Initial NH4 Research Articles

Advanced biological sequential treatment of mature landfill leachate using aerobic activated sludge SBR and fungal bioreactor.

This study utilized Penicillium spp. to treat mature landfill leachate (MLL) in a continuous bioreactor and batch experimental tests under non-sterile conditions. MLL characteristics such as chemical oxygen demand (COD), soluble COD (sCOD), total carbon (TC), total organic carbon (TOC), and color removal efficiency were determined. The lignocellulosic enzymatic activity of laccase (Lac), lignin-peroxidase (LiP), and manganese-peroxidase (MnP) was also determined. The batch experimental test was carried out with raw and pretreated MLL containing the initial NH4 +-N concentrations of 0, 105, 352, and 914mg/L. A maximum COD reduction of 41% and maximum enzymatic activity of 193, 37, and 25U/L for Lac, LiP and MnP was recorded for the MLL containing 352mg/L NH4 +-N. The continuous bioreactor exhibited maximum values of 52, 54, 60, 58, and 75 percentage of COD, sCOD, TC, TOC, and color removal efficiency with MLL containing 352mg/L NH4 +-N that was pretreated at HRT 120h, while the maximum detected lignocellulosic enzymatic activities were 149, 27, and 16U/L for Lac, LiP, and MnP, respectively. A total of 64% COD reduction was achieved from the raw MLL considering 12% COD and 100% NH4 +-N reduction in the aerobic activated sludge sequencing batch reactor pretreatment process. The steady and higher removal efficiency of the bioreactor over the entire study period is promising for further exploration to enhance removal of refractory contaminants from the MLL.

Catalytic oxidation of NH3 over circulating ash in the selective non-catalytic reduction process during circulating fluidized bed combustion

Selective non-catalytic reduction (SNCR) with NH3 as the reducing agent is widely used for the denitrification of flue gas in circulating fluidized bed combustion (CFB) process, where the circulating ash can cause the oxidation of NH3. In this study, the behaviors and mechanisms of NH3 catalytic oxidation over circulating ash were systematically investigated. The results revealed that NH3 could be catalytically oxidized to form NO efficiently by circulating ash. Along with the temperature increasing from 550 °C to 950 °C, the formation of NO increased at first and then decreased. Oxygen was crucial to NH3 catalytic oxidation, while its effects on NO formation were slight at high concentrations. Meanwhile, as the initial NH3 concentration increased, the concentration of NO in the flue gas increased while the selectivity of NO decreased because of the enhanced homogeneous reduction between the residual NH3 and NO. Fe2O3 was confirmed to be one of the principal mineral components in circulating ash to catalyze NH3 oxidation. In addition, the mechanisms of NH3 oxidation over circulating ash were also investigated. It was validated that NH2 on Lewis acid sites were the main NH3 adsorbed species (ad-species), and the main oxidation intermediates of NH3 ad-species were bidentate and bridged nitrates in the presence of O2.

Ammonium removal characteristics of heterotrophic nitrifying bacterium Pseudomonas stutzeri GEP-01 with potential for treatment of ammonium-rich wastewater.

A heterotrophic nitrifying bacterium was isolated from the activated sludge and identified as Pseudomonas stutzeri GEP-01. Strain GEP-01 exhibited an efficient heterotrophic nitrification capability and a high nitrogen utilization rate, 48mg/L NH4+-N was removed after culturing for 24h without NO2--N or NO3--N accumulation, and 64.7% of the NH4+-N was removed by heterotrophic nitrification. Single-factor experiments indicated that factors such as the carbon source, temperature, NH4+-N load, and inoculum size had significant effects on the ammonium removal efficiency of strain GEP-01. The preferred conditions for heterotrophic nitrification were sodium citrate, 30°C, 40mg/L NH4+-N, and 5% inoculum size. When the initial NH4+-N amounts were 100, 200, 500 and 1000mg/L, the removal rates were approximately 100%, 93%, 90.4%, and 78.9%, respectively, and higher ammonium concentrations require longer culture time. Nitrogen balance demonstrated that 40% of the initial nitrogen was lost, which was probably removed in the form of gas products under optimum culture conditions, and 36.3% of NH4+-N was converted to biomass. When incubated (adding a small amount of sodium citrate as carbon source and no carbon source) in swine wastewater containing 835mg/L of ammonium,the removal ratio reached 56.3% and 24.8%.Strain GEP-01 has potential applications in the treatment of ammonium-rich wastewater.

