Journal of Environmental Engineering

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.

Simple, analytical models for use in preliminary calculations are developed to approximate the steady‐state concentration and biofilm thickness in a biofilm reactor. The models consider the case in which a single substrate limits growth. These models assume that flux of substrate to the biofilm has a first‐order dependence on the bulk substrate concentration. This assumption restricts the use of the models to low initial substrate concentrations. One of the models assumes plug flow, and the other incorporates longitudinal dispersion of substrate. The models allow the substrate concentration to approach the minimum rate‐limiting concentration and the biofilm thickness to approach zero as predicted by the steady‐state theory. Predictions of these models are compared to those of a steady‐state numerical model developed by Rittmann. For an example taken from the literature, the solution of the model with longitudinal dispersion is in good agreement with the numerical solution.

Under the auspices of the Safe Drinking Water Act (SDWA) the U.S. EPA has promulgated the Surface Water Treatment Rule (SWTR) requiring public water systems using surface water to provide minimum disinfection to control Giardia lamblia, enteric viruses, and bacteria. The $C\cdot t$ concept (concentration of disinfectant in mg/L times time in minutes) is used to establish the appropriate criteria for a surface system to achieve at least 99.9% inactivation of Giardia lamblia and 99.99% inactivation for viruses. In the SWTR, an empirical equation was developed based on water temperature, pH, concentration of chlorine, and inactivation level to predict required disinfection criteria ($C\cdot t$ values). This paper describes the development of an equation based on Chick‐Watson kinetics that provides equivalent information but is theoretically more consistent.

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.

Conventional aerobic sludge stabilization requires extensive energy input. Incorporation of endogenous nitrate respiration (ENR) into the aerobic‐digestion system offers the energy‐saving advantage. In the ENR system, nitrate instead of oxygen is utilized for the biomass destruction. In this study, continuous preanoxic and aerobic digestion of waste‐activated sludge is studied to evaluate its effectiveness for volatile suspended solids (VSS) destruction and nitrogen removal. The ENR occurs in the anoxic digester because of the recycling of nitrate from the aerobic digester. The anoxic effluent, in turn, provides a high pH and adequate buffer capacity for enhancing the subsequent aerobic decay and nitrification. Two experimental runs, differing in hydraulic‐detention time in anoxic and aerobic tanks, are conducted with the same recycle rate. The results indicate that total nitrogen removal is approximately 25%, with 40% VSS destruction. The denitrification/nitrification efficiencies and rates are also determined. A mathematical model developed from the mass balance of biomass, ammonium, and nitrate reasonably predicts transient responses of these parameters.

The principles of proper site management, including adding the optimum water of solubilization and attaining optimal compaction, are applied to test patches subject to portland cement and quicklime (CaO) in‐situ additive treatment. Processed and compacted municipal‐solid‐waste (MSW) ash achieved in‐place compacted dry density of 113.31 lb/cu ft $(1\text{,}830\mathrm{kg}/m^3)$ and compacted wet density of 134.82 lb/cu ft $(2\text{,}180\mathrm{kg}/m^3)\text{.}$ Field testing yielded permeabilities between ${10}^{-6}\mathrm{cm}/s$ and ${10}^{-9}\mathrm{cm}/s\text{,}$ after 14–28 days curing, determined by laboratory (room temperature and humidity) and field (New England‐winter temperatures) measurements. The results of prior laboratory investigations confirmed portland cement and CaO treatment of MSW ash. Adding CaO achieved an order of magnitude reduction in permeability, suggesting a concrete‐like behavior of MSW ashes. Assuming a worst‐case 10% portland cement addition for in‐situ additive treatment, applied by an outside specialty contractor, savings of $200,000–$450,000 per acre ($494,000–$1,110,000 per hectare) could be realized compared to the single, double, synthetic, and clay liners currently under review for MSW‐ash monofill implementation. Pending legislation fails to consider such properties and concrete‐like behavior and fails to recognize the application of engineering management principles.

The wastewater treatment plant operator's problem in collecting, storing, manipulating, and interpreting data is an information‐management problem. It is believed that the operator's performance in controlling the treatment process can be improved if he is equipped with a convenient and efficient method for extracting useful information from the data. This paper presents a rule‐based expert system within an integrated information‐management system. The expert system only considers the activated sludge process, but the information system is for the entire treatment plant. The expert system provides the operator with timely advice based on the latest available process data as interpreted by a set of rules constructed with the help of experienced and skilled operators. The main purpose of the paper is to present case studies of an approach for developing and refining the control rules and for testing their accuracy and effectiveness. The expert system consistently reproduced the expert operator's decisions and performed better than nonexpert operators.

A wastewater‐treatment system can be represented by a multistage configuration consisting of a variety of unit processes from various stages. The number of treatment combinations may be very large when the number of unit processes in a stage and the number of stages in a system increase. Enumeration techniques, e.g., total enumeration and implicit enumeration, have been used to eliminate infeasible treatment combinations and to identify the least‐cost treatment system. A bounded implicit enumeration approach is proposed to make the implicit enumeration more efficient. A lower bound is calculated at each stage and added to the up‐to‐date objective function value to eliminate more combinations before reaching the final stage. The results for two wastewater‐treatment‐system‐synthesis models indicate that the bounded implicit enumeration is consistently more efficient than the total and implicit enumeration approaches in identifying least‐cost and feasible treatment alternatives.

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.

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 fauna is also not incorporated.

Paper presents a new formula for calculating the saturation value of oxygen applicable to seawater and fresh water from 0°C to 50°C. The average relative error δ is 0.031%, and the average absolute error Δ is 0.03 mg/1. In this paper, a new mechanism of gaseous solubility is proposed. It is assumed that two physical processes exist between the gaseous and liquid phases. Based on these assumptions, the following conclusion can be drawn. At constant partial pressure of gas, the relation between gaseous solubility and temperature can be expressed as $C_s={\mathrm{Ke}}^{H/\mathrm{RT}}$, where $C_s=$solubility of gaseous component (mg/1); K=constant (mg/1); δH-vaperization heat of gaseous component in liquid phase (kcal/mole); R=gas constant (0.001987 kcal/moleK); and T-temperature (K).

Activated sludge (AS) foams from two wastewater treatment plants are characterized. The foams contained a significant amount of substrate and lipid. Their contents varied from plant to plant and even within the same plant. The microbial activities of foam in terms of glucose utilization and ATP levels were similar to those of mixed liquor. Foams were subjected to acid hydrolysis and heat treatment as an alternative disposal method. The hydrolyzed byproducts were readily biodegradable in a standard AS process.

Using Escherichia coli sorption/inactivation and sorption-desorption studies and a down-flow column test, usefulness of incorporating silver into alum-treated bituminous coal and ferric hydroxide-impregnated lignite in improving their performance as filtration/adsorption media was assessed. Silver incorporation showed enhanced E. coli reduction for alum-treated bituminous coal while E. coli reduction by ferric hydroxide-impregnated lignite with and without silver was indistinguishable. This is presumably due to high E. coli sorption by the medium without silver and inability of the sorption/inactivation test to distinguish between sorption and inactivation. Silver incorporation more markedly reduced the number of viable E. coli in the eluate of silver-incorporated alum-treated bituminous coal in a sorption-desorption study. Effluent quality (turbidity, total coliforms, and heterotrophic plate count) of a column test, employing silver-incorporated alum-treated bituminous coal and canal water suggested potential useful of the medium for a domestic water filter in rural areas of developing countries.