Journal of Environmental Engineering

The effectiveness of landfill‐liner designs is evaluated in terms of the slope, drainage length, and saturated hydraulic conductivity of the lateral drainage layer, the saturated hydraulic conductivity of the soil liner, and the fraction of the area under a synthetic liner where leakage is occurring. The evaluation is performed using Version 1 of the Hydrologic Evaluation of Landfill Performance (HELP) model. The effectiveness is quantified by comparing the lateral drainage rate to the vertical percolation rate expressed as percentages of the total inflow. The two multiple‐liner systems specified in the Hazardous and Solid Waste Amendments (HSWA) minimum technology guidance are shown to have different leakage‐detection characteristics. One system detects significant leakage before leakage percolates out of the landfill, whereas the other system detects leakage only after significant leakage percolates out of the landfill. Four other designs were also examined—two with single liners and two with double liners. The two HSWA designs detected leakage at lower synthetic‐liner‐leakage fractions, but all designs with composite liners were nearly equally effective in reducing leakage from landfills.

An expanded‐bed anaerobic biological GAC reactor was connected to a GAC adsorber to form a hybrid reactor design for the treatment of inhibitory wastes that separates biological transformation from physical removal mechanisms. The performance of the hybrid GAC reactor was compared with a “conventional” expanded‐bed GAC anaerobic reactor. Both reactors were subjected to similar operating conditions. The synthetic wastewater used in the study was comprised of acetate and 3‐ethylphenol (3‐ep). The COD loading ranged from 13.3 to 23.8 kg $\mathrm{COD}/m^3\text{.}$ Partial replacement of GAC with virgin GAC was practiced in both reactors to control toxicity and facilitate the physical removal of 3‐ep. The hybrid GAC reactor provided greater biological‐removal efficiencies than the “conventional” GAC reactor. GAC replacement did not affect biomass retention in the hybrid GAC reactor, and sludge ages in the “conventional” GAC reactor were limited by the rate of GAC replacement. Sludge ages averaged 100 days in the hybrid GAC reactor, which allowed for significant biodegradation of 3‐ep. At a sludge age of 9.3 days, 3‐ep degrading organisms washed out of the conventional GAC reactor. The hybrid GAC reactor design demonstrated promise for the efficient treatment of biologically inhibitory wastewaters.

A five‐month pilot study was conducted to examine the effectiveness of the upflow anaerobic sludge blanket (UASB) process for the treatment of effluent from a brewery in rural China. Results indicate that the process operated at 26° C could reduce over 89% of chemical oxygen demand (COD) and 92% of five‐day biochemical oxygen demand $\left({\mathrm{BOD}}_5\right)$ from the brewery effluent, with a hydraulic retention time (HRT) of 13.3 hr and a COD loading rate of 4.9 kg $\mathrm{COD}/m^3/\mathrm{day}\text{.}$ The brewery effluent in this study on average contained 2,692 ppm COD and 1,407 ppm ${\mathrm{BOD}}_5\text{.}$ The treated effluent on the other hand contained 295 ppm COD and 122 ppm ${\mathrm{BOD}}_5;$ both of which could be further reduced should the suspended solids be more effectively removed. Overall, this process was operated satisfactorily and smoothly, as reflected by the constant effluent pH and gas production rate, as well as the consistently high degrees of reduction of COD and ${\mathrm{BOD}}_5\text{.}$ Parameters such as sludge density, distribution of volatile suspended solids (VSS) and soluble COD in sludge bed, gas production rate, and nutrient levels are discussed.

The oxidation‐reduction potential (ORP) was monitored within aerobic sludge digesters undergoing alternating aerated and nonaerated conditions. Observations were made on both bench‐scale and pilot‐scale reactors. Batch tests were also conducted on both reactors, involving a time series of chemical analyses, in conjunction with automated monitoring of reactor ORP and dissolved oxygen. The results indicated that a characteristic and reproducible ORP profile was associated with the cycled operation of the digesters. These real‐time ORP profiles had a number of distinctive features, directly related to changes in system chemistry and biological activity. The ranges of aerobic and anoxic respiration, as well as fermentation, were clearly defined by slope changes on the ORP profile. They also corresponded to the presence of the appropriate electron acceptors. The transition between the different ORP ranges was observed to be quite different during reaeration and deaeration. ORP was related to low levels of dissolved oxygen and nitrate. The data indicated that ORP could be used to measure very low oxygen concentrations. The reproducibility of the ORP profiles and sensitivity of the measured potential, to changes in biological or chemical activity, appears to make it an ideal parameter for automated monitoring and process control.

