Journal of Environmental Engineering

Any mechanism which creates turbulence at or near a water surface will tend to increase the rate of oxygen transfer across the surface. Mechanical mixing, wind action, and surface waves are examples of such mechanisms. On this basis, it seems apparent that rain falling on a body of water is another mechanism for the creation of surface turbulence. This phenomenon was examined by conducting 108 laboratory experiments. Test variables were rainfall rate, raindrop diameter and impact velocity, rotational velocity of a mixing impeller, and collector tank depth. From these experiments it was determined that the oxygen transfer coefficient is directly proportional to the power of the rainfall. It is concluded that heavy rainfalls over an extended period of time may contribute significantly to the overall oxygen balance in a body of water.

State controls on the disposal and utilization of municipal wastewater treatment sludge are cataloged and analyzed. Data gathered through reviews of documented state regulations and guidelines, and supplemented by contacts with state officials, is summarized for sludge landfilling, landspreading, distribution and marketing, thermal processing, ocean dumping, and lagoons/stockpiling. Results point to the states' track record of following federal leads in developing sludge management programs. State programs are noted to focus on the more common disposal and utilization practices of landfilling and landspreading, while other widely practiced operations, including distribution of marketing of sludge, remain largely uncontrolled.

Laboratory studies were conducted to investigate two assumptions of the hydrocarbon gas tracer technique for measurement of reaeration rate coefficients. First, the assumption of constant ratios between the mass transfer rate coefficients was examined by measuring the relative transfer rates of oxygen, ethylene, and propane in an open mixing tank at the temperatures of 4°, 20°, and 32° C. In agreement with previous studies, the ratios were found to be constant and equal to 1.14 for oxygen/ethylene and 1.36 for oxygen/propane. Second, the assumption that dissolved ethylene and propane are not adsorbed on suspended sediments was investigated using the batch equilibrium method with five soils. The tests showed negligible adsorptive losses. In addition, previous studies on relative gas transfer rates were reviewed to gain insight into the physical process.

The relationship between model formulation and dispersive transport is examined for lake water quality models. Two basic model types are identified: (1) The finite difference model (a continuum approach); and (2) the multiple‐box model (a discrete approach). Analysis of these two approaches indicates that the multiple‐box model formulation introduces substantial implicit dispersion as a consequence of its discrete structure. Due to this implicit dispersion, multiple‐box model exchange flow or dispersion parameters cannot be determined directly based on the hydrodynamics of the prototype lake—only calibration is a viable approach. A systematic procedure to construct and calibrate multiple‐box models that accounts for the model's implicit dispersion is presented.

A study of oil and grease in urban stormwaters was performed on a small watershed in Richmond, Calif., with the objective of determining the amount of oil and grease discharged into San Francisco Bay. Five sampling stations were selected at various places in the watershed that were indicative of specific land uses, and runoff from seven storms was sampled and analyzed. The results of the survey indicated that oil and grease concentration was highly dependent upon land use, ranging from 4.1 mg/L in residential areas to 15.3 mg/L in parking lots. A statistical analysis of oil and grease and storm characteristics showed that oil and grease concentration was independent of all storm characteristics, except that mass of oil and grease discharged was proportional to total rainfall. Qualitative analysis of the oil and grease by gas chromatography indicated that it most resembled used automobile crankcase oil. Several samples showed evidence of spills of specific compounds. A simulation of management techniques indicated that a 90% reduction in discharge from commercial properties and parking lots, which represented only 9.6% of the total surface area, would result in a 53% reduction in total oil and grease discharge. Growth simulation predicted a potential 27% increase in discharge if 5% of the watershed were converted from open land to commercial property.

