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A pilot plant with a conventional activated sludge (CAS) system with intermittent aeration (IA) was monitored. The system was configured as an Oxic Settling Anaerobic (OSA) process with the insertion of one anaerobic side-stream reactor (ASSR). The pilot plant was fed with real wastewater and an intensive experimental campaign was carried out including sludge minimization, nitrogen and carbon removal, GHG emissions and biokinetic parameters. The experimental campaign was divided into periods: Period I, II, and III. In Periods I and II, the ASSR reactor was operated with two different hydraulic retention times (HRT), 4 and 6 h, with an aeration/non-aeration ratio of 30 min/30 min. In Period III, the HRT in the anaerobic reactor was the same as in Period II. In contrast, the biological reactor's aerated/non-aerated ratio was increased to 40 min/20 min. Results demonstrated that combining IA and OSA might be effective in the reduction of excess sludge production. The yield coefficient decreased from Period I to Period II (Y obs from 0.41 to 0.25 gTSS gCOD -1 , in Period I and II, respectively). Nevertheless, the HRT increase in the ASSR compromised the system performance regarding nitrification and greenhouse gas emissions and worsened the sludge settleability. However, the increase in the aeration duration was beneficial in restoring the system's nitrification and denitrification ability and carbon footprint. The lowest carbon footprint was obtained during Period III (6.8 kgCO 2 /d)., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Author(s). Published by Elsevier Ltd.. All rights reserved.)

Volatile fatty acids (VFA) from sewage sludge represent an excellent recovered resource from wastewater treatment. This study investigated four sludge pre-treatments (namely, potassium permanganate - KMnO 4 , initial pH = 10, initial pH = 2.5 and low-temperature thermal hydrolysis) by operating batch reactors under acidogenic fermentation conditions. Results revealed that 0.1 g KMnO 4 /g of total suspended solids represents the best pre-treatment obtaining up to 2713 mgCOD L -1 and 452 mgCOD/g of volatile suspended solids. These results also paralleled metataxonomic analysis highlighting changes in prokaryotic microbial structures of sewage sludge of the batch fermentations subjected to the different pre-treatments., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 The Authors. Published by Elsevier Ltd.. All rights reserved.)

The present paper investigated an Integrated Fixed Film Activated Sludge (IFAS) Membrane BioReactor (MBR) system monitored for 340 days. In particular, the short-term effects of some operational parameters variation was evaluated. Results showed a decrease of the removal rates under low C/N values. Respirometry results highlighted that activated sludge was more active in the organic carbon removal. Conversely, biofilm has a key role during nitrification. The major fouling mechanism was represented by the cake deposition (irreversible)., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

A University of Cape Town Integrated Fixed-Film Activated Sludge Membrane Bioreactor (UCT-IFAS-MBR) pilot plant was operated at different values of the sludge retention time (SRT). Three SRTs were investigated at different durations: indefinitely, 30 and 15 days. The organic carbon, nitrogen and phosphorus removal, kinetic/stoichiometric parameters, membrane fouling tendency and sludge filtration properties were assessed. The findings showed that by decreasing the SRT, the pilot plant could maintain excellent carbon removal efficiencies throughout the experiments. In contrast, the biological carbon removal showed a slight nitrification and was slightly affected by the decrease of the SRT, showing high performance (approximately 91%, on average). Thus, the biofilm might have helped sustain the nitrification throughout the experiments. The average phosphorus removal performance increased slightly with a decrease in SRT, achieving the maximum efficiency (61.5%) at a SRT of 15 days. After a 30-day SRT, an increase in resistance due to pore blocking and a general worsening of the membrane filtration properties occurred.

This research elucidates the pollutants (nutrients and carbon) removal performance and nitrous oxide (N 2 O) emissions of two pilot plants. Specifically, a University of Cape Town (UCT) Membrane Bioreactor (MBR) plant and an Integrated Fixed Film Activated Sludge (IFAS)-UCT-MBR plant were investigated. The plants were fed with real wastewater augmented with acetate and glycerol in order to control the influent carbon nitrogen ratio (C/N). The short-term effect of the inlet C/N ratio variation (C/N = 5 mgCOD/mgN and C/N = 10 mgCOD/mgN) on the behaviour of both plants was investigated. The results showed that the IFAS-UCT-MBR configuration provided the best performance in terms of pollutants removal at the two investigated C/N ratios. Furthermore, the lowest N 2 O emission (with respect to the influent nitrogen) was observed in the IFAS-UCT-MBR configuration, thus suggesting a potential beneficial effect of the biofilm in the emission reduction. However, the membrane of the IFAS-UCT-MBR showed a greater fouling tendency compared to the UCT-MBR configuration. This result, likely related to the biofilm detached from carriers, could seriously affect the indirect GreenHouse Gas emissions due to the increase of the energy requirement for permeate extraction with the increase of membrane fouling., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

This paper compares two mathematical models (Model I and Model II) to predict greenhouse gases emission from a University Cape Town (UCT) - membrane bioreactor (MBR) plant. Model I considers N 2 O production only during denitrification. Model II takes into account the ammonia-oxidizing bacteria (AOB) formation pathways for N 2 O. Both models were calibrated adopting real data. Model comparison was performed in terms of (i) sensitivity analysis (ii) best fit and (iii) model prediction uncertainty. On average 6% of factors of Model I and 9% of Model II resulted to be important. In terms of best fit, Model II had a better capability of reproducing the measured data. The average efficiency related to the N 2 O model outputs was equal to 0.33 and 0.38 for Model I and Model II, respectively. On average, 73% (Model I) and 86% (Model II) of measured data lay inside the uncertainty bands., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

