Activated Sludge Treatment System Research Articles

Robust Optimal Design for Wastewater Treatment. Part II: Application

A general approach, called robust optimal design, is developed in a companion paper and applied here to a comprehensive, nonlinear, activated sludge treatment system. The treatment system robustness is related to the sensitivity of steady-state effluent biochemical oxygen demand and total suspended solids concentrations to changes in 55 uncertain model parameter values. Treatment system designs with lower sensitivity of the effluent water quality measures are likely to be more robust than designs with higher sensitivity. The robust optimal design approach is used to generate alternative designs that represent the trade-off between total system cost and robustness. The robust design trends are generally more consistent with recommended design practice than are typical minimum-cost design trends. In particular, improvements in the robustness of effluent biochemical oxygen demand concentration are associated with higher activated sludge mean solids-residence times, whereas typical minimum-cost designs are associated with low solids-residence times. The robustness of the alternative designs is evaluated further using a nonlinear worst-case analysis. The robust optimal design framework should be applicable to many design problems where uncertainty in parameter values is significant.

Robust Optimal Design for Wastewater Treatment. Part I: General Approach

One important problem with using mathematical optimization models for design of wastewater treatment systems is that parameter values, and thus, model results, are often uncertain. A general approach, called robust optimal design, is developed for extending nonlinear optimization models to include first-order sensitivity-based measures of system robustness. Robustness is defined narrowly as the ability of the system to maintain a level of performance even if the actual parameter values are different from the assumed values; thus less sensitive designs should be more robust. A solution procedure based on nonlinear optimization and system sensitivity analysis techniques is discussed. The approach can be used to generate alternative designs that recognize traditional modeled objectives such as cost and effluent water quality measures, and that also reflect concerns about uncertainty. The approach is applied in a companion paper to a complex activated sludge treatment system with 55 uncertain parameter values.

Activated Sludge Process Response to Variable Inputs of Volatile Organic Contaminants

Laboratory-scale activated sludge treatment systems were operated under dynamic loading conditions to investigate the non-steady state behaviour of volatile organic contaminants (VOCs) under controlled conditions. Four step tests were conducted in which an incremental increase in the concentrations of selected contaminants was applied to the reactor feed from background levels of about 15 µg/L to levels of about 100 µg/L for a duration of approximately three hydraulic retention times. Although it was not possible to define the relative contributions of stripping and biodegradation to the removal of the test VOCs, different mechanisms are responsible for the removal of short-term, non-steady state inputs of chlorinated and non-chlorinated VOCs. No apparent effect of SRT or HRT on VOC removal was observed at the conditions tested.

A laboratory-scale model for evaluating effluent toxicity in activated sludge wastewater treatment plants

Laboratory-scale wastewater treatment systems were used to assess the potential contribution of a specific waste source, a detergent manufacturing plant, to wastewater treatment plant (WWTP) effluent toxicity. Laboratory-scale, continuously-fed activated sludge treatment systems (CAS units) were established and seeded with sludge from one of two activated sludge WWTPs. The CAS units were fed influent from these WWTPs supplemented with detergent manufacturing plant waste (plant waste). CAS unit effluent toxicity was measured with the 7 day Ceriodaphnia dubia survival and reproduction test and the 4 day Selenastrum capricornutum population growth test. Control (ambient WWTP influent) CAS unit and actual WWTP effluents had similar toxicity, indicating the CAS units generated effluent toxicologically similar to actual effluent for the two species tested. Untreated WWTP influent was supplemented with atypically high concentrations of plant waste in an attempt to establish a dose-response relationship between influent plant waste levels and effluent toxicity. However, there was no trend toward increasing effluent toxicity to Ceriodaphnia or algae with increasing influent plant waste concentrations. Thus, the detergent manufacturing plant waste is not contributing to the toxicity of the municipal WWTP effluent. This case study demonstrated the utility of CAS units for assessing the impact of WWTP influent sources on final effluent toxicity.

