Journal of Environmental Engineering

The effects of temperature, pH, sludge age in the prior activated sludge process, initial sludge solids concentration, and sludge type on the rate of solids degradation during aerobic sludge stabilization are discussed. Primary sludge (PS), waste activated sludge (WAS), and mixed primary and waste activated sludges (PS/WAS) are stabilized. The results indicate that: (1) First‐order kinetics satisfactorily describe biodegradable volatile solids (BVS) degradation for WAS and mixed PS/WAS, but not for PS; (2) the BVS decay coefficient b increases with increasing temperatures between 10 to 30 °C with a thermal coefficient of 1.097; (3) b values decrease as the sludge age in the prior activated sludge process increases; (4) b values are higher at reactor pH values $⩾6.5;$ and (5) b values tend to decrease as the initial VS concentration of the sludge increases. The WAS has an initial BVS and refractory volatile solids (RVS) content of 44–67% and 33–56%, respectively; the mixed PS/WAS has a content of 33–40% and 60–67%, respectively; and the PS has a content of 74–91% and 9–26% respectively. The WAS has less biodegradable solids and a greater percent of residual refractory volatile solids requiring disposal than does the PS.

Numerical simulations were performed that examined the utilization of inhibitory substrates by steady‐state biofilms. Based on kinetic and energetic constraints, the growth of a monolayer of cells into a steady‐state biofilm requires that substrate concentrations be between $S_{\min }$ and $S_{\max }\text{.}$ The continued exposure of a monolayer or dispersed cells to substrate concentrations less than $S_{\min }$ or greater than $S_{\max }$ will not lead to the development of a self‐perpetuating biological treatment process. However, once developed, a steady‐state biofilm can tolerate bulk substrate concentrations greater than $S_{\max }\text{,}$ because the inner layers of the biofilm are exposed to substrate concentrations less than $S_{\max }$ due to mass transport resistance and substrate utilization in the outer layers of the biofilm. In such situations, maximal rates of substrate utilization and microbial growth occur in the middle or at the inner surface of the steady‐state biofilm. The simulations also indicated that there are two sets of steady‐state biofilms: one associated with $S_{\min }$ (stable steady‐state solutions) and the other associated with $S_{\max }$ (unstable steady‐state solutions).

A model is developed to describe mass transport resistance through a concentration boundary layer associated with an algal biofilm. This model is solved simultaneously with a model for attached algal growth subject to inorganic carbon limitation. The profile of inorganic carbon species through the boundary layer is found to be nonlinear due to the interaction of inorganic carbon speciation and pH. As ${\mathrm{CO}}_2$ is utilized by the algae, the pH in the biofilm increases, causing a pH gradient across the boundary layer. This pH increase across the boundary layer causes a corresponding shift of inorganic carbon species away from ${\mathrm{CO}}_2\text{,}$ which is the form utilized by the algae. As a result of this nonlinear interaction with pH, there is an especially significant decrease in the flux of inorganic carbon into the biofilm, and thus in biofilm growth, as the boundary layer increases in thickness. These results show that models that assume constant pH will overpredict the flux of inorganic carbon. Biofilm thickness is important in determining the impact of the boundary layer. Very thin biofilms that are fully penetrated with ${\mathrm{CO}}_2$ are not sensitive to boundary layer thickness. As the biofilm thickness increases, sensitivity to the boundary layer thickness increases, until the flux reaches the maximum possible $\left(J_{\max }\right)$ and becomes independent of biofilm thickness. The magnitude of the effect is dependent on a complex interaction of bulk pH, bulk inorganic carbon concentration, and alkalinity.

Ozone pretreatment studies of a refractory phenolic compound, ocresol, were conducted to evaluate the effects of ozonation on the anaerobic biodegradability and toxicity of the reaction products. Two types of batch studies, the biochemical methane potential (BMP) and the anaerobic toxicity assay (ATA), were performed on samples with and without preozonation. The ozonation products were well fermentable to methane after about 60% reduction in chemical oxygen demand (COD) or 32% reduction in dissolved organic carbon (DOC) was achieved by ozonation regardless of the initial concentration of o‐cresol. Salicylic acid, glyoxylic acid, oxalic acid, propionic acid, acetic acid, and formic acid were the oxidation products identified. The reaction products formed in the basic pH range were more biodegradable and less inhibitory than those formed in the acid pH range. Phenol degradation was more susceptible to inhibition caused by ozonation products than was acetate utilization.

The extracellular organic matter (EOM) released by laboratory algal monocultures of Chlorella was characterized in terms of its molecular weight distribution and its electrical charge concentration, and was found to compare well with the dissolved carbon found in natural algal‐rich impoundments. Reaction between EOM and cationic polymer was demonstrated, with concomitant turbidity development. A simple turbidimetric procedure for rapid estimation of the cationic polymer demand exerted by the EOM is proposed. The significance of this EOM demand was demonstrated in a series of direct filtration experiments with algal suspension. When just enough cationic polymer was added to quench the EOM demand, no polymer was available to flocculate the algal cells and cell removal was poor. If more polymer was added, the polymer that remained after reaction with the EOM did cause flocculation of the algal cells with improved removal. On an equal mass basis, a cationic polymer with higher charge density did better than a polymer with lower charge density. The qualitative effects of a prolonged mixing step between polymer addition and filtration were observed.