The influence of the main operational variables on N 2 O emissions from an Integrated Fixed Film Activated Sludge University of Cape Town membrane Bioreactor pilot plant was studied. Nine operational cycles (total duration: 340days) were investigated by varying the value of the mixed liquor sludge retention time (SRT) (Cycles 1-3), the feeding ratio between carbon and nitrogen (C/N) (Cycles 4-6) and simultaneously the hydraulic retention time (HRT) and the SRT (Cycles 7-9). Results show a huge variability of the N 2 O concentration in liquid and off-gas samples (ranged from 10 -1 μgN 2 O-NL -1 to 10 3 μgN 2 O-NL -1 ). The maximum N 2 O concentration (1228μgN 2 O-NL -1 ) in the off-gas samples occurred in the anoxic reactor at the lowest C/N value confirming that unbalanced C/N promotes the N 2 O emission during denitrification. The aerated reactors (aerobic and MBR) have been the major N 2 O emitters during all the three Phases., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

The aim of the present study was to investigate the nitrous oxide (N 2 O) emissions from a moving bed based Integrated Fixed Film Activated Sludge (IFAS) - membrane bioreactor (MBR) pilot plant, designed according to the University of Cape Town (UCT) layout. The experimental campaign had a duration of 110 days and was characterized by three different sludge retention time (SRT) values (∞, 30 d and 15 d). Results highlighted that N 2 O concentrations decreased when the biofilm concentrations increased within the aerobic reactor. Results have shown an increase of N 2 O with the decrease of SRT. Specifically, an increase of N 2 O-N emission factor occurred with the decrease of the SRT (0.13%, 0.21% and 0.76% of influent nitrogen for SRT = ∞, SRT = 30 d and SRT = 15 d, respectively). Moreover, the MBR tank resulted the key emission source (up to 70% of the total N 2 O emission during SRT = ∞ period) whereas the highest N 2 O production occurred in the anoxic reactor. Moreover, N 2 O concentrations measured in the permeate flow were not negligible, thus highlighting its potential detrimental contribution for the receiving water body. The role of each plant reactor as N 2 O-N producer/consumer varies with the SRT variation, indeed the aerobic reactor was a N 2 O consumer at SRT = ∞ and a producer at SRT = 30 d., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

The present study explores the interlinkages among the operational variables of a University of Cape Town (UCT) Integrated Fixed Film Activated Sludge (IFAS) membrane bioreactor (MBR) pilot plant. Specifically, dedicated experimental tests were carried out with the final aim to find-out a constitutive relationship among operational costs (OCs), effluent quality index (EQI), effluent fines (EF). Greenhouse gas (GHG) emissions were also included in the study. Results showed that the EQI increases at low flow rate likely due to the dissolved oxygen (DO) limitation in the biological processes. Direct GHGs increase with the increasing of the air flow due to the anoxic N 2 O contribution. Irreversible membrane fouling reduce from 98% to 85% at the air flow rate of 0.57m 3 h -1 and 2.56m 3 h -1 , respectively. However, the increase of the air flow rate leads to the increase of the N 2 O-N flux emitted from the MBR (from 40% to 80%)., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

In this study a new mathematical model to quantify greenhouse gas emissions (namely, carbon dioxide and nitrous oxide) from membrane bioreactors (MBRs) is presented. The model has been adopted to predict the key processes of a pilot plant with pre-denitrification MBR scheme, filled with domestic and saline wastewater. The model was calibrated by adopting an advanced protocol based on an extensive dataset. In terms of nitrous oxide, the results show that an important role is played by the half saturation coefficients related to nitrogen removal processes and the model factors affecting the oxygen transfer rate in the aerobic and MBR tanks. Uncertainty analysis showed that for the gaseous model outputs 88-93% of the measured data lays inside the confidence bands showing an accurate model prediction., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

The paper reports the results of an experimental campaign carried out on a University of Cape Town (UCT) integrated fixed-film activated sludge (IFAS) membrane bioreactor (MBR) pilot plant. The pilot plant was analysed in terms of chemical oxygen demand (COD) and nutrients removal, kinetic/stoichiometric parameters, membrane fouling and sludge dewaterability. Moreover, the cultivable bacterial community structure was also analysed. The pilot plant showed excellent COD removal efficiency throughout experiments, with average value higher than 98%, despite the slight variations of the influent wastewater. The achieved nitrification efficiency was close to 98% for most of the experiments, suggesting that the biofilm in the aerobic compartment might have sustained the complete nitrification of the influent ammonia, even for concentrations higher than 100 mg L -1 . The irreversible resistance due to superficial cake deposition was the mechanism that mostly affected the membrane fouling. Moreover, it was noticed an increase of the resistance due pore blocking likely due to the increase of the EPS Bound fraction that could derive by biofilm detachment. The bacterial strains isolated from aerobic tank are wastewater bacteria known for exhibiting efficient heterotrophic nitrification-aerobic denitrification and producing biofilm., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

The present paper reports the results of a nitrous oxide (N 2 O) production investigation in a moving bed based integrated fixed film activated sludge (IFAS) membrane bioreactor (MBR) pilot plant designed in accordance with the University of Cape Town layout for biological phosphorous removal. Gaseous and liquid samples were collected in order to measure the gaseous as well as the dissolved concentration of N 2 O. Furthermore, the gas flow rate from each reactor was measured and the gas flux was estimated. The results confirmed that the anoxic reactor represents the main source of nitrous oxide production. A significant production of N 2 O was, however, also found in the anaerobic reactor, thus indicating a probable occurrence of the denitrifying phosphate accumulating organism activity. The highest N 2 O fluxes were emitted from the aerated reactors (3.09 g N 2 ON m -2  h -1 and 9.87 g N 2 ON m -2  h -1 , aerobic and MBR tank, respectively). The emission factor highlighted that only 1% of the total treated nitrogen was emitted from the pilot plant. Furthermore, the measured N 2 O concentrations in the permeate flow were comparable with other reactors. Nitrous oxide mass balances outlined a moderate production also in the MBR reactor despite the low hydraulic retention time. On the other hand, the mass balance showed that in the aerobic reactor a constant consumption of nitrous oxide (up to almost 15 mg N 2 O h -1 ) took place, due to the high amount of stripped gas., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

