Wastewater electrolysis cells (WECs) for decentralized wastewater treatment/reuse coupled with H2 production can reduce the carbon footprint associated with transportation of water, waste, and energy carrier. This study reports Ir-doped NiFe2O4 (NFI, ~ 5 at% Ir) spinel layer with TiO2 overlayer (NFI/TiO2), as a scalable heterojunction anode for direct electrolysis of wastewater with circumneutral pH in a single-compartment cell. In dilute (0.1 M) NaCl solutions, the NFI/TiO2 marks superior activity and selectivity for chlorine evolution reaction, outperforming the benchmark IrO2. Robust operation in near-neutral pH was confirmed. Electroanalyses including operando X-ray absorption spectroscopy unveiled crucial roles of TiO2 which serves both as the primary site for Cl− chemisorption and a protective layer for NFI as an ohmic contact. Galvanostatic electrolysis of NH4+-laden synthetic wastewater demonstrated that NFI/TiO2 not only achieves quasi-stoichiometric NH4+-to-N2 conversion, but also enhances H2 generation efficiency with minimal competing reactions such as reduction of dissolved oxygen and reactive chlorine. The scaled-up WEC with NFI/TiO2 was demonstrated for electrolysis of toilet wastewater.
", "doi": "10.1007/s40820-024-01542-x", "issn": "2311-6706", "publisher": "Springer Science and Business Media LLC", "publication": "Nano-Micro Letters", "publication_date": "2024-10-28", "series_number": "1", "volume": "17", "issue": "1", "pages": "51" }, { "id": "authors:j97kj-6nx17", "collection": "authors", "collection_id": "j97kj-6nx17", "cite_using_url": "https://authors.library.caltech.edu/records/j97kj-6nx17", "type": "article", "title": "Controlling the Selectivity of Chlorine Evolution Reaction by IrTaO\u2093/TiO\u2082 Heterojunction Anodes: Mechanism and Real Wastewater Treatment", "author": [ { "family_name": "Rahman", "given_name": "Evandi", "clpid": "Rahman-Evandi" }, { "family_name": "Shin", "given_name": "Jieun", "orcid": "0000-0003-3817-6282", "clpid": "Shin-Jieun" }, { "family_name": "Hong", "given_name": "Sukhwa", "clpid": "Hong-Sukhwa" }, { "family_name": "Im", "given_name": "Sunmi", "clpid": "Im-Sunmi" }, { "family_name": "Kim", "given_name": "Jiseon", "clpid": "Kim-Jiseon" }, { "family_name": "Chung", "given_name": "Chong Min", "clpid": "Chung-Chong-Min" }, { "family_name": "Hong", "given_name": "Seok Won", "orcid": "0000-0003-0961-3842", "clpid": "Hong-Seok-Won" }, { "family_name": "Hoffmann", "given_name": "Michael R.", "orcid": "0000-0001-6495-1946", "clpid": "Hoffmann-M-R" }, { "family_name": "Cho", "given_name": "Kangwoo", "orcid": "0000-0002-1819-7687", "clpid": "Cho-Kangwoo" } ], "abstract": "This study investigated the effects of varied loadings of TiO2 overlayers in heterojunction with conventional Ir0.7Ta0.3Ox (IrTaOx) anodes on chlorine evolution reaction (ClER) and real (waste)water treatment at circum-neutral pH. With an optimized design of IrTaOx/TiO2, elevated ClER selectivity was attained by more facile chemisorption of chloride ions to a thin TiO2 layer on IrTaOx. The current efficiency (CE) of ClER in galvanostatic electrolysis of 50 mM NaCl solutions (at 30 mA cm–2) was maximized to ∼80% by a heterojunction architecture with ∼605 μg cm–2 of IrTaOx and ∼265 μg cm–2 of TiO2 after specific rounds of drop casting. Further increases in loading resulted in escalated film-pore resistance or deterioration of ClER selectivity. The observed CE values were correlated with experimental descriptors, such as potential of zero charge and flat band potential, demonstrating that the weaker metal–oxygen bond strength on TiO2 could enhance the ClER selectivity compared to bare IrTaOx. We concluded that ClER primarily occurs on TiO2 near the junction owing to the nanoporous nature of the TiO2 layer, while IrTaOx serves as ohmic contact. The optimized IrTaOx/TiO2 anodes effectively improved the treatment of reverse osmosis concentrate, but phosphate ions in livestock wastewater caused adverse effects due to complexation on TiO2. The heterojunction architecture effectively tunes the surface charge density for selective generation of oxidants, which can facilitate electrochemical water treatment with reduced use of the precious metals.
