Modelling of micropollutant removal in biological wastewater treatments: a review

A critical review on the pathways of carbamazepine transformation products in oxidative wastewater treatment processes

Carbamazepine (CBZ) is an anticonvulsant drug, released in domestic and hospital wastewater, and one of the drugs most commonly detected in surface water. Conventional secondary processes do a very poor job of removing it (<25 %), but its concentrations are significantly reduced by polishing oxidation processes. However, there are still many unknowns regarding the transformation products generated and their fate. This review first presents the journey of CBZ and its transformation products (TPs) in wastewater, from human consumption to discharge in water bodies. It then goes on to detail the diversity of mechanisms responsible for CBZ degradation and the generation of multiple TPs, laying the emphasis on the different types of advanced oxidation processes (AOP). 135 TPs were reported and a map describing their formation/degradation pathways was drawn up. This work highlights the wide range of physicochemical properties and toxicity effects of TPs on aquatic organisms and provides information about TPs of interest for future research. Finally, this review concludes on the importance of quantifying TPs and of determining kinetic characteristics to produce more accurate reaction schemes and computer-based fate predictions.

Rapid Method of Wastewater Classification by Electronic Nose for Performance Evaluation of Bioreactors with Activated Sludge

Currently, e-noses are used for measuring odorous compounds at wastewater treatment plants. These devices mimic the mammalian olfactory sense, comprising an array of multiple non-specific gas sensors. An array of sensors creates a unique set of signals called a "gas fingerprint", which enables it to differentiate between the analyzed samples of gas mixtures. However, appropriate advanced analyses of multidimensional data need to be conducted for this purpose. The failures of the wastewater treatment process are directly connected to the odor nuisance of bioreactors and are reflected in the level of pollution indicators. Thus, it can be assumed that using the appropriately selected methods of data analysis from a gas sensors array, it will be possible to distinguish and classify the operating states of bioreactors (i.e., phases of normal operation), as well as the occurrence of malfunction. This work focuses on developing a complete protocol for analyzing and interpreting multidimensional data from a gas sensor array measuring the properties of the air headspace in a bioreactor. These methods include dimensionality reduction and visualization in two-dimensional space using the principal component analysis (PCA) method, application of data clustering using an unsupervised method by Density-Based Spatial Clustering of Applications with Noise (DBSCAN) algorithm, and at the last stage, application of extra trees as a supervised machine learning method to achieve the best possible accuracy and precision in data classification.

Review of experimental biodegradation data on pharmaceuticals and comparison with predictive BIOWIN models

In this study the experimental data on the biodegradation of 16 pharmaceuticals in activated sludge were reviewed and also the theoretical biodegradation of these pharmaceuticals was calculated using BIOWIN models. The main aim was to show the similarities or discrepancies between the two. Experimental data were critically reviewed considering biodegradation rates, biodegradation mechanisms and biosorption of pharmaceuticals. For some pharmaceuticals, theoretical BIOWIN estimations and experimental findings deviated from each other. For example, if only BIOWIN estimations are considered, clarithromycin, azithromycin and ofloxacin would be defined as refractory. However, in experimental studies, they appeared to be not completely refractory. One of the reasons is that in most cases pharmaceuticals could be used as secondary substrates in the presence of sufficient bulk organic matter. In addition, all experimental studies indicate that at long Solids Retention Times (SRTs), nitrification activity becomes enhanced and the enzyme AMO leads to the cometabolic elimination of many pharmaceuticals. BIOWIN models prove to be very helpful for having an initial idea about biodegradability of pharmaceuticals. However, in order to estimate the biodegradability under real conditions, the models can be extended to include the different removal mechanisms reported in this study.

Predicting micropollutant fate during wastewater treatment using refined classical kinetic model based on quantitative monitoring in multi-metropolitan regions of South Korea

This study aimed to implement an extensive prediction model for the fate of micropollutants (MPs) in wastewater treatment plants (WWTPs). Five WWTPs equipped with seven different biological treatment processes were monitored from 2020 to 2022 with three to four sampling events in each year, and 27 datasets for 20 MPs were collected. Among these datasets, 12 were used to investigate the behavior and fate of MPs in WWTPs in South Korea. Metformin, acetaminophen, caffeine, naproxen, and ibuprofen were the MPs with the highest influent concentrations (ranging from 3,933.3-187,637.0 ng L-1) at all WWTPs. More than 90% of MPs were removed by biological treatment processes in all WWTPs. The Kruskal-Wallis test verified that their efficacy did not differ statistically (p-value > 0.05). Meanwhile, to refine the performance of the prediction model, this study optimized the biodegradation rate constants (kbio) of each MP according to the variation of seasonal water temperature. As a result, compared to the original prediction model, the mean difference between the actual data and predicted results (MEAN) decreased by 6.77%, while the Nash-Sutcliffe efficiency (NSE) increased by 0.226. The final MEAN and NSE for the refined prediction model were calculated to be 5.09% and 0.964, respectively. The prediction model made accurate predictions, even for MPs exhibiting behaviors different from other cases, such as estriol and atrazine. Consequently, the optimization strategy proposed in this study was determined to be effective because the overall removal efficiencies of MPs were successfully predicted even with limited reference datasets.

Assessment of the Presence of Transformation Products of Certain Pharmaceutical Products (Psychotropic Family) by Suspect and Non-Targeted HRMS Screening in Wastewater Treatment Plants

Aquatic environments are the final receptors of human emissions and are therefore contaminated by molecules, such as pharmaceuticals. After use, these compounds and their metabolites are discharged to wastewater treatment plants (WWTPs). During wastewater treatment, compounds may be eliminated or degraded into transformation products (TPs) or may be persistent. The aim of this study was to develop an analytical method based on high resolution mass spectrometry (HRMS) for the identification of six psychotropic drugs that are widely consumed in France and present in WWTPs, as well as their potential associated metabolites and TPs. Four out of six psychotropic drugs and between twenty-five and thirty-seven potential TPs were detected in wastewater, although this was based on full scan data. TPs not reported in the literature and specific to the study sites and therefore to the wastewater treatment processes were tentatively identified. For the selected drugs, most known and present TPs were identified, such as desmethylvenlafaxine or norcitalopram. Moreover, the short fragmentation study led rather to the identification of several TPs of carbamazepine as ubiquitous persistent TPs.

European-wide spatial analysis of sewage treatment plants and the possible benefits to nature of advanced treatment to reduce pharmaceutical emissions

Pharmaceuticals are known to widely occur in the environment and to affect the health of ecosystems. Sewage treatment plants (STPs) are main emission pathways for pharmaceuticals, which are often not sufficiently removed during wastewater treatment. In Europe, STP treatment requirements are specified under the Urban WasteWater Treatment Directive (UWWTD). The introduction of advanced treatment techniques, such as ozonation and activated carbon, under the UWWTD is expected to be an important option to reduce pharmaceutical emissions. In this study, we present a European-wide analysis of STPs reported under the UWWTD, their current treatment level and potential to remove a set of 58 prioritised pharmaceuticals. Three different scenarios were analysed to show 1) UWWTD present effectiveness, 2) the effectiveness at full UWWTD compliance, and 3) the effectiveness when advanced treatment is implemented at STPs with a treatment capacity of >100.000 person equivalents. Based on a literature study, the potential of individual STPs to reduce pharmaceutical emissions ranged from an average of 9% for STPs with primary treatment to 84% for STPs applying advanced treatment. Results of our calculations show that European-wide emission of pharmaceuticals can be reduced with 68% when large STPs are updated with advanced treatment, but spatial differences exist. We argue that adequate attention should also be paid with regards to preventing environmental impacts of STPs with a capacity <100.000 p.e. Circa 44% of total STP effluent is emitted near Natura2000 sites (EU nature protection areas). Of all surface waters receiving STP effluent for which the ecological status has been assessed under the Water Framework Directive, 77% have a status of less than good. Relatively often only primary treatment is applied to wastewater emitted into coastal waters. This analysis can be used to further model pharmaceutical concentrations in European surface waters, to identify STPs for which more advanced treatment might be required and to protect EU aquatic biodiversity.

