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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 (

While the impact of suspended solids on chemical disinfection kinetics has been widely recognized, a detailed modeling framework for assessing their contribution on disinfection efficiency in municipal contact tanks is yet unavailable. In this paper, we conducted experimental and modeling studies to mechanistically describe the interplay between suspended solids (not removed by gravity settling in secondary clarifiers) and disinfection performance of an emerging disinfectant, peracetic acid, operated in a municipal contact tank. Specifically, we developed an integrated computational fluid dynamics (CFD) model to simultaneously predict the fate and transport of suspended solids, Escherichia coli and peracetic acid in a hypothetical reactor using an exposure-based (i.e., CT-based) inactivation rate expression. The integrated CFD model, calibrated against laboratory data, was used to gain insights on the vertical distribution and local PAA decay effect associated with solids settling and their impact on disinfectant decay and microbial inactivation. Results indicated that: (a) solids settling in contact tanks is a significant phenomenon that cannot be neglected, which can substantially impact disinfection efficiency under low flow conditions; (b) vertical solids distribution and stratification in contact tanks can strongly affect Escherichia coli inactivation by peracetic acid, as highlighted by the CFD modeling studies; (c) Escherichia coli settling is experimentally measurable, and strongly correlated with solids settling. These phenomena can be successfully integrated into a CFD model to obtain a comprehensive description of the PAA disinfection process in presence of changes in secondary effluent quality and flow, a situation typically encountered in municipal contact tanks operated in full scale wastewater treatment plants.

A detailed computational fluid dynamics model is presented that integrates reactor hydrodynamics with advanced light models and UV-TiO2 advanced oxidation kinetics to yield the degradation of oxalic acid in a dispersed-phase photoreactor. Model predictions were first compared against experimental data obtained from the literature and subsequently used in a parametric study for investigating scale-up effects associated with both process and photoreactor variables. Investigated variables included: TiO2 concentration (5–400 mg L−1), initial oxalic acid concentration (0.9–32 mg L−1), lamp irradiance (100–10,000 W m−2), background fluid absorbance (0-30 m−1), reactor size (1/4-4 as relative scaling factor), lamp orientation (0-360°) and flowrate (2.5–10 m3 h−1). The analysis revealed that an optimum in oxalic acid degradation is observed when the TiO2 concentration was controlled in the 20–40 mg L−1 range (depending on lamp irradiance). While lamp orientation showed minimal impact, reactor size and flowrate emerged as key variables for photoreactor design. Moreover, an increase in initial oxalic acid concentration substantially reduced oxalic acid degradation performance observed at high loadings. Also, TiO2 activation and photoreactor degradation performance were impacted negatively by light competition with background fluid absorbance.

Light energy is one of the major costs for phototrophic systems. This study evaluated the photoreactor efficiency of purple phototropic bacteria anaerobic membrane bioreactor (PAnMBR) at low irradiance for the treatment of municipal wastewater. Infrared irradiance levels of 3.0 and 1.4 W/m2 produced by an infrared (IR) lamp emitting in the 800–900 nm wavelength range were investigated, with the ultimate goal of optimizing the irradiance energy demand. Experimental and modeling results demonstrated the ability of PPB to grow and treat raw municipal wastewater at the applied low irradiances, with effluent quality below target limits of TCOD˂50 mg/L, TN˂10 mg/L, and TP˂1 mg/L. While Monod kinetic parameters, km and Y, were determined to be lower than previous high-energy studies (1.9 mgCOD/mgVSS-d and 0.38 mgVSS/mgCOD, respectively), the photobioreactor performance were consistently maintained, indicating that energy cost associated with IR illumination can be reduced by up to 97%. To determine whether the treatment process could approach energy neutrality, subsequent anaerobic digestion experiments of the residual PPB biomass proved a potential for biogas recovery of up to 240 NmLCH4/gVSSadded, and a moderate biomass biodegradability of 41%. As a result, the net energy consumption of the process was estimated at 0.5 kWh/m3 of treated municipal wastewater, considering an energy demand for illumination of 0.67 kWh/m3 and an energy recovery attributed to the anaerobic digestion of 0.17 kWh/m3 from the excess PPB biomass wasted from PAnMBR.

While disinfection processes have been central for public health protection, new concerns have been raised with respect to their ability to control the spread of antibiotic resistance in the environment. In this study, we report the inactivation kinetics by peracetic and performic acids of a typical indicator, Escherichia coli and its corresponding antibiotic-resistant subpopulation, in secondary settled wastewater effluent. Performic acid always showed greater inactivation efficiency than peracetic acid, whether or not the indicator was Ampicillin-resistant. Observed inactivation data, fitted with an exposure-based inactivation model, predicted very well the inactivation profile of both total and ampicillin resistant Escherichia coli. Notably, the antibiotic resistance percentage decreased significantly in treated wastewater compared to untreated wastewater thus making the peracid-based disinfection processes beneficial in controlling antibiotic resistance in secondary settled wastewater. Moreover, the minimum inhibitory concentration values remained unchanged. Finally, antibiotic-resistant-specific inactivation kinetics were used to predict the disinfection efficiency in continuous-flow reactors under ideal and non-ideal hydraulics thus providing useful information for future design and operation of disinfection process in antibiotic-resistance controlling mode.

