Journal of Environmental Engineering

Various empirical and probabilistic kinetic inactivation models that can be used to assist in the design and analysis of potable water disinfection systems were reviewed. Models were derived for both disinfectant demand-free and demand conditions. Ozone was used to inactivate heterotrophic plate count bacteria that were grown in natural water under low nutrient conditions and enumerated using R2A agar at 20°C for 7 days. Experiments were conducted at 22°C in 0.05 M (pH 6.9) phosphate buffer in bench-scale, batch 250 mL reactors. This disinfection data set, characterized by tailing-off behavior, was used to assess Chick–Watson, Hom-type, Rational, Hom–Power law, and Selleck model fit to the observed logarithmic survival ratios. It was found that the Chick–Watson model did not adequately represent the ozone disinfection kinetics. A Hom-type model incorporating a first-order disappearance term for ozone residual was found to best describe the observed inactivation of heterotrophic plate count bacteria. Named the incomplete gamma Hom model, it was found to be a robust kinetic model. The proposed incomplete gamma Hom model can be used to generate simple design charts for a wide range of disinfectant types, organisms, and conditions, as an aid to the design of water disinfection systems.

Horseradish peroxidase catalyzes the oxidation of aqueous aromatic compounds by hydrogen peroxide, resulting in the formation of polymers, which spontaneously precipitate from solution. This process is being investigated as a means of removing toxic phenols and aromatic amines from industrial wastewaters. Models of plug-flow reactors and continuous-flow stirred tank reactors (CFSTR) were developed for the horseradish peroxidase–peroxide-aromatic substrate system as an aid for reactor design and process optimization. The models were verified for phenol removal at pH 7 and 25°C, both in the presence and absence of high molecular weight polyethylene glycol, a protective additive. Modeling suggests that the rate of enzyme inactivation is lower in a CFSTR than in a plug-flow reactor. Nevertheless, no single optimal reactor configuration can be identified, because the best configuration depends on the initial phenol concentration, the desired effluent quality, and the selected retention time. The CFSTR performance could be improved further by engineering a system that returns effluent active enzyme to the treatment process.

Natural organic matter (NOM) was extracted from a raw water source (Forge Pond, Granby, Mass.) and fractionated into eight groups: fulvic acid, humic acid, hydrophilic acid, weak hydrophobic acids, hydrophilic neutrals, hydrophobic neutrals, hydrophilic bases, and hydrophobic bases. The extent of adsorption of these fractions on preformed aluminum hydroxide flocs was determined. Also, the adsorption affinities of various fractions were correlated to selected NOM properties, i.e., organic charge, molecular weight, and specific ultraviolet absorbance. The nature of the reactions leading to adsorption was discussed, along with the induced dissolution of aluminum from the floc surface and its resulting association with NOM in particulate or colloidal forms.

Disposal of fly ash on land amounts to sacrificing precious land space. Recycling of fly ash is one of the methods of solving the disposal problem. Stabilization of a low lime fly ash with lime and gypsum was studied through large scale tests on the stabilized material designed to simulate field recycling conditions as closely as possible, and found to be a very effective means to control hydraulic conductivity and leachate characteristics. The effects of moulding water content, lime content, gypsum content, curing period, and flow period on hydraulic conductivity, and on leachate of metals flowing out of the stabilized fly ash are reported herein. With proper proportioning of the mix, and adequate curing, the values of hydraulic conductivity on the order of 10⁻⁷ cm/s were achieved. The concentrations of As, Cd, Cr, Cu, Fe, Hg, Mg, Ni, Pb, and Zn in the effluent emanating from the hydraulic conductivity specimens of mixes with higher proportions of lime or lime and gypsum were below threshold limits acceptable for contaminants flowing into ground water.

Pyrolysis-based technology for the epoxy resin compounds (molding resin) used for molding electronic components has been studied for the purpose of recovering useful materials and reusing them. The molding resin contains silica filler (70–85% by weight) and flame retardant consisting of bromine compounds and antimony oxides. This study has clarified those pyrolysis conditions best suited to reduction of the impurities (carbon, antimony, and ionic substances) in the recovered silica filler. This has contributed to the development of a practical pyrolysis technology in which a roller kiln-type furnace is used to recover high-purity silica filler. The recovered silica was sufficiently pure to be employed as an inorganic filler in epoxy resin compounds to be used as cast-insulating materials and original molding resins. The combustion exhaust gas generated in the pyrolysis of the molding resin has been successfully treated by a secondary combustion method that decomposed organic bromine compounds in the gas to a safe level, and it converted antimony bromides to antimony oxides, which could then be collected by a dry recovery process at a useful purity.