Predicting and improving the microbial removal of organic micropollutants during wastewater treatment: A review

Organic micropollutants (OMPs) consist of widely used chemicals such as pharmaceuticals and pesticides that can persist in surface and groundwaters at low concentrations (ng/L to μg/L) for a long time. The presence of OMPs in water can disrupt aquatic ecosystems and threaten the quality of drinking water sources. Wastewater treatment plants (WWTPs) rely on microorganisms to remove major nutrients from water, but their effectiveness at removing OMPs varies. Low removal efficiency might be the result of low concentrations, inherent stable chemical structures of OMPs, or suboptimal conditions in WWTPs. In this review, we discuss these factors, with special emphasis on the ongoing adaptation of microorganisms to degrade OMPs. Finally, recommendations are drawn to improve the prediction of OMP removal in WWTPs and to optimize the design of new microbial treatment strategies. OMP removal seems to be concentration-, compound-, and process-dependent, which poses a great complexity to develop accurate prediction models and effective microbial processes targeting all OMPs.

Recent advances in simultaneous nitrification and denitrification for nitrogen and micropollutant removal: a review

Simultaneous Nitrification and Denitrification (SND) is a promising process for biological nitrogen removal. Compared to conventional nitrogen removal processes, SND is cost-effective due to the decreased structural footprint and low oxygen and energy requirements. This critical review summarizes the current knowledge on SND related to fundamentals, mechanisms, and influence factors. The creation of stable aerobic and anoxic conditions within the flocs, as well as the optimization of dissolved oxygen (DO), are the most significant challenges in SND. Innovative reactor configurations coupled with diversified microbial communities have achieved significant carbon and nitrogen reduction from wastewater. In addition, the review also presents the recent advances in SND for removing micropollutants. The micropollutants are exposed to various enzymes due to the microaerobic and diverse redox conditions present in the SND system, which would eventually enhance biotransformation. This review presents SND as a potential biological treatment process for carbon, nitrogen, and micropollutant removal from wastewater.

Modelling and prediction of the effect of operational parameters on the fate of contaminants of emerging concern in WWTPs

Wastewater treatment plants (WWTPs) provide a barrier against the discharge of contaminants of emerging concern (CECs) into the environment. The removal of CECs is highly WWTP-specific and the underlying mechanisms are still poorly understood, hampering the optimization of biological treatment steps for their removal. To fill this knowledge gap, we assessed the influence of four operational parameters of activated sludge biological treatment, namely total suspended solids, temperature, pH and redox conditions, on the sorption and biodegradation of four CECs under controlled laboratory conditions. Design of Experiments was used to better address the factors influencing CECs removal and interactions among operational parameters. The derived statistical models showed results in concordance with previous studies and indicated how sorption and biodegradation of the investigated CECs depend on most tested parameters and few of their interactions. The predictions of the developed models have been compared with literature values, indicating how the tested parameters are responsible for most of the variability of sorption, while they could not reliably generalize biodegradation rates. The developed models were also implemented as an extension of a mechanistic biological treatment model, successfully describing the dynamic behaviour of a large-scale WWTP, which was observed during a three-day continuous monitoring campaign. Compared to a traditional modelling approach, the one including the developed models showed on average almost a three-fold uncertainty reduction, favouring its use to aid WWTP managers and regulators for improved assessment of CEC fate and removal. Finally, the models highlighted that, while higher temperatures and solids concentrations generically favoured CECs removal, removal efficiency vary significantly due to operational parameters and no globally optimum conditions for CECs removal exist. The use of these models opens the door to the combined dynamic management of both traditional contaminants and CECs in WWTPs.

Modelling of micropollutant fate in hybrid growth systems: model concepts, Peterson matrix, and application to a lab-scale pilot plant

Modelling the fate of micropollutants in different wastewater treatment processes is of present concern. Moreover, during the last few years, there has been an increasing interest in the development of hybrid reactors which contain both suspended biomass and biofilm. Here, a new model developed which tries to determine the fate of micropollutants in hybrid reactors such as moving bed biofilm reactor (MBBR) and called the ASM-biofilm-MPs model considered the main mechanisms leading to the micropollutant removal (sorption/desorption, biodegradation, cometabolism) in hybrid reactors. This dynamic model describes the fate of micropollutants in a hybrid reactor using first-order kinetics for biotransformation and sorption/desorption equations. Also, it considered the reactions for carbon oxidation, nitrification, and denitrification in attached and suspended biomass under aerobic conditions. The mathematical model consists of three connected models for the simulation of micropollutants, suspended biomass, and biofilm. Biochemical conversions are evaluated according to the Activated Sludge Model No. 1 (ASM1) for both attached and suspended biomass. The model is applied for a laboratory MBBR, which fed with synthetic wastewater containing 4-nonylphenol (4-NP) as micropollutant, and accurately describes the experimental concentrations of COD, attached and suspended biomass, nitrogen, and 4-NP micropollutant obtained during 180 days working at different loadings. The differences between simulations and experiments in all operational periods for sCOD, NH₄-N, NO₃-N, and attached and suspended biomass concentrations were less than 15%, 10%, 10%, 5% and 5%, respectively. Finally, the contribution of adsorption and biodegradation mechanisms in the fate of 4-NP was calculated, when 4-NP concentration is set to 1 µg/L (biodegradation = 86.5%, sorption = 5%) and 50 µg/L (biodegradation = 55.9%, sorption = 34.7%).

Enzymatic integrated in-situ advanced anaerobic digestion of sewage sludge for the removal of antibiotics and antibiotic resistance genes

Antibiotics and antibiotic resistance genes (ARGs) in sewage sludge can cause high ecotoxicological risks in the environment and public health concerns. The aims of this study were to establish enzymatic integrated in-situ advanced anaerobic digestion (AAD) by adding cellulase and papain as well as the two enzymes combined with zero valent iron (ZVI) directly into the anaerobic digesters to explore the removal of antibiotics and ARGs under the mesophilic condition (35 °C). The methane production potential during in-situ AAD was effectively improved. Papain and cellulase at 30 mg/gTSS were most effective in improving antibiotic removal. The removal of sulfamerazine (SMZ) and sulfadiazine (SMR) could reach 89.10 % and 71.75 %. Combined enzymes with ZVI also enhanced the removal of all target antibiotics, especially roxithromycin (ROX), SMZ and SMR most significantly. Except for sul1, tetA and tetB, the removal of ARGs by papain reached 6.33 %-82.15 %. The addition of cellulase effectively improved tetA removal. The combination of biological enzymes further enhanced the removal of qnrS and ermX. The tetG, tetB, sul3, ermX, ermT, qnrS, and aac(6')-IB-CR by combined enzymes with ZVI could even not be detected after digestion. Addition of papain, cellulase, and ZVI caused variations in the dominant bacteria. All target antibiotics presented significant positive correlations with the genera norank_f__Bacteroidetes_vadinHA17, norank_f__norank_o__SJA-15, norank_f__norank_o__Aminicenantales. Redundancy analysis showed archaea Methanosaeta and Candidatus_ Methanoacidiosum genera greatly contributed to antibiotics removal with the combination of enzymes and ZVI. Co-occurrence network analysis indicated the removal of ARGs was mainly based on the changes of existence of host bacteria.

Fluoxetine and Nutrients Removal from Aqueous Solutions by Phycoremediation

The tertiary treatment using microalgae offers an attractive alternative to the removal of low but relevant concentrations of pharmaceuticals from domestic wastewaters. The removal of fluoxetine from aqueous solutions by living and non-living (lyophilized) Chlorella vulgaris was assessed. The determination of the pH at the point of zero charge, Fourier transmittance infrared analysis, and scanning electron microscopy were performed to characterize the microalgae biomass. Kinetic and equilibrium experiments were performed. The pseudo-second-order model described the kinetics of fluoxetine. The corresponding kinetic constants indicated that biosorption was faster onto non-living biomass than onto living biomass. The equilibrium results showed that the systems followed the Langmuir isotherm model. The maximum capacity of living microalgae (1.9 ± 0.1 mg·g⁻¹) was slightly higher than the non-living microalgae (1.6 ± 0.2 mg·g⁻¹). Living Chlorella vulgaris, free and immobilized in calcium-alginate, were also used to remove fluoxetine and nutrients (nitrogen and phosphorus) from treated municipal wastewater in a batch system. In both experiments, fluoxetine was completely removed within six days. The total phosphorus (TP) and total nitrogen (TN) removal efficiencies achieved for free and immobilized cells were, null and 65.0 ± 0.1%, and 86.2 ± 0.1% and 81.8 ± 3.1, respectively.

