Journal of Environmental Engineering

A mathematical model of carbon fluxes through the heterotrophic microbial food web is developed from a synthesis of laboratory and field research. The basis of the model is the segregation of organic carbon into lability classes that are defined by bioassay experiments. Bacteria, phytoplankton, three trophic levels of zooplankton, and dissolved organic carbon (DOC) and particulate organic carbon (POC) are modeled. The descriptions of bacterial growth and utilization of the various classes of substrate were treated as “universal constants” in the application of the model to three distinct ecosystems, ranging from oligotrophic to highly eutrophic. The successful application of the model to these diverse ecosystems supports the basic validity of the description of the microbial food web and the dynamics of carbon flux. The model indicates that the dynamics of bacteria and protozoan zooplankton production govern the rates of oxidation of carbon entering the water column. Explicit consideration of these groups would improve the capability of eutrophication models to predict dissolved oxygen dynamics, particularly when projecting responses to loading changes.

There has been concern over the eutrophication in Lake Pepin in recent years, particularly following algal blooms and fish kills in 1988. Currently, the Metropolitan Wastewater Treatment Plant is the largest point source of phosphorus above the lake. In this study, the Environmental Protection Agency's EUTRO5 model was used to evaluate phosphorus control alternatives at the Metro Plant, using data from 1988, 1990, and 1991. Model results indicate that under summer low-flow conditions, the most optimistic improvement in Lake Pepin water quality would be to reduce the average chlorophyll a levels from 60 μg/L to 50 μg/L, still well above the goal of 30 μg/L. Chlorophyll a reductions are not expected under higher summer flow conditions such as those encountered in 1990 and 1991.

The retention and release of lead from eight different soils collected from the eastern United States were investigated. After characterization using well-established test procedures, the study soils were artificially contaminated with lead. Upon contamination, the lead-retention capacity of the study soils was statistically correlated with their physical and chemical properties. Lead capacity of the eight study soils was best correlated with the parameters of soil pH and the organic soil fraction. The efficiencies of six washing solutions in removing lead from the contaminated soils were then investigated via batch washing experiments. Unlike conventional field-scale soil washing, all particle size fractions were washed and recovered in these bench-scale experiments. HCl and EDTA obtained the best Pb-removal efficiencies. Removals tended to be independent of soil type and washing solution concentration. In addition to the physical/chemical properties of the washing solutions and of the study soils, the effects of the initial lead contamination level and washing solution concentration upon lead removals were examined. Lead-retention and release kinetic studies were performed to confirm equilibration between the aqueous and solid phases. Kinetics of both lead retention and release were very rapid for most study soils.

Prepared biomass from two Gram-negative and one Gram-positive bacterial strains was examined for single, binary, and quaternary mixtures of polyvalent metal cation binding to cell surfaces. The biosorption of ₂₄ Cr ³⁺ , ₂₇ Co ²⁺ , ₂₈ Ni ²⁺ , and ₂₉ Cu ²⁺ for each bacterial cell type was evaluated using a batch equilibrium method. The binding of each metal by all three bacterial cells could be described by the Freundlich sorption model. The isotherm binding constants suggest that E. coli cells are the most efficient at binding copper, chromium, and nickel; and M. luteus adsorbs cobalt most efficiently. The K -values for copper bound to P. aeruginosa and E. coli are >2-fold and >8-fold greater, respectively, than previously reported for intact cells. The general metal-affinity series observed was Cr ³⁺ > Cu ²⁺ > Ni ²⁺ > Co ²⁺ . There was a marked lower affinity of all biosorbents for Co ²⁺ and Ni ²⁺ . M. luteus and E. coli had a strong preference for Co ²⁺ over Ni ²⁺ . Metal-binding enhancement could be ascribed to increased cell barrier surface porosity to metal-bearing solutions.