\nThe long-term performance of an anaerobic bioreactor combined with electrochemical oxidation and integrated into a self-contained public bathroom under daily use was investigated over 14 months in Coimbatore (Tamil Nadu, India). With varying daily number of users and across all seasons, the electrochemical treatment of the bioreactor effluent consistently generated a highly chlorinated (>400 mg Cl\u2082 per L) and clear effluent that was negative to a fecal coliform assay. During 8 months of testing under water recycling conditions, the treatment maintained its performance for disinfection, as well as solid and nitrogen removal, due to breakpoint chlorination; however, the COD removal capacity of the system was slightly reduced. The strongly oxidizing condition of this electrochemical based disinfection raised the concern of generation of toxic disinfection byproducts (DPBs). This study also examined the formation of chloroform and haloacetic acid DBPs under non-recycling and recycling conditions.
", "doi": "10.1039/d3ew00454f", "issn": "2053-1400", "publisher": "Royal Society of Chemistry", "publication": "Environmental Science: Water Research & Technology", "publication_date": "2024-01-01", "series_number": "1", "volume": "10", "issue": "1", "pages": "157-167" }, { "id": "authors:1en5r-ms451", "collection": "authors", "collection_id": "1en5r-ms451", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20200424-090856301", "type": "article", "title": "Enhanced chlorine evolution from dimensionally stable anode by heterojunction with Ti and Bi based mixed metal oxide layers prepared from nanoparticle slurry", "author": [ { "family_name": "Hong", "given_name": "Sukhwa", "clpid": "Hong-Sukhwa" }, { "family_name": "Lee", "given_name": "Tai-kyu", "clpid": "Lee-Tai-kyu" }, { "family_name": "Hoffmann", "given_name": "Michael R.", "orcid": "0000-0001-6495-1946", "clpid": "Hoffmann-M-R" }, { "family_name": "Cho", "given_name": "Kangwoo", "clpid": "Cho-Kangwoo" } ], "abstract": "This study reports enhanced current (CE_(RCS)) and energy efficiency (EE_(RCS)) of reactive chlorine species (RCS) generation on Ir\u2087Ta\u2083O_y anode by Ti/Bi mixed metal oxide heterojunction layers despite reductions in pseudo-capacitance and film conductivity. In potentiostatic electrolysis of 50 mM NaCl solutions, dramatic improvement (0.61 mmol cm\u207b\u00b2 hr\u207b\u00b9 at 2.5 V NHE) was noted by simple coating of thin (~2 \u03bcm) TiO\u2082 layer from ball-milled TiO\u2082 nanoparticle (80\u2013100 nm) suspension, even with moderate elevation in voltammetric wave. Decoration of Bi\u2082O\u2083 particles (1 \u2013 2 \u03bcm) showed limited or adverse effects for RCS generation and stability. However, Bi-doped TiO\u2082 layers prepared from polyol-mediated or co-precipitation methods marked the highest CE_(RCS) (~100%) and EE_(RCS) (8.16 mmol Wh\u207b\u00b9 at 2.5 V NHE) by increased mixing level and effective shift in surface charge. Surface \u00b7OH exclusively mediated the RCS generation whose further transformation to higher oxide could be restrained by the heterojunction layer.", "doi": "10.1016/j.jcat.2020.04.009", "pmcid": "PMC7539370", "issn": "0021-9517", "publisher": "Elsevier", "publication": "Journal of Catalysis", "publication_date": "2020-09", "volume": "389", "pages": "1-8" }, { "id": "authors:015g2-sn379", "collection": "authors", "collection_id": "015g2-sn379", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20171031-140730625", "type": "article", "title": "Degradation of Organic Compounds in Wastewater Matrix by Electrochemically Generated Reactive Chlorine Species: Kinetics and Selectivity", "author": [ { "family_name": "Chung", "given_name": "Chong Min", "clpid": "Chung-Chong-Min" }, { "family_name": "Hong", "given_name": "Seok Won", "clpid": "Hong-Seok-Won" }, { "family_name": "Cho", "given_name": "Kangwoo", "clpid": "Cho-Kangwoo" }, { "family_name": "Hoffmann", "given_name": "Michael R.", "orcid": "0000-0001-6495-1946", "clpid": "Hoffmann-M-R" } ], "abstract": "In this study, we examined