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For many years the design and operation of the activated sludge process was directed toward the removal of Biochemical Oxygen Demand (BOD). BOD is nonspecific and measures all of the biodegradable carbon present in the wastewater. A variety of relationships have been developed to describe the kinetics of the process in terms of sludge age, hydraulic detention time, and biomass concentration. Biomass concentration, in most cases, has been related to the mixed liquor volatile suspended solids (MLVSS). There are several factors which considers with respect to biodegradation and achievable effluent concentrations for toxic organics in the activated sludge process. E. Katz and W. J. Weber noted that several species of bacteria commonly found in biological treatment systems are capable of degrading a multitude of toxic organic pollutants and other organic compounds. In a multisubstrate system, such effects as catabolite repression a non-competitive, competitive, an uncompetitive inhibition may occur between the various compounds which are potential substrates for the organisms.

This paper summarizes and evaluates past, current and expected actions concerning waste management in the chemical and petrochemical industries. Industrial waste management has evolved from an “end of pipe” treatment mentality to holistic environmental waste management with source reductions as the preferred option. In most cases significant costs savings have resulted and environmental and public health impacts minimized. This current thrust has resulted from recent regulatory actions. Future trends will require management changes. To be effective, the management approach selected must address the following issues: regulatory/legal considerations and trends; environmental management systems; toxicity measurement characterizations; ecotoxicity assessment evaluations; source reduction and waste minimization; treatment trends and innovative treatment techniques; residual management.

In the past, biological treatability studies were directed toward defining effluent BOD and TSS. Recent regulations now require effluent limitations on volatile organic carbon, specific priority pollutants, aquatic toxicity and in many cases nitrogen for complex wastewaters. This, in turn, has changed the focus of biological treatability studies. It is assumed that a screening protocol has been employed to define biological treatment as a candidate process [1]. (a) Priority Pollutants-If one or more priority pollutants are a permit issue, a fed batch reactor (FBR) is run using acclimated biosolids to determine the maximum degradation rate, q m , and the half velocity constant, K s . From these data, the required SRT to meet effluent limitations can be computed. (b) Aquatic Toxicity-If the wastewater exhibits aquatic toxicity in addition to priority pollutant requirements, bioassays are run on the biological units. Effluent toxicity and COD are tracked with time. Since effluent toxicity is frequently associated with soluble microbial products (SMP), the SMP is estimated from the effluent COD over time of aeration. (c) Nitrogen-Many organics including SMP are inhibitory to nitrification. The nitrification rate should be determined on the effluents using seeded NH 4 Cl as a control. From these data, the required SRT can be computed. This paper reviews the required protocols and presents several case histories from the chemical and pharmaceutical industry. In the past, biological treatability studies were directed toward defining effluent BOD and TSS. Recent regulations now require effluent limitations on volatile organic carbon, specific priority pollutants, aquatic toxicity and in many cases nitrogen for complex wastewaters. This, in turn, has changed the focus of biological treatability studies. It is assumed that a screening protocol has been employed to define biological treatment as a candidate process [1]. (a) Priority Pollutants-If one or more priority pollutants are a permit issue, a fed batch reactor (FBR) is run using acclimated biosolids to determine the maximum degradation rate, q m , and the half velocity constant, K s . From these data, the required SRT to meet effluent limitations can be computed. (b) Aquatic Toxicity-If the wastewater exhibits aquatic toxicity in addition to priority pollutant requirements, bioassays are run on the biological units. Effluent toxicity and COD are tracked with time. Since effluent toxicity is frequently associated with soluble microbial products (SMP), the SMP is estimated from the effluent COD over time of aeration. (c) Nitrogen-Many organics including SMP are inhibitory to nitrification. The nitrification rate should be determined on the effluents using seeded NH 4 Cl as a control. From these data, the required SRT can be computed. This paper reviews the required protocols and presents several case histories from the chemical and pharmaceutical industry.

