Reactor Hydraulics Research Articles

Pathogen Peak "Averaging" in Potable Reuse Systems: Lessons Learned from Wastewater Surveillance of SARS-CoV-2.

This study describes wastewater concentrations of SARS-CoV-2 at seven different sampling locations in Southern Nevada (ranging from 4.2 to 8.7 log10 gc/L) and highlights several key variables affecting those concentrations, including COVID-19 incidence, sample type, and service area population. This information is important for implementing wastewater-based epidemiology, but it also provides insight relevant to the design and regulation of potable reuse systems. Specifically, smaller systems may be more prone to influent concentration spikes that can drive enteric pathogen risk during disease outbreaks. It may be possible to leverage reactor hydraulics to achieve peak “averaging” in these scenarios, although it then becomes important to consider how elevated risks at the lower percentiles potentially offset benefits at the upper percentiles. Informed by SARS-CoV-2 concentration dynamics, the current study simulated relative risk for a hypothetical enteric pathogen. Simulated reactor hydraulics (i.e., dispersion) increased pathogen concentrations by up to 2.6 logs at lower percentiles but also decreased concentrations by up to 1.1 logs at the upper percentiles that sometimes drive public health risk. Collectively, these data highlight the importance of considering outbreak conditions, pathogen spikes, and peak “averaging” in the design and operation of treatment systems and in the development of regulatory frameworks.

Evaluating reactor hydraulics in a cost‐effective and environment‐friendly way: Numerical tracer study

AbstractTracer analysis is commonly used to evaluate the hydraulics of environmental and chemical engineering systems. The traditional tracer analysis is conducted through physical experiments that are usually complex, costly, time‐intensive, and may be impractical. Because of the continued advancement of computing technology, computational fluid dynamics (CFD) has demonstrated its applicability in simulating tracer transport. CFD can provide advantages, including no interruptions of existing water treatment process, no impacts of background concentration, and a relatively low cost. However, no reports have quantitatively studied the cost that CFD can save on tracer analysis. This study first proved the accuracy of CFD tracer analysis for an existing ozone disinfection tank and then compared the economic expenses and environmental impacts of CFD tracer analysis with those of a field tracer analysis. It was found that CFD‐based tracer analysis has accuracy on par with the physical‐based study but at relatively low economic cost and environmental impacts.

Detailed modeling and advanced control for chemical disinfection of secondary effluent wastewater by peracetic acid

Advanced control of chemical disinfection processes is becoming increasingly important in view of balancing under-treatment (low pathogen inactivation) and over-treatment (excessive consumption of disinfectant and disinfection byproducts formation) thereby providing considerable environmental and economic benefits. Conventional control strategies such as flow pacing or residual trim ignore chemical demand/decay, inactivation kinetics, and other factors governing disinfection performance in continuous-flow reactors such as reactor hydraulics and process variability. This study presents the development, verification, and pilot-scale validation of a novel CT-based real-time disinfection control strategy, derived from first principles, and applied to peracetic acid disinfection of municipal secondary effluent wastewater. Validation experiments were carried out using a 3-m3 pilot contact basin of which the hydraulic performance was first characterized by means of tracer tests and then mathematically modeled using the well-established theoretical framework of continuous stirred-tank reactors in series. The analytical model describing hydraulic performance was subsequently extended to take into account disinfectant demand/decay and microbial inactivation kinetics. The integrated model was successfully used to predict, and control, residual peracetic acid as well as microbial concentration in the pilot effluent. Validation studies conclusively supported that the novel CT-based control strategy was superior in maintaining constant disinfection performance, desired microbial counts, and low residual disinfectant under variable flow and wastewater quality. When compared with flow pacing, the CT-based control required two times less the amount of chemical for the same treatment objective (<100 cfu/100 mL). Remarkably, the CT-based control strategy could be extended to other chemical disinfection processes such as chlorination and ozonation, alone or in combination with physical treatment technologies such as membranes and ultraviolet irradiation.

