Journal of Environmental Engineering

Membrane bioreactors (MBRs), in which membranes are applied to biological wastewater treatment for biomass separation, provide many advantages over conventional treatment. However, membrane fouling in MBRs restricts their widespread application because it reduces productivity and increases maintenance and operating costs. Recently much research and development has taken place to investigate, model, and control membrane fouling processes. However, unified and well-structured theories on membrane fouling are not currently available because of the complexity of the biomass matrix, which is highly heterogeneous and includes living microorganisms. Membrane fouling in MBR systems can be reversible (i.e., removable by physical washing) or irreversible (removable by chemical cleaning only), and can take place on the membrane surface or into the membrane pores. Although establishing a general model to describe membrane fouling in such a process is made extremely difficult by the inherent heterogeneity of the system, the nature and extent of fouling in MBRs is strongly influenced by three factors: biomass characteristics, operating conditions, and membrane characteristics. Fouling control techniques which have been investigated include low-flux operation, high-shear slug flow aeration in submerged configuration, periodical air or permeate backflushing, intermittent suction operation or addition of powdered activated carbon (PAC). Of these, only PAC addition is currently not used in existing large-scale installations.

An experimental procedure was developed for the respirometric determination of bacterial storage yield as defined in the Activated Sludge Model No. 3. The proposed approach is based on the oxygen utilization rate (OUR) profile obtained from a batch test and correlates the area under the OUR curve to the amount of oxygen associated with substrate storage. Model simulation was used to evaluate the procedure for different initial experimental conditions. The procedure was tested on acetate. The same storage yield value of 0.76 gCOD/gCOD was calculated for two experiments, starting with different F/M ratios of 0.12 and 0.64 gCOD/g cellCOD.

The dynamic process of the dissolution of ozone in a countercurrent bubble column is studied for model establishment. Bubble columns have been used widely for ozone contacting in the plant and laboratory. Ozone is produced by oxygen-enriched gas through an ozone generator, and introduced into the bottom of the column equipped with the gas diffuser. The ozone contacting system proceeds for a temporary and unsteady period before reaching steady state. The available ozone dissolution models employed for the description of the dissolved ozone profiles were commonly developed for the steady state. Moreover, oxygen mass transfer is usually neglected in the preceding ozone dissolution models. However, this information is desirable for proper operation of ozone dissolution in a bubble column. Thus, the objective of this study is to model and investigate the dynamic ozone dissolution process in a bubble column with the oxygen mass transfer. The dynamic axial dispersion model proposed is employed to predict the variations of ozone and oxygen concentrations along the column, and the amount of off-gas. The validity of the model is demonstrated by comparing the predicted results with the experimental data. The dynamic model of ozone dissolution is useful and referable for proper prediction of the variables of the ozone contacting system in a bubble column.

The objective of this project was to determine the impact hydraulic dispersion has on the calibration of a flow-though model ultraviolet (UV)-disinfection system with chemical actinometry (potassium ferrioxalate) and MS 2 bacteriophage. Fluence was supplied by a medium-pressure ultraviolet lamp to a quartz tube (19 mm diameter) situated in a ventilated galvanized casing. The UV lamp was attached to a vertical position guide, for UV fluence to be varied by positioning the UV lamp at various vertical heights above the quartz tube. Water was pumped through the quartz tube at rates of 100–300 mL/min. An in-line pipe mixer was installed prior to the UV system to ensure adequate mixing with the bulk liquid and chemical actinometer and to mitigate jet formation within the quartz tube. Tracer studies were conducted with and without the in-line mixer using potassium chloride (3 mM). Dispersion coefficients were obtained from the tracer study and incorporated into an axial-dispersion model to determine the rate coefficient of potassium ferrioxalate in the model UV system. A numerical model was used to determine the fluence supplied by the lamp with a reduction in exposure time. After dispersion and kinetics are accounted for within the UV system, the model predicted UV fluence that was in general agreement with UV design curves for inactivation MS 2 bacteriophage. The differences in the design curves and the fluence–response model in the present investigation were found to be related to the experimental errors introduced from using a flowing system and because a medium pressure lamp was used in the present investigation.

A study has been done to evaluate the predictive capabilities of computational fluid dynamics (CFD) models of disinfection contactor hydraulics under model input uncertainty. The study consists of modeling the transport of a chemical tracer in a full-scale reactor and predicting the effluent residence time distribution (RTD) curve. An uncertainty analysis using Monte Carlo probabilistic techniques was used to determine the sensitivity of the effluent RTD to uncertainty in the influent turbulent kinetic energy constant, the turbulent Schmidt number, the wall roughness height, the influent turbulent length scale, and the turbulence model selection. Kruskal–Wallis, Friedman, and Spearman Rho statistical tests were used to evaluate changes in $T_{10}/\mathrm{HRT}$ and Morril index due to input uncertainties. The results show that there are some variations in the effluent RTD due to changes in the model input parameters. The effluent RTD variations increased with decreasing contactor hydraulic efficiency or increased mixing. The effluent RTD was most sensitive to uncertainty in the turbulent Schmidt number and the selected turbulence model.

