Ammonia Retention Research Articles

Enhanced granulation of activated sludge in an airlift reactor for organic carbon removal and ammonia retention from industrial fermentation wastewater: A comparative study

Ammonia retention and recovery from high-nitrogenous wastewater are new concepts being used for nitrogen management. A microaerophilic activated sludge system was developed to convert organic nitrogen into ammonia and retain it for its recovery; however, the settleability of activated sludge remains a challenge. Therefore, this study proposed an aerobic granular sludge system as a potential solution. Two types of sequencing batch reactors—airlift and upflow reactors—were operated to investigate the feasibility of fast granule formation, the performance of organic carbon removal and ammonia retention, and the dynamics of microbial community composition. The operation fed with industrial fermentation wastewater demonstrated that the airlift reactor ensured a more rapid granule formation than the upflow reactor because of the high shear force, and it maintained a superior ammonia retention stability of approximately 85 %. Throughout the operational period, changes in hydraulic retention time (HRT), settling time, and exchange ratio altered the granular particle sizes and microbial community compositions. Rhodocyclaceae were replaced with Comamonadaceae, Methylophilaceae, Xanthomonadaceae, and Chitinophagaceae as core taxa instrumental in granulation, likely because of their extracellular polymeric substance secretion. As the granulation process progressed, a significant decrease in the relative abundances of nitrifying bacteria—Nitrospiraceae and Nitrosomonadaceae—was observed. The reduction of settling time and HRT enhanced granulation and inhibited the activity of nitrifying bacteria. The success in granulation for ammonia conversion and retention in this study accelerates the paradigm shift from ammonia removal to ammonia recovery from industrial fermentation wastewater.

Evaluation of nitrous oxide emission during ammonia retention from simulated industrial wastewater by microaerobic activated sludge process

Considering the reciprocating processes of nitrogen gas (N2) fixation to ammonia (NH4-N) and NH4-N removal to N2 through nitrification and denitrification during wastewater treatment, a microaerobic activated sludge process (MAS) is proposed in this study as a pretreatment to retain NH4-N from high-strength nitrogenous wastewater for further NH4-N recovery through membrane technology, that is, inhibit nitrification, with sufficient removal of total organic carbon (TOC). With DO and pH control, the 3-reactor bench-scale MAS systems successfully realized an NH4-N retention rate of over 80 %, with TOC removal rates of over 90 %. In addition, the emissions of carbon dioxide (CO2) and nitrous oxide (N2O) during MAS were evaluated. The total N2O emissions were 407 and 475 mg-N/day when pH was controlled at 6.2 (S1) and 6.8 (S2), respectively, with average emission factors to total nitrogen load over 2 % in both systems. Also, the global warming potential of N2O is one order of magnitude larger than that of CO2, indicating the significance of N2O in the MAS process. Therefore, the mechanisms of N2O emission from each reactor were investigated. The first reactor, where most of the TOC was adsorbed, emitted only 1.98 % (S1) and 2.43 % (S2) of the total N2O emissions through the denitrification of nitrite and nitrate (NOx) from the return sludge. The second reactor emitted 79.9 % (S1) and 69.0 % (S2) of the total N2O with the emission rates the same order of magnitude as the NOx production rates. Multiple pathways were considered to contribute to the high N2O emissions, and biotic NH2OH oxidation was one potential pathway at pH 6.2. Finally, the third reactor emitted 9.98 % (S1) and 16.8 % (S2) of the total N2O by nitrifier denitrification. Overall, this study showed that the large N2O emissions under nitrification-inhibiting conditions of the MAS process owed to the incomplete nitrification under acidic conditions and large abundances of denitrifiers. On the other hand, the lower N2O emissions at pH 6.2 evidenced the potential N2O mitigation under slightly more acidic conditions, underlining the necessity of further study on N2O mitigation when adapting to the trend of NH4-N recovery.

