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.

Flow path monitoring by discontinuous time-lapse ERT: An application to survey relationships between secondary effluent infiltration and roots distribution.

The infiltration of secondary treated effluent (STE) into the soil downstream of wastewater treatment plants is becoming increasingly common in a climate change context. In STE infiltration, STE is discharged onto the soil over a large surface allowing for a gradual infiltration of the water. This paper investigates a novel time-lapse electrical resistivity tomography strategy to evaluate the impact of STE infiltration on the water pathways of two planted loamy-soil trenches located in a Fluvisol region in southwestern France. The system has been monitored for 3 years using discontinuous monitoring of electrical resistivity tomography during four saline tracer tests. Results show that: 1) the new methodology has successfully highlighted the evolution of water pathways in the soil over time; 2) such evolution is in agreement with reeds root distribution in the trenches which seems to be affected by water quality i.e. sludge losses and TSS, for this study case. Indeed, for the infiltration trench receiving STE with lower pollution levels (2.2 mg TSS. L-1, 26 mg COD. L-1), the infiltration capacity is maintained over the years (4-6 mm h-1) and reed roots developed deeper in the soil. A sludge deposit present at the bottom of the second infiltration trench receiving higher pollution levels (7.2 mg TSS. L-1, 45 mg COD. L-1, plus episodic sludge release) could lead roots to develop close to the surface affecting the infiltration capacity which did not evolve over time. This work highlights the importance of long-term flow pathway monitoring in understanding the hydraulic behavior of infiltration surfaces submitted to STE.

Comparative Life Cycle Assessment of two advanced treatment steps for wastewater micropollutants: How to determine whole-system environmental benefits?

Advanced wastewater treatment (AWT) technologies are now considered to target urban micropollutants (MPs) before discharge into receiving water bodies and to comply with specific criteria for reuse. Extra energy and/or resources are necessary to achieve the elimination of MPs. Using the Life Cycle Assessment framework, this study assesses net environmental efficiencies for two AWTs (i) ozone systems (air-fed and pure oxygen-fed) and (ii) granular activated carbon filter. Sixty-five MPs with proven removal efficiency values and toxicity and/or ecotoxicity potentials were included in this study building on results from recent research. Consolidated Life Cycle Inventories with data quality and uncertainty characterization were produced with an emphasis on operational inputs. Results show that the direct water quality benefits obtained from AWT are outweighed by greater increases in indirect impacts from energy and resource demands. Future research should include water quality aspects not currently captured in life cycle impact assessment, such as endocrine disruption and whole-effluent toxicity, in order to assess the complete policy implications of MP removal strategies.

Direct photodegradation of 36 organic micropollutants under simulated solar radiation: Comparison with free-water surface constructed wetland and influence of chemical structure.

Micropollutants such as pharmaceuticals and pesticides are still found in treated municipal effluent and are discharged into the natural environment. Natural direct photodegradation may be one pathway for removing these micropollutants in treatment processes such as free-water surface constructed wetlands (CW). This work was set out to evaluate the half-life (t1/2) of direct photodegradation of 36 micropollutants under controlled conditions of light exposure close to solar radiation. The results allowed to classify the micropollutants into three groups (fast, medium and slow). Seven micropollutants were classified in the fast group with t1/2 between 0.05 h and 0.79 h, 24 in the medium group with t1/2 between 5.3 h and 49.7 h, and five in the slow group with t1/2 between 56 h and 118 h. The t1/2 values obtained in laboratory were compared with those from a CW receiving treated wastewater. Correction factors were calculated to adjust the in situ data for the light intensity in laboratory and improved the correspondence especially for the micropollutants of the fast and medium groups. Finally, an innovative method based on statistical tests highlighted the chemical functions characteristic of micropollutants sensitive to photodegradation (OH-CË­O, CË­N-O-, =N-OH, -CH=N, -O-PË­O, -CË­C-) and with low sensitivity (-O-R, -Cl).

