Wastewater Treatment Processes (wastewater + treatment_process)

Distribution by Scientific Domains

Selected Abstracts

Fate of air toxics and VOCs in the odor control scrubbers at the deer island treatment plant

Thomas Myslinski
Process off-gases at the Deer Island wastewater treatment plant in Boston are collected and treated and its stack emissions regulated for selected gases including volatile organic compounds (VOCs), which are monitored as nonmethane hydrocarbons (NMHC). The air treatment processes of countercurrent wet oxidation scrubbing and granulated activated carbon adsorption are available for emissions control at Deer Island. In addition, since the wastewater treatment process of biochemical oxidation is fully enclosed at the site, microbial destruction of VOCs is an intrinsic treatment process for organic gases. Surveyed results of wastewater research literature indicate that the use of scrubbers for the removal of VOCs is controversial, as the fate of volatile hydrocarbon molecules across odor control scrubbers is complex and not fully understood. Continuous emission monitoring tests across the Deer Island scrubbers have consistently shown a VOC removal efficiency in excess of 50%. The fate of the scrubber inlet VOCs at Deer Island was researched as part of a plant-wide, on-going VOC study. Removal efficiencies across the pure oxygen bioreactors were also investigated. Preliminary results of this study indicate chemical reactions involving VOCs in odor control scrubbers partially oxidize and chlorinate derivatives possibly destroying a fraction of the compounds by complete oxidation. In addition, VOC reduction across the enclosed aerobic bioreactors was found to be significant. This article represents the opinions and(legal) conclusions of the authors and not necessarily those of the MWRA. [source]

Fate and effects of triclosan in activated sludge

Thomas W. Federle
Abstract Triclosan (TCS; 5-chloro-2-[2,4-dichloro-phenoxy]-phenol) is a widely used antimicrobial agent. To understand its fate during sewage treatment, the biodegradation and removal of TCS were determined in activated sludge. In addition, the effects of TCS on treatment processes were assessed. Fate was determined by examining the biodegradation and removal of TCS radiolabeled with 14C in the 2,4-dichlorphenoxy ring in laboratory batch mineralization experiments and bench-top continuous activated-sludge (CAS) systems. In batch experiments with unacclimated sludge, TCS was mineralized to 14CO2, but the total yield varied as a function of test concentration. Systems that were redosed with TCS exhibited more extensive and faster mineralization, indicating that adaptation was a critical factor determining the rate and extent of biodegradation. In a CAS study in which the influent level of TCS was incrementally increased from 40 ,g/L to 2,000 ,g/L, removal of the parent compound exceeded 98.5% and removal of total radioactivity (parent and metabolites) exceeded 85%. Between 1.5 and 4.5% of TCS in the influent was sorbed to the wasted solids, whereas >94% underwent primary biodegradation and 81 to 92% was mineralized to CO2 or incorporated in biomass. Increasing levels of TCS in the influent had no major adverse effects on any wastewater treatment process, including chemical oxygen demand, biological oxygen demand, and ammonia removal. In a subsequent experiment, a CAS system, acclimated to TCS at 35 ,g/L, received two separate 4-h shock loads of 750 ,g/L TCS. Neither removal of TCS nor treatment processes exhibited major adverse effects. An additional CAS study was conducted to examine the removal of a low level (10 ,g/L) of TCS. Removal of parent equaled 94.7%, and biodegradation remained the dominant removal mechanism. A subsequent series of CAS experiments examined removal at four influent concentrations (7.5, 11, 20, and 50 ,g/L) of TCS and demonstrated that removal of parent ranged from 98.2 to 99.3% and was independent of concentration. Although TCS removal across all experiments appeared unrelated to influent concentration, removal was significantly correlated (r2 = 0.87) with chemical oxygen demand removal, indicating that TCS removal was related to overall treatment efficiency of specific CAS units. In conclusion, the experiments show that TCS is extensively biodegraded and removed in activated-sludge systems and is unlikely to upset sewage treatment processes at levels expected in household and manufacturing wastewaters. [source]

Adaptive recurrent neural network control of biological wastewater treatment

Ieroham S. Baruch
Three adaptive neural network control structures to regulate a biological wastewater treatment process are introduced: indirect, inverse model, and direct adaptive neural control. The objective is to keep the concentration of the recycled biomass proportional to the influent flow rate in the presence of periodically acting disturbances, process parameter variations, and measurement noise. This is achieved by the so-called Jordan Canonical Recurrent Trainable Neural Network, which is a completely parallel and parametric neural structure, permitting the use of the obtained parameters, during the learning phase, directly for control system design. Comparative simulation results confirmed the applicability of the proposed control schemes. © 2005 Wiley Periodicals, Inc. Int J Int Syst 20: 173,193, 2005. [source]

