Journal of Environmental Engineering

This paper reviews the current state‐of‐understanding of biological fouling of fine bubble diffusers. Results of a survey conducted in the United Kingdom and United States which implicates biological sliming as a major cause of fine bubble diffuser clogging are reviewed. Factors contributing to the bioclogging of diffusers are discussed in light of current studies. Newly developed methods for the analysis of diffuser fouling both in the laboratory and the field are described. Included are procedures for the laboratory measurement of specific permeability, diffuser bubble release pressure, dynamic wet pressure and air flow profiles over the diffuser. Illustrations of these test methods are cited for one plant experiencing severe biofouling.

The gravity and wind‐driven flow in a river impoundment is simulated using a network of interconnected channels. The forcing wind is specified by a step‐function, and the response is calculated by quasi‐steady state simulation for each timestep. The transport of a conservative dissolved material through the system is simulated by a cells‐in‐series approach with appropriately sized subdivisions to account for dispersion. The model is formulated and applied to Pool No. 2 of the Mississippi River, and a comparison with dye tracer data is given. A review of some field studies showing the importance of weather dependent processes in a shallow river impoundment is also presented.

A simulation of dissolved oxygen (DO) dynamics and of biomass is incorporated in a dynamic wind and gravity driven hydrologic transport model. Quantitative expressions are given for the source and sink terms describing photosynthesis, respiration, settling, sedimentary oxygen uptake and reaeration in the mass transport equation. Simulations are made for a 6‐hr timescale. The magnitude of diurnal DO variations and the occurrence of other weather dependent DO responses is shown. The model is applied to Mississippi River Pool No. 2.

Land‐use regulations for reduction of nonpoint source pollution from surface‐applied contaminants do not usually consider the differing hydrologic responses of land areas based on soil type, slope, proximity to the stream, and expected rainfall. To help overcome this shortcoming, a technique is developed to define the area of a watershed contributing surface runoff directly to the stream as the result of any rain. Using design rainfalls and initial watershed soil moisture as input, a map can be drawn showing the return period with which any part of the watershed contributes surface runoff, and thereby potential nonpoint source pollution, to the stream. Use of the approach is illustrated by application to a small, agricultural watershed in east‐central Pennsylvania. Employing such a technique to define restricted‐use areas on a watershed eliminates the subjective nature of commonly proposed land‐use regulations by accounting for both the watershed characteristics and the probabilities controlling the generation of surface runoff and its direct affects on the stream.

When time‐series methods of parameter estimation are used to model the concentration of a pollutant in a natural waterway, the results may be grouped into a restricted class of models which are termed $\left(j\text{,}n\text{,}m\right)$ models. It is shown that the dispersion as represented in conservative forms of these models has a temporal variance that increases linearly with time (thus mimicking the variance of a Fickian process) and is consistent with dead zone mixing within rivers and streams. Data from a variety of rivers are used to demonstrate that the $\left(j\text{,}n\text{,}m\right)$ model provides an explanation of actual data that is superior to those obtained by manipulation of a Fickian equation. In addition, the model greatly simplifies computation of dead zone dispersive effects, is able to simply deal with non‐conservative pollutants and the results suggest that residence times are more meaningful physical parameters than dispersion coefficients in explaining dispersive phenomena.

One problem in the development of a large‐scale synthetic fuels industry is solid waste and disposal‐related environmental problems. Three synfuel wastewater sludges (SRC‐I, SRC‐II, and H‐Coal) and one petroleum refinery API separator sludge were chemically characterized and subjected to laboratory‐scale land application experiments. Leachate, recognized as a primary contaminant transport vector, was generated for study, and biodegradation (carbon dioxide evolution) of the organic component of sludge‐soil mixtures was measured and modeled for a 245‐day study period. Results indicate that the elemental composition varies considerably between wastes, with carbon being the dominant element ranging from 26% to 61% in the SRC‐I and H‐Coal samples, respectively. The petroleum refinery API sludge exhibited the most rapid degradation requiring only 96 days to reach 90% of the estimated maximum carbon dioxide production for that particular waste. The H‐Coal material was found to be the most biodegradable, with approximately 100 mg of carbon evolved per gram of sludge. In contrast, the SRC‐I sludge was more stable toward biodegradation, yielding only 3 mg of carbon per gram of sludge throughout the study period. With proper design, which includes runoff collection and treatment, land treatment is seen as an effective method of handling the relatively small volume organic‐laden synfuel wastewater sludges.