Use of Passive and Grab Sampling and High-Resolution Mass Spectrometry for Non-Targeted Analysis of Emerging Contaminants and Their Semi-Quantification in Water

Different groups of organic micropollutants including pharmaceuticals and pesticides have emerged in the environment in the last years, resulting in a rise in environmental and human health risks. In order to face up and evaluate these risks, there is an increasing need to assess their occurrence in the environment. Therefore, many studies in the past couple of decades were focused on the improvements in organic micropollutants’ extraction efficiency from the different environmental matrices, as well as their mass spectrometry detection parameters and acquisition modes. This paper presents different sampling methodologies and high-resolution mass spectrometry-based non-target screening workflows for the identification of pharmaceuticals, pesticides, and their transformation products in different kinds of water (domestic wastewater and river water). Identification confidence was increased including retention time prediction in the workflow. The applied methodology, using a passive sampling technique, allowed for the identification of 85 and 47 contaminants in the wastewater effluent and river water, respectively. Finally, contaminants’ prioritization was performed through semi-quantification in grab samples as a fundamental step for monitoring schemes.

A mathematical model for the activated sludge process with a sludge disintegration unit

We develop and investigate a model for sludge production in the activated sludge process when a biological reactor is coupled to a sludge disintegration unit (SDU). The model for the biological reactor is a slimmed down version of the activated sludge model 1 in which only processes related to carbon are retained. Consequently, the death-regeneration concept is included in our model which is an improvement on almost all previous models. This provides an improved representation of the total suspended solids in the biological reactor, which is the key parameter of interest. We investigate the steady-state behaviour of this system as a function of the residence time within the biological reactor and as a function of parameters associated with the operation of the SDU. A key parameter is the sludge disintegration factor. As this parameter is increased the concentration of total suspended solids within the biological reactor decreases at the expense increasing the chemical oxygen demand in the effluent stream. The existence of a maximum acceptable chemical oxygen demand in the effluent stream therefore imposes a maximum achievable reduction in the total suspended solids. This paper improves our theoretical understanding of the utility of sludge disintegration as a means to reduce excess sludge formation. As an aside to the main thrust of our paper we investigate the common assumption that the sludge disintegration processes occur on a much shorter timescale than the biological processes. We show that the disintegration processes must be exceptional slow before the inclusion of the biological processes becomes important.

Surface volatilization modeling of (semi-)volatile hydrophobic organic compounds: The role of reference compounds

Volatilization of hazardous hydrophobic organic compounds is often observed in many water, wastewater and soil treatment (bio)processes. Several models have been developed to quantify and predict gas-liquid pollutant transfer, being the proportionality coefficient model (PCM) one of the most commonly used, particularly in wastewater treatment. The PCM is based on the use of oxygen as a reference compound, which has a low resistance to the transfer in the gas phase. However, this resistance might be important for (semi-)volatile organic compounds - or (semi-)VOCs, which may render the use of the PCM model inaccurate. This study proposes an experimental methodology and a modeling approach for the use of the two-reference compound model (2RCM) that considers both the liquid-side and the gas-side resistances, by using water and oxygen as references. Results showed that the 2RCM predicts more accurately the overall mass transfer coefficients than the PCM for a VOC and two semi-VOCs tested in this study. In addition, the 2RCM was found to be a more robust method to estimate mass transfer coefficient of any compound and its use can be extrapolated to all substances. Finally, the relevance and limitations of both models was established.

Mathematical Analysis of Biodegradation Model under Nonlocal Operator in Caputo Sense

To lower the concentration of organic pollutants in the effluent stream, wastewater must be treated before being discharged into the environment. The question of whether wastewater treatment facilities can successfully reduce the concentration of micropollutants found in their influent streams is becoming increasingly pressing. The removal of micropollutants in treatment plants is investigated using a model that incorporates biodegradation and sorption as the key processes of micropollutant removal. This article provides the mathematical analysis of the wastewater model that describes the removal of micropollutant in treatment plants under a non-local operator in Caputo sense. The positivity of the solution is presented for the Caputo fractional model. The steady state’s solution of model and their stability is presented. The fixed point theorems of Leray–Schauder and Banach are used to deduce results regarding the existence of the solution of the model. Ulam–Hyers (UH) types of stabilities are presented via functional analysis. The fractional Euler method is used to find the numerical results of the proposed model. The numerical results are illustrated via graphs to show the effects of recycle ratio and the impact of fractional order on the evolution of the model.

Tetrabromobisphenol A (TBBPA) anaerobic biodegradation occurs during acidogenesis

This is the first study to bring evidence on the anaerobic biodegradation of TBBPA occurring during acidogenesis in domestic sewage at environmentally relevant concentrations by complex microbial communities. This was accomplished by continuously operating two anaerobic structured bed reactors (ASTBR) for over 100 days under acidogenic (Acidogenic Reactor, AR) and multistep methanogenic (Methanogenic Reactor, MR) conditions. In the AR, the temporal carbohydrates consumption and the acetic acid production were strongly correlated with TBBPA removal by the Pearson's test. The spatial concentration of TBBPA and carbohydrates along the MR and the kinetic degradation profiles corroborate the AR results. It is hypothesized that TBBPA biodegradation in the studied conditions occurs during acidogenesis via the cometabolism supported by non-specific enzymes and the metabolism (dehalorespiration) established by electrons donors such as H₂, which are both produced during the macrocomponents breakdown in the early stages of the anaerobic digestion. The TBBPA mass balance showed that approximately 86.8 ± 0.05% and 97 ± 0.01% of the removed TBBPA was biodegraded in the AR and MR, respectively. Furthermore, TBBPA biodegradation went further than reductive debromination as total phenols were detected in the reactors' effluent.

Model Based Simulation and Genetic Algorithm Based Optimisation of Spiral Wound Membrane RO Process for Improved Dimethylphenol Rejection from Wastewater

Reverse Osmosis (RO) has already proved its worth as an efficient treatment method in chemical and environmental engineering applications. Various successful RO attempts for the rejection of organic and highly toxic pollutants from wastewater can be found in the literature over the last decade. Dimethylphenol is classified as a high-toxic organic compound found ubiquitously in wastewater. It poses a real threat to humans and the environment even at low concentration. In this paper, a model based framework was developed for the simulation and optimisation of RO process for the removal of dimethylphenol from wastewater. We incorporated our earlier developed and validated process model into the Species Conserving Genetic Algorithm (SCGA) based optimisation framework to optimise the design and operational parameters of the process. To provide a deeper insight of the process to the readers, the influences of membrane design parameters on dimethylphenol rejection, water recovery rate and the level of specific energy consumption of the process for two different sets of operating conditions are presented first which were achieved via simulation. The membrane parameters taken into consideration include membrane length, width and feed channel height. Finally, a multi-objective function is presented to optimise the membrane design parameters, dimethylphenol rejection and required energy consumption. Simulation results affirmed insignificant and significant impacts of membrane length and width on dimethylphenol rejection and specific energy consumption, respectively. However, these performance indicators are negatively influenced due to increasing the feed channel height. On the other hand, optimisation results generated an optimum removal of dimethylphenol at reduced specific energy consumption for a wide sets of inlet conditions. More importantly, the dimethylphenol rejection increased by around 2.51% to 98.72% compared to ordinary RO module measurements with a saving of around 20.6% of specific energy consumption.