Glauconitic Siltstone: additive for ammonia retention and reduction of nitrogen volatilization loss

Glauconitic siltstone is sedimentary rock used as raw material to produce a multinutrient fertilizer that can combine with urea to increase their agronomic efficiency. The purpose of this study was to evaluate glauconitic siltstone as additive to reduce nitrogen losses by ammonia volatilization in nitrogen fertilizers. The experiment used randomized block, in a portion subdivided over time, following a 6 x 8 factorial with four replications and treatments comprising glauconitic siltstone mixture at a dose of 100 kg N ha-1 (control, without the application of nitrogen; conventional urea – 45% N; commercial fertilizer registered with the trade name of Super N®; urea with addition of glauconitic siltstone: 9% N; 20 and 31% N) and the remaining portion divided in the collection time at 3, 6, 9, 12, 15, 18, 24 and 30 days after fertilizer application. The collection of the volatilized ammonia was made in a semi-opened free static chamber. The use of glauconitic siltstone associated with urea provided a reduction in loss by volatilization from 10 to 27% in relation to conventional urea. The treatments with application of urea with the urease inhibitor showed the lowest volatilization rate and delay in the volatilization peak, which occurred 17 days after fertilizer application. In addition to providing nutrients to the plants, glauconitic siltstone reduces ammonia losses.

Microaerophilic Activated Sludge System for Ammonia Retention toward Recovery from High-Strength Nitrogenous Wastewater: Performance and Microbial Communities.

A transition to ammonia recovery from wastewater has started; however, a technology for sustainable nitrogen retention in the form of ammonia and organic carbon removal is still in development. This study validated a microaerophilic activated sludge (MAS) system to efficiently retain ammonia from high-strength nitrogenous wastewater. The MAS is based on conventional activated sludge (CAS) with aerobic and settling compartments. Low dissolved oxygen (DO) concentrations (<0.2 mg/L) and short solids retention times (SRTs) (<5 days) eliminated nitrifying bacteria. The two parallel MASs were successfully operated for 300 days and had ammonia retention of 101.7 ± 24.9% and organic carbon removal of 85.5 ± 8.9%. The MASs mitigated N2O emissions with an emission factor of <0.23%, much lower than the default value of CAS (1.6%). A short-term step-change test demonstrated that N2O indicated the initiation of nitrification and the completion of denitrification in the MAS. The parallel MASs had comparable microbial diversity, promoting organic carbon oxidation while inhibiting ammonia-oxidizing microorganisms (AOMs), as revealed by 16S rRNA gene amplicon sequencing, the quantitative polymerase chain reaction of functional genes, and fluorescence in situ hybridization of β-proteobacteria AOB. The microbial analyses also uncovered that filamentous bacteria were positively correlated with effluent turbidity. Together, controlling DO and SRT achieved organic carbon removal and successful ammonia retention, mainly by suppressing AOM activity. This process represents a new nitrogen management paradigm.

Experimental Design for Accurate Reporting of Catalyst Activity in Nitrogen Reduction Experiments: Determination of the Optimal Membrane for Ammonia Retention

Ammonia synthesis from dinitrogen provides a critical feedstock to agriculture worldwide. The dominant process for ammonia synthesis, Haber-Bosch, is fossil-fuel dependent, energy intensive, and highly centralized. Electrochemical nitrogen reduction (ENRR) could provide a decentralized and environmentally friendly route to ammonia synthesis. ENRR research is challenging due to low amounts of ammonia produced in a typical experiment relative to environmental levels. In the first part of this presentation, we will share a critical result in ENRR experimental design which significantly improves the retention of generated ammonia, specifically related to the selection of membrane separators for H-cell or gas diffusion electrode cell platforms. This result is applicable to both dinitrogen and nitrate reduction research. In the second part of this presentation, a VS2-based ENRR catalyst, which has experimentally shown promising activity and selectivity, will be presented. Additionally, the proposed mechanism of ENRR on VS2 will be discussed, and we will discuss density functional theory simulation of ENRR on VS2 and MoS2. Finally, we will address areas of opportunity for ENRR.

