Showing papers in "Journal of Environmental Engineering in 1990"

Molecular size distributions of dissolved organic matter

Abstract: Discrete molecular size distributions of dissolved organic matter (DOM) in natural waters and wastewaters are usually determined using an array of ultrafiltration membranes in stirred cells However, many researchers neglect membrane rejection, resulting in an underestimation of DOM in low molecular weight size classes In this paper, we develop a simple model, based on a permeation coefficient, that can be used to improve the accuracy of size distributions Since permeation coefficients are a function of membrane material and water composition, these coefficients must be determined for every water sample The utility of the model is demonstrated by comparing unadjusted and adjusted size distributions of dissolved organic carbon (DOC) in ground waters and municipal wastewaters For example, when membrane rejection is neglected, 41% of the DOC in Biscayne Aquifer ground water has an apparent molecular weight greater than 5,000 amu Size distributions determined using the permeating coefficient model, however, indicate only 16% of the DOC is greater than 5,000 amu

Generalized Lagrangian Model for Buoyant Jets in Current

Abstract: A general Lagrangian jet model formulation is presented for an inclined buoyant jet in a current, with a three‐dimensional trajectory. The shear‐induced entrainment is computed as a function of the local densimetric Froude number and jet orientation, while the forced entrainment is taken as the ambient flow intercepted by the “windward” side of the buoyant jet. Model predictions are compared with both trajectory and tracer concentration data for a wide range of discharge and ambient flow conditions: horizontal buoyant jets in a coflow; vertical jets, oblique jets, and dense plumes in a cross flow; buoyant jets in a stagnant uniform or stratified fluid; and a horizontal buoyant jet in a perpendicular cross flow. The model is also consistent with the concept of asymptotic flow regimes, and reproduces the correct behavior in both the near and far field of a vertical momentum of buoyancy‐dominated jet in a cross flow. The connection of the model with traditional integral jet models is also discussed.

Indexing Gas Transfer in Self-Aerated Flows

Abstract: 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.

Sediment Oxygen Demand Model: Methane and Ammonia Oxidation

Abstract: A model of sediment oxygen demand is presented that relates the sediment oxygen demand (SOD) to the extent of oxidation of dissolved methane and ammonia generated in the anaerobic zone of the sediment of lakes and streams. The fluxes of dissolved methane and ammonia from the sediment to the overlying water, as well as methane and nitrogen gas fluxes that escape as bubbles, are included in the model. The three model parameters—the dissolved methane mass transfer coefficient and the two oxidation rate parameters—are estimated from laboratory and field data sets. The effect of overlying water dissolved oxygen and temperature is examined. The importance of the gas fluxes and their quantitative relationship to SOD is established. Any field program that includes the measurement of SOD should also include the measurement of the nitrogen and methane fluxes as well. The model is limited to freshwater sediments since the oxidation of sulfides is not included. The contribution from the respiration of benthic macro f...

Freezing of Water and Wastewater Sludges

Abstract: When sludge is allowed to freeze slowly and then thaw, its dewatering properties are usually greatly improved. The mechanisms by which this improvement occurs are not well understood. This paper proposes a conceptual model for how sludge freezes. The validity of this model is discussed using past research findings as well as experimental evidence. The effectiveness of freeze/thaw is measured using the capillary suction time apparatus. The results indicate that colder temperatures, longer freezing times and slower freezing rates all have a beneficial effect. These results suggest that if freeze/thaw is to be used commercially, thin layers of sludge must be frozen slowly for long periods of time, thereby promoting the growth of crystals that will exclude the solid particles and promote particle aggregation.

Transformation of PAHs in soil systems.

Abstract: 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% HgC1\d2 was statistically significant (p<0.05). 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.

Use of ORP for Monitoring and Control of Aerobic Sludge Digestion

Abstract: 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.

