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Sulfide is produced in sewer networks, and previous studies suggest that sulfide in sewage could alter the activity of heterotrophic denitrification and lead to N2O accumulation during biological wastewater treatment. However, the details of this phenomenon are poorly understood. In this study, the potential inhibitory effects of sulfide on nitrate, nitrite, and N2O reduction were assessed with a methanol-utilizing denitrifying culture both prior to and after its exposure and adaptation to sulfide. Hydrogen sulfide was found to be strongly inhibitory to N2O reduction, with 50% inhibition observed at H2S concentrations of 0.04 mg H2S-S/L and 0.1 mg H2S-S/L for the unadapted and adapted cultures, respectively. In comparison, both nitrate and nitrite reduction was more tolerant to H2S. A 50% inhibition of nitrite reduction was observed at approximately 2.0 mg H2S-S/L for both unadapted and adapted cultures, while no inhibition of nitrate reduction occurred at the highest H2S concentrations applied (2.0 mg H2S-S/L) to either culture. N2O accumulation was observed during nitrate and nitrite reduction by the adapted culture when H2S concentrations were above 0.5 and 0.2 mg H2S-S/L, respectively. Additionally, we reveal that hydrogen sulfide (H2S), rather than sulfide, was likely the true inhibitor of N2O reduction, and the inhibitory effect was reversible. These findings suggest that sulfide management in sewers could potentially have a significant impact on N2O emission from wastewater treatment plants. [ABSTRACT FROM AUTHOR]

Abstract: Multi-walled carbon nanotubes (MWCNTs) are superadsorbents for perfluorooctane sulfonate (PFOS) and heavy metals, which coexist in wastewater. The interaction between PFOS and Cu(II) with regard to their adsorption and desorption on MWCNTs was evaluated in this study. The adsorption of PFOS on MWCNTs enhanced with an increase of Cu(II). Desorption of PFOS showed no hysteresis without Cu(II), while pronounced hysteresis with Cu(II). Increases of the adsorption and the occurrence of desorption hysteresis of PFOS in the presence of Cu(II) may due to the PFOS adsorption via a Cu(II) bridge. The adsorption of Cu(II) increased with an increase of PFOS. The desorption hysteresis factors in the presence of PFOS were lower than those in the absence of PFOS. Increases of the adsorption and decreases of desorption hysteresis factors may be attributed to the Cu(II) adsorption via a PFOS bridge. Results obtained by X-ray absorption spectroscopy verified the formation of inner-sphere complexes between Cu(II) and functional groups of MWCNTs without PFOS, while out-sphere complexes with large amount of PFOS. The effect of Cu(II) and PFOS adsorption on the zeta potential of MWCNTs was also studied. The results showed that the coexistence of Cu(II) and PFOS greatly affects their sorption and desorption behaviors on MWCNTs thereby their fate and transport in wastewater. [Copyright &y& Elsevier]

Abstract: Ammonia-oxidising bacteria (AOB) are a major contributor to nitrous oxide (N2O) emissions during nitrogen transformation. N2O production was observed under both anoxic and aerobic conditions in a lab-scale partial nitritation system operated as a sequencing batch reactor (SBR). The system achieved 55±5% conversion of the 1g NH4 +-N/L contained in a synthetic anaerobic digester liquor to nitrite. The N2O emission factor was 1.0±0.1% of the ammonium converted. pH was shown to have a major impact on the N2O production rate of the AOB enriched culture. In the investigated pH range of 6.0–8.5, the specific N2O production was the lowest between pH 6.0 and 7.0 at a rate of 0.15±0.01mgN2O-N/h/g VSS, but increased with pH to a maximum of 0.53±0.04mgN2O-N/h/g VSS at pH 8.0. The same trend was also observed for the specific ammonium oxidation rate (AOR) with the maximum AOR reached at pH 8.0. A linear relationship between the N2O production rate and AOR was observed suggesting that increased ammonium oxidation activity may have promoted N2O production. The N2O production rate was constant across free ammonia (FA) and free nitrous acid (FNA) concentrations of 5–78mg NH3-N/L and 0.15–4.6mg HNO2-N/L, respectively, indicating that the observed pH effect was not due to changes in FA or FNA concentrations. [Copyright &y& Elsevier]

Abstract: Hydrogen sulfide generation is a major issue in sewer management. A novel method based on electrochemical sulfide oxidation was recently shown to be highly effective for sulfide removal from synthetic and real sewage. Here, we compare the performance of five different mixed metal oxide (MMO) coated titanium electrode materials for the electrochemical removal of sulfide from domestic wastewater. All electrode materials performed similarly in terms of sulfide removal, removing 78±5%, 77±1%, 85±4%, 84±1%, and 83±2% at a current density of 10mA/cm2 using Ta/Ir, Ru/Ir, Pt/Ir, SnO2 and PbO2, respectively. Elevated chloride concentrations, often observed in coastal areas, did not entail any significant difference in performance. Independent of the electrode material used, sulfide oxidation by in situ generated oxygen was the predominant reaction mechanism. Passivation of the electrode surface by deposition of elemental sulfur did not occur. However, scaling was observed in the cathode compartment. This study shows that all the MMO coated titanium electrode materials studied are suitable anodic materials for sulfide removal from wastewater. Ta/Ir and Pt/Ir coated titanium electrodes seem the most suitable electrodes since they possess the lowest overpotential for oxygen evolution, are stable at low chloride concentration and are already used in full scale applications. [Copyright &y& Elsevier]

Abstract: One of the main challenging issues for the aerobic granular sludge technology is the long startup time when dealing with real wastewaters. This study presents a novel strategy to reduce the time required for granulation while ensuring a high level of nutrient removal. This new approach consists of seeding the reactor with a mixture of crushed aerobic granules and floccular sludge. The effectiveness of the strategy was demonstrated using abattoir wastewater, containing nitrogen and phosphorus at approximately 250 mgN/L and 30 mgP/L, respectively. Seven different mixtures of crushed granules and floccular sludge at granular sludge fractions (w/w in dry mass) of 0%, 5%, 10%, 15%, 25%, 30% and 50% were used to start eight granulation processes. The granulation time (defined as the time when the 10th percentile bacterial aggregate size is larger than 200 μm) displayed a strong dependency on the fraction of granular sludge. The shortest granulation time of 18 days was obtained with 50% crushed granules, in comparison with 133 days with 5% crushed granules. Full granulation was not achieved in the two trials without seeding with crushed granules. In contrast to the 100% floccular sludge cases, where a substantial loss of biomass occurred during granulation, the biomass concentration in all other trails did not decrease during granulation. This allowed that good nitrogen removal was maintained in all the reactors during the granulation process. However, enhanced biological phosphorus removal was achieved in only one of the eight trials. This was likely due to the temporary accumulation of nitrite, a strong inhibitor of polyphosphate accumulating organisms. [Copyright &y& Elsevier]

Abstract: In full-scale wastewater treatment systems, phosphorus removal typically occurs together with nitrogen removal. Nitrite, an intermediate of both the nitrification and denitrification processes, can accumulate in the reactor. The inhibitory effect of nitrite/free nitrous acid (FNA) on the aerobic metabolism of poly-phosphate accumulating organisms (PAOs) is investigated. A culture highly enriched (90 ± 5%) in Candidatus “Accummulibacter phosphatis”, a well-known PAO, was used to perform a series of batch experiments at various nitrite and pH levels. FNA was found to inhibit all key aerobic metabolic processes performed by PAOs, namely PHA oxidation, phosphate uptake, glycogen replenishment and growth. The inhibitory effect on the anabolic processes (growth, phosphate uptake and glycogen production) was much stronger than that on the catabolic processes (PHA oxidation). 50% inhibition on all anabolic processes occurred at FNA concentrations of approximately 0.5 × 10−3 mg HNO2–N/L (equivalent to 2.0 mg NO2 −–N/L at pH 7.0), while full inhibition occurred at FNA concentrations of approximately 6.0 × 10−3 mg HNO2–N. These concentrations could be found in full-scale wastewater treatment systems that achieve nitrogen removal via the nitrite pathway. In comparison, PHA oxidation remained at 40–50% of the highest rate at FNA concentrations in the range 2.0 × 10−3–10.0 × 10−3 mg HNO2–N/L. Interestingly, PAOs were able to reduce nitrite under aerobic conditions (DO ≈ 3 mg/L), with the rate increasing substantially with the FNA concentration. The inhibition on phosphate uptake was found to be reversible. [ABSTRACT FROM AUTHOR]

