Ammonia Degradation Research Articles

In situ growth of carbon nitride on titanium dioxide/hemp stem biochar toward 2D heterostructured photocatalysts for highly photocatalytic activity.

In this work, hierarchical structure TiO2/hemp stem biochar carbon (HSBC) and C3N4-TiO2/HSBC were successfully fabricated, which were used as efficient visible-light photocatalyst degradation for ammonia nitrogen from aqueous solution. The as-prepared C3N4-TiO2/HSBC hybrid catalyst showed the higher efficient photocatalytic activity for decomposition of ammonia nitrogen than those of pure TiO2 and TiO2/HSBC, suggesting suppressed recombination of photogenerated charges and promoted mass transfer due to synergistic effect, and thus increased photocatalytic degradation activity. The degradation of ammonia follows a pseudo-first-order kinetics. All prepared catalysts demonstrated extremely photocatalytic efficiency under visible-light and UV light illumination; the ammonia nitrogen photocatalytic degradation activity of C3N4-TiO2/HSBC can reach 90.3% under UV light while the degradation activity achieved about 50.7% under visible-light irradiation. The results revealed that the h+ was dominantly active intermediates in the process of photocatalytic degradation. The prepared catalysts are promising for the degradation of ammonia nitrogen from water resource.

Separating and Characterizing Functional Nitrogen Degraders via Magnetic Nanoparticle-Mediated Isolation

Magnetic nanoparticle-mediated isolation (MMI) is a new method for isolating active functional microbes from complex microorganisms without substrate labeling. In this study, the composition and properties of magnetic nanoparticles (MNPs) were characterized by a number of techniques, indicating that MNPs have characteristics such as microinterfaces and can be efficiently fixed on the surface of microbial cells. It also introduced the MMI technology in activated sludge after stable long-term treatment. With further addition of promotor carbon sources, the enrichment of the functional nitrogen degraders in MMI was significantly higher than in samples without MNPs, showing the advantages of MMI in identifying the active degraders. Redundancy analysis (RDA) also showed that the functional nitrogen degraders such as Comamonadaceae_unclassified and Thiobacillus absolutely dominated in situ ammonia degradation, and the change in dominant genera had the same trend as the degradation rate of ammonia nitrogen. In the magnetically functionalized system, the separated functional nitrogen degraders significantly improved ammonia nitrogen degradation efficiency, making it basically stable at more than 80%, up to 91.6%. These results prove that the complex flora created after the addition of MNPs is more adaptable to newly introduced pollutants, and MMI is a powerful tool for studying pollutant-degrading microorganisms under in situ conditions.

UiO-66(Ti)-Fe3O4-WO3 photocatalyst for efficient ammonia degradation from wastewater into continuous flow-loop thin film slurry flat-plate photoreactor

This work presents the characterization of novel synthesized UiO-66(Ti)-Fe3O4-WO3 magnetic photocatalyst and investigates their photocatalytic activity for the photodegradation of ammonia in a designed continuous flow-loop thin-film slurry flat-plate photoreactor (TFSR). Excellent ammonia degradation efficiency was achieved in the presence of the synthesized catalyst at ambient conditions using no more reactive oxidant species. Several independent variables involving catalyst mass, flowrate, pH, irradiation time and initial ammonia concentration as well as corresponding experiments were analyzed and design using the central composite design (CCD). The influence and significance of each parameter and their binary interactions were then evaluated by applying the analysis of variance. The ammonia degradation efficiency of 91.80 % with the desirability of 0.903 were obtained at optimum values of operational parameters including 550 mL/min,10, 0.125 g/L, 60 min and 30 mg/L for solution flowrate, pH, catalyst mass, irradiation time and initial ammonia concentration, respectively. Furthermore, the liquid phase products of ammonia degradation such as nitrate and nitrite ions were completely removed, and purified water was produced using the combination of reverse osmosis process and mixed resins beds. The photocatalyst mechanism study revealed that O2•− was the predominant reactive oxygen species in the ammonia photodegradation.

