Journal of Environmental Engineering

A kinetic model is presented to describe the interactions among microbial reactions that are important in single‐sludge treatment systems for nitrification/denitrification. This model describes the aerobic processes of organic carbon oxidation and nitrification and the anaerobic process of denitrification. It was used in a series of computer simulation experiments to delineate the effects of process variables on efficiency of nitrogen removal in an intermittently aerated, completely mixed, single‐sludge configuration. The effects of the following variables on nitrogen removal were studied: aeration fraction, solids retention time, hydraulic retention time, dissolved oxygen control, and the influent concentration of organic matter. Important interactions were observed between the solids retention time, aeration fraction, and influent organic matter concentration and were investigated in additional simulation experiments. Results of these experiments show the importance of solids retention time, aeration fraction, influent organic matter concentration, and dissolved oxygen control strategy to good nitrogen removal. Knowledge of the nature of the interactions among these variables is directly applicable to design and operation of single‐sludge biological treatment systems for concurrent removal of organic matter and nitrogen.

Using Kepone as the test compound, the relation of sediment suspension to fate of hydrophobic pollutants through adsorption is examined. Adsorption experiments show rapid attainment of an equilibrium condition that is a linear function of dissolved Kepone concentration and an inverse nonlinear function of adsorbing solids concentration. An apparatus creating a one‐dimensional distribution of suspended sediment over a sediment bed is used to experimentally simulate an estuarine tidal cycle during which the transfer of Kepone from the bed to water column is examined. A mathematical model of the adsorption and sediment resuspension process is used to analyze the experimental results. Resuspension and the variation of adsorption equilibrium with solids concentration are shown to be significant to the transfer. Adsorption kinetics are not significant because of the rapid approach to equilibrium.

The oxidation of a group of priority pollutants with different chemical structures and properties by the use of ferrate is studied. A comparison is made of the coagulation‐flocculation of the oxidized pollutants by ferrate with alum coagulation using the jar test. The efficiency of removal of the pollutants by simple air and mechanical (paddle) flocculation is also studied. The pollutants studied are Bromodicloromethane (BDCM), trichloroethylene (TCE), 1, 2‐dichlorobenzene (DCB), nitrobenzene (NB), and naphthalene (NAPH). It is shown that purification of water supply by coagulation with potassium ferrate and stripping with gas removes four out of five wastes listed as priority pollutants. Only nitrobenzene is unaffected. A mathematical model utilizing dipole momentum, solubility parameter and log activity coefficient predicts the efficiency of the process.

The results of the data collection program conducted by the New Orleans District of the U.S. Army Corps of Engineers in response to implementation of Section 404 of the Federal Water Pollution Control Act Amendment of 1972 and Section 103 of the Ocean Dumping Act are summarized. The results of data collection during maintenance dredging are presented. Dispersion studies conducted during cutterhead pipeline dredging, an ocean dumping operation, and agitation dredging are described, and the results are summarized. Specific conclusions reached as a result of each phase of the data collection program are presented, and it is generally concluded that the material dredged during these investigations did not present a hazardous waste disposal problem, as dilution was rapid and increased concentrations of pollutants were confined to the disposal area or mixing zone.

A simple mathematical model is presented for estimating nitrate‐nitrogen concentrations in percolation from sludge land application sites. The model is based on annual mass balances of sludge and soil inorganic nitrogen and includes the processes of mineralization, ammonia volatilization, crop uptake, and leaching. Most input parameters are readily obtained from published sources and standard sludge analyses. Default values are given for remaining parameters. Model predictions compared favorably with field measurements taken over three years in a previous study in Ocean County, New Jersey.

Fixed‐bed absorber dynamics have been predicted successfully using the homogeneous surface diffusion model (HSDM) for over 100 adsorbate‐adsorbent systems which include a number of the organics found in drinking water and wastewater treatment. User‐oriented solutions to the HSDM have been developed and can be used to: (1) Plan the scope of pilot‐plant studies; (2) interpret pilot‐scale test results; (3) investigate multistage absorber configurations; and (4) estimate preliminary costs for fixed‐bed adsorbers. This paper presents the model development and user‐oriented solutions for a batch reactor system. These are provided for the determination of the surface diffusion coefficient which is required for fixed‐bed predictions. A step‐by‐step procedure for the determination of the surface diffusion coefficient is presented and includes methods testing, statistical analysis, simplified algebraic equations which give quick and approximate representations to model solutions, and detailed examples for both fast and slow diffusion molecules.

The importance of sessile microbial populations in aquatic environments has been recognized for many years especially the heterotrophic slimes under polluted conditions. However, models proposed by previous researchers to predict substrate decay rates have been based on first order or Monod kinetic expressions describing substrate utilization by suspended biomass. The investigation carried out looks at two important aspects of organic carbon modeling in a shallow stream: (1) It compares the importance of suspended microbial populations to the biofilm community and (2) it determines the kinetics of organic carbon uptake rate by river biofilms using an artificial stream channel. The results confirmed the dominance of attached microbial films in removing organic carbon in a shallow turbulent river. The study provided the organic carbon uptake rate $\left(R_B\right)$ and the net scour rate $\left(R_D\right)$ for the biofilms while establishing the validity of first order kinetics in a specified range of substrate concentrations, flow velocity and temperature. Mathematical models were formulated and verified under steady state conditions for the organic carbon and biomass change below a sewage outfall in a selected river system.