New approach for optimization of urban drainage systems

Abstract: A new approach for the optimization of urban drainage systems including the optimal selection of layout using the searching direction method and the optimal design of a given layout by discrete differential dynamic programming (DDDP) is developed and applied to a typical field study. It is found that the inclusion of such hydraulic factors as flow rate, the sizes and gradients of pipes, and the effect of on‐line pumping stations into consideration, is very important in urban drainage systems layout selection. Also, the optimization of urban drainage systems including optimal layout selection can achieve much greater construction cost savings than that without the inclusion of layout optimization. It has also been demonstrated that the minimum buried depth design is not the global optimum design; instead, the global optimum design is the alternative of the optimal balance among the buried depth and the number and locations of on‐line pumping stations.

Least‐Cost Scheduling of Solid Waste Recycling

Abstract: The expense and controversy of siting new landfills and solid waste incinerators have brought new urgency to efforts to extend the life of existing landfills. The most common approach taken has been to encourage the recycling of some wastes by households and businesses. However, recycling is not costless, and it is unlikely that the costs of all possible recycling efforts are worthwhile in terms of deferring landfill closure and replacement costs. This paper develops a simple linear programming method for evaluating and scheduling a given set of recycling measures in this context. The method also determines the least‐cost landfill lifetime.

Biodegradation of Toxic Organics: Status and Potential

Abstract: The ability of biological treatment systems to degrade toxic organic compounds is assessed through a review of the literature. While much general information is available, there is little kinetic information that can be used directly by engineers making decisions about process alternatives. Nevertheless, useful kinetic information can be obtained from biodegradation studies in which the toxic compound of interest serves as the sole substrate for microbial growth; a scheme is proposed whereby such information can be used in mathematical models to predict the extent to which the toxic compounds can be removed from complex waste streams. A methodology is also proposed whereby the impacts of the toxic compounds on the biodegradation of the biogenic organic material in the waste streams can be predicted. Finally, it is noted that new information about environmental biotechnology is being generated by biologists faster than engineers can assimilate and apply it. Thus, close alliances must be formed between engineers and scientists to fully exploit the potential offered by biotechnology.

Modeling of Nitrification Under Substrate‐Inhibiting Conditions

Abstract: A mathematical model was developed for the biological-nitrification process. The model assumed two consecutive oxidation steps occurring under a substrate-inhibiting condition. The mathematical model was calibrated using data obtained from batch experiments performed on the contents of five chemostats operated to steady-state on a feed containing 1,000 mg/L of ammonia-nitrogen. In the batch experiments, initial ammonia concentrations ranging from 100 to 1,000 mg-N/L were used. Time-varying concentrations of ammonia and nitrite were collected until the oxidation of these constituents was complete. Parameter sets that optimized the fit on the mathematical model to the experimental data were obtained by nonlinear-regression analyses. The oxidation of ammonia to nitrite was well represented by the Haldane-inhibition model. The Haldane-inhibition model did not satisfactorily describe the oxidation of nitrite to nitrate. It was observed that the simultaneous presence of both nitrite and ammonia led to the inhibition of nitrite oxidation. Modification of the model to consider a revised inhibition mechanism that accounted for the observed behavior was quite successful for the interpretation of the nitrite-oxidation data.

Algorithm for Reliability‐Based Optimal Design of Water Networks

Abstract: This paper proposes a heuristic method to obtain a leastcost water distribution network design with a given reliability. The method first attempts an optimal design using a model without the consid...

Statistical Evaluation of Mechanistic Water‐Quality Models

Abstract: Current practice for the verification of water‐quality simulation models is to use a combination of modeler judgment and graphical analysis to assess the adequacy of a model. Statistical testing of goodness‐of‐fit is sometimes undertaken, but usually with a null hypothesis that does not allow distinction between acceptable fit and highly variable data. In this paper, statistical methods are proposed to augment, but not replace, this conventional approach with a quantitative expression of goodness‐of‐fit. Model verification is expressed as a problem in hypothesis testing that may be conducted using a variety of statistical methods. Guidance is provided on the appropriate structure of the null hypothesis so that good model fit is not confounded with highly variable predictions and observations. In addition, consequences and corrective measures associated with assumption violations are examined. The t‐test, the Wilcoxon test, regression analysis, and the Kolmogorov‐Smirnov test are extensively discussed, and...