Electrochemical treatment of leachate containing highly concentrated phenol and ammonia using a Pt/Ti anode at different current densities

Abstract The electrochemical oxidation of phenol in leachate was evaluated at current densities of 50, 100, and 150 mA/cm2 using a Pt/Ti anode electrode in a single-chambered reactor. The feasibility of electrochemical treatment for leachate containing phenol was determined in terms of phenol, chemical oxygen demand (COD), ammonia degradation rate, gas generation, energy consumption, and current efficiency. Phenol was removed within the first-hour of treatment in all study conditions. Galvanostatic electrolysis at a current density of 150 mA/cm2 removed COD and ammonia faster than the other conditions, possibly due to the formation of chloride-oxychloride radicals, which are strong oxidizing agents. The COD removal rate at 150 mA/cm2 was 1.73 h − 1 , which is 2.5–5 times higher than the values (0.35 h − 1 ) at 50 and (0.68 h − 1 ) at 100 mA/cm2. For ammonia removal, the electrochemical process at 150 mA/cm2 achieved a maximum removal rate of 438.6 M/h, which is at least two times higher than at the other current densities. Gas analysis during the electrolysis indicates that H 2 is generated as a valuable product of the reaction. This study reveals that electrochemical oxidation using the Pt/Ti electrode is promising for the treatment of landfill effluents containing toxic and low biodegradable contaminants and for efficient nutrient removal.

Generation and application of reactive chlorine species by electrochemical process combined with UV irradiation: Synergistic mechanism for enhanced degradation performance

Saline wastewater originates from many industries, containing a large amount of salt (NaCl) and other toxic and harmful organic matter, which have a great impact on the soil and groundwater. However, the treatment of saline wastewater is a serious problem because organic contents are hard to degrade with the high salinity by the common water treatment technologies. Herein, an electrochemical process coupled with ultraviolet (UV) irradiation was proposed for the saline wastewater treatment. High efficiency of p-nitrophenol (p-NP) and ammonia degradation were contributed from the in situ electrochemical produced active chlorine and photo-induced chlorine radicals. Under the optimal conditions (0.10 A, 0.05 M NaCl, and pH 6.00), approximately 98.91% p-NP was removed after 60 min with the rate constant of 7.521 × 10−2 min−1 in the electrochemical process, and 28.99% mineralization rate was obtained, while with the synergistic effect of UV and electrochemistry, approximately 100% of p-NP removal (k = 9.331 × 10−2 min−1) was achieved by 30 min treatment and about 83.70% of p-NP can be mineralized to CO2 after 60 min. The study on the synergistic mechanism of enhanced degradation performance illustrated that Cl with high oxidation capacity played an important role in the p-NP oxidation. Besides, based on the chlorine radical reactions, this method was also effectively applied to remove ammonia nitrogen (92.00% removal of total nitrogen in 100 min) for nitrogen-containing wastewater. Thus, this study offers a promising approach for the treatment of saline industry wastewater.

Degradation of ammonia from gas stream by advanced oxidation processes

The reduction of ammonia emissions from air was experimentally investigated by advanced oxidation processes (AOPs) utilizing the combination of ultraviolet irradiation with ozone. The influence of operating conditions such as initial ammonia concentration and flow rate of gas on the reduction of ammonia concentration was investigated in homemade photochemical unit. The conversion of ammonia decreased with increasing initial concentration of ammonia and with increasing flow rate of air (decreasing retention time). The highest conversion of ammonia (97%) was achieved under lower initial concentration of ammonia (30 ppm) and lower flow rate of air (28 m3/h). The energy per order was evaluated for the advanced oxidation process too. The energy consumption was about 0.037 kWh/m3/order for the 97% ammonia conversion at 30 ppm of initial ammonia concentration and 28 m3/h flow rate of air. Based on the results, the advanced oxidation process combining the UV irradiation and ozone was effective for mitigation of ammonia concentration and presents a promising technology for the reduction of odor emissions from livestock buildings. Moreover, the AOPs are suitable for application for high flow rate of air, especially for ammonia abatement from livestock buildings, where very high efficiency is expected.