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%.

Dynamic modeling of nitrogen removal for a three-stage integrated fixed-film activated sludge process treating municipal wastewater.

The integrated fixed-film activated sludge (IFAS) process is being increasingly used to enhance nitrogen removal for former activated sludge systems. The aim of this work is to evaluate a numerical model of a new nitrifying/denitrifying IFAS configuration. It consists of two carrier-free reactors (anoxic and aerobic) and one IFAS reactor with a filling ratio of 43% of carriers, followed by a clarifier. Simulations were carried out with GPS-X involving the nitrification reaction combined with a 1D heterogeneous biofilm model, including attachment/detachment processes. An original iterative calibration protocol was created comprising four steps and nine actions. Experimental campaigns were carried out to collect data on the pilot in operation, specifically for modelling purpose. The model used was able to predict properly the variations of the activated sludge (bulk) and the biofilm masses, the nitrification rates of both the activated sludge and the biofilm, and the nitrogen concentration in the effluent for short (4-10 days) and long (300 days) simulation runs. A calibrated parameter set is proposed (biokinetics, detachment, diffusion) related to the activated sludge, the biofilm and the effluent variables to enhance the model prediction on hourly and daily data sets.

Removal efficiencies and kinetic rate constants of xenobiotics by ozonation in tertiary treatment.

This study gives a full overview of the chemical oxidation by ozone of selected xenobiotics usually present in effluents of conventional wastewater treatment plants. A qualitative and quantitative overview of literature data was made, and describes the ozonation efficiency and processes for the elimination of 12 xenobiotics (pesticides and pharmaceuticals). A database was built, compiling literature results of experimental ozonation assays in laboratory and real-scale conditions. Special attention was paid to selecting the data and compiling reliable results on removal efficiencies and kinetic parameters. An original study was performed in a semi-batch reactor applying ozone on secondary effluent spiked beforehand with a cocktail of 12 xenobiotics. The results of this study were compared with the literature data to evaluate the influence of the kinetic competition of xenobiotics in spiked wastewater in the determination of kinetic rate constants. These 12 xenobiotics were classified into three groups (high-/medium-/low-oxidizable) according to the ranges of their direct kinetic rate constants (kO3). A best effective ozone dose between 0.2 and 0.4 gO3 gDOC-1 is proposed for the elimination of xenobiotics. The predominant elimination pathway between direct and indirect oxidation was identified for each xenobiotic.

Biofilm carrier migration model describes reactor performance.

The accuracy of a biofilm reactor model depends on the extent to which physical system conditions (particularly bulk-liquid hydrodynamics and their influence on biofilm dynamics) deviate from the ideal conditions upon which the model is based. It follows that an improved capacity to model a biofilm reactor does not necessarily rely on an improved biofilm model, but does rely on an improved mathematical description of the biofilm reactor and its components. Existing biofilm reactor models typically include a one-dimensional biofilm model, a process (biokinetic and stoichiometric) model, and a continuous flow stirred tank reactor (CFSTR) mass balance that [when organizing CFSTRs in series] creates a pseudo two-dimensional (2-D) model of bulk-liquid hydrodynamics approaching plug flow. In such a biofilm reactor model, the user-defined biofilm area is specified for each CFSTR; thereby, Xcarrier does not exit the boundaries of the CFSTR to which they are assigned or exchange boundaries with other CFSTRs in the series. The error introduced by this pseudo 2-D biofilm reactor modeling approach may adversely affect model results and limit model-user capacity to accurately calibrate a model. This paper presents a new sub-model that describes the migration of Xcarrier and associated biofilms, and evaluates the impact that Xcarrier migration and axial dispersion has on simulated system performance. Relevance of the new biofilm reactor model to engineering situations is discussed by applying it to known biofilm reactor types and operational conditions.

Rethinking micropollutant removal assessment methods for wastewater treatment plants - how to get more robust data?