Predicting Economic Optimal Nitrogen Rate with the Anaerobic Potentially Mineralizable Nitrogen Test

Estimates of mineralizable N with the anaerobic potentially mineralizable N (PMNan) test could improve predictions of corn (Zea mays L.) economic optimal N rate (EONR). A study across eight US midwestern states was conducted to quantify the predictability of EONR for single and split N applications by PMNan. Treatment factors included different soil sample timings (pre‐plant and V5 development stage), planting N rates (0 and 180 kg N ha−1), and incubation lengths (7, 14, and 28 d) with and without initial soil NH4–N included with PMNan. Soil was sampled (0–30 cm depth) before planting and N application and at V5 where 0 or 180 kg N ha−1 were applied at planting. Evaluating across all soils, PMNan was a weak predictor of EONR (R2 ≤ 0.08; RMSE, ≥67 kg N ha−1), but the predictability improved (15%) when soils were grouped by texture. Using PMNan and initial soil NH4–N as separate explanatory variables improved EONR predictability (11–20%) in fine‐textured soils only. Delaying PMNan sampling from pre‐plant to V5 regardless of N fertilization improved EONR predictability by 25% in only coarse‐textured soils. Increasing PMNan incubations beyond 7 d modestly improved EONR predictability (R2 increased ≤0.18, and RMSE was reduced ≤7 kg N ha−1). Alone, PMNan predicts EONR poorly, and the improvements from partitioning soils by texture and including initial soil NH4–N were relatively low (R2 ≤ 0.33; RMSE ≥ 68 kg N ha−1) compared with other tools for N fertilizer recommendations.Core Ideas Anaerobic potentially mineralizable N (PMNan) is a weak predictor of economic optimal N rate (EONR). Predictability of EONR by PMNan improves when accounting for soil texture. For coarse‐textured soils, PMNan at V5 improves EONR predictability. Increasing incubation length does not substantially improve EONR predictability. PMNan alone is not a reliable management tool for N rate determination.

Kinetic characteristics and N2O production of a heterotrophic nitrifying bacterium Pseudomonas putida YH capable of tolerating adverse environmental conditions

AbstractBACKGROUNDHeterotrophic nitrifying bacteria (HNB) have rapid growth rate, high activity and strong anti‐shock ability. These attributes are advantageous in engineering applications, yet the use of HNB is restricted by lack of clarity about the kinetics and metabolic mechanisms involved. Thus, nitrogen conversion characteristics, kinetics and N2O production of the HNB Pseudomonas putida YH were evaluated.RESULTSStrain YH exhibited superior heterotrophic nitrification‐aerobic denitrification (HNAD) ability in treating nitrogenous wastewater, with maximum removal rates of 10.07, 8.86 and 8.78 mg L−1 h−1 for NH4+–N, NO3−–N and NO2−–N, respectively. Mass balance analysis demonstrated that the removed TN was mainly due to bacterial assimilation (53–55%) and conversion into gaseous N2 (34–39%), instead of nitrification intermediate accumulation and N2O emission. In addition, the kinetics of nitrogen degradation and cellular growth of strain YH exactly conformed to the modified Gompertz equation and the Logistic equation, respectively. Moreover, strain YH showed excellent adaptability to variations of temperature, pH, C:N ratio and initial NH4+–N concentration in terms of nitrogen removal and N2O emission. The highest NH4+–N removal rate was obtained at pH 7.0, temperature 30 °C and C:N ratio of 15. Furthermore, the heterotrophic nitrification ability was just partially deteriorated after the addition of inhibitors, which further proved the multiple metabolic pathways of heterotrophic nitrification by strain YH.CONCLUSIONThe results demonstrated that strain YH exhibited excellent abilities of HNAD, N2O emission control and tolerance to adverse conditions, indicating that strain YH can be an effective candidate for treating nitrogenous wastewater without secondary pollution. © 2019 Society of Chemical Industry

Increased retention of available nitrogen during thermal drying of solids of digested sewage sludge and manure by acid and zeolite addition

Thermal drying is an increasingly common post-treatment for digestate-solids, but prone to N losses via ammonia (NH3) volatilization. Acidification with strong acids prior to drying may retain ammonium (NH4+) in the solids. Natural zeolites can provide adsorption sites for exchangeable cations as ammonium and porosity for free ammonia, which has the potential to contribute to higher N retention in the dried solids. The present study investigated whether the zeolite addition increases NH4+-N retention during thermal drying of two digestate solids (manure based, MDS; sewage sludge based, SDS), and whether any synergistic effects of combining acidification with sulfuric acid and the addition of zeolite exist. Operating conditions included four pH levels (non-acidified control, adjusted to 8.0, 7.5, 6.5 with concentrated sulfuric acid), four zeolite addition rates (0%, 1%, 5% and 10%), fixed drying temperature (130 °C) and fixed air ventilation rate (headspace exchange rate of 286 times hour−1). Zeolite addition significantly increased NH4+-N retention from 18.0% of initial NH4+-N in the non-acidified control up to a maximum of 57.4% for MDS, and from 76.6% to 94.5% for SDS. No positive synergistic effect between acidification and zeolite addition was observed, with acidification being the dominant. Nevertheless, zeolite has the potential to be a safe and easy-to-handle alternative to concentrated sulfuric acid.