Modeling Water Treatment Reactor Hydraulics Using Reactor Networks

Reactor hydraulics are integral to water treatment processes such as disinfection and chemical contaminant oxidation. This work uses reactor networks—conceptual reactors arranged in parallel and series combinations—to simplify the accurate modeling of residence time in water treatment reactors. Reactor networks were selected for 14 clearwells, ozone contactors, clarifiers, and filters using tracer data sets from literature. For seven of 14 full‐scale reactors, two parallel tanks‐in‐series reactors best balanced accuracy and simplicity. Reactor networks accurately represented tracer data using between two and eight fitting parameters, while segregated flow analysis required 32–164 inputs (two per tracer data point). The modeling work revealed that tracer data sets may have overestimated baffle factors by &gt;10% in 10 of the 14 full‐scale reactors, potentially as a result of inaccurate measurement of flow rate or volume. Applications of reactor networks include more accurate approaches to disinfection regulation and modeling the degradation of emerging contaminants.

Integrating hydrodynamics and biokinetics in wastewater treatment modelling by using smoothed particle hydrodynamics

Abstract In this work a novel integrated biokinetic wastewater treatment (WWT) model based on the smoothed particle hydrodynamics (SPH) method as hydraulic model is proposed. Significant outcomes of this work are the computation of a detailed spatial distribution of compounds in WWT basins and the quantification of the effects of the stirrer induced mixing on the evolution of compounds. SPH is a meshfree particle method which herein is applied to compute a treatment plant's reactor hydraulics. The characteristic feature of SPH is to describe a fluid's dynamics by particles that move along with the flow. The present WWT model takes advantage of this principle by assigning the compounds’ concentrations, which are defined by the activated sludge model no. 1, to SPH particles. A full-scale treatment plant simulation with a variable stirrer induced mixing intensity in the denitrification basin is performed. A spatial distribution of the compounds’ concentrations, which up to now was unknown for unsteady flows, is computed and analysed. The developed framework is generic and therefore expected to be applicable for modelling chemical engineering processes which are influenced by hydrodynamic effects.

Nondeterministic computational fluid dynamics modeling of Escherichia coli inactivation by peracetic acid in municipal wastewater contact tanks.

Wastewater disinfection processes are typically designed according to heuristics derived from batch experiments in which the interaction among wastewater quality, reactor hydraulics, and inactivation kinetics is often neglected. In this paper, a computational fluid dynamics (CFD) study was conducted in a nondeterministic (ND) modeling framework to predict the Escherichia coli inactivation by peracetic acid (PAA) in municipal contact tanks fed by secondary settled wastewater effluent. The extent and variability associated with the observed inactivation kinetics were both satisfactorily predicted by the stochastic inactivation model at a 95% confidence level. Moreover, it was found that (a) the process variability induced by reactor hydraulics is negligible when compared to the one caused by inactivation kinetics, (b) the PAA dose required for meeting regulations is dictated equally by the fixed limit of the microbial concentration as well as its probability of occurrence, and (c) neglecting the probability of occurrence during process sizing could lead to an underestimation of the PAA dose required by as much as 100%. Finally, the ND-CFD model was used to generate sizing information in the form of probabilistic disinfection curves relating E. coli inactivation and probability of occurrence with the average PAA dose and PAA residual concentration at the outlet of the contact tank.

Modelling of moving bed biofilm membrane reactors (MBBMR) for on-site greywater treatment.

The study evaluates with a mechanistic model the pilot plant results of a combined moving bed biofilm process and membrane filtration (MBBMR) treating single household greywater. It mainly includes the simulation of reactor hydraulics, degradation of pollutants, development of biomass and settlement of sludge. Iterative calibration was made with steady-state results of a 10-month pilot test. The model shows good predictions of readily biodegradable chemical oxygen demand and ammonium removal, as well as biomass concentration on carriers and in suspension. Also, a sensitivity analysis was made which calculates the relative significance factor of each model coefficient and by this provides comparability with other studies. Simulation data and actually measured parameters show that the suggested process was rather independent of ambient temperatures and short-term load fluctuations. Obtained datasets and model structure could be of use for future designers, as well as sellers and users of this process for on-site greywater reclamation.

