Ammonia Removal Rate Research Articles

Multilayered alginate–hydrogel-functionalized zeolite based on ionic cross-linking composed with a certain Ca2+ and Mg2+ ratio for ammonium adsorption

To enhance ammonium removal in wastewater treatment, a novel adsorbent, multilayered ionic cross–linked alginate–hydrogel–metal-coated zeolite (Al-H-M-Z), was synthesized. Essential divalent cations, 2.60 mmol of Ca2+ and Mg2+, were incorporated into Al-H-M-Z (10 g) in a Ca2+:Mg2+ ratio of 0.73:1.85, facilitating strong alginate–polymer interactions and significantly enhancing the adsorption efficiency. Langmuir and Freundlich isotherm analyses revealed that Al-H-M-Z had a maximum adsorption capacity of 56.5 ± 8.78 mg g−1 and an adsorption intensity of 0.703 ± 0.122, which were 7.24-fold and 1.59-fold higher than those of natural zeolite (7.80 ± 1.09 mg g−1 and 0.444 ± 0.254), respectively. These enhanced properties are attributed to the modified structural and surface chemistry. The Al-H-M-Z coating exhibited a 4.76-fold increase in surface area (3.91 m2 g−1), an 8.94-fold increase in micropore volume (17.8 × 10−3 cm3 g−1), and a 4.22-fold increase in pore diameter (4.14 nm) when compared to the traditional Al-only coating. For applicability, Al-H-M-Z and Z achieved ammonium removal rates of 7.94% and 5.61%, respectively, in actual fish farm wastewater, representing a 1.41-fold improvement in adsorption efficiency after the coating process.

Enhancing the nitrogen removal of anammox sludge by setting up novel redox mediators-mediated anammox process

Anaerobic ammonium oxidizing (anammox) bacteria have been proven weak-electroactive. However, the impact of exogenous anthraquinone-2,6-disulfonate (AQDS) on the anammox activity, although it usually plays essential roles in the life activities of many other electroactive microorganisms, is still unknown. Therefore, this study further explored the influences of AQDS on the anammox activity and the interaction mechanism with anammox bacteria, as well as the behaviors of NH4+, NO2−, and NO3−. The results showed that exogenous AQDS increased the ammonium and total nitrogen removal rates by 12.8% and 10.7%, respectively. Interestingly, the conversion from NO2− to NO3− was significantly reduced after adding AQDS, resulting in a 40.1% reduction in NO3− production of anammox process. In this study, we found for the first time that anammox bacteria could not only carry out the conventional anammox process but also perform a weak redox mediator-mediated anammox process, which could achieve the 1:1 consumption of NH4+ and NO2−. The redox mediator-mediated anammox process was related to an endogenous redox mediator (ERM) synthesized and secreted by anammox bacteria, whose redox midpoint potential was around −0.26 V (vs. Ag/AgCl). After adding AQDS, not only the ERM-mediated anammox process was enhanced, but also two novel redox mediator-mediated anammox processes were introduced, including the AQDS-mediated anammox process and ERM-AQDS-mediated anammox process. These three redox mediator-mediated anammox processes significantly improved the nitrogen removal performance of anammox bacteria and reduced energy consumption. These findings will help reduce the dependence of anammox technology on NO2−, reduce the cost of subsequent treatment of NO3−, and provide new visions for optimizing and applying anammox technology.

Investigating the impacts of a recirculation sedimentation application on microalgae biomass cultivation in wastewater treatment

Commercial microalgae production is often interrupted by contamination, leading to short production cycles, reinoculation needs, and culture collapses, significantly increasing costs. This study focuses on investigating Recirculated Sedimentation Application (RSA) to control contamination in microalgae culture systems used for wastewater treatment. Chlorella vulgaris culture was grown in an unsterilized mixture of tertiary treatment effluent and centrate of anaerobic digestion wastewater sludge over a 90-day experimental period. 60 L raceway reactor was operated under a light intensity of 275 μM m−2.s−1 with a 16:8 h light-dark photoperiod. To evaluate the effect of RSA on biological-based problems, the experiment was conducted in three phases. The benefits of utilizing RSA were established through the following observations: effective removal of contaminants at an acceptable level without releasing the culture; extension of the biofilm formation time on the inner walls; inhibition of heterotrophic bacteria and nitrification; enhancement of the suspended solids retention capacity of the raceway tank (up to 770 mg.L−1); and improvement in ammonium removal rate to approximately 30 mg.L−1d−1. The ideal salinity level for both ammonium removal and biomass concentration in RSA should be below 0.02%. These findings demonstrate the potential of phycoremediation for sustainable wastewater treatment and contribute to environmental bioremediation strategies.