Removal of Dissolved Organic Matter by Nanofiltration

Abstract: "A nanofiltration module is studied to determine its ability to remove dissolved organic matter (DOM) from two water sources: An effluent-impacted ground water and a low-turbidity surface water. Both feed and product waters from a single nanofiltration module are analyzed for trihalomethane precursors, as measured by bulk water dissolved organic carbon (DOC), UV absorbance, and trihalomethane formation potential (THMFP), as well as molecular weight (MW) distributions of these parameters. Results indicated excellent rejection of DOM accompanied by good rejection of inorganics, as reflected by conductivity data. Nanofiltration is very effective in rejecting higher molecular weight DOM (>1,000 amu) while moderately effective in rejecting lower molecular weight material (<1,000 amu).

Effects of ammonia on anaerobic digestion of simple organic substrates.

Abstract: The effects of ammonia on mesophilic digestion of acetate, propionate, acetate-propionate mixture, and lactate were studied in batch serum bottles. The un-ionized ammonia nitrogen (UAN) affected the acetate-utilizing microorganisms in the acclimated mixed cultures to a greater extent than propionate-utilizing bacteria or other trophic groups. The inhibitory effects were less severe in batch reactors supplemented with sulfate, pointing to an antagonistic action of the sulfate-reducing bacteria. Analysis of the inhibition pattern of methane/biogas production has shown that UAN displayed a moderate half-kill dose in the range of 10 millimole and demonstrated a high sensitivity exponent. The latter suggests potential for a sudden failure response of an anaerobic system subjected to an increasing ammonia concentration in the reactor.

Nitrosomonas and Nitrobacter interactions in biological nitrification.

Abstract: Biological‐nitrification experiments using chemostats were performed with three different nitrogenous substrates: ammonia, nitrate, and various mixtures of ammonia and nitrite The study focused on the interrelationship between two groups of nitrifying bacterial utilizing different substrates within the same environment It was shown that the activity of the Nitrobacter population was strongly dependent on the population of Nitrosomonas, but not vice versa Nitrite oxidation in the absence of ammonia resulted in a very unstable system and required hydraulic‐retention times of 10 days or greater to obtain complete nitrite oxidation This is in sharp contrast to the complete oxidation of ammonia to nitrate at the hydraulic‐retention time of 27 days Data are presented to show the effect of the ratio of the population of Nitrosomonas to Nitrobacter on the activity of Nitrobacter

Treatment of Brewery Effluent by UASB Process

Abstract: 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 (BOD\d5) from the brewery effluent, with a hydraulic retention time (HRT) of 13.3 hr and a COD loading rate of 4.9 kg COD/m³/day. The brewery effluent in this study on average contained 2,692 ppm COD and 1,407 ppm BOD\d5. The treated effluent on the other hand contained 295 ppm COD and 122 ppm BOD\d5; 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 BOD\d5. 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.

Immobilized‐Cell Degradation of Chlorophenols

Abstract: The ability of immobilized cells grown under oxic and fluidized conditions to degrade 4-chlorophenol (4-CP) and 2,4-dichlorophenol (2,4-DCP) is evaluated under different dilute rate conditions. Microcarriers with 6.5-m pores are employed for cell immobilization and retention. Results indicate that, with feed 4-CP and 2,4-DCP concentrations at 35.7 and 45.3 mg/l, respectively, good and stable removal performance is achievable at empty-bed hydraulic retention times as low as one hour. Stoichiometric release of chloride and removal of total organic carbon are also observed, implying that complete mineralization of 4-CP and 2,4-DCP is attainable. This observation is further validated with the gas; chromatography/mass; spectrometry (GC/MS) data obtained in the 2,4-DCP experimentation. Colonization of immobilized cells on the microcarrier surface is a slow but selective process. Extensive growth of filamentous bacteria is observed with rod-shaped bacteria grown underneath and adhered to the filaments. Detachment of immobilized cells from the microcarrier surface is negligible. The formation of microbial films on the microcarrier surface with measurable thickness is absent.

