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.

Treatment of micropollutants in wastewater: Balancing effectiveness, costs and implications

In this contribution, we analyse scenarios of advanced wastewater treatment for the removal of micropollutants. By this we refer to current mainstream, broad spectrum processes including ozonation and sorption onto activated carbon. We argue that advanced treatment requires properly implemented tertiary (nutrient removal) treatment in order to be effective. We review the critical aspects of the main advanced treatment options, their advantages and disadvantages. We propose a quantification of the costs of implementing advanced treatment, as well as upgrading plants from secondary to tertiary treatment when needed, and we illustrate what drives the costs of advanced treatment for a set of standard configurations. We propose a cost function to represent the total costs (investment, operation and maintenance) of advanced treatment. We quantify the implications of advanced treatment in terms of greenhouse gas emissions. Based on the indicators of total toxic discharge, toxicity at the discharge points and toxicity across the stream network discussed in Pistocchi et al. (2022), we compare costs and effectiveness of different scenarios of advanced treatment. In principle the total toxic load and toxicity at the points of discharge could be reduced by about 75 % if advanced treatment processes were implemented virtually at all wastewater treatment plants, but this would entail costs of about 4 billion euro/year for the European Union as a whole. We consider a "compromise" scenario where advanced treatment is required at plants of 100 thousand population equivalents (PE) or larger, or at plants between 10 and 100 thousand PE if the dilution ratio at the discharge point is 10 or less. Under this scenario, the length of the stream network exposed to high toxicity would not increase significantly compared to the previous scenario, and the other indicators would not deteriorate significantly, while the costs would remain at about 1.5 billion Euro/year. Arguably, costs could be further reduced, without a worsening of water quality, if we replace a local risk assessment to generic criteria of plant capacity and dilution in order to determine if a WWTP requires advanced treatment.

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 (t_1/2) 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 t_1/2 between 0.05 h and 0.79 h, 24 in the medium group with t_1/2 between 5.3 h and 49.7 h, and five in the slow group with t_1/2 between 56 h and 118 h. The t_1/2 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-C˭O, C˭N-O-, =N-OH, -CH=N, -O-P˭O, -C˭C-) 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.

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.

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 (k_O3). 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, X_carrier 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 X_carrier and associated biofilms, and evaluates the impact that X_carrier 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.

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.

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.

Lab-scale experimental strategy for determining micropollutant partition coefficient and biodegradation constants in activated sludge

The nitrifying/denitrifying activated sludge process removes several micropollutants from wastewater by sorption onto sludge and/or biodegradation. The objective of this paper is to propose and evaluate a lab-scale experimental strategy for the determination of partition coefficient and biodegradation constant for micropollutant with an objective of modelling their removal. Four pharmaceutical compounds (ibuprofen, atenolol, diclofenac and fluoxetine) covering a wide hydrophobicity range (log Kow from 0.16 to 4.51) were chosen. Dissolved and particulate concentrations were monitored for 4 days, inside two reactors working under aerobic and anoxic conditions, and under different substrate feed conditions (biodegradable carbon and nitrogen). We determined the mechanisms responsible for the removal of the target compounds: (i) ibuprofen was biodegraded, mainly under aerobic conditions by cometabolism with biodegradable carbon, whereas anoxic conditions suppressed biodegradation; (ii) atenolol was biodegraded under both aerobic and anoxic conditions (with a higher biodegradation rate under aerobic conditions), and cometabolism with biodegradable carbon was the main mechanism; (iii) diclofenac and fluoxetine were removed by sorption only. Finally, the abilities of our strategy were evaluated by testing the suitability of the parameters for simulating effluent concentrations and removal efficiency at a full-scale plant.

Understanding the contribution of biofilm in an integrated fixed-film-activated sludge system (IFAS) designed for nitrogen removal

The objective of this study is to improve knowledge on the integrated fixed-film-activated sludge (IFAS) system designed for nitrogen removal. Biofilm growth and its contribution to nitrification were monitored under various operating conditions in a semi-industrial pilot-scale plant. Nitrification rates were observed in biofilms developed on free-floating media and in activated sludge operated under a low sludge retention time (4 days) and at an ammonia loading rate of 45-70 gNH4-N/kgMLVSS/d. Operational conditions, i.e. oxygen concentration, redox potential, suspended solids concentration, ammonium and nitrates, were monitored continuously in the reactors. High removal efficiencies were observed for carbon and ammonium at high-loading rate. The contribution of biofilm to nitrification was determined as 40-70% of total NOx-N production under the operating conditions tested. Optimal conditions to optimize process compacity were determined. The tested configuration responds especially well to winter and summer nitrification conditions. These results help provide a deeper understanding of how autotrophic biomass evolves through environmental and operational conditions in IFAS systems.