Abstract: A sub-microscopic mechanism model named Fully Coupled Activated Sludge Model (FCASM) about biological nutrient removal in the wastewater treatment process was developed in the present study. The functional organisms existing simultaneously in the activated sludge system were separated into eight groups, including aerobic heterotrophic organisms, nitrite reducing organisms, nitrate reducing organisms, ammonium oxidizing autotrophs, nitrite oxidizing autotrophs, non-denitrifying phosphorus-accumulating organisms (PAOs), denitrifying phosphorus-accumulating bacteria (DPB), and glycogen-accumulating organisms (GAOs). In FCASM, the interaction relationships of the eight functional microorganisms were taken fully into account. FCASM could model biological nitrogen removal via nitrite by splitting nitrification process and denitrification process into two-step reactions, and the autotrophs and denitrifying organisms were divided into two groups, respectively. What’s important, FCASM included the anaerobic maintenance processes of sequential utilization of polyphosphate followed by glycogen for PAOs and DPB and glycolysis of the intracellular stored glycogen for GAOs. [Copyright &y& Elsevier]

Abstract: The effect of long term anaerobic and intermittent anaerobic/aerobic starvation on the structure and activity of aerobic granules was studied. Aerobic granular sludge treating abattoir wastewater and achieving high levels of nutrient removal was subjected to 4–5week starvation under anaerobic and intermittent anaerobic/aerobic conditions. Microscopic pictures of granules at the beginning of the starvation period presented a round and compact surface morphology with a much defined external perimeter. Under both starvation conditions, the morphology changed at the end of starvation with the external border of the granules surrounded by floppy materials. The loss of granular compactness was faster and more pronounced under anaerobic/aerobic starvation conditions. The release of Ca2+ at the onset of anaerobic/aerobic starvation suggests a degradation of extracellular polymeric substances. The activity of ammonia oxidizing bacteria was reduced by 20 and 36% during anaerobic and intermittent anaerobic/aerobic starvation, respectively. When fresh wastewater was reintroduced, the granules recovered their initial morphology within 1week of normal operation and the nutrient removal activity recovered fully in 3weeks. The results show that both anaerobic and intermittent anaerobic/aerobic conditions are suitable for maintaining granule structure and activity during starvation. [Copyright &y& Elsevier]

Abstract: Electrochemical oxidation of sulfide is a promising technique for its removal from wastewaters. Generally, the main product of this oxidation reaction is elemental sulfur. The latter deposits as a solid on the electrode and deactivates it. Therefore, an efficient and effective regeneration technique of sulfur loaded electrodes is required for the practical implementation of this technology. Here we demonstrate a method for in situ reduction of electrodeposited sulfur on carbon fibre electrodes to sulfide/polysulfides, at low energy input. The intermediary coulombic efficiency (CE) values strongly depend on pH and buffer capacity of the solution. These values were recorded up to 435±5% due to simultaneous chemical dissolution of sulfur to polysulfides under alkaline conditions. This process demonstrates the potential for continuously removing dissolved sulfide from wastewaters at an anode as sulfur and recovering the deposited sulfur based on regular switching between anodic sulfide oxidation and cathodic sulfur reduction. [Copyright &y& Elsevier]

The treatment of wastewater containing sulfides in bioelectrochemical systems (BES) causes deposition of sulfur on the anode as a result of a solely electrochemical process. In this study, we investigate whether microorganisms can use this sulfur, rather than the anode or soluble sulfate, as an electron acceptor for the oxidation of acetate. Our results indicate that microorganisms use electrodeposited sulfur as preferable electron acceptor over the anode and sulfate and produce sulfide irrespective of electrochemical conditions. Bioelectrochemical and biological sulfide generation pathways were studied under different electrochemical conditions. The obtained results show that the sulfide generation rate at open circuit condition (anode potential -235 ± 5 mV versus standard hydrogen electrode, SHE) was higher in comparison to the electrochemical sulfide generation even at a lower potential of -275 mV (vs SHE), confirming that sulfide is produced through biological processes without any current generation. However, during closed circuit operation, the overall Coulombic efficiency (97% ± 2%) is not affected as the produced sulfide (originating from the reduction of deposited sulfur) is spontaneously reoxidized to sulfur when a favorable potential is maintained. This confirms the mediator role of sulfur during acetate oxidation in BES. A diagrammatic representation of the mechanism is proposed to characterize the interactions between acetate oxidation and sulfur conversions on the anode. [ABSTRACT FROM AUTHOR]

Abstract: Most of the existing sulfide removal processes from wastewaters and waste gases require substantial amounts of energy inputs. Here we present an electrochemical method by means of a fuel cell that removes sulfide while producing energy. A lab scale fuel cell was operated at ambient temperature and neutral pH, which was capable of removing aqueous sulfide continuously for 2 months at a rate of 0.62±0.1kgSm−3 d−1 of net anodic compartment (NAC) (0.28±0.05kgSm−3 d−1 of total anodic compartment, TAC). During continuous operation, on average, the power generated was 12±2Wm−3 NAC (5±1Wm−3 TAC), with a maximum capacity of the cell of 166Wm−3 NAC (74Wm−3 TAC). Potassium ferricyanide was used as cathodic electron acceptor. Elemental sulfur was identified as the predominant final oxidation product that was deposited on the anode. In this abiotic fuel cell, the sulfide oxidation rate was not diminished by the presence of an organic electron donor (acetate) during batch experiments while the acetate concentration remained unchanged. This is particularly important for selective sulfide removal from wastewater where organics are essential for downstream nutrient removal. Elemental sulfur deposited on the anode appeared to limit the operation of the fuel cell after 3 months of operation, necessitating periodic removal of the accumulated sulfur from the electrode. [Copyright &y& Elsevier]

Abstract: Oxygen is the most sustainable electron acceptor currently available for microbial fuel cell (MFC) cathodes. However, its high overpotential for reduction to water limits the current that can be produced. Several materials and catalysts have previously been investigated in order to facilitate oxygen reduction at the cathode surface. This study shows that significant stable currents can be delivered by using a non-catalyzed cathode made of granular graphite. Power outputs up to 21Wm−3 (cathode total volume) or 50Wm−3 (cathode liquid volume) were attained in a continuous MFC fed with acetate. These values are higher than those obtained in several other studies using catalyzed graphite in various forms. The presence of nanoscale pores on granular graphite provides a high surface area for oxygen reduction. The current generated with this cathode can sustain an anodic volume specific COD removal rate of 1.46kgCOD m−3 d−1, which is higher than that of a conventional aerobic process. This study demonstrates that microbial fuel cells can be operated efficiently using high surface graphite as cathode material. This implies that research on microbial fuel cell cathodes should not only focus on catalysts, but also on high surface area materials. [Copyright &y& Elsevier]

Nitrospira and Nitrobacter are nitrite-oxidising bacteria commonly identified in nitrogen removal wastewater treatment plants. Little is known about the growth parameters of Nitrospira or the effects of environmental conditions or inhibitory compounds on Nitrospira activity. These bacterial properties were investigated using an enriched Nitrospira culture and an enriched Nitrobacter culture or Nitrobacter literature values. Compared to Nitrobacter, Nitrospira was found to have a comparable optimal pH range (8.0–8.3); similar normalised activity–temperature relationship (0.44e0.055(T–15)) for temperatures between 15 and 30°C and a similar oxygen half-saturation constant, K O (0.54±0.14mgL−1). The major differences identified were that Nitrospira had a lower nitrite half-saturation constant, K S (0.9±0.07mgNO2-NL−1); lower inhibition threshold concentrations for free ammonia (between 0.04 and 0.08mgNH3-NL−1) and free nitrous acid (less than 0.03mgHNO2-NL−1) and a higher yield (0.15±0.04gVSSg N−1). Therefore, Nitrospira is more likely to dominate nitrite oxidation under conditions with low ammonium and nitrite concentrations, which would provide an advantage to them due to their lower K S value while avoiding any free ammonia or free nitrous acid inhibition. [Copyright &y& Elsevier]