Machine learning revealing overlooked conjunction of working volume and mixing intensity in anammox optimization

Extensive studies on improving anammox performance have taken place for decades with particular focuses on its operational and environmental factors, but such parameter-based optimization is difficult, because of the sheer number of possible combinations and multidimensional arrays of these factors. Utilizing machine-learning algorithm and published anammox data, Bayesian nonparametric general regression (BNGR) was applied to identify the possible governing variable(s) from among 11 operating and environmental parameters: reactor type, mixing type, working volume, hydraulic retention time, temperature, influent pH, nitrite, ammonium, nitrate concentration, nitrogen loading rate, and organic concentration. The results showed that working volume is a key but oft-overlooked governing parameter. By integrating the BNGR findings with computational fluid dynamics simulation, which assessed mixing properties, it became feasible to conclude that working volume and mixing intensity co-regulated flow fields in reactors and had a significant influence on anammox performance. Furthermore, this study experimentally validated how mixing intensity affected performance, and specific input power (x), a parameter that conjugates both working volume and mixing intensity, was used to establish the relationship with ammonium removal rate (NH4+-N RR, y) y = 49.90x+1.97 (R2 = 0.94). With specific input power increased from 3.4 × 10−4 to 2.6 × 10−2 kW m−3, the ammonium removal rate exhibited a rise from 1.8 to 3.2 mg L−1h−1. Following, a relationship among input power-working volume-nitrogen removal rate was also established with a view to determining the design variables for anammox reactor. Consequently, the study highlighted the necessity to consider the working volume-mixing intensity correlation when optimizing the anammox process.

Simultaneous aerobic nitrogen and phosphorus removal by novel halotolerant fungus Mucor circinelloides SNDM1: Function and metabolism pathway

Fungi capable of simultaneous nitrogen and phosphorus removal from wastewater is rarely found. Here, a novel fungal strain (SNDM1) performing heterotrophic nitrification, aerobic denitrification, and phosphate removal was isolated and identified as Mucor circinelloides. The favorable nutrient removal conditions by the strain using glucose were C/N ratios of 25–30, salinities of 0 %–3 %, and pH of 7.5. Strain SNDM1 achieved ammonium, nitrite, nitrate, and phosphate removal rates of 5.23, 10.08, 4.88, and 0.97 mg/L/h. Nitrogen balance indicated that gaseous (18.60 %–24.55 %) and intracellular nitrogen (43.76 %–70.63 %) were primary fate of initial nitrogen. Enzyme activity revealed that ammonium removal occurred through heterotrophic nitrification and aerobic denitrification. Removed phosphorus was mainly transformed into cell membranes (56 %–64 %) and extracellular polymeric substances (20 %–26 %). Orthophosphate was the major intracellular phosphorus species, while polyphosphate and pyrophosphate existed extracellularly. These findings highlight the potential of this fungal strain for bioremediating polluted wastewater.

Performances and mechanisms of anaerobic nitrogen removal through Fe (III)/Fe (II) cycle with sponge iron biofilm without external iron addition

Anaerobic ammonia oxidation coupled to Fe (III) reduction (Feammox) plays an important role in the natural nitrogen cycle. However, for its application in wastewater treatment process, the source of iron is a major limitation. In this study, Feammox process was successfully achieved without external iron addition using sponge iron biofilm. The products of Feammox process, nitrate and Fe (II), provided substrates for nitrate dependent ferrous oxidation (NDFO). Therefore, nitrogen removal and Fe (II)/Fe (III) cycle were achieved in reactor and nitrogen removal efficiency by Feammox and NDFO pathways was up to 58.4 %. The X-ray diffraction indicated the sludge contained magnetite and lepidocrocite, which provided Fe (III) for the occurrence of Feammox. Microorganisms related to Feammox process were dominated by Geothrix. It was found Feammox activity was similar at pH of 8 and 7, while inhibited at pH of 6, which was caused by the decrease of Feammox bacteria. And Feammox activity decreased with the decrease of temperature, in which the ammonia removal rate was 2 times faster at 30 °C than at 10 °C. Under micro‑oxygen aeration, the ammonia removal rate improved and Feammox and NDFO processes still played roles in system, nevertheless, under high dissolved oxygen condition, Feammox bacteria-Geothrix and NDFO bacteria Thiobacillus would be gradually eliminated from the system.