Dynamic multidimensional modelling of submerged membrane bioreactor fouling

Existing membrane fouling models are limited to simple hydraulic profiles which is a limitation particularly for planar membranes. Here, we present a new model that allows for a distributed shear profile, with dynamic linking of flux and transmembrane pressure (TMP). Shear profile is calculated using a multi-phase computational fluid dynamic approach, and is applied to a distributed parameter model to simulate membrane fouling profile and flux distribution. This allows for simulation of complex flux-step experiments, or situations where non-uniform shear is present. The model was applied to filtration experiments conducted in a pilot-scale anaerobic membrane bioreactor treating slaughterhouse wastewater comprising 1950±250mg/L total solids and was able to effectively fit experiments under dynamic critical flux conditions. Cake compressibility was a key parameter, and was estimated at 870±80Pa. Non-uniform gas distribution decreased critical flux from 12LMH to 8.5LMH. This emphasises the importance of local flow conditions on membrane fouling behaviour and that performance can depend heavily on reactor configuration and hydraulics.

Kinetic assessment and modeling of an ozonation step for full-scale municipal wastewater treatment: Micropollutant oxidation, by-product formation and disinfection

The kinetics of oxidation and disinfection processes during ozonation in a full-scale reactor treating secondary wastewater effluent were investigated for seven ozone doses ranging from 0.21 to 1.24 g O3 g−1 dissolved organic carbon (DOC). Substances reacting fast with ozone, such as diclofenac or carbamazepine (kP,O3 > 104 M−1 s−1), were eliminated within the gas bubble column, except for the lowest ozone dose of 0.21 g O3 g−1 DOC. For this low dose, this could be attributed to short-circuiting within the reactor. Substances with lower ozone reactivity (kP,O3 < 104 M−1 s−1) were only fully eliminated for higher ozone doses.The predictions of micropollutant oxidation based on coupling reactor hydraulics with ozone chemistry and reaction kinetics were up to a factor of 2.5 higher than full-scale measurements. Monte Carlo simulations showed that the observed differences were higher than model uncertainties. The overestimation of micropollutant oxidation was attributed to a protection of micropollutants from ozone attack by the interaction with aquatic colloids. Laboratory-scale batch experiments using wastewater from the same full-scale treatment plant could predict the oxidation of slowly-reacting micropollutants on the full-scale level within a factor of 1.5. The Rct value, the experimentally determined ratio of the concentrations of hydroxyl radicals and ozone, was identified as a major contribution to this difference.An increase in the formation of bromate, a potential human carcinogen, was observed with increasing ozone doses. The final concentration for the highest ozone dose of 1.24 g O3 g−1 DOC was 7.5 μg L−1, which is below the drinking water standard of 10 μg L−1. N-Nitrosodimethylamine (NDMA) formation of up to 15 ng L−1 was observed in the first compartment of the reactor, followed by a slight elimination during sand filtration. Assimilable organic carbon (AOC) increased up to 740 μg AOC L−1, with no clear trend when correlated to the ozone dose, and decreased by up to 50% during post-sand filtration. The disinfection capacity of the ozone reactor was assessed to be 1–4.5 log units in terms of total cell counts (TCC) and 0.5 to 2.5 log units for Escherichia coli (E. coli). Regrowth of up to 2.5 log units during sand filtration was observed for TCC while no regrowth occurred for E. coli. E. coli inactivation could not be accurately predicted by the model approach, most likely due to shielding of E. coli by flocs.