Industrial wastewaters may have a significant impact on municipal activated sludge plants. Depending on the degradability of the wastewater, the overall reaction coefficient, K, may be increased or decreased. Readily degradable wastewaters will render the process more susceptible to filamentous bulking. Increasing the soluble BOD fraction will increase the temperature effect. Sludge dewaterability may be decreased with readily degradable soluble wastewaters or increased with pulp and paper mill wastewaters containing pulp and fibre. Volatile organics which do not biodegrade require source treatment. Effluent toxicity should be controlled by industrial pretreatment where possible. In some cases, PAC will eliminate toxicity in the activated sludge process.

Stringent effluent guidelines relating to volatile organic carbon (VOC), effluent toxicity and priority pollutants require a reappraisal of design criteria for wastewater treatment plants in the chemical and petrochemical industry. In the case of volatiles, the biodegradability of the VOC as well as the type of aeration equipment needs to be considered. High temperatures in covered aeration basins can create serious sludge settling problems. Priority pollutant removal requires careful consideration of adequate sludge age. Temperature is particularly significant in reducing priority pollutants to acceptable levels. The generation of non-degradable by-products, SMP, can create effluent toxicity problems. This may require tertiary treatment with activated carbon.

Recent legislation in the United States is placing emphasis on the removal of priority pollutants and aquatic toxicity from industrial wastewaters. A protocol has been developed to select candidate technologies for specific effluent objectives. Design parameters for biological treatment are developed using a modified FBR test. The applicability of alternative physical-chemical technologies are discussed.

Experimental data from continuous-flow activated-sludge reactors with selectors fed with highly biodegradable, soluble feed were correlated using a simple, semi-empirical formula. Rate of the substrate removal in the selector was demonstrated to be a function of the organic loading in the initial mixing chamber. The formula allows prediction of the substrate concentration in the selector and was used for the optimization of the selector's design for bulking control. Analysis of the equation demonstrated that an optimum sludge recycle rate exists for a set of systems parameters. The optimum recycle rate is always less than 100 percent and approaches this value as the system constant decreases. The substrate concentration in the contactor at the optimum sludge recycle rate is equal to one-half of the influent concentration.

The formation of soluble microbial products was evaluated in batch reactors using radiolabeled 14C-phenol and 14C-glucose. Soluble microbial products, SMP, resulted from intermediates or end products of substrate degradation and endogenous cell decomposition. On an organic carbon basis, the SMP produced after A8 hours averaged 1A.7 (±3.7) percent of the initial phenol and 3.1 (±0.4) percent of the initial glucose. The SMP were categorized as substrate utilization products, having a biodegradable and non-biodegradable fraction, and biomass associated products, which were only non-biodegradable. A model was developed based on kinetic relationships between several macroscopic compartments, which consisted of the initial substrate, cell mass, and the three SMP categories. Based on the experimental data, zero and first order kinetics were sufficient to describe the disappearance of the initial substrates and the net SMP, i.e., total SMP produced less SMP biodegraded to yield CO2 and/or new biomass. Both phenol and glucose adhered to the same kinetic model, but the rate constants were considerably different.

This paper presents a perspective of wastewater management in the chemical industries as related to sustainable development. The scope of wastewater management must therefore further be expanded to include the concept of ecological integrity of receiving waters. Ecological integrity of receiving waters is compromised by contaminants which are not effectively removed by Best Conventional Technology (BCT). Biological treatment typically offers the most cost-effective conversion and/or stabilization of wastewaters; however, modifications must be employed in the design and operation to provide satisfactory effluent quality. Enhanced treatment techniques for wastewaters containing high organic concentrations, VOCs, elevated TDS levels, toxics and priority pollutants are discussed. The importance of design and operational procedures including pretreatment technologies, two stage vs. single stage activated sludge, selector design and maximum specific oxygen uptake rate determinations are also presented.