A series of bench‐ and pilot‐scale experiments was conducted to evaluate the ability of biochemical oxygen demand (BOD) bottle‐based oxygen uptake rate (OUR) analyses to represent accurately in situ OUR in complete mix‐activated sludge systems. Aeration basin off‐gas analyses indicated that, depending on system operating conditions, BOD bottle‐based analyses could either underestimate in situ OUR rates by as much as 58% or overestimate in situ rates by up to 285%. The use of a continuous flow respirometer system was used to verify the off‐gas analysis observations and assess better the rate of change in OUR after mixed liquor samples were suddenly isolated from their normally continuous source of feed. OUR rates for sludge samples maintained in the completely mixed bench‐scale respirometer decreased by as much as 42% in less than two minuts after feeding was stopped. Based on these results, BOD bottle‐based OUR results should not be used in any complete mix‐activated sludge process operational control strategy, process mass balance, or system evaluation procedure requiring absolute accuracy of OUR values.

The adsorption of two dyestuffs from aqueous solutions onto bagasse pith was studied using an agitated batch adsorber. A three‐resistance mass transfer model, based on external mass transport, macropore diffusion, and micropore diffusion, was used to predict concentration versus time decay curves. The predicted curves were correlated with experimental data for up to 24 hours in order to determine the three mass transport parameters.

An indexing relationship, used to index and directly compare measurements, is developed for liquid phase‐controlled gas transfer in self‐aerated flows from theoretical considerations. The indexing relation is shown to describe temperature effects as well as existing equations that use fitted coefficients. The relation may be used to index adsorption and volatilization rates of any compound exhibiting liquid phase controlled gas transfer and may be used to compare the gas transfer measurements of different compounds. It is proposed that the relationship be used to index liquid phase controlled gas transfer measurements in self‐aerated flows to a common reference temperature, 20° C, and to a gas, oxygen, most often used in gas transfer experiments. The indexing relationship is also shown to be valid for any bubbly flow where the gas transfer is predominantly across the bubble interface, such as occurs with aeration bubblers.

Flow and mixing in a wastewater dechlorination basin are investigated by tracing dye concentrations in a 1:12 scale sectional model and in a fullscale installation. The injection of an ${\mathrm{SO}}_2$ solution that neutralizes residual chlorine is simulated by dye. Time series measurements of dye concentrations are obtained in the model and in the full‐scale basin. Mean dye concentrations and standard deviations of concentration fluctuations measured throughout the model and the full‐scale basin compare favorably. Both show incomplete mixing of ${\mathrm{SO}}_2$ solution and residual chlorine. The model is then used to develop a substantially improved basin design by relocation of ${\mathrm{SO}}_2$ injection and addition of a columnar wall to redistribute the flow and create small‐scale turbulence. The modifications can be implemented without interruption of wastewater treatment. The performance of the improved design is again validated in the full‐scale operation. The study shows that existing problems of mixing and flow processes can be explored and corrected efficiently and effectively using a scale model. It is recommended that this method be used for the study of novel designs before construction.

A simple yet effective approach is presented for solving regional wastewater treatment system capacity expansion problems. The approach decomposes a model into two levels, upper and lower. The lower level treats the subproblems related to separate facilities of a regional treatment system. These subproblems are solved independently by dynamic programming. The upper level is used to coordinate the subproblems in the lower level and is updated using a random polyhedron search algorithm that identifies progressively superior solutions. Constraints imposed on treatment plant or transfer capacities are considered first, and then constraints relating to the in‐stream quality of the receiving water are incorporated. The procedures developed are tested in a hypothetical problem with seven communities along a river and its tributary. The results obtained indicate that it is economically attractive to consider time‐staging of capacity whenever possible. It is also observed that the model with in‐stream quality constraints required more computational resources, the amount of which is somewhat dependent on the level of in‐stream quality requirement imposed. However, the incremental computational efforts required might not be excessive.

Graphs are developed based on the concept of feasible diameter set for the rapid design of sanitary sewers. They are developed for various hydraulic criteria, such as full flow and best hydraulic cross section, taking into account the hydraulic constraints such as velocity and partial depth of flow. These graphs can be used by practicing engineers to perform quick and improved designs, thereby eliminating any need for trial‐and‐error procedures. Procedures for preparation of the graphs are detailed. An illustrative example describing the application of design graphs is included.

This paper proposes a heuristic method to obtain a least‐cost water distribution network design with a given reliability. The method first attempts an optimal design using a model without the consideration of reliability. The reliability of the obtained network design is then assessed. Finally an iterative feedback procedure is employed, moving between two models, which improves the reliability with a small increase in cost. Reliability is measured as the complement of the ratio of the expected minimum total shortfall in flow to the total demand, and the maximum total flow supplied under a link failure is computed by a network flow analysis. The reliability is improved by increasing link flows (or link capacities) along a longest path from the source node, in such a way that reliability increment is achieved with a small cost increment. The new link flows are used to find the new optimal pipe sizes. The iterative procedure continues until a satisfactory reliability is obtained.

