Adrian Oehmen

Modeling the PAO–GAO competition: Effects of carbon source, pH and temperature

The influence of different carbon sources (acetate to propionate ratios), temperature and pH levels on the competition between polyphosphate- and glycogen-accumulating organisms (PAO and GAO, respectively) was evaluated using a metabolic model that incorporated the carbon source, temperature and pH dependences of these microorganisms. The model satisfactorily described the bacterial activity of PAO (Accumulibacter) and GAO (Competibacter and Alphaproteobacteria-GAO) laboratory-enriched cultures cultivated on propionate (HPr) and acetate (HAc) at standard conditions (20 degrees C and pH 7.0). Using the calibrated model, the effects of different influent HAc to HPr ratios (100-0, 75-25, 50-50 and 0-100%), temperatures (10, 20 and 30 degrees C) and pH levels (6.0, 7.0 and 7.5) on the competition among Accumulibacter, Competibacter and Alphaproteobacteria-GAO were evaluated. The main aim was to assess which conditions were favorable for the existence of PAO and, therefore, beneficial for the biological phosphorus removal process in sewage treatment plants. At low temperature (10 degrees C), PAO were the dominant microorganisms regardless of the used influent carbon source or pH. At moderate temperature (20 degrees C), PAO dominated the competition when HAc and HPr were simultaneously supplied (75-25 and 50-50% HAc to HPr ratios). However, the use of either HAc or HPr as sole carbon source at 20 degrees C was not favorable for PAO unless a high pH was used (7.5). Meanwhile, at higher temperature (30 degrees C), GAO tended to be the dominant microorganisms. Nevertheless, the combined presence of acetate and propionate in the influent (75-25 and 50-50% HAc to HPr ratios) as well as a high pH (7.5) appear to be potential factors to favor the metabolism of PAO over GAO at higher sewage temperature (30 degrees C).

The role of nitrite and free nitrous acid (FNA) in wastewater treatment plants

Nitrite is known to accumulate in wastewater treatment plants (WWTPs) under certain environmental conditions. The protonated form of nitrite, free nitrous acid (FNA), has been found to cause severe inhibition to numerous bioprocesses at WWTPs. However, this inhibitory effect of FNA may possibly be gainfully exploited, such as repressing nitrite oxidizing bacteria (NOB) growth to achieve N removal via the nitrite shortcut. However, the inhibition threshold of FNA to repress NOB (∼0.02 mg HNO2-N/L) may also inhibit other bioprocesses. This paper reviews the inhibitory effects of FNA on nitrifiers, denitrifiers, anammox bacteria, phosphorus accumulating organisms (PAO), methanogens, and other microorganisms in populations used in WWTPs. The possible inhibition mechanisms of FNA on microorganisms are discussed and compared. It is concluded that a single inhibition mechanism is not sufficient to explain the negative impacts of FNA on microbial metabolisms and that multiple inhibitory effects can be generated from FNA. The review would suggest further research is necessary before the FNA inhibition mechanisms can be more effectively used to optimize WWTP bioprocesses. Perspectives on research directions, how the outcomes may be used to manipulate bioprocesses and the overall implications of FNA on WWTPs are also discussed.

Photodegradation kinetics and transformation products of ketoprofen, diclofenac and atenolol in pure water and treated wastewater

Pharmaceutical compounds such as ketoprofen, diclofenac and atenolol are frequently detected at relatively high concentrations in secondary effluents from wastewater treatment plants. Therefore, it is important to assess their transformation kinetics and intermediates in subsequent disinfection processes, such as direct ultraviolet (UV) irradiation. The photodegradation kinetics of these compounds using a medium pressure (MP) lamp was assessed in pure water, as well as in filtered and unfiltered treated wastewater. Ketoprofen had the highest time- and fluence-based rate constants in all experiments, whereas atenolol had the lowest values, which is consistent with the corresponding decadic molar absorption coefficient and quantum yield. The fluence-based rate constants of all compounds were evaluated in filtered and unfiltered wastewater matrices as well as in pure water. Furthermore, transformation products of ketoprofen, diclofenac and atenolol were identified and monitored throughout the irradiation experiments, and photodegradation pathways were proposed for each compound. This enabled the identification of persistent transformation products, which are potentially discharged from WWTP disinfection works employing UV photolysis.

