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Rieger L.,Eawag - Swiss Federal Institute of Aquatic Science and Technology | Rieger L.,EnviroSim Associates Ltd. | Takacs I.,EnviroSim Europe | Siegrist H.,Eawag - Swiss Federal Institute of Aquatic Science and Technology
Water Environment Research | Year: 2012

Aeration consumes about 60% of the total energy use of a wastewater treatment plant (WWTP) and therefore is a major contributor to its carbon footprint. Introducing advanced process control can help plants to reduce their carbon footprint and at the same time improve effluent quality through making available unused capacity for denitrification, if the ammonia concentration is below a certain set-point. Monitoring and control concepts are cost-saving alternatives to the extension of reactor volume. However, they also involve the risk of violation of the effluent limits due to measuring errors, unsuitable control concepts or inadequate implementation of the monitoring and control system. Dynamic simulation is a suitable tool to analyze the plant and to design tailored measuring and control systems. During this work, extensive data collection, modeling and fullscale implementation of aeration control algorithms were carried out at three conventional activated sludge plants with fixed pre-denitrification and nitrification reactor zones. Full-scale energy savings in the range of 16-20% could be achieved together with an increase of total nitrogen removal of 40%.

Weissenbacher N.,University of Vienna | Takacs I.,EnviroSim Associates Ltd. | Murthy S.,District of Columbia Water and Sewer Authority | Fuerhacker M.,University of Vienna | Wett B.,University of Innsbruck
Water Environment Research | Year: 2010

The aim of this work was to give a quantitative description of the gaseous nitrogen and carbon emissions of a full-scale deammonification plant (DEMON system). Deammonification accounted for the net carbon sequestration of 0.16 g CO2/g NO2-N. Both nitrogen dioxide (NO2) and nitric oxide (NO) were minor trace gases (<0.1% nitrogen output). However, in comparison, the nitrous oxide (N2O) emission (1.3% nitrogen output) was significant. The global warming potential of the N2O emissions from the DEMON were similar to those found in conventional simultaneous nitrification/denitrification systems; however, CO2 emissions in the investigated system were significantly lower, thereby lessening the overall environmental effect. This was the first time such an analysis has been performed on a DEMON system.

Ramdani A.,Ecole Polytechnique de Montreal | Dold P.,EnviroSim Associates Ltd. | Deleris S.,Veolia | Lamarre D.,John Meunier Inc. | And 2 more authors.
Water Research | Year: 2010

This study evaluated the potential biodegradability of the endogenous residue in activated sludge subjected to batch digestion under either non-aerated or alternating aerated and non-aerated conditions. Mixed liquor for the tests was generated in a 200 L pilot-scale aerobic membrane bioreactor (MBR) operated at a 5.2 days SRT. The MBR system was fed a soluble and completely biodegradable synthetic influent composed of sodium acetate as the sole carbon source. This influent, which contained no influent unbiodegradable organic or inorganic materials, allowed to generate sludge composed of essentially two fractions: a heterotrophic biomass XH and an endogenous residue XE, the nitrifying biomass being negligible (less than 2%). The endogenous decay rate and the active biomass fraction of the MBR sludge were determined in 21-day aerobic digestion batch tests by monitoring the VSS and OUR responses. Fractions of XH and XE: 68% and 32% were obtained, respectively, at a 5.2 days SRT. To assess the biodegradability of XE, two batch digestion units operated at 35 °C were run for 90 days using thickened sludge from the MBR system. In the first unit, anaerobic conditions were maintained while in the second unit, alternating aerated and non-aerated conditions were applied. Data for both units showed apparent partial biodegradation of the endogenous residue. Modeling the batch tests indicated endogenous residue decay rates of 0.005 d-1 and 0.012 d-1 for the anaerobic unit and the alternating aerated and non-aerated conditions, respectively. © 2009 Elsevier Ltd. All rights reserved.

Hauduc H.,IRSTEA | Hauduc H.,Laval University | Rieger L.,EnviroSim Associates Ltd. | Oehmen A.,New University of Lisbon | And 5 more authors.
Biotechnology and Bioengineering | Year: 2013

This work critically reviews modeling concepts for standard activated sludge wastewater treatment processes (e.g., hydrolysis, growth and decay of organisms, etc.) for some of the most commonly used models. Based on a short overview on the theoretical biochemistry knowledge this review should help model users to better understand (i) the model concepts used; (ii) the differences between models, and (iii) the limits of the models. The seven analyzed models are: (1) ASM1; (2) ASM2d; (3) ASM3; (4) ASM3+BioP; (5) ASM2d+TUD; (6) Barker & Dold model; and (7) UCTPHO+. Nine standard processes are distinguished and discussed in the present work: hydrolysis; fermentation; ordinary heterotrophic organisms (OHO) growth; autotrophic nitrifying organisms (ANO) growth; OHO & ANO decay; poly-hydroxyalkanoates (PHA) storage; polyphosphate (polyP) storage; phosphorus accumulating organisms PAO) growth; and PAO decay. For a structured comparison, a new schematic representation of these processes is proposed. Each process is represented as a reaction with consumed components on the left of the figure and produced components on the right. Standardized icons, based on shapes and color codes, enable the representation of the stoichiometric modeling concepts and kinetics. This representation allows highlighting the conceptual differences of the models, and the level of simplification between the concepts and the theoretical knowledge. The model selection depending on their theoretical limitations and the main research needs to increase the model quality are finally discussed. © 2012 Wiley Periodicals, Inc.

Cao J.-S.,Hohai University | Lin J.-X.,Hohai University | Fang F.,Hohai University | Zhang M.-T.,Hohai University | Hu Z.-R.,EnviroSim Associates Ltd.
Bioresource Technology | Year: 2014

A novel, low cost and easy regeneration biosorbent, chem-modified walnut shell (MWNS), was studied to investigate its potential for removal of an anionic dye, reactive brilliant red K-2BP. The MWNS was synthesized with epichlorohydrin and diethylenetriamine as etherifying agent and crosslinking agent, respectively, and its characteristics were performed with Fourier transform infrared spectroscopy, scanning electron microscope, electron dispersive spectroscopy and thermogravimetric analysis. The influences of pH (0.5-11) and adsorbent dosage (0.1-6g/L) on adsorption capacity of MWNS were evaluated. The maximum K-2BP adsorption capacities (Qm) calculated by best fitting model (Langmuir) were 568.18mg/g at 313K, which was almost 10 times than that of raw material. The adsorption kinetic was well confirmed with pseudo-second-order equation. Thermodynamic studies demonstrated adsorption process by MWNS was spontaneous and endothermic. Furthermore, the regeneration capability of MWNS implied MWNS was a cheap, excellent and promising biosorbent for K-2BP removal in azo dye wastewater treatment. © 2014 Elsevier Ltd.

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