the kinetics and selectivity of chemical oxygen demand (COD) degradation by electrochemically generated reactive oxygen species (RCS) in variable wastewater matrix. According to measurements on reactive oxidants and linear sweep voltammetry, oxidation of organics either via reactive oxygen species or direct electron transfer played a minor role for the active IrO_2 anode. The RCS (mostly free chlorine in bulk solution) exclusively mediated an indirect oxidation with mean current efficiency from 25 to 40%. In batch galvanostatic experiments for single polymeric compounds, the rate of COD reduction showed marginal variations in spite of the large difference in reactivity with the RCS. Eight different wastewater samples prepared from greywater and urine for potentiostatic experiments. The kinetics of COD degradation in municipal wastewater was observed to more sluggish than in the urinary samples with initial elevations in [COD]. Fractionation of COD into proteins, carbohydrates, and carboxylates could explain the shift in kinetics, in terms of the reactivity with RCS and the ratio of COD to theoretical oxygen demand (ThOD) for each components. The anaerobic biodegradation of the organic matrix greatly improved the subsequent reactivity with RCS, which rationalizes a combination of electrochemical processes with biological pretreatment.", "doi": "10.1016/j.cattod.2017.10.027", "issn": "0920-5861", "publisher": "Elsevier", "publication": "Catalysis Today", "publication_date": "2018-09-01", "volume": "313", "pages": "189-195" }, { "id": "authors:a8frn-kdp13", "collection": "authors", "collection_id": "a8frn-kdp13", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20161208-083729182", "type": "article", "title": "Molecular hydrogen production from wastewater electrolysis cell with multi-junction BiO_x/TiO_2 anode and stainless steel cathode: Current and energy efficiency", "author": [ { "family_name": "Cho", "given_name": "Kangwoo", "clpid": "Cho-Kangwoo" }, { "family_name": "Hoffmann", "given_name": "Michael R.", "orcid": "0000-0001-6495-1946", "clpid": "Hoffmann-M-R" } ], "abstract": "Electrochemical hydrogen evolution reaction (HER) has been recognized as a viable approach to generate a clean energy fuel. However, substantial technical breakthroughs are needed to reduce the costs for electricity and chemical reagents. In this study, we explore a specific wastewater electrolysis cell (WEC) as an alternative of decentralized H_2 production coupled with onsite water treatment. A prototypical WEC consists of a multi-junction semiconductor anode and a stainless steel cathode paired in single compartment cell. A distinct layer of BiO_x/TiO_2 on anode surface had relatively low crystallinity that was shown to be beneficial for higher oxide formation and O_2 evolution. The over-potential and Tafel slope of the BiO_x/TiO2 anode were determined to be 0.32 V and 120 mV decade^(\u22121). In a single compartment WEC with a NaCl electrolyte ([Cl\u2212] \u226450 mM), the current density (j) ranged up to 500 A m^(\u22122) at cell voltages less than 6 V, while the current efficiency (CE) for free chlorine (FC) evolution showed maximum value near 0.3. The CE and energy efficiency (EE) for the HER were assessed using NaCl solutions (50 mM with or without 2.5 g L^(\u22121) urea) and real wastewater with variable compositions ([Cl\u2212]: 6\u201333 mM, [chemical oxygen demand]: 60\u2013790 mg L^(\u22121)). The ohmic resistance of wastewater electrolyte rules out the usage of membrane separation, resulting in side reactions such as reduction of O_2 whose CE values monotonically decreased with an increasing j under the diffusion controlled regime. Chloride ions reduce the electron consumption during O_2 reduction, while elevated levels of FC significantly lower the CE for the HER. The combined presence of oxidizable organic compounds and Cl\u2212 enhance the CE for the HER as long as the concentration of organics is enough to quench FC to maintain a pseudo steady-state concentration. The highest CE (0.8) and EE (0.23) for HER were observed during electrolysis of real wastewater at j values