A research effort was undertaken to investigate the genesis of particles produced during in situ chemical oxidation (ISCO) of trichloroethene (TCE) with permanganate $\left({\mathrm{MnO}}_4^{-}\right)$ and to explore the effects of those particles on system permeability and metal mobility. The experimental approach included characterization of soil and groundwater samples from an ISCO field site, batch experiments with a replicated $2^5$ factorial design, and flow-through column experiments. Analyses of intact soil cores from an ISCO field site revealed that ${\mathrm{MnO}}_2$ solids were present in the subsurface near an injection well for ${\mathrm{NaMnO}}_4$ but at low levels (2.3–2.5 mg/g dry wt media) calculated to fill <1% v/v of the aquifer porosity. Batch tests revealed that the mass of filterable solids (>0.45 μm) produced during chemical oxidation with ${\mathrm{MnO}}_4^{-}$ was increased at higher TCE concentrations (54 versus 7 mg/L) and in the presence of ambient silt/clay-sized particles in the groundwater (750 versus 7.5 mg/L). Under otherwise comparable conditions, increasing the ${\mathrm{MnO}}_4^{-}$ dose markedly increases the oxidant consumption and also increases the solids production. The oxidant form $({\mathrm{NaMnO}}_4$ versus ${\mathrm{KMnO}}_4)$ or reaction time (15 versus 300 min) had little effect on oxidant consumption or filterable solids production. During ${\mathrm{MnO}}_4^{-}$ oxidation of higher levels of TCE in a groundwater with ambient silt/clay particles present, there can be substantial increases in filterable solids generated, which are <1 μm in size and consist of ${\mathrm{MnO}}_2\text{,}$ commingled with other mineral matter. Conceivably, low volumetric fillings of these solids could cause permeability loss. Flow-through column experiments revealed that permeability loss was possible during ISCO but only under conditions with very high ${\mathrm{MnO}}_2$ solids production. On the positive side, the ${\mathrm{MnO}}_2$ solids produced can increase the sorption potential for metals such as cadmium and can represent a mode of immobilization. This research demonstrated that ISCO with permanganate has the potential to yield system permeability loss under some conditions as well as to affect metal mobility. The magnitude of these effects is related to the subsurface conditions, target organic chemical mass, and permanganate dose and delivery method. The production of solids during ISCO needs to be carefully considered during process design and operation to avoid solids-related performance problems while exploiting potential benefits.

Carbonaceous and noncarbonaceous adsorbents were impregnated with elemental sulfur to evaluate the chemical and physical properties of the adsorbents and their equilibrium mercury adsorption capacities. Simulated coal combustion flue gas conditions were used to determine the equilibrium adsorption capacities for ${\mathrm{Hg}}^0$ and ${\mathrm{HgCl}}_2$ gases to better understand how to remove mercury from gas streams generated by coal-fired utility power plants. Sulfur was deposited onto the adsorbents by monolayer surface deposition or volume pore filling. Sulfur impregnation increased the total sulfur content and decreased the total and micropore surface areas and pore volumes for all of the adsorbents tested. Adsorbents with sufficient amounts of active adsorption sites and sufficient microporous structure had mercury adsorption capacities up to 4,509 μg Hg/g adsorbent. Elemental sulfur, organic sulfur, and sulfate were formed on the adsorbents during sulfur impregnation. Correlations were established with $R^2>0.92$ between the equilibrium ${\mathrm{Hg}}^0/{\mathrm{HgCl}}_2$ adsorption capacities and the mass concentrations of elemental and organic sulfur. This result indicates that elemental and organic sulfur are important active adsorption sites for ${\mathrm{Hg}}^0$ and ${\mathrm{HgCl}}_2\text{.}$

A voluminous and hazardous sludge containing a high amount of hydrocarbons and several trace metals is generated in petroleum oil field effluent treatment plants. The aim of this study was to utilize the sludge in preparing environmentally acceptable masonry bricks in a commercial brick plant. The effect of the sludge on the plasticity behavior of the brick raw mix was investigated. The addition of the sludge reduces the requirement of process water and fuel. The fired bricks meet all the requirements of the Indian Standard Specification. The bricks were subjected to toxicity characteristics leaching protocol leaching tests. Most of the toxic metals are fixed in the vitrification process and the leachates values meet the Environmental Protection Agency’s requirement for recycling of hazardous materials.

A simple method for simultaneous and explicit estimation of dispersion coefficient and porosity from laboratory data on soil-column tests is presented. It makes use of the peak derivative of the observed breakthrough curve (BTC). An objective procedure for approximate location of the peak is suggested based upon a parabolic fit through three consecutive points around the peak. The computations involved are simple and can be done on a calculator. The method does not require either the rate of flow or the cross-sectional area of the soil-column for estimating the dispersion coefficient. This completely avoids the possible errors involved in the measurement of these quantities. The new method does not require the full BTC to be observed, however, its application does require data slightly beyond the time at which the exit concentration reaches half the input concentration. Application of the method on a number of laboratory data sets shows that it can yield a reliable estimate of the dispersion coefficient and porosity using only a few points near the peak. The method is applicable for high values (>100) of the piclet number.

In this work we investigated the use of a short time, low superheat boiling process to treat biological sludge. The treated sludge would exhibit a deteriorated filterability, and a marked increase in soluble organics content. A large portion of extracellular polymers was released from the solid phase by boiling. The microbial density levels of the total coliform bacteria and the heterotrophic bacteria were reduced after treatment. Dilution in sludge concentration could allow more organic compounds to be hydrolyzed and a greater fraction of microbes to be disinfected when compared with the undiluted samples.