Journal of Environmental Engineering

A graphical model is developed that offers a convenient solution to wastewater disposal problems through submarine outfalls. The model is intended to perform preliminary analysis under worst-case dilution conditions for outfalls with line diffusers, currents from any direction, stratified or unstratified ambient, and submerged or surfacing plumes, and it is also valid for outfalls with single horizontal or vertical ports. The model is thus applicable for most outfall configurations and ambient conditions of practical interest. The model simultaneously considers three dilution mechanisms: initial dilution, dilution through dispersion, and effective dilution due to decay of nonconservative substances. This enables analysis of functional dependencies and grouping of model variables in a way that permits a generalized graphical solution. It also allows one to study the sensitivity of the overall dilution to current speeds and compare the relative performance of perpendicular and parallel line diffusers. The results showed that, contrary to what is widely believed, in most situations of practical interest, high rather than low current speeds are critical in outfall design and parallel rather than perpendicular line diffusers often deliver the best overall performance.

Environmental engineers frequently employ the assumption that steady-state conditions are approximated after three hydraulic residence times. In this paper, the conditions under which this assumption is valid are elucidated. For well-mixed systems, the time to approach steady state depends on the kinetic order of removal mechanisms, the initial pollutant concentration in the control volume (=C₀), and the kinetic rate constant. The assumption of three hydraulic residence times to steady state was found to be conservative if C₀ = 0. However, if C₀ equals the influent concentration, then more than three hydraulic residence times may be required to approach steady-state conditions with some zero-order reactions.

Accurate estimation of sediment microbial biomass is needed for studies in microbial ecology. The most common techniques currently used to estimate biomass in sediments are not only prone to considerable uncertainty, but are also time-consuming and labor-intensive. In the present study, a relatively new separation and sizing technique, sedimentation field flow fractionation (SdFFF), previously developed for biomass determination of bacteria in cell cultures and natural waters, was used to determine sediment bacterial biomass. SdFFF together with epifluorescence microscopy for cell counting in separated fractions was used for estimating the biomass in sediment samples from a wetland and a river site. Cell counting was required as yellow autofluorescing particles interfered with the on-line detector signal from the fluorescent tagged bacteria (blue) making this simple method of monitoring cell numbers impossible. Calibration curves were obtained that can be used for calculation of sediment bacterial biomass from cell count data for the two sites under study. This demonstrates that for specific systems the less tedious total counts method can be used to generate quantitative biomass estimates using SdFFF to provide accurate calibration for the conversion of counts to biomass. This approach overcomes the serious problems associated with conventional methods that often assume a constant biomass to cell counts or cell volume ratio between collection sites. The SdFFF method was applied to monitor cell growth in sediment samples after addition of phosphate and several types of carbon sources. On incubation for eight days, carbon-amended sediments showed higher bacterial biomass and contained more aggregated colonies, which needed to be dislodged by more vigorous treatment than those treated with phosphate alone.

The presence of hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) in surface soil, the vadose zone, and ground water can present serious environmental problems. The processes governing the release and transformation of RDX into soils and the aquatic environment are not well understood. The objective of this study was to determine the effects of differing environmental conditions as reflected by redox potential and pH on the fate of RDX in soil. Laboratory investigations consisted of testing three redox potentials and four pH levels in an 18:1 (2,600 m³ water:150 g soil) suspension spiked with 10 mg/L RDX. Results indicated that RDX was unstable under highly reducing conditions (−150 mV) and relatively stable over the short term (15 days) under oxidizing and moderately reducing conditions at all pH values. RDX in areas of intense reduction would not persist. However, RDX deposited or moving into areas under moderately reducing or oxidizing conditions would be highly mobile and persistent.

A new theoretical model to analyze the measurements obtained from a typical soil column venting experiment is proposed. The principles of mass transfer, Darcy's law, and air compressibility in the form of pressure-volume relationships were coupled to calculate the contaminant concentration in the gas phase (air), and the rate of contaminant removal. The proposed model relates soil air permeability with the contaminant removal and is capable of calculating the variation of soil air permeability with time during the venting process. The contaminated sand sample was idealized as a system of straight capillary tubes in the direction of flow, lined by the liquid contaminant. A closed-form solution for radial diffusion of the contaminants in a cylinder, coupled with axial advection of air, was used to model contaminant removal. The results from the mass transfer model were then used to trace the change of soil air permeability with time. The model also uses, as an alternative approach, a modified form of Darcy's law for compressible flow.

In this study, phenol degradation was investigated, with and without glucose as a cosubstrate, in batch and continuous studies. The two 2-L lab upflow anaerobic sludge blanket reactors were operated at a constant hydraulic retention time of 12 h with a gradual stepwise increase in phenol concentration from 105 to 1,260 mg/L. Batch studies showed that a 1,000-mg/L glucose supplement provided the fastest phenol removal and sludge acclimation. The effect of the glucose supplement was assessed based on microbial acclimation and granulation, phenol degradation, and resistance to shock loading. The reactor with the 1,000-mg/L glucose supplement had a shorter start-up and granulation period (4 months, compared to 7 months for the reactor without glucose supplement), larger granule size (2.76 mm, compared to 1.77 mm), and higher phenol removal efficiency under steady-state operation at 6-kg phenol-COD/L⋅day (98% compared to 88%). The reactor with the glucose supplement also exhibited a higher resistance to shock load or temperature change and faster recovery than the reactor without a glucose supplement.

