IWA Activated Sludge Models Research Articles

Determination of optimal dose of allylthiourea (ATU) for the batch respirometric test of activated sludge.

Allylthiourea is a known specific inhibitor for ammonium oxidiser to suppress its oxygen uptake, and is commonly used for various kinds of batch respirometric tests to detect heterotrophic respiration in activated sludge. However, when high heterotrophs were present in the sample, it appeared the inhibitor was noticeably degraded and reached below the inhibition threshold after a couple of days, which resulted in overestimation of the heterotrophic respiration. The biological decomposition of the inhibitor was expressed with a Monod-type rate expression having a half-saturation coefficient of 980 mg-COD/L and maximum specific growth rate of 1.0 d-1. The developed kinetic model, including the growth and decay of the heterotrophs and nitrifiers, indicated that the ATU with about 90 mg-ATU/L which was initially dosed to the system would reach below the inhibition threshold of 1.0 mg-ATU/L after 10 days when 750 mg-COD/L of heterotrophs were present. From the kinetic model, an empirical formula to calculate a safe minimum ATU dose for the batch respirometric test was elaborated. The model also provided a modified experimental procedure to accurately estimate the initial heterotrophic biomass concentration in the sample and its specific decay rate based on IWA Activated Sludge Models.

Modeling nitrous oxide production by a denitrifying-enhanced biologically phosphorus removing (EBPR) activated sludge in the presence of different carbon sources and electron acceptors

In this study, the IWA Activated Sludge Model No. 2d (ASM2d) was expanded to identify the most important mechanisms leading to the anoxic nitrous oxide (N2O) production in the combined nitrogen (N) and phosphorus (P) removal activated sludge systems. The new model adopted a three-stage denitrification concept and was evaluated against the measured data from one/two-phase batch experiments carried out with activated sludge withdrawn from a local, large-scale biological nutrient removal wastewater treatment plant. The experiments were focused on investigating the effects of different external carbon sources (acetate, ethanol) and electron acceptors (nitrite, nitrate) on the mechanisms of N2O production in enhanced biological P removal by polyphosphate accumulating organisms (PAOs) and external carbon-based denitrification by ordinary heterotrophic organisms (OHOs). The experimental results explicitly showed that N2O production was predominantly governed by the presence of nitrite in the reactor regardless of the examined carbon source and the ratio COD/N in the reactor. The model was capable of accurately predicting (with R2 > 0.9) the behavior of not only N2O-N, but also NO3-N, NO2-N, soluble COD, and PO4-P. The simulation results revealed that only OHOs were responsible for N2O production, whereas the present denitrifying PAOs reduced only nitrate to nitrite.

A protocol for the use of computational fluid dynamics as a supportive tool for wastewater treatment plant modelling.

To date, computational fluid dynamics (CFD) models have been primarily used for evaluation of hydraulic problems at wastewater treatment plants (WWTPs). A potentially more powerful use, however, is to simulate integrated physical, chemical and/or biological processes involved in WWTP unit processes on a spatial scale and to use the gathered knowledge to accelerate improvement in plant models for everyday use, that is, design and optimized operation. Evolving improvements in computer speed and memory and improved software for implementing CFD, as well as for integrated processes, has allowed for broader usage of this tool for understanding, troubleshooting, and optimal design of WWTP unit processes. This paper proposes a protocol for an alternative use of CFD in process modelling, as a way to gain insight into complex systems leading to improved modelling approaches used in combination with the IWA activated sludge models and other kinetic models.

Modeling External Carbon Addition in Combined N-P Activated Sludge Systems with an Extension of the IWA Activated Sludge Models

Modeling External Carbon Addition in Combined N-P Activated Sludge Systems with an Extension of the IWA Activated Sludge ModelsThe aim of this study was to expand the IWA Activated Sludge Model No. 2d (ASM2d) to include the effect of adding a readily biodegradable exogenous substrate to anoxic zones of biological N/P removal systems, where it can be used as growth substrate by the Polyphosphate Accumulating Organisms (PAOs) but can not be used by PAOs in the anaerobic zone. The model change was to add a new biodegradable...Author(s)M. SwinarskiJ. MakiniaH.D. StenselK. CzerwionkaJ. DrewnowskiSourceProceedings of the Water Environment FederationSubjectSession 7: External Carbon Sources - Optimization and ModelingDocument typeConference PaperPublisherWater Environment FederationPrint publication date Jan, 2011ISSN1938-6478SICI1938-6478(20110101)2011:1L.439;1-DOI10.2175/193864711802867630Volume / Issue2011 / 1Content sourceNutrient Removal and Recovery SymposiumFirst / last page(s)439 - 453Copyright2011Word count292Subject keywordsActivated sludgeASMdenitrificationexternal carbonmathematical modelingnutrient removalsimulation