This paper covers the pitfalls, recommendations and a new methodology for assessing micropollutant removal efficiencies in wastewater treatment plants. The proposed calculation rules take into account the limit of quantification and the analytical and sampling uncertainty of measured concentrations. We identified six cases for which a removal efficiency value is reliable and four other cases where result is highly variable (uncertain) due to very low or unquantified concentrations in effluent or when the influent-effluent concentrations differential is below the measurement uncertainty. The influence of the proposed calculation rules on removal efficiency values was scrutinized using actual results from a research project. The paper arrives at detailed recommendations for limiting the impact of other sources of uncertainty during sampling (sampling strategy, cleaning and field blank), chemical analyses (suspended solids and sludge) and data processing according to the targeted objectives.

A one dimensional moving bed biofilm reactor model for nitrification of municipal wastewaters.

This work presents a one-dimensional model of a moving bed bioreactor (MBBR) process designed for the removal of nitrogen from raw wastewaters. A comprehensive experimental strategy was deployed at a semi-industrial pilot-scale plant fed with a municipal wastewater operated at 10-12 °C, and surface loading rates of 1-2 g filtered COD/m2 d and 0.4-0.55 g NH4-N/m2 d. Data were collected on influent/effluent composition, and on measurement of key variables or parameters (biofilm mass and maximal thickness, thickness of the limit liquid layer, maximal nitrification rate, oxygen mass transfer coefficient). Based on time-course variations in these variables, the MBBR model was calibrated at two time-scales and magnitudes of dynamic conditions, i.e., short-term (4 days) calibration under dynamic conditions and long-term (33 days) calibration, and for three types of carriers. A set of parameters suitable for the conditions was proposed, and the calibrated parameter set is able to simulate the time-course change of nitrogen forms in the effluent of the MBBR tanks, under the tested operated conditions. Parameters linked to diffusion had a strong influence on how robustly the model is able to accurately reproduce time-course changes in effluent quality. Then the model was used to optimize the operations of MBBR layout. It was shown that the main optimization track consists of the limitation of the aeration supply without changing the overall performance of the process. Further work would investigate the influence of the hydrodynamic conditions onto the thickness of the limit liquid layer and the "apparent" diffusion coefficient in the biofilm parameters.

A review of the photodegradability and transformation products of 13 pharmaceuticals and pesticides relevant to sewage polishing treatment.

Many xenobiotics are only partially treated by conventional wastewater treatment plants. Photodegradation is one promising solution currently being investigated to improve their removal from effluents. We present an in-depth review of the photodegradation kinetic parameters of selected pesticides and pharmaceuticals and assess whether the data available in the literature are applicable to polishing treatment processes under sunlight. We made a thorough inventory of literature data describing the photodegradation of pesticides and pharmaceuticals in water, the laboratory, pilot plants, and in situ conditions. To this end, we built a database compiling results on photodegradation experiments from 70 scientific publications covering 13 xenobiotics commonly found in secondary effluents. Special care was taken to compile reliable data on photolysis kinetic parameters (half-life and kinetic rate constant) and removal efficiencies. We also include a comprehensive description of experimental operating conditions and an up-to-date inventory of known phototransformation products. As practical outputs we (i) propose a classification for the xenobiotics according to their photodegradability: fast-, medium- and slow-photodegradable, (ii) compare kinetic parameters in direct and indirect photodegradation conditions, and (iii) list 140 phototransformation products formed by direct or indirect photodegradation. We conclude by identifying gaps in the literature that need to be filled to adapt these available results to the conditions of polishing processes.

Perspectives on modelling micropollutants in wastewater treatment plants.

