Journal of Environmental Engineering

A model for capital and operating costs of low‐pressure membrane filtration is presented. The model is used to explore the impact of variables describing system operation and membrane characteristics on treatment costs as well as to compare the cost of treating raw waters of different qualities using nanofiltration (NF), ultrafiltration (UF), and microfiltration (MF). The cost of UF or MF to remove particles from raw waters of moderate to high turbidity and concentrations of dissolved organic carbon (DOC) is calculated to be approximately twice that required to treat low‐turbidity streams or ground waters. At small design capacities (2,000 m³/hr), UF and MF are calculated to be competitive or less expensive processes for liquid‐solid separation in potable water treatment when compared with conventional filtration. MF and UF costs calculated for small facilities (≈20 m³/hr) treating low‐turbidity waters are comparable. For larger design capacities, UF may be less costly than MF. Treatment applications requiring significant removal of DOC and/or divalent ions may warrant the higher costs calculated for NF.

Increased rates of municipal solid‐waste (MSW) recycling are resulting in large increases in the amount of material available for reuse. We present a framework for assessment of the technical and business potential to recycle a constituent from MSW. The methodology is applied to plastics recycling in North Carolina. It includes estimation of the quantity of waste that could be available for recycle, assessment of the state of recycling technology, estimation of manufacturing capacity, and evaluation of potential markets for products manufactured from recycled resin. High‐density polyethylene milk containers and household‐chemical containers and polyethylene‐terephthalate beverage containers are the most recyclable components of the postconsumer plastics stream because these are easily recognized and separated. These constituents are projected to make up 1.1% of MSW in 1993. Proven technology, adequate manufacturing capacity, and large markets are available to handle increased quantities of these materials. There is not, at present, an adequate market for the commingled plastics remaining after removal of the aforementioned components of the MSW stream.

Fertilizers were used in the summer of 1989 to accelerate bacterial growth in a bioremediation effort to clean up the beaches following the EXXON Valdez oil spill. Mathematical models were used to quantify the eutrophication potential in two selected embayments in Prince William Sound: Passage Cove and Snug Harbor. First, mass transport in these two embayments was determined. Next, eutrophication models were developed for these two embayments to simulate the seasonal algal concentrations prior to fertilizer application. Finally, a series of nutrient‐loading scenarios based on different fertilizer and other chemical application rates were developed to investigate the impact. Model results and the data available indicated that the rapid exchange between embayments and the open water limits algal growth and buildup of concentrations of other chemicals applied to beaches. The exception is the potential for some ammonia toxicity at high application rates. Despite the limited data available it is clear that no significant increased algal growth would be expected following fertilizer application.

Efforts are being made to devise technologies and treatment systems to remediate contaminated soil on site without generating significant wastes for off‐site disposal. Heap leaching, a technique used extensively in the mining industry, has been investigated as a method for remediation of hazardous metal contamination of the vadose zone. In the mining industry, metal bearing ore is excavated and mounded on a pad. The metals are removed by passing a special leaching solution through the ore. In this study, the removal of Chromium (VI) from four New Mexico soils (sand, sandy loam, and clay) using heap leaching was evaluated at a column scale. The heap leaching study demonstrated greater than 99% removal of Cr(VI), using tap water as the leaching agent. The soils were typical of arid climate soils with low organic content (<1%).

Deep‐rooted trees planted as a buffer zone can intercept runoff and eroded sediments, thus reducing non‐point‐source pollution due to agricultural chemicals. In this study, Populus sp. were grown in bioreactors with an agricultural soil (silt‐loam) and in a silica‐sand media; both were spiked with ¹⁴C uniformly ring‐labeled atrazine. The plants took up over 11% of the ¹⁴C labeled atrazine applied to the silt‐loam soil and over 91% of that applied to the silica sand media, with the majority of the ¹⁴C accumulating as nonphytotoxic metabolites in the leaves. Research suggests that, in addition to nutrient uptake, poplar tree buffer strips may be effective in removing atrazine from agricultural percolation and runoff water.