Metatranscriptome Revealed the Efficacy and Safety of a Prospective Approach for Agricultural Wastewater Reuse: Achieving Ammonia Retention during Biological Treatment by a Novel Natural Inhibitor Epsilon-Poly-l-Lysine.

Appropriate inhibitors might play important roles in achieving ammonia retention in biological wastewater treatment and its reuse in agriculture. In this study, the feasibility of epsilon-poly-l-lysine (ε-PL) as a novel natural ammonia oxidation inhibitor was investigated. Significant inhibition (ammonia oxidation inhibition rate was up to 96.83%) was achieved by treating the sludge with ε-PL (400 mg/L, 12 h soaking) only once and maintaining for six cycles. Meanwhile, the organic matter and nitrite removal was not affected. This method was effective under the common environmental conditions of biological wastewater treatment. Metatranscriptome uncovered the possible action mechanisms of ε-PL. The ammonia oxidation inhibition was due to the co-decrease of Nitrosomonas abundance, ammonia oxidation genes, and the cellular responses of Nitrosomonas. Thauera and Dechloromonas could adapt to ε-PL by stimulating stress responses, which maintained the organic matter and nitrite removal. Importantly, ε-PL did not cause the enhancement of antibiotic resistance genes and virulent factors. Therefore, ε-PL showed a great potential of ammonia retention, which could be applied in the biological treatment of wastewater for agricultural reuse.

Microaerophilic activated sludge system for ammonia retention from high-strength nitrogenous wastewater: Biokinetics and mathematical modeling

It is crucial to shift from conventional ammonia removal to recovery to solve environmental problems and resource scarcity. Recovering ammonia from high-strength nitrogenous wastewater can simultaneously save the energy and cost involved in ammonia oxidation, produce ammonia without CO2 emissions, and prevent N2O emissions. A technology for concentrating and recovering ammonia by retrofitting a conventional activated sludge (CAS) system is promising but faces significant challenges in oxidizing organic carbon but not ammonia in wastewater. This study employed biokinetic analysis and mathematical modeling to comprehensively assess the operation and effectiveness of a microaerophilic activated sludge (MAS) system for simultaneously removing chemical oxygen demand (COD) and retaining ammonia. We show that heterotrophic bacteria (HB) in the MAS system had higher maximum specific growth rate (µHB), biomass yield coefficient (YHB), and decay coefficient (bHB) but lower affinities for oxygen and COD than HB in CAS. Simulations using the developed model demonstrated that COD removal efficiencies of > 90%, ammonia retention efficiencies of > 90%, and low N2O emission factors (N2OEF) of < 0.01% can be achieved at solids retention times (SRTs) of 3–50 d, hydraulic retention times (HRTs) of 0.1–1 d, and a volumetric oxygen transfer coefficient (KLa) of (24.58 ± 0.30)HRT−1. The combination of the biokinetics and mathematical modeling revealed the favorable MAS operating conditions allowing efficient ammonia retention and COD removal, which paves the way for turning a CAS system into a MAS system by retrofitting the configuration without high capital expenditures, requiring future intensive study.

Effects of Hydroxypropyl Methylcellulose (HPMC) on the Reinforcement of Sand by Microbial-Induced Calcium Carbonate Precipitation (MICP)

