Benchmarking Biological Nutrient Removal in Wastewater Treatment Plants:Influence of Mathematical Model Assumptions

This paper examines the effect of different model assumptions when describing biological nutrient removal (BNR) by the activated sludge models (ASM) 1, 2d & 3. The performance of a nitrogen removal (WWTP1) and a combined nitrogen and phosphorus removal (WWTP2) benchmark wastewater treatment plant was compared for a series of model assumptions. Three different model approaches describing BNR are considered. In the reference case, the original model implementations are used to simulate WWTP1 (ASM1 & 3) and WWTP2 (ASM2d). The second set of models includes a reactive settler, which extends the description of the non-reactive TSS sedimentation and transport in the reference case with the full set of ASM processes. Finally, the third set of models is based on including electron acceptor dependency of biomass decay rates for ASM1 (WWTP1) and ASM2d (WWTP2). The results show that incorporation of a reactive settler: (1) increases the hydrolysis of particulates; (2) increases the overall plant's denitrification efficiency by reducing the S(NOx) concentration at the bottom of the clarifier; (3) increases the oxidation of COD compounds; (4) increases X(OHO) and X(ANO) decay; and, finally, (5) increases the growth of X(PAO) and formation of X(PHA,Stor) for ASM2d, which has a major impact on the whole P removal system. Introduction of electron acceptor dependent decay leads to a substantial increase of the concentration of X(ANO), X(OHO) and X(PAO) in the bottom of the clarifier. The paper ends with a critical discussion of the influence of the different model assumptions, and emphasizes the need for a model user to understand the significant differences in simulation results that are obtained when applying different combinations of 'standard' models

Optimization of Wastewater Treatment Plant Design using Process Dynamic Simulation: A Case Study from Kurdistan, Iraq

Satisfactory effluent characteristics are indispensable to evaluate the performance of any wastewater treatment plant (WWTP) design. Dynamic simulation software has a great role in pursuing this objective, in which an efficient and cost-effective design is constantly performed. In this study, a dynamic simulator sewage treatment operation analysis over time (STOAT) has been used under certain influent conditions to optimize design possibilities for modifying an existing primary WWTP College of Engineering Wastewater Treatment Plant (COEWWTP) at Erbil, Kurdistan, Iraq. The optimization was established on the basis of total suspended solids (TSS) and biochemical oxygen demand (BOD) characteristics in the effluent. Two alternative design schemes were proposed; trickling biofilter and aeration basin. In the dynamic simulation for the investigated design schemes, the predicted effluent profile showed that each of the existing and trickling biofilter processes has failed to correspond to the valid effluent limitation, whereas predicted results of the aeration basin exhibited an effluent profile that meets TSS and BOD allowable limits. Different simulation models have been implemented by STOAT to simulate treatment processes in studied design approaches: ASAL 1 model; BOD model; BOD semi-dynamic model; and SSED 1 model. This study offers an additional understanding of WWTP design and facilitates the application of dynamic simulators as tools for wastewater treatment development in Kurdistan

Multi-objective optimal control of small-size wastewater treatment plants

In this work, a multi-objective dynamic optimization of the operating strategy of a small-size wastewater treatment plant is carried out. In-situ incineration of the excess sludge produced for electricity production is investigated in order to reduce the operating costs. The trade-offs between the treatment quality and the operating costs are characterized. Compared to the literature, emphasis is put on a more rigorous formulation of the problem and an accurate modeling of the underlying phenomena so as to get physically relevant solutions. Thus, from a mathematical perspective, the problem is formulated so that the solution is less sensitive to the – arbitrarily chosen – plant initial conditions. Modeling of physical phenomena e.g. the detrimental effect of the concentration of suspended solids in the mixed liquor, on oxygen transfer rate, has been included in the model. Several constraints are added to the problem so as to maintain the optimal solutions within the limits of validity of the mathematical model. The results provided a clear picture about the trade-offs between the treatment quality and the exploitation costs. Sludge incineration was shown to be of a high energetic profit, but it does not allow the plant to be electrically autonomou

Assessment and modelling of the effect of precipitated ferric chloride addition on the activated sludge settling properties