A number of papers have been published on the treatment of inhibitory substrates in completely mixed, continuous activated sludge (CMAS) systems, but little information exists on the treatment of inhibitory compounds in batch reactors. With the increasing use of sequencing batch reactors (SBRs) for industrial waste treatment, it is important to evaluate the effects of reactor design and operation on treatment performance. A procedure for optimizing inhibitory substrate removal rate in an SBR is presented in this paper. The average rate of removal over the course of one batch cycle is shown to depend on the initial substrate concentration in the reactor. For a given loading rate, the initial substrate concentration can be controlled by adjusting cycle times and through other operating strategies. Within physical constraints of the system, an optimum value for initial concentration can be selected to maximize loading rates in reactor design, or to maximize substrate removal rates for existing plants.

Nitrosophenol is an intermediate organic chemical used in dye synthesis. Wastewater from nitrosophenol production is high‐strength in terms of chemical oxygen demand (COD), phenol, and total dissolved solids concentrations. Previous reports on treatment of wastewaters containing nitrosophenol addressed chemical oxidation methods. Biological treatment of nitrosophenol wastewater was evaluated in this study using a bench‐scale sequencing batch reactor. Substrate inhibition by phenol was observed, but methods to overcome inhibitory effects were developed. Biodegradation of nitrosophenol was concluded to occur by cometabolism in the presence of phenol, based primarily on COD balances and by ruling out abiotic mechanisms of nitrosophenol removal. The biomass developed in the reactor was unable to grow on nitrosophenol as a sole carbon source, and consisted predominantly of two eukaryotic morphotypes and a dispersed bacterial population. Based on results from the study, nitrosophenol wastewater is amenable to biological treatment but the effluent may require further treatment before discharge.

Methanotrophic degradation of vinyl chloride (VC) is investigated using a laboratory‐scale methanotrophic attached‐film expanded‐bed (MAFEB) bioreactor. This study provides a basis for applying a microbial cometabolizing reaction to practical treatment of toxic chlorinated compounds. The MAFEB reactor was operated at 20°C with influent VC concentrations ranging from 1,800 to 9,600 μg/L and bed hydraulic retention times ranging from 3.7 to 7.6 h. VC effluent concentrations during steady continuous operation ranged from 3 to 140 μg/L, with most values less than 26 μg/L, resulting in removal efficiencies of 96.3% to 99.8%. The maximum continuous‐flow VC degradation rate observed at 20°C was 2.5 mg VC per gram volatile solids (VS) per day [2.5 mg VC/(g VS d)] or 30 mg VC per liter expanded bed per day $30\mathrm{mg}\mathrm{VC}/L_{\mathrm{eb}}d$), under substrate‐limited conditions. During semibatch runs at 35°C, vinyl chloride degradation rates up to 60 mg VC/ (g VS d) or $1g/\left(L\mathrm{eb}d\right)$ were observed. Degradation rates increased with temperature between 20°C and 35°C, approximately doubling every 10°C. Dissolved methane concentrations above 0.5 mg/L inhibited VC degradation, with no VC degradation observed with 8 mg/L dissolved methane. The methane consumed during VC degradation was about $40g{\mathrm{CH}}_4/g\mathrm{VC}$. Toxic effects were observed after prolonged exposure of the methanotrophic culture to high concentrations of VC.

Steady‐state substrate utilization in biofilms has traditionally been modeled by coupling Fickian diffusion with Monod reaction kinetics. An inherent assumption in most of the previous models was that the pH remains constant within the biofilm. Experiments have shown differences between the pH in the bulk solution and in the biofilm. Since the rate of substrate utilization in biological systems can be affected severely by changes in pH, recent models have tried to account for the pH variations within the biofilm. However, these models neglected ionic interactions during mass transport. A fundamental approach incorporating the effects of pH in any chemical or biological system involving diffusion with reaction is presented. The approach is applied to a steady‐state model of substrate utilization in carbon‐limited algal biofilms.