Models for predicting the fate of micropollutants (MPs) in wastewater treatment plants (WWTPs) have been developed to provide engineers and decision-makers with tools that they can use to improve their understanding of, and evaluate how to optimize, the removal of MPs and determine their impact on the receiving waters. This paper provides an overview of such models, and discusses the impact of regulation, engineering practice and research on model development. A review of the current status of MP models reveals that a single model cannot represent the wide range of MPs that are present in wastewaters today, and that it is important to start considering classes of MPs based on their chemical structure or ecotoxicological effect, rather than the individual molecules. This paper identifies potential future research areas that comprise (i) considering transformation products in MP removal analysis, (ii) addressing advancements in WWTP treatment technologies, (iii) making use of common approaches to data acquisition for model calibration and (iv) integrating ecotoxicological effects of MPs in receiving waters.

Rethinking wastewater characterisation methods for activated sludge systems - a position paper.

Increasingly stringent effluent limits and an expanding scope of model system boundaries beyond activated sludge has led to new modelling objectives and consequently to new and often more detailed modelling concepts. Nearly three decades after the publication of Activated Sludge Model No1 (ASM1), the authors believe it is time to re-evaluate wastewater characterisation procedures and targets. The present position paper gives a brief overview of state-of-the-art methods and discusses newly developed measurement techniques on a conceptual level. Potential future paths are presented including on-line instrumentation, promising measuring techniques, and mathematical solutions to fractionation problems. This is accompanied by a discussion on standardisation needs to increase modelling efficiency in our industry.

Xenobiotics removal by adsorption in the context of tertiary treatment: a mini review.

Many xenobiotics, including several pharmaceuticals and pesticides, are poorly treated in domestic wastewater treatment plants. Adsorption processes, such as with activated carbons, could be a solution to curb their discharge into the aquatic environment. As adsorbent-like activated carbon is known to be expensive, identifying promising alternative adsorbent materials is a key challenge for efficient yet affordable xenobiotic removal from wastewaters. As part of the effort to address this challenge, we surveyed the literature on pharmaceutical and pesticide xenobiotics and built a database compiling data from 38 scientific publications covering 65 xenobiotics and 58 materials. Special focus was given to the relevance and comparability of the data to the characteristics of the adsorbent materials used and to the operating conditions of the batch tests inventoried. This paper gives an in-depth overview of the adsorption capacities of various adsorbents. The little data on alternative adsorbent materials, especially for the adsorption of pharmaceuticals, makes it difficult to single out any one activated carbon alternative capable of adsorbing pesticides and pharmaceuticals at the tertiary stage of treatment. There is a pressing need for further lab-scale experiments to investigate the tertiary treatment of discharged effluents. We conclude with recommendations on how future data should best be used and interpreted.

Concentrations and fate of sugars, proteins and lipids during domestic and agro-industrial aerobic treatment.

This work investigates the composition and the fate of sugars, lipids, proteins, amino acids under aerobic conditions for 13 domestic and 4 agro-industrial wastewaters, sampled before and after treatment. The rates of aerobic degradation were moreover studied with a 21-day continuous aeration batch test. It is shown that the sum of the biochemical forms represented 50 to 85% of the total chemical oxygen demand (COD). Lipids represented the half of the identified COD; sugars and proteins correspond to a quarter of the identified COD. Aerobic processes provided an increase of the relative fractions for proteins, whereas the ones of lipids decreased and sugars fraction remains stable. For the wastewaters released from cheese dairy (lipid-rich) and slaughterhouses (protein/lipid-rich), the dissolved phase after biological treatment is composed of proteins whereas the particulate one is composed of lipids. After the 21-day test, the concentration in proteins was nearby 10 mg/L. The results should be used for operations of WWTP to detect when a dysfunction is about to occur. They can be used to predict the concentrations in the treated water when upgrading an existing municipal plant that will admit agro-industrial discharge.

Solid respirometry to characterize nitrification kinetics: a better insight for modelling nitrogen conversion in vertical flow constructed wetlands.