Elucidating the role of organic loading rate on the performance and microbial dynamics of a novel continuous-flow aerobic granular sludge reactor

Aerobic granular sludge technology operated in continuous-flow reactors enables the upgrading of existing conventional wastewater treatment plants. The viability of applying this technology at full-scale increases with the simplicity of the bioreactor design. Hence, in contrast to previous research carried out in complex configurations, this study is based on evaluating the capacity of a novel single-chamber continuous-flow bioreactor to operate at different loads found in domestic sewage, highlighting that this configuration combines and joins the advantages of activated sludge and granular sludge technologies. At organic loading rates ranging from 0.45 to 1.85 kg COD•m−3•d−1, the reactors achieved high performance, removing >80 % of the chemical oxygen demand, regardless influent characteristics. The trend of ammonium removal rates was risen over operational time. Moreover, the granular size and biomass concentration increased with the organic loading rate. Changes in the influent did not compromise the structure of the granules. Microbiota studies showed a high diversity in communities at lower organic loading rates, whereas a strong microbial competition was detected at high loading rates, linking with lower evenness. Phylotypes belonging to Hypocreales played a key role in mature granules.

Performances of full-scale biological nitrogen pre-treatment process for drinking water source: Seasonal variations and microbial community

This study investigated the performance of the full-scale unit over a two-year period to enhance nitrification efficiency and provide operational strategies. Results indicated that raw water quality from Donggan River was notably influenced by seasonal variations, particularly during dry and wet seasons, impacting the nitrification efficiency of the biological pretreatment process. Factors such as influent concentrations of ammonia and total Kjeldahl nitrogen were found to have significant effects on nitrification, with temperature and conductivity also showing correlations. The specific rate of ammonia removal was calculated to be approximately 0.1 kg-N/m3/d under the existing operational setup. Moreover, elevating dissolved oxygen levels above 4 mg/L was proposed to potentially boost ammonia oxidation based on findings from experiments conducted in lab-scale bioreactors. In times of increased influent ammonia levels, the elimination of about 1–3 mg-N/L of total nitrogen signified the activation of denitrification processes. This observation was corroborated by results from next-generation sequencing techniques, verifying the existence of denitrifying microorganisms. The real-time PCR analysis results indicated that the abundance of comammox amoA gene was comparable with the abundance of the AOB amoA gene, indicating the presence of comammox Nitrospira and their potential role on nitrification in the system.

Landfill leachate treatment using sequential natural zeolite adsorption and peroxymonosulfate activated by UV/Fe2+ system: Effects of main operating parameters and application of fluorescence EEM to monitor organic matters’ transformation

The significant increase in global Landfill Leachate is a pressing challenge directly linked to the growing global population. Among the strategies for landfill leachate treatment, advanced oxidation processes using sulfate radical (SR-AOP) have gained considerable interest, despite the challenge of nitrate generation during ammonia oxidation. This study introduces a sequential treatment method that combines adsorption and a UV/PMS/Fe2+ system to assess its impact on COD (Chemical Oxygen Demand) and ammonia removal efficiencies.The results show that the sequential process achieves optimal COD and ammonia removal rates of 88 % and 88.3 % respectively. The increase in UV254 absorbance removal during the adsorption phase indicates the removal of UV quenching substances (UVQS), supporting the effectiveness of using adsorption as a pretreatment for the UV-assisted systems (UV/PMS/Fe2+). Additionally, analysis using Inductively Coupled Plasma-Optical Emission Spectrometry (ICP-OES) reveals that the adsorption treatment before the SR-AOP process not only enhances COD and ammonia removal efficiencies, but also eliminates heavy metals such as vanadium (V), titanium (Ti), zinc (Zn), and aluminum (Al) present in leachate.Moreover, the higher BOD/COD ratio suggests improved biodegradability of the effluent. When compared to other systems at optimal conditions, the sequential adsorption and UV/PMS/Fe2+ systems demonstrate superior performance, focusing on removing refractory matter and reducing ammonia content, especially effective at a pH level of 7.25. Analysis using Excitation-Emission Matrix (EEM) shows a shift from primary peaks in raw leachate spectra associated with humic and fulvic acid-like compounds to lower-intensity peaks from fulvic-like small molecule materials in the treated effluent.

