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In this work, the modification of Bi2MoO6 with critic acid (CA-BMO) to achieve enhanced adsorption of methylene blue (MB) solution in dark and desorption under visible light irradiation was reported. The as-prepared materials were synthesized by a hydrothermal method and characterized via SEM, FT-IR, XRD, and XPS techniques. Only 16.5% of 10 mg L−1 MB was removed within 10 min by using 0.5 g L−1 Bi2MoO6, while 92.9% removal of MB could be achieved by using 0.5 g L−1 CA-BMO, which enhanced the adsorption removal by a factor of 4.6. The adsorption capacity for MB was 18.9 mg g−1. Desorption efficiency of MB was only observed in CA-BMO system, and it depends on the wavelength of the light source, pH, and the presence of metal ions. Characterization results suggested that carboxyl groups, which were modified onto the surface of Bi2MoO6, could serve as adsorption sites for MB, and the connections were damaged under light, thus leading to the desorption of MB from the surface of the CA-BMO. This study provides a novel reagent-free desorption strategy for dye recovery without secondary pollution, which facilitates the development and application of Bi-based adsorbent for dye-containing wastewater treatment. [ABSTRACT FROM AUTHOR]

Anaerobic microorganisms are thought to play a critical role in regulating the flux of short-chain gaseous alkanes (SCGAs; including ethane, propane and butane) from terrestrial and aquatic ecosystems to the atmosphere. Sulfate has been confirmed to act as electron acceptor supporting microbial anaerobic oxidation of SCGAs, yet several other energetically more favourable acceptors co-exist with these gases in anaerobic environments. Here, we show that a bioreactor seeded with biomass from a wastewater treatment facility can perform anaerobic propane oxidation coupled to nitrate reduction to dinitrogen gas and ammonium. The bioreactor was operated for more than 1000 days, and we used 13C- and 15N-labelling experiments, metagenomic, metatranscriptomic, metaproteomic and metabolite analyses to characterize the microbial community and the metabolic processes. The data collectively suggest that a species representing a novel order within the bacterial class Symbiobacteriia is responsible for the observed nitrate-dependent propane oxidation. The closed genome of this organism, which we designate as 'Candidatus Alkanivorans nitratireducens', encodes pathways for oxidation of propane to CO2 via fumarate addition, and for nitrate reduction, with all the key genes expressed during nitrate-dependent propane oxidation. Our results suggest that nitrate is a relevant electron sink for SCGA oxidation in anaerobic environments, constituting a new microbially-mediated link between the carbon and nitrogen cycles. Anaerobic microorganisms can oxidize short-chain gaseous alkanes such as ethane, propane and butane using sulfate as electron acceptor. Here, the authors show that a bioreactor enrichment of a wastewater microbial community can perform anaerobic propane oxidation coupled to nitrate reduction. [ABSTRACT FROM AUTHOR]