[EN] This research studies the effect of the widely used coagulant ferric chloride on the activated sludge sedimentability through a vast array of hindered settling tests considering different application modes and a wide range of reagent doses. Direct application of ferric chloride improved the hindered settling velocity (up to twice the settling velocity of the activated sludge with no coagulant addition), but sharply decreased the pH to levels where the biological process was unfeasible (pH < 4). When the pH was adjusted during coagulation to avoid biological inhibition, the impact on the settling velocity depended on the adjusted pH value. When the added coagulant was previously precipitated and neutralized, no pH inhibition occurred and the hindered settling velocity increased linearly with the dose (up to 8 times). This velocity improvement was caused by the increase in flocs density due to the capture within the flocs of the formed precipitates. Based on these experimental results, the usefulness and reliability of the standard hindered settling velocity mathematical models used for the secondary settler design and optimization (Richardson & Zaki model and the Vesilind's exponential model), was expanded to situations in which precipitated ferric chloride is used in wastewater treatment plants. Two empirical equations were proposed and fitted to relate these mathematical models¿ parameters with the dose of coagulant.Asensi Dasí, EJ.; Alemany Martínez, E.; Duque-Sarango, P.; Aguado García, D. (2019). Assessment and modelling of the effect of precipitated ferric chloride addition on the activated sludge settling properties. Chemical Engineering Research and Design. 150:14-25. https://doi.org/10.1016/j.cherd.2019.07.018S142515

Eliminación de contaminantes emergentes presentes en aguas residuales tratadas en operaciones de recarga de acuíferos con barreras reactivas

El aumento de la demanda de agua debida principalmente al incremento de la población requiere la aplicación de tecnologías de tratamiento de aguas residuales que permitan la utilización de las aguas regeneradas. La recarga artificial de acuíferos es una técnica de gestión del agua que consiste en favorecer la introducción de aguas al acuífero mediante diversos posibles sistemas como por ejemplo las balsas de infiltración y los pozos de recarga directa entre otros. El agua del acuífero puede transportarse por él, almacenarse y/o extraerse de nuevo para su uso. En el proceso de infiltración a través del suelo la calidad del agua mejora aprovechando los servicios ecosistémicos, principalmente a la adsorción y la biotransformación

Development and economic assessment of different WWTP control strategies for optimal simultaneous removal of carbon, nitrogen and phosphorus

This paper presents the comparison of four control strategies for the A²/O WWTP configuration for simultaneous C, N and P removal. The control strategies: (i) external COD-P control; (ii) external recycle flow-P control; (iii) nitrate control in the last anoxic reactor; (iv) ammonia control in the last aerobic reactor, were combined with other common control loops to build different control structures and were simulated in Matlab/Simulink under different influent conditions. A systematic approach was conducted with all the strategies to assess their potential effectiveness, according to the following steps: theoretical design, setpoint optimization and, finally, a detailed comparison of the control results against a reference operation and an optimized reference scenario. The optimization of the reference operation presented a 7% reduction of the total operational cost. The simulation results showed that some control strategies further reduced 3-7.5% the WWTP operational costs while the effluent quality is greatly improved

Propuesta de diseño de una planta de tratamiento de aguas residuales domesticas para el distrito de Hunter-Arequipa, 2022

La presente investigación se realizó en la ciudad de Arequipa, distrito de Hunter, cuyo objetivo principal fue determinar Propuestas de diseño de una planta de tratamiento de aguas residuales domesticas para el distrito de Hunter- Arequipa. Para la realización de la tesis se utilizó un diseño no experimental, el muestreo fue probabilístico, la recolección de datos se hizo mediante la revisión de literatura, recopilación de tatos y tablas resumen por cada etapa, el instrumento utilizado fue la guía de observación, para analizar los datos y parámetros requeridos en el predimensionamiento. Arequipa es uno de los departamentos que mayores aguas residuales no tratadas genera a nivel nacional, sin embargo, el 92% de sus aguas de origen doméstico, industrial y hospitalario son vertidas a cuerpos de agua sin ningún tipo de tratamiento y esto se debe principalmente a la falta de infraestructuras y al inadecuado diseño de estas plantas. Con el predimensionamiento se espera presentar la propuesta de diseño para que las autoridades competentes puedan tomar cartas en el asunto y puedan tener una base para el planteamiento de futuras estructuras de plantas de tratamiento de aguas residuales. Se logró calcular los parámetros de predimensionamiento acuerdo a los diseños tomados como base de otras plantas de tratamiento

