Journal of Environmental Engineering

A computer‐aided data acquisition system was developed for the generation of slurry filtration data. The system has some advantages over the traditional Buchner funnel apparatus, including: (1) Operation at pressure differences up to 200 psi (1.4 MPa); (2) a more desirable aspect ratio for the filtration vessel; (3) the ability to record filtrate volumes at intervals of 1 s or less; (4) improved accuracy and precision; (5) avoidance of the need for constant attention to data collection during filtration experiments; and (6) convenient computerized manipulation of data. The data acquisition system was used to investigate nonparabolic filtration behavior. The results show that nonparabolic filtration data are associated with filtration runs accompanied by sedimentation prior to filtration, sedimentation concomitant with filtration, or slurry‐media interactions. In many instances, nonparabolic filtrations can be redone to produce parabolic filtration data by applying pressure immediately following the introduction of the slurry into the filtration vessel, thickening the slurry prior to filtration to reduce the significance of sedimentation with respect to filtration, and choosing a different support medium.

A computer‐aided data acquisition system was used with three sludges, two chemical‐conditioning systems and nine support media to investigate the effect of slurry solids concentration on specific resistance, the effect of initial time and filtrate volume readings on filtration data, and factors affecting the precision and accuracy of specific resistance measurements. The results of the study show that: (1) The specific resistance of a flocculent slurry is a very strong function of suspended solids concentration at low concentrations and relatively independent of concentration at high values; (2) improper determinations of the onset of filtration or errors in filtrate volume measurements produce slurry filtration data that do not fit the standard model (nonsynchronous data); and (3) specific resistance values are not as accurate and translatable as they might be because of differences in methods used in different laboratories. Several suggestions for improving the translatability of specific resistance measurements are presented.

Predicted flux, or process rates, must be considered along with predicted state variables when calibrating or validating water quality models. Concentrating only on changes of state variables and ignoring predicted fluxes could result in the implementation of inappropriate management strategies. To illustrate this, the Corps of Engineers' one‐dimensional reservoir water quality model, CE‐QUAL‐R1, was calibrated using data collected at DeGray Lake, Arkansas. Initial predictions of dissolved oxygen, using coefficient values obtained from the literature, were not satisfactory. Evaluation of the flux predictions for oxygen showed which processes were most important in regulating dissolved oxygen, and showed those that were incorrect when compared to measured values. During the ensuing calibration simulations, as the flux predictions were brought more in line with measured values, the predictions of dissolved oxygen improved markedly.

A clear layer flow rising under inclined surfaces (particle‐free flow stratified on the suspension), which can be utilized for particle settling enhancement, has been theoretically analyzed in order to apply it to design and operation of high‐rate settlers in water and wastewater treatments. The flow proves to be driven by settling convection due to the density difference between the clear liquid and the suspension. A mathematical model for the flow simulation has been obtained by making use of the boundary layer approximation and the clear‐layer‐averaged inertia terms in the momentum equations. A dimensionless number, Γ, which controls the model and is given by the ratio of Grashof number, Gr, to Reynolds number, R, plays an important role in the flow. The flow velocity and the layer thickness predicted by the analytical solutions agree fairly well with previous experimental results observed in a batch settler to verify the analysis.

Various authorities and regulating agencies have set standards for deciding the suitability of a water for drinking purposes. These standards prescribe the permissible concentrations of quality variables. When some variables exceed the permissible levels, a decision for permitting further use of the water supply has to be based on the importance of those variables with exceeded concentrations. It is proposed that standards for a drinking water supply should be set through a single number representing the integrated effect of all the variables, keeping due regard to the importance of each variable. Such an integrated water quality index (WQI) would help in decision making. Models and curves have been presented to evolve a WQI for drinking water supplies. It is suggested that water with a WQI lower than 90 should not be permitted. The acceptable quality therefore, should be in the 90–100 range of the WQI.

Calcium sulfate solubility product and ion pair dissociation constant were measured in clean water, and these results were employed in tests with a pretreated coal conversion process wastewater to assess the tendency for organic matter in the wastewater to function as a complexing agent for calcium. It was demonstrated that wastewater organic matter interacted with calcium to form a calcium‐organic complex. The extent of this interaction in wastewater was as significant as that for formation of the ${\mathrm{CaSO}}_4^0$ ion pair in assessing solubility of ${\mathrm{CaS}}_4^0\text{.}$ It was shown that the organic matter complexed with calcium to an extent comparable to humic acid, and that the complexing strength was similar to that predicted for citrate when compared on an equivalent COD or TOC basis. The results of this study are important for evaluating CaS04 scaleforming reactions if wastewater is to be reused as makeup water to an evaporative cooling tower.

Buffalo Bayou, a major stream in Houston, Texas, was the subject of a detailed water quality study. The stream is heavily stressed by domestic waste loads and has shown significant degradation in water quality since 1970. Currently, the stream reaches critically low DO values through much of its length during low flow, high temperature periods. The $\mathrm{QUAL}‐{\mathrm{II}}_{\mathrm{TX}}$ model was calibrated, verified, and applied to simulate worst case conditions and to test a series of stream protection alternatives. A combined program of sewage plant regionalization, stream aeration, and flow augmentation was found to be the most cost‐effective solution.

This study was conducted to: (1) Evaluate the effect of DO on cell yield in a fixed film reactor using 1,000 mg/L sucrose as a substrate; (2) evaluate the correlations of the biofilm thickness and density with DO and their resultant substrate stabilization rates; and (3) examine the response of biofilm communities as a result of DO and biofilm thickness changes. Data obtained from this study indicate that DO has only a minor effect on the cell yield. However, the thickness of aerobic biofilm is definitely related to DO, or thickness $\left(\mathrm{mm}\right)=(2.08\times \mathrm{DO})/(9.2+\mathrm{DO})\text{.}$ The biofilm density is also related to its thickness. At a DO of 5 mg/L or lower, the biofilm texture is firm and has a wet density of $27-48\mathrm{mg}/{\mathrm{cm}}^3\text{.}$ At a higher DO (5–16 mg/L), the biofilm becomes porous and filled with air pockets, with its density being reduced to $25\mathrm{mg}/{\mathrm{cm}}^3\text{.}$ The biological community in biofilm at a high DO environment (16 mg/L) is predominantly short rods grouped in a chain structure. At a low DO environment (0.5 mg/L), however, the prevalent forms are large rods, none of which are in chain grouping.

Observations at Woods Lake‐watershed in the Adirondacks (New York) indicate that precipitation is further acidified by passage through coniferous canopies; conversely, passage through deciduous canopies has a net alkalizing effect. Both effects are dependent upon the levels of air quality. If the aerosol concentrations were to decrease to 35% of the current levels, both types of canopy would have a net alkalizing effect on incident precipitation. If the aerosol concentrations doubled, both canopy types would be net acidifiers of throughfall. The experimental procedure of varying aerosol concentration in an enclosed chamber may provide a means for measuring foliar exudation.

A multiple objective programming model of the Boston sludge disposal problem was formulated in which the objectives of net economic benefits, environmental impact, and variability of impacts were included. A generating technique was used to solve for the noninferior solutions. To reduce information overloading on the part of decision‐makers and redundancy among solutions, cluster analysis was used to prune the noninferior set of solutions.