Zonal control for selective catalytic reduction system using a model-based multi-objective genetic algorithm

It is challenging for aqueous urea injection control to achieve high NO x conversion efficiency while restricting tailpipe ammonia (NH3) slip. Optimizing the selective catalytic reduction systems can reduce diesel engine emissions, potentially improve fuel economy and urea utilization efficiency, and finally reduce aftertreatment costs. In this article, a model-based multi-objective genetic algorithm is adopted to optimize selective catalytic reduction systems related to trade-off between NO x emission and NH3 slip. Selective catalytic reduction model is a one-state selective catalytic reduction model based on continuous stirred tank reactor theory, which significantly reduces the computational burden. The optimal NH3 coverage ratio map was obtained globally based on world harmonized transient cycle. The effect of temperature on optimal NH3 coverage ratio, Zonal control logics extracted from the optimal solution, and the control problems on different zones were analyzed. The zonal control logics were validated on multiple test cycle with different initial NH3 coverage ratios. Results show that the zonal control achieves high NO x conversion while restricting the tailpipe NH3 slip. With this method, NO x emission and NH3 slip of optimal solution can meet the requirements of the Euro VI emission regulation for heavy-duty diesel engines.

Optimization of the Parameters for Microalgae Immobilization and Analysis of Its Recovery Potential for Ammonia Nitrogen in Wastewater

Application of microalgae in wastewater treatment is regarded as a potential green technology. However, its engineering application has been largely hindered because of the difficulty of biomass separation and harvesting. This study aimed to identify the key parameters influencing the process of microalgae immobilization. To do this, the study focused on immobilization technology and Scenedesmus obliquus, and employed the response surface methodology (RSM) and the Box-Behnken design (BBD). In an evaluation of the performance of microalgae beads, the fixing agent concentration, the cross-linking agent concentration, and the cross-linking time were selected as the independent variables, and the mechanical strength, the mass transfer rate, and the growth rate of immobilized microalgae beads were the response values. The optimal conditions and the uptake potential of the microalgae beads with respect to ammonia nitrogen (NH4+-N) were further explored and analyzed. The results showed that the optimal parameters for the preparation of immobilized microalgae beads were 5%, 2%, and 16 h, and the maximum removal capacity was obtained using mixotrophic cultivation with an embedding density of 1×106 cells·mL-1 and an organic matter concentration of 300 mg·L-1. In addition, the removal capacity of immobilized microalgae with respect to high concentrations of NH4+-N was significantly higher than for free-living microalgae. When the initial concentrations of NH4+-N were approximately 50 and 70 mg·L-1, NH4+-N was removed by the immobilized microalgae (after a 5-day mixotrophic cultivation) at a rate of (96.6±0.1)% and (65.2±4.5)%, respectively. With an initial NH4+-N concentration of 30 mg·L-1, the dominance of free-living microalgae was clear, with a removal rate of (97.8±0.6)% after a 3-day cultivation. However, under heterotrophic cultivation, the removal rate of NH4+-N by immobilized microalgae was generally low and gradually decreased with increasing concentrations. When the initial concentration was approximately 30 mg·L-1, the removal rate was only (49.0±3.1)%. This study provides new prospects for sustainable urban wastewater treatment, a new approach for resource recycling, and a strong theoretical foundation for the popularization and application of microalgae in wastewater treatment.

Experimental and Numerical Study of the Fuel-NOx Formation at High CO2 Concentrations in a Jet-Stirred Reactor

New experimental results of the characteristics of fuel-NOx formation at high CO2 concentrations are obtained in a jet-stirred reactor. NH3 is selected as the source of N. The effects of the CO2 concentration (0–97.4%), reaction temperature (873–1323 K), equivalence ratio (0.56–1.61), initial NH3 concentration (10–1000 ppm), and residence time (0.01–10 s) on the production and destruction of fuel-NOx are experimentally and numerically investigated in both N2 and CO2 atmospheres. Under fuel-lean conditions, the NO emissions decrease with increasing residence time, equivalence ratio, or CO2 concentration. Under stoichiometric conditions, the NO production from the N2 and CO2 atmospheres are nearly the same, irrespective of the temperature. Under fuel-rich conditions, the NO-reburning chemistry can reduce the majority of the NO emission. Under fuel-rich conditions and at temperatures above 1200 K, the NO production is lower in the N2 atmosphere because the NO-reburning is stronger than that in the CO2 atmosphere. Moreover, the critical temperature for the peak N2O formation is obtained. Although fuel oxidation is slightly delayed at high CO2 concentrations, the N2O formation is essentially insensitive to the CO2 concentration. Furthermore, the numerical results are consistent with the vast majority of experiments, and important reactions are identified for future development of fuel-NOx formation at high CO2 concentrations.

