Conventional diffused aeration systems (such as fine-bubble diffusers) exhibit a poor oxygen transfer in wastewater treatment plants (WWTPs), particularly when operating at sludge concentrations higher than 15 g L−1. The supersaturated dissolved oxygen (SDOX) system has been proposed as an alternative for supplying dissolved oxygen (DO) at high mixed liquor suspended solids (MLSS) concentrations. The advantages introduced by such technology include the possibility of operating WWTPs at much higher than usual MLSS concentrations, increasing the treatment capacity of WWTPs. Recent studies have demonstrated that the SDOX system has higher oxygen transfer rates (OTRs) and oxygen transfer efficiencies (OTEs) relative to fine-bubble diffusers. However, it is unknown if the high-pressure conditions introduced by SDOX may possibly impact the biological performance of WWTPs. In this study, the effects of SDOX technology on the biological performance of a membrane bioreactor (MBR) were evaluated. The MBR was operated at an MLSS concentration of approximately 15 g L−1 in four phases as follows: (P1) with bubble diffusers, (P2) with an SDOX unit, (P3) with the bubble diffusers, and (P4) with the SDOX unit. The performance of the MBR was assessed by monitoring the sludge concentration, as well as changes in the particle size distribution (PSD), sludge activity, organic matter removal and nitrification performance, and changes in the microbial community within the MBR. The operational conditions exerted by the SDOX technology did not affect the concentration of active biomass during the study period. The biological performance of the MBR was not affected by the introduction of the SDOX technology. Finally, the microbial community was relatively stable although some variations at the family and genus level were evident during each of the study phases. Therefore, the SDOX system can be proposed as an alternative technology for DO supply in WWTPs increasing the overall treatment capacity.@en

The use of near-infrared (NIR) spectroscopy in wastewater treatment has continuously expanded. As an alternative to conventional analytical methods for monitoring constituents in wastewater treatment processes, the use of NIR spectroscopy is considered to be cost-effective and less time-consuming. NIR spectroscopy does not distort the measured sample in any way as no prior treatment is required, making it a waste-free technique. On the negative side, one has to be very well versed with chemometric techniques to interpret the results. In this study, filtered and centrifuged wastewater and sludge samples from a lab-scale membrane bioreactor (MBR) were analysed. Two analytical methods (conventional and NIR spectroscopy) were used to determine and compare major wastewater constituents. Particular attention was paid to soluble microbial products (SMPs) and extracellular polymeric substances (EPSs) known to promote membrane fouling. The parameters measured by NIR spectroscopy were analysed and processed with partial least squares regression (PLSR) and artificial neural networks (ANN) models to assess whether the evaluated wastewater constituents can be monitored by NIR spectroscopy. Very good results were obtained with PLSR models, except for the determination of SMP, making the model qualitative rather than quantitative for their monitoring. ANN showed better performance in terms of correlation of NIR spectra with all measured parameters, resulting in correlation coefficients higher than 0.97 for training, testing, and validation in most cases. Based on the results of this research, the combination of NIR spectra and chemometric modelling offers advantages over conventional analytical methods.@en

Ca. Accumulibacter was the predominant microorganism (relative FISH bio-abundance of 67 ± 5%) in a lab-scale sequential batch reactor that accomplished enhanced biological phosphorus removal (EBPR) while using glucose and acetate as the carbon sources (1:1 COD-based ratio). Both organic compounds were completely anaerobically consumed. The reactor's performance in terms of P/C ratio, phosphorous release and uptake, and overall kinetic and stoichiometric parameters were on the high end of the reported spectrum for EBPR systems (100:9.3 net mg phosphate removal per mg COD consumed when using glucose and acetate in a 1:1 ratio). The batch tests showed that, to the best of our knowledge, this is the first time a reactor enriched with Ca. Accumulibacter can putatively utilize glucose as the sole carbon source to biologically remove phosphate (COD:P (mg/mg) removal ratio of 100:6.3 when using only glucose). Thus, this research proposes that Ca. Accumulibacter directly anaerobically stored the fed glucose primarily as glycogen by utilizing the ATP provided via the hydrolysis of poly-P and secondarily as PHA by balancing its ATP utilization (glycogen generation) and formation (PHA storage). Alternative hypotheses are also discussed. The reported findings could challenge the conventional theories of glucose assimilation by Ca. Accumulibacter, and can be of significance for the biological removal of phosphorus from wastewaters with high contents of fermentable compounds or low VFAs.@en