Toward optimum control of the activated sludge process with reliability analysis

Abstract A scheme to maximize reliability and to identify upsets caused by influent and process disturbances of the activated sludge treatment system with recycle is presented. Reliability is the probability that the effluent wastewater quality meets the maximum contamination standard for BOD5. The plant is assumed to operate under steady-state conditions. Since influent flow and substrate concentration have significant variation, they are introduced into the model as random variables. thus concerns about plant stability are addressed. Reliability is expressed as a function of return sludge concentration and recycle flow. Control charts are used to identify upsets caused by influent disturbance, combinations of flow and BOD5. and process disturbance, combinations of F/M (food to microorganism ratio) and MLSS (mixed liquor suspended solids). Recommendations to maximize reliability in the overall context of plant performance are presented and discussed.

Fate of Toxic Organic Compounds in Activated Sludge and Integrated PAC Systems

The addition of powdered activated carbon (PAC) to activated sludge treatment systems to enhance removal of specific toxic organic compounds from wastewater was evaluated. Nine organic compounds encompassing a range of solubility, volatility, biodegradability, and adsorptive properties were studied. Kate and equilibrium investigations were conducted to quantify the removal mechanisms of volatilization, biodegradation, biosorption, and carbon adsorption. Results from steady-state bioreactor studies showed that the addition of less than 100 mg/ℓ powdered activated carbon to the influent did not enhance the removal of the biodegradable target compounds investigated: benzene, toluene, ethylbenzene, o-xylene, chlorobenzene, and nitrobenzene. Significantly improved removals of the poorly degradable and non-biodegradable compounds 1,2-dichlorobenzene, 1,2,4-trichlorobenzene, and lindane occurred at influent powdered carbon concentrations in the 12.5 to 25 mg/ℓ range. Influent powdered carbon concentrations of 100 mg/ℓ effected overall removals of greater than 90%. The addition of powdered activated carbon not only reduced effluent concentrations but also reduced the amounts of the volatile compounds stripped to the atmosphere.

し尿処理場の週休運転方式 低希釈二段活性汚泥処理方式を中心に

し尿処理場の週休運転方式 低希釈二段活性汚泥処理方式を中心に

Starch waste treatment by the activated sludge system

Corn starch waste is easily degraded by the completely mixed activated sludge treatment system. The bio-kinetic coefficients are calculated from the 2-level activated sludge operational processes using four influent COD concentrations and four values of solids retention time. The results indicate that the effluent COD is related to the influent COD concentration. Furthermore, the effluent COD is proportional to the product of the influent COD concentration and the specific growth rate. The multiple-substrate model of Adams et al. predicts well the effluent COD under variable influent COD concentrations. There is no sludge bulking problem in this study, apparently due to high DO concentrations, buffered system and balanced C:N:P ratio. However, the critical DO concentration, in which sludge volume index begins to increase, increase as F M ratio increases. A cost analysis is provided for a hypothetical wastewater plant with a flow rate of 300 m 3 day −1.

Oxygen uptake rates associated with biological treatment of pentachlorophenol wastewater

Abstract This research examined the biodegradability of a recalcitrant or inhibitory waste stream with the use of an electrotytic respirometer. Specifically, it addressed the oxygen uptake rates associated with biological treatment of pentachlorophenol waste‐water from a wood preserving operation. Results indicated that the respirometer can be successfully used to develop an acclimatization program for biological treatment of inhabitory waste streams. Based on a gradual introduction of the PCP wastewater, overall COD reductions of 71.4 percent were realized in a bench scale activated sludge treatment system.

Secondary emissions from subsurface aerated treatment systems. A mathematical attack on the air‐stripping of pollutants from subsurface layers in wastewater‐treatment basins

A material-balance model for an activated sludge treatment system is presented. The equations completely describe the behavior of the aeration basin. There are two main parameters in the equations. The mass transfer between the air stream and the basin contents must be found. Likewise, the rate of biological oxidation of the organic must be determined. Experimental results are reported which were obtained when acrylonitrile was treated in a subsurface activated-sludge apparatus. Included in the study are data for air stripping of acrylonitrile from a sterile biologically inactive system. By solving for the amount of air stripping and liquid concentrations, a direct comparison with experimental data is possible. 7 references, 1 figure, 1 table.

Does improved waste treatment have demonstrable biological benefits?

