Journal of Environmental Engineering

A study of the fate of volatile organic contaminants (VOCs) in trickling filters (TF) and rotating biological contactors (RBC) was performed. Of the target compounds investigated, tetrachloroethylene was volatilized to the greatest extent, while 1,1,2,2-tetrachloroethane was the least volatilized in the TF and bromoform was least volatilized in the RBC. Toluene, o-xylene and 1,3,5-trimethylbenzene were biodegraded to the greatest extent and 1,1,2,2-tetrachloroethane was least biodegraded. Increasing the hydraulic loading tended to increase the proportion of influent VOCs found in the TF effluent. Imposing effluent recycle on the TF increased the fraction of influent VOCs found in the effluent, but also decreased the fraction stripped and increased the fraction that was biodegraded. Increasing hydraulic loading to the RBC tended to increase the proportion of influent VOCs found in the effluent and off-gas. Increasing the RBC disc rotational speed increased the fraction that was biodegraded and decreased the fraction of VOCs found in the effluent and off-gas streams. The TF tended to have greater losses to volatilization than the RBC while the RBC maintained a greater fraction of the candidate VOCs in the process effluent than the TF. Differences between the processes with respect to biodegradation could not be inferred.

Models incorporating liquid-gas mass-transfer and biofilm mass-transfer resistances were developed for trickling filters (TF) and rotating biological contractors (RBC). Biodegradation and volatilization coefficients were estimated from the previously described pilot-scale studies. The volatilization coefficients of a given compound in the TF and RBC were generally constant across the experimental conditions investigated. While biodegradation-rate coefficients were constant in the TF across experimental conditions, in the RBC the biodegradation-rate coefficients appeared to be greatest under conditions of low loading and high disc rotation speed and lowest under conditions of high loading and low disk rotational speed. The biofilm was completely penetrated by most of the contaminants and diffusional resistance did not limit the rate of biodegradation of any of the compounds. In the RBC, diffusion in the biofilm appeared to be limiting the biodegradation of toluene, o-xylene, and 1,3,5-trimethylbenzene. The ratio of gasand liquid-phase mass-transfer coefficients ranged from 91.4 for the TF to 5.6 for the RBC. Due to the relatively wide confidence intervals associated with these estimates, the values could not be statistically differentiated, however, the results suggest a significant contribution of gas-phase resistance to mass transfer in some cases.

A methodology for selecting the least-cost treatment technology for waters contaminated by organic wastes was developed using performance and cost models. This methodology simplifies the selection of the least expensive treatment process(es) for a given set of conditions. Two aqueous-phase treatment options were considered: air stripping and liquid-phase adsorption (granular activated carbon). When the off-gases from air stripping must be treated, four off-gas treatment options were considered: gas-phase adsorption (with both onand off-site regeneration of the granular activated carbon), thermal incineration, and catalytic oxidation. Methodologies were developed for rapidly selecting the least-cost off-gas treatment option [for volatile organic compound (VOC) sources such as an air stripping tower], for selecting the least-cost overall (liquid and gas phase treatment) system, and for selecting the least-cost overall system for a multicomponent mixture. The comparison methodology is based on physical parameters of the target chemical: Henry's constant and the solute distribution parameter. The results are a set of diagrams and heuristics for rapid identification of cases for which one treatment option is significantly less expensive than the other.

Biodegradation of trichloroethylene (TCE) was studied using a mixed culture of aerobic, phenol-induced organisms. Abiotic experiments showed that sorption of TCE to biomass was negligible in the systems studied. The effects of influent phenol and TCE concentration on the TCE degradation capacity of the culture were studied using chemostats. A relationship exists between the influent phenol/TCE ratio and TCE biodegradation. TCE transformation yields ranged from 0.052 to 0.222 mg TCE removed/mg phenol removed. Monod kinetic coefficients for phenol degradation were determined. Monod kinetic coefficients were also determined for TCE biotransformation by resting cells. The concept of transformation capacity was used to model the decrease in active biomass concentration caused by TCE transformation. In mineralization studies using ¹⁴ C-labeled TCE, 22% of the degraded mass of TCE was transformed to carbon dioxide, 8.8% was incorporated into biomass, 42% was transformed to nonvolatile products, with the remaining, unrecovered 27% most likely transformed into volatile or semivolatile products.