A recirculated upflow anaerobic sludge blanket (RUASB) reactor was operated with three effluent recirculation ratios (5:1, 4:1, and 3:1) to evaluate the influence of hydraulic loading rate on the RUASB treatment of concentrated phenolic wastewater. The results indicate that following an adjustment of the recirculation ratio, a 2- or 3-week lag in methane production occurred, and the effluent concentrations of volatile suspended solid and phenol apparently increased. The results obtained emphasize that the sludge loading rate of 1.40 g phenol-chemical oxygen demand/g volatile suspended solid per day was a threshold limit for the methanogens to generate methane. A substrate metabolic activity experiment was carried out to measure the biogas converting capacity of the phenol-consuming granular sludge. A modified Gompertz equation then was applied to evaluate the biogas production potential and rate. The phenolic biodegradation characteristics were described using the Haldane relationship. The half-saturation constant (K_s) decreased with a decrease in the recirculation ratio, indicating that the granules inside the RUASB reactor had a higher substrate affinity under a low hydraulic loading rate than at a high hydraulic loading rate.

Current design criteria for free-water-surface constructed wetlands are based on either empirical relationships or first-order reaction rates and do not emphasize the microbial activity. This study was conducted to evaluate the role of biofilm bacteria present in free-water-surface constructed wetland beds in the removal of organic matter. A kinetic model incorporating the biofilm kinetics and dispersion number was proposed to predict chemical oxygen demand removal in free-water-surface constructed wetlands. The model parameters were determined from laboratory experiments and from the literature. The proposed kinetic model satisfactorily predicted chemical oxygen demand removal efficiencies in a pilot-scale constructed wetland unit located in the tropics. A design chart and a design example based on the kinetic model are given.

This paper reports the result of studies using a biotrickling filter with blast-furnace slag packings (sizes = 2–4 cm and specific surface area = 120 m²/m³) for treatment of styrene in an airstream. The effects of volumetric styrene loading L, superficial gas velocity U₀ and liquid recirculation rate V_L on the styrene elimination capacity K, and the removal efficiency K/L were tested. Variations of styrene concentration with packing height as well as rates of nutrient utilization were also tested. The results show that for L< 30 g/m³$\dot{s}$h, K/L was nearly independent of U₀ in the range of 29–67 m/h and was independent of V_L in the range of 3.84–9.60 m/h. In this range, the rate of styrene removal was both reaction and diffusion limited and the reaction was of zero-order kinetics. For higher loadings, K/L decreased with increasing U₀ and increased with increasing V_L and the system approached the condition of reaction limitation.

A two-dimensional numerical model is developed to study contaminant transport resulting from the dissolution of single- and multicomponent dense nonaqueous-phase liquid (DNAPL) pools in heterogeneous porous media. The aqueous-phase concentration of each dissolved component is assumed to undergo first-order decay as well as sorb under local equilibrium conditions. Pool shrinkage is accounted for by modeling the progressive reduction of the DNAPL pool surface area as a time-dependent boundary. Multicomponent pool dissolution is modeled using an effective solubility (or equilibrium aqueous solubility) relationship, where the nonaqueous-phase activity coefficient for each constituent is evaluated at each and every time step. Subsurface heterogeneities are depicted by an ideally stratified porous formation and by a statistically anisotropic aquifer. In the stratified formation, a multicomponent DNAPL pool is assumed to be formed at the interface between a sand layer and a clay layer, where DNAPL dissolution occurs simultaneously in both strata. The ground-water velocity inside the sand stratum is uniform in the longitudinal direction whereas the interstitial liquid in the aquitard is stagnant. In the statistically anisotropic aquifer, a single-component DNAPL pool is assumed to be formed on top of an impermeable bedrock, where DNAPL dissolution occurs in the aquifer only. Results from several model simulations indicate that dissolved contaminant concentrations in aquifers are reduced significantly in the presence of aquitards, and most importantly, the transfer of dissolved contaminants along the pool-water interface is slower within statistically anisotropic than within homogeneous aquifers.

A procedure is presented for estimating the total pollutant mass loss from the interrill flow region of an agricultural field during a runoff event. It involves applications of an overland flow model and a mass transport model. A two-dimensional interrill flow model by Limback and other researchers provides lateral depth and velocity distributions that are used to determine the dispersion and entrainment coefficients required by the transport model. The transport model of Wallach and van Genuchten with variable rather than constant dispersion and entrainment coefficients served to model the transport process that carries solute from the soil interstices to the overland flow. Wallach's mass loss rate equation was integrated over space (laterally) and time to determine total mass loss. The effects of rainfall rate, infiltration rate, surface roughness, surface slopes, and soil properties are included in the analysis. An example application and an explicit sensitivity analysis of the effect of infiltration rate on mass loss are presented. The procedure represents a significant improvement over the model of Parr and other researchers that did not account for the effects of infiltration and the model of Wallach and van Genuchten that did not account for mechanical dispersion.