Modelling waste stabilisation ponds with an extended version of ASM3

In this paper an extended version of IWA's Activated Sludge Model No 3 (ASM3) was developed to simulate processes in waste stabilisation ponds (WSP). The model modifications included the integration of algae biomass and gas transfer processes for oxygen, carbon dioxide and ammonia depending on wind velocity and a simple ionic equilibrium. The model was applied to a pilot-scale WSP system operated in the city of Florianópolis (Brazil). The system was used to treat leachate from a municipal waste landfill. Mean influent concentrations to the facultative pond of 1,456 g(COD)/m(3) and 505 g(NH4-N)/m(3) were measured. Experimental results indicated an ammonia nitrogen removal of 89.5% with negligible rates of nitrification but intensive ammonia stripping to the atmosphere. Measured data was used in the simulations to consider the impact of wind velocity on oxygen input of 11.1 to 14.4 g(O2)/(m(2) d) and sun radiation on photosynthesis. Good results for pH and ammonia removal were achieved with mean stripping rates of 18.2 and 4.5 g(N)/(m(2) d) for the facultative and maturation pond respectively. Based on measured chlorophyll a concentrations and depending on light intensity and TSS concentration it was possible to model algae concentrations.

Simulation of a wastewater treatment plant receiving industrial effluents

A process model simulating the Mariannridge Wastewater Treatment Plant, located in the eThekwini Municipality, has been developed in the WEST (Worldwide Engine for Simulation, Training and Automation) modelling environment, based on the IWA Activated Sludge Model No. 3 (ASM3). The treatment plant receives a high proportion of industrial effluents.The development of the model involves the characterisation of the influent wastewater and determining model parameters (kinetic and stoichiometric coefficients) by undertaking batch respirometric tests on the wastewater and activated sludge, flocculation filtration and simulation of the batch respirometric experiment. To account for equipment-specific factors, thesimulation model was calibrated against plant data covering a year’s operation. The model is intended to be used as part of a system to evaluate the ability of a receiving wastewater treatment works to adequately treat a particular industrial effluent before granting a permit for it to be discharged to sewer.

CWM1: a general model to describe biokinetic processes in subsurface flow constructed wetlands

This paper presents the Constructed Wetland Model No1 (CWM1), a general model to describe biochemical transformation and degradation processes for organic matter, nitrogen and sulphur in subsurface flow constructed wetlands. The main objective of CWM1 is to predict effluent concentrations from constructed wetlands without predicting gaseous emissions. CWM1 describes aerobic, anoxic and anaerobic processes and is therefore applicable to both horizontal and vertical flow systems. 17 processes and 16 components (8 soluble and 8 particulate) are considered. CWM1 is based on the mathematical formulation as introduced by the IWA Activated Sludge Models (ASMs). It is important to note that besides the biokinetic model a number of other processes including porous media hydrodynamics, the influence of plants, the transport of particles/suspended matter to describe clogging processes, adsorption and desorption processes and physical re-aeration must be considered for the formulation of a full model for constructed wetlands.

Granulation of activated sludge in a pilot-scale sequencing batch reactor for the treatment of low-strength municipal wastewater

Aerobic granulation of activated sludge was achieved in a pilot-scale sequencing batch reactor (SBR) for the treatment of low-strength municipal wastewater (<200 mg L −1 of COD, chemical oxygen demand). The volume exchange ratio and settling time of an SBR were found to be two key factors in the granulation of activated sludge grown on the low-strength municipal wastewater. After operation of 300 days, the mixed liquor suspended solids (MLSS) concentration in the SBR reached 9.5 g L −1 and consisted of approximate 85% granular sludge. The average total COD removal efficiency kept at 90% and NH 4 +-N was almost completely depleted (∼95%) after the formation of aerobic granules. The granules (with a diameter over 0.212 mm) had a diameter ranging from 0.2 to 0.8 mm and had good settling ability with a settling velocity of 18–40 m h −1. Three bacterial morphologies of rod, coccus and filament coexisted in the granules. Mathematical modeling was performed to get insight into this pilot-scale granule-based reactor. The modified IWA activated sludge model No 3 (ASM3) was able to adequately describe the pilot-scale SBR dynamics during its cyclic operation.