The joint effect of wastewater salinity and hydrocarbons on nitrous oxide emission was investigated. The membrane bioreactor pilot plant was operated with two phases: i. biomass acclimation by increasing salinity from 10gNaClL(-1) to 20gNaClL(-1) (Phase I); ii. hydrocarbons dosing at 20mgL(-1) with a constant salt concentration of 20gNaClL(-1) (Phase II). The Phase I revealed a relationship between nitrous oxide emissions and salinity. During the end of the Phase I, the activity of nitrifiers started to recover, indicating a partial acclimatization. During the Phase II, the hydrocarbon shock induced a temporary inhibition of the biomass with the suppression of nitrous oxide emissions. The results revealed that the oxic tank was the major source of nitrous oxide emission, likely due to the gas stripping by aeration. The joint effect of salinity and hydrocarbons was found to be crucial for the production of nitrous oxide., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

In this work, a sequential batch membrane bioreactor pilot plant is investigated to analyze the effect of a gradual increase in salinity on carbon and nutrient removal, membrane fouling and biomass kinetic parameters. The salinity was increased by 2gNaClL(-1) per week up to 10gNaClL(-1). The total COD removal efficiency was quite high (93%) throughout the experiment. A gradual biomass acclimation to the salinity level was observed during the experiment, highlighting the good recovery capabilities of the system. Nitrification was also influenced by the increase in salinity, with a slight decrease in nitrification efficiency (the lowest value was obtained at 10gNaClL(-1) due to lower nitrifier activity). Irreversible cake deposition was the predominant fouling mechanism observed during the experiment. Respirometric tests exhibited a stress effect due to salinity, with a reduction in the respiration rates observed (from 8.85mgO2L(-1)h(-1) to 4mgO2L(-1)h(-1))., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

The effect of a sharp variation of C/N ratio in a moving bed membrane bioreactor (MB-MBR) pilot plant treating high strength wastewater has been investigated. The experimental campaign was divided into two periods, each characterized by a different C/N ratio (namely, 2.5 and 15, Period 1 and Period 2, respectively). The MB-MBR system was analyzed in terms of organic carbon removal, nitrification efficiency, biokinetic activity and fouling behavior. The results showed that the nitrification process was severely affected by lower C/N value and by high concentration of ammonia. It was noticed an extensive stress effect on the autotrophic bacteria. Furthermore, it was observed an increase of the resistance related to particle deposition into membrane pores, likely due to a worsening of the cake layer features, with a reduction of the "pre-filter" effect, also related to the increase of the total Extracellular Polymeric Substances production with the C/N ratio., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

Two pilot plant systems were investigated for the treatment of wastewater subject to a gradual increase of salinity. In particular, a membrane bioreactor (MBR) and a moving bed biofilm membrane bioreactor (MB-MBR) were analyzed. Carbon and ammonium removal, kinetic constants and membranes fouling rates have been assessed. Both plants showed very high efficiency in terms of carbon and ammonium removal and the gradual salinity increase led to a good acclimation of the biomass, as confirmed by the respirometric tests. Significant biofilm detachments from carriers were experienced, which contributed to increase the irreversible superficial cake deposition. However, this aspect prevented the pore fouling tendency in the membrane module of MB-MBR system. On the contrary, the MBR pilot, even showing a lower irreversible cake deposition, was characterized by a higher pore fouling tendency., (Copyright © 2014 Elsevier Ltd. All rights reserved.)

In contraposition to conventional activated sludge processes, the foaming phenomenon in membrane bioreactor (MBR) is still in its infancy. On the other hand, although several studies have been carried out for better understanding the fouling phenomenon in MBR there are still some gaps in the up-to-date knowledge. The extracellular polymeric substances (EPSs) may have a primary role in fouling and foaming phenomena which in turn can be crucial for MBRs. The aim of this study is to detect a possible relationship that EPSs may have with fouling and foaming in an MBR for wastewater treatment. Foaming phenomenon is monitored by performing specific foam-tests: Foam Power, Scum Index, Foam Rating and filamentous abundance. Results show a high correlation between fouling vs EPS and foaming vs bound EPSs. A relationship between foaming and fouling was also found: in general, when foaming occurred the fouling rate decreases because the EPS bound remained trapped in the floating scum., (Copyright © 2013 Elsevier Ltd. All rights reserved.)

Membrane bioreactors (MBR) are being increasingly used for wastewater treatment. Mathematical modeling of MBR systems plays a key role in order to better explain their characteristics. Several MBR models have been presented in the literature focusing on different aspects: biological models, models which include soluble microbial products (SMP), physical models able to describe the membrane fouling and integrated models which couple the SMP models with the physical models. However, only a few integrated models have been developed which take into account the relationships between membrane fouling and biological processes. With respect to biological phosphorus removal in MBR systems, due to the complexity of the process, practical use of the models is still limited. There is a vast knowledge (and consequently vast amount of data) on nutrient removal for conventional-activated sludge systems but only limited information on phosphorus removal for MBRs. Calibration of these complex integrated models still remains the main bottleneck to their employment. The paper presents an integrated mathematical model able to simultaneously describe biological phosphorus removal, SMP formation/degradation and physical processes which also include the removal of organic matter. The model has been calibrated with data collected in a UCT-MBR pilot plant, located at the Palermo wastewater treatment plant, applying a modified version of a recently developed calibration protocol. The calibrated model provides acceptable correspondence with experimental data and can be considered a useful tool for MBR design and operation.