The objective of this research was to determine the toxic effects and degradation of pentachlorophenol (PCP) in the presence of zinc in anaerobic propionate systems. Anaerobic toxicity assays (ATA), batch kinetic studies, and biodegradation studies were performed using serum bottles. PCP inhibition was modeled using both uncompetitive and noncompetitive inhibition kinetic models with an inhibition coefficient, K _I , of 0.06 mg/L. Zinc toxicity showed that the competitive inhibition model was the best-fit with a K _I of 1.1 mg/L. A combined competitive-uncompetitive inhibition model was the best-fit model in the presence of both PCP and zinc for propionate degradation. In the biodegradation studies, PCP removals were 72, 64, and 54% with spiked PCP concentrations of 2, 3, and 5 mg/L, respectively. In the presence of zinc, the removal of 2 mg/L and 3 mg/L of PCP decreased to 60% and 53%, respectively. The intermediates of PCP degradation were 2,4,6-trichlorophenol, 2,4-dichlorophenol, 4-chlorophenol, 2,3,5-trichlorophenol, 3,5-dichlorophenol, and 3-chlorophenol; lower concentrations of these intermediates were observed in the presence of zinc.

A microbial system for removal of nitrate from drinking water in which the denitrification reactions are physically separated from the water being treated by a microporous membrane was studied. The experimental system was composed of two equal-volume cells separated by a 0.02 μm pore size polytetrafluoroethylene membrane. No pressure difference existed across the membrane, and nitrate ions were transported through the membrane by diffusion. Results of experiments with biofilm denitrification and suspended-culture systems are presented. Deoxygenation by N ₂ stripping and by $\mathrm{SO}{}^{-2}$ produced equivalent results. Removal rates with the suspended culture systems were greater than those with biofilms. Effective membrane diffusivities calculated for suspended-culture systems were approximately the same as for sterile systems, indicating that resistance to transport was not changed by the addition of the suspended microbial culture. The methanol requirement observed in the experiments was 1.4 g total organic carbon (TOC) per g $\mathrm{NO}{}^{-}-N$ removed. Removal rates followed first-order pseudotransport controlled models for both the biofilm and suspended-culture systems. A prototype continuous-flow system is presented.

A study was conducted to evaluate the performance of eight full-scale advanced wastewater treatment (AWT) facilities using biological nutrient removal (BNR) processes as the primary mechanism for removing carbon, nitrogen, and phosphorus from domestic wastewater. One year of operating data from each facility was obtained from monthly operating reports (MORs) provided by plant operators. BNR processes evaluated were: 5-Stage Bardenpho, A ² /O, and Carrousel systems and/or oxidation ditches preceded by anaerobic/anoxic selectors. Plant inspections and interviews with chief operators were undertaken to understand how each facility was operated, and the type and quantity of chemicals used. Influent and effluent five-day carbonaceous biochemical oxygen demand (CBOD ₅ ), total suspended solids (TSS), and total phosphorus (TP) were evaluated in addition to influent total Kjeldahl nitrogen (TKN) and effluent total nitrogen (TN). In all cases, annual average effluent requirements of 5 mg/L, 5 mg/L, and 3 mg/L for CBOD ₅ , TSS, and TN were achieved. Facilities with a 1 mg/L annual average effluent TP limit met permit requirements. Percent removals, monthly average effluent concentrations, detention times, secondary clarifier design information, and chemical dosages are presented.

If a single contaminant concentration in soil were to be used as the remediation goal at all potential remediation sites in a region, risk would be expected to vary across sites due to differences in site characteristics that affect transport and fate. A methodology is developed to evaluate such variability. It is applied to Ross County, Ohio, a region for which compiled, detailed hydrogeologic information is available. Four carcinogenic contaminants (benzene, trichloroethylene, chlordane, and benzo[a]pyrene) and exposure scenarios (on-site commercial, on-site recreational, and on-site and off-site residential) are evaluated. Results vary, but in general, indicate that for contaminants that are highly degradable such as benzene or immobile in the subsurface such as benzo[a]pyrene, specifying a uniform soil remediation goal would result in relatively small degree of regional risk variability. However, for highly mobile and persistent contaminants like trichloroethylene, a uniform goal would result in a large degree of regional risk variability. Application of the methodology to a larger, less well-characterized region is analyzed.

Surface water pollution in rural areas is related to agricultural practices. Field applications of pesticide can contribute to water degradation. The model HSPF includes a module for simulating the degradation and transport of pesticides. This model was tested using data from a 78 ha watershed in the province of Québec, Canada. Model parameters related to hydrologic and pesticide transport processes were calibrated. The study period extended from June 1991 to November 1993. For the calibration period, correlations between observed and simulated streamflows were 0.73, 0.87, and 0.90 for daily, weekly, and monthly intervals, respectively; whereas for the verification period, values of 0.67, 0.91, and 0.93 were obtained. Pesticide concentrations were measured at the outlet of the watershed from February to November 1993. This short period of time allowed calibration of the pesticide component but precluded verification. Variations of atrazine concentration were well simulated by Hydrological Simulation Program FORTRAN (HSPF), with simulated concentrations in the same range as observed values, and with peak concentrations occurring at the same time.