Continuous water quality measurements of storm runoff into a single road inlet have been carried out at two experimental catchments, in Belgrade, Yugoslavia, and Lund, Sweden. Both sites were equipped with similar instrumentation for measurements of overland flow, turbidity, pH, conductivity, and temperature. The data were recorded at 10-s time intervals during rainfall events. To measure suspended solids concentration, turbidity meters were calibrated in conditions very similar to the real world. A detailed description of the field-measuring facilities used in the Belgrade catchment and the results of the measurements from both sites are presented. After detailed examination of possible errors in measurement, only the reliable data were used for statistical analysis. Event mean, extreme, and aggregated values were analyzed. The results indicate that the antecedent dry weather period length has only a minor effect upon road sediments wash-off, but it has an influence upon conductivity. The “first-flush effect” of suspended solids appears only in a limited number of events. Cross-correlation coefficients of rainfall, overland flow, and water quality were calculated for each event, taking into account the time lag between observed characteristics. These coefficients showed that suspended solids loading rate is influenced by rainfall intensity and overland flow rate. The results presented in this paper have been used in development of the physically based wash-off model published by Deletic and coworkers.

Model studies using geometrically similar 300-mm-diameter and 1,600-mm-diameter hydrodynamic separators operating with an underflow have confirmed earlier results indicating that a combination of Froude and Hazen scale laws should be used when predicting prototype separator performance. A hybrid equation is proposed to scale the model inflow rates. This equation provides a good fit to the observed prototype flow versus efficiency data. The need to scale particles using a Hazen scale for settling velocity and a Froude scale for flows is discussed. Treatment factors are calculated for the different particle sizes used, and these confirm the suitability of the device to remove particles with higher settling velocities while passing organic particles with low settling velocities forward to treatment when the device is configured as a grit separator.

A method of wastewater treatment was developed by using in-situ production of hypochlorous acid from the soak liquor of tannery for chlorine generation. The hypochlorous acid was produced in an undivided electrolytic cell. The cell contained graphite anode and stainless steel cathode. The hypochlorous acid was utilized for the oxidation of organic matter present in the wastewater. In the case of vegetable tanning wastewater for an initial chemical oxygen demand concentration of 9,600 mg/L, at the end of 120 min of electrolysis, the chemical oxygen demand remaining was 59 mg/L with the residual chlorine concentration and turbidity as 65 mg/L and 3 NTU, respectively, for an optimum current density of 34 mA/cm². In the case of chrome tanning wastewater, chromium(III) was oxidized to chromium(VI) by the hypochlorous acid produced during electrolysis with a conversion efficiency of 96 ± 3% at a pH range of 2.5–5.5. The resulting chromium(VI) can be converted easily to basic chromium sulphate [(Cr(H₂O)₅OH)SO₄] for reuse in tanning operation, and the work pertaining to this aspect is in progress.

The thermal degradation kinetics of polypropylene (PP) in steam was investigated with a thermal gravimetric analysis (TGA) reaction system. The experiments were carried out in the 500–800 K temperature range at various constant heating rates of 1, 2, and 5 K/min. The partial pressure of steam in the system was adjusted to 0.24 atm, which is seen in most municipal solid waste (MSW) incinerators in Taiwan. The results indicated that the water molecule significantly enhanced the thermal degradation rate of PP. The corresponding activation energy, preexponential factor, and reaction order were determined. It was found that thermal degradation of PP in steam can be adequately described by an overall rate equation.

Light non-aqueous-phase liquid (LNAPL) pools at the interface of unsaturated and saturated zones fluctuate with ground-water table and create a “smear zone” occupied by ganglia or blobs. These ganglia dissolve slowly and constitute a long-term threat to ground-water resources. Prior investigations reported in this journal indicated that vibrations, when induced locally in an LNAPL-contaminated porous medium, cause momentary particle rearrangement and provide necessary conditions for mobilization of these ganglia. These investigations were laboratory scale involving shaking table and sand columns. This paper reports on a bench-scale investigation of the implementation of vibrorecovery. A probe-type vibrator was used to create vibrations in a polyvinyl chloride tank filled with Soltrol-contaminated sand. The vibrator was housed in a well chamber wherein the NAPL ganglia, mobilized using controlled flow gradients, were collected before being pumped out. The flow domain around the vibrator was delineated using a dye tracer, and the density variations in the vibrated soil were determined. The design of the prototype vibrator was adequate in creating a zone of reduced LNAPL residual saturations in the flow domain.