exceeding 200 A m^(\u22122). However, a dependency of value of EE on the applied cell voltage needs to be addressed further.", "doi": "10.1016/j.apcatb.2016.09.067", "issn": "0926-3373", "publisher": "Elsevier", "publication": "Applied Catalysis B", "publication_date": "2017-03", "volume": "202", "pages": "671-682" }, { "id": "authors:qcexe-5kw82", "collection": "authors", "collection_id": "qcexe-5kw82", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20150310-090722359", "type": "article", "title": "Bi_xTi_(1\u2212x)O_z Functionalized Heterojunction Anode with an Enhanced Reactive Chlorine Generation Efficiency in Dilute Aqueous Solutions", "author": [ { "family_name": "Cho", "given_name": "Kangwoo", "clpid": "Cho-Kangwoo" }, { "family_name": "Hoffmann", "given_name": "Michael R.", "orcid": "0000-0001-6495-1946", "clpid": "Hoffmann-M-R" } ], "abstract": "Ir_(0.7)Ta_(0.3)O_y/Bi_xTi_(1\u2013x)O_z heterojunction anodes have been developed and characterized for reactive chlorine species (RCS) generation in dilute aqueous solution (50 mM NaCl). The primary objective of the research was to control the electro-stationary speciation of hydrous metal oxides between hydroxyl radical (>MO_x(\u00b7OH)) and higher valence-state oxides (>MO_(x+1)). An underlying layer of the mixed-metal oxide, Ir_(0.7)Ta_(0.3)O_y, was synthesized to serve as a primary Ohmic contact and electron shuttle. Binary thin films of Bi_xTi_(1\u2013x)O_z were prepared from the thermal decomposition of an aqueous solution mixture of Ti/Bi complexes. With these core components, the measured current efficiency for RCS generation (\u03b7_(RCS)) was enhanced where the values observed for x = 0.1 or 0.3 were twice of the \u03b7_(RCS) of the Ir_(0.7)Ta_(0.3)O_y anode. At the same time, the rates of RCS generation were enhanced by factors of 20\u201330%. Partial substitution of Ti with Bi results in a positive shift in surface charge allowing for stronger interaction with anions, as confirmed by FTIR-ATR analysis. A kinetic model to describe the formate ion degradation showed that an increasing fraction of Bi in the composite promotes a redox transition of >MO_x(\u00b7OH) to >MO_(x+1). In accelerated life tests under conditions corresponding to a service life of 2 years under an operational current density of 300 A m^(\u20132), dissociation of the Ti component from Ir_(0.7)Ta_(0.3)O_y/TiO_2 was found to be minimal, while Bi_xTi_(1\u2013x)O_z in the surface layers undergoes oxidation and a subsequent dissolution.", "doi": "10.1021/acs.chemmater.5b00376", "issn": "0897-4756", "publisher": "American Chemical Society", "publication": "Chemistry of Materials", "publication_date": "2015-03-24", "series_number": "6", "volume": "27", "issue": "6", "pages": "2224-2233" }, { "id": "authors:v2408-6ke58", "collection": "authors", "collection_id": "v2408-6ke58", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141120-111400084", "type": "article", "title": "Urea Degradation by Electrochemically Generated Reactive Chlorine Species: Products and Reaction Pathways", "author": [ { "family_name": "Cho", "given_name": "Kangwoo", "clpid": "Cho-Kangwoo" }, { "family_name": "Hoffmann", "given_name": "Michael R.", "orcid": "0000-0001-6495-1946", "clpid": "Hoffmann-M-R" } ], "abstract": "This study investigated the transformation of urea by electrochemically generated reactive chlorine species (RCS). Solutions of urea with chloride ions were electrolyzed using a bismuth doped TiO_2 (BiOx/TiO_2) anode coupled with a stainless steel cathode at applied anodic potentials (E_a) of either +2.2 V or +3.0 V versus the normal hydrogen electrode. In NaCl solution, the current efficiency of RCS generation was near 30% at both potentials. In divided cell experiments, the pseudo-first-order rate of total nitrogen decay was an order of magnitude higher at E_a of +3.0 V than at +2.2 V, presumably because dichlorine radical (Cl_2\u2013\u2022) ions facilitate the urea transformation primary driven by free chlorine. Quadrupole mass spectrometer analysis of the reactor headspace revealed that N_2 and CO_2 are the primary gaseous products of the oxidation of