A comparison of methods used for analyzing the long‐term pollutant removal efficiency in a stormwater detention basin points out some fundamental differences between simulation, using EPA's Storm Water Management Model, and a statistical technique advanced by Hydroscience, Inc. For the 24.6‐yr record of Atlanta, Georgia hourly rainfall, the mean runoff event volume predicted by each method is similar. However, the inability of the statistical method to account for the reduction in the number of events (due to indigenous catchment storage) results in an estimate of total runoff 30% greater than the simulation results. The statistical technique employs a pollutant removal expression applied to the total flow captured in the detention basin, as contrasted to the simulation's utilization of intra‐event pollutant kinetics for removal within the basin. Solution surfaces of runoff flow capture and pollutant removal efficiencies are developed for each method as a function of basin volume and drawdown rate. The differences in performance estimates between the two methods increase as the basin volume and drawdown rate increase, with the statistical technique yielding the lower estimate of flow capture. An optimal combination of basin volume and drawdown rate was determined for each technique by incorporating a cost constraint. For a long‐term pollutant removal efficiency of 70%, the annual cost associated with a basin designed by the statistical technique is approximately twice that of a basin designed by simulation. The program SYNOP generates rainfall event statistics which may be incorporated with simulation, providing a coordinated approach for analyzing the performance of stormwater detention basins.

The growth response of the green alga, Selenastrum capricornutum to varying additions of either sewage or reconstituted water containing equivalent levels of inorganic nitrogen and phosphorus, was compared to algal growth levels calculated from the inorganic nutrient concentrations of these additions using the algal yield factor of the test alga. The additions resulted in a linear increase in algal growth with percent of sewage or chemical equivalent solution addition which was in close agreement to the values predicted from the total soluble inorganic nitrogen concentration in the algal cultures alone. Thus, the Algal Assay: Bottle Test (AA:BT) did not permit sufficient organic mineralization during incubation, owing to the exclusion of heterotrophic bacteria and protozoa by the test procedure. This occurrence could result in an underestimation by the AA:BT of the algal growth potential occurring from the entry of a wastewater containing inorganic and organic nitrogen and phosphorus compounds into the aquatic environment.

Equations for predicting the gas‐film coefficient for the volatilization of organic solutes from streams are developed. The film coefficient is a function of windspeed and water temperature. The dependence of the coefficient on windspeed is determined from published information on the evaporation of water from a canal. The dependence of the coefficient on temperature is determined from laboratory studies on the evaporation of water. Procedures for adjusting the coefficients for different organic solutes are based on the molecular diffusion coefficient and the molecular weight. The molecular weight procedure is easiest to use because of the availability of molecular weights. However, the theoretical basis of the procedure is questionable. The diffusion coefficent procedure is supported by considerable data. Questions, however, remain regarding the exact dependence of the film coefficient on the diffusion coefficient. It is suggested that the diffusion coefficient procedure with a 0.68‐power dependence be used when precise estimate of the gas‐film coefficient are needed and that the molecular weight procedure be used when only approximate estimates are needed.

A planning model is developed for the determination of optimal water reuse allocation and wastewater treatment alternatives that minimizes the overall cost of water supply and wastewater treatment over a planning period. The planning model consists of two models, each based upon dynamic programming (DP). The models are: (1) An allocation DP model, which is used for the optimal allocation of water to users for each treatment alternative considered; and (2) a treatment DP model, which performs the optimal selection of treatment alternatives over time. The allocation DP model is used to define the state space for the treatment DP model. Application of the planning model is made to San Antonio, Texas.