Aeration is a major contributor to the high energy demand in municipal wastewater treatment plants. Thus, it is important to understand the dynamic impact of wastewater characteristics on oxygen transfer efficiency to develop suitable control strategies for minimizing energy consumption since aeration efficiency is influenced by the biodegradation of pollutants in the influent. The real-time impact of acetate as a readily biodegradable substrate and cellulose as a slowly biodegradable substrate were studied at different operational conditions. Cellulose in the influent wastewater can be removed efficiently using primary treatment technologies, such as the rotating belt filter (RBF). At an ambient DO of 2 mg l−1 and air flow of 1.02 m3 h−1 (0.6 SCFM), the α-factor was more sensitive to readily biodegradable substrates than to cellulose. On average, α-factor decreased by 48% and 19% due to the addition of acetate and cellulose, respectively. At a DO of 4 mg l−1 and air flow of 1.7 m3 h−1 (1 SCFM), α-factor remained constant irrespective of cellulose and acetate concentrations. Without active biomass, α-factor decreased by 47% and 43% at a DO of 2 mg l−1 (air flow of 1.02 m3 h−1) and high DO of 5 mg l−1 (air flow of 1.7 m3 h−1), respectively. An inverse correlation between α-factor and sCOD was defined and incorporated into a dynamic model to estimate the real-time airflow rates associated with the improvement of the oxygen transfer efficiency due to biodegradation. Finally, the RBF operated with a 158-μm mesh selectively removed cellulose, thus reducing air requirements, and energy by 25%.

Peracetic acid (PAA) has attracted growing attention as an alternative oxidant and disinfectant in wastewater treatment due to the increased demand to reduce chlorine usage and control disinfection byproducts (DBPs). These applications have stimulated new investigations on PAA-based advanced oxidation processes (AOPs), which can enhance water disinfection and remove micropollutants. The purpose of this review is to conduct a comprehensive analysis of scientific information and experimental data reported in recent years on the applications of PAA-based AOPs for the removal of chemical and microbiological micropollutants from water and wastewater. Various methods of PAA activation, including the supply of external energy and metal/metal-free catalysts, as well as their activation mechanisms are discussed. Then, a review on the usage of PAA-based AOPs for contaminant degradation is given. The degradation mechanisms of organic compounds and the influence of the controlling parameters of PAA-based treatment systems are summarized and discussed. Concurrently, the application of PAA-based AOPs for water disinfection and the related mechanisms of microorganism inactivation are also reviewed. Since combining UV light with PAA is the most commonly investigated PAA-based AOP for simultaneous pathogen inactivation and micropollutant oxidation, we have also focused on PAA microbial inactivation kinetics, together with the effects of key experimental parameters on the process. Moreover, we have discussed the advantages and disadvantages of UV/PAA as an AOP against the well-known and established UV/H2O2. Finally, the knowledge gaps, challenges, and new opportunities for research in this field are discussed. This critical review will facilitate an in-depth understanding of the PAA-based AOPs for water and wastewater treatment and provide useful perspectives for future research and development for PAA-based technologies.

A computational fluid dynamic (CFD) model was developed to describe the process performance of a semi-batch annular TiO 2 –UV photoreactor in an Eulerian framework. The model accounted for the optical behaviour of titanium dioxide (TiO 2 ) suspensions, the flow distribution and the oxalic acid degradation in the reactor. The scattering component of the optical model, explicitly included in the CFD simulations using a TiO 2 -specific scattering phase function integrated in the radiative transfer equation, was calibrated using an optical goniometer by comparing simulated scattering light profiles against irradiance measurements collected for various TiO 2 concentrations and UV wavelengths and subsequently solved by the discrete ordinate (DO) radiation model. Several scattering phase functions were tested against the goniometric measurements confirming that the Henyey-Greenstein (HG) equation was the most appropriate angular distribution function at 254 and 355 nm, irrespective of the TiO 2 concentration. Using the calibrated HG function, a new approach for quantifying the absolute values of absorption and scattering coefficients in TiO 2 suspensions was proposed. It consists of iteratively solving, using the DO model, the radiative transfer equation for various combinations of absorption and scattering coefficients until the error between observed and predicted angular irradiance measurements is minimized. The accuracy of the optical parameters was verified with independent CFD simulations carried out for an annular photoreactor and already available in the literature. Predicted and simulated irradiance and oxalic acid degradation data were found to be in excellent agreement, confirming the considerable potential of the integrated modelling approach presented in this paper for the design, optimization and scale-up of photocatalytic technologies for water and wastewater treatment applications.