The role of the flow pattern in wastewater aeration tanks

Reactor hydraulics is one of the key factors for plant performance and plant control. The residence time distribution is a good but limited indicator of reactor hydraulics. A more detailed view is obtained by direct observations within the reactor. Two different techniques (conservative tracer, reactive tracer) are discussed to detect major anomalies in the flow field of a wastewater aeration tank. Experiments with conservative tracers give valuable information over a very limited period of time making the analysis of the flow field difficult. On the other hand, reactive tracers can be monitored long term which helps identifying the flow pattern provided that a high spatial and temporal resolution of the measurements is applied. Experimental data is used to determine the structure and the parameters of a compartment model that corresponds well with the measurements.

Simulation for the Flowing Water Purification with Spring Shape Inside Chamber

Interest in application of ultraviolet light technology for primary disinfection of potable water in drinking water treatment plants has increased significantly in recent years. The efficacy of disinfection processes in water purification systems is governed by several key factors, including reactor hydraulics, disinfectant chemistry, and microbial inactivation kinetics. The objective of this work was to develop a computational fluid dynamics(CFD) model to predict velocity fields, mass transport, chlorine decay, and microbial inactivation in a continuous flow reactor. In this paper, It describe the how to design optimal UV disinfection device for ground water, BWT and rainwater. Spring shape instrument silver coated located in inner side of disinfection chamber. It make lead the active flowing movement target water and maximize disinfection performance. To search the optimal design method, it was performed computer simulation with 3D-CFD discrete ordinates model and manufactured prototype. Using proposed design method, performed simulation and proved satisfied performance.

Elimination of Organic Micropollutants in a Municipal Wastewater Treatment Plant Upgraded with a Full-Scale Post-Ozonation Followed by Sand Filtration

The removal efficiency for 220 micropollutants was studied at the scale of a municipal wastewater treatment plant (WWTP) upgraded with post-ozonation followed by sand filtration. During post-ozonation, compounds with activated aromatic moieties, amine functions, or double bonds such as sulfamethoxazole, diclofenac, or carbamazepine with second-order rate constants for the reaction with ozone >10(4) M(-1) s(-1) at pH 7 (fast-reacting) were eliminated to concentrations below the detection limit for an ozone dose of 0.47 g O3 g(-1) dissolved organic carbon (DOC). Compounds more resistant to oxidation by ozone such as atenolol and benzotriazole were increasingly eliminated with increasing ozone doses, resulting in >85% removal for a medium ozone dose (approximately 0.6 g O3 g(-1) DOC). Only a few micropollutants such as some X-ray contrast media and triazine herbicides with second-order rate constants <10(2) M(-1) s(-1) (slowly reacting) persisted to a large extent. With a medium ozone dose, only 11 micropollutants of 55 detected in the secondary effluent were found at >100 ng L(-1). The combination of reaction kinetics and reactor hydraulics, based on laboratory-and full-scale data, enabled a quantification of the results by model calculations. This conceptual approach allows a direct upscaling from laboratory- to full-scale systems and can be applied to other similar systems. The carcinogenic by-products N-nitrosodimethylamine (NDMA) (< or =14 ng L(-1)) and bromate (<10 microg L(-1)) were produced during ozonation, however their concentrations were below or in the range of the drinking water standards. Furthermore, it could be demonstrated that biological sand filtration is an efficient additional barrier for the elimination of biodegradable compounds formed during ozonation such as NDMA. The energy requirement for the additional post-ozonation step is about 0.035 kWh m(-3), which corresponds to 12% of a typical medium-sized nutrient removal plant (5 g DOC m(-3)).