Assessing the removal of pharmaceuticals and personal care products in a full-scale activated sludge plant

PurposeThis study aimed to investigate the removal mechanisms of pharmaceutical active compounds (PhACs) and musks in a wastewater treatment plant (WWTP). Biological removal and adsorption in the activated sludge tank as well as the effect of UV radiation used for disinfection purposes were considered when performing a mass balance on the WWTP throughout a 2-week sampling campaign.MethodsSolid-phase extraction (SPE) was carried out to analyse the PhACs in the influent and effluent samples. Ultrasonic solvent extraction was used before SPE for PhACs analysis in sludge samples. PhAC extracts were analysed by LC-MS. Solid-phase microextraction of liquid and sludge samples was used for the analysis of musks, which were detected by GC-MS. The fluxes of the most abundant compounds (13 PhACs and 5 musks) out of 79 compounds studied were used to perform the mass balance on the WWTP.ResultsResults show that incomplete removal of diclofenac, the compound that was found in the highest abundance, was observed via biodegradation and adsorption, and that UV photolysis was the main removal mechanism for this compound. The effect of adsorption to the secondary sludge was often negligible for the PhACs, with the exceptions of diclofenac, etofenamate, hydroxyzine and indapamide. However, the musks showed a high level of adsorption to the sludge. UV radiation had an important role in reducing the concentration of some of the target compounds (e.g. diclofenac, ibuprofen, clorazepate, indapamide, enalapril and atenolol) not removed in the activated sludge tank.ConclusionsThe main removal mechanism of PhACs and musks studied in the WWTP was most often biological (45%), followed by adsorption (33%) and by UV radiation (22%). In the majority of the cases, the WWTP achieved >75% removal of the most detected PhACs and musks, with the exception of diclofenac.

Analysis of 65 pharmaceuticals and personal care products in 5 wastewater treatment plants in Portugal using a simplified analytical methodology

Pharmaceuticals and personal care products (PPCPs) are becoming increasingly recognised as important micropollutants to be monitored in wastewater treatment plants (WWTPs), since WWTP effluents represent an important point source to natural aquatic systems. In this study, the abundance of 65 PPCPs was analysed in 5 Portuguese WWTPs during the spring and autumn. Due to the fact that analytical approaches normally used to quantify the abundance of these compounds are labour intensive and require various specific procedures, this study proposes a set of simplified analytical methods for the quantification of pharmaceutically active compounds (PhACs) and polycyclic musks in liquid and sludge samples. The analytical methods were validated using influent wastewater matrices, showing comparable limits of detection and quantification as literature values for most PPCPs, with the exception of the estrogenic compounds. The PhAC concentrations detected in the WWTP survey were in the range of 0.050-100 µg L(-1) in the influent and up to 50 µg L(-1) in the effluent, where the non-steroidal anti-inflammatory drugs (NSAIDs) were the most abundant and frequently detected group. Some musks were detected up to 11.5 µg L(-1) in the influent and 0.9 µg L(-1) in the effluent, and adsorbed in the sludge up to 22.6 µg g(-1).

Modelling the population dynamics and metabolic diversity of organisms relevant in anaerobic/anoxic/aerobic enhanced biological phosphorus removal processes

In this study, enhanced biological phosphorus removal (EBPR) metabolic models are expanded in order to incorporate the competition between polyphosphate accumulating organisms (PAOs) and glycogen accumulating organisms (GAOs) under sequential anaerobic/anoxic/aerobic conditions, which are representative of most full-scale EBPR plants. Since PAOs and GAOs display different denitrification tendencies, which is dependent on the phylogenetic identity of the organism, the model was separated into six distinct biomass groups, constituting Accumulibacter Types I and II, as well as denitrifying and non-denitrifying Competibacter and Defluviicoccus GAOs. Denitrification was modelled as a multi-step process, with nitrate (NO(3)), nitrite (NO(2)), nitrous oxide (N(2)O) and di-nitrogen gas (N(2)) being the primary components. The model was calibrated and validated using literature data from enriched cultures of PAOs and GAOs, obtaining a good description of the observed biochemical transformations. A strong correlation was observed between Accumulibacter Types I and II, and nitrate-reducing and non-nitrate-reducing PAOs, respectively, where the abundance of each PAO subgroup was well predicted by the model during an acclimatization period from anaerobic-aerobic to anaerobic-anoxic conditions. Interestingly, a strong interdependency was observed between the anaerobic, anoxic and aerobic kinetic parameters of PAOs and GAOs. This could be exploited when metabolic models are calibrated, since all of these parameters should be changed by an identical factor from their default value. Factors that influence these kinetic parameters include the fraction of active biomass, relative aerobic/anoxic fraction and the ratio of acetyl-CoA to propionyl-CoA. Employing a metabolic approach was found to be advantageous in describing the performance and population dynamics in such complex microbial ecosystems.