Combined sewer overflows contain a highly variable, wide range of contaminants, both in particulate and soluble form, making conventional water treatment processes unable to offer adequate public health protection. In this study, an integrated treatment process designed to simultaneously remove typical combined sewer overflow pollutants (suspended solids, chemical oxygen depends, turbidity) in conjunction with nutrient (nitrogen and phosphorus), was developed. The removal of particulates as well as dissolved nitrogen and phosphorus was achieved by first adsorbing soluble pollutants on zeolite and powdered activated carbon, and subsequently applying filtration carried out by polymer-enhanced microsieving. Laboratory experiments were designed using design-of-experiment techniques and carried out to assess the effects of the various treatment variables (cationic polymer, zeolite, powder activated carbon and microsieve size) in the designed combinations. A response surface model was fitted to the experimental dataset in order to capture and describe the non-linear relationships between treatment variables and treatment objectives. Finally, an optimization study was carried out using Pareto analysis showing that cationic polymer, zeolite, and powdered activated carbon, followed by fine mesh microsieving, worked synergistically in the integrated treatment process. Several optimal process conditions emerged, in particular, a treatment combination consisting of 1.1 mg/L of the cationic polymer, 250 mg/L of zeolite, 5 mg/L of powdered activated carbon, and a 370 μm mesh size. Under this condition, expected performance would be reductions of 72%, 56%, 35%, and 75% for turbidity, total Kjeldahl nitrogen, total chemical oxygen demand, and total phosphorous, respectively. The findings presented in this paper demonstrate the possibility of achieving multiple treatment objectives in a single and integrated treatment step, hence providing municipalities with viable treatment options where the issues of combined sewer overflow and nutrient management are simultaneously tackled.

A detailed computational fluid dynamics model is presented that integrates reactor hydrodynamics with advanced light models and UV-TiO

The present study examines the relationship between the degree of solubilization and biodegradability of wastewater sludge in anaerobic digestion as a result of low-temperature thermal pre-treatment. The main effect of thermal pre-treatment is the disintegration of cell membranes and thus solubilization of organic compounds. There is an established correlation between chemical oxygen demand (COD) solubilization and temperature of thermal pre-treatment, but results of thermal pre-treatment in terms of biodegradability are not well understood. Aiming to determine the impact of low temperature treatments on biogas production, the thermal pre-treatment process was first optimized based on an experimental design study on waste activated sludge in batch mode. The optimum temperature, reaction time and pH of the process were determined to be 80 °C, 5 h and pH 10, respectively. All three factors had a strong individual effect (p

A novel mechanistic model that describes the vacuum UV advanced oxidation process in an annular photoreactor initiated by 172 nm and 185 nm (in combination with 253.7 nm, with and without exogenous H 2 O 2 ) is presented in this paper. The model was developed from first principles by incorporating the vacuum UV-AOP kinetics into the theoretical framework of in-series continuous flow stirred tank reactors. After conducting a sensitivity analysis, model predictions were compared against experiments conducted under a variety of conditions: (a) photo-induced formation of hydrogen peroxide by water photolysis at 172 nm (for both air- and oxygen-saturated conditions); (b) photo-induced formation of hydrogen peroxide by water photolysis at 185 + 253.7 nm (in the presence of formic acid, with and without the initial addition of hydrogen peroxide); (c) direct photolysis of hydrogen peroxide by 253.7 nm; (d) degradation of formic acid by 185 + 253.7 nm (with and without initial addition of hydrogen peroxide); and (e) degradation of formic acid by 253.7 nm (with the addition of exogenous hydrogen peroxide). In all cases, the model was able to accurately predict the time-dependent profiles of hydrogen peroxide and formic acid concentrations. Two newly recognized aspects associated with water photolysis were identified through the use of the validated model. Firstly, unlike the 185 nm and 253.7 nm cases, water photolysis by the 172 nm wavelength revealed a depth of photoactive water layer an order of magnitude greater (∼230–390 μm, depending on the specific operating conditions) than the 1-log photon penetration layer (∼18 μm). To further investigate this potentially very important finding, a computational fluid dynamics model was set up to assess the role of transport mechanisms and species distributions within the photoreactor annulus. The model confirmed that short-lived hydroxyl radicals were present at a radial distance far beyond the ∼18 μm photon penetration layer. Secondly, kinetic simulations showed that the higher penetration depth of hydroxyl radicals was not caused by diffusive or convective transport phenomena but rather the effect of non-linear behavior of the complex reaction kinetics involved in the process.