New pollutants, pharmaceuticals and personal care products (PPCPs), accumulate in sewage sludge (SS) in wastewater treatment plants (WWTPs), posing risks to the environment and to human health. In the present study, the fates of typical PPCPs, carbamazepine (CBZ), triclosan (TCS), ibuprofen (IBU) and galaxolide (HHCB), were examined during WW treatment. Additionally, SS collected from a WWTP was used for aerobic composting to investigate the influences of micron-sized Fe 3 O 4 (M-Fe) and nano-sized Fe 3 O 4 (N–Fe) on the degradation of these PPCPs and the succession of microbial communities during the composting process. The results showed that the mean concentrations of CBZ, TCS, IBU and HHCB in the influent of the WWTP were 926.5, 174.4, 8869, and 967.3 ng/g, respectively, and in the effluent were 107.6, 47.0, 283.4, and 88.4 ng/g, respectively. The removal rate averaged ∼80%, while the enrichment rates of the PPCPs in SS ranged from 37.2% to 60.5%. M-Fe and N–Fe reduced NH 3 emissions by 32.9% and 54.1% and N 2 O emissions by 26.2% and 50.8%, respectively. Moreover, the addition of M-Fe and N–Fe effectively increased PPCP degradation rates 1.12–1.66-fold. During the whole process, the additions of M-Fe and N–Fe significantly shifted microbial community structure, and the abundances of Proteobacteria, Chloroflexi, and Actinobacteria were increased during the thermophilic stage, marking them as key PPCP-degrading phyla. Taken together, our results indicated that the addition of M-Fe and N–Fe is an effective method for improving the quality of end compost and accelerating the degradation of PPCPs. The removal rate of the four PPCPs averaged ∼80% after the wastewater treatment plant (WWTP), while the enrichment rates of the PPCPs in sewage sludge (SS) ranged from 37.2% to 60.5%. The M-Fe and N–Fe reduced NH 3 emission by 32.9% and 54.1%, and N 2 O emission by 26.2% and 50.8%, respectively. Meanwhile, adding M-Fe and N–Fe effectively promoted the PPCPs degradation rates by 1.12–1.66 times. During the whole process, the additions of M-Fe and N–Fe significantly shifted the microbial community structure, and the abundances of Proteobacteria, Chloroflexi, and Actinobacteria were boosted during the thermophilic stage, marking as key PPCPs-degrading phyla. [Display omitted] • The enrichment rates of four PPCPs in sewage sludge ranged from 37.2% to 60.5%. • M-Fe and N–Fe reduced NH 3 emission by 32.9% and 54.1%, and N 2 O by 26.2% and 50.8%. • M-Fe and N–Fe effectively promoted the PPCPs degradation rates by 1.12–1.66 time. • M-Fe and N–Fe were effective method to improve compost and PPCPs degradation. [ABSTRACT FROM AUTHOR]

[Display omitted] • IWWTPs bacterial communities exhibited a clear species abundance distribution. • Deterministic processes dominate IWWTPs bacterial communities assembly. • Different IWWTPs harbor unique core bacterial community. • IWWTP bacterial community was strongly linked to activated sludge function. Microbial communities are responsible for biological treatment of many industrial wastewater, but our knowledge of their diversity, assembly patterns, and function is still poor. Here, we analyzed the bacterial communities of wastewater and activated sludge samples taken from 11 full-scale industrial wastewater treatment plants (IWWTPs) characterized by the same process design but different wastewater types and WWTP compartments. We found significantly different diversity and compositions of bacterial assemblages among distinct wastewater types and IWWTPs compartments. IWWTPs bacterial communities exhibited a clear species abundance distribution. The dispersal-driven process was weak in shaping IWWTP communities. Meanwhile, environmental and operating conditions were important factors in regulating the structure of the activated sludge community and pollutants removal, indicating that bacterial community was largely driven by deterministic mechanisms. The core microbial community in IWWTPs was different from that in municipal wastewater treatment plants (MWWTPs), and many taxa (e.g. the genus Citreitalea) rarely were detected before, indicating IWWTPs harbored unique core bacterial communities. Furthermore, we found that bacterial community compositions were strongly linked to activated sludge function. These findings are important to both microbial ecologists and environmental engineers, who may optimize the operation strategies jointly for maintaining biodiversity, which in turn may promote a more stable performance of the IWWTP. Overall, our study enhances the mechanistic understanding of the IWWTP microbial community diversity, assembly patterns, and function, and provides important implications for microbial ecology and wastewater treatment processes. [ABSTRACT FROM AUTHOR]