Metabolic shift of polyphosphate-accumulating organisms with different levels of polyphosphate storage

Previous studies have shown that polyphosphate-accumulating organisms (PAOs) are able to behave as glycogen-accumulating organisms (GAOs) under different conditions. In this study we investigated the behavior of a culture enriched with Accumulibacter at different levels of polyphosphate (poly-P) storage. The results of stoichiometric ratios Gly(degraded)/HAc(uptake), PHB(synthesized)/HAc(uptake), PHV(synthesized)/HAc(uptake) and P(release)/HAc(uptake) confirmed a metabolic shift from PAO metabolism to GAO metabolism: PAOs with high poly-P content used the poly-P to obtain adenosine tri-phosphate (ATP), and glycogen (Gly) to obtain nicotinamide adenine dinucleotide (NADH) and some ATP. In a test where poly-P depletion was imposed on the culture, all the acetate (HAc) added in each cycle was transformed into polyhydroxyalkanoate (PHA) despite the decrease of poly-P inside the cells. This led to an increase of the Gly(degraded)/HAc(uptake) ratio that resulted from a shift towards the glycolytic pathway in order to compensate for the lack of ATP formed from poly-P hydrolysis. The shift from PAO to GAO metabolism was also reflected in the change in the PHA composition as the poly-P availability decreased, suggesting that polyhydroxyvalerate (PHV) is obtained due to the consumption of excess reducing equivalents to balance the internal NADH, similarly to GAO metabolism. Fluorescence in situ hybridization analysis showed a significant PAO population change from Type I to Type II Accumulibacter as the poly-P availability decreased in short term experiments. This work suggests that poly-P storage levels and GAO-like metabolism are important factors affecting the competition between different PAO Types in enhanced biological phosphorus removal systems.

New framework for standardized notation in wastewater treatment modelling.

Many unit process models are available in the field of wastewater treatment. All of these models use their own notation, causing problems for documentation, implementation and connection of different models (using different sets of state variables). The main goal of this paper is to propose a new notational framework which allows unique and systematic naming of state variables and parameters of biokinetic models in the wastewater treatment field. The symbols are based on one main letter that gives a general description of the state variable or parameter and several subscript levels that provide greater specification. Only those levels that make the name unique within the model context are needed in creating the symbol. The paper describes specific problems encountered with the currently used notation, presents the proposed framework and provides additional practical examples. The overall result is a framework that can be used in whole plant modelling, which consists of different fields such as activated sludge, anaerobic digestion, sidestream treatment, membrane bioreactors, metabolic approaches, fate of micropollutants and biofilm processes. The main objective of this consensus building paper is to establish a consistent set of rules that can be applied to existing and most importantly, future models. Applying the proposed notation should make it easier for everyone active in the wastewater treatment field to read, write and review documents describing modelling projects.

Critical review of activated sludge modeling: State of process knowledge, modeling concepts, and limitations

This work critically reviews modeling concepts for standard activated sludge wastewater treatment processes (e.g., hydrolysis, growth and decay of organisms, etc.) for some of the most commonly used models. Based on a short overview on the theoretical biochemistry knowledge this review should help model users to better understand (i) the model concepts used; (ii) the differences between models, and (iii) the limits of the models. The seven analyzed models are: (1) ASM1; (2) ASM2d; (3) ASM3; (4) ASM3 + BioP; (5) ASM2d + TUD; (6) Barker & Dold model; and (7) UCTPHO+. Nine standard processes are distinguished and discussed in the present work: hydrolysis; fermentation; ordinary heterotrophic organisms (OHO) growth; autotrophic nitrifying organisms (ANO) growth; OHO & ANO decay; poly‐hydroxyalkanoates (PHA) storage; polyphosphate (polyP) storage; phosphorus accumulating organisms PAO) growth; and PAO decay. For a structured comparison, a new schematic representation of these processes is proposed. Each process is represented as a reaction with consumed components on the left of the figure and produced components on the right. Standardized icons, based on shapes and color codes, enable the representation of the stoichiometric modeling concepts and kinetics. This representation allows highlighting the conceptual differences of the models, and the level of simplification between the concepts and the theoretical knowledge. The model selection depending on their theoretical limitations and the main research needs to increase the model quality are finally discussed. Biotechnol. Bioeng. 2013; 110: 24–46.

Assessing the diurnal variability of pharmaceutical and personal care products in a full-scale activated sludge plant

An intensive sampling campaign has been carried out in a municipal wastewater treatment plant (WWTP) to assess the dynamics of the influent pharmaceutical active compounds (PhAC) and musks. The mass loadings of these compounds in wastewater influents displayed contrasting diurnal variations depending on the compound. The musks and some groups of PhACs tended to follow a similar diurnal trend as compared to macropollutants, while the majority of PhACs followed either the opposite trend or no repeatable trend. The total musk loading to the WWTP was 0.74 ± 0.25 g d(-1), whereas the total PhAC mass loading was 84.7 ± 63.8 g d(-1). Unlike the PhACs, the musks displayed a high repeatability from one sampling day to the next. The range of PhAC loadings in the influent to WWTPs can vary several orders of magnitude from one day or week to the next, representing a challenge in obtaining data for steady-state modelling purposes.