In situ electro-generated Ni(OH)2 synergistic with Cu cathode to promote direct ammonia oxidation to nitrogen.

To solve the problem of low removal rate and poor N2 selectivity in direct electrochemical ammonia oxidation (EAO), commercial Ni foam and Cu foam were used as anode and cathode of the EAO system, respectively. The coupling effect between the cathode and anode promoted nitrogen cycling during the reaction process, which improved N2 selectivity of the reaction system and promoted it to achieve a high ammonia removal rate. This study showed that the thin Ni(OH)2 with oxygen vacancy formed on the surface of Ni foam anode played an effective role in the dimerization of intermediate products in ammonia oxidation to form N2. This electrochemical system was used to treat real goose wastewater containing 422.5 mg/L NH4+-N and 94.5 mg/L total organic carbon (TOC). After treatment, this electrochemical system achieved good performance with an ammonia removal rate of 87%, N2 selectivity of 77%, and TOC removal rate of 72%. Therefore, this simple and efficient system with Ni foam anode and Cu foam cathode is a promising method for treating ammonia nitrogen wastewater.

Direct Electrooxidation of Ammonia-Enriched Wastewater Using a Bipolar Membrane-Integrated Electrolytic Cell

The treatment of reject water containing concentrated ammonia and non-biodegradable organics is a challenging task in wastewater treatment plants. To address this problem, we propose a novel process consisting of a selective ammonium-exchange resin and an ammonia electrooxidation reaction (AmER-AOR). Because an alkaline condition is essential for direct ammonia oxidation, the use of a bipolar membrane (BPM) was helpful. Nonetheless, an initial pH of 13 and KOH addition were required to maintain a high alkalinity for the complete elimination of ammonia. The linear sweep voltammogram elucidated the high pH requirement and ammonia oxidation promotion. When the current density varied from 30 to 80 mA cm−2, 60 mA cm−2 showed the highest current efficiency (30.39%) and the lowest specific energy demand (95.3 kWh/kg-N), indicating the most energy-effective condition. Increasing the initial concentration of ammonia from 0.1 M to 0.5 M improved the current efficiency (51.57%), demonstrating an additional energy-effective strategy for the AmER-AOR. The energy efficiency of pure H2 production in the cathodic chamber was 30%. To estimate the viability for practical applications, reject water collected from a local wastewater treatment plant was applied in the AmER-AOR. Notably, no significant difference in the ammonia removal rate was observed with synthetic wastewater. To the best of our knowledge, this is the first study that employs a BPM as a separator and OH− supplier for direct ammonia oxidation. Our findings reveal that the AmER-AOR with a BPM has promising practical applicability in the treatment of reject water and energy production.

Excellent phenol removal ability of Acinetobacter guillouiae BY18 under different inorganic nitrogen conditions

Phenol and inorganic nitrogen generally exist in industrial wastewater and contaminated soil. In this study, Acinetobacter guillouiae BY18, which can simultaneously remove high concentrations of phenol and inorganic nitrogen, was isolated from a wet meadow in Weining County, Guizhou Province, China. The optimal remediation conditions for strain BY18 were 25 °C and pH 7.20–8.20, with a C/N ratio of 10, rotation speed of 150 r/min, and inoculation amount of 0.2×108 CFU. When phenol and ammonium were both present, strain BY18 could remove 982.86 mg/L of phenol and 64.76 mg/L of ammonium within 18 h. Strain BY18 was able to eliminate 979.71 mg/L, 55.84 mg/L, and 49.20 mg/L of phenol, nitrite, and nitrate, respectively, within 36 h when ammonium was substituted by nitrate or nitrite. In the simultaneous nitrification and denitrification reaction system, the maximum removal rates of phenol and ammonium were 92.53 mg/(L·h) and 5.7 mg/(L·h), respectively. Overall, strain BY18 had a remarkable phenol removal ability under different inorganic nitrogen conditions.