Wet air oxidation is ideally suited to liquid wastes which are too dilute to be incinerated and too refractory to be handled by chemical or biological oxidation. This process relies on high temperature (470°–600° K) and pressure (2–20 mPa) conditions for oxidation of the organic substances by molecular oxygen in the liquid phase. Several types of industrial wastes, mainly paper‐mill black liquors, biological sludges, and acidic organic wastes, have been tested for oxidation in a batch reactor. This research provides evidence for the high efficiency of the wet air oxidation process for the transformation of most of the pollutants to carbon dioxide. An average removal efficiency of 98% was obtained. As acetic acid is the main intermediate appearing during oxidation of the heavier organics, the study of the behavior of sodium acetate under treatment conditions enabled the most efficient oxidation conditions to be determined for numerous wastes. The various data available are compiled in a general chart which makes a quick determination of the working conditions possible for any indexed waste. Moreover, it has been established that a continuous process usually leads to a net production of energy. It is believed that this research is the first step in the design of a large‐scale wet air oxidation unit.

A manganese‐laden seep from a reclaimed strip‐mined area in north Alabama was successfully treated on a small‐scale basis using packed column technology. Manganese concentrations were reduced from about 10 mg/L to below 2 mg/L to meet Alabama discharge standards. The process looks very promising as a new manganese treatment method. The three columns developed during this research used chert, sandstone, and glass marbles as packing material. The olumns were either four or six feet tall and hydraulically loaded at about $5.4m^3/\sec \mathrm{per}100\text{,}000M^2\text{.}$ The mass loading with a dissolved manganese concentration of 9 mg/L was about 0.24 mg/min. The pH of the seep water ranged from 5.8 to 6.3. The columns were operated in a submerged, upflowing manner at temperatures between 20° and 30 °C. The acclimation of the columns required eight weeks using seed from a river having manganese oxidizing slimes on the stream‐bed stones.

The effect of varying the time of particle injection within pulse periods, called the pulse injection time, in active‐pulse air classification is examined. A mathematical model based on a fluid mechanical force balance is used to study the behavior of spheres injected at different pulse times into a periodic, time‐varying, incompressible air flow, and the results are related to laboratory results of active‐pulse air classification experiments. Pulse injection time is found to affect the forces governing particle movement and particle separation. The results of theoretical modeling suggest that synchronizing feed inputs with pulse time can result in increased separation efficiency. A sawtoothed wave form airflow with a decay fraction equal to 0.1 is found to separate the particles studied most effectively over the full range of varying pulse injection times. Laboratory results, confined only to the measurement of particle drop times, are consistent with the mathematical predictions.

An event‐based computer model, GRAPH, was developed to simulate phosphorus (P) transport in grass buffer strips (GBS) by incorporating submodels into SEDIMOT II, a stormwater and sediment transport model developed for strip mine reclamation. GRAPH considers the effects of advection processes, infiltration, biological uptake, P desorption from the land surface to runoff, adsorption of dissolved P to suspended solids in runoff, and the effects of changes in sediment size distribution on P transport. Required input data include: rainfall intensity and duration, an inflow hydrograph, a sediment graph, sediment size distribution, GBS dimensions and hydraulic characteristics, inflow graphs for dissolved P, P desorption and adsorption reaction coefficients for soil and plant matter, and the P content of each soil particle size class. GRAPH simulates time varying infiltration, runoff discharge, sediment yield, particle size distribution, and dissolved and sedimentbound P discharge along with sediment and P trapping efficiencies in GBS. GRAPH was verified using data from experimental field plots. Model predictions and observed P transport in the GBS compared favorably.

A submerged fabric dam was constructed underwater across the mouth of a small cove in a large reservoir. The dam trapped cool hypolimnetic water in the spring and prevented it from being withdrawn for hydropower releases throughout the summer. A liquid oxygen aeration system aerated the water trapped behind the dam. The purpose of the dam and aeration system was to provide an artificial refuge for striped bass. The bass have historically suffered in summer months from unsuitable dissolved oxygen (DO) and temperature conditions in the reservoir. The dam has promise for providing different aquatic conditions in portions of a large reservoir compared to the main reservoir body. Such dams, therefore, might be used to provide optimal conditions for both warmwater and coldwater species in the same reservoir. They could also provide an inexpensive alternative to aeration of an entire reservoir or changes in reservoir operation to furnish the desired aquatic conditions. Such dams, on a scale larger than described here, might also be used to allow hydropower projects to release cooler water later in the summer. Cooling the releases from a reservoir in warm months could help maintain a coldwater fishery in the tailwater and reduce stress on migrating fish such as salmon.

Incinerator ash produced due to mass burning of MSW may have significantly high concentration of water leachable constituents and may be classified as hazardous. A detailed waste characterization program undertaken for a MSW incinerator ash is included. Detailed chemical characterization indicate that incinerator ash may be classified as hazardous and does contain water leachable constituents that may impact groundwater. Both physical and chemical characteristics of the incinerator ash are reported.

In this study an equation of iso-percentage curves as a function of settling time and depth is developed which is applicable both to discrete and flocculent suspensions. Using this model, an expression for the solids removal ratio of quiescent settling suspensions is obtained. Results of the proposed expression are found to be in good agreement for most cases when predicted and reported solids removal ratios are compared. Observed differences are interpreted as results of manual interpolation of iso-percentage curves and as assumptions made in graphical evaluations of solids removal efficiencies in the literature. It is concluded that the presented expression can be used as a numerical approach in the evaluation of ideal settling column test results of suspensions.

Harmonic mean conductivity equations for deep bed filters are developed. Differences between harmonic mean conductivity and hydraulic conductivity based on arithmetic average of specific deposit are explained.