Aeration‐Basin Heat Loss

Abstract: Recent developments in wastewater aeration systems have focused on aeration efficiency and minimum energy cost. Many other operating characteristics are ignored. The impact of aeration system alternatives on aeration‐basin temperature can be substantial, and design engineers should include potential effects in evaluation of alternatives. To predict aeration‐basin temperature and its influence on system design, previous research has been surveyed and a spreadsheet‐based computer model has been developed. Calculation has been improved significantly in the areas of heat loss from evaporation due to aeration and atmospheric radiation. The model was verified with 17 literature‐data sets, and predicts temperature with a root‐mean‐squared (RMS) error of 1.24° C for these sets. The model can be used to predict aeration basin temperature for plants at different geographical locations with varying meteorological conditions for surface, subsurface, and high‐purity aeration systems. The major heat loss is through eva...

Three-resistance transport model for dye adsorption onto bagasse pith

Abstract: This paper reports the adsorption of two dyestuffs from aqueous solutions onto bagasse pith 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.

Acoustic Imaging of Subsurface Features

Abstract: The characterization of sites containing buried hazardous wastes and the selection of new waste disposal sites have become important problems for environmental engineers. Because of the potential risks associated with uncertainty of the subsurface environment, increasing effort has been dedicated to application of available remote sensing techniques. One such technique which is quantitative and offers high resolution is geophysical tomography (GT). Two approaches to GT are examined: backprojection, which traces straight ray paths, and backpropagation, which inverts the wave equation. Results of field studies demonstrate that buried inclusions having length scales on the order of 0.5 m can be resolved using GT and that identification of differing buried waste forms is possible. This method has been successfully demonstrated for a number of applications and shows great promise for many more.

Decomposition of Large Water Distribution Systems

Abstract: Designing a large water distribution network as a single entity is difficult. The present practice of designing such a system is by decomposing or splitting it into a number of subsystems. Each subsystem is separately designed and finally interconnected at the ends for reliability considerations. The decision regarding the area to be covered by each subsystem depends upon the designer’s intuition. Similarly even on computers, to design a large water distribution system as a single entity has computational difficulty in terms of computer time and storage. Such a system can also efficiently designed on computers if divided into small subsystems. Presented herein is an algorithm which divides a large water distribution system of predecided multiple input points into small subsystems of single input. The algorithm will not only eliminate the present practice of decomposing or splitting by designer’s intuition but also enable the designer to design a large water distribution system in a reasonable computation effort.

DO model uncertainty with correlated inputs

Abstract: The effect of correlation among the input parameters and variables on the output uncertainty of the Streeter‐Phelps water‐quality model is examined. Three uncertainty analysis techniques are used: sensitivity analysis, first‐order error analysis, and Monte Carlo simulation. A modified version of the Streeter‐Phelps model that includes nitrification, net algal oxygen production, and sediment oxygen demand is used. Analyses are performed for a wide variety of simulated stream‐flow conditions. Results show that the standard deviation of the predicted dissolved oxygen deficit (DOD) with correlated inputs potentially can be 20‐40% larger than with independent inputs. Under conditions of moderate to high velocity, the reaeration and bio‐oxidation coefficients are the dominant contributors to DOD uncertainty, while net oxygen production from algal activity and sediment oxygen demand are the major factors at low velocity. The largest effect of input correlation on DOD occurs in the vicinity of the sag point. Unce...

Fundamentals and Application of Windrow Composting

Abstract: The conventional windrow and aerated windrow processes are viable sludge‐disposal options that produce marketable end products. Both methods entail constructing long parallel rows containing a mixture of sludge cake and amendment and turning the rows frequently with mobile equipment. The conventional process relies on natural ventilation whereas the aerated method uses forced mechanical aeration in addition to natural ventilation. Major drawbacks of the conventional process include excess odor generation and susceptibility to upset from adverse weather. Odor control is a major advantage of aerated windrow composting; these systems, however, are more capital intensive than the simpler conventional systems. The Sanitation Districts of Los Angeles County, California, operate a state‐of‐the‐art conventional windrow facility at the Joint Water Pollution Control Plant in Carson, California. The operation uses two composting steps and two different composting machines. Quality‐control monitoring has shown that t...

