Journal of Environmental Engineering

A simple and efficient heuristic screening methodology is presented for use in the regional planning of wastewater‐treatment systems. The proposed approach provides a powerful tool to aid practicing engineers in the decision‐making process regarding optimal locations of regional wastewater collection and treatment facilities. The criterion for eliminating nonoptimal treatment‐plant sites for every wastewater source in the region considered is the critical distance parameter. This nonoptimality conditional parameter is derived from the interrelation between the lower bound on transportation cost and the upper bound on regionalization efficiency. The resulting method is able to significantly reduce the number of candidate locations of shared facilities for regionalized treatment. The final optimal solution may then be selected from the remaining attractive alternative plans by employing conventional mathematical programming precedures. One case example, taken from a previous paper, and four actual large‐scale problems are analyzed and discussed. Enhancement of regional systems management is a principal benefit of the proposed methodology.

This pilot‐scale study comprises a one‐year field evaluation of slow sand filtration as a tertiary treatment of secondary wastewater effluents using two different effective sizes of local sand, i.e. 0.31 and 0.56 mm. to find a simple advanced wastewater treatment method. The filter was operated at sand depths of 135, 105, and 55 cm, respectively, for each size of the sand, to determine the operational range of the sand depth. Secondary effluent from North Aramco Wastewater Treatment Plant (NAWTP) was applied at a hydraulic loading of 0.16 m/h. The filter consistently gave over 90% removal of turbidity for both sizes of the sand at various depths of the filter bed along with over 93% removal of total coliform bacteria. It was observed that the use of coarse sand resulted in longer duration of filter operation as compared to the fine sand for similar removal of turbidity and coliform. i.e., 84 days in the case of coarse sand compared to a maximum of 26 days for the finer sand. The development of the head loss in the sand media was extremely small during the initial period of the operation, which later increased exponentially with most of the head loss occurring in the top dirty surface of the filter, known as Schumtzdecke in German.

Characterization of municipal and county solid wastes as well as projection of waste‐generation and ‐disposal rates are need to plan and implement disposal and recycling activities. A literature review of solid‐waste characterization studies revealed that conventional sorting methods are expensive and yield data with great variability. The results of such characterization studies for metropolitan regions have large standard errors, and individual results often fall within the error bounds of reported national average values. An alternative and more cost‐effective methodology for estimating county‐ and city‐level solid‐waste composition and generation is proposed. The method is based on converting economic sales data for a metropolitan region into estimates of kilograms of solid waste generated. Prototype conversion factors were derived using a material balance approach. The methodology was calibrated using King County, Wash., data and validated on two adjacent counties. The results are promising enough that the methodology should be tested in other parts of the nation. The cost to apply this the methodology is a small fraction of the cost of conventional sorting methods, and comparable estimates of major solid‐waste components may be possible.

Experimental landfills were spiked with known amounts of trace volatile organic compounds (VOCs) in order to estimate their emission behavior over time. The study was set up in two phases. Phase I involved spiking benzene, toluene, and ethyl benzene into municipal solid waste (MSW) to simulate small amounts of residual chemical that might be disposed in household wastes. The emission of the three compounds was monitored for 5–7 years. In phase II, the same compounds were spiked into sewage sludge that was codisposed with MSW solid waste. The emissions were monitored over the first 20 months after disposal. The data from this study indicate that emission rates of the compounds studied, may be first order with respect to the initial chemical load. The data also showed that biogas flux rate was an important factor in emission of VOCs from landfill. The data were compared to emission models found in the literature. The data came close to a fit in a model proposed earlier.

Air streams contaminated with chlorinated solvents are increasingly common as by‐products of air‐stripping and soil‐vapor‐extraction operations. This research investigated treatment of such gas streams with a bioreactor that supported the growth of methanotrophic bacteria. These bacteria cometabolize many chlorinated solvents. Trichloroethylene (TCE) and 1,2‐dichloroethane (DCA) were selected as model contaminants. Removals ranged from 20% to 80% at influent concentrations of 300–1,000 μg/L of air and packed‐bed gas‐resident times of 5–12 min. Biofilm models were able to describe bioreactor performance well. Pseudo‐first‐order rate constants from reactor modeling were considerably smaller than those measured in batch systems, suggesting that much of the biofilm was inactive, which also was supported by methane‐removal data. Enzyme competition between methane and chlorinated solvents and toxicity from chlorinated solvent metabolites both appeared significant.

