Journal of Environmental Engineering

Tetrachloroethylene has been used in the manufacture of vinyl‐lined asbestos cement pipe installed in water distribution systems in certain New England communities. Tetrachloroethylene was used as a solvent for Piccotex, a vinyl‐toluene α‐methyl styrene co‐polymer, which was then sprayed on the interior of the finished asbestos cement pipe. The migration of tetrachloroethylene through the vinyl lining was modeled as a diffusive process in which the diffusion coefficient was an exponential function of concentration. The parameters of the model were found by fitting a numerical solution of the diffusion equation to data from laboratory experiments involving the evaporation of tetrachloroethylene from a Piccotex layer. The conclusion was reached that significant quantities of tetrachloroethylene may be leached into the water supply for a time period on the order of years.

Zone settling data can generally be linearized with solids concentration when the logarithm of the settling velocity is plotted as a function of either the concentration or the logarithm of the concentration. The resulting mathematical expressions were used to develop two generalized dimensionless solutions that describe the steady‐state performance of thickeners. Graphical solutions of these models were also developed. These solutions could be used for controlling the performance of a thickener operating under transient conditions.

The use of probability models derived from a long‐term (30 yr) color record forms an approach of forecasting raw water color and assigning an alum dose for treatment of surface waters. Three probabilistic models are developed which incorporate the uncertainties associated with forecasting raw water color and alum dose. These forecasts are based upon the risk or probability associated with underdosing. The effect of seasonal and daily color variation is incorporated into one time series model. In the other time series model, daily color variation is considered exclusively. All models are compared for treatment performance. The methods of model identification, parameter estimation, and forecasting are presented for each model. The results indicate that the two time series models are feasible methods because they lead to the judicious use of alum without excessive overdosing.

The partially‐mixed or dispersed‐flow equation is proposed for use in pond design for organic and bacterial reductions. This equation considers the effects of hydraulic detention time (θ), reaction rate coefficients, and the dispersion factor including short‐circuiting, and other hydraulic transport processes which influence the pond's performance. Some hydraulic models of dispersion were reviewed. A dispersion prediction formula for ponds is proposed which relates the value of the dispersion number to θ, kinematic viscosity, and the pond's geometric shape, i.e., length, width, and depth.

A biological treatability study by activated algae process was performed with synthetic wastewater containing a high concentration of nitrogen. It was found that the wastewater could be processed at all nitrogen removal rates. The yield coefficient and decay coefficient for heterotrophic bacteria were 0.06 (COD basis) and $0.019{\mathrm{day}}^{-1}$ (COD bases) respectively. The yield coefficient and decay coefficient for nitrifiers were 0.06 and $0.02{\mathrm{day}}^{-1}$ respectively. ${\mathrm{NH}}_{4-}^{+}N$ seemed to inhibit bacteriological growth as the yield coefficients values were significantly lower. Nitrification was observed at all the nitrogen loadings. Diffusion of ${\mathrm{NH}}_3$ into the atmosphere was the dominant mechanism of nitrogen removal. The results demonstrated a symbiotic relationship between algae and bacteria.

Oxygen transfer tests were conducted on surface rotor aerators installed in a plant scale oxidation ditch. The effects of rotor rotational speed on the standard oxygen transfer rate, the net power input, and the standard aeration efficiency are presented. Initial nonuniform distribution of deoxygenating chemical in a circulating tank can result in poorly behaved data. The circulation pattern in an oxidation ditch is accurately modeled by the first order oxygen transfer rate equations applied to a completely mixed batch reactor. Oxygen transfer rates estimated by the nonlinear regression and best fit log deficit methods of data analysis vary less than $\pm 10\%\text{,}$ and the results of the two analytical methods are identical for practical purposes. A rotor cover which restricts the spray pattern of the rotor can result in increased oxygen transfer rates at the expense of an increase in power and a decrease in ditch flow velocity.

Residence time has been the traditional indicator of the ability of primary and secondary clarifiers in wastewater treatment plants to remove pollutants from the waste stream. The steady-state definition of residence time used in these applications has also been applied to stormwater detention basins in which the flows are unsteady. A computer simulator is used to show that theoretical residence in basins receiving unsteady flows can deviate significantly from the steady state values.