The molecular weight, MW, distribution of soluble microbial products, SMP, was examined. Phenol, an inhibitory substrate, and glucose, a non-inhibitory substrate, were degraded using acclimated cultures of bacteria. Three distinct regions were found to exist, Region I: Original substrate present, Region II: Biodegradable SMP present, and Region III: Endogenous respiration. Phenol degradation resulted in more SMP than glucose, about 25 percent versus 3 percent as residual SMP at the end of Region I, and 3 percent versus 1 percent at the end of Region II, respectively. In Region III, the production of SMP due to endogenous decay, SMPE, was proportional to the rate of cell degradation. The rate coefficient for SMPE production for cells grown on phenol was higher than for glucose, 0.005 mg SMPE per mg cell carbon per day for phenol versus 0.002 mg per mg per day for glucose. Although differences existed in the magnitude of SMP produced, the MW distributions for phenol and glucose were similar in each region. While in Region I most of the SMP consisted of the lowest MW ( 100 K.

Effluent limitations now being imposed on industry for low levels of specific priority pollutants requires a re-evaluation of both the design and operation of the activated sludge process. Removal of multiple organics in a wastewater (defined in terms of BOD or COD) has been modelled in accordance with the relationship Figure options Download full-size image Download as PowerPoint slide So = influent BOD S = effluent BOD Xv = volatile suspended solids A = hydraulic retention time K = reaction coefficient In a multistage process, since the more readily degradable organics are removed in the first stage, the coefficient K will decrease stage to stage, generally proportional to the concentration of organic remaining. Because of this phenomena, there is little to be gained by multistage treatment. When considering a specific organic; i.e., phenol, however, the reaction follows Monod kinetics and it can be shown that multistage operation offers distinct advantages over a completely mixed system. Each stage can be modelled: Figure options Download full-size image Download as PowerPoint slide in which b = endogenous coefficient Xd = degradable fraction of the VSS a = yield coefficient qm = maximum pollutant removal rate Ks = pollutant concentration when the rate is one-half the maximum rate While the coefficients b, a, and Xd can be readily determined by conventional methodology, Ks and qm will depend on the wastewater mixture and process operating conditions. It has been found that these parameters can be estimated using the fed batch reactor (FBR) technique as described by Templeton and Grady (1988) and Watkin (1986). Using a mathematical rearrangement of Equation (2), the impact of shock loads on the specific process effluent concentration can also be estimated. This paper provides several examples for computing the operating conditions to achieve specific effluent priority pollutant levels.

The objectives of this investigation were: (1) to examine the overall substrate removal of a three component mixture by an acclimated seed using total organic carbon measurements, (2) to observe the rates of removal of each of the three components in the mixture at four different food-to-microorganism ratios (F/M), (3) to show the effects of the composition of the substrate with varying degradability on effluent quality, and (4) to observe the effects of sludge age on total substrate removal. To accomplish these objectives, sludge from a municipal sewage treatment plant was acclimated as seed in a continuous flow, completely mixed laboratory reactor. A multicomponent substrate consisting of a mixture of glucose, phenol and sulfanilic acid, was fed at different F/M ratios. The removal rate was determined as total organic carbon and specific analytical measurements for each substrate in the influent and effluent samples were also made. Various combinations of glucose, phenol and sulfanilic acid were used as a substrate in three runs. This made it possible to observe the removal rate of each substrate in the mixture as related to their individual biodegradability as well as their influent concentrations. The results showed that for the three substrates employed in this study, the overall removal rate, in terms of total organic carbon in a mixed acclimated culture, is the sum of the individual specific removal rates. The effluent quality in terms of soluble TOC was related to the F/M or to the sludge age using Eckenfelder's kinetic model.

Floc-load and enzymatic transfer of soluble substrate from a wastewater into microorganisms in an activated sludge floe are related. In the absence of other metabolic selectivity pressures, this rapid sequestering of available soluble organics is required for the avoidance of filamentous sludge bulking in various reactor configurations. The specific oxygen utilization rate response to floc-loading is a measure of the magnitude of the enzymatic transfer capacity of a biomass and can be used to determine its maximum sorptive capacity. During the transfer process the biomass Adenosine triphosphate (ATP) content undergoes a rapid depletion for 20-30 minutes before increasing again. Relevant parameters associated with soluble substrate removal and floc-forming selectivity mechanisms are summarized.

