Journal of Environmental Engineering

The formate-utilizing sludge was first enriched in a chemostat reactor for over 90 days; at steady state, the sludge yield averaged 0.066 mg volatile suspended solids (VSS)/mg chemical oxygen demand (COD). The methanogenic characteristics of this sludge were then investigated in three series of batch experiments at 37°C using formate, acetate, and H₂/CO₂, individually, as substrates. At pH 6.4–8.0, the formate-degrading rate averaged 0.76 mg/mg VSS/h (6.35 mg COD/mg VSS/d). At pH 3.0, the sludge completely lost its bioactivity, and required a lengthy recovery period to regain a fraction of its bioactivity after the pH was adjusted to pH 7.1. The sludge was also able to utilize H₂/CO₂ as substrate at an average rate of 0.0167 mg H₂/mg VSS/h (3.21 mg COD/mg VSS/d). At pH ≤ 8.0, the sludge degraded acetate at a very low rate of 3.0 μg/mg VSS/h (0.077 mg COD/mg VSS/d). The sludge exhibited a slight homoacetogenic activity at pH > 8.0 using formate as substrate; the homoacetogenic reaction using H₂/CO₂ as substrate was thermodynamically infeasible, according to chemical free energy analysis.

Biodegradation of aminobenzene, which is used as the only source of carbon and nitrogen, is evaluated in a single fluidized bed reactor operated in a temporal, anoxic/oxic mode. The experimental evidence indicates that total organic carbon (TOC) is removed with >91% efficiency at a feed concentration of 100 mg/L and a dilution rate of 2.4 day⁻¹. Moreover, about 53–63% of feed total Kjeldahl nitrogen (TKN) is also removed, confirming that effective removal of nitrogenous matter in aminobenzene (i.e., the −NH₂ group) is achievable in a temporal, anoxic/oxic environment. The kinetic analysis shows that TOC removal in oxic cycles is rapid and substantial, which enables nitrification to proceed at a discernible rate. In addition, the data on TOC and ${\mathrm{NO}}_{\mathit{3}}^{\mathit{-}}-N$ removal in anoxic cycles reveal that carbonaceous matter in aminobenzene and/or its intermediate metabolites is effectively utilized for denitrification. The best treatment performance, in terms of carbon and nitrogen removal and potential savings in aeration costs, is obtained by coupling a 6 h oxic cycle with a 6 h anoxic cycle. All reaction rates estimated in anoxic/oxic experiments remain relatively constant over the range of conditions tested.

The objective of this work was to calibrate and verify a modified version of a mathematical model of a single-sludge system for nitrification and denitrification. The new model is based on long-term experimental results, and the main modifications are related to the biological oxygen demand removal kinetics and biomass activity expressions. The model consists of 22 equations with 54 parameters, including 19 kinetic and stoichiometric coefficients. Experiments were performed on four bench-scale units and one pilot plant fed with domestic wastewater. Six sets of runs were carried out under different operational conditions. In the calibration procedure, a mathematical algorithm was implemented, in which an optimal set of coefficients was selected. Several coefficients were directly determined experimentally. Model verification was based on the comparison of experimental results with the values predicted by the mathematical model using a fixed set of model coefficients for each set of runs. From the verification results, the model is considered to be a useful one for the design of a new treatment system and operation of an existing one.

Engineering practice in trickling filter design has been influenced by the propagation of myths as much as by the analysis of data and factual determinations. In this paper, several common myths encountered by the writer in his engineering practice are examined. The myths are tied to source(s) where possible, and then the factual underpinnings (if any) are examined. Common myths include the following: (1) Trickling filter processes are less reliable than activated sludge processes; (2) trickling filters are poor performers in cold weather; (3) trickling filters are more expensive; (4) motorized distributor speed control is always needed; (5) cross-flow media should not be used at total organic loadings exceeding 1.6 kg BOD₅/m³⋅d and (6) all media are created equal.

Laboratory-scale experiments were conducted to determine optimum sludge residence time (SRT) and temperature of aerobic thermophilic pretreatment (ATP) of mixed sludge (thickened waste activated sludge and primary sludge) to achieve maximum pathogen reduction and best process performance. 4-L laboratory-scale ATP reactors were operated at SRTs of 0.6, 1.0, and 1.5 days and temperatures of 55, 58, 62, and 65°C. ATP at temperatures ≥62°C and SRT ≥0.6 day reduced the feed sludge fecal coliform density from 10⁷ MPN/g total solids (TS) to <10⁴ MPN/g TS. Salmonella in the feed sludge was reduced to <1 MPN/4 g TS from 2 to 18 MPN/4 g TS by ATP at temperatures ≥55°C and SRT ≥0.6 day. ATP was able to increase sludge volatile acids concentration by 100–200% over the feed sludge volatile acid concentration and to reduce sludge supernatant chemical oxygen demand from 20,000 to 22,000 mg/L in the feed to 13,000–17,000 mg/L in the ATP reactor. Volatile solids reduction by ATP increased from 25 to 40% when SRT was increased from 0.6 to 1.5 days, and a 5% increase in volatile solids reduction was seen at SRTs of 0.6, 1.0, and 1.5 days when ATP temperature was increased from 55 to 65°C.

Water saturation in the vadose zone is an important parameter for many nonaqueous phase liquid (NAPL) remediation technologies. Conventional soil boring analyses may not provide accurate average water saturation data. Previous studies have shown that a partitioning interwell tracer test (PITT) can provide an accurate estimate of average subsurface NAPL saturations. The PITT is proposed as a suitable technology for estimating average subsurface water saturations. In this research, difluoromethane was evaluated as a suitable tracer compound to partition among air, water, and NAPL phases. Method of moments analyses were used to develop equations necessary to determine water saturations from difluoromethane PITT results. One-dimensional column experiments provided air-water and air-NAPL partition coefficient data for difluoromethane. Difluoromethane is shown to be a suitable tracer for use in field PITTs to predict water saturations in the vadose zone.

