Journal of Environmental Engineering

The Ridgewood Wastewater Treatment Plant in Ridgewood, New Jersey underwent a retrofit from a coarse‐bubble to fine‐pore aeration system. Also, process modification from contact stabilization to tapered air occurred. This paper provides a review of the case history of plant and aeration performance of each system from 1981 through 1986. Non‐steady state and off‐gas oxygen transfer field testing at the plant over the 6‐yr period provides the data base for the objective evaluation. An economic evaluation of retrofit impact is presented. Oxygen transfer efficiency of the fine pore system was approximately double that of the coarse bubble system. However, power costs were not reduced proportionately since a higher oxygen demand was supplied by the fine pore system to attain nitrification and meet the revised permit requirements. Severe nocardia foaming problems were encountered in the summer during the first three years of fine pore operation. These were controlled in the last two years by minimizing sludge recycle loads and preventing septic conditions in the aeration tanks.

Fixed‐film nitrification was studied in a pilot‐scale fluidized bed treating municipal secondary effluent. A mechanistic mathematical model incorporating reaction stoichiometry, diffusion, multisubstrate kinetics with product inhibition, fluidization, and a reactor model developed from the observed residence‐time distribution, was developed to predict the steady‐state and short‐term dynamic performance of the reactor. The model equations were solved using orthogonal collocation with trial functions tailored to the spherical‐shell biofilm geometry, and a semi‐implicit third‐order Runge‐Kutta integration technique. The steady‐state model closely fit measured concentration profiles using the maximum specific growth rates for Nitrosomonas and Nitrobacter as adjustable parameters. The dynamic model predicted observed responses to step and impulse changes in ammonium and nitrite concentrations to within 3 mg/L without further parameter adjustment. The fluidization model predicted the observed fluidized bed height within 1 cm. External mass transfer resistance was small for the conditions employed and was not included in the model.

Voluminous research has been published regarding the denitrification of drinking water. Most of this work has been done in Europe. Unfortunately, much of the European literature has not been translated into English, and as a consequence there may be a gap in the understanding of the international state of the art with regard to drinking‐water denitrification. Numerous substrates have been evaluated including methanol, ethanol, acetic acid, methane, carbon monoxide, hydrogen, and various sulfur compounds. Various unit processes have been utilized including biofilters, fluidized‐bed and packed‐bed reactors, packed towers containing cells immobilized in polymer gels, and completely mixed reactors with cells attached to bouyant porous carriers. There are several commercial facilities currently providing drinking water to European communities. Most include post‐treatment with flocculation, filtration, and disinfection. A common concern in denitrification operations is the minimization of nitrite accumulation. This requires careful process control, and more research regarding the nitrite problem is needed. The European literature is a valuable source of information regarding the denitrification of drinking water.

A methodology for quantifying the net contribution by algae to the oxygen resources of rivers is presented. The approach recognizes natural variation in incident light as a key factor mediating the character and magnitude of the algal source‐sink term. Required input data include algal biomass, the light attenuation coefficient, daily average incident light, river depth, and the relationship between net oxygen production and light. Systems that are particularly sensitive to algal metabolism, and therefore incident light, are those with high plant biomass, light attenuation, depth, and low reaeration. Graphical relationships are applied as screening tools to identify potentially sensitive river environments on the basis of incident light, light attenuation, and depth. Example calculations show that failure to accommodate natural variation in incident light in wasteload allocation models may impart substantial uncertainty to model output. The methodology presented here permits calculation of oxygen deficits over the natural range in incident light values and thus can serve to improve the credibility of management actions when used as a screening tool. Incorporation of these concepts into existing wasteload allocation models seems necessary and useful.

The bactericidal action of solar radiation was investigated in pilot scale waste stabilization ponds under the tropical climate of Dar es Salaam, Tanzania. Bacterial reduction was observed to proceed with increasing direct solar intensity and hydraulic detention time. The mortality rate of faecal coliforms used as test micro‐organisms was higher in samples incubated near the surface and decreased rapidly when the samples were incubated at greater depths in the pond. The disappearance rate of faecal coliforms for samples incubated at the pond surface and at a depth of 1.0 m was $1.66d^{-1}$ and $0.37d^{-1}$ respectively. Faecal coliforms were also found to be reduced rapidly in shallow ponds. The mortality rate in 1.0 m and 1.5 m deep ponds was respectively 0.43 and $0.32d^{-1}\text{.}$ The dieoff rate constant was observed to vary significantly with pond depth but was independent of hydraulic detention time.