This study primarily investigates the role of competition in completely mixed anaerobic granular activated carbon (GAC) reactors treating a synthetic wastewater consisting of acetic acid, phenol, and o -cresol, and also addresses dual substrate biodegradation. The fate of the biodegradable nonadsorbable substrate followed very closely that of the biodegradable adsorbable substrate. As adsorption complemented biodegradation in this system, with the two being oppositely influenced by the GAC replacement rate, the removal of both biodegradable substrates exhibited both a maximum and minimum at GAC residence times of 30 and 12 days, respectively. On comparing the experimental capacities for o -cresol, which resisted biodegradation in the GAC reactors, with the o -cresol isotherm capacities, the effect of phenol competition for adsorption was found to be negligible when the effluent o -cresol concentrations were orders of magnitude higher than the concentrations of the biodegradable phenol. Competition effects decreased the adsorptive capacities of the reactors' GAC for o -cresol when phenol and o -cresol concentrations were of the same order of magnitude, although phenol sorptive capacities were predicted much more closely than at very low phenol concentration. The ideal adsorbed solution theory (IAST) was found to fairly describe the competition for adsorption between phenol and o -cresol despite some discrepancies between the experimental and the model-predicted capacities at low adsorbate concentrations.

The conventional practice for an anoxic denitrification basin has been to minimize oxygen input on the basis that it is detrimental to the process. For existing secondary treatment systems, allotting 25–35% of the aeration volume for an unaerated anoxic zone will significantly reduce plant capacity. Further, a group has held that bulking sludge control is best achieved by eliminating all forms of oxygen, including nitrates, from the initial contact or biological selector zones. The 6.75 m ³ /s Phoenix 91st Avenue wastewater-treatment plant (WWTP) was designed with nitrate recycle to the selector zones for bulking sludge control and the anoxic zones were provided with fine-bubble diffusers to increase oxidation capacity while simultaneously removing the recycled nitrates. This paper provides the process, design rationale, plant-layout features, plant modifications to existing structures, and the operating results for the facility. The successful performance of the 1.3 m ³ /s prototype plant resulted in the initiation of the design for conversion of the other four plants, totaling 5.4 m ³ /s capacity, to the aerated anoxic design.

Although the conventional gas collection and measurement system using the principle of brine water displacement is simple, it encounters a gradual pressure buildup during each cycle of gas monitoring. A novel design has been developed to modify the conventional method, so that during each gas collection cycle there is no pressure change inside the biological reactor. The use of this new device in a four-stage anaerobic rotating biological contactor (RBC) research has proved its effectiveness in maintaining a constant pressure throughout the four stages.

Titanium dioxide (TiO ₂ ) sedimentation, enhanced through charge neutralization and coagulation/flocculation with metal salts and polymers, was investigated to evaluate the potential for its recovery from the effluents of suspended photocatalyst reactors. The application emphasizes reuse of the TiO ₂ after separation from the reactor effluent. Zeta-potential analysis showed that the zero point of charge (ZPC) of TiO ₂ suspensions was at pH 2.5, and settling rates for the photocatalyst were greatest at ±0.5 pH unit of the ZPC. Aluminum sulfate, ferric chloride, and ferrous sulfate were effective in enhancing TiO ₂ sedimentation through coagulating and flocculating the dispersed TiO ₂ catalyst at neutral pH. However, two cationic polymers and one anionic polymer were effective in enhancing TiO ₂ sedimentation only at pH 3. Using 1,2-bis(2-chloroethoxy)ethane as a photocatalytic substrate, ferrous sulfate-coagulated TiO ₂ and acid-precipitated TiO ₂ had the highest rates of photocatalytic activity after sedimentation.

The objective of this research was to measure capture efficiency of local exhaust hoods used to control vapor degreasing tanks during normal operations and to compare the observed capture efficiencies to the American Conference of Governmental Industrial Hygienists (ACGIH) design criteria. Solvent emission rates and local exhaust hood capture efficiencies were measured at 15 vapor degreasers. The degreasers were located in 12 private industrial settings and studied under normal operating conditions. Where possible, hourly concentration data were collected during two 8-h shifts for each degreaser. Site-average fugitive emissions to the workspace (mean = 0.173 g/m²/s, range = 0.001–1.08 g/m²/s) were in excellent agreement with previously reported tests for vapor degreasers under operating conditions. The ACGIH recommended flow of 0.25 m³/s/m² (50 cu ft/min/sq ft) of tank surface appears to be adequate for some conditions but inadequate for other conditions. An increase in flow, above design recommendations, did not necessarily improve hood performance. Hood capture efficiency was slightly correlated with hood face velocity, although there is significant variability in the data. Emissions of solvent to the workspace were only slightly correlated with duct emissions. This suggests that fugitive emissions are as strongly related to work practices as they are to control device design.