• Dosing Mg (OH) 2 in sewers increases sewage pH and reduces the transfer of H 2 S. • Long-term pH elevation partially inhibits biological processes in sewers. • Mg (OH) 2 offers additional alkalinity which improves nitrification rate. • In sewer Mg (OH) 2 -dosing reduces soluble phosphate concentration in digested sludge. • Mg (OH) 2 -dosing improves sludge settleability and digested sludge dewaterability. Magnesium hydroxide [ Mg (OH) 2 ] is a non-hazardous chemical widely applied in sewer systems for managing odour and corrosion. Despite its proven effectiveness in mitigating these issues, the impacts of dosing Mg (OH) 2 in sewers on downstream wastewater treatment plants have not been comprehensively investigated. Through a one-year operation of laboratory-scale urban wastewater systems, including sewer reactors, sequencing batch reactors, and anaerobic sludge digesters, the findings indicated that Mg (OH) 2 dosing in sewer systems had multifaceted benefits on downstream treatment processes. Compared to the control, the Mg (OH) 2 -dosed experimental system displayed elevated sewage pH (8.8 ± 0.1 vs 7.1 ± 0.1), reduced sulfide concentration by 35.1 % ± 4.9 % (6.7 ± 0.9 mg S L − 1 ), and lower methane concentration by 58.0 % ± 4.9 % (19.1 ± 3.6 mg COD L − 1 ). Additionally, it increased alkalinity by 16.3 % ± 2.2 % (51.9 ± 5.4 mg CaC O 3 L − 1 ), and volatile fatty acids concentration by 207.4 % ± 22.2 % (56.6 ± 9.0 mg COD L − 1 ) in sewer effluent. While these changes offered limited advantages for downstream nitrogen removal in systems with sufficient alkalinity and carbon sources, significant improvements in ammonium oxidation rate and NOx reduction rate were observed in cases with limited alkalinity and carbon sources availability. Moreover, Mg (OH) 2 dosing in upstream did not have any detrimental effects on anaerobic sludge digesters. Magnesium-phosphate precipitation led to a 31.7 % ± 4.1 % reduction in phosphate concertation in anaerobic digester sludge supernatant (56.1 ± 10.4 mg P L − 1 ). The retention of magnesium in sludge increased settleability by 13.9 % ± 1.6 % and improved digested sludge dewaterability by 10.7 % ± 5.3 %. Consequently, the use of Mg (OH) 2 dosing in sewers could potentially reduce downstream chemical demand and costs for carbon sources (e.g., acetate), pH adjustment and sludge dewatering. [Display omitted] [ABSTRACT FROM AUTHOR]

• Low DO can initiate NOB suppression in MABRs. • Low DO cannot suppress active NOB in MABRs once prevail. • The presence of anammox increases the DO threshold to suppress NOB. • NOB suppression is more challenging in counter-diffusion biofilms than in co-diffusion biofilms. Membrane aerated biofilm reactor (MABR) and shortcut nitrogen removal are two types of solutions to reduce energy consumption in wastewater treatment, with the former improving the aeration efficiency and the latter reducing the oxygen demand. However, integrating these two solutions, i.e., achieving shortcut nitrogen removal in MABR, is challenging due to the difficulty in suppressing nitrite-oxidizing bacteria (NOB). In this study, four MABRs were established to demonstrate the feasibility of initiating, maintaining, and restoring NOB suppression using low dissolved oxygen (DO) control, in the presence and absence of anammox bacteria, respectively. Long-term results revealed that the strict low DO (< 0.1 mg/L) in MABR could initiate and maintain stable NOB suppression for more than five months with nitrite accumulation ratio above 90 %, but it was unable to re-suppress NOB once they prevailed. Moreover, the presence of anammox bacteria increased the threshold of DO level to maintain NOB suppression in MABRs, but it was still incapable to restore the deteriorated NOB suppression in conjunction with low DO control. Mathematical modelling confirmed the experimental results and further explored the differences of NOB suppression in conventional biofilms and MABR biofilms. Simulation results showed that it is more challenging to maintain stable NOB suppression in MABRs compared to conventional biofilms, regardless of biofilm thickness or influent nitrogen concentration. Kinetic mechanisms for NOB suppression in different types of biofilms were proposed, suggesting that it is difficult to wash out NOB developed in the innermost layer of MABR biofilms because of the high oxygen level and low sludge wasting rate. In summary, this study systematically demonstrated the challenges of NOB suppression in MABRs through both experiments and mathematical modelling. These findings provide valuable insights into the applications of MABRs and call for more studies in developing effective strategies to achieve stable shortcut nitrogen removal in this energy-efficient configuration. [Display omitted] [ABSTRACT FROM AUTHOR]

Three TiO 2 and Zn-Al-layered double hydroxide composites, denoted LDH-TiO 2 composites, were prepared using the sol–gel method and characterized utilizing scanning and transmission electron microscopy with energy dispersive spectroscopy, ultraviolet–visible diffuse reflectance spectroscopy, X-ray diffraction, N 2 adsorption–desorption, X-ray photoelectron spectroscopy, photocurrent, photoluminescence and electrochemical impedance spectroscopy techniques. The characterization results illustrated that TiO 2 was attached onto the surface of LDH and the sizes of both TiO 2 and LDH particles were in the nanoscale range. The combination of LDH and TiO 2 promoted the photogenerated electron–hole transfer and separation. The removal abilities of the LDH-TiO 2 composites for Cr(VI) were evaluated using the synergistic adsorption and photocatalytic method. The adsorption percentages of the three LDH-TiO 2 composites for 20.0 mg/L Cr(VI) solutions ranged between 26% and 75%, and upon ultraviolet irradiation, the total removal percentages rapidly increased to approximately 100%. The removal efficiency for Cr(VI) depended on the TiO 2 contents of the LDH-TiO 2 composites. Increasing the TiO 2 percentage resulted in decrease in the adsorption capacities and increase in the photocatalytic removal ratios. The kinetic and isothermal data well fitted the pseudo-second-order and Langmuir equations, respectively. The high removal efficiencies suggested that the composites were suitable for the treatment of Cr(VI)-containing wastewater. Unlabelled Image • The removal percentage of LDH-TiO 2 composites for 20 mg/L Cr(VI) approached 100%. • The combination of Zn-Al-LDH and TiO 2 promoted photoinduced charge transport. • Cr(VI) was removed using LDH-TiO 2 via synergistic adsorption and photocatalysis. [ABSTRACT FROM AUTHOR]

Sidestream sludge treatment approaches have been developed in recent years to achieve mainstream nitrite shunt or partial nitritation, where NOB are selectively inactivated by biocidal factors such as free nitrous acid (FNA) or free ammonium (FA) in a sidestream reactor. The existence of NOB in raw wastewater has been increasingly realized and could pose critical challenge to stable NOB suppressions in those systems. This study, for the first time, evaluated the impact of influent NOB on the NOB suppressions in a mainstream nitrite shunt system achieved through sidestream sludge treatment. An over 500-day sequential batch reactor operation with six experimental phases rigorously demonstrated the negative effects of influent NOB on mainstream NOB control. Continuously seeding of NOB contained in influent stimulated NOB community shifts, leading to different extents of ineffective NOB suppression. The role of primary wastewater treatment in NOB removal from raw wastewater was also investigated. Results suggest primary settling and High Rate Activated Sludge system could remove a large part of NOB contained in raw wastewater. Primary treatment for raw wastewater is necessary for ensuring stable mainstream NOB suppressions. Image 1 • Influent NOB challenge NOB suppression by stimulating community shift and resistance. • Primary settling substantially reduces NOB in raw wastewater. • High-rate activated sludge treatment substantially reduces NOB in raw wastewater. • This study expanded the current knowledge of mainstream NOB suppression. [ABSTRACT FROM AUTHOR]

Starvation and antibiotics pollution are two frequent perturbations during breeding wastewater treatment process. Supplying magnetite into anaerobic system has been proved efficient to accelerate microbial aggregates and alleviate the adverse effect caused by process disturbance. Nevertheless, whether these magnetite-based granules are still superior over normal granules after a long-term starvation period remains unknown, the responsiveness of these granules to antibiotics stress is also ambiguous. In current study, we investigated the resilience of magnetite-based anaerobic granular sludge (AnGS) to starvation and oxytetracycline (OTC) stress, by unravelling the variations of reactor performance, sludge properties, ARGs dissemination and microbial community. Compared with the AnGS formed without magnetite, the magnetite assisted AnGS appeared more robust defense to starvation and OTC stress. With magnetite supplement, the average methane yield after starvation recovery, 50 mg/L and 200 mg/L OTC stress was enhanced by 48.95%, 115.87% and 488.41%, respectively, accompanied with less VFAs accumulation, improved tetracycline removal rate (76.3–86.6% vs. 51.0–53.5%) and higher ARGs reduction. Meanwhile, magnetite supplement effectively ameliorated the potential sludge breakage by triggering more large granules formation. Trichococcus was considered an important impetus in maintaining the stability of magnetite-based AnGS process. By inducing more syntrophic methanogenesis partnerships, especially for hydrogenotrophic methanogenesis, magnetite ensured the improved reactor performance and stronger resilience at stress conditions. [Display omitted] • Magnetite-based AnGS showed strong resistance to starvation and OTC stress. • Magnetite supplement particularly enhanced the methane yield at stress conditions. • Magnetite ameliorated the risk of sludge breakage and induced more large granules. • More syntrophic methanogenesis partnerships were established with magnetite. [ABSTRACT FROM AUTHOR]