Preparation of floatable TiO 2 /poly(vinyl alcohol)‐alginate composite for the photodegradation of ammonia wastewater

The use of floatable photocatalyst supports is an operable strategy of increasing photocatalytic performance in terms of improving light absorption. In this work, floatable organic support based on poly(vinyl alcohol) (PVA) was used to float commercial TiO2 P25 nanoparticles. At first, by the use of CaCl2 and boric acid at pH 3 the cross-linking of PVA blended with sodium alginate (PVA-Alg) was improved to enhance chemical and mechanical stability, and then it was chemically modified by trimethylchlorosilane to achieve floatable organic support (modified or MPVA-Alg). The prepared support and photocatalyst were characterized by X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy, energy-dispersive X-ray spectroscopy (EDX)-elemental mapping, inductively coupled plasma optical emission spectroscopy, ultraviolet-visible (UV-vis) diffuse reflectance spectroscopy, photoluminescence (PL), thermalgravimetry, Brunauer-Emmett-Teller (BET), and water contact angle (WCA) analyses and applied for the ammonia degradation under UV to visible regions. Results of WCA and FTIR confirmed that chemical modification of PVA-Alg led to lowering hydrophilicity to be floated on the ammonia wastewater. UV-vis analysis indicated that the MPVA-Alg acts as a light absorbent in UV-vis ranges and makes TiO2/MPVA-Alg a visible light active composite. Also, the PL analysis showed that the charge recombination process was strongly suppressed in the case of the TiO2/MPVA-Alg sample. BET theory suggested that the textural properties were not the key factor in determining photocatalytic performance. The maximum photocatalytic ammonia removal was obtained to be 63% and 57% by the TiO2/MPVA-Alg composite under UV-vis light irradiations, respectively. The MPVA-Alg and TiO2 exhibited the ammonia degradation of 28.5% and 15.2% under visible and 29.4% and 40.0% under UV irradiation, respectively. The TiO2/MPVA-Alg showed favorable reuse ability after five runs due to desirable chemical and mechanical resistance. This study provides an insight into the modification of polymeric structures to be used as both floatable photocatalyst support and light sensitizer.

Sn-doped V2O5 nanoparticles as catalyst for fast removal of ammonia in air via PEC and PEC-MFC

Abstract Effective removal of ammonia from air at room temperature is rarely reported by photocatalysis, PEC (photo-electro-catalysis) or PEC-MFC (microbial fuel cell), but realized by a Sn-doped V2O5 nanocatalyst. The doping ratio of Sn influenced catalytic activity and 1 wt%Sn-V2O5 exhibited optimal degradation (96.4% NH3) and competitive stability. By integrating PC with electro-catalysis and microbial fuel cells, the removal is enhanced (nearly complete ammonia removal). The structural and electronic properties of the Sn-doped V2O5, effect of Sn doping, the active species for ammonia degradation are investigated. The Sn-doping decreased the size of the nanoparticles and increased the oxidizing capacity and number of active sites. Oxygen vacancies played key roles in ammonia oxidation. This research provides an innovative and stable room temperature catalyst for air purification and malodor control.

Tetraphenyl–porphyrin decorated anatase TiO2 catalysts for the visible–light photocatalytic oxidation of gaseous ammonia at room temperature

Tetraphenyl–porphyrin (1 wt% TPP) decorated anatase TiO2 catalysts were optimized by one–step solvothermal method and presented high–efficient photo–catalytic activity of ammonia oxidation under visible–light irradiation with above 98% removal efficiency at room temperature within 8 h. TPP modifiers were successfully loaded onto TiO2 surface via TiOC bands determining the transfer direction of photo-excited hot charge carriers. The surface radical species including OH and O2− generated from H2O/OH and surface oxygen species were fleeting and hyperactive for the photocatalytic degradation of ammonia. TPP gave an evident promotion via the stimulative reactions due to the contributions of H+ and gave VB holes (h+), which had strong oxidation power for the direct oxidation of OH/H2O and adsorbed oxygen to generate OH and O2− radicals, being beneficial to the fundamental NH3 oxidation reaction. Furthermore, the remaining electrons were transferred to the surface of TiO2 via TiOC bonds, thus promoting the transformation of Ti4+ → TiO2-η to generate oxygen vacancy defects for the efficient oxidation of gaseous NH3 and adsorbed NHx species during photocatalytic reaction. However, the thermodynamic stable NH4NO3 products were generated via the combination of NH4+ and NO3 species that could exist on the catalyst surface stably, resulting in the decline of photocatalytic activity.