We developed an original method to measure nitrification rates at different depths of a vertical flow constructed wetland (VFCW) with variable contents of organic matter (sludge, colonized gravel). The method was adapted for organic matter sampled in constructed wetland (sludge, colonized gravel) operated under partially saturated conditions and is based on respirometric principles. Measurements were performed on a reactor, containing a mixture of organic matter (sludge, colonized gravel) mixed with a bulking agent (wood), on which an ammonium-containing liquid was applied. The oxygen demand was determined from analysing oxygen concentration of the gas passing through the reactor with an on-line analyzer equipped with a paramagnetic detector. Within this paper we present the overall methodology, the factors influencing the measurement (sample volume, nature and concentration of the applied liquid, number of successive applications), and the robustness of the method. The combination of this new method with a mass balance approach also allowed determining the concentration and maximum growth rate of the autotrophic biomass in different layers of a VFCW. These latter parameters are essential inputs for the VFCW plant modelling.

The role of loading rate, backwashing, water and air velocities in an up-flow nitrifying tertiary filter.

The vertical distribution of nitrification performances in an up-flow biological aerated filter operated at tertiary nitrification stage is evaluated in this paper. Experimental data were collected from a semi-industrial pilot-plant under various operating conditions. The actual and the maximum nitrification rates were measured at different levels inside the up-flow biofilter. A nitrogen loading rate higher than 1.0 kg NH4-Nm(-3)_mediad(-1) is necessary to obtain nitrification activity over all the height of the biofilter. The increase in water and air velocities from 6 to 10 m h(-1) and 10 to 20 m h(-1) has increased the nitrification rate by 80% and 20% respectively. Backwashing decreases the maximum nitrification rate in the media by only 3-14%. The nitrification rate measured at a level of 0.5 m above the bottom of the filter is four times higher than the applied daily average volumetric nitrogen loading rate up to 1.5 kg NH4-N m(-3)_mediad(-1). Finally, it is shown that 58% of the available nitrification activity is mobilized in steady-state conditions while up to 100% is used under inflow-rate increase.

A biofiltration model for tertiary nitrification of municipal wastewaters.

The main objective of this work concerns the evaluation of the biological aerated filtration model found in GPS-X, which had never been evaluated with adequate data. This model is interesting since it integrates the physical and biological phenomena involved during filtration with a low complexity of use. The validation of the model parameters combines experimental and theoretical approaches. Experimental data were recorded at a semi-industrial pilot scale submerged biofilter operated at a tertiary nitrification stage, receiving the effluent of a medium loaded activated sludge process for municipal wastewater. Also, several protocols were regularly applied to characterize the biofilm and the nitrogen removal performances: dry density and thickness of biofilm, nitrification rates and corresponding quantity of autotrophic biomass accumulated inside the filtering media, quantity of extracted autotrophic bacteria in the backwash water, nitrification capacity along the biofilter, as well as nitrogen compounds in the effluent. For short-term dynamic conditions, a set of reliable parameter values has been used to predict nitrogen removal for different data sets. For long-term dynamic periods, the need to adapt some of the parameters from one set of data to another is demonstrated. It is shown that the hydraulic loading rate and the backwashing frequency are the main parameters responsible for these modifications.

Updated activated sludge model number 1 parameter values for improved prediction of nitrogen removal in activated sludge processes: validation at 13 full-scale plants.

The Activated Sludge Model number 1 (ASM1) is the main model used in simulation projects focusing on nitrogen removal. Recent laboratory-scale studies have found that the default values given 20 years ago for the decay rate of nitrifiers and for the heterotrophic biomass yield in anoxic conditions were inadequate. To verify the relevance of the revised parameter values at full scale, a series of simulations were carried out with ASM1 using the original and updated set of parameters at 20 degrees C and 10 degrees C. The simulation results were compared with data collected at 13 full-scale nitrifying-denitrifying municipal treatment plants. This work shows that simulations using the original ASM1 default parameters tend to overpredict the nitrification rate and underpredict the denitrification rate. The updated set of parameters allows more realistic predictions over a wide range of operating conditions.