Modelling an industrial anaerobic granular reactor using a multi-scale approach

The objective of this paper is to show the results of an industrial project dealing with modelling of anaerobic digesters. A multi-scale mathematical approach is developed to describe reactor hydrodynamics, granule growth/distribution and microbial competition/inhibition for substrate/space within the biofilm. The main biochemical and physico-chemical processes in the model are based on the Anaerobic Digestion Model No 1 (ADM1) extended with the fate of phosphorus (P), sulfur (S) and ethanol (Et−OH). Wastewater dynamic conditions are reproduced and data frequency increased using the Benchmark Simulation Model No 2 (BSM2) influent generator. All models are tested using two plant data sets corresponding to different operational periods (#D1, #D2). Simulation results reveal that the proposed approach can satisfactorily describe the transformation of organics, nutrients and minerals, the production of methane, carbon dioxide and sulfide and the potential formation of precipitates within the bulk (average deviation between computer simulations and measurements for both #D1, #D2 is around 10%). Model predictions suggest a stratified structure within the granule which is the result of: 1) applied loading rates, 2) mass transfer limitations and 3) specific (bacterial) affinity for substrate. Hence, inerts (XI) and methanogens (Xac) are situated in the inner zone, and this fraction lowers as the radius increases favouring the presence of acidogens (Xsu,Xaa, Xfa) and acetogens (Xc4,Xpro). Additional simulations show the effects on the overall process performance when operational (pH) and loading (S:COD) conditions are modified. Lastly, the effect of intra-granular precipitation on the overall organic/inorganic distribution is assessed at: 1) different times; and, 2) reactor heights. Finally, the possibilities and opportunities offered by the proposed approach for conducting engineering optimization projects are discussed

MODEL DEVELOPMENT AND SYSTEM OPTIMIZATION TO MINIMIZE GREENHOUSE GAS EMISSIONS FROM WASTEWATER TREATMENT PLANTS

As greenhouse gas emissions (GHG) reduction has drawn considerable attention, various methods have been established to estimate greenhouse gas emissions from wastewater treatment plants (WWTPs). In order to establish a design and operational strategy for GHG mitigation, accurate estimates are essential. However, the existing approaches (e.g. the IPCC protocol and national greenhouse gas inventories) do not cover emissions from all sources in WWTPs and are not sufficient to predict facility-level emissions. The ultimate goal of this research was to improve the quantification of GHG emissions from WWTPs. This was accomplished by creating a new mathematical model based on an existing activated sludge model. The first part of the research proposed a stepwise methodology using elemental balances in order to derive stoichiometry for state variables used in a mass balance based whole-plant wastewater treatment plant model. The two main advantages of the elemental balance method are the inclusion of carbon dioxide (CO2) into the existing model with no mass loss and ease of tracking elemental pathways. The second part of the research developed an integrated model that includes (1) a direct emission model for onsite emissions from treatment processes and (2) an indirect emission model for offsite emissions caused by plant operation. A sensitivity analysis of the proposed model was conducted to identify key input parameters. An uncertainty analysis was also carried out using a Monte Carlo simulation, which provided an estimate of the potential variability in GHG estimations. Finally, in the third part, the research identified an optimal operational strategy that resulted in minimizing operating costs and GHG emission, while simultaneously treating the wastewater at better levels. To do this, an integrated performance index (IPI) was proposed to combine the three criteria. The IPI was then incorporated into an optimization algorithm. The results obtained in this research demonstrated that the variation of GHG emissions is significant across the range of practical operational conditions. With system optimization, however, WWTPs have the potential to reduce GHG emissions without raising operating costs or reducing effluent quality. Further research should include a mechanistic examination of processes that produce methane (CH4) in the wastewater treatment stream and nitrous oxide (N2O) in the sludge treatment stream