This research investigated the general effects and equilibrium behavior of copper in the activated sludge process under a range of organic loadings and influent copper concentrations. This was achieved in a two‐phase experiment using continuous‐flow laboratory scale activated sludge units.

The activated sludge process has been employed for the treatment of municipal and industrial wastewaters for many years. Modifications and improvements to the process have been the result of extensive research from both a theoretical and practical viewpoint. This article reviews the activated sludge process as it is presently applied. Design approaches are developed including examples for both municipal and industrial wastewaters. Special consideration for industrial wastewaters are discussed. Process modifications including nitrification denitrification and priority pollutant removal are considered.

A technique for rapidly determining Monod and inhibition kinetic parameters in activated sludge is evaluated. The method studied is known as the fed-batch reactor technique and requires approximately three hours to complete. The technique allows for a gradual build-up of substrate in the test reactor by introducing the substrate at a feed rate greater than the maximum substrate utilization rate. Both inhibitory and non-inhibitory substrate responses are modeled using a nonlinear numerical curve-fitting technique. The responses of both glucose and 2,4-dichlorophenol (DCP) are studied using activated sludges with various acclimation histories. Statistically different inhibition constants, KI, for DCP inhibition of glucose utilization were found for the various sludges studied. The curve-fitting algorithm was verified in its ability to accurately retrieve two kinetic parameters from synthetic data generated by superimposing normally distributed random error onto the two parameter numerical solution generated by the algorithm.

The laboratory bench-scale experiments were conducted to investigate the effects of varying degrees of waste treatment and the flow conditions in the receiving waters on the deoxygenation rate constant (k), and ultimate biochemical oxygen demand (L), and the total O2 utilisation of the receiving waters. Industrial wastewaters were collected from 10 major industrial plants located along the Houston Ship Channel in Texas. Two different degrees of treatment for industrial wastewaters were studied. Three different flow conditions studied were the high, the average and the low flow in the Houston Ship Channel. The k values increased for both further treatment and decreased flow in the reactor runs. The L values were higher for the average flow conditions than for the low flow conditions. The total O2 utilization was found to increase with a decrease in the flow of the receiving waters.

Generally, aerobic digestion of biological sludges is conducted in completely-mixed aeration basins. Although first-order kinetics have classically been used to predict and design aerobic digestors, it is shown that these models will result in underdesign and that a model based on a mass balance around the digestor more accurately predicts digestor performance. The experimental work discussed herein demonstrates that a first-order rate coefficient, determined under batch conditions, can be employed in the completely-mixed model for design purposes. Certain design constraints are discussed, such as laboratory scale-up, temperature, etc. A design example is illustrated using the approach presented herein.

A continuous oxygen uptake meter or continuous respirometer was developed which produced a rapid and reliable response to systemic shocks. The respirometer basically is a 101. Plexiglas laboratory activated sludge unit with a variable volume air tight side car. The feed enters the completely mixed aeration basin and is pumped into the side car. The side car is the site of the oxygen uptake measurements as indicated by a continuously monitoring dissolved oxygen probe. The system was most sensitive to changes in influent concentrations when run at an F / M = 0.1. Response time for a change in DO of 0.1 ppm was less than 4 min. The continuous respirometer was tested employing both synthetic and raw industrial wastes.

The performance of the activated sludge process is functionally dependent on the settling and compaction properties of the activated sludge. The settling properties of activated sludges vary markedly depending on the presence or absence of filamentous organisms and on the process operating conditions. In this study the process was operated to minimize the presence of filamentous organisms and to investigate the effects of operating process variables, mainly organic loading. It was found that over the range of organic loadings tested, the ZSV increased with organic loading due to the size of the sludge floc which was also directly proportional to the organic loading. The ZSV in aerobically digested sludge was found to decrease with sludge age.