The high frequency and intensity of urban floods caused by climate change, urbanisation and infrastructure failures increase public health risks when the flood water contaminated from combined sewer overflows (CSOs) or other sources of faecal contamination remains on urban surfaces. This study contributes to a better understanding of the effects of urban and recreational surfaces on the occurrence of waterborne pathogens. The inactivation of selected indicator organisms was studied under controlled exposure to artificial sunlight for 6 h followed by 18 h in dark conditions. Concrete, asphalt, pavement blocks and glass as control were inoculated with artificial floodwater containing, as indicator organisms, Escherichia coli bacteria, which are common faecal indicator bacteria (FIB) for water quality assessment, Bacillus subtilis spores chosen as surrogates for Cryptosporidium parvum oocysts and Giardia cysts, and bacteriophages MS2 as indicators for viral contamination. On practically all the surfaces in this study, E. coli had the highest inactivation under light conditions followed by MS2 and B. subtilis, except asphalt where MS2 was inactivated faster. The highest inactivation under light conditions was seen with E. coli on a concrete surface (pH 9.6) with an inactivation rate of 1.85 h−1. However, the pH of the surfaces (varying between 7.0 and 9.6) did not have any influence on inactivation rates under dark conditions. MS2 bacteriophage had the highest inactivation under light conditions on asphalt with a rate of 1.29 h−1. No die-off of B. subtilis spores was observed on any of the surfaces during the experiment, neither in light nor in dark conditions. This study underpins the need to use different indicator organisms to test their inactivation after flooding. It also suggests that given the sunlight conditions, concentration of indicator organisms and type of surface, the fate of waterborne pathogens after a flood could be estimated.@en

Anaerobic ammonia oxidation to nitrogen gas using nitrite as the electron acceptor (anammox process) is considered a cost-effective solution for nitrogen removal after an anaerobic pre-treatment process. In this study, we conducted a laboratory-scale experiment to develop a single-stage partial nitritation–anammox process in a sponge-based trickling filter (STF) reactor, inoculated with anammox sludge, simulating the treatment of anaerobically pretreated concentrated domestic sewage without mechanical oxygen control. The influent ammonia concentration was 100 mg-N·L−1. The KLa of the STF reactor was higher than those observed for conventional activated sludge processes. The STF reactor performed at 89.8 ± 8.2% and 42.7 ± 16.9% ammonia and TN removal efficiency, respectively, with a nitrogen loading rate of 0.55 ± 0.20 kg-N·m−3·day−1 calculated based on sponge volume. Microbial community analysis of the STF-retained sludge indicated that both autotrophic and heterotrophic nitrogen removal occurred in the reactor.@en

To investigate the influence of high-pressure and shear effects introduced by a concentrated oxygen supply system on the membrane filtration performance, a laboratory-scale membrane bioreactor (MBR) fed artificial municipal wastewater was operated continuously for 80 days in four phases equipped with different aerations systems: (P1) bubble diffusers (days 0–40), (P2) concentrated oxygen supply system, the supersaturated dissolved oxygen (SDOX) (days 41–56), (P3) bubble diffusers (days 57–74), and (P4) SDOX (days 75–80). Various sludge physical-chemical parameters, visual inspection of the membrane, and permeability evaluations were performed. Results showed that the high-pressure effects contributed to fouling of the membranes compared to the bubble diffuser aeration system. Biofouling by microorganisms appeared to be the main contributor to the cake layer when bubble diffusers were used, while fouling by organic matter seemed to be the main contributor to the cake layer when SDOX was used. Small particle size distribution (PSD) (ranging from 1 to 10 and 1–50 μm in size) fractions are a main parameter affecting the intense fouling of membranes (e.g., formation of a dense and thin cake layer). However, PSD alone cannot explain the worsened membrane fouling tendency. Therefore, it can be assumed that a combination of several factors (which certainly includes PSD) led to the severe membrane fouling caused by the high-pressure and shear.@en