Selecting serum-free hepatocyte cryopreservation stage and storage temperature for the application of an “off-the-shelf” bioartificial liver system

The bioartificial liver (BAL) system can potentially rescue acute liver failure (ALF) patients by providing partial liver function until a suitable donor liver can be found or the native liver has self-regenerated. In this study, we established a suitable cryopreservation process for the development of an off-the-shelf BAL system. The viability of hepatocyte spheroids cryopreserved in liquid nitrogen was comparable to that of fresh primary hepatocyte spheroids. When hepatocyte spheroids were subjected to cryopreservation in a deep freezer, no statistically significant differences were observed in ammonia removal rate or urea secretion rate based on the cryopreservation period. However, the functional activity of the liver post-cryopreservation in a deep freezer was significantly lower than that observed following liquid nitrogen cryopreservation. Moreover, cryopreserving spheroid hydrogel beads in a deep freezer resulted in a significant decrease (approximately 30%) in both ammonia removal and urea secretion rates compared to the group cryopreserved in liquid nitrogen. The viabilities of spheroid hydrogel beads filled into the bioreactor of a BAL system were similar across all four groups. However, upon operating the BAL system for 24 h, the liver function activity was significantly higher in the group comprising hydrogel beads generated after thawing hepatocyte spheroids cryopreserved in liquid nitrogen. Consequently, the manufacturing of beads after the cryopreservation of hepatocyte spheroids is deemed the most suitable method, considering efficiency, economic feasibility, and liver function activity, for producing a BAL system.

Microalgae cultivation trials in a membrane bioreactor operated in heterotrophic, mixotrophic, and phototrophic modes using ammonium-rich wastewater: The study of fouling.

In this work, microalgae cultivation trials were carried out in a membrane bioreactor to investigate fouling when the cultures of Chlorellavulgaris were grown under mixotrophic, heterotrophic, and phototrophic cultivation regimes. The Chlorella cultures were cultivated in wastewater as a source of nutrients that contained a high concentration of ammonium. In mixotrophic cultivation trials, the results showed that the elevated contents of carbohydrates in the soluble microbial product and proteins in extracellular polymeric substances probably initiated membrane fouling. In this case, the highest protein content was also found in extracellular polymeric substances due to the high nitrogen removal rate. Consequently, transmembrane pressure significantly increased compared to the phototrophic and heterotrophic regimes. The data indicated that cake resistance was the main cause of fouling in all cultivations. Higher protein content in the cake layer made the membrane surface more hydrophobic, while carbohydrates had the opposite effect. Compared to a mixotrophic culture, a phototrophic culture had a larger cell size and higher hydrophobicity, leading to less membrane fouling. Based on our previous data, the highest ammonia removal rate was reached in the mixotrophic cultures; nevertheless, membrane fouling appeared to be the fundamental problem.

Inorganic carbon limitation decreases ammonium removal and N2O production in the algae-nitrifying bacteria symbiosis system

Ammonium removal by a symbiosis system of algae (Chlorella vulgaris) and nitrifying bacteria was evaluated in a long-term photo-sequencing batch reactor under varying influent inorganic carbon (IC) concentrations (15, 10, 5 and 2.5 mmol L−1) and different nitrogen loading rate (NLR) conditions (270 and 540 mg-N L−1 d−1). The IC/N ratios provided were 2.33, 1.56, 0.78 and 0.39, respectively, for an influent NH4+-N concentration of 90 mg-N L−1 (6.43 mmol L−1). The results confirmed that both ammonium removal and N2O production were positively related with IC concentration. Satisfactory ammonium removal efficiencies (>98 %) and rates (29–34 mg-N gVSS−1 h−1) were achieved regardless of NLR levels under sufficient IC of 10 and 15 mmol L−1, while insufficient IC at 2.5 mmol L−1 led to the lowest ammonium removal rates of 0 mg-N gVSS−1 h−1. The ammonia oxidation process by ammonia oxidizing bacteria (AOB) played a predominant role over the algae assimilation process in ammonium removal. Long-time IC deficiency also resulted in the decrease in biomass and pigments of algae and nitrifying bacteria. IC limitation led to the decreasing N2O production, probably due to its negative effect on ammonia oxidation by AOB. The optimal IC concentration was determined to be 10 mmol L−1 (i.e., IC/N of 1.56, alkalinity of 500 mg CaCO3 L−1) in the algae-bacteria symbiosis reactor, corresponding to higher ammonia oxidation rate of ∼41 mg-N gVSS−1 h−1 and lower N2O emission factor of 0.13 %. This suggests regulating IC concentrations to achieve high ammonium removal and low carbon emission simultaneously in the algae-bacteria symbiosis wastewater treatment process.