• A biofilm-based anammox process was set up to treat acidic nitritation effluent. • Over 80% nitrogen removal at a rate of 149.7 ± 3.9 mg N/L/day was achieved. • Higher than 95% of activity of anammox biofilms can be retained at pH 5. • FNA rather than pH and nitrite plays a key role in anammox activity suppression. • Biofilm plays a key role in protecting anammox bacteria from acidic environment. Acidic partial nitritation (PN) has emerged to be a promisingly stable process in wastewater treatment, which can simultaneously achieve nitrite accumulation and about half of ammonium reduction. However, directly applying anaerobic ammonium oxidation (anammox) process to treat the acidic PN effluent (pH 4−5) is susceptible to the inhibition of anammox bacteria. Here, this study demonstrated the adaptation of anammox process to acidic pH in a moving bed biofilm reactor (MBBR). By feeding the laboratory-scale MBBR with acidic PN effluent (pH = 4.6 ± 0.2), the pH of an anammox reactor was self-sustained in the range of pH 5 − 6. Yet, a high total nitrogen removal efficiency of over 80% at a practical loading rate of up to 149.7 ± 3.9 mg N/L/d was achieved. Comprehensive microbial assessment, including amplicon sequencing, metagenomics, cryosection-FISH, and qPCR, identified that Candidatus Brocadia, close to known neutrophilic members, was the dominant anammox bacteria. Anammox bacteria were found present in the inner layer of thick biofilms but barely present in the surface layer of thick biofilms and in thin biofilms. Results from batch tests also showed that the activity of anammox biofilms could be maintained when subjected to pH 5 at a nitrite concentration of 10 mg N/L, whereas the activity was completely inhibited after disturbing the biofilm structure. These results collectively indicate that the anammox bacteria enriched in the present acidic MBBR could not be inherently acid-tolerant. Instead, the achieved stable anammox performance under the acidic condition is likely due to biofilm stratification and protection. This result highlights the biofilm configuration as a useful solution to address nitrogen removal from acidic PN effluent, and also suggests that biofilm may play a critical role in protecting anammox bacteria found in many acidic nature environments. [Display omitted] [ABSTRACT FROM AUTHOR]

Abstract Inline sludge treatment using free nitrous acid (FNA) was recently shown to be effective in establishing the nitrite pathway in a biological nitrogen removal system. However, the effects of FNA treatment conditions on the nitrite pathway performance remained to be investigated. In this study, three different FNA treatment frequencies (daily sludge treatment ratios of 0.22, 0.31 and 0.38, respectively), two FNA concentrations (1.35 mgN/L and 4.23 mgN/L, respectively) and two influent feeding regimes (one- and two-step feeding) were investigated in four laboratory-scale sequencing batch reactors. The nitrite accumulation ratio was positively correlated to the FNA treatment frequency. However, when a high treatment frequency was used e.g., daily sludge treatment ratio of 0.38, a significant reduction in ammonia oxidizing bacteria (AOB) activity occurred, leading to poor ammonium oxidation. AOB were able to acclimatise to FNA concentrations up to of 4.23 mgN/L, whereas nitrite oxidizing bacteria (NOB) were limited by an FNA concentration of 1.35 mgN/L over the duration of the study (up to 120 days). This difference in sensitivity to FNA could be used to further enhance nitrite accumulation, with 90% accumulation achieved at an FNA concentration of 4.23 mgN/L and a daily sludge treatment ratio of 0.31 in this study. However, this high level of nitrite accumulation led to increased N 2 O emission, with emission factors of up to 3.9% observed. The N 2 O emission was mitigated (reduced to 1.3%) by applying two-step feeding resulting in a nitrite accumulation ratio of 45.1%. Economic analysis showed that choosing the optimal FNA treatment conditions depends on a combination of the wastewater characteristics, the nitrogen discharge standards, and the operational costs. This study provides important information for the optimisation and practical application of FNA-based sludge treatment technology for achieving the mainstream stable nitrite pathway. Graphical abstract Unlabelled Image Highlights • Study result and analysis guide free nitrous acid treatment condition determination • Stable mainstream nitrite pathway reached with nitrite accumulation ratio over 90%. • Distinct nitrifying bacteria acclimation behaviours to high treatment concentration • Treatment frequency negatively related to in-reactor nitrifying bacteria activities. • N 2 O emission mainly from nitrifier denitrification, can be reduced by multi-feeding. [ABSTRACT FROM AUTHOR]

Abstract The effect of iron-dosing in the sewer system, on wastewater treatment processes, was investigated using laboratory-scale wastewater systems comprising sewers, wastewater treatment reactors, sludge thickeners, and anaerobic sludge digesters. Two systems, fed with real domestic wastewater, were operated for over a year. The experimental system received ferric chloride (FeCl 3) dosing at 10 mgFe L−1 in the sewer reactor whereas the control system received none. Wastewater, sludge and biogas were extensively sampled, and analysed for relevant parameters. The FeCl 3 -dosed experimental system displayed a decreased sulfide concentration (by 4.3 ± 0.5 mgS L−1) in sewer effluent, decreased phosphate concentration (by 4.7 ± 0.5 mgP L−1) in biological treatment reactor effluent, and decreased hydrogen sulfide concentration in biogas (911.5 ± 189.9 ppm to 130.0 ± 5.9 ppm), as compared with the control system. The biological nitrogen removal performance of the treatment reactor, and biogas production in the anaerobic digester were not affected by FeCl 3 -dosing. Furthermore, the dewaterability of the anaerobically digested sludge was enhanced by 17.7 ± 1.0%. These findings demonstrate that iron-dosing to sewers can achieve multiple benefits including sulfide removal in sewers, phosphorus removal during wastewater treatment, and hydrogen sulfide (H 2 S) removal during biogas generation. Therefore, an integrated approach should be taken when considering iron salts usage in an urban wastewater system. Highlights • Dosing of FeCl 3 in sewers can effectively decrease dissolved sulfide concentration. • In sewer Fe-dosing contributes to P removal in the downstream wastewater treatment. • In sewer Fe-dosing decreases the H 2 S content in biogas. • In sewer Fe-dosing enhances dewaterability of digested sludge. [ABSTRACT FROM AUTHOR]

Photosynthetic bacteria (PSB) were reported to have great potential for nitrogen removal when treating high-ammonia wastewater. Light-oxygen conditions are the most important parameter; however, the role of the microbial community composition for PSB nitrogen removal remains unclear. This study focussed on the effects of three light-oxygen conditions on PSB performance and the microbial community during high-ammonia wastewater treatment. The results showed that light-oxygen conditions had a significant impact on nitrogen removal efficiency, microbial community diversity and composition. PSB under light-aerobic condition had the highest biomass, highest COD, NH 4 + -N, and NO 3 − -N removal efficiency, and the highest community diversity; these results have not been reported before. The dominant genus in samples under light-aerobic condition was Pseudomonas (with a proportion of 58.23%). The correlation analysis showed that Pseudomonas was positively correlated with NH 4 + -N and NO 3 − -N removal, with high correlation coefficients of 0.9. These results further revealed the underlying nitrogen removal mechanism of PSB in high-ammonia wastewater treatment. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Ordered mesoporous carbons are proposed as adsorbent for treatment of the CGW. • The pore sizes of OMCs can be controlled by varying the synthesis conditions. • The adsorption process of OMC is a spontaneous and endothermic process. • It is proved that physical adsorption takes place during the adsorption process. • The adsorption of samples on phenol from CGW has reached an ideal level. Abstract Coal gasification wastewater (CGW) possess a high phenolics content, how to remove phenols is the crux of the environmental problems. In this work, we report the design and synthesis of a several highly graphitized ordered mesoporous carbons (OMCs) by carbonization of precursors from phenol and formalin. The obtained porous OMCs have uniform structures with the pore size, order degree, and surface areas being controllable by varying the synthesis conditions. In depth study of the prepared materials reveals that the OMCs carbonized at 923.15 K exhibit ordered 2D hexagonal mesoporous structures with high degree of graphitization, high surface area (590.6 m2 · g−1), appropriate pore size (mean diameter about 10 nm) and large mesoporous pore volume (0.512 cm3 · g−1). The prepared OMCs are applied as adsorbent for treatment of the CGW collected directly from the biochemical effluent of coal chemical enterprise in Inner Mongolia Autonomous region, China. The OMCs show excellent adsorption properties for phenol effluent with the removal efficiency of phenols being up to 92.3%. The adsorption experiment data demonstrates that the adsorption is a multi-molecular layer adsorption process, during which the physical adsorption takes place. In addition, the study of adsorption thermodynamics indicates that the adsorption process is spontaneous and endothermic. The adsorption of samples on phenol from CGW has reached an ideal level. [ABSTRACT FROM AUTHOR]