Bioelectrochemical systems for environmental remediation of estrogens: A review and way forward

Globally estrogenic pollutants are a cause of concern in wastewaters and water bodies because of their high endocrine disrupting activity leading to extremely negative impacts on humans and other organisms even at very low environmental concentrations. Bioremediation of estrogens has been studied extensively and one technology that has emerged with its promising capabilities is Bioelectrochemical Systems (BESs). Several studies in the past have investigated BESs applications for treatment of wastewaters containing toxic recalcitrant pollutants with a primary focus on improvement of performance of these systems for their deployment in real field applications. But the information is scattered and further the improvements are difficult to achieve for standalone BESs. This review critically examines the various existing treatment technologies for the effective estrogen degradation. The major focus of this paper is on the technological advancements for scaling up of these BESs for the real field applications along with their integration with the existing and conventional wastewater treatment systems. A detailed discussion on few selected microbial species having the unusual properties of heterotrophic nitrification and extraordinary stress response ability to toxic compounds and their degradation has been highlighted. Based on the in-depth study and analysis of BESs, microbes and possible benefits of various treatment methods for estrogen removal, we have proposed a sustainable Hybrid BES-centered treatment system for this purpose as a choice for wastewater treatment. We have also identified three pipeline tasks that reflect the vital parts of the life cycle of drugs and integrated treatment unit, as a way forward to foster bioeconomy along with an approach for sustainable wastewater treatment.

A review of the adsorption-biological hybrid processes for the abatement of emerging pollutants: Removal efficiencies, physicochemical analysis, and economic evaluation

The limited efficiency of conventional wastewater treatment plants (WWTPs) in emerging pollutants (EPs) removal encourages the development of alternative technologies for the adequate treatment of wastewater, due to its adverse effects on human health and ecosystems. The biological, physical or chemical hybrid technologies to treat EPs results interesting since they can enhance the performance of WWTPs. Among them, hybrid adsorption/biological technology could offer different possibilities that are explored in this work (PAC-MBR, PACT/GAC-CAS, BAC configurations). In this way, different variations in the adsorption process have been considered: the form of the adsorbent, the feed to the system, and the type of biological process, either conventional activated sludge (CAS), membrane bioreactor (MBR) or biofilm systems. For each combination, the removal efficiency of micropollutants, classified according to their use into pharmaceuticals, personal care products (PCPs) and other micropollutants (mainly benzotriazoles) was analysed. From reported data, it was observed a beneficial synergistic effect of dipole moment and octanol-water partition coefficient on the removal efficiency of micropollutants by adsorption/biological hybrid technology. Finally, a preliminary economic evaluation of the powdered activated carbon in a conventional activated sludge reactor (PACT), powdered activated carbon-membrane bioreactor (PAC-MBR) and biological activated carbon (BAC) hybrid systems was carried out by analysing the capital expenditure (CAPEX) of plants for capacities up to 75,000 m³d^-1. Likewise, estimations of adsorbent concentration for a hypothetical plant with a capacity of 10,000 m³d^-1 is presented. Among these hybrid configurations, PAC-MBR achieved the highest micropollutant elimination percentages; however, it presents the highest CAPEX and activated carbon requirements.

Development and implementation of an analytical procedure for the quantification of natural and synthetic steroid hormones in whole surface waters

Natural and synthetic steroid hormones are chronically released into aquatic spheres. Whereas knowledge on their combined mode of action and the cocktail effect are needed, only few multi-class methods address the challenge of their trace quantification in surface waters. The current study describes a sensitive multi-residue analytical strategy aiming to quantify 23 steroid hormones belonging to androgens, estrogens, glucocorticoids and progestogens in whole surface waters. The procedure relies on a two-step solid-phase extraction followed by an ultra-performance liquid chromatography separation coupled to tandem mass spectrometry detection (UPLC-MS/MS). Isotope dilution was implemented when possible in order to ensure the reliability of the measurement. The procedure was optimized toward the reliable quantification of the 23 target compounds at the predicted no-effect concentrations when existing or below the ng L^-1 level. Satisfactory absolute global recoveries ≥ 77% were obtained for almost all compounds (21 out of 23) in intermediate precision conditions. Measurement errors were comprised between -27% and +17% for the great majority of compounds (21 out of 23) with standard deviations < 20% in intermediate precision conditions. Despite signal suppression was observed in water samples, satisfactory limits of quantification were achieved, ranging from 0.035 ng L^-1 for 17alpha-ethinylestradiol to 1 ng L^-1 for 6beta-hydroxycortisol and 6beta-hydroxydexamethasone. Abiotic stability was demonstrated for the great majority of target compounds (22 out of 23) in reference water samples stored at 4 ± 3 °C during 48 h, driving our sampling strategy. To demonstrate its fitness for purpose, the procedure was implemented in a preliminary monitoring survey of Belgian surface waters. As a result, 6 out of 23 target compounds were detected or quantified, showing a contamination by some estrogens and glucocorticoids at levels ranging from 0.1 to 0.9 ng L^-1.

Removal of Heavy Metals during Primary Treatment of Municipal Wastewater and Possibilities of Enhanced Removal: A Review

Resource reuse has become an important aspect of wastewater management. At present, use of sludge in agriculture is one of the major reuse routes. Conventional municipal wastewater treatment does not involve any designated process for removal of heavy metals, and these distribute mainly between effluent and sludge. Enhanced removal of heavy metals during primary treatment may decrease the heavy metal concentrations in both effluent and sludge from secondary treatment and promote long-term reuse of secondary sludge. This review considers heavy metal occurrence and removal during primary settling, together with possible treatment technologies for heavy metal removal in primary settlers and their theoretical performance. The variation in total heavy metal concentrations and dissolved fraction in raw municipal wastewater points to a need for site-specific assessments of appropriate technologies for improved heavy metal removal. Studies examining the heavy metal speciation beyond dissolved/particulate are few. Missing or disparate information on process parameters such as hydraulic retention time, pH and composition of return flows makes it hard to generalize the findings from studies concerning heavy metal removal in primary settlers. Coagulation/flocculation and use of low-cost sorbents were identified as the most promising methods for enhancing heavy metal removal during primary settling. Based on the available data on heavy metal speciation and removal during primary settling, sorption technologies may be most effective for enhancing the removal of Cu and Ni, while coagulation may be efficient for Cd, Cr, Cu, Pb, Zn and Hg removal (but not as efficient for Ni removal).

WITHDRAWN: Progress in the removal of organic microcontaminants from wastewater using high retention membrane bioreactors: A critical review

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The organic loading rate affects organic micropollutants' cometabolic biotransformation kinetics under heterotrophic conditions in activated sludge

Several studies have shown that organic micropollutants (OMPs) are biotransformed cometabolically in activated sludge systems. However, the individual role of heterotrophs in the microbial consortium is still not clear, i.e., there is still a gap regarding the influence of the heterotrophic activity on the cometabolic biotransformation kinetics and yield of the OMPs. Aiming to answer these questions, experiments with increasing primary substrate concentrations were performed under aerobic heterotrophic conditions in a continuous stirred tank reactor operated at several organic loading rates (OLR) with fixed hydraulic retention time. Moreover, the individual kinetic parameters were determined in batch assays with different initial substrate concentrations using the sludges from the continuous reactor. A set of 15 OMPs displaying a variety of physicochemical properties were spiked to the feeding in the ng L^-1 - µg L^-1 range. Results reveal that the biodegradation of the primary carbon source and the biotransformation of the OMPs occur simultaneously, in clear evidence of cometabolic behavior. Moreover, we conclude that the OMPs biotransformation kinetic constant (k_biol) shows a linear dependence with the OLR of the primary substrate for most of the compounds studied, suggesting that the heterotrophic activity seriously affects the OMPs biotransformation kinetics. However, under typical activated sludge systems operating conditions (hydraulic retention times above 8 h), their biotransformation yield would not be significantly affected.