Compartmental Models for Continuous Flow Reactors Derived from CFD Simulations

Reactor modeling is of major interest in environmental technology. In this context, new contaminants with higher degradation requirements increase the importance of reactor hydraulics. CFD (Computational Fluid Dynamics) may meet this challenge but is expensive for everyday use. In this paper, we provide research and practice with a methodology designed to automatically reduce the complexity of such a high-dimensional flow model to a compartmental model. The derivation is based on the concentration field of a reacting species which is included in the steady state CFD simulation. While still capturing the most important flow features, the compartmental model is fast, easy to use, and open for process modeling with yet unknown compounds. The inherent overestimation of diffusion by compartmental models has been corrected by locally adjusting turbulent fluxes. We successfully applied the methodology to the ozonation process and experimentally verified it with tracer experiments. The loss of information was quantified as a deviation from CFD performance prediction for different reactions. With increasing discretisation of the compartmental model, these deviations diminish. General advice on the necessary discretisation is given.

Effect of Flow Characteristics on Online Sterilization of Cheese Whey in UV Reactors

An ultraviolet (UV) coil reactor was designed and used for the online sterilization of cheese whey. Its microbial destruction efficiency was compared to that of the conventionally used UV reactor. Both reactors have the same geometry (840 ml volume and 17 mm gap size) and were tested at 11 flow rates of 5, 10, 15, 20, 25, 30, 35, 40, 50, 60, and 70 ml/min. The results obtained from this study showed that despite of its high turbidity, cheese whey could be sterilized using UV radiation if the proper reactor design and flow rate are used. The performances of the UV reactors were governed by the flow rate and the hydraulics of flow inside the reactor. The flow was laminar in both the reactors, as the Reynolds number was in the range of 1.39-20.10. The phenomenon of Dean Flow was observed in the coil reactor and the Dean number was in the range of 1.09-15.41. Dean vortices resulted in higher microbial destruction efficiency in the coil reactor in a shorter retention time. The rate of microbial destruction was found to be exponential in the conventional reactor and polynomial in the coil reactor. Increasing the flow rate from 5 ml/min to 70 ml/min decreased the microbial destruction efficiency of the conventional reactor from 99.40 to 31.58%, while the microbial destruction efficiency in the coil reactor increased from 60.77% at the flow rate of 5 ml/min to 99.98% at the flow rate of 30 ml/min and then decreased with further increases in flow rate reaching 46.2% at the flow rate of 70 ml/min. The maximum effluent temperatures in the conventional and coil reactors were 45.8 and 46.1 degrees C, respectively. Fouling in the coil reactor was significantly less compared to the conventional reactor. The extent of fouling was influenced by flow rate and reactor's hydraulics.

Computational Fluid Dynamics Analysis of the Effects of Reactor Configuration on Disinfection Efficiency

The efficacy of disinfection processes in water purification systems is governed by several key factors, including reactor hydraulics, disinfectant chemistry, and microbial inactivation kinetics. The objective of this work was to develop a computational fluid dynamics (CFD) model to predict velocity fields, mass transport, chlorine decay, and microbial inactivation in a continuous flow reactor. The CFD model was also used to evaluate disinfection efficiency in alternative reactor designs. The CFD reactor analysis demonstrates that disinfection efficiency is affected by both kinetics and mixing state (i.e., degree of micromixing or segregation). Residence time distributions (RTDs) derived from tracer analysis do not describe intrinsic mixing conditions. The CFD-based disinfection models account for reactor mixing patterns by resolution of the reactor velocity field and thus provide a better prediction of microbial inactivation than models that use an RTD.

Numerical simulation of chlorine disinfection processes

The efficacy of disinfection processes in water purification systems is governed by several key factors including reactor hydraulics, disinfectant chemistry and microbial inactivation kinetics. The objective of this work was to develop a computational fluid dynamics (CFD) model to predict flow structure, mass transport and chlorine decay in a continuous flow pilot scale reactor. These predictions were compared with experimental measurements for model validation. The current research demonstrates that inlet configurations can significantly impact reactor hydrodynamics.