In order to achieve simple pollutant removal and simultaneous resource recovery in high-COD-non-toxic wastewater treatment, a one-step photosynthetic bacteria (PSB) method was established using batch study experiment. The effluent COD met the national discharge standard, and biomass with rich protein and high-value substances was efficiently produced. It eliminated the demand of post-treatment for conventional PSB treatment. Results showed that Rhodopseudomonas effectively treated brewery wastewater and achieved biomass proliferation. Yeast extract was the best additive for PSB growth and the effluent COD was below 80 mg/L with 400 mg/L yeast extract, meeting the national discharge standard. In addition, the PSB biomass increased by 2.6 times, and the cells were rich in protein, polysaccharide, carotenoids, bacteriochlorophyll and coenzyme Q10, reaching 420.9, 177.6, 2.53, 10.75 and 38.6 mg/g respectively. This work demonstrated the great potential of PSB for high-COD non-toxic wastewater treatment in one-step process. [ABSTRACT FROM AUTHOR]

Reliable modelling of sulfide and methane production in sewer systems is required for efficient sewer emission management. Wastewater compositions affect sulfide and methane production kinetics through both its short-term variation influencing the substrate availability to sewer biofilms, and its long-term variation affecting the sewer biofilm structure. While the short-term effect is well considered in existing sewer models with the use of Monod or half-order equations, the long-term effect has not been explicitly considered in current sewer models suitable for network modelling. In this study, the long-term effect of wastewater compositions on sulfide and methane production activities in rising main sewers was investigated. A detailed biofilm model was firstly developed, and then calibrated and validated using experimental data measured during the entire biofilm development period of a laboratory sewer reactor. Based on scenario simulations using the detailed biofilm model, empirical equations describing the long-term effect of sulfate and sCOD (soluble chemical oxygen demand) concentrations on k H2S (the maximum sulfide production rate of sewer biofilm) and k CH4 (the maximum methane production rate of sewer biofilm) were proposed. These equations require further verification in future studies before their potential integration into network-wide sewer models. [ABSTRACT FROM AUTHOR]

Nitrous oxide (N 2 O) is an important greenhouse gas and an ozone-depleting substance which can be emitted from wastewater treatment systems (WWTS) causing significant environmental impacts. Understanding the N 2 O production pathways and their contribution to total emissions is the key to effective mitigation. Isotope technology is a promising method that has been applied to WWTS for quantifying the N 2 O production pathways. Within the scope of WWTS, this article reviews the current status of different isotope approaches, including both natural abundance and labelled isotope approaches, to N 2 O production pathways quantification. It identifies the limitations and potential problems with these approaches, as well as improvement opportunities. We conclude that, while the capabilities of isotope technology have been largely recognized, the quantification of N 2 O production pathways with isotope technology in WWTS require further improvement, particularly in relation to its accuracy and reliability. [ABSTRACT FROM AUTHOR]

• The degradation system could effectively remove BHA-metal complexes. • Acidic conditions were conducive to the removal of TOC, As (V) and Cr (VI). • Alkaline conditions promoted the immobilization of metal cations. • ΔG values of various BHA-metal complexes played key roles in TOC removal. • C–C, C O and Fe–O sites participated in the metals immobilization process. The organometal complexes pollution in beneficiation wastewater has aroused increasing attentions because they were difficult to remove by traditional technologies. In this study, eleven kind of benzohydroxamic acid (BHA)-metal (Pb2+, Cu2+, Mg2+, Ca2+, Zn2+, Cd2+, Fe3+, Fe2+, Sb3+, Cr(Ⅵ) and As(V)) complexes were chosen to investigate their removal performance and mechanism in heterogeneous persulphate degradation system. The metal-biochar/peroxymonosulfate (PMS) system showed the highest and worst total organic carbon (TOC) removal efficiency for BHA-Fe2+ (68.4%) and BHA-As(V) (22.8%), respectively. Meanwhile, the metal-biochar composite had different immobilization abilities toward multiple metal ions. Density functional theory (DFT) revealed that ΔG values of various BHA-metal complexes played key roles for TOC removal. While, metal adsorption was mainly depended on the functional groups on the catalyst surface. After the reaction, Cu, Pb, Fe, Sb, Cr and As mainly existed as residuals. Overall, this study has provided valuable and novel insights into the removal of BHA-metal complexes and broadened the practical applicability of the waste solid-based metal-biochar catalyst coupled with persulphate in beneficiation wastewater treatment. [ABSTRACT FROM AUTHOR]

• Significant loss of total nitrogen is observed in an acidic aerobic sludge digester. • Nitrite is mainly reduced to NO and N 2 O under the acidic aerobic condition. • Rate of aerobic nitrite reduction is comparable to that of aerobic ammonia oxidation. • Controlling the nitrite reduction is critical to development of acidic sludge treatment. The acidic (i.e., pH ∼5) activated sludge process is attracting attention because it enables stable nitrite accumulation and enhances sludge reduction and stabilization, compared to the conventional process at neutral pH. Here, this study examined the production and potential pathways of nitric oxide (NO) and nitrous oxide (N 2 O) during acidic sludge digestion. With continuous operation of a laboratory-scale aerobic digester at high dissolved oxygen concentration (DO>4 mg O 2 L−1) and low pH (4.7±0.6), a significant amount of total nitrogen (TN) loss (i.e., 18.6±1.5% of TN in feed sludge) was detected. Notably, ∼40% of the removed TN was emitted as NO, with ∼8% as N 2 O. A series of batch assays were then designed to explain the observed TN loss under aerobic conditions. All assays were conducted with a low concentration of volatile solids (VS), i.e., VS<4.5 g L−1. This VS concentration is commensurate with the values commonly found in the aeration tanks of full-scale wastewater treatment systems, and thus no significant nitrogen loss should be expected when DO is controlled above 4 mg O 2 L−1. However, nitrite disappeared at a significant rate (with the chemical decomposition of nitrite excluded), leading to NO production in the batch assays at pH 5. The nitrite reduction could be associated with endogenous microbial activities, e.g., nitrite detoxification. The significant NO production illustrates the importance of aerobic nitrite reduction during acidic aerobic sludge digestion, suggesting this process cannot be neglected in developing acidic activated sludge technology. [Display omitted] [ABSTRACT FROM AUTHOR]

In Australia, recycled water schemes have been implemented in residential developments to contribute to sustainable urban development, improve water supply security and reduce pollutant discharges to the environment. A proportion of these schemes, however, have been decommissioned well before the end of their design life which raises questions about the adequacy of the risk assessment and management practices adopted for recycled water schemes. Through a detailed literature review, an investigation of 21 residential recycled water schemes and in-depth interviews with nine scheme stakeholders, we identified 34 risk factors arising from six sources which have the potential to impact the long-term viability of residential recycled water schemes. Of the 34 risk factors identified, 17 were reported to have occurred during the development and implementation of the 21 schemes investigated. The overall risk rating of the 17 factors was qualitatively defined on the basis of the likelihood of occurrence and the impact of the risk factors on the scheme objectives. The outcomes of the assessment indicate that the critical risks to the long-term viability of residential recycled water schemes are 1. unanticipated operational costs, 2. legal and contractual arrangements, 3. regulatory requirements and approval process and 4. customer complaints and expectations not met. To date, public health risks associated with the provision of recycled water have been of primary concern, though the outcomes of this study indicate that the impact to public health has been low. Evidently there is a need for improved assessment and management practices which address the range of critical risk factors, in addition to the routine consideration of public health risks. [ABSTRACT FROM AUTHOR]