Microbial-induced calcium carbonate precipitation (MICP) is a new technology used for reinforcing soils through microbial mineralization. However, the existing MICP treatment technology is more suiTable for deeper soils due to its high permeability. In this study, HPMC, a cohesive material combined with Sporosarcina pasteurii-induced calcium carbonate precipitation was used to improve the surface layer of the soil. It was also tested in different contents of bacterial solutions and cementation solutions and with a different number of MICP treatments, and was analyzed and discussed by measuring the surface layer strength, calcium carbonate content generated in the crust, rainfall erosion resistance, wind erosion resistance, and ammonia retention rate of the specimens. The microstructure of the samples was investigated by XRD and SEM. It was shown that the addition of HPMC and increasing the number of MICP treatments were effective in the increase in the calcium carbonate content in the surface crust, but had no effect on the total amount of induced calcium carbonate. The combination of HPMC addition and MICP technology can effectively reduce rainwater scour loss and wind erosion loss, and increase its rainfall erosion resistance and wind erosion resistance. Rainfall losses were reduced by up to 30% in specimens treated with HPMC for MICP technology. When the wind speed was 12 m/s, the maximum mass loss rate of the specimens treated with HPMC for MICP was only 0.828%. The addition of HPMC can effectively improve the ammonia absorption rate and reduce the release of ammonia in the process of MICP technology, which is of great significance for environmental protection. The microstructure showed that the addition of HPMC and the increase in the number of treatments using MICP technology can make the surface structure of the specimens more compact, and the calcium carbonate can more effectively fill the pores and cement the soil particles, while the addition of HPMC may not change the calcium carbonate crystal type.

Spatial Correlations Don't Predict Changes in Agricultural Ecosystem Services: A Canada-Wide Case Study

Improving the management of multiple ecosystem services (e.g., food provision, water and air quality regulation, carbon storage, and erosion control) in agricultural landscapes is a critical challenge to improve food system sustainability. However, we currently lack spatially-resolved national-level assessments of the relationships among services in agricultural landscapes over time. This limits our ability to make decisions and predict how environmental changes or agricultural management actions will impact multiple services. How do multiple ecosystem services vary across both space and time, at regional-to-national scales? To address this question, we quantified eight indicators of four ecosystem services across 290 Canadian agricultural landscapes in 1996, 2001, and 2006. We observed consistent correlations between pairs of services across the 290 ecodistricts in each of the 3 years of our study. In particular, ecodistricts with high livestock production had low provision of most regulating services, while ecodistricts with high air quality (ammonia retention) also had high soil and water quality regulation services. However, these ‘snapshot’ correlations poorly predicted how pairs of services changed through time. Ecosystem service change from 1996–2001 to 2001–2006 (as measured by pairwise correlations) showed markedly different patterns than snapshot correlations. In particular, where livestock production increased between years, so did most regulating services. Ecosystem service bundles also showed similar divergent patterns. The distribution of ecosystem service “snapshot” bundles—sets of ecodistricts with similar levels of provision across multiple ecosystem services in a single year—was generally stable between 1996 and 2006; only 15% of ecodistricts changed bundle types in this time period. However, ecosystem service “change” bundles—sets of ecodistricts with similar changes in ecosystem service provision through time—were much more dynamic. Nearly 60% of ecodistricts exhibited a different set of ecosystem service changes from 2001 to 2006 compared to 1996 to 2001. Our results add to the growing evidence that relationships between services across space do not necessarily predict service change through time. Improved understanding of the spatial patterns and temporal dynamics of ecosystem services, and better understanding of underlying processes, is crucial to improve agricultural landscape management for multifunctionality and sustainability.

BSA/ASN/Pol407 nanoparticles for acute lymphoblastic leukemia treatment

During the treatment of acute lymphoblastic leukemia (ALL) with asparaginase (ASN) there is an accumulation of ammonia in the body as result of asparagine hydrolysis. This accumulation known as hyperammonemia is one of the main side-effects of this therapy. To avoid hyperammonemia is urgent to develop new strategies for ammonia retention. Herein is presented the immobilization of ASN into bovine serum albumin/poloxamer 407 (BSA/Pol407) nanoparticles. The ability of the developed nanoparticles to hydrolyze asparagine while retaining the forming ammonia is also explored. Different percentages of ASN were entrapped into BSA nanoparticles coated with Poloxamer 407 and were prepared by high-pressure homogenization. The nanoparticles were characterized regarding their physico-chemical properties, stability, capacity to retain ammonia and safety using zebrafish embryos as an in vivo model of toxicity. The BSA/ASN25%/Pol407 nanoparticles were selected as the best formulation to hydrolyze asparagine using the lowest nanoparticle concentration. These nanoparticles presented physical characteristics suitable for an intravenous application and were capable to retain the forming ammonia decreasing the negative effect of free ASN on zebrafish survival. These nanoparticles could potentially be used to prevent hyperammonemia during ALL treatment with ASN.

