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This paper presents a study on reducing sewage sludge by an oxic-settling-anaerobic (OSA) pilot plant compared to the conventional activated sludge (CAS) process in view of resource recovery and moving towards plant carbon neutrality. The OSA plant was supplied with real wastewater and the anaerobic reactor was operated under two hydraulic retention times (HRT) (4 and 6 h). Greenhouse gas (GHG) emissions were monitored for the first time to determine the OSA process's production mechanism. The results highlighted that under the lowest HRT (4 h), the removal efficiencies of COD and PO 4 - P, increased from 75 to 89% and from 39 to 50% for CAS and OSA configurations, respectively. The observed yield coefficient was reduced from 0.58 gTSS gCOD -1 (CAS period) to 0.31 gTSS gCOD -1 (OSA period). A remarkable deterioration of nitrification efficiency under OSA configuration was obtained from 79% (CAS) to 27% (OSA with HRT of 6 h). The huge deterioration of nitrification significantly affected the GHG emissions, with the N 2 O-N fraction increasing from 1% (CAS) to 1.55% (OSA 4 h HRT) and 3.54% (OSA 6 h HRT) of the overall effluent nitrogen, thus suggesting a relevant environmental implication due to the high global warming potential (GWP) of N 2 O., (© 2024. The Author(s).)

Chemical absorption-biological reduction based on Fe(II)EDTA is a promising technology to remove nitric oxide (NO) from flue gases. However, limited effort has been made to enable direct energy recovery from NO through production of nitrous oxide (N 2 O) as a potential renewable energy rather than greenhouse gas. In this work, the enhanced energy recovery in the form of N 2 O via biological NO reduction was investigated by conducting short-term and long-term experiments at different Fe(II)EDTA-NO and organic carbon levels. The results showed both NO reductase and N 2 O reductase were inhibited at Fe(II)EDTA-NO concentration up to 20 mM, with the latter being inhibited more significantly, thus facilitating N 2 O accumulation. Furthermore, N 2 O accumulation was enhanced under carbon-limiting conditions because of electron competition during short-term experiments. Up to 47.5% of NO-N could be converted to gaseous N 2 O-N, representing efficient N 2 O recovery. Fe(II)EDTA-NO reduced microbial diversity and altered the community structure toward Fe(II)EDTA-NO-reducing bacteria-dominated culture during long-term experiments. The most abundant bacterial genus Pseudomonas , which was able to resist the toxicity of Fe(II)EDTA-NO, was significantly enriched, with its relative abundance increased from 1.0 to 70.3%, suggesting Pseudomonas could be the typical microbe for the energy recovery technology in NO-based denitrification.

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.)

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 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.)

Abstract 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. Graphical abstract Image Highlights • A full comparison of UCT-MBR vs IFAS-UCT-MBR is reported. • Two COD/N ratios were investigated in both systems. • IFAS-UCT-MBR configuration provided the best pollutant removal efficiency. • IFAS-UCT-MBR configuration showed lower N 2 O emission. • A greater tendency of membrane fouling was noticed for the IFAS system. [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]

Abstract: Biological nutrient removal was operated at different solids (SRT) and hydraulic retention times (HRT) in order to assess their influence on nitrous oxide (N2O) emission from a hybrid moving‐bed membrane bioreactor. The observed results show that the N2O production decreased when the SRT/HRT was decreased. The maximum N2O gaseous concentration was measured in the aerobic reactor at the end of phase I, and it decreased through phases II and III. From mass balances over the reactors of the system, the aerated (aerobic and membrane) reactors were the largest producers of N2O, showing that the greater part of N2O was produced during the nitrification process. [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]

This paper presents the sensitivity and uncertainty analysis of a mathematical model for greenhouse gas emission (GHG) and energy consumption assessment in wastewater treatment plants. A sensitivity analysis was carried out (using two different methods) to determine which model factors have the greatest effect on the predicted values of the GHG production. Further, an uncertainty analysis was carried out to quantify the uncertainty of the key model outputs, such as carbon dioxide production from activated sludge treatment. The results show that influent fractionation factors, which characterize influent composition, have an important role on direct and indirect GHGs production and emission. Moreover, model factors related to the aerobic biomass growth show a relevant influence on GHGs in terms of emission from off-site power generation (mCO2eq;PG). Further, model factors related to the autotrophic biomass growth were found to strongly interact with other factors especially in modeling mCO2eq;PG. Finally, nitrous oxide (N2O) emission associated with the effluent has the highest uncertainty, suggesting the need for a mechanistic model for N2O production in biological treatment. [ABSTRACT FROM AUTHOR]

Nitrous oxide, carbon dioxide and methane are greenhouse gases (GHG) emitted from wastewater treatment that contribute to its carbon footprint. As a result of the increasing awareness of GHG emissions from wastewater treatment plants (WWTPs), new modelling, design, and operational tools have been developed to address and reduce GHG emissions at the plant-wide scale and beyond. This paper reviews the state-of-the-art and the recently developed tools used to understand and manage GHG emissions from WWTPs, and discusses open problems and research gaps. The literature review reveals that knowledge on the processes related to N 2 O formation, especially due to autotrophic biomass, is still incomplete. The literature review shows also that a plant-wide modelling approach that includes GHG is the best option for the understanding how to reduce the carbon footprint of WWTPs. Indeed, several studies have confirmed that a wide vision of the WWPTs has to be considered in order to make them more sustainable as possible. Mechanistic dynamic models were demonstrated as the most comprehensive and reliable tools for GHG assessment. Very few plant-wide GHG modelling studies have been applied to real WWTPs due to the huge difficulties related to data availability and the model complexity. For further improvement in GHG plant-wide modelling and to favour its use at large real scale, knowledge of the mechanisms involved in GHG formation and release, and data acquisition must be enhanced. [ABSTRACT FROM AUTHOR]

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]

The aim of this work was to study the effect of organic loading rate on the production of Polyhydroxyalkanoates (PHA) from sewage sludge. Synthesis of PHA using sewage sludge as platform was achieved in this work. Three pilot-scale selection-sequencing batch reactors (S-SBR) were used for obtaining a culture able to accumulate PHA following a strategy of aerobic dynamic feeding (ADF) at different volumetric organic-loading-rate (vOLR): 1.3, 1.8 and 0.8 g COD L−1 d−1 for S-SBR 1, S-SBR 2 and S-SBR 3, respectively. Decreasing the vOLR enhanced the general performance of the process as for organic matter removal (from 99.2% ± 0.3% in S-SBR-3 to 92 ± 2 in S-SBR-2) while the opposite trend was recorded for PHA production (6.0 PHA % w/w in S-SBR-3 vs 13.7 PHA % w/w in S-SBR-2 at the end of the feast phase). Furthermore, indirect and direct emissions, as N2O, were evaluated during the process for the first time. Finally, three accumulation tests were performed achieving 24% w/w. [Display omitted] • Effect of different OLR in MMC selection was studied. • OLR influenced F/F and PHA storage yield. • Low OLR enhance reactor's performance. • Higher OLR enhanced PHA production (13% w/w at the end of the feast). • Indirect GHG were higher than direct. [ABSTRACT FROM AUTHOR]