• Electrochemical Fe-dosing decreases TSS, COD, dissolved S2−, and P concentrations. • Electrochemical Fe-dosing also decreases H 2 S and CO 2 contents in biogas. • Electrochemical Fe-dosing can mitigate organic fouling of membrane filtration. • The in-situ electrochemical Fe-dosing can generate more benefits than the ex-situ. • Electrochemically generated iron is cost-effective compared to use of iron chemicals. Although iron salts such as iron(III) chloride (FeCl 3) have widespread application in wastewater treatment, safety concerns limit their use, due to the corrosive nature of concentrated solutions. This study demonstrates that local, electrochemical generation of iron is a viable alternative to the use of iron salts. Three laboratory systems with anaerobic membrane processes were set up to treat real wastewater; two systems used the production of either in-situ or ex-situ electrochemical iron (as Fe2+ and Fe2+(Fe3+) 2 O 4 , respectively), while the other system served as a control. These systems were operated for over one year to assess the impact of electrochemically produced iron on system performance. The results showed that dosing of electrochemical iron significantly reduced sulfide concentration in effluent and hydrogen sulfide content in biogas, and mitigated organics-based membrane fouling, all of which are critical issues inherently related to sustainability of anaerobic wastewater treatment. The electrochemical iron strategy can generate multiple benefits for wastewater management including increased removal efficiencies for total and volatile suspended solids, chemical oxygen demand and phosphorus. The rate of methane production also increased with electrochemically produced iron. Economic analysis revealed the viability of electrochemical iron with total cost reduced by one quarter to a third compared with using FeCl 3. These benefits indicate that electrochemical iron dosing can greatly enhance the overall operation and performance of anaerobic membrane processes, and this particularly facilitates wastewater management in a decentralized scenario. [Display omitted] [ABSTRACT FROM AUTHOR]

Several mathematical models have been proposed to describe nitrous oxide (N 2 O) production by ammonia oxidizing bacteria (AOB) under varying operational conditions. However, none of these N 2 O models are able to capture N 2 O dynamics caused by the variation of inorganic carbon (IC) concentration, which has recently been demonstrated to be a significant factor influencing N 2 O production by AOB. In this work, a mathematical model that describes the effect of IC on N 2 O production by AOB is developed and experimentally validated. The IC effect is considered by explicitly including the AOB anabolic process in the model, which is coupled to the catabolic process with the use of the Adenosine triphosphate (ATP) and Adenosine diphosphate (ADP) pools. The calibration and validation of the model were conducted using experimental data obtained with two independent cultures, including a full nitrification culture and a partial nitritation culture. The model satisfactorily describes the N 2 O data from both systems at varying IC concentrations. This new model enhances our ability to predict N 2 O production by AOB in wastewater treatment systems under varying IC conditions. [ABSTRACT FROM AUTHOR]

"Sludge-drying lagoons" are a preferred sludge treatment and drying method in tropical and subtropical areas due to the low construction and operational costs. However, this method may be a potential significant source of methane (CH4) because some of the organic matter would be microbially metabolized under anaerobic conditions in the lagoon. The quantification of CH4 emissions from lagoons is difficult due to the expected temporal and spatial variations over a lagoon maturing cycle of several years. Sporadic ebullition of CH4, which cannot be easily quantified by conventional methods such as floating hoods, is also expected. In this study, a novel method based on mass balances was developed to estimate the CH4 emissions and was applied to a full-scale sludge-drying lagoon over a three year operational cycle. The results revealed that processes in a sludge-drying lagoon would emit 6.5 kg CO2-e per megaliter of treated sewage. This would represent a quarter to two-thirds of the overall greenhouse gas (GHG) emissions from wastewater-treatment plants (WWTPs). This work highlights the fact that sludge-drying lagoons are a significant source of CH4 that adds substantially to the overall GHG footprint of WWTPs despite being recognized as a cheap and energy-efficient means of drying sludge. [ABSTRACT FROM AUTHOR]

The presence of a high level of dissolved methane (e.g., 20–26 g m −3 ) in the anaerobic sludge digestion liquor represents a major challenge to the treatment of this stream, as its emission to the atmosphere contributes significantly to the carbon footprint of wastewater treatment. Here we propose a new approach to simultaneous ammonium and dissolved methane removal from the anaerobic digestion liquor through integrating partial nitritation-Anammox and denitrifying anaerobic methane oxidation (DAMO) processes in a single-stage membrane biofilm reactor (MBfR). In such an MBfR, the anaerobic digestion liquor is provided in the bulk liquid, while oxygen is supplied through gas-permeable membranes to avoid dissolved methane stripping. A previously developed model with appropriate extensions was applied to assess the system performance under different operational conditions and the corresponding microbial interactions. Both influent surface loading (or hydraulic retention time) and oxygen surface loading are found to significantly influence the total nitrogen (TN) and dissolved methane removal, which jointly determine the overall system performance. The counter diffusion and concentration gradients of substrates cause microbial stratification in the biofilm, where ammonia-oxidizing bacteria (AOB) attach close to the membrane surface (biofilm base) where oxygen and ammonium are available, while Anammox and DAMO microorganisms jointly grow in the biofilm layer close to the bulk liquid where methane, ammonium, and nitrite are available with the latter produced by AOB. These results provide first insights and useful information for the design and operation of this new technology for simultaneous ammonium and dissolved methane removal in its potential future applications. [ABSTRACT FROM AUTHOR]

Recent studies have shown that sewer systems produce and emit a significant amount of methane. Methanogens produce methane under anaerobic conditions in sewer biofilms and sediments, and the stratification of methanogens and sulfate-reducing bacteria may explain the simultaneous production of methane and sulfide in sewers. No significant methane sinks or methanotrophic activities have been identified in sewers to date. Therefore, most of the methane would be emitted at the interface between sewage and atmosphere in gravity sewers, pumping stations, and inlets of wastewater treatment plants, although oxidation of methane in the aeration basin of a wastewater treatment plant has been reported recently. Online measurements have also revealed highly dynamic temporal and spatial variations in methane production caused by factors such as hydraulic retention time, area-to-volume ratio, temperature, and concentration of organic matter in sewage. Both mechanistic and empirical models have been proposed to predict methane production in sewers. Due to the sensitivity of methanogens to environmental conditions, most of the chemicals effective in controlling sulfide in sewers also suppress or diminish methane production. In this paper, we review the recent studies on methane emission from sewers, including the production mechanisms, quantification, modeling, and mitigation. [ABSTRACT FROM AUTHOR]

• Mass balance of 11 PFAAs in a laboratory wastewater system was investigated. • Total mass of PFAAs increased by 112% in the system. • Mass increase of PFAAs: activated sludge > sewer process > anaerobic digestion. • Mass of 11 PFAAs in the effluent was 5 times higher than that in digested sludge. The fate and formation of perfluoroalkyl acids (PFAAs) have been investigated during wastewater treatment processes but studies for the entire urban wastewater system comprising the sewage transport and wastewater and sludge treatment processes are scarce. This work performs an integrated assessment of the formation and fate of PFAAs in the urban wastewater system together with their behavior in separate components of the system. To achieve this, PFAAs were monitored over five weeks in a laboratory-scale urban wastewater system comprising sewer reactors, a wastewater treatment reactor, and an anaerobic sludge digester. The system was fed with real domestic wastewater. The total mass of 11 PFAAs flowing out of the laboratory wastewater system significantly (p < 0.05) increased by 112 ± 14 (mean ± standard error)% compared to that entering the system. Formation of PFAAs was observed in all three biological processes of the system. In anaerobic sewer process, perfluoropentanoic acid (PFPeA), perfluoroheptanoic acid (PFHpA), and perfluorooctane sulfonate (PFOS) exhibited significant formation (p < 0.05) with the mass flow increased by 79 ± 24%, 109 ± 31%, and 57 ± 17%, respectively. During the wastewater treatment process, perfluorohexanoic acid (PFHxA), perfluorooctanoic acid (PFOA), and perfluorododecanoic acid (PFDoDA) demonstrated significant increase (p < 0.05) in their mass flows by 176 ± 56%, 92 ± 21%, and 516 ± 184%, respectively. In contrast, only PFHxA was found to significantly (p < 0.05) increase by 130 ± 40% during anaerobic digestion process. The total mass of 11 PFAAs discharged through the effluent (201 ± 24 ng day−1) was 5 times higher than that through the digested sludge (29 ± 6 ng day−1). [Display omitted] [ABSTRACT FROM AUTHOR]

The effect of inorganic carbon (IC) on nitrous oxide (N 2 O) production by ammonia oxidizing bacteria (AOB) was investigated over a concentration range of 0–12 mmol C/L, encompassing typical IC levels in a wastewater treatment reactors. The AOB culture was enriched along with nitrite-oxidizing bacteria (NOB) in a sequencing batch reactor (SBR) to perform complete nitrification. Batch experiments were conducted with continuous carbon dioxide (CO 2 ) stripping or at controlled IC concentrations. The results revealed a linear relationship between N 2 O production rate (N 2 OR) and IC concentration ( R 2 = 0.97) within the IC range studied, suggesting a substantial effect of IC on N 2 O production by AOB. Similar results were also obtained with an AOB culture treating anaerobic sludge digestion liquor. The fundamental mechanism responsible for this dependency is unclear; however, in agreement with previous studies, it was observed that the ammonia oxidation rate (AOR) was also influenced by the IC concentration, which could be well described by the Monod kinetics. These resulted in an exponential relationship between N 2 OR and AOR, as previously observed in experiments where AOR was altered by varying dissolved oxygen and ammonia concentrations. It is therefore possible that IC indirectly affected N 2 OR by causing a change in AOR. The observation in this study indicates that alkalinity (mostly contributed by IC) could be a significant factor influencing N 2 O production and should be taken into consideration in estimating and mitigating N 2 O emissions in wastewater treatment systems. [ABSTRACT FROM AUTHOR]