Phosphate accumulating organisms (PAO) are assumed to use nitrate as external electron acceptor, allowing an efficient integration of simultaneous nitrogen and phosphate removal with minimal organic carbon (COD) requirements. However, contradicting findings appear in literature regarding the denitrification capacities of PAO due to the lack of clade specific highly enriched PAO cultures. Whereas some studies suggest that only PAO clade I may be capable of using nitrate as external electron acceptor for anoxic P-uptake, other studies indicate that PAO clade II may be responsible for anoxic P-removal. In the present study, a highly enriched PAO clade IC culture (>99% according to FISH) was cultivated in an SBR operated under Anaerobic/Oxic conditions and subsequently exposed to Anaerobic/Anoxic/Oxic conditions using nitrate as electron acceptor. Before and after acclimatization to the presence of nitrate, the aerobic and anoxic (nitrate and nitrite) activities of the PAO I culture were assessed through the execution of batch tests using either acetate or propionate as electron donor. In the presence of nitrate, significant P-uptake by PAO I was not observed before or after acclimatization. Using nitrite as electron acceptor, limited nitrite removal rates were observed before acclimatization with lower rates in the acetate fed reactor without P-uptake and slightly higher in the propionate fed reactor with a marginal anoxic P-uptake. Only after acclimatization to nitrate, simultaneous P and nitrite removal was observed. This study suggests that PAO clade IC is not capable of using nitrate as external electron acceptor for anoxic P-removal. The elucidation of the metabolic capacities for individual PAO clades helps in better understanding and optimization of the relation between microbial ecology and process performance in enhanced biological phosphate removal processes.@en

The operation of membrane bioreactors (MBRs) at higher than usual mixed liquor suspended solids (MLSS) concentrations may enhance the loading rate treatment capacity while minimizing even further the system’s footprint. This requires operating the MBR at the highest possible MLSS concentration and biomass activity (e.g., at high loading rates and low solid retention times (SRTs)). Both a negative effect of the MLSS concentrations and a positive effect of the SRT on the oxygen transfer have been reported when using conventional fine bubble diffusers. However, most of the evaluations have been carried out either at extremely high SRTs or at low MLSS concentrations eventually underestimating the effects of the MLSS concentration on the oxygen transfer. This research evaluated the current limitations imposed by fine bubble diffusers in the context of the high-loaded MBR (HL-MBR) (i.e., high MLSS and short SRT—the latter emulated by concentrating municipal sludge from a wastewater treatment plant (WWTP) operated at a short SRT of approximately 5 days). The high MLSS concentrations and the short SRT of the original municipal sludge induced a large fraction of mixed liquor volatile suspended solids (MLVSS) in the sludge, promoting a large amount of sludge flocs that eventually accumulated on the surface of the bubbles and reduced the free water content of the suspension. Moreover, the short SRTs at which the original municipal sludge was obtained eventually appear to have promoted the accumulation of surfactants in the sludge mixture. This combination exhibited a detrimental effect on the oxygen transfer. Fine bubble diffusers limit the maximum MLSS concentration for a HL-MBR at 30 g L −1 ; beyond that point is either not technically or not economically feasible to operate; an optimum MLSS concentration of 20 g L −1 is suggested to maximize the treatment capacity while minimizing the system’s footprint. @en