Comparing methanol and glycerol as carbon sources for mainstream partial denitrification/anammox in an IFAS process.

This study explored the implementation of mainstream partial denitrification with anammox (PdNA) in the second anoxic zone of a wastewater treatment process in an integrated fixed film activated sludge (IFAS) configuration. A pilot study was conducted to compare the use of methanol and glycerol as external carbon sources for an IFAS PdNA startup, with a goal to optimize nitrogen removal while minimizing carbon usage. The study also investigated the establishment of anammox bacteria on virgin carriers in IFAS reactors without the use of seeding, and it is the first IFAS PdNA startup to use methanol as an external carbon source. The establishment of anammox bacteria was confirmed in both reactors 102 days after startup. Although the glycerol-fed reactor achieved a higher steady-state maximum ammonia removal rate because of anammox bacteria (1.6 ±0.3g/m2/day) in comparison with the methanol-fed reactor (1.2±0.2g/m2/day), both the glycerol- and methanol-fed reactors achieved similar average in situ ammonia removal rates of 0.39 ±0.2g/m2/day and 0.40 ±0.2g/m2/day, respectively. Additionally, when the upstream ammonia versus NOx (AvN) control system maintained an ideal ratio of 0.40-0.50 g/g, the methanol-fed reactor attained a lower average effluent TIN concentration (3.50 ±1.2mg/L) than the glycerol-fed reactor (4.43 ±1.6mg/L), which was prone to elevated nitrite concentrations in the effluent. Overall, this research highlights the potential for PdNA in IFAS configurations as an efficient and cost-saving method for wastewater treatment, with methanol as a viable carbon source for the establishment of anammox bacteria. PRACTITIONER POINTS: Methanol is an effective external carbon source for an anammox startup that avoids the need for costly alternative carbon sources. The methanol-fed reactor demonstrated higher TIN removal compared with the glycerol-fed reactor because of less overproduction of nitrite. Anammox bacteria was established in an IFAS reactor without seeding and used internally stored carbon to reduce external carbon addition. Controlling the influent ammonia versus NOx (AvN) ratio between 0.40 and 0.50 g/g allowed for low and stable TIN effluent conditions.

Nitrogen Removal Mechanism and Microbial Community Changes of the MBR Bioaugmented with Two Novel Fungi Pichia kudriavzevii N7 and Candida tropicalis N9

Ammonia nitrogen wastewater causes dissolved oxygen concentrations to decrease and the content of harmful substances to increase. To characterize the application properties of two novel strains of highly efficient ammonium transforming fungi—Pichia kudriavzevii N7 and Candida tropicalis N9—this study used both as compound microbial agents to treat nitrogenous wastewater. Here, we investigated the bioaugmentation effect of compound fungi N7 and N9 in the MBR bioreactor and the effect of N7 and N9 on the fungal and bacterial microbial communities in the system. The results revealed that in the first week after inoculation of N7 and N9, the average removal rate of ammonium in the experimental and control groups were 89.43% and 82.86%, respectively, and the NO3−-N accumulation concentrations were 12.56 mg·L−1 and 17.73 mg·L−1, respectively. The average transformation rate of total nitrogen in the experimental and control groups were 46.32% and 30.6%, respectively. ITS sequencing results indicated that N9 could be a dominant fungus in the complex MBR system. The results of 16S rRNA sequencing showed that the dominant bacterial communities in the system were changed by the inoculation of compound fungi. Therefore, the compound fungi can be applied to strengthen the treatment of nitrogenous wastewater due to its compatibility.

Tuning Cu2O morphologies of Cu2O/Ni foam electrodes for the control of reactivity and nitrogen selectivity in direct ammonia electrooxidation reaction