Benefits and drawbacks of thermal pre-hydrolysis for operational performance of wastewater treatment plants

This paper presents benefits and potential drawbacks of thermal pre-hydrolysis of sewage sludge from an operator's prospective. The innovative continuous Thermo-Pressure-Hydrolysis Process (TDH) has been tested in full-scale at Zirl wastewater treatment plant (WWTP), Austria, and its influence on sludge digestion and dewatering has been evaluated. A mathematical plant-wide model with application of the IWA Activated Sludge Model No.1 (ASM1) and the Anaerobic Digestion Model No.1 (ADM1) has been used for a systematic comparison of both scenarios--operational plant performance with and without thermal pre-hydrolysis. The impacts of TDH pre-hydrolysis on biogas potential, dewatering performance and return load in terms of ammonia and inert organic compounds (Si) have been simulated by the calibrated model and are displayed by Sankey mass flow figures. Implementation of full scale TDH process provided higher anaerobic degradation efficiency with subsequent increased biogas production (+75-80%) from waste activated sludge (WAS). Both effects--enhanced degradation of organic matter and improved cake's solids content from 25.2 to 32.7% TSS--promise a reduction in sludge disposal costs of about 25%. However, increased ammonia release and generation of soluble inerts Si was observed when TDH process was introduced.

Operation and model description of a sequencing batch reactor treating reject water for biological nitrogen removal via nitrite

The aim of this study was the operation and model description of a sequencing batch reactor (SBR) for biological nitrogen removal (BNR) from a reject water ( 800 – 900 mg NH 4 + – N L - 1 ) from a municipal wastewater treatment plant (WWTP). The SBR was operated with three cycles per day, temperature 30 °C, SRT 11 days and HRT 1 day. During the operational cycle, three alternating oxic/anoxic periods were performed to avoid alkalinity restrictions. Oxygen supply and working pH range were controlled to achieve the BNR via nitrite, which makes the process more economical. Under steady state conditions, a total nitrogen removal of 0.87 kg N (m 3 day) −1 was reached. A four-step nitrogen removal model was developed to describe the process. This model enlarges the IWA activated sludge models for a more detailed description of the nitrogen elimination processes and their inhibitions. A closed intermittent-flow respirometer was set up for the estimation of the most relevant model parameters. Once calibrated, model predictions reproduced experimental data accurately.

Biological nutrient removal from meat processing wastewater using a sequencing batch reactor

Meat processing effluents are rich in nutrients (nitrogen: 75-200 mg L(-1) and phosphorus: 20-40 mg L(-1)) and COD (800-2,000 mg L(-1)) after primary treatment. A laboratory scale sequencing batch reactor (SBR) was operated for the treatment of a beef processing effluent from slaughtering and boning operations. An effective SBR cycle was found for removal of COD, nitrogen and phosphorus at 22 degrees C. The solid retention time was 15 days while the hydraulic retention time (HRT) was 2.5 days. The total nitrogen in the wastewater was reduced to less than 10 mg L(-1), while the total phosphorus decreased to less than 1.0 mg L(-1). The residual effluent soluble COD was found to be non-biodegradable as reflected by no further soluble COD removal following prolonged aeration. Removal of biodegradable soluble COD, ammonia nitrogen and soluble phosphate phosphorus of greater than 99% was achieved in the SBR. Good prediction of ammonia and nitrate nitrogen removal was obtained using IWA Activated Sludge Model. The operating cycle is shown to be appropriate to achieve simultaneous removal of COD and nutrients from the meat processing wastewater. Alkalinity and pH have an inverse relationship during the initial anaerobic and aerobic stages due to production and stripping of CO2. Use of a low level of DO in the final aerobic stage ensured complete ammonia removal and enhanced denitrification.