Colloid Removal in Fluidized‐Bed Biofilm Reactor

Abstract: A methanogenic fluidized‐bed biofilm reactor was successfully operated for the removal of 1‐μm organic colloids. The removal efficiency of total suspended solids was 72–76%, and the total chemical oxygen demand removal was 91–93%. Since some of the effluent suspended solids were biomass, the actual removal efficiency of the original organic particles was approximately 90%. Mechanistic filtration theory was modified to include bed fluidization, biofilm attachment to the collector surface, and effluent recycle. Independent filtration experiments showed that biofilm accumulation increased the cohesion coefficient from zero to 0.04. The predictions using a measured cohesion efficiency of 0.04 agreed with the findings from the methanogenic system: Removal of input suspended solids was 90% at 31% bed expansion; the recycle of effluent was an important determinant of the ability of the fluidized‐bed system effectively to filter the particle material; and, for the organic loading conditions of this study, the rem...

Prediction of stream volatilization coefficients

Abstract: 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 equati...

Heuristic design of sewer networks

Abstract: This paper presents a heuristic approach for the design of sewer networks that can handle the introduction of lift stations and the use of standard diameters. This heuristic provides good and logical (rather than optimal) designs of sewer networks. The necessary and sufficient conditions to determine the position of a lift station are presented in a theorem. Based on this theoretical result, a heuristic design algorithm, using either the Manning or the modified Hazen‐Williams hydraulic equation, is developed. The proposed heuristic design algorithm takes into account all the structural and hydraulic requirements. The approach is validated and illustrated by designing several hypothetical and two real large sewer networks on a microcomputer. The CPU time for designing sewer networks using the proposed heuristic is less than 10% of the time required for the optimization procedure. Such application indicates the effectiveness of the heuristic in rapidly providing “good” sewer network designs that are compara...

Tube Settler Modeling

Abstract: A new tube settler model useful for tube design and performance evaluation is developed based on the assumption of uniformly distributed flow velocity at the tube entrance. As flow through the tube occurs, the velocity distribution in the tube changes from uniform flow to a fully developed parabolic velocity (laminar) profile at some distance along the tube. The varying velocity encountered by a settling particle results in variations in its settling path. A model is developed based on these effects and is verified in laboratory tests. Using the model, the effects of solids accumulation on the bottom of essentially horizontal tubes on particle settling is predicted. Laboratory tests indicate that the model predictions are accurate up to the point that 40% of the tube diameter is used for solids storage.

Two‐Dimensional Mixing in Rivers with Unsteady Pollutant Source

Abstract: A numerical model, the mixing analysis based on the Concept of Stream Tubes (MABOCOST), has been developed for the analysis of two‐dimensional, transient mixing of nonconservative substances in natural streams. The model can be applied to steady flows in sinuous, nonprismatic channels. A curvilinear coordinate system is used to account for variations in velocity, depth, and channel curvature. By dividing the stream tubes into variable length elements so that the Courant number for the grid space is always equal to unity, the problem of numerical diffusion and dispersion in the computation of streamwise advection is avoided. The model has been verified with analytical solutions for the cases of simple advection, continuous line source and instantaneous injection. Dispersion experiments were carried out in a sinuous channel with irregular bottom topography, using both slug injection and a variable rate injection of tracer. Measured time‐concentration data agree quite well with predictions using MABOCOST.

Pilot-scale distillery spentwash biomethanation.

Abstract: Mesophilic biomethanation of distillery spentwash has been investigated at a pilot scale with a diphasic anaerobic process. An operational strategy to suppress sulfide inhibition through pH control in the methane phase has also been validated. The acid phase has been operated on lime‐neutralized spentwash at an organic loading rate of 30kgCOD/m3/day. Methane phase operation without solids recycling enabled 65% COD reduction and 0.3m3 of biogas production with 60% methane per kilogram COD utilized at an organic loading rate of 3.25kgCOD/m3/day. The contact methane phase at 5kgCOD/m3/day and 27 day mean cell‐residence time achieved 70% COD reduction and 0.3m3 gas production with 70% methane per kilogram of COD utilized. An energy audit revealed over 13 times the energy production per unit energy consumed in the process. A mathematical model for the acid phase predicted volatile acid concentrations within 15% of experimental results. The methane phase model incorporated inhibition and was independent of grow...