Occurrence and removal of chemicals of emerging concern in wastewater treatment plants and their impact on receiving water systems

Wastewater treatment plants (WWTPs) are considered the main sources of chemicals of emerging concern (CECs) in aquatic environments, and can negatively impact aquatic ecosystems. In this study, WWTP influent, effluent, and sludge, and upstream and downstream waters from the WWTP recipient were investigated at 15 locations for a total of 164 CECs, including pharmaceuticals, personal care products, industrial chemicals, per- and polyfluoroalkyl substances (PFASs), and pesticides. In addition, zebrafish (Danio rerio) embryo toxicity tests (ZFET) were applied to WWTP influent and effluent, and upstream and downstream waters from WWTP recipients. A total of 119 CECs were detected in at least one sample, mean concentrations ranging from 0.11 ng/L (propylparaben) to 64,000 ng/L (caffeine), in wastewater samples and from 0.44 ng/L (ciprofloxacin) to 19,000 ng/L (metformin) in surface water samples. Large variations of CEC concentrations were found between the selected WWTPs, which can be explained by differences in CEC composition in influent water and WWTP treatment process. The sludge-water partitioning coefficient (K_d) of CECs showed a significant linear correlation to octanol/water partition coefficient (K_OW) (p < 0.001), and thus could be used for predicting their fate in the aqueous and solid phase. The ΣCEC concentrations in WWTPs declined by on average 60%, based on comparisons of WWTP influent and effluent concentrations. The high concentrations of CECs in WWTP effluent resulted in, on average, 50% higher concentrations of CECs in water downstream of WWTPs compared with upstream. Some WWTP samples showed toxicity in ZFET compared with the respective control group, but no individual CECs or groups of CECs could explain this toxicity. These results could provide a theoretical basis for optimization of existing treatment systems of different designs, and could significantly contribute to protecting recipient waters.

Ozonation in advanced treatment of secondary municipal wastewater effluents for the removal of micropollutants

The objective of this study was the experimental evaluation of ozonation as an additional treatment step for the removal emerging contaminants from secondary effluents of two wastewater treatment plants (WWTPs), one receiving a primarily domestic wastewater (WWTP-A), and the other one domestic sewage together with pretreated tannery wastewater streams (WWTP-B). The experimental runs were conducted at two different pH values (i.e., original pH and adjusted pH of 10) and at six different ozone doses ranging between 0.2 and 1.5 mg O₃/mg DOC. A total of 20 compounds, including 12 micropollutants (MPs) and 8 metabolites, were selected as the target analytes for the evaluation of ozonation performance. When the tested MPs and metabolites were considered individually, the maximum elimination level for each compound was reached at different doses; therefore, optimum ozone doses were determined based on the reduction of the total MP content. Ozonation at the original pH with an ozone dose in the range of 0.4-0.6 and 0.8-1.0 mg O₃/mg DOC was selected as the optimum operating condition for WWTP-A and WWTP-B, respectively, both resulting in an average overall removal efficiency of 55%. Ozone treatment yielded only poor elimination for o-desmethyl naproxen (15%), which was found to be by far the main contributor accounting alone for approximately 30% of the total MP concentration in the secondary effluents. The systematic approach used in this study could well be adopted as a guide to other domestic and municipal WWTPs, which are thought to have a highly variable composition in terms of the MPs and metabolites.

Modeling anaerobic digestion metabolic pathways for antibiotic-contaminated wastewater treatment

Anaerobic digestion has been used to treat antibiotic-contaminated wastewaters. However, it is not always effective, since biodegradation is the main removal mechanism and depends on the compound chemical characteristics and on how microbial metabolic pathways are affected by the reactor operational conditions and hydrodynamic characteristics. The aim of this study was to develop a mathematical model to describe 16 metabolic pathways of an anaerobic process treating sulfamethazine-contaminated wastewater. Contois kinetics and a useful reaction volume term were used to represent the biomass concentration impact on bed porosity in a N continuously stirred tank modeling approach. Two sulfamethazine removal hypotheses were evaluated: an apparent enzymatic reaction and a cometabolic degradation. Additionally, long-term modeling was developed to describe how the operational conditions affected the performance of the process. The best degradation correlations were associated with the consumption of carbohydrates, proteins and it was inversely related to acetic acid production during acidogenesis.

Application of a QWASI model to produce validated insights into the fate and transport of six emerging contaminants in a wastewater lagoon system

The occurrence and fate of emerging contaminants (ECs) in surface water bodies is of increasing interest to water quality managers and environmental regulators throughout the world. Wastewater treatment plants are a major source of ECs in many aquatic environments. A modified Quantitative Water Air Sediment Interaction (QWASI) fugacity model was developed for a municipal wastewater lagoon system to study the behaviour of six representative ECs. As the wastewater lagoons were exposed to extensive periods of sunlight, the original model was modified by the addition of photolytic degradation as a removal mechanism. Laboratory studies were conducted over different seasons of a year to obtain the rate constants for the key processes of sunlight photodegradation, water and sediment transformation, as well as sediment sorption coefficients for the target ECs in the system to serve as model inputs. The model predicted the pathways for the different ECs and that at least 65% of the concentration of the ECs remained in the outflow of the first lagoon of the lagoon system after treatment. The greatest removal was predicted for sulfamethoxazole (35%) and the least for carbamazepine (5%). Multi-segment theory was applied to the single lagoon model and the predictions for the sequential six lagoon system were validated through field sampling. Sensitivity analysis revealed that the mass transfer coefficient between the water and sediment phases was the most influential parameter, with the four key process rate constants having various impacts depending on the EC. These results suggest that the modified QWASI model could be used to more accurately represent the fate and transport of ECs in this unique wastewater lagoon/stabilisation pond treatment system. Furthermore, it can be adapted to model a wide range of ECs in other wastewater treatment lagoon systems and thus assist with process optimisation and risk assessment of the treated water.

Removal of pharmaceutical compounds commonly-found in wastewater through a hybrid biological and adsorption process

Nowadays, alternative options to conventional wastewater treatment should be studied due to rising concerns emerged by the presence of pharmaceuticals compounds (PhCs) in the aquatic environment. In this work, a combined system including biological treatment by activated sludge plus adsorption with activated carbon is proposed to remove three selected drugs (acetaminophen (ACT), caffeine (CAF) and ibuprofen (IBU)) in a concentration of 2 mg L^-1 of each one. For it three sequencing batch reactors (SBR) were operated. SBR-B treated a synthetic wastewater (SWW) without target drugs and SBR-PhC and SBR-PhC + AC operated with SWW doped with the three drugs, adding into SBR-PhC + AC 1.5 g L^-1 of a mesoporous granular activated carbon. Results showed that the hybrid system SBR-activated carbon produced an effluent free of PhCs, which in addition had higher quality than that achieved in a conventional activated sludge treatment in terms of lower COD, turbidity and SMP concentrations. On the other hand, five possible routes of removal for target drugs during the biological treatment were studied. Hydrolysis, oxidation and volatilization pathways were negligible after 6 h of reaction time. Adsorption route only was significant for ACT, which was adsorbed completely after 5 h of reaction, while only 1.9% of CAF and 5.6% of IBU were adsorbed. IBU was the least biodegradable compound.

Assessment of the fate of organic micropollutants in novel wastewater treatment plant configurations through an empirical mechanistic model

Novel wastewater treatment plants (WWTPs) are expected to be less energetically demanding than conventional ones. However, scarce information is available about the fate of organic micropollutants (OMPs) in these novel configurations. Therefore, the objective of this work is to assess the fate of OMPs in three novel WWTP configurations by using a plant-wide simulation that integrates multiple units. The difference among the three configurations is the organic carbon preconcentration technology: chemically enhanced primary treatment (CEPT), high-rate activated sludge (HRAS) combined or not with a rotating belt filter (RBF); followed by a partial-nitritation (PN-AMX) unit. The simulation results show that the three selected novel configurations lead mainly to comparable OMPs removal efficiencies from wastewater, which were similar or lower, depending on the OMP, than those obtained in conventional WWTPs. However, the presence of hydrophobic OMPs in the digested sludge noticeably differs among the three configurations. Whereas the configuration based on sole HRAS to recover organic carbon leads to a lower presence of OMPs in digested sludge than the conventional WWTP, in the other two novel configurations this presence is noticeable higher. In conclusion, novel WWTP configurations do not improve the OMPs elimination from wastewater achieved in conventional ones, but the HRAS-based WWTP configuration leads to the lowest presence in digested sludge so it becomes the most efficient alternative.