Since 1972, 10 benthic surveys and 9 static fish bioassays have been conducted to assess the impact of AVTEX Fibers, Inc. effluent on the lower South Fork of the Shenandoah River. AVTEX (formerly FMC Corp.) is a rayon and polyester fibers plant located in Front Royal, Virginia. Benthic samples were taken at four stations, one above and three below the plant discharges. Single surveys in 1972 and 1973 indicated a severe impact on the benthic community along the right side of the river, below the plant, as a result of the channelized effluent. Diversity values (¯d) were low (0–2.42) and numbers of taxa and organisms were reduced. A fish bioassay in 1973 indicated the effluent to be acutely toxic at the 34.5% level (mixture of effluent and river water). In early 1974, FMC Corp. constructed an activated sludge treatment system to reduce BOD and supplement the neutralization and chemical precipitation (zinc hydroxide and liquid-solid separation) facilities that had been used to treat waste waters since 1948. After the new equipment was placed in operation, the previously stressed area became more stable. In 1975 and 1976 the stressed area exhibited greater ¯d values (1.19–3.39) and an increased number of taxa and organisms. Bioassays showed the effluent to be acutely toxic to fish only once since 1973. The major improvements in the effluent were a 70% reduction in BOD5 and a 60% reduction in the amount of zinc entering the river. Community conditions in 1977 indicated a partial remission of improvement, probably due to drought conditions. The rehabilitation of damaged ecosystems is a process important to all biologists. An important factor in encouraging industry to participate in this activity is evidence that improved waste treatment will often have demonstrable biological benefits rather soon. As data accumulate on the recovery process it may be possible to predict the degree of rehabilitation and time required more precisely.

Long-Term Activated Sludge Treatment of Winery Waste Waters

Winery waste water, consisting primarily of clean-up water containing grape and wine residues, is being successfully treated by a long-term activated sludge treatment system. Retention time in the activated sludge basins ranges from 10 to 20 days. The system includes a screen, two activated sludge basins, clarifier, chlorination system, reaeration basin, sludge recycle and sludge digestion basin. Nutrients (anhydrous ammonia and phosphoric acid) are added to the influent. A polymer flocculant is added to enhance settleability of suspended solids in the clarifier. Characteristics of the treatment system influent and effluent are given, for both pressing (two months) and processing (10 months) seasons. System has achieved an efficiency of 99% in reduction of BOD₅. Nitrogen and phosphorus removal has exceeded 90%. Total suspended solids concentration in the effluent was less than 20 mg/l. Problems encountered in the operation of the system generally have been related to low temperature. Ice formation in the wintertime resulted in loss of biological activity in the activated sludge basins and equipment damage. Installation of a submerged turbine aeration system solved the wintertime aeration and mixing problems.

Long-Term Activated Sludge Treatment of Winery Waste Waters

Winery waste water, consisting primarily of clean-up water containing grape and wine residues, is being successfully treated by a long-term activated sludge treatment system. Retention time in the activated sludge basins ranges from 10 to 20 days. The system includes a screen, two activated sludge basins, clarifier, chlorination system, reaeration basin, sludge recycle and sludge digestion basin. Nutrients (anhydrous ammonia and phosphoric acid) are added to the influent. A polymer flocculant is added to enhance settleability of suspended solids in the clarifier. Characteristics of the treatment system influent and effluent are given, for both pressing (two months) and processing (10 months) seasons. System has achieved an efficiency of 99% in reduction of BOD₅. Nitrogen and phosphorus removal has exceeded 90%. Total suspended solids concentration in the effluent was less than 20 mg/l. Problems encountered in the operation of the system generally have been related to low temperature. Ice formation in the wintertime resulted in loss of biological activity in the activated sludge basins and equipment damage. Installation of a submerged turbine aeration system solved the wintertime aeration and mixing problems.

Effects of Iron on Activated Sludge Treatment

The importance of inorganic nutrients on activated sludge treatment has not been emphasized or studied extensively. Studies of the fundamentals of inorganic ions have been limited to nitrogen and phosphorus, yet basic microbiology has shown the importance of many other nutrients. Iron plays a major role in the oxidation-reduction reactions involved with the treatment of organic wastes and was the subject of this investigation. This work showed that insufficient iron in activated sludge treatment systems decreases the rate of organic metabolism and causes bulking conditions. Variations in other biological treatment parameters may be associated with iron or other inorganic nutrient limitation conditions.