Removal of xenobiotics from effluent discharge by adsorption on zeolite and expanded clay: an alternative to activated carbon?

Xenobiotics such as pesticides and pharmaceuticals are an increasingly large problem in aquatic environments. A fixed-bed adsorption filter, used as tertiary stage of sewage treatment, could be a solution to decrease xenobiotics concentrations in wastewater treatment plants (WWTPs) effluent. The adsorption efficiency of two mineral adsorbent materials (expanded clay (EC) and zeolite (ZE)), both seen as a possible alternative to activated carbon (AC), was evaluated in batch tests. Experiments involving secondary treated domestic wastewater spiked with a cocktail of ten xenobiotics (eight pharmaceuticals and two pesticides) known to be poorly eliminated in conventional biological process were carried out. Removal efficiencies and partitions coefficients were calculated for two levels of initial xenobiotic concentration, i.e, concentrations lower to 10 μg/L and concentrations ranged from 100 to 1,000 μg/L. While AC was the most efficient adsorbent material, both alternative adsorbent materials showed good adsorption efficiencies for all ten xenobiotics (from 50 to 100 % depending on the xenobiotic/adsorbent material pair). For all the targeted xenobiotics, at lower concentrations, EC presented the best adsorption potential with higher partition coefficients, confirming the results in terms of removal efficiencies. Nevertheless, Zeolite presents virtually the same adsorption potential for both high and low xenobiotics concentrations to be treated. According to this first batch investigation, ZE and EC could be used as alternative absorbent materials to AC in WWTP.

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.

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.

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.

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.

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.

On-site evaluation of the removal of 100 micro-pollutants through advanced wastewater treatment processes for reuse applications

The next challenge of wastewater treatment is to reliably remove micro-pollutants at the microgram per litre range in order to meet reuse applications and contribute to reach the good status of the water bodies. A hundred priority and relevant emerging substances were measured to evaluate at full-scale the removal efficiencies of seven advanced treatment lines (one membrane bioreactor process and six tertiary treatment lines) that were designed for reuse applications. To reliably compare the processes, specific procedures for micro-pollutants were applied for sampling, analysis and calculation of removal efficiencies. The membrane bioreactor process allowed to upgrade the removal efficiencies of about 20% of the substances measured, especially those that were partially degraded during conventional processes. Conventional tertiary processes like high rate clarification, sand filtration and polishing pond achieved significant removal for some micro-pollutants, especially for adsorbable substances. Advanced tertiary processes, like ozonation, activated carbon and reverse osmosis were all very efficient to complete the removal of polar pesticides and pharmaceuticals; metals and less polar substances were better retained by reverse osmosis.

Limiting the emissions of micro-pollutants: what efficiency can we expect from wastewater treatment plants?

The next challenge of wastewater treatment is to reliably remove micro-pollutants at the microgram per litre range in order to meet the environmental quality standards set by new regulations like the Water Framework Directive. The present work assessed the efficiency of different types of primary, secondary and tertiary processes for the removal of more than 100 priority substances and other relevant emerging pollutants through on-site mass balances over 19 municipal wastewater treatment lines. Secondary biological processes proved to be in average 30% more efficient than primary settling processes. The activated sludge (AS) process led to a significant reduction of pollution loads (more than 50% removal for 70% of the substances detected). Biofilm processes led to equivalent removal efficiencies compared to AS, except for some pharmaceuticals. The membrane bioreactor (MBR) process allowed to upgrade removal efficiencies of some substances only partially degraded during conventional AS processes. Preliminary tertiary processes like tertiary settling and sand filtration could achieve significant removal for adsorbable substances. Advanced tertiary processes, like ozonation, activated carbon and reverse osmosis were all very efficient (close to 100%) to complete the removal of polar pesticides and pharmaceuticals; less polar substances being better retained by reverse osmosis.