Removal of hazardous substances in municipal wastewater treatment plants

Chemical pollution poses a threat to the aquatic environment and to human health. Wastewater treatment plants are the last defensive line between the aquatic environment and emissions of pollutants. This study focuses on identification of most relevant hazardous substances in Estonian municipal wastewater and their fate in the treatment process. During this study, seasonal wastewater and sewage sludge samples were collected from nine municipal wastewater treatment plants and analyzed for 282 hazardous substances, including EU (n = 45) and Estonian (n = 31) priority substances. Results of this study show that several substances that are subject to international restrictions (e.g. Stockholm Convention) are still present in untreated sewage. Wastewater treatment systems that had a greater level of complexity (TEC >5) were more successful in removing hazardous substances. Statistical analyses showed that removal efficiency of organic hazardous substances had significant (p-value <0.05) linear correlation with removal efficiencies of chemical oxygen demand (COD) and total suspended solids (TSS), but a monotonic relationship with operators' competency. This study showed that operators' competency had a strong influence on the stability of the wastewater treatment efficiency and removal of organic hazardous substances.

Fugacity modelling of the fate of micropollutants in aqueous systems - Uncertainty and sensitivity issues

The application of multimedia fugacity models is useful to facilitate understanding of the behaviour of emerging contaminants during wastewater treatment, as well as after their release to the environment. In this paper, twenty-two fugacity modelling applications (reported over 1995-2019) describing the distribution of organic micropollutants in wastewater treatment plants and surface water bodies were analysed in terms of model application and modelling strategy. Disparities and similarities in strategies including selection of micropollutants, data sources for internal and external model inputs, sensitivity and uncertainty analysis, as well as model validation were discussed. This review confirmed that fugacity modelling is very applicable for providing qualitative predictions of the fate and removal of organic micropollutants in the various aqueous systems. However, it was also noted that there are issues related to the uncertainties and sensitivities of fugacity models such as the sources of model inputs and selection of default settings. The issues associated with the uncertainties in the investigated fugacity models are pointed out. Recommendations are given regarding the selection of the sources of model inputs, sensitivity analysis strategies and model validation methods. This review presents the challenges and opportunities for improving multimedia fugacity models, and so paves the way for future research in this field.

Understanding the mechanisms of trace organic contaminant removal by high retention membrane bioreactors: a critical review

High retention membrane bioreactors (HR-MBR) combine a high retention membrane separation process such as membrane distillation, forward osmosis, or nanofiltration with a conventional activated sludge (CAS) process. Depending on the physicochemical properties of the trace organic contaminants (TrOCs) as well as the selected high retention membrane process, HR-MBR can achieve effective removal (80-99%) of a broad spectrum of TrOCs. An in-depth assessment of the available literature on HR-MBR performance suggests that compared to CAS and conventional MBRs (using micro- or ultra-filtration membrane), aqueous phase removal of TrOCs in HR-MBR is significantly better. Conceptually, longer retention time may significantly improve TrOC biodegradation, but there are insufficient data in the literature to evaluate the extent of TrOC biodegradation improvement by HR-MBR. The accumulation of hardly biodegradable TrOCs within the bioreactor of an HR-MBR system may complicate further treatment and beneficial reuse of sludge. In addition to TrOCs, accumulation of salts gradually increases the salinity in bioreactor and can adversely affect microbial activities. Strategies to mitigate these limitations are discussed. A qualitative framework is proposed to predict the contribution of the different key mechanisms of TrOC removal (i.e., membrane retention, biodegradation, and sorption) in HR-MBR.

Modeling of micropollutant removal in full-scale membrane bioreactors: calibration and operations to limit the emissions

Micropollutants are a major concern for aquatic organisms and human health. Membrane bioreactors (MBRs) are an efficient wastewater treatment and water reuse solution, but their micropollutant removal performances are still not fully determined. Modeling micropollutant behavior in MBRs could help better understand and optimize the removal process. Here we provide detailed explanation on a model of micropollutant removal in MBRs that predicts biodegradation and sorption rates. Parameters were calibrated following an iterative two-step procedure developed in this work and using data from two full-scale plants. The calibrated set of parameters was then used (i) to determine the influence of MBR operating conditions such as the duration of aerobic time and the sludge concentration in bioreactor, on micropollutant removal, and (ii) to better understand micropollutant behavior and removal performances in MBRs in response to sudden changes in operating conditions (rain event, F:M ratio). These predictive simulations showed that increasing sludge concentration in bioreactor can decrease effluent concentrations of most of the micropollutants studied by up to 15%, and increasing the duration of aerobic time decreases effluent concentrations of few organic micropollutants tested by up to 15%. Rain events and F:M ratio can increase effluent concentrations of six out of nine micropollutants tested by more than 15%.

Modelling PAHs removal in activated sludge process: effect of disintegration

The removal of polycyclic aromatic hydrocarbons (PAHs) in activated sludge was evaluated using two laboratory-scale bioreactors, coupled or not with a disintegration system (sonication). Mass balances performed on each system underlined that PAHs removal was significantly improved after sludge disintegration, especially for the higher molecular weight PAHs studied, which tended to adsorb to suspended matter. A model was developed in order to study the effect of sludge disintegration on the content of dissolved and colloidal matter (DCM), and to predict the potential impacts on PAHs availability and degradation. Results showed that this new model was efficient for capturing apparent degradation improvement trends and for discriminating between the involved mechanisms. This study showed that DCM content increased after sludge disintegration, and proved to be the main driver for improving PAHs apparent degradation.

Removal and dissipation pathway of typical fluoroquinolones in sewage sludge during aerobic composting

To observe the effect of aeration strategies on the dissipation of fluoroquinolones (FQs) during aerobic composting and explore their dissipation pathways, 60-L composting and 0.5-L incubation experiments were carried out in this study. Three aeration strategies (windrow, static aeration, feedback aeration) were applied to remove two typical FQs (Norfloxacin (NOR) and Ofloxacin (OFL)) during the 60-L composting of sewage sludge with 5 mg kg^-1 of FQs added. Then, three 0.5 L-sample groups were taken during the three phases of the 60-L composting matrixes without FQs under static aeration, and were inoculated separately at 35 °C, 55 °C and 40 °C after being added with 5 mg kg^-1 of FQs. In each group, incubation was carried out for three treatments (sterilization + no aeration, sterilization + aeration, and no sterilization + aeration). The FQs in the sewage sludge were mainly removed in the mesophilic and thermophilic phases in all the aeration strategies. The removal efficiencies were high for the whole process: 89.6-95.4% for NOR and 87.2-95.4% for OFL. The order of removal efficiency of FQs was static aeration > feedback aeration > windrow. The combination of composting phases facilitated to the rapid dissipation of FQs, which reduced the half-life to about 1/6 to 1/5 of the values in each phase. In the mesophilic and thermophilic compost, biodegradation was the main pathway for the dissipation of FQs followed by irreversible adsorption. Irreversible adsorption and biodegradation provided similar removal efficiencies for the curing compost. The volatilization of FQs was non-negligible in all phases.

Insights into the Fate and Removal of Antibiotics in Engineered Biological Treatment Systems: A Critical Review

Antibiotics, the most frequently prescribed drugs of modern medicine, are extensively used for both human and veterinary applications. Antibiotics from different wastewater sources (e.g., municipal, hospitals, animal production, and pharmaceutical industries) ultimately are discharged into wastewater treatment plants. Sorption and biodegradation are the two major removal pathways of antibiotics during biological wastewater treatment processes. This review provides the fundamental insights into sorption mechanisms and biodegradation pathways of different classes of antibiotics with diverse physical-chemical attributes. Important factors affecting sorption and biodegradation behavior of antibiotics are also highlighted. Furthermore, this review also sheds light on the critical role of extracellular polymeric substances on antibiotics adsorption and their removal in engineered biological wastewater treatment systems. Despite major advancements, engineered biological wastewater treatment systems are only moderately effective (48-77%) in the removal of antibiotics. In this review, we systematically summarize the behavior and removal of different antibiotics in various biological treatment systems with discussion on their removal efficiency, removal mechanisms, critical bioreactor operating conditions affecting antibiotics removal, and recent innovative advancements. Besides, relevant background information including antibiotics classification, physical-chemical properties, and their occurrence in the environment from different sources is also briefly covered. This review aims to advance our understanding of the fate of various classes of antibiotics in engineered biological wastewater treatment systems and outlines future research directions.