The James River in Virginia is one of the major tributaries to the Chesapeake Bay. In Virginia, control measures to reduce phosphorus loads to the bay include phosphate detergent bans and removal of phosphorus at the wastewater treatment plants in the bay region. Important questions to be addressed for the James River basin are: how much reduction in algal biomass can be expected from phosphorus load reductions and how much phosphorus in the algal biomass in the estuary comes from point sources, nonpoint sources, or the upper basin? A modeling analysis has been conducted to address these questions. In the analysis, a numerical tagging technique was used to track the fate and transport of phosphorus along the entire estuary. The model results show that while phosphorus control in the upper estuary would provide additional inorganic nitrogen input to the lower estuary, the additional nitrogen would not affect the algal growth potential.

In most streams, reaeration makes an important contribution to the oxygen budget. It is unfortunate that despite recent developments in the use of hydrocarbon gas tracers, there is no simple satisfactory technique for reaeration measurement. This paper describes a new technique based on the rate of dissolution of a floating soluble solid. The theoretical basis of the new method is described, and laboratory experiments showing the correlation between the atmospheric reaeration and solids dissolution processes are reported. A comparison with the gas tracer technique showed overall correlations between the rate of reaeration, solids dissolution, and propane desorption, but differences became apparent at high Reynolds numbers. The limiting factor between oxygen absorption and solids dissolution was identified as being the difference in the surface area of contact between the two phases. Nevertheless, it is suggested that solids dissolution is a simple and inexpensive technique for estimating reaeration.

A modeling technique for water‐quality management that incorporates both simulation and optimization is presented. The proposed methodology should be of use in the allocation of waste load for a number of dischargers located on a water body. A Monte Carlo simulation model is utilized to generate a series of water quality responses that lead to the formulation of a constraint set for the optimization model. Repeated solution of the optimization model, using an appropriate mathematical programming technique, yields a distribution for the required treatment cost. Additionally, the distribution for the required pollutant removal fraction at each of the point source locations is obtained from the combined use of simulation and optimization. From the treatment cost distribution function, attractive alternatives can be identified for further analysis prior to the implementation of a water‐quality management plan. Elements of the proposed methodology are illustrated through an example of allocating biochemical oxygen demand.

A bench‐scale, continuous, stirred‐tank reactor is used to study the removal of a volatile organic compound, toluene, from air through absorption into water and subsequent adsorption onto powdered activated carbon in the reactor. Both steady and unsteady state data are used to calibrate and test a mathematical model, which is based on gas transfer at the gas/liquid interface, diffusional resistance in the boundary layer around activated carbon particles, and diffusional resistance through activated carbon pores. The model is solved numerically using the orthogonal collocation method on finite elements. Both the steady and unsteady state data are described well with the model. The experimental and modeling results show that the removal of toluene from air is greatly enhanced by adding activated carbon to the scrubbing water. The presence of activated carbon lowers dissolved toluene concentrations and thus maintains a high driving force for toluene absorption into water. The effect of carbon pore diffusion is found to be appreciable. The value of the effective diffusivity that gives the best fit for both steady state and unsteady state data is $0.001{\mathrm{cm}}^2/\min \text{,}$ which is on the same order of magnitude with the bulk diffusivity.

A procedure is developed to identify the receptor sites which influence optimized emission abatement strategies. These “influential receptors” are the most critical sites in terms of meeting environmental objectives. Influential receptors represent only a small portion of the modeled region. After their identification, standard optimization techniques may be used. The procedure increases the speed of optimization, decreases memory requirements, and enables the solution of realistic problems using microcomputers. Influential receptors are found for several emission abatement strategies aimed at reducing peak concentrations and surface depositions of sulfur and nitrogen in North America and Europe.

A laboratory investigation was conducted to determine the relative importance of the physiological state of the reactor population and biomass concentration on mitigating short-term toxic shocks. The studies were conducted using 2-chlorophenol (2-CP) as a model toxic compound. Both factors were identified as having a probable benefit in reducing toxic inhibition caused by transient events of 2-CP. Of the two, the inhibition rate was more significantly influenced by the physiological state of the organisms (i.e. ϴ_c) than by biomass concentration. Consequently, prediction of toxic inhibition as a function of biomass concentration without regard to changes in cell physiological state may lead to erroneous conclusions.

Estuarine reaeration rates induced by wind and bottom stresses are compared through calculation of air-water-mass-transfer coefficients. For typical tidal velocities and depths, the transfer coefficient (and hence reaeration) induced by wind speed greater than 5 m/s exceeds the transfer coefficient generated by bottom stress. For wind speed less than 1.5 m/s, wind influence on the transfer coefficient is negligible relative to bottom stress. For intermediate wind speeds, the transfer coefficient may be dominated by wind or by bottom stress.