Consideration of Orimulsion, a bitumen/water emulsion, for use as an alternative fuel in power generation facilities has prompted interest in methods for responding to environment spills during transport. The adhesive nature of the 70% bitumen (asphalt) emulsion, however, poses a unique challenge for cleanup. The results of a study to investigate filtration as a cleanup alternative are presented in this paper. Pilot tests were conducted to evaluate the feasibility of diatomaceous earth precoat filtration and ultrafiltration for cleanup of marine and freshwaters contaminated with Orimulsion. Volatile suspended solids removal rates up to 99.9% were obtained for diluted Orimulsion (<1.0%) at a flux of 2,140–10,700 Lph/m² (1,440–7,200 gpd/ft²) using a constant flow, plate and frame pilot filter with flux-calcined grades of marine diatomite. Higher permeate quality, less than 2.0 mg/L as volatile suspended solids, with 99.99% rejection was obtained using tubular polyvinyldiene fluoride ultrafiltration membranes, at a flux of 30–220 Lph/m² (18–130 gpd/ft²) with filtration additives. Recommendations for process selection are suggested based on feed strength, desired effluent quality, and residuals preference.

Surface characteristics of activated carbons can play critical roles on adsorption performance of volatile organic compounds (VOCs). Attempts were made to correlate the specific physicochemical characteristics of various activated carbons with the VOC adsorption. Eight commercial activated carbons and ten VOC species were studied. Detailed physicochemical properties of activated carbon were established in this study. Results indicate that both factor analysis and correspondence analysis can provide satisfactory information on the relationship among the surface characteristics of activated carbon, the VOC properties, and the VOC adsorption on activated carbon. Results also suggest that boiling point, critical temperature, cross-sectional area, and dipole moment of the VOCs are the most important properties governing activated carbon adsorption. Additionally, pore volume and specific surface area of activated carbon are still considered as the most important factors regarding the VOC adsorption.

This study investigated the adsorption mechanism of heavy metals Cr, Cu, Pb, and Cd on the sorbent during incineration by the following technologies: (1) thermal desorption of heavy metals from the sorbent; (2) identification of heavy metal species in the adsorbed sorbent by x-ray diffraction technique; (3) thermodynamic equilibrium simulation of heavy metals and sorbent; and (4) micrography of the sorbent by scanning electron microscopy. Experimental results indicated that adsorption mechanism of heavy metals on sorbent is related to the volatility of heavy metal species formed at high temperatures and the chemical reactivity with the sorbent. For less volatile heavy metals Cr and Cu, chemical reaction is the major adsorption mechanism, and particle growth due to condensation, coagulation, and sedimentation will become important as the reacting time is increased. For highly volatile metal Cd and most metal chlorides, physical molecular adsorption and particle growth processes are the major mechanisms. Most volatile metal species are adsorbed/distributed on the surface of the sorbent. For Pb (which has been classified as medium to high volatility), chemical and physical adsorption mechanisms are all-important depending on the reacting environment.

The pyrolysis of high-density polyethylene (HDPE), the principal component of plastics in municipal solid waste, was studied in the thermal gravimetric analysis reaction system containing hydrogen chloride (HCl) gas. The pyrolysis experiments were carried out over a range of room temperatures to 850 K. The results indicated that HCl retarded the pyrolytic reaction of HDPE at high HCl concentration C_HCl range. The gas/liquid products and solid residues were collected and analyzed by gas chromatography, mass spectrometer, and elemental analyzer. The distributions of gas/liquid products and solid residues as well as the effects of HCl on the pyrolytic products were investigated. The results of this study are useful for the utilization of HDPE as an energy resource and determining the thermal degradation behavior of HDPE in an incinerator.

The energy flow of an existing municipal solid waste incinerator (MWI) was analyzed for better understanding of the energy balance and efficiency in a typical MWI located in Taiwan. The MWI investigated is of mass-burn type and is equipped with electrostatic precipitators followed by wet scrubbers for removing air contaminants from gas streams. The results of energy balance analysis indicate that the rate of energy input is 73,000 MJ/h based on the lower heating value of 7,600 kJ/kg of municipal solid wastes for single incineration unit. Furthermore, energy distribution analysis demonstrates that the heat loss of incinerator, heat absorbed by boiler, heat loss of air pollution control devices, and heat discharge from stacks are 3.8%, 68.8%, 11.1%, and 15.1% of total energy input, respectively. The sum of heat absorbed by boiler and the heat discharged with the flue gas via stack accounts for more than 80% of the total energy input.