Experiences from an investigation on the potential of packed bed reactors for high rate nitrification of mature landfill leachates

Due to high specific surface area, high biomass concentration and handling convenience, packed bed reactor technology is a highly competitive option for nitrification of landfill leachates. Nitrification would solve the problem of insufficient ammonia retention faced by the high pressure membrane systems at the Ihlenberg landfill, which aims to achieve clean water recoveries up to 95%. This study investigated the feasibility for ammonia removal using four lab-scale reactors packed with three different packing materials (coke, expanded clay beads and polyethylene carrier) over a period of about 400 days. The research work studied the nitrification of two process streams: reverse osmosis concentrate (RO) of raw leachate (having high dissolved organics content) and nanofiltration permeate of RO retentate (with a low concentration of organics), to identify advantages/disadvantages arising from the differences in their composition. The organics contained in the leachate were observed to cause inhibition. Due to this reason, the maximum nitrification rate obtained in the presence of organics was about 570 g N-NH4+/(m3 d), whereas in their absence up to 1.2 kg N-NH4+/(m3 d) could be achieved. Although coke packing because of its higher specific surface area and rugged surface favoured faster biofilm development; due to its ability to adsorb organics and thus also promoting the growth of heterotrophs, it was found to be more vulnerable to clogging.

Ammonia excretion in the marine polychaete Eurythoe complanata (Annelida).

Ammonia is a toxic waste product from protein metabolism and needs to be either converted into less toxic molecules or, in the case of fish and aquatic invertebrates, excreted directly as is. In contrast to fish, very little is known regarding the ammonia excretion mechanism and the participating excretory organs in marine invertebrates. In the current study, ammonia excretion in the marine burrowing polychaete Eurythoe complanata was investigated. As a potential site for excretion, the 100-200 µm long, 30-50 µm wide and up to 25 µm thick dentrically branched, well ventilated and vascularized branchiae (gills) were identified. In comparison to the main body, the branchiae showed considerably higher mRNA expression levels of Na+/K+-ATPase, V-type H+-ATPase, cytoplasmic carbonic anhydrase (CA-2), a Rhesus-like protein, and three different ammonia transporters (AMTs). Experiments on the intact organism revealed that ammonia excretion did not occur via apical ammonia trapping, but was regulated by a basolateral localized V-type H+-ATPase, carbonic anhydrase and intracellular cAMP levels. Interestingly, the V-type H+-ATPase seems to play a role in ammonia retention. A 1week exposure to 1 mmol l-1 NH4Cl (HEA) did not cause a change in ammonia excretion rates, while the three branchial expressed AMTs showed a tendency to be down-regulated. This indicates a shift of function in the branchial ammonia excretion processes under these conditions.

Ammonia retention capacity of nanofiltration and reverse osmosis membranes in a non steady state system, to be use in recirculation aquaculture systems (RAS)

Recirculation aquaculture systems (RAS) need to control ammonia level because the high toxicity on fish. For this, nanofiltration membrane has been proposed in the first part of our study to separate ammonia from water. We discussed different membranes as well as transmembrane pressure (TMP) and pH to achieve the best results for ammonia retention (AR). In this second part we analyze the influence of the ammonia concentration on AR to obtain higher concentrated volume that can be separated of the system and treated later. A model solution in a non-steady state was used, where the ammonia concentration increase over the time. Since water has similar molecular weight that ammonium ions, the mechanisms for the rejection of ammonia are based on the repulsive electrochemical forces on the active layer. A RO membrane DSS-HR98PP and three NF membranes, NF90, NF200 and NF270 were tested over a range of 0–11.45mg/L under optimal TMP of 16bar for NF membranes and 24.5bar for the RO membrane. Projecting the results to the RAS, NF270 is the most efficient for ammonia retention, as both flux and AR influence the engineering design concept. For example, treating 2000L/h with an ammonia concentration of 7mg/L, removal is 17.5g/m2day with a membrane area of 13m2 and TMP of 16bar.