The paper presents the comparison between the traditional activated sludge system (AS) and a hybrid moving bed biofilm reactor (HMBBR). In particular, an experimental campaign has been carried out at the WWTP in Palermo (Italy), on a pilot plant consisting of two pre-anoxic schemes. The aerated tank of the HMBBR line was filled with suspended carriers (AnoxKaldnes K1), with a 30% filling ratio. The hydraulic load of the HMBBR line was increased up to two times the AS one. Further, in order to distinguish the additional contribution of the attached biomass for the HMBBR system, in the two lines the Mixed Liquor Suspended Solids (MLSS) was maintained as equal as possible. The monitoring period lasted three months during which several parameters were monitored. The obtained results showed a good treatment ability of the HMBBR system, referring to the organic matter removal as well as to the ammonium removal. In particular, in spite of the increase of the hydraulic load for the HMBBR line, the two systems showed a similar performance in terms of both organic and nitrogen removal. The results demonstrate the higher treatment capacity of the HMBBR addressing such system as an effective technology for the upgrading of overloaded wastewater treatment plants.

Over the last decade new technologies are emerging even more for wastewater treatment. Among the new technologies, a recent possible solution regards Moving Bed Biofilm Reactors (MBBRs) that represent an effective alternative to conventional processes. More specifically such systems consist in the introduction of plastic elements inside the aerobic reactor as carrier material for the growth of attached biomass. Recently, one of the mostly used alternatives is to couple the Moving Bed Biofilm Reactor (MBBR) process with the conventional activated sludge process, and the resulting process is usually called HMBBR (Hybrid MBBR). In the MBBR process the biofilm grows attached on small plastic elements that are kept in constant motion throughout the entire volume of the reactor. Indeed, in such a system, a competition between the two biomasses, suspended and attached, can arise for the availability of the substrates, leading, as a consequence, to a modification in the biokinetic parameters of the two biomasses, compared to that of a pure suspended or attached biomass process. This paper presents the first results of a study aimed at estimating the kinetic heterotrophic constants in a HMBBR pilot plant using respirometric techniques. The pilot plant was built at the Acqua dei Corsari (Palermo) wastewater treatment plant and consisted of two parallel lines realized in a pre-anoxic scheme, in one of which the carrier material was added to the aerobic reactor with a filling ratio of 30%.

Over the last few years there has been a growing attention regarding the receiving water body quality state. As a matter of a fact, the Directive 91/271 of the European Union (EU) replaced the "emission standard" concept that fixes discharge limits depending on polluting emission characteristics, with the "stream standard" concept that fixes discharge limits for each polluting substance depending on self-depurative characteristics of the RWB. In this context, several WWTPs need to be upgraded in order to meet stricter effluent limits. The need of WWTP upgrading was also emphasized by the growing urbanization that have led, in most cases, to get overloaded WWTP due to an overcoming of the maximum WWTP capacity. In order to upgrade existing WWTP basically two main possibilities can be chosen: building new tanks or modify the WWTP by introducing new technologies such as the HMBBR systems. In this paper, such latter possibility was explored and as a case study an existing Italian WWTP (Acqua dei Corsari) located in Palermo (IT) was analysed. The main goal was to test the effectiveness of HMBBR systems with respect to the WWTP upgrading. The survey was carried out by means of model simulation and an HMBBR pilot plant. This latter was employed for the evaluation of the model parameters as well as kinetic coefficients for the HMBBR. The model results are encouraging towards the WWTP upgrading by means of HMBBR. As a matter of fact, the model simulation results showed that the WWTP maximum capacity can be upgraded from 480,000 up to one million PE.

An integrated membrane bioreactor (MBR) model was previously proposed and tested. The model provides a comprehensive and detailed description of the nitrogen biological removal processes with respect to up-to-date literature. This paper presents a sensitivity and uncertainty analysis aimed at identifying the key factors affecting the variability of the model predictions. The Standardized Regression Coefficients (SRC) method was adopted for the sensitivity analysis. The uncertainty analysis was employed by running Monte Carlo simulations by varying only the value of the key factors affecting the model outputs. The sensitivity analysis combined with the uncertainty analysis applied here enabled to gain useful insights about the robustness of the model. By means of the SRC method 45 model factors (of 122) were selected as important. The results obtained here allowed to investigate the advantage of a detailed description of the nitrogen transformation bioprocesses (nitrification/denitrification) in terms of model accuracy and uncertainty bandwidth. The model allows to simulate the intermediate product during nitrification/denitrification, thus providing the possibility to control the nitrogen compounds that favour the formation of nitrous oxide. [ABSTRACT FROM AUTHOR]

This study aimed at evaluating the nitrous oxide (N2O) emissions from membrane bioreactors (MBRs) for wastewater treatment. The study investigated the N2O emissions considering multiple influential factors over a two-year period: (i) different MBR based process configurations; (ii) wastewater composition (municipal or industrial); (iii) operational conditions (i.e. sludge retention time, carbon-to-nitrogen ratio, C/N, hydraulic retention time); (iv) membrane modules. Among the overall analysed configurations, the highest N2O emission occurred from the aerated reactors. The treatment of industrial wastewater, contaminated with salt and hydrocarbons, provided the highest N2O emission factor (EF): 16% of the influent nitrogen for the denitrification/nitrification-MBR plant. The lowest N2O emission (EF = 0.5% of the influent nitrogen) was obtained in the biological phosphorus removal-moving bed-MBR plant likely due to an improvement in biological performances exerted by the co-presence of both suspended and attached biomass. The influent C/N ratio has been identified as a key factor affecting the N2O production. Indeed, a decrease of the C/N ratio (from 10 to 2) promoted the increase of N2O emissions in both gaseous and dissolved phases, mainly related to a decreased efficiency of the denitrification processes. [ABSTRACT FROM AUTHOR]