A prototype computer‐based design environment was developed to facilitate wastewater treatment plant design tasks. The design environment includes several mathematical techniques, interactive graphic displays, and user‐friendly interfaces. The mathematical techniques are mass and water balances for an analysis program for plant design and a rule‐based system for evaluating the likelihood of sludge bulking. A processor is also used to check a given design using existing design standards. The interactive graphic displays and the user interfaces are intended to provide a user‐friendly environment for manipulating data, models, and solutions. Sensitivity analyses can be performed for models as well as parameters. The features of the computer‐based system are described, and suggestion for extensions are given.

Three sets of experiments were conducted to study the effects of hydraulic retention time (HRT), elevated ammonium nitrogen $({\mathrm{NH}}_3‐N)$ concentration and system breakdown on the removal of chemical oxygen demand (COD) and nitrogen in wastewater. Each set of experiments was conducted in parallel using three 21.7‐L reactors with submerged fibrous packing. One reactor was aerated continuously, and the other two were aerated half the time intermittently. When tested with synthetic wastewater having an average COD of 958 mg/L and ${\mathrm{NH}}_3‐N$ of 94 mg/L at 4–14 hr of HRT, all reactors had similar levels of carbonaceous oxidation (95–97%) and nitrification (85%). The nitrite/nitrate produced were effectively denitrified in the intermittently aerated reactors because of the anoxic condition in the interior of the “bio‐pompons”; but the continuously aerated reactor had little denitrification activity. Elevated ${\mathrm{NH}}_3‐N$ concentrations were toxic to microorganisms in all reactors, affecting adversely both the nitrification and carbonaceous oxidation. Nitrification was affected more in the intermittently aerated reactors; and carbonaceous oxidation was affected more in the continuously aerated reactor. All reactors showed rapid recovery from a simulated system breakdown.

Three types of wastewater based on acetate, sucrose, and ice cream were used to investigate the long‐term effect of wastewater composition on the stability of the upflow anaerobic sludge blanket (UASB) process using laboratory‐scale reactors. Experimental results revealed that variations in the carbon source in the wastewater caused gradual changes in both the physical structures and the bacterial distribution of the seeding granular sludge, which resulted in disintegration or floatation of the granular sludge under certain conditions. The rate of such changes was found to be relatively slow, and depended on the sludge‐loading rate. A semiquantitative mathematical model on the ecological characteristics of the granular sludge was developed and was able to explain the experimental results. The study suggests that the failure of the UASB process under certain circumstance was primarily due to the limitation in the ecological structure of the granular sludge.

The present paper describes an approach for the overall evaluation of anaerobic reactor alternatives with an ultimate objective of developing a tool to assist in the selection of a particular anaerobic reactor type for a given set of conditions using systems approach. A formulation has been proposed to evaluate overall reactor performance in terms of reactor evaluation index (REI). This involves identification and quantification of the factors essential for reactor evaluation, and the development of the sensitivity function and assignment of weightages to each factor. Evaluation of REI requires the design of the reactor. Since no theoretical (rational) design criteria are available, a semirational design technique that takes advantage of both phenomenological and theoretical approaches is proposed. The semirational design approach considers a reference loading rate and the design loading under a given condition is obtained from the reference loading by applying waste and reactor correction factors.

A small field site adjacent to a lake in Amana, Iowa was used to investigate the fate of nitrate fertilizer in the unsaturated zone. The fertilizer was applied to a barren plot, a plot planted with corn, and a plot planted with deep‐rooted poplar trees (Populus spp.) to study the characteristic behavior of a typical agricultural environment and a novel pollutant‐interception technique in comparison to unmanaged land. Nitrate concentrations were lower in the corn and especially the poplar plot due to plant uptake, but concentrations increased markedly in September after the plants began to shut down and nitrification occurred. The poplar trees were most effective in long‐term nitrate reduction; they provide perennial interception. Statistical analysis confirmed plant uptake was an important process in the fate of nitrate, and hence, vegetative buffer strips hold promise for protecting water supplies.