surface runoff are small and were neglected. Hydrologic results indicated that increasing drain spacing or decreasing drain depth reduces drainage discharge while it increases runoff. The use of controlled drainage reduces subsurface drainage and increases runoff. Results also revealed that increasing the drain spacing or decreasing the drain depth reduces nitrate-nitrogen $({\mathrm{NO}}_3-N)$ drainage losses and net mineralization, while increasing denitrification and runoff losses. Controlled drainage caused a predicted reduction in drainage losses and an increase in denitrification and runoff losses. The optimal combination of drain density and management is one that maximizes profits and minimizes environmental impacts. Simulated results indicated that ${\mathrm{NO}}_3-N$ losses to the environment could be substantially reduced by reducing the drainage density below the level required for maximum profits based on grain sales. The study concluded that, if the environmental objective is of importance equal to or greater than profits, drainage systems can be designed and managed to reduce ${\mathrm{NO}}_3-N$ losses while still providing an acceptable profit.

The stream reaeration coefficient inferred from a single-station diurnal oxygen curve analysis is a function only of the photoperiod duration and of the time lag between solar noon and oxygen maximum—it is independent of rates of primary production and respiration. Solutions of this function, already presented in this journal as graphs by Chapra and Di Toro in 1991, arise from numerical solution of an implicit transcendental equation and so do not have a simple analytical expression. A simple alternative approximate logistic curve-fit equation is presented here, enabling quite accurate direct calculation of the coefficient from the time lag and photoperiod duration alone. A temperature correction factor is also included. The equation may be useful for incorporation in decision support systems.

Two laboratory-scale anaerobic sequencing batch reactors (anSBRs) were used to investigate the effectiveness of polymer addition for enhancing granulation. Mixed liquor volatile suspended solids (MLVSS) concentrations in R1 (with a polymer supplement) and R2 (control) were maintained at approximately 5 g/L. Granule development was measured by determination of the average bioparticle diameter of biosolids from the anSBRs. Addition of cationic polymer to R1 started on the 47th day after reactor start-up at a dosage of 1 ppm (on reactor volume) once per every two cycles. The cationic polymer had a beneficial effect on granulation. Compared to the control, it shortened the granulation process by approximately four months. Within the range investigated, food-to-microorganism (F/M) ratios at 0.5–0.6 g COD/g VSS d were also beneficial to granulation. After 300 days operation (at F/M ratio 0.5 g COD/g VSS d), the average bioparticle diameter of R1 was 0.78 mm, while R2 was only 0.39 mm. R1, aside from having a larger granule size, also had a higher methane production and lower soluble COD in effluent at F/M ratio 0.6 g COD/g VSS d compared to R2.

Nitrogen is removed in suspended growth wastewater treatment systems by passing mixed liquor from an aerobic zone in which nitrification takes place to an anoxic zone in which denitrification takes place. Following the switch from oxygen to nitrate as terminal electron acceptor, a diauxic lag may occur. The present study tested the hypothesis that lower dissolved oxygen concentrations in the aerobic phase lead to shorter diauxic lags. Bacterial cultures exposed to low dissolved oxygen concentrations (<0.70 mg/L) during the aerobic growth phase had significantly shorter diauxic lags than cultures grown at air saturation. Furthermore, these cultures generally grew faster during the anoxic phase. These results indicate that the effect of dissolved oxygen concentration in aerobic reactors on diauxic lags and anoxic growth rates in anoxic reactors should be considered in the design and operation of nitrogen-removing, suspended growth biological treatment processes.