Direct electrochemical oxidation of ammonia (AEO) using non-precious metal catalysts is an energy-efficient and low-carbon-footprint method for ammonia removal from wastewater. In this work, Cu2O with three types of morphologies, including flower, particle, and sheet, were electrodeposited on Ni foam substrates (Cu2O/NF) for direct AEO. The Cu2O flower-deposited NF electrode showed the largest electrochemical surface area (19.6 cm2) and the smallest Cu2O size (200–600 nm) among all Cu2O/NF electrodes. In the ammonia solution, the peak current densities of direct AEO from cyclic voltammograms (CVs) at 10 mVs−1 on the Cu2O flower, Cu2O particle, and Cu2O sheet-deposited NF electrodes reached 4.6, 3.1, and 2.2 mAcm−2, respectively. The result showed that, at an initial pH of 11 and an applied potential of 0.95 V vs. Hg/HgO, the order of three types of Cu2O morphologies with respect to ammonia removal efficiency and rate is: Cu2O flower (52%, 4.1×10−3 min−1) > Cu2O particle (38%, 2.6×10−3 min−1) > Cu2O sheet (30%, 1.8×10−3 min−1). Interestingly, ammonia oxidation to N2 on the Cu2O sheet-deposited NF electrode exhibited the highest selectivity (SN2: 60%), which was much higher than the Cu2O flower-deposited NF electrode (SN2: 31%). The high SN2 of Cu2O sheets was ascribed to the presence of the stable Cu(I) sheet structure during direct AEO, confirmed by X-ray photoelectron spectroscopy analysis. On the other hand, the Cu(II)-rich flower structure facilitated the formation of NO3-. Our findings demonstrate that the surface morphologies of Cu2O deposited on the NF electrode show significant stability difference of Cu(I), which determines reactivity and N selectivity during direct AEO.

Pulsed electric field drives chemical-free membrane stripping for high ammonia recovery from urine

Recovering ammonia from waste streams (e.g., urine) is highly desirable to reduce natural gas-based NH3 production and nitrogen discharge into the water environment. Electrochemical membrane stripping is an attractive alternative because it can drive NH4+ transformation to NH3 via cathodic OH− production; however, the conventional configurations suffer from relatively low ammonia recovery (<80 %) and significant acid/material usage for ammonia adsorption. To this end, we develop a novel stack system that simply uses an oxygen evolution reaction to in-situ produce acid from water, enabling chemical-free ammonia recovery from synthetic urine. In batch mode, the percentage removal and recovery increased respectively from 74.5 % to 97.9 % and 81.8 % to 92.7 % when the electrode pairs increased from 2 to 4 in the stack system. To address the gas-sparging issue that deteriorated ammonia recovery in continuous operation, pulsed electric field (PEF) mode was applied, resulting in ∼100 % recovery under optimized conditions. At an ammonia removal rate of 35.1 g-N m−2 h−1 and electrical energy consumption of 28.9 kWh kg-N−1, our chemical-free system in PEF mode has achieved significantly higher ammonia recovery (>90 %) from synthetic urine. The total cost to recover 1 kg of NH3–N from real human urine was $15.9 in the proposed system. Results of this study demonstrate that this novel approach holds great promise for high ammonia recovery from waste streams, opening a new pathway toward sustainable nitrogen management.

Synergistic mechanisms between chlorine-mediated electrochemical advanced oxidation and ultraviolet light for ammonia removal

The combination of chlorine-mediated electrochemical advanced oxidation (Cl-EAO) and ultraviolet (UV) radiation (UV-E/Cl) can efficiently remove ammonia from wastewater. However, the synergistic mechanisms between Cl-EAO and UV need to be explored in more detail. Thus, in this study, the ammonia oxidation performance of Cl-EAO and UV-E/Cl systems were compared, while the synergistic mechanisms were identified by the performance of UV/chlorine oxidation (UV–ClO) system and the results of electron paramagnetic resonance (EPR) analysis, free radical inhibition assays, and determination of steady-state concentration of free radicals. It was found that, compared with the Cl-EAO system, UV increased the ammonia removal rate by 42.85% and reduced the active chlorine concentration (56.64%) and nitrate yield (53.61%). In the Cl-EAO, and UV-E/Cl systems, Cl• were detected, and the free radical inhibition assays and determination of steady-state concentration of free radicals suggested that UV increased the concentration of Cl• by 51.47%, resulting in Cl• becoming the major contributor to ammonia oxidation in the UV-E/Cl system. Besides, UV also increase the concentrations of HO• and Cl2•-, which further promoted the organic matter removal in the real domestic wastewater. This study also discussed the ammonia oxidation performance of the UV-E/Cl system in real domestic wastewater, even with the presence of significant levels of organic and inorganic anions in the wastewater, UV increased the ammonia oxidation by 21.95%. The results of this study thus clarify the mechanisms and potential applications of UV-E/Cl technology.