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.

Influent concentrations and removal performances of metals through municipal wastewater treatment processes

This extensive study aimed at quantifying the concentrations and removal efficiency of 23 metals and metalloids in domestic wastewater passing through full-scale plants. Nine facilities were equipped with secondary biological treatment and three facilities were equipped with a tertiary treatment stage. The metals investigated were Li, B, Al, Ti, V, Cr, Fe, Ni, Co, Cu, Zn, As, Se, Rb, Mo, Ag, Cd, Sn, Sb, Ba, TI, Pb and U. Particulate and dissolved metals were measured using 24 h composite samples at each treatment stage. In influents, total concentrations of Cd, Sb, Co, Se, U, Ag, V were below a few microg/L, whereas at the other extremity Zn, B, Fe, Ti, Al were in the range of 0.1 to > 1 mg/L. It was demonstrated that secondary treatment stage (activated sludge, biodisc and membrane bioreactor) were efficient to remove most metals (removal rate > 70%), with the exception of B, Li, Rb, Mo, Co, As, Sb and V due to their low adsorption capacities. With the tested tertiary stages (polishing pond, rapid chemical settler, ozonation), a removal efficiency was obtained for Ti, Cr, Cd, Cu, Zn, Sn, Pb, Fe, Ag and Al, whereas a little removal (< 30%) was obtained for other metals.

Occurrence and removal of estrogens and beta blockers by various processes in wastewater treatment plants

This study aims at evaluating occurrence and treatment efficiency of five estrogenic hormones and ten beta blockers in wastewater treatment plants (WWTP). The use of consistent sampling procedures, analytical techniques and data processing enabled to achieve an accurate comparison of the performances of the different treatment processes. First, the occurrence of molecules was evaluated in fourteen rural and urban WWTP located in France. Free and total estrogens were analyzed showing that more than 84% of estrogens in the dissolved phase of influent samples are in the free form. In effluent samples, comparable mean values but higher variation are underlined (RSD from 13 to 54% depending on the estrogen, compared to 11-21% for influents). Most of the target molecules are quantified in 30 influent and 31 effluent samples. Similar occurrence frequencies are obtained for influents from rural (6 WWTP) and urban areas (8 WWTP), except for betaxolol which is only quantified in urban wastewaters. Removal efficiencies of 8 biological treatments were studied: suspended growth biomass (activated sludge) and attached growth systems (biofilter, rotating biological contactor, reed-bed filter, trickling filter). Biological treatments are efficient to remove estrogens from the dissolved phase, with removal rate around 90%. For beta blockers, acebutolol and nadolol are efficiently removed (mean removal rate of 80%), whereas sotalol and propranolol are hardly impacted by biological treatments (removal rate below 20%). Finally, 9 tertiary treatment processes were evaluated. Ozonation, reverse osmosis and activated carbon filtration prove a high removal efficiency for beta blockers (above 80%). On the contrary, high speed chemical settler, sand filtration, silex filtration, microfiltration and UV present generally removal rates below 30% for all beta blockers. The polishing pond studied presents variable removal performances depending on the molecules (up to 75% for propranolol). The role of the hydraulic retention time on the removal efficiencies is confirmed.

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.

Modelling a full scale membrane bioreactor using Activated Sludge Model No.1: challenges and solutions

A full-scale membrane bioreactor (1,600 m(3) d(-1)) was monitored for modelling purposes during the summer of 2006. A complete calibration of the ASM1 model is presented, in which the key points were the wastewater characterisation, the oxygen transfer and the biomass kinetics. Total BOD tests were not able to correctly estimate the biodegradable fraction of the wastewater. Therefore the wastewater fractionation was identified by adjusting the simulated sludge production rate to the measured value. MLVSS and MLSS were accurately predicted during both calibration and validation periods (20 and 30 days). Because the membranes were immerged in the aeration tank, the coarse bubble and fine bubble diffusion systems coexisted in the same tank. This allowed five different aeration combinations, depending whether the 2 systems were operating separately or simultaneously, and at low speed or high speed. The aeration control maintained low DO concentrations, allowing simultaneous nitrification and denitrification. This made it difficult to calibrate the oxygen transfer. The nitrogen removal kinetics were determined using maximum nitrification rate tests and an 8-hour intensive sampling campaign. Despite the challenges encountered, a calibrated set of parameters was identified for ASM1 that gave very satisfactory results for the calibration period. Matching simulated and measured data became more difficult during the validation period, mainly because the dominant aeration configuration had changed. However, the merit of this study is to be the first effort to simulate a full-scale MBR plant.