A petri nets-based process planning system for wastewater treatment,

Albert W. L. Yao
Abstract It is always challenging to simulate, debug or diagnose automated systems. The aim of this paper is to present the development of a convenient tool for reengineering the control system in a complicated industrial wastewater treatment plant. In this project, a PC-based Human-Machine Interface (HMI) in conjunction with Petri nets (PN) theory is adopted to develop and simulate the operational process for wastewater treatment. The resultant tool offers many advantages to the reality of the automated control world. It not only reduces the process reengineering time and the cost of error recovery, but also builds a panel of human interface for the process. The discrete event control sequence of wastewater treatment can be easily modeled and evaluated before its build-up. Furthermore, this PN-based system can be used as an online diagnostic tool when the wastewater treatment process is malfunctioning. That is, the presented PN tool provides an adequate means for offline process development, simulation, performance evaluation, and quick online process diagnosis. Copyright © 2010 John Wiley and Sons Asia Pte Ltd and Chinese Automatic Control Society [source]

A Kinetic Model for Suspended and Attached Growth of a Defined Mixed Culture

Kawai Tam
Kinetic experiments were carried out in a semicontinuous wastewater treatment process called self-cycling fermentation (SCF) using a defined mixed culture and various concentrations of synthetic brewery wastewater. The same consortium, which had been previously identified as Acinetobacter sp., Enterobacter sp., and Candida sp., were used in these experiments. The overall rate of substrate removal was attributable to both suspended microbes and the biofilm that formed during the treatment process. A rate expression was developed for the SCF system for a range of synthetic wastewaters containing glucose and various initial concentrations of ethanol and maltose. The data indicated that substrate removal by the suspended cells was directly related to the biomass concentration. However, substrate removal by the biofilm was apparently not affected by the biofilm thickness and was a function of substrate concentration only. [source]

Wastewater treatment for production of H2S-free biogas

Sk Z Ahammad
Abstract BACKGROUND: In anaerobic wastewater treatment processes, the presence of sulfate-reducing bacteria (SRB) produces H2S. Many techniques are being used to remove H2S from biogas to obtain H2S-free biogas but none of those are cost effective or efficient enough to remove the H2S completely. The objective of the present study was to introduce some changes/modifications to the process parameters of the wastewater treatment operation to eliminate SRB from the system. RESULTS: The growth of SRB was found to be completely suppressed under thermophilic conditions (55 °C) but not at 37 °C. H2S-free biogas containing 56.5% methane was obtained at 55 °C after 180 days of treatment. The effect of higher concentrations of volatile fatty acids (VFAs) on the growth of SRB and methanogens at 37 °C and 55 °C were also studied. At higher VFA concentrations, SRB outgrew the methanogens at 37 °C but at 55 °C the situation was found to be reversed. For continuous operation at 55 °C and low dilution rate (0.0075 h,1), SRB was suppressed and biogas having 29% methane but free of H2S was obtained. CONCLUSION: Operating the reactor at high temperature (550C) and low hydraulic retention time (HRT) can result in the production of H2S-free biogas, with a high concentration of methane. Copyright © 2008 Society of Chemical Industry [source]

A property-based optimization of direct recycle networks and wastewater treatment processes

AICHE JOURNAL, Issue 9 2009
José María Ponce-Ortega
Abstract This article presents a mathematical programming approach to optimize direct recycle-reuse networks together with wastewater treatment processes in order to satisfy a given set of environmental regulations. A disjunctive programming formulation is developed to optimize the recycle/reuse of process streams to units and the performance of wastewater treatment units. In addition to composition-based constraints, the formulation also incorporates in-plant property constraints as well as properties impacting the environment toxicity, ThOD, pH, color, and odor. The MINLP model is used to minimize the total annual cost of the system, which includes the cost for the fresh sources, the piping cost for the process integration and the waste stream treatment cost. An example problem is used to show the application of the proposed model. The results show that the simultaneous optimization of a recycle network and waste treatment process yields significant savings with respect to a commonly-used sequential optimization strategy. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source]

Quantitative analysis of amoA mRNA expression as a new biomarker of ammonia oxidation activities in a complex microbial community