Simultaneous removal of ammonia and phosphate by electro-oxidation and electrocoagulation using RuO2–IrO2/Ti and microscale zero-valent iron composite electrode

Electro-oxidation using RuO2–IrO2/Ti plate anode and electrocoagulation using iron plate anode were widely applied to remove ammonia and phosphate in an aquatic environment, respectively. In this work, we designed magnetically bound ZVI microparticles on RuO2–IrO2/Ti plate as a composite electrode for the simultaneous removal of ammonia and phosphate from aqueous solution via combined EO and EC (EO/EC) processes. We present a series of experiments to study such simultaneous removal under an electric field via the EO/EC process. In the electrochemical unit, mZVI-RuO2-IrO2/Ti, mZVI-graphite, and RuO2–IrO2/Ti electrodes were used as anodes. The influence of applied voltage, initial pH, zero-valent iron dosage, reaction temperature, and organic compounds on the EO/EC process was also examined. Ammonia and phosphate could be completely removed at an applied voltage of 10 V, pH of 7, zero-valent iron dosage of 0.1 g, and reaction temperature of 35 °C using mZVI-RuO2-IrO2/Ti anode when influent ammonia and phosphate concentrations is 200 and 100 mg L−1. Ammonia degradation was consistent with pseudo-zero-order kinetic model. The characterization was analyzed by scanning electron microscope-energy dispersive spectrometer (SEM-EDS), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Hence, the mZVI-RuO2-IrO2/Ti electrode can be used for efficient simultaneous removal of ammonia and phosphate.

Direct Z-scheme photocatalytic removal of ammonia via the narrow band gap MoS2/N-doped graphene hybrid catalyst upon near-infrared irradiation

Near-infrared (NIR) irradiation accounts for approximately 54.3% of the solar spectrum. Therefore, MoS2 and N-doped graphene (NG) were utilised to fabricate a direct Z-scheme NIR-response photocatalytic system (MoS2/NG). The photocatalytic tests showed that MoS2/NG Z-scheme photocatalytic system can result in a 99.6% degradation ratio of ammonia under NIR irradiation, whereas the removal ratio of ammonia was only 64.0% using MoS2 as the photocatalyst under similar conditions. The catalytic efficiency is still over 90.7% even if the MoS2/NG catalyst was used for five runs, indicating that it is extremely stable. The kinetic research indicated the average apparent rate constant kapp for ammonia degradation into N2 was at approximately 0.251 h−1. The enhanced photocatalytic activity of MoS2/NG was attributed to the more positive valence band level of the Z-scheme system.

Ammonia removal mechanism by the combination of air stripping and ultrasound as the function of pH

Ammonia removal mechanism by the combination of airstripping and ultrasound (AU) as the function of pH was investigated. The synergistic effects were observed for air stripping and ultrasound, which was obviously enhanced with the decrease in pH. Ammonia degradation and ammonia stripping were the ammonia removal pathways by AU. Ammonia degradation was the main ammonia removal pathway at the pH of lower than 8, but at a higher pH, ammonia stripping was the main pathway. Air stripping strengthens ammonia degradation by ultrasound in two ways of providing reactive radicals and more cavitation bubbles for pyrolysis. Ammonia degradation depended on the oxidation of radicals at a pH of lower than 8 and did on pyrolysis at a higher pH. Ultrasound also strengthens ammonia stripping by increasing mass transfer coefficient and accelerating the shift of the equilibrium of free ammonia and ammonium ions, which resulted in more strongly strengthening effect at a lower pH.

Application of mixture experimental design for photocatalytic ammonia degradation by sunlight‐driven WO 3 ‐Ag 3 PO 4 ‐ZnO ternary photocatalysts

Application of mixture experimental design for photocatalytic ammonia degradation by sunlight‐driven WO ₃ ‐Ag ₃ PO ₄ ‐ZnO ternary photocatalysts

Effects of ultraviolet-enhanced ozonation on the degradation of ammonia and urea in fertilizer plant wastewater