[Display omitted] • The Zn substituted Co 3 O 4 catalysts were prepared and applied in PMS activation for florfenicol removal. • The Zn substitution induced electron rearrangement and promoted oxygen vacancies formation in Co 3 O 4. • The Zn substituted Co 3 O 4 (Zn 0.03 Co) exhibited superior florfenicol removal and higher reaction rate than Co 3 O 4. • The florfenicol degradation is highly dependent on PMS/Zn 0.03 Co/florfenicol dosage, temperature and initial pH. • The degradation mechanism and routes were proposed combining LC-MS/MS and theoretical calculation results. Florfenicol (FLO) is a broad-spectrum halogenated antibiotic (containing F and Cl atoms), and the discharged FLO in wastewater exhibits potential biotoxicity. Peroxymonosulfate (PMS) activation can generate reactive oxygen species (ROSs) to realize efficient degradation of organic pollutants. Herein, Zn-substituted Co 3 O 4 (Zn x Co) catalysts were prepared and applied in PMS activation for FLO degradation. The physicochemical properties were systematically studied by combining experiments and density functional theory (DFT) calculation. The Zn partial substitution induced electron rearrangement and promoted oxygen vacancy (OV) formation in Co 3 O 4. Zn 0.03 Co catalyst exhibited superior FLO removal, achieving a higher reaction rate of 0.112 min−1 than Co 3 O 4 (0.053 min−1). The FLO degradation was highly dependent on the factors of PMS/Zn 0.03 Co/FLO dosage, temperature, initial pH, and coexisting inorganic anions. The Zn 0.03 Co also displayed outstanding performance in PMS activation for degradation of various typical organic pollutants. Electron paramagnetic resonance (EPR) spectra and quenching experiments indicated that both radical species ( · OH , SO 4 · - , and · O 2 -) and nonradical species (1O 2) contribute to FLO removal. The redox cycle of Co3+/Co2+ and OVs played an essential role in PMS activation. The electron structure of FLO and parameters of PMS adsorbed on Zn x Co were calculated. The longer length of Co O and O O bonds for the adsorbed PMS could enhance its activation to generate ROSs. The intermediates were detected, and five degradation pathways were proposed. The acute and chronic toxicities of intermediates suggested that the dechlorination process is important for the toxicity attenuation of FLO. This study clarified the performance enhancement mechanism of Zn substitution on FLO degradation by PMS activation using Co 3 O 4 based catalyst, which favors the development of PMS-based advanced oxidation processes for wastewater treatment. [ABSTRACT FROM AUTHOR]

The formation of aerobic granular sludge (AGS) is relatively difficult during the treatment of refractory wastewater, which generally shows small granular sizes and poor stability. The formation of AGS is regulated by N-Acyl homoserine lactones (AHLs)-mediated quorum sensing (QS). However, the potential role of AHLs in AGS formation under the toxic stress of refractory pollutants and the heterogeneity in the distribution and function of AHLs across different aggregates are not well understood. This study investigated the potential effects of AHLs on the formation of AGS during phenolic wastewater treatment. The distribution and succession of AHLs across varying granular sizes and development stages of AGS were investigated. Results showed that AGS was successfully formed in 13 days with an average granular size of 335 ± 39 μm and phenol removal efficiency of >99%. The levels of AHLs initially increased and then decreased. C4-HSL and 3-oxo-C10-HSL were enriched in large granules, suggesting they may play a pivotal role in regulating the concentration and composition of extracellular polymeric substances (EPS). The content of EPS constantly increased to 149.4 mg/gVSS, and protein (PN) was enriched in small and large granules. Luteococcus was the dominant genus constituting up to 62% after the granulation process, and exhibited a strong association with C4-HSL. AHLs might also regulate the bacterial community responsible for EPS production, and pollutant removal, and facilitate the proliferation of slow-growing microorganisms, thereby enhancing the formation of AGS. The synthesis and dynamics of AHLs were mainly governed by AHLs-producing bacterial strains of Rhodobacter and Pseudomonas , and AHLs-quenching strains of Flavobacterium and Comamonas. C4-HSL and 3-oxo-C10-HSL might be the major contributors to promoting sludge granulation under phenol stress and play critical roles in large granules. These findings enhance our understanding of the roles that AHLs play in sludge granulation under toxic conditions. [Display omitted] • C4-HSL and 3-oxo-C10-HSL were mainly involved in granular formation. • Concentration of N-Acyl homoserine lactones (AHLs) in large granules was higher. • Protein was more effective in granules formation as compared to polysaccharides. • AHLs regulating functional microflora contributed to granules formation. • Mechanism of AHLs on granular formation under phenol condition was proposed. [ABSTRACT FROM AUTHOR]