In this study a University of Cape Town (UCT) Integrated Fixed Film Activated Sludge (IFAS) Membrane BioReactor (MBR) wastewater treatment plant was monitored in terms of nitrous oxide (N 2 O) emissions. The short term effect on the N 2 O emission due to the influent carbon-to-nitrogen (C/N) ratio variation (C/N ratios of 2, 5 and 10 gCOD/gN) was evaluated. Since in a previous study, the effect of the C/N ratio was studied in the same system without biofilm (UCT-MBR configuration) the main aim here was to investigate the role of biofilms on N 2 O emissions. Under all the investigated C/N ratios, the N 2 O fluxes and the average emission factors were lower than that of previous studies with no biofilm presence. The total average N 2 O emission was 0.5% of the influent nitrogen with biofilm (IFAS system) and 3.5% without biofilm. This result emphasizes the potential role of the biofilms in attenuating the N 2 O emissions especially in the case of stress conditions (i.e., low C/N influent ratios). An increase of N 2 O flux from the anoxic reactor (till 28 mgN 2 O m −2 h −1 ) occurred at the lowest influent C/N tested (2 gCOD/gN - phase III). At C/N equal to 2 gCOD/gN the anoxic reactor was the main source of N 2 O, contributing 45% of all produced N 2 O. This result was attributed to an incomplete denitrification caused by a lack of organic carbon and a slight increase of dissolved oxygen concentration. [ABSTRACT FROM AUTHOR]

A comprehensive integrated membrane bioreactor (MBR) model for wastewater treatment is here proposed. The model quantifies the main biological and physical processes. The model describes the biological removal of organic matter, nitrogen and phosphorus including greenhouse gases (carbon dioxide, CO 2 and nitrous oxide, N 2 O). The model takes into account the following main innovative aspects jointly: i. Two-step nitrification process; ii. N 2 O formation due to ammonia-oxidizing bacteria as a product of the hydroxylamine oxidation (NH 2 OH) and of the nitrite (NO 2 − ) reduction; iii. Soluble microbial product (SMP) formation/degradation due to microbial growth and endogenous respiration; iv. Interlink between SMP and membrane fouling. The model was calibrated by employing a detailed calibration protocol and data from a University Cape Town (UCT) – MBR pilot plant. The key processes contributing to the N 2 O formation were properly described (total efficiency related to the calibrated model equal to 0.55). Results suggested that the incomplete hydroxylamine oxidation and the heterotrophic denitrification were the predominant processes influencing the N 2 O production. The model was able to describe the membrane fouling as demonstrated by the high efficiency (0.92) for the resistance state variable. This result confirms the importance in the modelling approach of considering both biological and physical processes jointly. [ABSTRACT FROM AUTHOR]

The aim of the present paper was to investigate the effect of solids (SRT) and hydraulic (HRT) retention time on Integrated Fixed Film Activated Sludge (IFAS) University of Cape Town (UCT) membrane Bioreactor (MBR). In particular, three different pairs of SRT and HRT values were analysed, namely, Phase I 56 d/30 h, Phase II 31 d/15 h and Phase III 7 d/13 h. The short-term effect of these three SRT/HRT conditions was assessed by analysing several system performance indicators: organic carbon and biological nutrient (nitrogen and phosphorus) removal, biomass respiratory activity, activated sludge filtration properties and membrane fouling. The results showed that the decrease of SRT/HRT had a positive influence on system performance. Specifically, the IFAS-UCT-MBR showed excellent removal of organic matter - highest value (99%) at the shortest SRT/HRT (7 d/13 h). Also, the increase in organic loading rate resulting from the decrease of SRT and HRT led to improved nitrogen removal due to higher N removal by sludge wasting requiring less N removal (as N 2 ) by denitrification. Complete nitrification of influent ammonia was achieved at all three SRT/HRT phases, guaranteed by the presence of biofilm carriers in the aerobic reactor, which ensured a higher media SRT than suspended biomass SRT. The increase of the organic loading rate and decrease in SRT led also to a higher heterotrophic activity as demonstrated by the respirometric batch tests, which is due to the increasing active biomass fraction of the volatile suspended solids as SRT decreases. The SRT/HRT decrease over the three phases resulted in an overall increase of the Extracellular Polymeric Substance concentration, which caused an increase in membrane fouling. [ABSTRACT FROM AUTHOR]

The influence of the main operational variables on N 2 O emissions from an Integrated Fixed Film Activated Sludge University of Cape Town membrane Bioreactor pilot plant was studied. Nine operational cycles (total duration: 340 days) were investigated by varying the value of the mixed liquor sludge retention time (SRT) (Cycles 1–3), the feeding ratio between carbon and nitrogen (C/N) (Cycles 4–6) and simultaneously the hydraulic retention time (HRT) and the SRT (Cycles 7–9). Results show a huge variability of the N 2 O concentration in liquid and off-gas samples (ranged from 10 −1 μg N 2 O-N L −1 to 10 3 μg N 2 O-N L −1 ). The maximum N 2 O concentration (1228 μg N 2 O-N L −1 ) in the off-gas samples occurred in the anoxic reactor at the lowest C/N value confirming that unbalanced C/N promotes the N 2 O emission during denitrification. The aerated reactors (aerobic and MBR) have been the major N 2 O emitters during all the three Phases. [ABSTRACT FROM AUTHOR]

The effect of the carbon-to-nitrogen (C/N) ratio in the influent on the nitrous oxide (N 2 O) emission from a University of Cape Town Membrane BioReactor pilot plant was investigated. The membrane was located in a separate tank to single out the production of N 2 O due to the biological processes from N 2 O stripping as a result of the extra aeration needed for the mitigation of membrane fouling. The experimental campaign was divided into two phases, each characterized by a different C/N ratio (namely, 10 and 5 mgCOD/mgTN, Phase I and Phase II, respectively). The decrease of the C/N ratio promoted the increase of N 2 O emissions in both gaseous and dissolved phases, mainly due to a decreased nitrification/denitrification capacity of the system. The highest N 2 O concentration in the dissolved phase was found in the permeate. This result suggests that the dissolved N 2 O in the permeate stream discharged from a MBR cannot be neglected. The total N 2 O emission was approximately of 0.01% and 0.1% of the total influent nitrogen load for the Phase I and Phase II, respectively. The findings suggest that the C/N ratio represents an indirect cause of N 2 O emission; the low C/N value (Phase II) led to the increase of pH and free ammonia causing a stress effect on the growth of nitrifying species increasing the N 2 O emission. [ABSTRACT FROM AUTHOR]