The removal of dissolved organic carbon (DOC) by granular activated carbon (GAC) in a fixed‐bed adsorber was simulated using an approximate analytical solution and was found to agree satisfactorily with the performance observed at a full‐scale plant. Laboratory equilibrium isotherm studies were conducted to estimate the partition parameter and the nonadsorbable fraction of the organic matter. A modified linear isotherm model was found to fit the data acceptably. External and internal mass transfer parameters were based upon general correlations that have been widely applied in fixed‐bed modeling. A mass transfer model based upon the assumption of pore diffusion was utilized to describe the intraparticle transport. An estimation of the biodegradable fraction of DOC was based upon numerous case studies of the application of GAC for water and wastewater treatment. The applicability of this approach was confirmed with operating data from three full‐scale GAC adsorbers. The apparent diffusivities, both predicted and estimated from breakthrough data, were in the range of $6\times {10}^{-11}$ to $14\times {10}^{-11}\text{.}$

The history of phosphorus loading to, and efflux from, Onondaga Lake, New York, is presented for a 12‐yr period (1970–1981), during which several phosphorus management measures were taken. A ten‐fold reduction in phosphorus loading since 1970 has been achieved through implementation of reclamation measures, which included a ban on high phosphorus detergents and the addition of secondary and tertiary processes at the adjoining sewage treatment plant. Significant reductions in lake phytoplankton concentrations have not accompanied the reduction in phosphorus loading, indicating the lake remains nutrient‐saturated. An unusually high fraction of phosphorus received by the lake is retained, apparently as a result of enhanced phosphorus deposition associated with the industrial loading of calcium from an adjoining chloralkali manufacturer. One‐tenth of the reported substantial reduction in phosphorus loading to Lake Ontario from 1970–1979 is attributable to the reduction in loading to Onondaga Lake. The nature of the phosphorus associations in the lake's sediments indicates that sediment interactions should not act to compensate for further reductions in external phosphorus loading.

The efficiency of Giridih coal and crushed coconut shell in removing cadmium from solution was investigated in batch experiments after eliminating other sorbents in the initial screening tests. Both sorbents were found to adsorb cadmium from solution. The batch sorption kinetics and equilibria may be described by a first order reversible reaction and Freundlich isotherm respectively. The first order rate constant for forward and reverse reactions have been calculated for both sorbents. In order to establish the rate limiting step the pore and film diffusion coefficients were evaluated from the half time equations. Film diffusion appears to be rate limiting. The cadmium adsorption for both the sorbents was found to be a function of pH of the reaction mixture, which increased with pH increase up to pH 10. A decreasing trend in sorption was observed beyond pH 10. The mechanism of sorption in terms of electrostatic forces and chemical interactions has been indicated with the aid of zero point of charge $\left({\mathrm{pH}}_{\mathrm{zpc}}\right)\text{.}$

A one dimensional vertical model of water quality in reservoirs was developed, calibrated, and verified on the data available for the years 1978 and 1979 on Grangent reservoir in France. The model was subsequently used for the study of the influence of outlet location on both reservoir and outflow water quality. Three different outlet locations were considered on the Grangent reservoir, as well as various conditions in inflow water quality, reservoir size and reservoir operation. The model proved to be an efficient tool, both at the cognitive and the predictive level.

Relationships to estimate confidence intervals for linear regressions were presented to determine the uncertainty of estimates obtained from firstorder models, when the concentration in grab samples of the parameter studied has a lognormal distribution. This uncertainty is a function of the number of samples on which the model was calibrated, the locations where these samples were taken, and the variance of the grab sample. Also shown is an estimate of the probability that the true value of the predicted parameter lies above a given critical value, even though its estimate is below that value. This probability can be used as a criterion to determine if the model's results are adequate for the modeler's purposes, or to estimate how many additional samples are required to reduce this probability to levels that are acceptable, or both. As a consequence, sampling, modeling, and decision making based on the model's output is presented as one cycle within an iterative process.

This theory emphasizes diffusion resistance to mass transfer in the floc particles and biopolymer production from recycled bacterial protoplasm. The diffusive effectiveness factor is a simple function of sludge age and hydraulic residence time. The diameters and settling velocities of the floc particles are predicted. Specific bacterial respiration rate, specific soluble substrate as‐similation rate, and floc settling velocity data from the literature are correlated by the theory.