Y. Aoi
Abstract Aims:, To quantitatively analyse the changes to amoA mRNA (ammonia mono-oxygenase encoding mRNA) profiles in response to a change in ammonia oxidation activity in a complex microbial community. Methods and Results:, The amoA mRNA levels in both a batch-mode incubation and a continuously fed nitrification reactor were determined by real-time reverse transcription-PCR analysis. The amoA mRNA level changed rapidly in response to the change in environmental conditions which affect ammonia oxidation activity. Conclusion:, An increase in amoA mRNA level can be detected within 1,2 h in response to an initiation of cell activity whereas a decrease in amoA mRNA level is detected within 24 h in response to a cessation of activity. Significance and Impact of the Study:,amoA mRNA, which shows sensitive response to ammonia oxidation activity, can be used as a biomarker of ammonia oxidation activity in wastewater treatment processes where many bacterial species exist. [source]

Understanding the properties of aerobic sludge granules as hydrogels

Thomas Seviour
Abstract Aerobic sludge granules are larger, denser microbial aggregates than activated sludge flocs with a smoother and more regular surface, which facilitates greater wastewater treatment intensity. Factors important in their growth are still poorly understood, which is an impediment to the construction and operation of full-scale aerobic sludge granule processes. Data in this article obtained with granules treating an abattoir wastewater provide evidence that aerobic sludge granules are hydrogels. The results also demonstrate a method for characterizing macromolecular associations. The rheological profile of these granules was found to be analogous with that of typical polymer gels. Water uptake or swelling reflects an equilibrium between granule elastic modulus and osmotic pressure, whereby uptake is increased by reducing solute concentration or the elastic modulus. A weakening of the extracellular polymeric substance (EPS) matrix as demonstrated with mechanical spectroscopy was induced by several environmental factors including temperature, pH and ionic strength. Uniform and elastic deformation was observed at low strain. Enzymatic degradation studies indicate that proteins and ,-polysaccharides were the major granule structural materials. The aerobic sludge granules in the current study were therefore protein,polysaccharide composite physical hydrogels. While aerobic sludge granules treating an abattoir wastewater are used as a case study, many of the fundamental principles detailed here are relevant to other granulation processes. The paradigm established in this study can potentially be applied to better understand the formation of aerobic sludge granules and thus overcome a hurdle in the acceptance of aerobic sludge granulation as an alternative to more traditional wastewater treatment processes. Biotechnol. Bioeng. 2009;102: 1483,1493. © 2008 Wiley Periodicals, Inc. [source]

Hydrodynamics and mass transfer coefficient in activated sludge aerated stirred column reactor: experimental analysis and modeling

Bo Jin
Abstract The aerated stirred reactor (ASR) has been widely used in biochemical and wastewater treatment processes. The information describing how the activated sludge properties and operation conditions affect the hydrodynamics and mass transfer coefficient is missing in the literature. The aim of this study was to investigate the influence of flow regime, superficial gas velocity (UG), power consumption unit (P/VL), sludge loading, and apparent viscosity (,ap) of activated sludge fluid on the mixing time (tm), gas hold-up (,), and volumetric mass transfer coefficient (kLa) in an activated sludge aerated stirred column reactor (ASCR). The activated sludge fluid performed a non-Newtonian rheological behavior. The sludge loading significantly affected the fluid hydrodynamics and mass transfer. With an increase in the UG and P/VL, the , and kLa increased, and the tm, decreased. The ,, kLa, and tm, were influenced dramatically as the flow regime changed from homogeneous to heterogeneous patterns. The proposed mathematical models predicted the experimental results well under experimental conditions, indicating that the UG, P/VL, and ,ap had significant impact on the tm, ,, and kLa. These models were able to give the tm, ,, and kLa values with an error around ±8%, and always less than ±10%. © 2005 Wiley Periodicals, Inc. [source]

Estimation of Biological Kinetic Parameters from a Continuous Integrated Ozonation-Activated Sludge System Treating Domestic Wastewater

Fernando J. Beltrán
The feasibility of treating municipal wastewater by a combined ozone-activated sludge continuous flow system was studied. Lab-scale experiments of both single activated sludge and combined ozone-activated sludge processes were carried out to determine the kinetic coefficients of the biological stage. The results obtained indicated a clear improvement in the kinetic parameters of the aerobic oxidation when a pre-ozonation stage was applied. Particularly, COD removal and nitrification rates were highly increased. The biokinetic parameters were also used to simulate and optimize the continuous reaction system. From the model prediction it was concluded that the integrated process (i.e., ozone-ASP) may significantly increase the waste reduction capacity. The results presented here provide a useful basis for further scaling up and efficient operation of ozone-ASP units in wastewater treatment processes. [source]