The concept of bubbleless aeration with microporous hollow fiber membranes is tested in a system that does not require external energy input, other than pressurizing oxygen, and is designed to add oxygen to surface waters. Microporous hollow fiber membranes, potted at one end and connected to an oxygen supply, with the other end individually sealed, were installed vertically in a flume to simulate their performance in rivers and lakes. The gas-filled fibers tend to rise vertically due to buoyancy, while bending downstream due to the drag force exerted by the flowing water. When operated at differential pressures of up to 3 atm during the experiments, this cross-flow configuration resulted in high rates of gas transfer with no supplemental energy input. Gas-transfer coefficients were found to depend on cross-flow velocity and internal gas pressure for the tested fibers. Two possible applications for passive hollow fiber membrane aeration are considered, and contrasted with traditional methods of aeration.

The multiple-tray aerator is an effective technology for chemical stabilization and corrosion control at small, medium, and large public drinking-water treatment facilities, because of significant savings in chemical costs. A pilot-scale tray tower was built at the University of New Orleans Urban Waste Management and Research Center to study the factors affecting carbon dioxide removal by plain aeration. Several series of tests were conducted to develop a general statistical model to predict the value of the empirical kinetic coefficient which, in turn, can be used in designing a tray tower. The model includes the effect of spacing between trays, hydraulic loading rate, temperature, wind speed, and Langelier index. A method for the optimum design of tray aerators for corrosion control in drinking-water treatment is also discussed. This method is based on a computer program developed to solve the equations needed to predict both the pH after any tray in the tower and the supplemental chemical dosage that may be needed to render the water at equilibrium with respect to calcium carbonate.

The emphasis on waste reduction and recycling requirements prior to incineration and the promulgation of Good Combustion Practice (GCP) for emission control of trace organic compounds during incineration have created conflicting solid-waste management goals. The most critical questions in system planning include: to what extent are recycling and incineration compatible? And what are the subsequent economic impacts on the private and public sectors under specific management scenarios? However, the inherent complexity of composition, generation, and heat value of the waste streams as well as the stability of the secondary material market may result in additional difficulties in management decision making. This paper presents a nonlinear fuzzy goal programming approach for solving such questions. In particular, it demonstrates how fuzzy, or imprecise, objectives of the decision makers can be quantified through the use of specific membership functions in various types of management-planning scenarios.

A method has been developed that gives analytical solutions for estimation of the standard deviations σ_y and σ_z in the Gaussian model from observed data without requiring knowledge of the change in wind direction. With a defined concentration ratio term, R , estimates for σ_y can be obtained by solving the Gaussian model. By introducing a dimensionless concentration factor, c ′, estimates for σ_z can be approximated at different downwind ranges. This method can be used in field applications and also for model calibration and verification.

An analysis of the rate and extent of lead leaching from a lead-based paint was completed. At low-solution pH, dissolution was rapid and approached 80 of the total lead. Residual lead can be estimated based on the predicted solubility of lead carbonate and basic lead carbonate. Release of lead from the paint was slower than that from pure basic lead carbonate due to inhibition by the paint matrix. Although the dissolved concentration of lead in solution at neutral/high pH was low, the paint binder was apparently destroyed at these pH values, releasing colloidal lead pigment particles. The presence of ethylenediaminetetraacetic acid (EDTA) and nitrilotriacetic acid (NTA) enhanced both the rate and degree of lead dissolution, while benzoic acid had a minimal effect.

The purpose of this paper is to demonstrate seasonal subseries and multipercentile graphs for analyzing trends in environmental data time series (Tukey 1977; Cleveland 1985). These simple graphical methods do not require the user to make assumptions regarding properties of the data, such as normality, constant variance, and serial independence. A modest number of missing values (up to 30, assuming they occur at random intervals) should not affect the plots enough to alter the interpretation. The plots allow one to see more clearly what is happening at the extremes, and seasonal effects are revealed. The methods are illustrated by using five day BOD data, measured at monthly intervals from 1977 to 1992 at the DePere station on the Fox River in Wisconsin.

Carbonaceous BOD₅ and ammonia effluent limitations for low-dilution-ratio receiving waters are often determined by using wasteload allocation studies. These studies are labor intensive. They require one-third to one-half a work year to complete. Due to bacteria population dynamics, biological-wastewater treatment plants producing a highly nitrified effluent also produce an effluent low in carbonaceous BOD₅. Using the BOD-ammonia relationship, regulators can achieve the same net results as labor-intensive load allocation studies with only 1% or 2% of the labor, if they concentrate on just protecting the receiving water's un-ionized ammonia standard. Four years of monthly effluent reports from 22 nitrifying wastewater treatment facilities were examined. This examination showed that this alternative to time-consuming wasteload allocation studies is practical.