Improvement of sludge dewaterability is crucial for reducing the costs of sludge disposal in wastewater treatment plants. This study presents a novel method based on combined conditioning with zero-valent iron (ZVI) and hydrogen peroxide (HP) at pH 2.0 to improve dewaterability of a full-scale waste activated sludge (WAS). The combination of ZVI (0–750 mg/L) and HP (0–750 mg/L) at pH 2.0 substantially improved the WAS dewaterability due to Fenton-like reactions. The highest improvement in WAS dewaterability was attained at 500 mg ZVI/L and 250 mg HP/L, when the capillary suction time of the WAS was reduced by approximately 50%. Particle size distribution indicated that the sludge flocs were decomposed after conditioning. Economic analysis showed that combined conditioning with ZVI and HP was a more economically favorable method for improving WAS dewaterability than the classical Fenton reaction based method initiated by ferrous salts and HP. [ABSTRACT FROM AUTHOR]

Although the limitation or deficiency of nutrients, such as nitrogen (N) and phosphorus (P), has been one of the frequently reported factors causing filamentous or non-filamentous bulking of activated sludge, the mechanisms are still unclear. In this work, the long-term effects of N and P limitation or deficiency on sludge settleability and bioflocculation characteristics were investigated in six sequencing batch reactors (SBRs) fed with wastewater with different nutrient availability. The sludge volume index (SVI), microbial community structures, intracellular poly-β-hydroxyalkanoates (PHAs) and extracellular polymeric substances (EPS) were characterised over time. Bulking was not observed in SBRs with N limitation or deficiency, in which SVI remained below 150 mL/g. In contrast, bulking was encountered in those reactors with P deficiency. The occurrence of non-filamentous bulking was associated with a higher carbohydrates fraction and a lower proteins fraction in EPS. In the case of filamentous bulking, SVI correlated negatively with the amount of PHAs. Our experimental data support the hypothesis that the occurrence and/or the type of bulking in activated sludge could be affected by the combination of kinetic selection, microbial storage, as well as the EPS composition. [ABSTRACT FROM AUTHOR]

Abstract: Volatile organic sulfur compounds (VOSCs) are important sources of unpleasant odor in wastewater systems. However, the study of VOSCs is usually hindered by their complicated measurement method and highly reactive nature. In this work, a static headspace method utilising gas chromatography (GC) with a sulfur chemiluminescence detector (SCD) was developed to quantitatively analyze VOSCs in wastewater matrices. The method has low detection limits and requires no pre-concentration treatment. Three typical VOSCs, namely methanethiol (MT), dimethyl sulfide (DMS) and dimethyl disulfide (DMDS), were chosen as examples for this study. The calibration curves of all three compounds covering a wide range from 0.5 ppb to 500 ppb showed good linearity (R 2 > 0.999). The method detection limits (MDL) were 0.08, 0.12 and 0.21 ppb for MT, DMS and DMDS, respectively. The reproducibility (relative standard deviation) was approximately 2%. The recovery ratio of MT, DMS and DMDS in spiked wastewater samples were 83 ± 4%, 103 ± 4% and 102 ± 3%, respectively. Sample preservation tests showed that VOSCs in wastewater samples could be preserved in vials without headspace under acidified conditions (pH ∼1.1) for at least 24 h without significant changes (<1.8 ppb). The analysis of real wastewater samples from both a laboratory-scale sewer system and a full-scale sewer pipe demonstrated the suitability of this method for routine wastewater VOSC measurement. [Copyright &y& Elsevier]

Autotrophic ammonia oxidizing bacteria (AOB) have been recognized as a major contributor to N2O production in wastewater treatment systems. However, so far N2O models have been proposed based on a single N2O production pathway by AOB, and there is still a lack of effective approach for the integration of these models. In this work, an integrated mathematical model that considers multiple production pathways is developed to describe N2O production by AOB. The pathways considered include the nitrifier denitrification pathway (N2O as the final product of AOB denitrification with NO2- as the terminal electron acceptor) and the hydroxylamine (NH2OH) pathway (N2O as a byproduct of incomplete oxidation of NH2OH to NO2-). In this model, the oxidation and reduction processes are modeled separately, with intracellular electron carriers introduced to link the two types of processes. The model is calibrated and validated using experimental data obtained with two independent nitrifying cultures. The model satisfactorily describes the N2O data from both systems. The model also predicts shifts of the dominating pathway at various dissolved oxygen (DO) and nitrite levels, consistent with previous hypotheses. This unified model is expected to enhance our ability to predict N2O production by AOB in wastewater treatment systems under varying operational conditions. [ABSTRACT FROM AUTHOR]

Abstract: Wastewater pH affects the transfer of H2S from liquid to gas and hence impacts on the extent of odour and corrosion. Sewage pH may change significantly in sewer networks due to, for example, the fermentation of organic compounds, particularly when the hydraulic retention time is long, the discharge of trade wastes that are organic-rich or with extreme pH, and the intentional addition of alkali to raise the sewage pH. Such a variation of pH is expected to affect sulfate reduction by sewer biofilms. In this work, experimental studies were carried out to reveal the detailed effects of pH on sulfidogenesis by anaerobic sewer biofilms developed in a laboratory sewer reactor fed with real sewage, and the potential causes for the inhibitory effects observed under both high and low pH conditions. The data clearly showed that the sewer biofilm had the highest sulfate reduction rate at around neutral pH (6.5–7.5), and the activity decreased when pH was higher or lower. The data also suggested that the inhibiting effect at a higher pH is likely due to the inhibitory effects of free ammonia, while at a lower pH it is more likely due to the pH itself. An inhibition model formulated based on the above hypotheses was able to adequately describe the measured sulfide production rates under different pH levels and different free ammonia concentrations, as well as data previously reported in literature. The calibrated model was used to simulate sulfide production in a sewer network receiving alkali dosage. The model adequately predicted sulfide production in the network, which could not be achieved with a model not considering the pH effect. [Copyright &y& Elsevier]

Abstract: The stability of five illicit drug markers in wastewater was tested under different sewer conditions using laboratory-scale sewer reactors. Wastewater was spiked with deuterium labelled isotopes of cocaine, benzoyl ecgonine, methamphetamine, MDMA and 6-acetyl morphine to avoid interference from the native isotopes already present in the wastewater matrix. The sewer reactors were operated at 20 °C and pH 7.5, and wastewater was sampled at 0, 0.25, 0.5, 1, 2, 3, 6, 9 and 12 h to measure the transformation/degradation of these marker compounds. The results showed that while methamphetamine, MDMA and benzoyl ecgonine were stable in the sewer reactors, cocaine and 6-acetyl morphine degraded quickly. Their degradation rates are significantly higher than the values reportedly measured in wastewater alone (without biofilms). All the degradation processes followed first order kinetics. Benzoyl ecgonine and morphine were also formed from the degradation of cocaine and 6-acetyl morphine, respectively, with stable formation rates throughout the test. These findings suggest that, in sewage epidemiology, it is essential to have relevant information of the sewer system (i.e. type of sewer, hydraulic retention time) in order to accurately back-estimate the consumption of illicit drugs. More research is required to look into detailed sewer conditions (e.g. temperature, pH and ratio of biofilm area to wastewater volume among others) to identify their effects on the fate of illicit drug markers in sewer systems. [Copyright &y& Elsevier]

Abstract: The quantification of nitrous oxide (N2O) emissions from open-surface wastewater treatment systems with surface aerators is difficult as emissions from the surface aerator zone cannot be easily captured by floating hoods. In this study, we propose and demonstrate a novel methodology to estimate N2O emissions from such systems through determination of the N2O transfer coefficient (k L a) induced by surface aerators based on oxygen balance for the entire system. The methodology is demonstrated through its application to a full-scale open oxidation ditch wastewater treatment plant with surface aerators. The estimated k L a profile based on a month-long measurement campaign for oxygen balance, intensive monitoring of dissolved N2O profiles along the oxidation ditch over a period of four days, together with mathematical modelling, enabled to determine the N2O emission factor from this treatment plant (0.52 ± 0.16%). Majority of the N2O emission was found to occur in the surface aerator zone, which would be missed if the gas hood method was applied alone. [Copyright &y& Elsevier]