The process design and evaluation of sludge incinerator performance is generally conducted using either generalized average parameters or, alternatively, complex and detailed calculations which require computer programming for their use. In the first instance the generalized parameters are found to be applicable only to an “average” incinerator which is not encountered in actual practice. In the second instance, the calculations are so numerous that a clear and general picture of what is occurring cannot be readily obtained. This paper presents a new analytical approach to incineration performance evaluation which has been developed in an attempt to redress this situation. A three-term linear equation is developed for the combustion heat balance using net heat value of the fuels. Net heat value is defined as that heat value, per pound of fuel, which is available to perform useful thermal work other than the discharge of its own combustion products. The well-established procedure of using ultimate chemical analyses of fuels together with an element by element accounting for combustion components has been simplified by defining three combustion ratios for a given fuel. These ratios are then used to determine the net available heat values for use in the heat balance equation. Operating data are used to illustrate the application of the analysis technique and to demonstrate the practical application of the procedure.

Specific oxygen uptake rate (SOUR) can be employed for the process control of the activated sludge process. SOUR can be related to pertinant process variables such as sludge age and effluent quality. This paper develops relationships for a variety'of industrial wastewaters.

The effect of inorganic salts such as sodium chloride and sodium sulfate on the performance of the activated sludge process was examined. When proper acclimation procedures were followed, the adverse effects of salts on the process were minimized. One of the parameters monitored, effluent suspended solids, had very low values (less than 10 mg l −1 ) up to an inflow sodium chloride concentration of about less than 35 gl −1 . The chemical oxygen demand of the effluent increased steadily with increasing sodium chloride concentrations, but biochemical oxygen demand values remained very low (less than 5 mg l −1 ) which indicated that the increase in chemical oxygen demand was due to the portion that cannot be degrated biologically. The effect of sodium sulfate on the system was even less profound. In addition to the effluent being very clear and low in suspended solids, the chemical oxygen demand removal efficiency remained high.

Statistical correlation of filter performance to depth, hydraulic loading, and media characteristics is presented; effects of oxygen and temperature on filter performance; new design formulations. ...

A modified activated sludge process called “contact-stabilization-denitrification” makes it possible to eliminate 80% to 90% of the incoming total nitrogen in addition to the usual BOD removal. A correlation between the organics removal and denitrification was made with laboratory data obtained and the data of other investigators. The principle of the process is as follows: Following the contact period, the activated sludge is separated from the clarified liquor by sedimentation. The clarified liquor, low in carbon, is pumped to the trickling filter for nitrification. The nitrified effluent and the sludge loaded with soluble and colloidal organic materials are contacted with each other in the denitrification tank for the stabilization of the organic matter and denitrification. The oxygen requirement for the stabilization of organic matter removed in the contact tank is supplied by the nitrate as the stabilization tank is kept anaerobic. The final effluent obtained after clarification is low, both in carbon and nitrogen.

This research examines conventional substrate removal and oxygen uptake kinetic models, which have been justified previously for steady state circumstances, to determine of these models can be employed to predict system responses under transient loadings. Three different wastes were used, a synthetic, an industrial, and a domestic wastewater. The systems were periodically monitored for sludge settlability, microorganism changes, effluent quality, and oxygen requirements. The conventional kinetic models for substrate removal and oxygen uptake are shown to predict both steady state and transient conditions with no major alterations in the models provided average transient values are used. The substrate removal rate coefficient appeared to increase under most transient situations as compared to the steady state value. The efficiency of oxygen utilization seemed to vary under different loading conditions for the same waste.

With the emphasis being given to the development of biologically soft detergents, it is necessary to establish eriteria defining biodegradability of these materials. It is the authors' opinion that a biologically soft detergent should have the following characteristics: (1) Under normal operations the material should be 85% removable by activated sludge. (2) Normally high discharges of the detergent should not influence biological activity. (3) The detergent should ultimately degrade to carbon dioxide and water.

Correlations developed to define absorption; relationships developed between liquid film coefficient, KL and Reynolds and Schmidt Numbers at liquid submergence depths up to 15 ft; correlations cove...