Water‐distribution systems require reorganization to derive increased water demand resulting from an increase in population through either increased population density or expansion into new internal areas. If the increased demand is marginal, then the improvement of pumping is generally sufficient. On the other hand, if the increase is substantial, one must provide parallel pipelines, lay new pipelines, increase the pumping capacity of the existing pumping plants, and/or provide new pumping stations. This process is called reorganization of an existing water‐distribution system. No attempt has been made so far to solve this problem in its original form. Attempts, however, remained confined to providing parallel pipelines and increasing the pumping capacity of a modified branched configuration. Presented herein is a criteria for utilization of an existing water‐distribution system by improved pumping for catering the increased demand. An algorithm has also been developed to reorganize a water‐distribution network.

The tightening of dissolved oxygen (DO) standards in recent years suggests the employment of an accurate predictive method of the BOD‐DO conditions in streams. An advanced method should account for dispersion, which can be significant under transient loadings and attendant large concentration gradients. Such a numerical algorithm is presented in this paper; it is based on the premise that advection is the dominant but not exclusive transport mechanism. The method is accurate (can resolve steep fronts), efficient, robust, and easy to implement. The proposed model has been validated against exact and perturbation‐derived analytical solutions. It has been shown to perform well under quite severe transient source loadings, conditions in which the error of the classical Streeter‐Phelps model is sizeable.

Equations are developed for predicting the liquid‐film and gas‐film reference‐substance parameters for quantifying volatilization of organic solutes from streams. Molecular weight and molecular‐diffusion coefficients of the solute are used as correlating parameters. Equations for predicting molecular‐diffusion coefficients of organic solutes in water and air are developed, with molecular weight and molal volume as parameters. Mean absolute errors of prediction for diffusion coefficients in water are 9.97% for the molecular‐weight equation, 6.45% for the molal‐volume equation. The mean absolute error for the diffusion coefficient in air is 5.79% for the molal‐volume equation. Molecular weight is not a satisfactory correlating parameter for diffusion in air because two equations are necessary to describe the values in the data set. The best predictive equation for the liquid‐film reference‐substance parameter has a mean absolute error of 5.74%, with molal volume as the correlating parameter. The best equation for the gas‐film parameter has a mean absolute error of 7.80%, with molecular weight as the correlating parameter.

Transformation kinetics, corrected for abiotic loss and for volatilization, of 14 polycyclic aromatic hydrocarbon (PAH) compounds were studied in two nonacclimated soils. Mean volatilization losses for naphthalene and 1‐methylnaphthalene were measured as 31% and 22%, respectively, of the total masses applied. Volatilization of the other twelve PAH compounds studied was less than 0.1%. The abiotic loss (1.8‐17.4%) of two‐ and three‐ring PAH compounds in soil samples bio‐inhibited by 2% ${\mathrm{HgCl}}_2$ was statistically significant $\left(p<0.05\right)\text{.}$ No significant loss from bio‐inhibited soil was found for PAH compounds with more than three rings. Transformation half‐lives corrected for volatilization and for abiotic loss were approximately 2 days for two‐ring PAHs including naphthalene and 1‐methylnaphthalene. Half‐lives values for nonvolatile PAHs increased from 59 days for three‐ring PAHs (anthracene and phenantherene) to more than 300 days for PAH compounds containing more than three rings. The PAH transformation rate was inversely proportional to molecular weight and compound ring number.

The effect of flavoring agents containing chemicals, such as ascorbic acid, NutraSweet, saccharin, citric acid, and tannic acid (in tea mixes) on the disinfection, by iodine, of small quantities of water is studied experimentally. It is found that ascorbic acid and tannic acid react with $I_2$ in less than 0.2 s to form non-germicidal $I^{-}$ ions. Thus, the addition of flavoring agents is recommended only after disinfection by iodine is considered to be sufficiently complete. The heating of iodinated water to remove dissolved iodine and thereby render it more palatable is also studied and found to be ineffective.

The effect of freeze-thaw conditioning for enhanced sludge dewatering is effective only when sludge freezes completely and slowly. This recognition has inhibited the development of commercialized freeze-thaw conditioners. If sludge is frozen in thin layers, however, the freezing can be slow, complete, and fairly rapid. The studies reported here suggest that the freezing rate can be assumed to be only a function of the temperature and the convection coefficient, and that the insulating effect of the ice can be ignored.