A comprehensive wastewater treatment plant mathematical model is developed. The model includes primary sedimentation followed by a singlestage activated sludge system for both BOD reduction and nitrification. Primary and waste activated sludges are assumed to be mixed, chemicaly‐conditioned prior to vacuum filtration and the cake incinerated. Capital, materials, and operating and maintenance costs are utilized in arriving at a least cost system design. The sensitivity of the optimum design to selected values of various model constants and effluent constraints is evaluated to establish which variables most significantly affected system design.

Granular Activated Carbon (GAC) is an effective technique for removing synthetic organics from both ground and surface waters. Questions have been raised, however, over the cost of using GAC in this manner. In order to provide insight into these cost issues, the Drinking Water Research Division has developed a series of cost curves for various unit processes including those related to GAC. This paper presents a modification of these cost curves into continuous analytic equations. These equations can be used to estimated unit cost for various treatment configurations. Sensitivity analysis can be performed and design configurations listed. Regional options are explored using these equations as the basis for analysis.

Settling characteristics of coal ashes collected from TVA power plants are studied. Since the interface between a clarified zone and a suspension is not distinctly visible, a graphical method is developed to determine the settling velocity of the interface and to estimate the suspended solids concentration in effluent from a sedimentation basin. Effects of the initial suspended solids concentration and the types of ashes on settling are also examined. The types of ashes studied include fly ash collected by electrostatic precipitators, fly ash collected by cyclones, and bottom ash.

During a water quality survey of the Ganga and Yamuna of the Indogangetic plain, the assimilation of biochemical oxygen demand (BOD) after the waste outfalls at the urban centers along these rivers was found to be exceedingly fast. During the two‐stage BOD removal in these streams, the early reaches resulted from bioflocculation of waste colloidal matter with river water. It was found to follow a straight line law approximating a BOD rate constant (k) of as high values as 30 to $100{\mathrm{day}}^{-1}$ (base e) resulting in about 60% BOD removal in 30 min‐60 min. In the later reaches, the BOD removal was found to follow the usual first order kinetics with k ranging from 1.5 to $5.5{\mathrm{day}}^{-1}$ (base e) which are higher by an order of magnitude than the usual range of 0.2 to $0.5{\mathrm{day}}^{-1}$ (base e). The dissolved oxygen (DO), which dropped to low values after the waste outfalls, was also found to recover in short times showing extremely fast reaeration. Such BOD exertion and reaeration have been modelled. The integrated effect of several drains releasing at an urban center has also been included in the prediction of BOD and DO.

A method is developed for the optimal design of multisource, looped, gravity‐fed water distribution systems subjected to a single loading pattern. The method is based on linear programming (LP) techniques and produces a locally optimal solution. Initially, design feasibility constraints are derived to check whether network design and therefore network optimization is feasible. Based on classical transportation problem principles, a theory is developed to formulate an LP problem for obtaining design paths from the source nodes to the demand nodes and thereby for obtaining the design distribution graph for the entire distribution system. Separate LP optimization models are then formulated to deal with the either the D‐specified condition in which the nonprimary links are of some minimum or specified diameter, or the Q‐specified condition in which the nonprimary links carry some minimum or specified discharge. The proposed method is illustrated through a design example in an accompanying paper dealing with application. General comments and limitations of the proposed method are also provided therein.

Some residential canal networks may be designed to eliminate zones of poor circulation and to improve flushing by utilizing the parallel canal concept. Applicable in rivers and in bounded tidal waterbodies, the canal system must have two connections to the main flow and these must be separated by a sufficient distance to ensure unidirectional flow through the entire network. The Dynamic Estuary Model, with minor modifications, simulates water surface elevations and flow in a canal network and can assist the designer in predicting whether unidirectional flow will occur. Simulations of flow in the Intracoastal Waterway at a proposed canal site in Martin County, Florida, established boundary conditions that matched current measurements in the waterway. These boundary conditions were then applied to a numerical model of the waterway connected to the proposed canal network. Unidirectional flow was predicted by the hydrodynamic model, and the computed flows were used to estimate the advective transport of pollutants from the proposed canal system. The model could be used for further refinements of entrance channel and canal geometry, if necessary.

Estimates of the amount of pollutants which are carried by rivers from land sources to receiving water bodies are calculated from measurements of river flow rate and pollutant concentration. River flow can be measured frequently, but pollutant concentration will usually be sampled infrequently during the period of transport. This paper analyzes the strategy of sampling the pollutant concentration so that the errors in the transport estimates are minimal. In particular, strategies for event response rivers are considered. Sampling strategies for suspended sediment and total phosphorus in rivers located in western Ohio are presented.

Experiments were carried out to determine the effect of mechanical mixing on the oxygen transfer coefficient at a water surface. This phenomenon was examined by conducting 78 experiments with a flat‐bladed impeller in which the water depth, impeller diameter, impeller velocity and impeller submergence were varied over fairly wide ranges. All experiments were conducted at values of Reynolds numbers sufficiently large to assure a constant value of the power coefficient. The rotating impeller caused no deformation of the water surface. The experimental results were compatible with the results obtained from a dimensional analysis and a simple fluid mechanical model. It was found that the oxygen transfer coefficient is directly proportional to the angular velocity of the impeller and to the square of the impeller diameter. The transfer coefficient is increased when the submergence of the impeller below the water surface is reduced.

A method for predicting the amount of phosphorus required for activated sludge treatment of phosphorus deficient wastewater is presented. Operational parameters are related to sludge age to obtain a functional relationship that can be used by the operator in the day-to-day operation of a treatment system.