Clearing and snagging is used as an economical technique for reducing the frequency and duration of high frequency flooding in environmentally sensitive locations. Riparian vegetation and the organic debris it produces influence stream morphology, water quality, and aquatic and terrestrial ecosystems. Complete clearing and snagging has detrimental effects on these stream characteristics. Modified clearing and snagging is less damaging to the environment. Major modifications involve: (1) Selective removal and disposal of trees and snags based on size, location, condition, and habitat value; (2) labor intensive construction techniques; (3) access controls; and (4) work scheduling to avoid fish spawning or other environmentally sensitive periods. Guidelines for modified clearing and snagging are discussed, and analytical approaches to estimating effects of vegetation and snags on flow resistance are reviewed.

The reliability of river‐treatment plant systems is determined by considering fluctuations in both the streamflow rate and waste loading rate. The method involves an application of the elementary theory of hydrologic statistics and waste assimilation models to the cumulative density functions of the flow rates and loading rates. The products of the method are the expected number of system failures per drought, the interval between failures and the annual return period of droughts containing at least one systems failure. It is shown that the usual methods based on rare drought flows (e.g., the seven‐day average flow with a 10‐yr return period) cannot provide this information. Also, designs based on rare drought flows are not conformable to stream standards, whereas designs based on the proposed method are intrinsically conformable to stream standards.

The development of an empirical equation for description of the distribution of flocculent solids in quiescent settling columns is described. The equation is predicated on observations made in the course of concentrationdepth‐time analyses of settling data for flocculent and nonflocculent solids in quiescent and agitated settling columns. The validity of the equation is verified by its application to ten different quiescent flocculent settling studies involving several sewages and natural lake and river suspensions.

A refined version of an ecologic and water quality mathematical model is applied to a small Atlantic coast estuarine network. The temporal and spatial variations in the water quality of the system are examined through the analysis of the nitrogen cycle developed for estuarine environments. The model is based on the mass conservation of elemental nitrogen in its various biotic and abiotic states. The ecologic model structure contains two trophic levels: primary producers, and herbivorous copepods. A concerted effort is made to derive realistic model‐governing transformations and rate parameters. The hydrodynamic and water quality model simulations are calibrated and verified using short‐term, transient data gathered in the Manasquan Estuary and Point Pleasant Canal. Model verification for abiotic constituents of the nitrogen cycle is achieved, with biotic constituent verification needing more detailed field data. Model results show the influence of transport processes on the temporal and spatial distribution of nitrogen‐cycle constituents in the network examined.

Attempts by various local, state, and federal agencies to quantify the degree of emission reductions in Los Angeles, California needed to attain the federal ozone standard have recently been extended to include the use of sophisticated air pollution simulation models. In particular, the Systems Applications Airshed Model—a grid‐based, time‐dependent photochemical simulation model—has been applied to the region in recent air management studies. After initial model verification analysis using field measurements obtained during an historical smog episode in southern California, the model was used to evaluate the impacts on future ozone levels of alternative emission controls for principal ozone precursors i.e., reactive organic gases and oxides of nitrogen. Modeling results exemplify the highly nonlinear characteristics of hydrocarbon nitrogen oxides/ozone cycles in the atmosphere and the inherent difficulties in ameliorating the Los Angeles smog problem within federally mandated timetables.

Factors that influence the adsorption of cadmium on aerobic lake sediments were investigated, including sediment type, pH, and soluble ligand composition. Conditional adsorption constants were experimentally determined for sediments samples in native lake water from Sturgeon Lake, Oregon. Correlation of adsorption constant values with sediment characteristics including mean grain size, iron and manganese content, volatile solids content, and cation exchange capacity indicated significant dependence only on mean grain size. Another approach, using specific geochemical phase adsorption constants from another study to assess that phase's contribution to adsorption, predicted that iron oxides controlled cadmium adsorption. A speciation‐distribution model for cadmium in the water column indicated that the dominant chemical forms were the free cadmium ion and cadmium adsorbed to suspended solids. As pH increased from 5 to 9, the adsorbed fraction increased and the free ionic fraction decreased markedly. Organic ligand complexes were predicted to be the dominant soluble cadmium complex in the neutral pH range, while the cadmium carbonate complex dominated at pH 9.