The integrated disinfection design framework approach to reactor hydraulics characterization

The integrated disinfection design framework (IDDF) is a new approach to determine disinfection requirements for drinking water treatment facilities. The framework may be applied to enhance or improve disinfection performance in lieu of using the surface water treatment rule (SWTR) Guidance Manual. The overall IDDF approach consists of four modules: hydraulic characterization, disinfectant demand/decay, inactivation kinetics, and disinfection by-product (DBP) formation. In this study, a review of the hydraulic characterization module is presented. The module was applied to two full-scale water treatment plant processes (1: a group of six filter beds, 2: a disinfection contactor). The data from the hydraulic characterization module, which consists of three methods to generate the residence time distribution (RTD) curve, was then used to demonstrate the microbial inactivation and DBP formation level that might be produced at the process effluent. Results suggest that the predicted microbial inactivation level is sensitive to the hydraulic characterization method. However, all three methods predict very similar DBP formation despite differences in the RTD data. Results also showed that the disinfectant dose applied to the contactor could be reduced by 35% and still maintain the same credit for Giardia inactivation specified by the USEPA CT tables. This reduction in disinfectant dose could result in a reduction in the total trihalomethane (TTHM) level by 10% and haloacetic acids (HAAs) by 20%.

Modelling anaerobic degradation of complex wastewater. II: parameter estimation and validation using slaughterhouse effluent

This is the second part of a two-part paper developing and validating a structural model to describe the high rate anaerobic digestion of complex wastewater. A full-scale, two-stage hybrid upflow anaerobic reactor treating pig slaughterhouse effluent is assessed. Parameters and hydraulics are proposed for this system and validated. Characterisation of the system indicated that influent was a combination of equal parts (in terms of COD) particulate fat, particulate protein, and soluble protein. Reactor hydraulics were close to completely stirred tank reactor (CSTR) hydraulics, as indicated by a residence time distribution (RTD) study. The Monday morning abattoir start-up was identified as a key disturbance suitable for parameter estimation. A stepwise parameter estimation procedure was used as proposed in the previous paper. An experimental data set without recycle was used for parameter estimation. The model with these parameters performed well on independent data sets with and without recycle. The model identified several anomalies in the experimental data that may be unique to reactors treating complex wastewater.

Ozonation of bromide-containing drinking waters:a delicate balance between disinfection and bromate formation

The occurrence of Cryptosporidium in raw waters and bromate formation during ozonation of bromide-containing waters leads to a difficult optimisation of ozonation processes. On the one hand inactivation of Cryptosporidium requires high ozone exposures, on the other hand under these conditions bromate formation is favored. In order to overcome this problem we need information about (i) the oxidant concentrations (ozone and OH radicals) during an ozonation process, (ii) kinetics of the inactivation of Cryptosporidium, (iii) kinetics and mechanism of bromate formation, and (iv) the reactor hydraulics. The strong temperature dependence of the inactivation of Cryptosporidium which results in a higher ozone exposure (time-integrated action of ozone) at low temperatures makes it more difficult to fulfil disinfection and bromate standards at low temperatures. Underthese conditions control options for bromate formation can be applied. Depressionof pH and addition of ammonia have been selected to be the best options. For a given ozone exposure both measures lead to a reduction of bromate formation in the order of 50%.

Calibration of full-scale ozonation systems with conservative and reactive tracers

A full-scale ozonation reactor was characterised with respect to the overall oxidation budget by coupling laboratory kinetics with reactor hydraulics. The ozone decomposition kinetics and the ratio of the OK radical to the ozone concentration were determined in laboratory batch experiments. With the computer model AQUASIM these parameters could be coupled with the hydraulics of the ozonation reactor which allowed the prediction of the behaviour of ozone, chlorine, and micropollutants (e.g. atrazine) in the reactor. The comparison of measured and modelled concentration showed an excellent agreement. The present study summarises a general approach of how full scale ozonation reactors can be calibrated to assess disinfection, oxidation and minimise disinfection by-products, such as bromate.