Analysis of the chemical and physical factors affecting reactive adsorption of ammonia on graphene/nanoporous carbon composites

Adsorption of ammonia was studied on composites of graphene and nanoporous carbon (5 and 20 wt.% graphene). The breakthrough curves were measured in three consequent adsorption–desorption runs in either dry or wet conditions. The mechanism of ammonia retention was evaluated from the point of view of either reactive or physical adsorption. The important finding is the insensitivity of the ammonia adsorption on the composites on the water content in the challenge gas. An about 50% decrease in the surface area and volume of micropores compared to nanoporous carbons does not affect the amount of physically adsorbed ammonia. It is governed by the volume of ultramicropores (pore width <0.7nm), density of groups on the surface, hydrophobicity level, and the electronic conductivity. The surface acidity level and thus the amounts and strength of oxygen groups being able to react with ammonia at ambient conditions are of paramount importance for the reactive adsorption process.

Retention and nitrification of injected anhydrous NH3as affected by soil pH

Benke, M. B., Goh, T. B., Karamanos, R., Lupwayi, N. Z. and Hao, X. 2012. Retention and nitrification of injected anhydrous NH3as affected by soil pH. Can. J. Soil Sci. 92: 589–598. Anhydrous ammonia is an economical and extensively used fertilizer, yet loss after injection can reduce its agronomic efficiency. A laboratory experiment was conducted to examine how soil properties affect ammonia retention and nitrification following anhydrous NH3injection using 10 different Canadian prairie soils. Soils were also injected with atmospheric air for comparison. Following injection, soils were incubated for up to 216 h at field capacity. Among the soil properties studied [pH (1:2 water), clay, total N, and organic C contents], only pH was negatively related (R2=0.55, n=10, 24 h incubation) to percentage injected N retained by soil. The amount of N retained by soil 24 h following injection was 92±2% (mean±SEM) when pH &lt;6, compared with 64±2% when pH&gt;7.5. Rate of nitrification increased (P&lt;0.001) about 48–96 h following injection and was greater in pH&gt;7.5 than pH&lt;6 soils. There was no difference (P&gt;0.05) in bacterial diversity between ammonia- and air-injected soils. The slower nitrification rates suggest that potential leaching and denitrification losses in acid soils could be smaller than in alkaline soils.

Retention and nitrification of injected anhydrous NH3 as affected by soil pH

Benke, M. B., Goh, T. B., Karamanos, R., Lupwayi, N. Z. and Hao, X. 2012. Retention and nitrification of injected anhydrous NH 3 as affected by soil pH. Can. J. Soil Sci. 92: 589-598. Anhydrous ammonia is an economical and extensively used fertilizer, yet loss after injection can reduce its agronomic efficiency. A laboratory experiment was conducted to examine how soil properties affect ammonia retention and nitrification following anhydrous NH3 injection using 10 different Canadian prairie soils. Soils were also injected with atmospheric air for comparison. Following injection, soils were incubated for up to 216 h at field capacity. Among the soil properties studied [pH (1:2 water), clay, total N, and organic C contents], only pH was negatively related (R 2=0.55, n=10, 24 h incubation) to percentage injected N retained by soil. The amount of N retained by soil 24 h following injection was 92±2% (mean±SEM) when pH 7.5. Rate of nitrification increased (P<0.001) about 48-96 h...