Ammonia and urea contained in fertilizer plant wastewater are pollutants to the environment. High concentration of ammonium and urea in wastewater can affects algae blooms in the ecosystem which will generate various diseases in aquatic biota. It is known that there are many methods for degradation of ammonium and urea contained in fertilizer plant wastewater. One of the potential method is ultraviolet-enhanced ozonation. Ozonation is oxidation with O3 that generates hydroxyl radicals which subsequently react with organic contaminants, while UV irradiation can break down O3 molecules and produce radical ions OH∗. The objectives of this study were to examine the effects of the utilization of the ultraviolet-enhanced ozonation method in degradation of various initial ammonium (100-300 ppm) and urea concentration (100-300 ppm) in inlet feed of ozonation-UV irradiation combination system. Some important variables such as contact time (0-120 minutes) and ozone feed rate of 0.2, 0.6, and 1.21 g/h were evaluated. Degradation process was carried out in two steps; ozonation and UV irradiation. Ozonation process was carried out in a contacting tank at a constant feed flow rate of 1.5 l/min and at room temperature, while UV irradiation process was conducted in pipeline equipped with a UV lamp at various contact time. The ultraviolet-enhanced ozonation could degrade ammonium and urea nitrogen up to 83.6% and 63.8%, respectively, at ozone feed rate 1,21 g/h, contacting time 60 and 120 min, initial feed concentration of ammonia (100 ppm) and urea (40 ppm).

Effects of Ultraviolet-Enhanced Ozonation on Degradation of Ammonia and Urea in Fertilizer Plant Wastewater

Ammonia and urea contained in fertilizer plant wastewater are pollutants to the environment. High concentration of ammonium and urea in wastewater can affects algae blooms in ecosystem which will generate various diseases in aquatic biota. It is known that there are many methods for degradation of ammonium and urea contained in fertilizer plant wastewater. One of potential method is ultraviolet-enhanced ozonation. Ozonation is oxidation with O3 that generates hydroxyl radicals which subsequently react with organic contaminants, while UV irradiation can break down O3 molecules and produce radical ions OH∗. The objectives of this study were to examine the effects of the utilization of the ultraviolet-enhanced ozonation method in degradation of various initial ammonium (100-300 ppm) and urea concentration (100-300 ppm) in inlet feed of ozonation-UV irradiation combination system. Some important variables such as contact time (0-120 minutes) and ozone feed rate of 0.2, 0.6, and 1.21 g/h were evaluated. Degradation process was carried out in two steps; ozonation and UV irradiation. Ozonation process was carried out in a contacting tank at constant feed flow rate of 1.5 l/min and at room temperature, while UV irradiation process was conducted in pipeline equipped with UV lamp at various contact time. The ultraviolet-enhanced ozonation could degraded ammonium and urea nitrogen up to 83.6% and 63.8%, respectively, at ozone feed rate 1,21 g/h, contacting time 60 and 120 min, initial feed concentration of ammonia (100 ppm) and urea (40 ppm).

Ozonation of ammonia at low temperature in the absence and presence of MgO.

Ozone oxidation and ozonation catalyzed with MgO were applied to remove ammonia in water at low temperature (10℃). Results show that pH played a critical role in both ozonation and catalytic ozonation for ammonia removal, especially in the ozonation rate of ammonia and the types of oxidation products. For single ozonation, both O3 and OH contributed to ammonia degradation. Lower pH is beneficial to high selectivity of gaseous products (N2 or N2O) in the presence of Cl-. Significantly enhanced efficiency of ammonia removal was obtained under the catalysis of MgO, which worked as a solid alkali as well as a catalyst, facilitating ammonia oxidation both in the solution and on the MgO surface. Molecular O3 dominated ammonia removal in the heterogeneous catalytic ozonation system, while the contribution of OH was not significant in quantity and a small part of ammonia was degraded by the reaction of ClOx- with NH4+. A relatively high removal efficiency (77.53%˜80.17%) of ammonia could also be achieved in the temperature range of 0℃˜10℃, which indicates that catalytic ozonation over catalysts like MgO may be a potential method to control ammonia pollution during cold weather or under other conditions difficult for biological treatment.