The paper reports the main results of an experimental campaign carried out on two bench scale pilot plants for the treatment of synthetic shipboard slops. In particular, two membrane bioreactors (MBRs) with submerged configuration were analyzed. One MBR pilot plant (namely, Line A) was fed with synthetic shipboard slop and was subjected to a gradual increase of salinity. Conversely, the second MBR pilot plant (namely, Line B) was fed with the same synthetic shipboard slop but without salt addition, therefore operating as a “control” unit. Organic carbon, hydrocarbons and ammonium removal, kinetic constants, extracellular polymeric substances (EPSs) production and membranes fouling rates have been assessed. The observed results highlighted a stress effect exerted by salinity on the biological performances, with lower removal efficiencies in the Line A compared to Line B. Significant releases of soluble EPS in Line A promoted an increase of the resistance related to particle deposition into membrane pores (pore fouling tendency), likely due to a worsening of the mixed liquor features. Such a condition enhanced the reduction of the “pre-filter” effect of the cake layer. [ABSTRACT FROM AUTHOR]

The effect of the carbon-to-nitrogen (C/N) ratio variation in a University of Cape Town Membrane bioreactor (UCT-MBR) was investigated. The experimental campaign was divided into two phases, each characterized by a different C/N ratio (namely, 10 and 5, Phase I and Phase II, respectively). The UCT-MBR pilot plant was analysed in terms of carbon and nutrients removal, biomass respiratory activity, activated sludge features and membrane fouling. The results highlighted that the nutrients removal was significantly affected by the decrease of the C/N ratio during the Phase II. The biological carbon removal was also affected by the low C/N value during the Phase II. Indeed, the average biological COD removal efficiency was equal to 72.9% during the Phase II, while the average value was 82.8% in the Phase I. The respirometric batch test suggested that both heterotrophic and autotrophic species were severely affected by the lower C/N ratio in the Phase II. Moreover, a decrease of the membrane filtration properties was observed during the Phase II, mainly due to the worsening of the activated sludge features, which enhanced the increase of SMP production. [ABSTRACT FROM AUTHOR]

The paper reports the main results of an experimental campaign performed on a membrane bioreactor pilot plant designed to treat synthetic shipboard slops. The experimental campaign was divided into two phases: salinity acclimation up to 20 g NaCl L −1 (Phase I) and hydrocarbon (diesel fuel) dosing (Phase II). The observed results show that the carbon removal was not severely affected by the wastewater features. Conversely, respirometric tests showed that nitrification was strongly affected by the salinity (33% of nitrification efficiency at 20 g NaCl L −1 – Phase I) as a result of the salinity in the autotrophic biomass. Moreover, the sludge viscosity increased during Phase II due to the wastewater composition, leading to an increase in the membrane resistance, and severe degradation of the sludge dewaterability was also observed. Indeed, the capillary suction time increased by a factor of 3 times compared with that of Phase I. [ABSTRACT FROM AUTHOR]

Sensitivity and uncertainty analysis, although can be of primarily importance in mathematical modelling approaches, are scarcely applied in the field of membrane bioreactor (MBR). An integrated mathematical model for MBR is applied with the final aim to pin down sources of uncertainty in MBR modelling. The uncertainty analysis has been performed combining global sensitivity analysis (GSA) with the generalized likelihood uncertainty estimation (GLUE). The model and methodology were applied to a University Cape Town pilot plant. Results show that the complexity of the modelled processes and the propagation effect from the influent to the effluent increase the uncertainty of the model prediction. It was found that the uncertainty of nitrogen and phosphorus model outputs increases from the first reactor-section plant to the last. Results show also that the GSA-GLUE methodology is a valid tool for uncertainty assessment for MBR modelling. Furthermore, the GSA-GLUE allows to identify the most critical processes/plant sections and the key sources of uncertainty where attention should be paid in view of model predictions improvement. [ABSTRACT FROM PUBLISHER]

A new mathematical model able to quantify greenhouse gas (GHG) emissions in terms of carbon dioxide (CO 2 ) and nitrous oxide (N 2 O) for a Membrane Bioreactor (MBR) is presented. The proposed mathematical model is of the Activated Sludge Model (ASM) family and takes into account simultaneously both biological and physical processes (e.g., membrane fouling). An analysis of the key factors and sources of uncertainty influencing GHG emissions is also presented. Specifically, the standardized regression coefficient, the Extended-FAST and a Monte Carlo based method are employed for assessing model factors which influence three performance indicators: effluent quality index, operational costs and GHGs. Model factors are classified as important, non-influential and interacting. The model is applied to a University Cape Town–MBR pilot plant which was object of an extensive field gathering campaign. The results reveal that model factors related to nitrogen transformation and membrane separation processes play a central role in the uncertainty of GHG estimation. Model factors that are associated with physical processes exhibit large first-order and total-order effects, which emphasises the importance of a holistic approach that jointly considers biological and physical processes. Furthermore, the membrane has a key role in GHG emissions as a result of the cake layer thickness which in turns influences the mass of substrate retained by the membrane and, thus, the biological process in the MBR. The results show that a modeller should not exclude the role of phosphorus in the contribution of accumulating organisms during the prediction of GHGs due to the high interaction of N 2 O. The results reveal that the uncertainty in the emission factors for CO 2 is higher than the uncertainty in the emission factors for N 2 O (namely, 2.2 and 0.17%, respectively). [ABSTRACT FROM AUTHOR]

