Batstone D.J.,University of Queensland |
Amerlinck Y.,Ghent University |
Ekama G.,University of Cape Town |
Goel R.,Environment Canada |
And 9 more authors.
Water Science and Technology | Year: 2012
Process models used for activated sludge, anaerobic digestion and in general wastewater treatment plant process design and optimization have traditionally focused on important biokinetic conversions. There is a growing realization that abiotic processes occurring in the wastewater (i.e. 'solvent') have a fundamental effect on plant performance. These processes include weak acid-base reactions (ionization), spontaneous or chemical dose-induced precipitate formation and chemical redox conversions, which influence pH, gas transfer, and directly or indirectly the biokinetic processes themselves. There is a large amount of fundamental information available (from chemical and other disciplines), which, due to its complexity and its diverse sources (originating from many different water and process environments), cannot be readily used in wastewater process design as yet. This position paper outlines the need, the methods, available knowledge and the fundamental approaches that would help to focus the effort of research groups to develop a physicochemical framework specifically in support of whole-plant process modeling. The findings are that, in general, existing models such as produced by the International Water Association for biological processes are limited by omission of key corrections such as non-ideal acid-base behavior, as well as major processes (e.g., ion precipitation). While the underlying chemistry is well understood, its applicability to wastewater applications is less well known. This justifies important further research, with both experimental and model development activities to clarify an approach to modeling of physicochemical processes. © IWA Publishing 2012.
Shaw A.,Black and Veatch Corporation |
Shaw A.,Illinois Institute of Technology |
Takacs I.,Dynamita |
Pagilla K.R.,Illinois Institute of Technology |
Murthy S.,DC Water
Water Research | Year: 2013
The Monod equation is often used to describe biological treatment processes and is the foundation for many activated sludge models. The Monod equation includes a "half-saturation coefficient" to describe the effect of substrate limitations on the process rate and it is customary to consider this parameter to be a constant for a given system. The purpose of this study was to develop a methodology, and its use to show that the half-saturation coefficient for denitrification is not constant but is in fact a function of the maximum denitrification rate. A 4-step procedure is developed to investigate the dependency of half-saturation coefficients on the maximum rate and two different models are used to describe this dependency: (a) an empirical linear model and (b) a deterministic model based on Fick's law of diffusion. Both models are proved better for describing denitrification kinetics than assuming a fixed KNO3 at low nitrate concentrations. The empirical model is more utilitarian whereas the model based on Fick's law has a fundamental basis that enables the intrinsic KNO3 to be estimated. In this study data was analyzed from 56 denitrification rate tests and it was found that the extant KNO3 varied between 0.07mgN/L and 1.47mgN/L (5th and 95th percentile respectively) with an average of 0.47mgN/L. In contrast to this, the intrinsic KNO3 estimated for the diffusion model was 0.01mgN/L which indicates that the extant KNO3 is greatly influenced by, and mostly describes, diffusion limitations. © 2013 Elsevier Ltd.
Friedrich M.,Ingenieurburo Friedrich |
Takacs I.,Dynamita |
Tranckner J.,University of Rostock
Water Environment Research | Year: 2016
In current process models activated sludge consists of biodegradable and unbiodegradable organic fractions. Recent evidence suggests that this approach may not be accurate because some of this "unbiodegradable" material may indeed be degradable. To improve sludge production predictions, it is important to know to what extent the "unbiodegradable" organic fraction is degradable. Assuming that volatile suspended solids (VSS) is a measure of the sum of biodegradable and unbiodegradable organic solids and the integral of the oxygen uptake rate (OUR) is representative of the biodegradable organics, the combination of these measurements can be used to predict the change of unbiodegradable organic solids within an aerobic digestion batch experiment. This procedure was used to estimate degradation rates of "unbiodegradable" VSS between 0.006 to 0.029 d-1. The advantage of the proposed method is that the degradation rate can be determined directly based onmeasurements and relies on a limited number of assumptions.
Wilson C.A.,Greeley and Hansen Inc. |
Novak J.,Virginia Polytechnic Institute and State University |
Takacs I.,Dynamita |
Wett B.,University of Innsbruck |
Murthy S.,District of Columbia Water and Sewer Authority
Water Research | Year: 2012
Advanced anaerobic digestion processes aimed at improving the methanization of sewage sludge may be potentially impaired by the production of inhibitory compounds (e.g. free ammonia). The result of methanogenic inhibition is relatively high effluent concentrations of acetic acid and other soluble organics, as well as reduced methane yields. An extreme example of such an advanced process is the thermal hydrolytic pretreatment of sludge prior to high solids digestion (THD). Compared to a conventional mesophilic anaerobic digestion process (MAD), THD operates in a state of constant inhibition driven by high free ammonia concentrations, and elevated pH values. As such, previous investigations of the kinetics of methanogenesis from acetic acid under uninhibited conditions do not necessarily apply well to the modeling of extreme processes such as THD. By conducting batch ammonia toxicity assays using biomass from THD and MAD reactors, we compared the response of these communities over a broad range of ammonia inhibition. For both processes, increased inhibitor concentrations resulted in a reduction of biomass growth rate (rmax = μmax.X) and a resulting decrease in the substrate half saturation coefficient (KS). These two parameters exhibited a high degree of correlation, suggesting that for a constant transport limited system, the KS was mostly a linear function of the growth rate. After correcting for reactor pH and temperature, we found that the THD and MAD biomass were both able to perform methanogenesis from acetate at high free ammonia concentrations (equivalent to 3-5 g/L total ammonia nitrogen), albeit at less than 30% of their respective maximum rates. The reduction in methane production was slightly less pronounced for the THD biomass than for MAD, suggesting that the long term exposure to ammonia had selected for a methanogenic pathway less dependent on those organisms most sensitive to ammonia inhibition (i.e. aceticlastic methanogens). © 2012 Elsevier Ltd.
Olsson G.,Lund University |
Carlsson B.,Uppsala University |
Comas J.,University of Girona |
Copp J.,Primodal Inc. |
And 12 more authors.
Water Science and Technology | Year: 2014
Key developments of instrumentation, control and automation (ICA) applications in wastewater systems during the past 40 years are highlighted in this paper. From the first ICA conference in 1973 through to today there has been a tremendous increase in the understanding of the processes, instrumentation, computer systems and control theory. However, many developments have not been addressed here, such as sewer control, drinking water treatment and water distribution control. It is hoped that this review can stimulate new attempts to more effectively apply control and automation in water systems in the coming years. © IWA Publishing 2014.