Journal of Environmental Engineering

A conceptual process model was developed to examine the potential for late summer ammonia toxicity in shallow lakes. Processes represented in the model were macrophyte decay; growth, death, and sedimentation of phytoplankton; growth and death of zooplankton; nitrification; volatilization; and chemical equilibria (carbonate and ammonium systems). Peak NH₃ concentrations occur at the peak of the phytoplankton bloom that develops about 2 weeks after macrophyte decay starts, when the pH is elevated. Ammonia peaks are highly transient, lasting <1 day. It is hypothesized that late summer ammonia toxicity following macrophyte senescence may be a common but generally unrecognized phenomenon in shallow lakes.

Benthal respiration rates are often measured in situ by a sediment oxygen demand (SOD) chamber in which a continuous flow is generated above the sediment. The steady three-dimensional turbulent flow field inside a triangular SOD chamber (previously used in field investigations) is computed using the renormalization group (RNG) k–ε model on an unstructured tetrahedral mesh. The numerical predictions reveal a highly complicated flow characterized by (1) a jet flow near the level of the inlet, with strong downflow near the outlet end; (2) significant reverse bottom currents; and (3) strong secondary circulations in the triangular cross section. Good mixing is achieved, with mean near-bottom velocities about 10 times greater than that determined from the inflow discharge and cross-sectional area. The computed velocity field is well supported by laboratory velocity measurements using laser-Doppler anemometry (LDA). The implications on SOD chamber design are also discussed with reference to computed flow fields in representative dome-shaped and rectangular chambers used in field application. The present study explains the previous large discrepancies in SOD field measurement using chambers of different designs, and points to the importance of hydrodynamics of SOD chambers.

Given the significant urban runoff impacts on many receiving waters and the massive costs of future investments in drainage infrastructure, the design of urban runoff control systems must be cost-effective. Cost-effective design requires that various runoff control system alternatives be investigated at the planning stage so that cost-effective runoff control systems can be identified for design level analysis. To analyze the runoff control performance of various combinations of runoff control systems at the planning stage, efficient screening models are acutely needed. For this purpose, analytical probabilistic models were applied to analyze the runoff quantity/quality control performance of various combinations of storage and treatment systems. These analytical probabilistic models are developed with derived probability distribution theory whereby the input meteorology to the catchment is described by probability density functions (PDFs) of the meteorological characteristics that are transformed by hydrologic/hydraulic functions to PDFs of the system performance variables. The resulting PDFs are then used to determine the average performance conditions. These models provide closed-formed solutions of the performance equations that are highly efficient in both a conceptual and computational sense. As a result, they are particularly useful for the screening analysis of urban runoff control alternatives.

Sophisticated laboratory equipment and procedures are developed and used in controlled experiments to measure nitric oxide (NO) emissions ranging from 42 to 75 ng N/m²⋅s from sludge-amended soil of concern to environmental engineers because nitric oxide emitted to the troposphere is a precursor to troublesome ozone formation and also of concern to agricultural engineers because valuable nitrogen as fertilizer is lost from the soil. Water-filled pore space is confirmed to be of critical importance to NO flux, and the upper layers of soil are determined to contribute the larger portion of the NO fluxing from the soil to the troposphere. More than 42% of the total NO flux comes from the top 1 cm of soil, with NO contributions decreasing exponentially with soil depth and very little if any tropospheric NO contributed from soil at a depth of 20 cm or greater. The results are discussed in terms of microbiological, chemical, and soil transport processes that influence NO flux from sludge-amended soil.

Improving air pollution control systems is crucial for incinerators to be an option for sewage sludge disposal. Combinations of venturi and tray tower scrubbers are the most popular air pollution control system for sewage sludge incinerators. Recently wet electrostatic precipitators have been installed downstream of the scrubbing system to ensure the compliance of new regulations. Performance and stack tests were conducted on sludge incinerators at Somerset Raritan Valley Sewage Authority and New England Treatment Company. Efficiencies in terms of heavy metal and particulate removals are presented. This paper also describes sewage sludge incinerators, existing air pollution control systems, design considerations of the wet electrostatic precipitator, as well as sampling and analysis methods.

The chemical composition, molecular weight (MW) distribution, and biodegradability (both aerobic and anaerobic) of soluble microbial products (SMPs) in an anaerobic baffled reactor (ABR) treating low-strength wastewater were investigated. The effect of various process parameters on the production of SMPs was also examined. Results indicated that high MW (>300 kDa) compounds were produced in the middle compartments of the reactor and formed 22% of the effluent chemical oxygen demand (COD). This fraction was found to be 86% degradable under aerobic conditions but only 4% under anaerobic conditions. Low MW (<1 kDa) material represented the highest portion (36%) of the effluent COD and was mainly found in the first compartment of the ABR and in the effluent. This fraction was more easily degraded under anaerobic conditions (33%) than aerobic conditions (17%). Analysis of a hydrolyzed sample of the high MW fraction revealed the presence of several sugars and volatile fatty acids. Therefore, it was concluded that the high MW material contains heteropolysaccharides. Nuclear magnetic resonance analysis of the low MW fraction revealed the possible presence of alcohol, carboxylate, and aromatic chemical groups. SMP production increased with increasing hydraulic retention time (HRT), probably due to enhanced biomass decay at high HRTs, and also increased with decreasing temperature, probably due to increased stress on the biomass and a reduced metabolism of the SMP at low temperatures. Finally, SMP production in an ABR containing higher levels of initial biomass concentration was greater than for an ABR operating at the same conditions but with lower levels of initial biomass.