Mathematical models were developed to predict design and operational conditions needed to implement oxide‐coated media as a treatment process for soluble manganese removal. Two separate models were developed to predict the continuous removal of soluble manganese in the presence of free chlorine (continuous regeneration model), and the eventual breakthrough of soluble manganese without oxidant addition (intermittent regeneration model). Each model was derived from chemical reaction, mass balance, or isotherm equations and was further developed by a sensitivity analysis and parameter estimation. Model verification involved review of independent research studies regarding soluble manganese removal.

Heterogeneous advanced oxidation involves the use of photoactive metal oxide catalysts illuminated with near‐UV light to generate highly reactive species that can oxidize organic chemicals. This study examined the technical feasibility of using heterogeneous advanced oxidation for the regeneration of spent adsorbents. Adsorbability and regenerability of nonimpregnated and photocatalyst‐impregnated adsorbents were evaluated. The nonimpregnated adsorbents were regenerated in titanium dioxide suspensions, whereas the photocatalyst impregnated adsorbents were regenerated in water in which no suspended photocatalyst particles were present. The results showed that the regeneration rates for the impregnated adsorbents were much faster than those for the nonimpregnated ones. To obtain adsorption capacity recoveries of >90%. a regeneration time of about one‐fifth of the adsorption time was required for the regeneration of an adsorbent impregnated with platinized titanium dioxide whereas regeneration times longer than the adsorption times were required for the regeneration of the nonimpregnated adsorbents.

Bench‐scale studies were conducted using a constant‐head ground‐water flow chamber and natural soil. Initial experiments with chlorides and dye were conducted to test the hydraulic and adsorptive characteristics of the chamber. A constant flow of phenol was then introduced into the chamber and contaminant movement with time was monitored under freezing and nonfreezing conditions. The chamber was located in a controlled‐temperature room, and freezing fronts were induced from the soil surface downward using cooled Freon circulated through freezer pads placed on the surface of the soil. The results conclusively demonstrate that phenol is excluded from the freezing front and pushed downward through the system. Extensive exclusion of the chemical occurs even though the freezing point of phenol (43°C) is significantly higher than water. The information gained through this research is applicable in cold regions outside Alaska and the Arctic where ground water systems may undergo periodic freezing, and may also be of extreme importance in artificial‐freezing scenarios such as those currently being investigated by the Environmental Protection Agency (EPA) as a method of contaminant containment.

The change in hydraulic conductivity of saturated clays due to short‐term and long‐term exposure of organic chemicals to clays is investigated to explain the change in hydraulic conductivity of contaminated soils. The long‐term exposure of soils to chemicals is simulated in a laboratory environment by premixing chemicals with soils. Under short‐term and simulated long‐term exposures of water soluble chemicals to soils, the hydraulic conductivities of laboratory consolidated clays are measured and reported. The permeability tests are performed using the both flexi‐wall and modified fixed‐wall permeameters with soil samples subjected to confining pressures. The fixed‐wall and flexi‐wall permeameters produced similar results. The short‐term permeability tests showed a change in hydraulic conductivity values but not the intrinsic permeabilities of soils. The simulated long‐term exposure of organic chemicals to soils showed a change in the soil structure and an increase in the intrinsic permeability of soils. The increasing trend in the intrinsic permeability of a given soil was weakly correlated to the decreasing dielectric constant of the pore fluid.

In this technical note, results are presented from a series of laboratory experiments involving the enhancement of hydraulic conductivity of clayey sands using ultrasonic excitation. An increase in hydraulic conductivity was observed in all the tests with a maximum being reached after about 8 to 10 min of excitation. Grain‐size distribution anlayses of the soils conducted before and after ultrasonic treatment indicated that particles smaller than 0.04 mm were mobilized by ultrasonics, and that particles in the size range of 0.04 mm to 1 mm were subjected to fracturing. Some practical implications of these results are discussed in terms of technical and economic feasibility of in situ implementation of ultrasonics.