An analysis has been performed on the fluid flow and convective mass transfer in a system consisting of many gas bubbles. Both interference effects of neighboring bubbles and the influence of the circulation induced inside the bubbles on the flow field and the mass transfer rate were taken into account in the analysis. Analytical solutions were obtained for the mass transfer rate. The results indicate that both the packing density and the viscosity ratio of fluid spheres and surrounding fluid have significant effects on the flow field and the mass transfer rate. It was found that the mass transfer rate in a system of bubbles becomes much higher than that for a system of solid spheres. Based on the analytical results, discussions are provided concerning the mass transfer onto gas bubbles from liquid flow.

A parametric waste-specific study was conducted to assess the effects of membrane rotational speed and feed oil concentration on the pressure independent “limiting” flux in a high-shear rotary ultrafiltration (HSRUF) system. The limiting flux data were adequately described by the thin-film model. The transition from pressure dependent to pressure independent behavior occurred at lower oil concentrations as membrane rotational speed was decreased and pressure was increased due to an increase in the thickness of the solute boundary layer at the membrane surface. A gel layer oil concentration, OC_gel, of 39% was reported, and OC_gel was determined to be constant with respect to average transmembrane pressure and membrane rotational speed. The solute mass transfer coefficient increased with membrane rotation and was greater than reported for conventional ultrafiltration systems. The greater mass transfer characteristics determined for the HSRUF system were attributed to the efficient delivery of “cleaning energy” to the membrane surface due to the effective decoupling of feed pressurization from recirculation/hydraulic turbulence.

The transport properties of aqueous solutions of benzene, dichloromethane, and trichloroethylene through extended polyvinyl chloride and high-density polyethylene geomembranes are investigated. It is found that extension enhances the permeation rates of the penetrants through polyvinyl chloride geomembranes, and the opposite effect is found in the case of high-density polyethylene. This difference in response is attributed to the type of structural change, which occurred as a result of the extension. The diffusivities of a mixture of the three organic solvents through the geomembranes are also determined.

A decision support system (DSS) was developed to calculate total maximum daily loads (TMDLs) of various pollutants for water quality limited sections (WQLS) within a river basin. The DSS includes a watershed simulation model, a database, a consensus building module, and a TMDL module that provides a worksheet for the calculations. The system can generate multiple combinations of waste load allocation and non-point-load allocation to meet the water quality criteria for the intended uses of the WQLS. Considering various possible solutions, the regulatory agency and local stakeholders can negotiate an option most agreeable to all parties. The methodology is demonstrated with an example application in the Catawba River Basin, which extends from North Carolina to South Carolina.

The Monte Carlo method is a popular method for incorporating uncertainty relative to parameter values in risk assessment modeling. But risk assessment models are often used as screening tools in situations where information is typically sparse and imprecise. In this case, it is questionable whether true probabilities can be assigned to parameter estimates, or whether these estimates should be considered as simply possible. This paper examines the possibilistic approach of accounting for parameter value uncertainty, and provides a comparison with the Monte Carlo probabilistic approach. The comparison illustrates the conservative nature of the possibilistic approach, which considers all possible combinations of parameter values, but does not transmit (through multiplication) the uncertainty of the parameter values onto that of the calculated result. In the Monte Carlo calculation, on the other hand, scenarios that combine low probability parameter values have all the less chance of being randomly selected. If probabilities are arbitrarily assigned to parameter estimates, without being substantiated by site-specific field data, possible combinations of parameter values (scenarios) will be eliminated from the analysis as a result of Monte Carlo averaging. This could have a detrimental impact in an environmental context, when the mere possibility that a scenario may occur can be an important element in the decision-making process.

To improve the feasibility of soil-aquifer remediation using bioaugmentation, more efficient methods are needed to widely disperse pollutant-degrading bacteria in porous media. Under water-saturated conditions, bacteria readily adhere to soil particles, but under unsaturated conditions, bacteria preferentially accumulate at the air-water interface. Air sparging a saturated porous medium produces a mobile water interface that was hypothesized to facilitate bacterial transport. To investigate whether gas sparging increased bacterial transport relative to saturated-water conditions, the transport of three strains of bacteria and negatively charged microspheres of different relative hydrophobicities R_H was measured in saturated and gas-sparged quartz-packed columns. Gas sparging increased (>60%) the bacterial transport in only one case (Pseudomonas fluorescens P17; R_H = 27%). Transport of the other two strains were either unaffected by gas sparging (Mycobacterium vaccae JOB5; R_H = 33%), or was reduced (Pseudomonas aeruginosa; R_H = 75%) relative to water-saturated conditions. Microspheres were the most hydrophobic (R_H = 98%) and the most retained of all particles under saturated conditions, but microsphere transport was unaffected by gas sparging. These preliminary results suggest that the effect of gas sparging on colloid transport is particle specific and not predictable from measurement of relative hydrophobicity.

Detention basins with a low-flow concrete channel or a vegetated channel are two types of storm water collection basins examined in this study to assess effectiveness in water quality improvement. Influent and effluent data collected from four storm events include flow, petroleum hydrocarbons, nutrients, total suspended solids, three major ions, and indicator organisms. The calculation of influent and effluent mass loading for each basin determines the removal efficiency, which is used to rank the more effective basin for water quality improvement. As expected, the detention basin with a low-flow concrete channel was found to be ineffective for improving the water quality of storm water. The vegetated detention basin was also found essentially ineffective for water quality improvement for all four storms, with low influent mass loading and flushing of stored water the most probable reasons for this result.