urea, whose urea-N was completely transformed into N_2 (91%) and NO_3\u2013 (9%). The higher reaction selectivity with respect to N_2 production can be ascribed to a low operational ratio of free available chlorine to N. The mass-balance analysis recovered urea-C as CO_2 at 77%, while CO generation most likely accounts for the residual carbon. In light of these results, we propose a reaction mechanism involving chloramines and chloramides as reaction intermediates, where the initial chlorination is the rate-determining step in the overall sequence of reactions.", "doi": "10.1021/es5025405", "issn": "0013-936X", "publisher": "American Chemical Society", "publication": "Environmental Science and Technology", "publication_date": "2014-10-07", "series_number": "19", "volume": "48", "issue": "19", "pages": "11504-11511" }, { "id": "authors:gcth9-jhy83", "collection": "authors", "collection_id": "gcth9-jhy83", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20140204-111726022", "type": "article", "title": "Effects of Anodic Potential and Chloride Ion on Overall Reactivity in Electrochemical Reactors Designed for Solar-Powered Wastewater Treatment", "author": [ { "family_name": "Cho", "given_name": "Kangwoo", "clpid": "Cho-Kangwoo" }, { "family_name": "Qu", "given_name": "Yan", "clpid": "Qu-Yan" }, { "family_name": "Kwon", "given_name": "Daejung", "clpid": "Kwon-Daejung" }, { "family_name": "Zhang", "given_name": "Hao", "clpid": "Zhang-Hao" }, { "family_name": "Cid", "given_name": "Cl\u00e9ment A.", "orcid": "0000-0002-7293-035X", "clpid": "Cid-C-A" }, { "family_name": "Aryanfar", "given_name": "Asghar", "orcid": "0000-0002-8890-077X", "clpid": "Aryanfar-A" }, { "family_name": "Hoffmann", "given_name": "Michael R.", "orcid": "0000-0001-6495-1946", "clpid": "Hoffmann-M-R" } ], "abstract": "We have investigated electrochemical treatment of real domestic wastewater coupled with simultaneous production of molecular H2 as useful byproduct. The electrolysis cells employ multilayer semiconductor anodes with electroactive bismuth-doped TiO_2 functionalities and stainless steel cathodes. DC-powered laboratory-scale electrolysis experiments were performed under static anodic potentials (+2.2 or +3.0 V NHE) using domestic wastewater samples, with added chloride ion in variable concentrations. Greater than 95% reductions in chemical oxygen demand (COD) and ammonium ion were achieved within 6 h. In addition, we experimentally determined a decreasing overall reactivity of reactive chlorine species toward COD with an increasing chloride ion concentration under chlorine radicals (Cl\u00b7, Cl2\u2013\u00b7) generation at +3.0 V NHE. The current efficiency for COD removal was 12% with the lowest specific energy consumption of 96 kWh kgCOD\u20131 at the cell voltage of near 4 V in 50 mM chloride. The current efficiency and energy efficiency for H2 generation were calculated to range from 34 to 84% and 14 to 26%, respectively. The hydrogen comprised 35 to 60% by volume of evolved gases. The efficacy of our electrolysis cell was further demonstrated by a 20 L prototype reactor totally powered by a photovoltaic (PV) panel, which was shown to eliminate COD and total coliform bacteria in less than 4 h of treatment.", "doi": "10.1021/es404137u", "issn": "0013-936X", "publisher": "American Chemical Society", "publication": "Environmental Science and Technology", "publication_date": "2014-02-18", "series_number": "4", "volume": "48", "issue": "4", "pages": "2377-2384" }, { "id": "authors:hz8xt-0v487", "collection": "authors", "collection_id": "hz8xt-0v487", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20140129-155158774", "type": "article", "title": "Electrochemical treatment of human waste coupled with molecular hydrogen production", "author": [ { "family_name": "Cho", "given_name": "Kangwoo", "clpid": "Cho-Kangwoo" }, { "family_name": "Kwon", "given_name": "Daejung", "clpid": "Kwon-Daejung" }, { "family_name": "Hoffmann", "given_name": "Michael R.", "orcid": "0000-0001-6495-1946", "clpid": "Hoffmann-M-R" } ], "abstract": "We have developed a wastewater treatment system that incorporates an