Synthesis, Characterization, and Ammonia Adsorption Properties of Mesoporous Metal–Organic Framework (MIL(Fe))–Graphite Oxide Composites: Exploring the Limits of Materials Fabrication

AbstractComposites of MIL‐100(Fe) and graphite oxide (GO) were prepared with various ratios of the two components and tested for ammonia removal in dynamic conditions. The initial and exhausted samples were characterized by X‐ray diffraction, nitrogen adsorption, thermal analysis, Fourier Transform infrared spectroscopy, Raman spectroscopy, and scanning electron microscopy. The results indicate that the formation of well‐defined MIL‐100(Fe)/GO composites is not favored. This is linked to the specific geometry of MIL‐100(Fe). The attachment of the GO carbon layers to the spherical cages of MIL‐100(Fe) (via coordination between the oxygen groups of GO and the metallic sites of the metal–organic framework) prevents the proper formation of the MIL‐100(Fe) structure. Therefore, the composite with the highest GO content has a lower porosity and smaller ammonia adsorption capacity than those calculated for the physical mixture of MIL‐100(Fe) and GO. The main mechanism of ammonia retention is via Brönsted interactions between ammonia and the water molecules present in MIL‐100(Fe). Nevertheless, the presence of excess water in the system lowers the acidity of the MIL material, and consequently causes a decrease in the ammonia adsorption. The Lewis interactions between ammonia and the metal centers in MIL also take place during the adsorption process.

Graphite Oxides Obtained from Porous Graphite: The Role of Surface Chemistry and Texture in Ammonia Retention at Ambient Conditions

AbstractGraphite oxides (GO) synthesized using Brodie and Hummers methods are tested for ammonia adsorption at ambient conditions with different contents of water in the system. Surface characterization before and after exposure to ammonia is performed using XRD, FTIR spectroscopy, potentiometric titration, thermal analysis, adsorption of nitrogen, and XPS. Oxidation of the same porous graphite using two methods results in materials with different textural and chemical features. On GO obtained using the Brodie method mainly epoxy and carboxylic groups are present whereas on the GO obtained using the Hummers method chemisorbed oxygen is also found. The contribution of the carboxylic groups in the latter material is greater. It also contains sulfur either in sulfones or as residual sulfuric acid. Ammonia is adsorbed either via reaction with surface groups or dissolution in water. The former is responsible for strong adsorption. The evidence of the catalytic effect of the carbon surface on activation of oxygen leading to surface oxidation is also observed.

The role of sulfur-containing groups in ammonia retention on activated carbons

Two carbons with different contents of sulfur were prepared and oxidized either by heating in air or by chemical treatment. The materials were then tested as adsorbents of ammonia in dynamic conditions, at room temperature. Their chemical and structural features were analyzed by energy dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, X-ray fluorescence spectroscopy, scanning electron microscopy, thermogravimetric analyses, potentiometric titration and sorption of nitrogen. It was found that not only oxygen-containing groups but also sulfur-containing groups enhance ammonia adsorption. In particular, sulfonic groups play a predominant role. In the presence of superoxide anions, they are converted into sulfates that react with ammonia to form ammonium sulfates. These salts are strongly retained in the micropores of the adsorbents.

Graphite Oxide/Polyoxometalate Nanocomposites as Adsorbents of Ammonia

Adsorbents for ammonia were prepared by modifications of graphite oxide with addition of a polymer followed by impregnation with either one of two different Keggin polyanions: H3PW12O40 or H3PMo12O40. The high acidity of those polyoxometalates combined with the functionalities and acidity of graphite oxide are expected to initiate strong interactions with NH3. The materials were characterized before and after exposure to ammonia by X-ray diffraction, transmission electron microscopy, sorption of nitrogen, potentiometric titration, thermal analyses, and Fourier transform infrared spectroscopy. Even though the nanocomposites prepared have a disordered structure, an improvement in ammonia retention compared to the parent graphite oxide was observed owing to the formation of complexes between ammonium and polyanions. It was proposed that, in the process of nanocomposite formation, the negatively charged carboxylic groups, located at the edges of graphene-like layers, first interact with the positively charged polymer. Then, the introduced polyacids are attracted via polar interactions to the polymer and oxygen-containing groups, mainly epoxy type, attached to the GO layers forming the house-of-card structure. Interaction of polyacids with the groups located at the edges of the carbon layers causes formation of aggregates and thus limits the accessibility of the interlayer space which results in a decrease in the amount of ammonia adsorbed.