Emerging pollutants in the urban water cycle in Latin America: A review of the current literature

Emerging pollutants (EP) are increasingly studied and characterized worldwide to improve the understanding of their environmental and toxicological impacts and their occurrence and behaviors in different environmental systems. Latin America has been subject to both environmental and toxicological impacts due to EP. To better understand these impacts, studies concerning pollutants have increased for the last ten years. The current study presents a critical review on the occurrence of different emerging pollutants in various components of the urban water cycle (UWC) in Latin America. The review is based on studies performed in 11 different countries between 1999 and 2018. The countries where the higher number of investigations were conducted are Brazil (53%) and Mexico (15%). The EP most often studied within the literature are pharmaceuticals, followed by personal care products. The most common EP reported were 17β-estradiol, bisphenol A and estrone; The UWC component with the greatest number of measurements in the reported studies were effluents from wastewater treatment plants.

Roles of ammonia-oxidizing bacteria in improving metabolism and cometabolism of trace organic chemicals in biological wastewater treatment processes: A review

While there has been a significant recent improvement in the removal of pollutants in natural and engineered systems, trace organic chemicals (TrOCs) are posing a major threat to aquatic environments and human health. There is a critical need for developing potential strategies that aim at enhancing metabolism and/or cometabolism of these compounds. Recently, knowledge regarding biodegradation of TrOCs by ammonia-oxidizing bacteria (AOB) has been widely developed. This review aims to delineate an up-to-date version of the ecophysiology of AOB and outline current knowledge related to biodegradation efficiencies of the frequently reported TrOCs by AOB. The paper also provides an insight into biodegradation pathways by AOB and transformation products of these compounds and makes recommendations for future research of AOB. In brief, nitrifying WWTFs (wastewater treatment facilities) were superior in degrading most TrOCs than non-nitrifying WWTFs due to cometabolic biodegradation by the AOB. To fully understand and/or enhance the cometabolic biodegradation of TrOCs by AOB, recent molecular research has focused on numerous crucial factors including availability of the compounds to AOB, presence of growth substrate (NH₄-N), redox potentials, microorganism diversity (AOB and heterotrophs), physicochemical properties and operational parameters of the WWTFs, molecular structure of target TrOCs and membrane-based technologies, may all significantly impact the cometabolic biodegradation of TrOCs. Still, further exploration is required to elucidate the mechanisms involved in biodegradation of TrOCs by AOB and the toxicity levels of formed products.

Biotransformation of organic micropollutants by anaerobic sludge enzymes

Biotransformation of organic micropollutants (OMPs) in wastewater treatment plants ultimately depends on the enzymatic activities developed in each biological process. However, few research efforts have been made to clarify and identify the role of enzymes on the removal of OMPs, which is an essential knowledge to determine the biotransformation potential of treatment technologies. Therefore, the purpose of the present study was to investigate the enzymatic transformation of 35 OMPs under anaerobic conditions, which have been even less studied than aerobic systems. Initially, 13 OMPs were identified to be significantly biotransformed (>20%) by anaerobic sludge obtained from a full-scale anaerobic digester, predestining them as potential targets of anaerobic enzymes. Native enzymes were extracted from this anaerobic sludge to perform transformation assays with the OMPs. In addition, the effect of detergents to recover membrane enzymes, as well as the effects of cofactors and inhibitors to promote and suppress specific enzymatic activities were evaluated. In total, it was possible to recover enzymatic activities towards 10 out of these 13 target OMPs (acetyl-sulfamethoxazole and its transformation product sulfamethoxazole, acetaminophen, atenolol, clarithromycin, citalopram, climbazole, erythromycin, and terbutryn, venlafaxine) as well as towards 8 non-target OMPs (diclofenac, iopamidol, acyclovir, acesulfame, and 4 different hydroxylated metabolites of carbamazepine). Some enzymatic activities likely involved in the anaerobic biotransformation of these OMPs were identified. Thereby, this study is a starting point to unravel the still enigmatic biotransformation of OMPs in wastewater treatment systems.

Organic micropollutants in a large wastewater treatment plant: What are the benefits of an advanced treatment by activated carbon adsorption in comparison to conventional treatment?

Several advanced treatments, such as ozonation or activated carbon adsorption, are currently considered for the removal of organic micropollutants (OMPs) in wastewater treatment plants (WWTP). However, little is known on the overall performances of a WWTP upgraded with those processes and the benefits provided regarding the elimination of multiple families of OMPs. In this study, 5 sampling campaigns were performed to determine the removal of 48 OMPs in a WWTP followed by an activated carbon pilot. The primary treatment had no effect on OMPs (removals < 20%), whereas the biological treatment removed OMPs that can be easily sorbed onto sludges or biodegraded (>60%). The additional elimination provided by the advanced treatment was not significant (<10%) for OMPs already well removed in the WWTP) but was substantial (>30%) for recalcitrant OMPs. Removals higher than 60% were obtained for all OMPs (except azithromycin and sulfamethoxazole) over the WWTP and the activated carbon pilot. The adsorption conditions (10 g/m³ fresh activated carbon addition) were not sufficient to achieve the 80% removal targeted in Switzerland for compounds suggested as indicator substances for wastewater treatment. A higher dose of activated carbon or the combination with another advanced treatment should be used to achieve a satisfactory removal of those compounds.

Biotransformation and sorption of trace organic compounds in biological nutrient removal treatment systems

This study determined biotransformation rates (k_bio) and sorption-distribution coefficients (K_d) for a select group of trace organic compounds (TOrCs) in anaerobic, anoxic, and aerobic activated sludge collected from two different biological nutrient removal (BNR) treatment systems located in Nevada (NV) and Ohio (OH) in the United States (US). The NV and OH facilities operated at solids retention times (SRTs) of 8 and 23 days, respectively. Using microwave-assisted extraction, the biotransformation rates of the chosen TOrCs were measured in the total mixed liquor. Sulfamethoxazole, trimethoprim, and atenolol biotransformed in all three redox regimes irrespective of the activated sludge source. The biotransformation of N, N-diethyl-3-methylbenzamide (DEET), triclosan, and benzotriazole was observed in aerobic activated sludge from both treatment plants; however, anoxic biotransformation of these three compounds was seen only in anoxic activated sludge from NV. Carbamazepine was recalcitrant in all three redox regimes and both sources of activated sludge. Atenolol and DEET had greater biotransformation rates in activated sludge with a higher SRT (23 days), while trimethoprim had a higher biotransformation rate in activated sludge with a lower SRT (8 days). The remaining compounds did not show any dependence on SRT. Lyophilized, heat inactivated sludge solids were used to determine the sorption-distribution coefficients. Triclosan was the most sorptive compound followed by carbamazepine, sulfamethoxazole, DEET, and benzotriazole. The sorption-distribution coefficients were similar across redox conditions and sludge sources. The biotransformation rates and sorption-distribution coefficients determined in this study can be used to improve fate prediction of the target TOrCs in BNR treatment systems.

Kinetics of Biological Removal of the Selected Micropollutants and Their Effect on Activated Sludge Biomass

17α-Ethinylestradiol (EE2), diclofenac (DCF), and 4-nonylphenol (4NP) belong to the most common micropollutants (MPs) occurring in municipal wastewater treatment plants (WWTPs). The WWTPs are the primary barrier against the spread of micropollutants in the environment. The aim of this work was to study the kinetics of biological removal of the three aforementioned micropollutants from wastewater and to check whether the acclimation of biomass influenced on the kinetic parameters. In addition, the effect of MPs on the biochemical activity of microorganisms was tested. DCF inhibited the respiration activity of biomass to the highest extent, followed by 4NP and EE2, respectively. DCF occurred to be less susceptible to microbial decomposition than the other two MPs and was removed from wastewater at the lowest degree of 58%. The degrees of removal of EE2 and 4NP were higher than that of DCF and equal to 93 and 71%, respectively. The kinetic parameters determined in this work can be used in modelling and simulation of the removal of micropollutants from wastewater. They improve the predictive ability of the biokinetic models. The acclimation of the biomass to the relevant micropollutant does not influence on the kinetic parameters of biomass growth; however, it causes the increase of the yield coefficient for heterotrophic biomass.