Heterostructure Cu2O/(001)TiO2 Effected on Photocatalytic Degradation of Ammonia of Livestock Houses

In this paper, a heterogeneous composite catalyst Cu2O/(001)TiO2 was prepared by the impregnation-reduction method. The crystal form, highly active facet content, morphology, optical properties, and the photogenerated electron-hole recombination rate of the as-prepared catalysts were investigated. The performance of Cu2O/(001)TiO2 was appraised by photocatalytic degradation of ammonia under sunlight and was compared with lone P25, Cu2O, and (001)TiO2 at the same reaction conditions. The results showed that 80% of the ammonia concentration (120 ± 3 ppm) was removed by Cu2O/(001)TiO2, which was a higher degradation rate than that of pure P25 (12%), Cu2O (12%), and (001)TiO2 (15%) during 120 min of reaction time. The reason may be due to the compound’s (Cu2O/(001)TiO2) highly active (001) facets content that increased by 8.2% and the band gap width decreasing by 1.02 eV. It was also found that the air flow impacts the photocatalytic degradation of ammonia. Therefore, learning how to maintain the degradation effect of Cu2O/(001)TiO2 with ammonia will be important in future practical applications.

Study of nitrogen fate and microbial community structure relating to ammonia degradation for optimization of biofiltration systems used in livestock industry

Study of nitrogen fate and microbial community structure relating to ammonia degradation for optimization of biofiltration systems used in livestock industry

Study on degradation of marine product processing waste water by Zeolite/Bi/ZnO catalyst

Nano-supported Zeolite/Bi/ZnO photocatalyst was successfully prepared and characterized by XRD, SEM testing means. Under the visible light, the effects of different factors such as Bi/Zn loading concentration, calcination time, calcination temperature, initial concentration of ammonia nitrogen /COD, illumination time and catalyst dosage on degradation of ammonia nitrogen/COD in deep processing of seafood wastewater were investigated. Furthermore, by carrying out orthogonal experiment, the study explored the optimal reaction conditions of self-made photocatalyst in practical application. It can be concluded that the self-made photocatalyst has a good degradation effect on the deep processing wastewater of marine products with lower concentration of pollutants, obvious effect has been obtained on the treatment of deep processing wastewater of marine product containing lower concentration of pollutants. The optimal experimental conditions for the degradation of ammonia nitrogen concluded as follows: when the calcination temperature of photocatalyst was 600 °C, the calcination time was 4 h, the catalyst dosage was 0.8 g/L, the initial concentration of ammonia nitrogen was 100 mg/L, illumination time was 2 h, the degradation rate can reach 80.9%. And the optimal experimental conditions of degradation of COD was concluded: when the calcination temperature of photocatalyst was 500 °C, the calcination time was 4 h, the catalyst dosage was 1.0 g/L, initial concentration of COD was 540 mg/L, illumination time was 3 h, the degradation rate can reach 94.1%. The results showed that compared with ZnO photocatalyst and Bi/ZnO photocatalyst, the Zeolite/Bi/ZnO photocatalyst has a significant effect on the degradation of COD and ammonia nitrogen.

Effects of abrupt salinity increase on nitrification processes in a freshwater moving bed biofilter

The nitrification process is a widely used biological approach responsible for ammonia and nitrite removal in recirculating aquaculture system (RAS) biofilters. Given this pivotal role, the influence of different water quality parameter on nitrification efficiency is important information for RAS operations. One influencing parameter is salinity, and salinity fluctuations in freshwater RAS biofilters are reported to affect the nitrifying bacteria. This study investigated the effects of abrupt increase in salinity in freshwater RAS on substrate-dependent (1’-order) as well as substrate independent (0’-order) nitrification rates. A 100% inhibition was found for surface specific removal (STR) of total ammonia nitrogen (TAN) and surface specific nitrite removal (SNR) when salinity was abruptly increased to 25‰ and above. A fast turnover (i.e. steep decline in [NH4-N+] and [NO2-N−]) were observed at lower salinities (≤10‰), while limited/no degradation of either ammonia or nitrite was seen at salinities above 25‰. At low substrate loading (1’-order process), removal rate constants (k1a) of 0.22 and 0.23 m d-1 were observed for ammonia and nitrite degradation, respectively, declining to 0.01 m d-1when adding marine RAS water increasing the salinity to 15‰. Similar observations followed at high nutrient loadings (0’-order process) with STR and SNR of 0.10 and 0.12 g N m-2 d-1, respectively, declining to 0.01 g N m-2 d-1 at 15‰. When salinities of 25‰ and 35‰ were applied, neither TAN nor nitrite degradation was seen. The results thus demonstrate a pronounced effect of salinity changes when freshwater RAS biofilters are subjected to fast/abrupt changes in salinity. RAS facility operators should be aware of such potential effects and take relevant precautions.