Several investigators have shown that membrane oxygenation provides a number of advantages in biological treatment. These include operational flexibility, reduced energy requirements, and less stripping of volatile compounds. Membranes have also been observed to provide a support surface for microbial growth. This steady-state model study investigates the microbial uptake of oxygen and a carbon-source substrate for aerobic, heterotrophic biofilms on gas permeable membrane- and impermeable solid-supported surfaces. The model predictions indicate that very different concentration and activity profiles may be found in biofilms grown on solid surfaces and gas permeable membranes. For a solid-supported biofilm the highest concentrations of oxygen and substrate and the greatest microbial activity are located on the outside of the biofilm. For a membrane-supported film, the oxygen and substrate are never present at the same location in their maximum concentrations, and the location of maximum biological activity in the biofilm can occur at other locations within the film. These differences may lead to significant differences in the microbial ecology and populations of biofilms and, in turn, in biofilm morphology.

A procedure is developed to provide measurements of particle size by adapting parts of a commercially available particle image velocimetry system to obtain in situ digital images of the particles. The procedure is nonintrusive and is able to capture images of the particles as they are mixed, thus avoiding the need for disturbing the flow or withdrawing samples for later analysis. Measured size distributions are shown to compare closely with manufacturer's values for standard polystyrene spherical particles, and particles with diameters as small as 6 μm are resolved. The system also is shown to track changes in particle-size distribution during an aggregation test. In addition, information on particle geometry is obtained, which should be useful for improving the ability to model aggregation processes. A simple modeling framework based on the Smoluchowski equation is presented to demonstrate the use of data obtained with this procedure in particle aggregation modeling.

The Qi-Hay-Rood adsorption isotherm equation is shown to provide an improved description of equilibrium water vapor adsorption onto microporous activated carbon between 298 and 373 K and total pressure at 101 kPa, when compared with an existing isotherm model. The influence of temperature on the isotherm equation's parameters is also quantified. An expression for the isosteric heat of adsorption is derived from the Clausius-Clapeyron equation. It is shown that the isosteric heat of adsorption decreases with increasing temperature and increasing adsorption capacity of water vapor. This new isotherm model can be inverted to describe water vapor concentration dependence on adsorption capacity and is therefore well suited for use in dynamic models for activated-carbon adsorption systems.

Effective solidification/stabilization (S/S) of arsenic- and barium-containing D004/D005 waste was accomplished by using a binder of cement with 40% class C fly ash and either ferrous sulfate or ferric sulfate as an additive. Addition of iron salts improves arsenic solidification/stabilization (S/S). Barium may be encapsulated within the stabilized matrix as barium sulfate. Recommended mole ratios for iron/arsenic and barium/sulfate are at least 6 and 1.2, respectively. A binder/waste ratio of 0.15 is volume efficient, but the mix design must be carefully controlled to achieve adequate S/S. In practice, the heterogeneity of waste and large-scale mix operations may preclude close control of reagent dosages, so a binder/waste ratio of 0.40 is preferable. Ferrous sulfate additive is preferable for arsenic S/S because it is effective over a wider range of mix designs and over a long-term curing period. Toxicity characteristic leaching procedure results degraded with long curing time for some mix designs with ferric sulfate additive.

Industrial sludge is generated at a rate of 100 metric tons/day, from a copper slag recycling plant. The industrial sludge is currently being landfilled. However, limited availbility of landfill sites has raised the need of an alternative disposal. A renewed interest in converting the industrial sludge into construction materials has been prompted to achieve a viable disposal option in saving the depleting natural resources of raw materials as well as the environment. This study describes the use of sintered sludge pellets as a complete replacement for regular granite aggregates in concrete. The pelletized sludge was fired to a temperature of 1,135°C at which the sintering process occurs, producing a hard fused basalt-like mass. In comparison with normal granite aggregates, the sintered sludge pellets display a higher aggregate strength, a higher porosity, and a lower aggregate density that manifests attributes better than that required of construction aggregates. The concrete cast with the pelletized aggregtes achieved a compressive strength of 38.5 N/mm² after 28 days and was comparable to the control specimen. Leaching tests conducted on the sludge pellets and concrete showed that all leachate contamination levels determined using the column leaching test are within acceptable ranges after 130 days of stabilization. The experimental results indicated that a complete replacement of conventional aggregates with sintered sludge pellets for structural concrete is both technically and environmentally feasible.

Wet air oxidation was attempted on synthetic (mixture of plastics of various compositions) and natural (cellulose substances) solid polymers. The temperature was maintained at 270°C and the oxygen pressure varied from 0 to 2 MPa (from understoichiometric conditions to oxygen excess). No valorizable compounds were found, even in runs carried out under an oxygen deficit. Suitable conditions for the total destruction of the initial polymers were temperatures above 270°C, an excess of oxygen, and a residence time of less than 1 h. Only such degradable compounds as acetic and benzoic acids are found at low concentrations. Formation of chlorine and gaseous hydrochloric acid can be limited by adding CaCO₃ as a neutralizing agent.