Sulfate rich wastewaters can be generated from industry, use of seawater in urban environments, or by saline water infiltration into the sewerage. Under anaerobic conditions sulfate can be converted to sulfide, which may affect micro-organisms performing biological nutrient removal. The objective of this study was to evaluate the effect of sulfide on the activity of polyphosphate-accumulating organisms (PAO) in the anaerobic stage of the enhanced biological phosphorus removal process (EBPR). In this regard, a highly enriched culture of PAO was exposed in short-term activity tests to a range of sulfide concentrations at different operational pH values. The PAO activity was mainly affected by un-dissociated H2S. The specific acetate uptake rate was inhibited by 50% at around 60 mg H2S.L−1. With increasing H2S concentrations, higher phosphate release rate to acetate uptake rate ratios were observed, possibly due to increased energy requirements for cell detoxification. Mathematical expressions were developed, which satisfactorily described the sulfide effects on the acetate uptake rate and phosphate release rate. The results show that, dependent on the pH, EBPR might be negatively affected by total sulfide concentrations exceeding 275 mg SO4.L−1 at pH 6.5 or 1200 mg SO4.L−1 at pH 7.8 mg SO4.L−1 or when freshwater is partially replaced by seawater more than 45% (pH 7.8) or 10% (pH 6.5) used as secondary quality water. The findings of this study imply that sulfide, which is commonly found in different type of wastewaters, affects the anaerobic metabolism of PAO and may play an important role in the process performance of treatment plants treating wastewaters with high sulfide content.@en

Oxygen transfer in wastewater treatment is significantly influenced by the mixed liquor suspended solids (MLSS). The effect is more pronounced at MLSS concentrations higher than 20 g L−1 when supplying air by conventional diffused aeration systems. The oxygen transfer performance of a supersaturated oxygenation technology (i.e., the supersaturated dissolved oxygen (SDOX) system) was evaluated in clean water and in activated sludge with MLSS concentrations from 4 to 40 g L−1 as a promising technology for uncapping such limitation. The evaluation was carried out at the laboratory facilities of the faculty of food technology and biotechnology at the University of Zagreb. The sludge was collected from a full-scale conventional activated sludge (CAS) wastewater treatment plant (WWTP) operated at a solid retention time (SRT) of approximately 5 days. The evaluation was carried out using a laboratory-scale setup consisting of a bench-scale SDOX system (2.75 L) supplying pure oxygen to a 5 L biological reactor. The SDOX exhibited oxygen mass transfer rate coefficient (KLa) values (2.6 h−1) in clean water lower than for fine bubble diffusers (11 h−1). However, higher oxygen transfer rate (OTR) values and alpha factors (mass transfer ratio of process-water to clean-water) as a function of the MLSS concentration were observed. A standard oxygen transfer efficiency (SOTE) of approximately 100 % in clean water was reported. The SDOX technology can be presented as a promising alternative for supplying dissolved oxygen (DO) into mixed liquor solutions; particularly, at the high MLSS concentrations required by high-loaded membrane bioreactor (HL-MBR) systems and aerobic digesters.@en

A better understanding of the effects of different urban and recreational surfaces on the die-off of water-borne pathogens that can cause infections after urban floods if released from surcharged combined sewers and other sources of fecal contamination is needed. The die-off of fecal indicator Escherichia coli was studied under controlled exposure to simulated sunlight on a range of different surfaces found in urban environments: gravel, sand, asphalt, pavement blocks, concrete, playground rubber tiles and grass, using glass as control. The surfaces were inoculated with artificial flooding water containing 105 colony forming units (CFU) of E. coli per mL and sampled periodically using the sterile cotton swab technique, after lowering the water level. The results show that dark inactivation was not statistically significant for any surface, suggesting that chemical composition and pH (varying between 6.5 ± 0.8 and 9.2 ± 0.4) did not affect the die-off rates. The highest light-induced die-off rates for E. coli after the floodwater recession, observed on rubber (>3.46 h−1) and asphalt (2.7 h−1), were attributed to temperature stress and loss of surface moisture.@en