The purpose of this paper is to illustrate the applicability of the Reactive mass-exchange (REAMEN) synthesis methodology in designing cost-effective desulfurization systems for synthetic-fuel plants. The REAMEN design technique provides a systematic framework to simultaneously screen several potentially applicable technologies and separating agents and identify the most cost-effective solution for a given waste-minimization task. It is based on developing mass-exchange pinch diagrams for the process. These diagrams can be employed to identify the type and flow rate of optimal mass-separating agents. A case study using the REAMEN framework for the desulfurization of gaseous emissions for a coal-liquefaction plant is presented in this paper. The optimal desulfurization network features one mass-exchange operation (absorption) utilizing both a physical solvent (water) and a reactive solvent (diethanolamine).

The upflow anaerobic sludge blanket (UASB) process removed 97–99% of soluble chemical oxygen demand (COD) from wastewater containing concentrated benzoate at 37°C, pH 7.5, a hydraulic retention time of 9.8 h, and loading rates up to 30.6 g-COD/(L$\dot{s}$day) based on the reactor volume. About 95.2% of the total COD removed was converted to methane; 0.034 g of volatile suspended solids (VSS) was yielded for each gram of COD removed. The highly settleable granules were 1–3 mm in size with a layered microstructure and were composed in abundance of bacteria resembling the benzoate-degrading Syntrophus buswellii . Two interesting observations have led to the postulation that the degradation of benzoate into acetate was probably conducted completely inside the cell of Syntrophus buswellii -like bacteria: (1) No fatty acids except acetate were found in the effluent; and (2) the granules showed very limited butyrate-degrading capability and could not degrade propionate. This study demonstrated the feasibility of removing aromatic pollutants in wastewater by anaerobic processes.

The factors leading to the loss of disinfectant residual in well-mixed drinking-water storage tanks are studied. Equations relating disinfectant residual to the disinfectant's reaction rate, the tank volume, and the fill and drain rates are presented. An analytical solution for the minimum disinfectant residual in the tank under constant inflow/outflow conditions is found. It shows that significant disinfectant loss begins when the product of disinfectant decay constant and the refill time for an empty tank exceeds 0.1, and that disinfectant residuals are relatively insensitive to the fraction of total volume devoted to emergency storage. A second, numerical solution to the model is developed to account for the fact that tank fill and drain rates are constrained by system demand patterns, pump capacity, and pump scheduling. Results show that pulsed or periodic pumping during a portion of the day can maintain much higher disinfectant residuals than continuous pumping can. However, such pumping policies require additional pump capacity and operating storage volume.

Water-quality models to predict oxygen dynamics in streams require estimates of rates of reaeration, respiration, and primary production, which are often evaluated through diel studies. Simple, approximate methods of parameter estimation are desirable at the scoping level, and are often used for waste-load allocation studies. Scoping methods often assume that reaeration and respiration are constant over the diel period. Use of such methods, however, can yield unrealistic parameter estimates for shallow streams with a significant range of diel water temperatures, because both reaeration and respiration rates as well as the saturation concentration of dissolved oxygen are temperature-dependent. Based on our work on the Santa Margarita River in Southern California, this paper presents a modified approach to dissolved-oxygen–rate parameter estimation that takes temperature variation into account. Using a simple finite-difference approximation, temperature-normalized parameter estimates are readily optimized in a spreadsheet application. The approach is applicable to many shallow streams in which diel temperature variability is significant.

During summer months, dissolved oxygen (DO) concentrations in the lower Hudson estuary were usually lower than atmospheric equilibrium values. Distributions of DO along the axis of the estuary can be described by three general characteristics. Firstly, surface and bottom values lie on a single trend when plotted against salinity. Secondly, maximum DO concentrations were observed 50–75 km upstream of Manhattan at salinities of 5–15 ppt. Thirdly, the lowest DO concentrations were observed near Manhattan, New York, at salinities of 15–25 ppt and vary systematically with freshwater discharge rate. Minimum DO concentrations during times of similar freshwater discharge were substantially lower for water samples collected between 1978 and 1984 than for those collected between 1989 and 1993. These two periods were also distinguished by occurrences of intense phytoplankton blooms that produced supersaturated DO concentrations at salinities of 5–15 ppt for the period of 1989 to 1993. The increase in the minimum DO concentration in the water near Manhattan is probably in response to improved wastewater treatment at Passaic Valley, N.J.; North River, N.Y.; and other wastewater-treatment facilities.