Abstract: Three global sensitivity analysis (GSA) methods are applied and compared to assess the most relevant processes occurring in wastewater treatment systems. In particular, the Standardised Regression Coefficients, Morris Screening and Extended-FAST methods are applied to a complex integrated membrane bioreactor (MBR) model considering 21 model outputs and 79 model factors. The three methods are applied with numerical settings as suggested in literature. The main objective considered is to classify important factors (factors prioritisation) as well as non-influential factors (factors fixing). The performance is assessed by comparing the most reliable method (Extended-FAST), by means of proposed criteria, with the two other methods. In particular, similarity to results obtained from Extended-FAST is assessed for sensitivity indices, for the ranking of sensitivity indices, for the classification into important/non-influential factors and for the method's ability to detect interaction among factors and to provide results in a reasonable time. It was found that the computationally less expensive SRC method was applied outside its range of applicability (R 2) = (0.3–0.6) < 0.7. Still, the SRC produced a ranking of important factors similar to Extended-FAST. For some variables significant interactions among the factors were revealed by computing the total effect indices STi using Extended-FAST. This means that to obtain reliable variance decomposition and to detect and quantify interactions among the factors, the use of the Extended-FAST is recommended. Regarding the comparison between Morris screening and Extended-FAST a poor agreement was found. In particular, the Morris screening overestimated the number of both important and non-influential factors compared to Extended-FAST for the analysed case study. [Copyright &y& Elsevier]

Abstract: Membrane fouling represents one of the major issues for a membrane bioreactor (MBR). Membrane fouling and high aeration requirements (for inducing shear stress to limit fouling) make MBR operation economically demanding due to high energy costs. Although several studies on MBR fouling have been performed, comprehensive knowledge on how to reduce membrane fouling and consequently save energy is still lacking. An integrated mathematical model for MBR is applied to a University of Cape Town membrane bioreactor with the final aim to reduce the energy costs. In particular, the influence of the aeration intensity, the duration of filtration/backwashing cycles, and the number of membrane cleanings are investigated. Five scenarios are analyzed and compared, each implementing different operating conditions. The features of the analyzed scenarios are quantified by employing Monte Carlo simulations and performance indices partially drawn from literature. The results provide insights about the role played by the main physical/chemical/biological processes in view of a system optimization. As expected, MBR operation at low air flow rate (qa) leads to a substantial reduction of the operational costs (specifically, 20% with respect to the suggested manufacturers ones in terms of qa). Despite such a reduction of qa, a good effluent quality is also obtained as an effect of a high biological cake thickness. Results also show that the values of filtration time (Tf) higher than those suggested by manufacturers (e.g., Tf=9min) can be used to increase effluent quality. This study demonstrates that both energy savings and effluent quality can be improved by varying the operational variables with respect to those of the suggested manufacture. One of the main insights gained from this study is that the values of the operating variables (i.e., qa, Tb and Tf) suggested by the manufactures can be changed to obtain a system that still respects high effluent quality and is characterized by lower economical cost. The proposed modeling approach can be an useful tool for the optimization of the operating conditions in order to reduce the operational costs for MBR systems. [Copyright &y& Elsevier]

Abstract: The performance of a membrane bioreactor (MBR), and mechanisms of fouling formation, may differ due to the start-up. Therefore, the start-up can constitute an aspect that critically influences MBR performance during its lifespan. Indeed, the start-up can influence the mechanisms of membrane fouling, which is of paramount importance in an MBR. In order to gain insights on the effects of the start-up, both experimental and mathematical modelling studies were carried out on an MBR pilot plant. The MBR pilot plant constituted of a hollow fibre membrane module, in a submerged configuration, was fed by real wastewater. Two experimental periods were carried out, lasting 65 days each, characterised by two different MBR start-ups: without inoculum of activated sludge, and with inoculum of activated sludge. An integrated MBR mathematical model was applied to the two periods in order to combine the insights gained from the experimental survey. The MBR model simulates both biological and physical processes simultaneously, taking into account the interactions between them. Two MBR model calibrations were carried out for the two different experimental start-ups. Model calibration was carried out by means of an innovative calibration protocol, based on the global sensitivity analysis, and the Generalised Likelihood Uncertainty Estimation. Thus, two sets of model parameters were assessed and compared. Both experimental and mathematical model results were analysed to quantify the effects of the two start-ups on membrane fouling. The results showed only slight differences in terms of total pollutant removal efficiency. However, relevant differences appeared with respect to the fouling phenomenon between the two start-ups. The results demonstrated that the best choice, in terms of the start-up of MBR systems, comes from a compromise between minimisation of the fouling issues and high system performance. [Copyright &y& Elsevier]

Abstract: A mathematical model for the simulation of physical-biological organic removal by means of a membrane bioreactor (MBR) has been previously developed and tested. This paper presents an analysis of the uncertainty of the MBR model. Particularly, the research explores the applicability of the Generalised Likelihood Uncertainty Estimation (GLUE) methodology that is one of the most widely used methods for investigating the uncertainties in the hydrology and that now on is spreading in other research field. For the application of the GLUE methodology, several Monte Carlo simulations have been run varying the all model influential parameters simultaneously. The model was applied to an MBR pilot plant located at the Acqua dei Corsari WWTP (Palermo, IT) where water quality data were gathered. In particular, the MBR pilot plant consists of a lab-scale hollow fibre membrane module in submerged configuration. The GLUE methodology enabled us to gain useful insight about the robustness of the model approach. Particularly, the results showed that the biological process is influenced mainly by the parameters characterising the formation and degradation of Soluble Microbial Products, whereas the fouling phenomenon is mainly influenced by the backwashing efficiency. The application of the GLUE methodology shows that the model considered for the MBR simulation is somehow too simple in order to predict plants performances. Indeed, GLUE enabled us to identify the main model components that needs to be improved and where much attention has to be paid both in terms of model algorithms and quality data to be gathered. This studies confirmed the suitability of the GLUE methodology as a powerful tool for simplified screening methodology to assess the uncertainty also in the field of wastewater treatment. [ABSTRACT FROM AUTHOR]