Abstract: To better understand granule growth and breakage processes in aerobic granular sludge systems, the particle size of aerobic granules was tracked over 50 days of wastewater treatment within four sequencing batch reactors fed with abattoir wastewater. These experiments tested a novel hypothesis stating that granules equilibrate to a certain stable granule size (the critical size) which is determined by the influence of process conditions on the relative rates of granule growth and granule breakage or attrition. For granules that are larger than the critical size, granule breakage and attrition outweighs granule growth, and causes an overall reduction in granule size. For granules at the critical size, the overall growth and size reduction processes are balanced, and granule size is stable. For granules that are smaller than the critical size, granule growth outweighs granule breakage and attrition, and causes an overall increase in granule size. The experimental reactors were seeded with mature granules that were either small, medium, or large sized, these having respective median granule sizes of 425 μm, 900 μm and 1125 μm. An additional reactor was seeded with a mixture of the sized granules to represent the original source of the granular sludge. The experimental results were analysed together with results of a previous granule formation study that used mixed seeding of granules and floccular sludge. The analysis supported the critical size hypothesis and showed that granules in the reactors did equilibrate towards a common critical size of around 600–800 μm. Accordingly, it is expected that aerobic granular reactors at steady-state operation are likely to have granule size distributions around a characteristic critical size. Additionally, the results support that maintaining a quantity of granules above a particular size is important for granule formation during start-up and for process stability of aerobic granule systems. Hence, biomass washout needs to be carefully managed to optimize granule formation during the reactor start-up. [Copyright &y& Elsevier]

Abstract: This study reports the presence of fossil organic carbon in wastewater and its fate in wastewater treatment plants. The findings pinpoint the inaccuracy of current greenhouse gas accounting guidelines which defines all organic carbon in wastewater to be of biogenic origin. Stable and radiocarbon isotopes (13C and 14C) were measured throughout the process train in four municipal wastewater treatment plants equipped with secondary activated sludge treatment. Isotopic mass balance analyses indicate that 4–14% of influent total organic carbon (TOC) is of fossil origin with concentrations between 6 and 35 mg/L; 88–98% of this is removed from the wastewater. The TOC mass balance analysis suggests that 39–65% of the fossil organic carbon from the influent is incorporated into the activated sludge through adsorption or from cell assimilation while 29–50% is likely transformed to carbon dioxide (CO2) during secondary treatment. The fossil organic carbon fraction in the sludge undergoes further biodegradation during anaerobic digestion with a 12% decrease in mass. 1.4–6.3% of the influent TOC consists of both biogenic and fossil carbon is estimated to be emitted as fossil CO2 from activated sludge treatment alone. The results suggest that current greenhouse gas accounting guidelines, which assume that all CO2 emission from wastewater is biogenic may lead to underestimation of emissions. [Copyright &y& Elsevier]

Abstract: Sludge treatment and disposal is one of the major challenges for biological wastewater treatment plants and can represent up to 60% of their total operating costs. This study presents a novel strategy based on free nitrous acid (FNA or HNO2) treatment to achieve sludge reduction. Two sequencing batch reactors treating synthetic domestic wastewater were used, with one serving as an experimental reactor and the other as a control. In the experimental system, 50% of the excess sludge was exposed to FNA at 2.0 mg N/L for 24–42 h in an FNA treatment unit and then returned to the parent reactor. The sludge wastage flow from the experimental reactor was adjusted to obtain a similar mixed liquor suspended solids concentration to that in the control reactor, which was operated at a sludge retention time of 15 days. It was found that sludge production in the experimental system was 28% lower in comparison to the control. The addition of the FNA-treated sludge did not negatively affect the treatment performance and sludge properties of the experimental reactor, namely the organic carbon and nitrogen removal, nitrous oxide (N2O) emission and sludge settleability. Endogenous denitrification batch tests indicate that FNA-treated sludge is available as a carbon source for denitrification. [Copyright &y& Elsevier]

Abstract: Limited availability of carbon sources has been regarded as an important factor leading to N2O accumulation during denitrification in wastewater treatment. By varying the carbon (methanol) loading rate to a methanol utilizing denitrifying culture in the presence of various electron acceptors (nitrate, nitrite, N2O and their combinations), this study quantitatively investigated the electron distribution among different nitrogen oxide reductases during denitrification. The results showed that electron competition occurs under not only carbon limiting but also carbon abundant conditions. The electron distribution among the nitrogen oxide reductases is affected by the carbon loading rate, with a lower fraction of electrons distributed to the N2O reductase with reduced carbon loading rate. N2O accumulation occurs when the electron flux going to nitrite reduction is higher than that going to N2O reduction. The study also showed that, for the culture investigated, the carbon to nitrogen ratio is not a key factor leading to N2O accumulation. [Copyright &y& Elsevier]

The application of aerobic sludge granules in wastewater treatment could increase the intensity of wastewater treatment processes because of their greater density and size relative to conventional sludge flocs. It has been suggested that granules are distinguished from flocs by gel forming exopolysaccharides. In this study, evidence is presented linking a specific exopolysaccharide component with granule extracellular polymeric substance (EPS) gelation. Granular EPS comprised three components: high-molecular-weight (MW) exopolysaccharide, medium-MW proteins and glycosides, and low-MW proteins and glycosides. The high-MW fraction was separated by fractional precipitation and preparatory-scale gel permeation chromatography (GPC). The MW profile of this fraction appears to be exclusively attributable to high-MW polysaccharide. The exopolysaccharide exists as a gel at normal wastewater treatment operating pH (i.e., 6.0-8.5), whereas the low/medium-MW material does not. Conformational analysis by atomic force microscopy (AFM) of the dried material showed that the polysaccharide forms pearl-necklace-like, intramolecularly condensed structures when dissolved in Milli-Q water and partially relaxed helical aggregates when in alkali solution. Consequently, the gel-forming property of EPS in the aerobic sludge granules tested is probably associated with high-MW polysaccharide components. [ABSTRACT FROM AUTHOR]

Abstract: Chemical phosphorus (P) removal during aerobic wastewater treatment induced by iron salt addition in sewer systems for sulfide control is investigated. Aerobic batch tests with activated sludge fed with wastewater containing iron sulfide precipitates showed that iron sulfide was rapidly reoxidised in aerobic conditions, resulting in phosphate precipitation. The amount of P removed was proportional to the amount of iron salts added, and for the sludge used, ratios of 0.44 and 0.37 mgP/mgFe were obtained for ferric and ferrous dosages, respectively. The hydraulic retention time (HRT) of iron sulfide in sewers was found to have a crucial impact on the settling of iron sulfide precipitates during primary settling, with a shorter HRT resulting in a higher concentration of iron sulfide in the primary effluent and thus enabling higher P removal. A mathematical model was developed to describe iron sulfide oxidation in aerated activated sludge and the subsequent iron phosphate precipitation. The model was used to optimise FeCl3 dosing in a real wastewater collection and treatment system. Simulation studies revealed that, by moving FeCl3 dosing from the WWTP, which is the current practice, to a sewer location upstream of the plant, both sulfide control and phosphate removal could be achieved with the current ferric salt consumption. This work highlights the importance of integrated management of sewer networks and wastewater treatment plants. [Copyright &y& Elsevier]

Nitrogen removal via nitrite (the nitrite pathway) is beneficial for carbon-limited biological wastewater treatment plants. However, partial nitrification to nitrite has proven difficult in continuous processes treating domestic wastewater. The nitrite pathway is achieved in this study in a pilot-scale continuous pre-denitrification plant (V =300L) treating domestic wastewater by controlling the dissolved oxygen (DO) concentration at 0.4–0.7mg/L. It is demonstrated that the nitrite pathway could be repeatedly and reliably achieved, with over 95% of the oxidized nitrogen compounds at the end of the aerobic zone being nitrite. The nitrite pathway improved the total nitrogen (TN) removal by about 20% in comparison to the nitrate pathway, and also reduced aeration costs by 24%. FISH analysis showed that the nitrite oxidizing bacteria (NOB) population gradually reduced at low DO levels, and reached negligible levels when stable nitrite pathway was established. It is hypothesized that NOB was washed out due to its relatively lower affinity with oxygen. A lag phase was observed in the establishment of the nitrite pathway. Several sludge ages were required for the onset of the nitrite pathway after the application of low DO levels. However, nitrite accumulation increased rapidly after that. A similar lag phase was observed for the upset of the nitrite pathway when a DO concentration of 2–3mg/L was applied. The nitrite pathway negatively impacted on the sludge settleability. A strong correlation between the sludge volume index and the degree of nitrite accumulation was observed. [Copyright &y& Elsevier]