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.

Fate of pharmaceuticals and personal care products in wastewater treatment plants--conception of a database and first results

We created a database in order to quantitatively assess the occurrence and removal efficiency of pharmaceuticals and personal care products (PPCPs) in wastewater treatment plants (WWTPs). From 117 scientific publications, we compiled 6641 data covering 184 PPCPs. Data included the concentrations of PPCPs in WWTP influents and effluents, their removal efficiency and their loads to the aquatic environment. The first outputs of our database allowed to identify the most investigated PPCPs in WWTPs and the most persistent ones, and to obtain reliable and quantitative values on their concentrations, frequency of detection and removal efficiency in WWTPs. We were also able to compare various processes and pointed out activated sludge with nitrogen treatment and membrane bioreactor as the most efficient ones.

Removal efficiency of pharmaceuticals and personal care products with varying wastewater treatment processes and operating conditions - conception of a database and first results

We created a database in order to quantitatively assess the occurrence and removal efficiency of PPCPs in WWTPs. From 113 scientific publications, we compiled 5887 data on the concentrations and loads of PPCPs in WWTP influents and effluents, and on their removal efficiency. The first outputs of our database include: (1) a list of the most frequently studied molecules, their frequency of detection, their mean concentration and removal in liquid influent and effluent; (2) a comparison of the removal efficiency for different WWTP processes; (3) a study of the influence of the operating conditions (sludge and hydraulic retention times).

Semi-quantitative analysis of a specific database on priority and emerging substances in wastewater and sludge

The Water Framework Directive (WFD) has drawn attention to a series of metals and organic compounds because of their demonstrated or potential harmfulness for aquatic environments. The aim of our work was to build and to process a "practical" database focused on the role of wastewater treatment plants for the removal of the 37 priority compounds that have to be reduced or stopped by 2015, and of 34 additional relevant contaminants. About 11,000 concentration values in raw and treated wastewater and sludge, from more than 100 peer-reviewed articles and six French national screening programs, were integrated. A systematic approach showed the global low quality of data for most of the compounds, with missing information about the treatment process, sampling and analysis, leading to 10% of the data available for removal efficiency calculations. A semi-quantitative analysis allowed the identification of 20 priority and 10 additional relevant substances more frequently quantified at significant concentrations in raw wastewater and treated wastewater. Conventional activated sludge was able to remove more than 70% of half of the studied compounds, leaving only 10% of them with less than 50% removal. Physical-chemical treatments appeared to be about 30% less efficient than biological treatments. In addition, very few data are available concerning some compounds and some processes, especially sludge treatment and tertiary wastewater treatment processes. Therefore, complementary on-site measurements and modeling are required to propose adapted solutions for the treatment of priority and emerging substances in wastewater treatment plants.

Toward an operational dynamic model for tertiary nitrification by submerged biofiltration

This work deals with the methodology put in place to fit and validate the parameters of a biofiltration model (BAF) in tertiary nitrification treatment and dynamic conditions. For an average loading rate of 0.65 kg NH4-N/m(3) media/d, different time loading rates are applied inside a filtration-backwash run using a semi-industrial pilot. Comparisons between predicted and observed values on the NH4-N, NO3-N and TSS in treated water and the total head loss deltaP are carried out firstly using default values of BAF parameters. Model predictions overestimate values measured but trends are well reproduced. A sensitivity analysis is carried out and the hierarchy of BAF parameters has been set up classifying them into strong and low influence on the effluent concentrations. Among parameters revealing the strongest influence are those of the filtration module and the mean density of biofilm for the TSS effluent and the total AP, the specific autotrophic growth rate, the maximum biofilm thickness and the reduction coefficient of diffusivity in the biofilm for the NH4-N, NO3-N effluent. Finally, this classification leads to setting a calibration procedure, thanks to specific experimental tests directly measuring some BAF parameters.