electrolysis cell for on-site wastewater treatment coupled with molecular hydrogen production for use in a hydrogen fuel cell. Herein, we report on the efficacy of a laboratory-scale wastewater electrolysis cell (WEC) using real human waste for the first time with semiconductor electrode utilizing a mixed particle coating of bismuth oxide doped titanium dioxide (BiO_x/TiO_2). A comprehensive environmental analysis has been coupled together with a robust kinetic model under the chemical reaction limited regime to investigate the role of various redox reactions mediated by chloride present in human waste. The oxidative elimination of the chemical oxygen demand (COD) and ammonium ion can be modelled using empirical, pseudo-first-order rate constants and current efficiencies (CE). In combination with an anaerobic pre-treatment step, human waste containing high-levels of COD, protein, and color are eliminated within 6 hours of batch treatment in the WEC. The reactor effluent has a residual inorganic total nitrogen (TN) concentration of [similar]40 mM. The CE and specific energy consumption were 8.5% and 200 kWh per kgCOD for the COD removal, 11% and 260 for kWh per kgTN for the TN conversion. The CE and energy efficiencies (EE) for hydrogen production were calculated to be 90% and 25%, respectively.", "doi": "10.1039/C3RA46699J", "issn": "2046-2069", "publisher": "Royal Society of Chemistry", "publication": "RSC Advances", "publication_date": "2014-02", "series_number": "9", "volume": "4", "issue": "9", "pages": "4596-4608" }, { "id": "authors:ame84-7r404", "collection": "authors", "collection_id": "ame84-7r404", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20131204-133521300", "type": "article", "title": "Electroflotation clarifier to enhance nitrogen removal in a two-stage alternating aeration bioreactor", "author": [ { "family_name": "Cho", "given_name": "Kangwoo", "clpid": "Cho-Kangwoo" }, { "family_name": "Chung", "given_name": "Chong Min", "clpid": "Chung-Chong-Min" }, { "family_name": "Kim", "given_name": "Yun Jung", "clpid": "Kim-Yun-Jung" }, { "family_name": "Hoffmann", "given_name": "Michael R.", "orcid": "0000-0001-6495-1946", "clpid": "Hoffmann-M-R" }, { "family_name": "Chung", "given_name": "Tai Hak", "clpid": "Chung-Tai-Hak" } ], "abstract": "Stringent water treatment criteria and rapidly growing pollutant loads provoke the demand for retrofitting wastewater treatment plants towards a higher capacity. In this study, we assess a two stage alternating aeration (AA) bioreactor equipped with electroflotation (EF) clarifier, for nitrogen removal within a short hydraulic reTENTion time (HRT). The EF under steady solids loading required a minimum unit height and gas:solids ratio of 0.006 for efficient clarification. The separated sludge blanket was further thickened with retaining stability when the cyclic solids loading was smaller than 1.0 kg m^(\u22122). In the continuous operation of the bioreactor, the returned activated sludge concentration increased to more than 18,000 mg L^(\u22121), while the effluent suspended solids concentration was lowered below 5 mg L^(\u22121). Under influent chemical oxygen demand (COD)/total inorganic nitrogen (TIN) concentration of 300/30 mg L^(\u22121), the TIN removal efficiency was near 70% with cycle time ratios of 0.17 and 0.27. Under higher influent COD concentration of 500 mg L^(\u22121), TIN removal efficiency was found to be 73.4% at a carbon:nitrogen (C:N) ratio of 10 and even higher (80.4%) at a C:N ratio of 16.6. The increased mixed liquor suspended solids concentrations (>6000 mg L^(\u22121)) under the high COD loading were efficiently maintained by using the EF clarifier. The results of this study demonstrate that an EF clarifier with a HRT of less than 1 h can support reliable nitrogen removal in the AA process that has a HRT of 6 h, even under increasing influent loadings.", "doi": "10.1080/09593330.2013.788072", "issn": "0959-3330", "publisher": "Taylor & Francis", "publication": "Environmental Technology", "publication_date": "2013-10", "series_number": "19", "volume": "34", "issue": "19", "pages": "2765-2772" } ]