• Stable NOB suppression is maintained in MABR treating low-strength wastewater for > 200 days. • Acidic pH of 5.0–5.2 and in situ FNA of 1 mg N/L jointly result in NOB suppression. • An unprecedentedly high AOB activity at around 2.4 kg N/(m3 d) is achieved at a short HRT of a mere 30 min. • Acid-tolerant AOB in MABR-biofilms show different apparent kinetics and responses to environmental factors. Shortcut nitrogen removal holds significant economic appeal for mainstream wastewater treatment. Nevertheless, it is too difficult to achieve the stable suppression of nitrite-oxidizing bacteria (NOB), and simultaneously maintain the activity of ammonia-oxidizing bacteria (AOB). This study proposes to overcome this challenge by employing the novel acid-tolerant AOB, namely " Candidatus Nitrosoglobus", in a membrane-aerated biofilm reactor (MABR). Superior partial nitritation was demonstrated in low-strength wastewater from two aspects. First, the long-term operation (256 days) under the acidic pH range of 5.0 to 5.2 showed the successful NOB washout by the in situ free nitrous acid (FNA) of approximately 1 mg N/L. This was evidenced by the stable nitrite accumulation ratio (NAR) close to 100 % and the disappearance of NOB shown by 16S rRNA gene amplicon sequencing and fluorescence in situ hybridization. Second, oxygen was sufficiently supplied in the MABR, leading to an unprecedentedly high ammonia oxidation rate (AOR) at 2.4 ± 0.1 kg N/(m3 d) at a short hydraulic retention time (HRT) of a mere 30 min. Due to the counter diffusion of substrates, the present acidic MABR displayed a significantly higher apparent oxygen affinity (0.36 ± 0.03 mg O 2 /L), a marginally lower apparent ammonia affinity (14.9 ± 1.9 mg N/L), and a heightened sensitivity to FNA and pH variations, compared with counterparts determined by flocculant acid-tolerant AOB. Beyond supporting the potential application of shortcut nitrogen removal in mainstream wastewater, this study also offers the attractive prospect of intensifying wastewater treatment by markedly reducing the HRT of the aerobic unit. [Display omitted] [ABSTRACT FROM AUTHOR]

• 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]

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]

• 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]

• 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]

• 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]

• Anaerobically-digested sludge is acidified to pH 2.0 driven by ammonium oxidation. • The ammonium-based bioleaching solubilizes 88 ± 4% of Cu and 96 ± 3% of Zn. • A new ammonia-oxidizing bacterium Ca. Nitrosoglobus play a critical role in bioleaching. Anaerobically digested (AD) sludge is widely applied to agricultural land as fertilizer. However, heavy metals in AD sludge potentially pose a significant threat to environment. This study reports a novel bioleaching approach, with no need for externally added chemicals. Sludge acidification was achieved using the protons produced from microbial oxidation of the inherent ammonium in AD sludge. An acid-tolerant microbial consortium, dominated by ammonia-oxidizing bacteria from the genus Candidatus Nitrosoglobus (i.e. relative abundance of 72.5 ± 2.3% based on 16S rRNA gene sequencing), was enriched after 120 days incubation in a laboratory sequencing batch reactor. The consortium oxidizes ammonium even at pH 2.5, at approximately 30% of its maximum rate, measured at pH 5.5. Inoculating the consortium at a solid ratio of 1:20, caused the pH of the AD sludge to decrease from 7.5 to 2.0 over five days under aerobic conditions. As a result, metals in the AD sludge were efficiently extracted into the liquid phase. In particular, two of the most abundant toxic metals, Cu and Zn, were solubilized with high efficiencies of 88 ± 4% and 96 ± 3%, respectively. Overall, the results of this study enable the economical and safe reuse of excess sludge generated during biological wastewater treatment. [Display omitted] [ABSTRACT FROM AUTHOR]