Abiotic, biotic and photolytic degradation affinity of 14 antibiotics and one metabolite - batch experiments and a model framework

In this study, degradation affinities of 14 antibiotics and one metabolite were determined in batch experiments. A modelling framework was applied to decrypt potential ranges of abiotic, biotic and photolytic degradation coefficients. In detail, we performed batch experiments with three different sewages in the dark at 7 °C and 22 °C. Additionally, we conducted further batch experiments with artificial irradiation and different dilutions of the sewage at 30 °C - de novo three different sewages were used. The batch experiments were initially spiked with a stock solution with 14 antibiotics and one metabolite to increase background concentrations by 1 μg L^-1 for each compound. The final antibiotic concentrations were sub-inhibitory with regard to sewage bacteria. The here presented modelling framework based on the Activated Sludge Model No. 3 in combination with adsorption and desorption processes. The model was calibrated with monitored standard sewage compounds before antibiotic degradation rates were quantified. The model decrypted ranges of abiotic, biotic and photolytic degradation coefficients. In detail, six antibiotics were not abiotic degradable at 7 °C, five antibiotics not at 22 °C and only 2 antibiotics at 30 °C. Finally, nine antibiotics were not significantly biodegradable at 7 °C and 22 °C. The model determined the link between adsorption characteristics and biodegradation rates. In detail, the rate was significantly affected by the bio-solid partition coefficient and the duration until adsorption was balanced. All antibiotics and the metabolite were photolytic degradable. In general, photolytic degradation was the most efficient elimination pathway of presented antibiotics except for the given metabolite and penicillin antibiotics.

Why are organic micropollutants not fully biotransformed? A mechanistic modelling approach to anaerobic systems

Biotransformation of most organic micropollutants (OMPs) during wastewater treatment is not complete and an unexplained steady decrease of the biotransformation rate with time is reported for many OMPs in different biological processes. To minimize and accurately predict the emission of OMPs into the environment, the mechanisms and limitations behind their biotransformations should be clarified. Aiming to achieve this objective, the present study follows a mechanistic modelling approach, based on the formulation of four models according to different biotransformation hypotheses: Michaelis-Menten kinetics, chemical equilibrium between the parent compound and the transformation product (TP), enzymatic inhibition by the TP, and a limited compound bioavailability due to its sequestration in the solid phase. These models were calibrated and validated with kinetic experiments performed in two different anaerobic systems: continuous reactors enriched with methanogenic biomass and batch assays with anaerobic sludge. Model selection was conducted according to model suitability criteria (goodness of fitting the experimental data, confidence of the estimated parameters, and model parsimony) but also considering mechanistic evidences. The findings suggest that reversibility of the biological reactions and/or sequestration of compounds are likely the causes preventing the complete biotransformation of OMPs, and biotransformation is probably limited by thermodynamics rather than by kinetics. Taking into account its simplicity and broader applicability spectrum, the reversible biotransformation is the proposed model to explain the incomplete biotransformation of OMPs.

Estimating environmental fate of tricyclic antidepressants in wastewater treatment plant

TCAs are known to be toxicants and endocrine disrupting agents. Generally, after being used, TCAs are passed through wastewater treatment plants (WWTPs) to be treated. However, still trace amounts (ng/L to μg/L) of TCAs have been founded even in the treated water. Therefore, the aim of this study is to elucidate the environmental behaviors of TCAs in the sewage water from WWTPs (Jeonju, Korea). For the experiments, seven TCAs (amitriptyline, imipramine, clomipramine, desipramine, protriptyline, nortriptyline, and doxepin) were selected. Hydrolysibility, biodegradability, and adsorbability of the selected seven TCAs were evaluated. Based on the results, it was concluded that TCAs are not readily hydrolyzed in water and also not biodegraded by aerobic sludge. The 60% to 85% of TCAs were adsorbed immediately onto the activated sludge within 1 s via electrostatic and hydrophobic interactions. It was clearly observed that adsorption affinities were dependent on the types of activated sludge (i.e. anaerobic and aerobic sludge). The affinities of aerobic and anaerobic sludge towards the TCAs at trace concentrations e.g., 1 to 10 μg/L, were estimated to be in the range from 0.021 ± 0.000 to 0.087 ± 0.000 L/μg and from 0.001 ± 0.000 to 0.108 ± 0.001 L/μg, respectively.

The influence of solid-liquid coefficient in the fate of pharmaceuticals and personal care products in aerobic wastewater treatment

Wastewater treatment plants (WWTPs) are considered to be a source of environmental contamination by micropollutants, especially from pharmaceuticals and personal care products (PCPs). The pathway of those compounds during sewage treatment has been investigated, but data from real-scale WWTPs is still missing (for example, the values of the solid-liquid coefficient (K_d) during treatment). This paper uses the K_d values for some pharmaceuticals and PCPs (fenofibrate, gemfibrozil, propranolol, metoprolol, salicylic acid, acetylsalicylic acid, ibuprofen, diclofenac, naproxen, fenoprofen, caffeine, triclosan, methylparaben, ethylparaben, propylparaben, butylparaben, and benzylparaben) to describe the micropollutants' behavior in the treatment process. In order to attain this data, an aerobic wastewater treatment plant located in Brazil was studied. Six samplings were carried out and a mass balance was performed, associating the concentrations of the micropollutants in the liquid phase with the solid phase (sludge and suspended solids). Of all the compounds analyzed, caffeine was the most biodegradable pollutant, as almost 98% of its mass was biodegraded. In contrast, triclosan had the highest load in sludge (median of 163.0 mg day^-1) and adsorbed in SS (median of 0.593 mg day^-1) at the output. Summing up, each micropollutant had a specific way to be removed during wastewater treatment.

A Simple Compartment Model for the Dynamical Behavior of Medically Derived 131I in a Municipal Wastewater Treatment Plant

A compartmental model for the reactive flow of the radioisotope ¹³¹I, frequently introduced into the sewer system at varying concentrations through radiotherapy of thyroid diseases, has been developed for an existing municipal wastewater treatment plant (WWTP). It includes the transition of activity from dissolved to suspended particulate and colloid matter, and the separation of phases in sedimentation basins. It has been parametrized by experimental data obtained at key locations in the plant, and validated by measured time series of activity concentration of inflow and outflow. It can be used to predict concentrations at various locations in the WWTP, including outflow and primary sludge. It can also be reparameterized to be applied to other WWTPs based on activated sludge systems. In principle, a modification for the simulation of other nuclides is possible as well. As radioisotopes of iodine form an important part of accidental releases from nuclear power plants, they are monitored, and their environmental behavior is predicted by models. The present work can contribute to these efforts by improving predictions of radioiodine transport in the public sewer system.

Monitoring of 943 organic micropollutants in wastewater from municipal wastewater treatment plants with secondary and advanced treatment processes

To perform a systematic survey on the occurrence and removal of micropollutants during municipal wastewater treatment, 943 semi-volatile organic chemicals in 32 wastewater samples including influents of secondary treatments, secondary effluents and final effluents (effluents of advanced treatments), which were collected from seven full-scale municipal wastewater treatment plants (MWTPs) in China, were examined by gas chromatography-mass spectrometry (GC-MS) coupled with an automated identification and quantification system with a database (AIQS-DB). In total, 196 and 145 chemicals were detected in secondary and final effluents, respectively. The majority of the total concentrations (average removal efficiency, 87.0%±5.9%) of the micropollutants were removed during secondary treatments. However, advanced treatments achieved different micropollutant removal extents from secondary effluents depending on the different treatment processes employed. Highly variable removal efficiencies of total concentrations (32.7%-99.3%) were observed among the different advanced processes. Among them, ozonation-based processes could remove 70.0%-80.9% of the total concentrations of studied micropollutants. The potentially harmful micropollutants, based on their detection frequency and concentration in secondary and final effluents, were polycyclic aromatic hydrocarbons (PAHs) (2-methylnaphthalene, fluoranthene, pyrene, naphthalene and phenanthrene), phosphorus flame retardants (tributyl phosphate (TBP), tris(2-chloroethyl) phosphate (TCEP) and tris(1,3-dichloro-2-propyl) phosphate (TDCP)), phthalates (bis(2-ethylhexyl)phthalate (DEHP)), benzothiazoles (benzothiazole, 2-(methylthio)-benzothiazol, and 2(3H)-benzothiazolone) and phenol. This study indicated that the presence of considerable amounts of micropollutants in secondary effluent creates the need for suitable advanced treatment before their reuse.