Expressions for the coordinates of a critical point, occurring along a given lateral boundary of a limited use zone within a mixing zone below a bank outfall in a river channel, are developed. A family of curves is developed for a range of dimensionless coordinates of the critical point. An expression for allowable effluent concentration of a pollutant is obtained in terms of critical concentration and water quality criterion. A graphical procedure for determining the longitudinal boundary of a limited use zone is described. The predictions of the critical point method are validated using total residual chlorine distribution data from a natural stream. The application of the methodology is outlined in a step‐by‐step design procedure and illustrated by an example for ammonia. In general, the method is applicable to exponentially decaying nonconservative pollutants.

Pre‐or simultaneous precipitation combined with contact filtration for final treatment is an excellent method to achieve low phosphorus residuals in waste‐water discharges to lakes. The two dosing steps are optimized to allow for low chemical use and sufficiently long filter runs. If an Fe/P dissolvedratio of about 2.0 is used in the first step, the Fe(III)‐dosage to the second step may be kept below $4\mathrm{gFe}\left(\mathrm{III}\right)/m^3\text{.}$ This allows the precipitates together with the solids from the secondary clarifier to be removed in multi‐media filters. The unfavorable filtering characteristics of the precipitates may be improved by dosing filter aids. In laboratory scale experiments low concentrations of nonionic polyacrylic polymers with high molecular weight showed best filter performance. Under optimized conditions with respect to precipitant and filter aid dosage, a full‐scale treatment plant was investigated. Consistent low phosphorus residuals at $0.1-0.2gP/m^3$ was reached at mean filtration rates of $7.4m/h$ and average filter runs of 20 hr.

A design velocity was determined to prevent disease-bearing snails from inhabiting irrigation canals. In tropical irrigation systems many people in the argicultural community are infected with a parasitic disease spread by aquatic snails living in the canals and reservoirs. The disease, bilharzia (schistosomiasis) can have a serious impact on agricultural productivity as well as being a general health problem, thus it is of concern to engineers and agricultural planners. High flow velocities have been suggested as a means of eliminating snails from canals, thus data from existing canals were collected to verify predictions made from hydrodynamic considerations. A study of the Patillas Irrigation Canal in Puerto Rico showed that populations of the local bilharzia snail Biomphalaria glabrata, would be overpowered by mean water velocities greater than 2 ft/s (0.6 m/s), the velocity at which the compulsive forward motion of the snail against the current was halted. This confirmed theoretical calculations for the canals of this size.

Septic tanks are used in rural areas to settle solids from wastewater, provide for some anaerobic digestion, and store the undigested solids. The accumulated solids must be pumped out periodically. The frequency of septic tank pumping can be estimated for any given tank and household size by estimating the per capita volume and solids loading rates, the trapping efficiency, percent solids digested, percent solids in sludge, and the liquid detention time. Estimated septic tank pumping frequencies are calculated by using average values reported in the literature.

The effects of temperature on the rheology of five municipal wastewater sludges was examined using a Stormer rotational viscometer. The sludges had total solids concentrations ranging from 2.0 percent to 6.6 percent by weight. The temperatures utilized were 10°C, 15°C, 20°C, and 25°C. Two types of non-Newtonian models, the Bingham plastic and the pseudoplastic, were used in the analysis. The results demonstrate that temperature has a significant effect on the viscosity of wastewater sludges. The apparent viscosity of the plastic and pseudoplastic models were found to vary with temperature in a fashion analogous to the viscosity of Newtonian fluids. The yield stress and consistency index both vary exponentially with temperature. The coefficient of rigidity for the plastic model and the flow behavior index for the pseudoplastic model were found to be essentially independent of temperature.

At water treatment plants which practice coagulation using alum, alkalinity in the form of lime (Ca(OH)₂) is almost always added either prior to dosing with alum (pre-liming) or after (post-liming). Most water works which use alum in Nigeria practice post-liming. Some problems have been observed to be associated with this mode of operation; namely, corrosive (low pH) water continuously passes through the slow mix, sedimentation and filter units and tends to shorten their service lives, and lime sludge is deposited in the clear well or underground storage tank where its removal poses health problems. Laboratory studies relating to alkalinity consumption and turbidity removal show that although post-liming consumes more lime than pre-liming, the latter enhances settleability, thus reducing required detention time. Pre-liming may thus translate into savings in capital or operational costs or both, in addition to eliminating unsanitary conditions in underground storage tanks.