Over the last decade new technologies are emerging even more for wastewater treatment. Among the new technologies, a recent possible solution regards Moving Bed Biofilm Reactors (MBBRs) that represent an effective alternative to conventional processes. More specifically such systems consist in the introduction of plastic elements inside the aerobic reactor as carrier material for the growth of attached biomass. Recently, one of the mostly used alternatives is to couple the Moving Bed Biofilm Reactor (MBBR) process with the conventional activated sludge process, and the resulting process is usually called HMBBR (Hybrid MBBR). In the MBBR process the biofilm grows attached on small plastic elements that are kept in constant motion throughout the entire volume of the reactor. Indeed, in such a system, a competition between the two biomasses, suspended and attached, can arise for the availability of the substrates, leading, as a consequence, to a modification in the biokinetic parameters of the two biomasses, compared to that of a pure suspended or attached biomass process. This paper presents the first results of a study aimed at estimating the kinetic heterotrophic constants in a HMBBR pilot plant using respirometric techniques. The pilot plant was built at the Acqua dei Corsari (Palermo) wastewater treatment plant and consisted of two parallel lines realized in a pre-anoxic scheme, in one of which the carrier material was added to the aerobic reactor with a filling ratio of 30%. [ABSTRACT FROM AUTHOR]

Abstract: The paper presents the setting up of a mathematical model for membrane bioreactor able to simulate physical-biological wastewater organic removal. The model is basically divided into two sub-models: the first sub-model is basically devoted for the simulation of the biological features and the second one for the physical processes. In particular regarding the biological aspects, the ASM concept has been employed. On the other hand, the physical processes have been modelled considering the deep-bed theory taking into account not only the effect of the physical membrane filtration but also the cake layer effect. This latter operates as a biological membrane leading to a further reduction of the effluent COD. The model was applied to a SMBR pilot plant characterized by hollow fibre membrane module in submerged configuration. The SMBR was fed by raw wastewater collected from the Palermo (IT) WWTP and it was in operation for a total period of 130 days. During the whole experimentation the TSS was maintained meanly constant with periodic sludge withdrawal, in order to analyse the role of cake layer on organic removal. The model results are interesting and confirm the importance of cake deposition in the filtration process. The developed model can be employed as a useful tool in optimizing operation conditions as well as design issues for SMBR systems. [Copyright &y& Elsevier]

[Display omitted] • A literature review on integrated MBR modelling and control is presented. • The use of integrated MBR models should be more encouraged. • A new framework was proposed to pursue good practice for MBR modelling. • Integrated MBR modelling applications to real case studies is needed. Integrated Membrane Bioreactor (MBR) models, combination of biological and physical models, have been representing powerful tools for the accomplishment of high environmental sustainability. This paper, produced by the International Water Association (IWA) Task Group on Membrane Modelling and Control, reviews the state-of-the-art, identifying gaps for future researches, and proposes a new integrated MBR modelling framework. In particular, the framework aims to guide researchers and managers in pursuing good performances of MBRs in terms of effluent quality, operating costs (such as membrane fouling, energy consumption due to aeration) and mitigation of greenhouse gas emissions. [ABSTRACT FROM AUTHOR]

• Comparison between conventional activated sludge (CAS) and membrane bioreactor (MBR) • Higher indirect greenhouse gas emissions (GHG) for MBR than CAS. • Influent carbon to nitrogen ratio influences nitrification in MBRs. • In MBR the membrane aeration favors the stripping of dissolved GHG. • MBR energy consumption higher than CAS. A comprehensive plant-wide mathematical modelling comparison between conventional activated sludge (CAS) and Membrane bioreactor (MBR) systems is presented. The main aim of this study is to highlight the key features of CAS and MBR in order to provide a guide for an effective plant operation. A scenario analysis was performed to investigate the influence on direct and indirect greenhouse gas (GHG) emissions and operating costs of (i) the composition of inflow wastewater (scenario 1), (ii) operating conditions (scenario 2) and (iii) oxygen transfer efficiency (scenario 3). Scenarios show higher indirect GHG emissions for MBR than CAS, which result is related to the higher energy consumption in MBR. The simultaneous variation of the investigated factors (scenario 4) exacerbates direct and indirect GHG emissions for both CAS and MBR. Indeed, during scenario 4 a maximum direct GHG emissions of 0.94 kgCO 2eq m−3 and 1.56 kgCO 2eq m−3 for CAS and MBR, respectively, was obtained. [ABSTRACT FROM AUTHOR]

Abstract: Over the last two decades, Membrane Bioreactors (MBRs) emerged even more for wastewater treatment, ensuring high removal efficiencies as well as very small footprint requirements. Indeed, in this kind of process, a modification in biomass activity and viability can exist compared to that of a CAS process. In this context, respirometric analysis represents a reliable tool in order to evaluate the actual biomass kinetic parameters, to insert in mathematical models in the design phase, as well as to monitor the biomass viability, especially when these processes are operated with high SRT values. The paper presents some results of respirometric techniques applied for the characterisation of wastewater and biomass activity in a pilot UCT-MBR plant for nutrient removal, operating with high SRT. In particular, the respirometric tests were specifically aimed at investigating heterotrophic and autotrophic bacterial activity. The pilot plant was built at Palermo WWTP and consisted of three reactors: anaerobic, anoxic and aerobic, followed by an aerobic compartment containing two submerged hollow fibre membrane modules with typical recycling lines. The kinetic parameters for heterotrophic bacteria resulted lower respect to the CAS; regarding the nitrifying bacteria, the kinetic constants were in the range of CAS, suggesting a good nitrification activity. [Copyright &y& Elsevier]