Anaerobic digestion of classified municipal solid waste is a proposed disposal method for the mushrooming quantities of solid waste. To determine the suitability of anaerobic digestion to Los Angeles area wastes, a two‐year pilot‐scale study was conducted. A survey of a Southern California community was made to determine typical municipal waste composition. Municipal solid waste with characteristics conforming to survey results was classified using the Cal Recovery Process to provide a feedstock for digestion. Four 50‐gal $(0.19‐m^3)$ digesters were operated at organic loading rates from 0.065 lb VS/cu ft‐day‐0.25 lb VS/cu ft‐day $(1.04\mathrm{kg}/m^3\cdot \mathrm{day})\text{.}$ Feed concentration ranged from 2.6%‐8% VS and hydraulic retention time ranged from 15–30 days. Feed solids were composed of 80% classified municipal solid waste and 20% primary sludge. Results of the experimental investigation showed that gas containing 55%‐60% methane can be produced at a rate of 7.0 cu ft‐9.0 cu ft gas/lb‐VS applied ($0.44m^3‐0.56m^3/\mathrm{kg}\cdot \mathrm{VS}$ applied). The highest gas production rate was obtained at the lowest digester loading rates. Digester mixing ability appeared to be the controlling process variable. No chemicals for pH control or nutrients were required to maintain normal process operation.

The Ames test is used to detect the presence of mutagenic/carcinogenic by‐products in ferrate treated water samples that had been spiked with selected priority pollutants. The gas chromatograph analysis is used to measure the efficiency of removing the substance to be removed but could not be used to detect the production of such by‐products. Negative Ames test results suggested the ferrate treatment was not only effective in removing the substance but also did not produce any remaining mutagenic by‐products during the treatment process. Increasing concern about the chemical pollution of drinking water sources and the possible generation of mutagenic/carcinogenic substances by water and wastewater treatment processes suggests the Ames test could become an index of treatment performance.

Fly ash is currently being generated at a rate of millions of tons every year and represents a growing solid waste disposal problem. In an effort to examine alternative uses for this waste product, fly ash was investigated as a source for wastewater treatment chemicals. Through a sequential caustic/acid leaching process, portions of the iron, aluminum, and silica in fly ash were solubilized allowing for the recovery of these materials in a useable form. Synthetic additives derived from this process were evaluated as coagulants in wastewater treatment and as conditioners for sludge prior to mechanical dewatering. Conventional laboratory scale jar tests were conducted for comparing coagulant effectiveness. Sludge conditioners were evaluated by performing vacuum filtration tests using a Buchner Funnel apparatus. The fly ash derived additives performed as well or better than commercially available chemicals. Synergistic activity is believed to occur when using the synthetic materials due to the mutual effectiveness of the solubilized portions of aluminum, iron, and silica present in the treatment additive. The synthetic additives are more cost effective in the treatment of wastewater and sludge than ferric chloride and aluminum sulfate.

The performance of a fixed bed slag desorption (leaching) column was investigated and a mathematical model describing the desorption process was developed by considering intraparticle and external film diffusion resistances as rate controlling mechanisms. A linear equilibrium relationship between leachate metals in the liquid, and on the slag phase was developed. Four grades of GFETC “Lurgi‐type” fixed bed slagging coal gasification solid waste particles with diameters of 20‐40, 40‐60, 60‐100 and 100‐200 mesh were used for application of the developed model. Slags were derived from the gasification of North Dakota lignite coals. The model used a finite‐difference technique (implicit method) for solution and for generation of effluent concentration profiles. Calibration of the model was done using column studies. The effect of intraparticle diffusion and external film diffusion resistances were evaluated by conducting experiments with different slag particle sizes keeping fluid velocity constant and with different fluid velocities keeping particle size constant.

A computer algorithm for the selection of optimal depth‐diameter combinations for all links of a complete gravity wastewater collection system has been developed using dynamic programming. The algorithm incorporates two subprocesses $P_1$ and $P_2\text{.}$ The subprocesses $P_1$ generates all feasible designs of inflowing lines at a junction manhole whereas $P_1$ uses these feasible designs to provide the upstream invert level of the outflow line, simultaneously solving the matching problem encountered at each junction manhole. The problem of dimensionality has been minimized by exploiting the characteristic features of wastewater collection system. The optimal design for a 10.7 km long collection system at Indian Institute of Technology, Bombay with 52 lines, 245 links, 224 ordinary manholes and 21 junction manholes has been compared with conventional design to bring out that the algorithm requires small computer memory, small execution time and leads to optimal solution of a complete gravity wastewater collection system.