Electro-sorption of ammonium ion onto nickel foam supported highly microporous activated carbon prepared from agricultural residues (dried Luffa cylindrica)

An electrode made of loofah sponge derived activated carbon supported on nickel foam (AC/Ni) was successfully fabricated and used to remove ammonium ion (NH4+) from aqueous solution. A multilayer adsorption isotherm was used to describe ammonium electro-sorption on AC/Ni electrodes at different temperature, initial NH4+ concentration, and electrical field. The cyclic voltammetry (CV) results suggested that the electrical capacitance of AC/Ni electrodes, with the AC being prepared without preheating (OAC) or with low temperature heating (i.e., 300 AC), were higher than those prepared at high preheating temperature (i.e., 400 AC and 500 AC). Increasing the electro-sorption temperature from 10 to 50 °C decreased the monolayer NH4+ adsorption capacity from 5 to ca. 2–3 mg-N g−1, respectively. Background electrolyte, namely, sodium sulfate, exhibited significant competitive effect on the adsorption of ammonium ion at sodium ion concentration > 10−2 M. The activation energy and heat of adsorption were 9–23.2 kJ mol−1 and −3.7–−10.7 kJ mol−1, respectively, indicating a physisorption and exothermic adsorption characteristics. Based on the kinetics and thermodynamics analysis, there was slight increase in the activation energy with elevating preheating temperature, which increased the quantity of micro-pores and surface heterogeneity of the AC materials. Overall, results clearly demonstrated that carbon pyrolysis played a role on the capacitive charging behaviors of electrodes and the efficiency of NH4+ electro-sorption on the AC/Ni electrodes.

Enhanced bio-methane production from ammonium-rich waste using eggshell-and lignite-modified zeolite (ELMZ) as a bio-adsorbent during anaerobic digestion

Abstract In this study, a calcium-rich natural material utilized bio-adsorbent, composed of eggshell-and lignite-modified zeolite (ELMZ) was developed for enhancing methane production at high ammonia concentrations. The ELMZ showed a maximum NH4+-N adsorption capacity of 55 mg/g, which was 5.9 folds of the natural zeolite (9.2 mg/g) and 1.4 folds zeolite modified by calcium chloride (40 mg/g), respectively. The ammonium adsorption process well fitted the pseudo-second-order kinetic model and the Freundlich isotherm. It indicated that its process was an ion-exchange process. The high abundance of cations, especially high Ca2+ in ELMZ supported the ion-exchange, which stimulated the anaerobic digestion process. The anaerobic digestion with ELMZ as a fixed-bed (initial NH4+-N concentration: 4.1 g/L), exhibited the best performance at methane yield of 250 mL CH4/g-DOCremoval, which is 7 folds higher than that achieved with natural zeolite (32 mL/g-DOCremoval) at the same ammonia level. As a bio-adsorbent, ELMZ contributes to enhance methane production and further benefits to a sustainable process since the eggshell waste is re-circulated.

Treatment of Aquaculture Wastewater through Chitin/ZnO Composite Photocatalyst

This paper proposed a newly explored composite photocatalyst, Chitin/ZnO, prepared via the sol-gel method for exploring its photocatalytic activity in the simulated aquaculture wastewater under UV irradiation. The study mainly involves the application of Chitin/ZnO from three aspects: the structure, the principle and the degradation efficiency. The effects of purification operation factors including mass ratio rate, dosage, calcination temperature, initial NH4+–N concentration and illumination conditions on the NH4+–N removal effectiveness were investigated. Optimum conditions were explored through orthogonal experiments, which revealed that 88.73% NH4+–N removal from 60 mg/L synthetic wastewater was achieved by direct illumination for 120 min. Additionally, Chitin/ZnO photocatalysts (mass ratio of 2:3) at a calcination temperature of 500 °C were favorable for Chitin loaded over a ZnO lattice. The obtained nanoparticles of Chitin/ZnO were characterized using SEM and X-ray diffraction. The purpose of this paper is to grope for an economical and easy method of Chitin/ZnO powder preparation and to provide a practical approach for future research on the photocatalytic purification of aquaculture wastewater.

Zeolite as a Potential Medium for Ammonium Recovery and Second Cheese Whey Treatment

The efficiency of natural zeolite to remove ammonium from artificial wastewater (ammonium aqueous solutions) and to treat second cheese whey was examined, aiming to recover nitrogen nutrients that can be used for further applications, such as slow-release fertilizers. Sorption experiments were performed using artificial wastewater and zeolite of different granulometries (i.e., 0.71–1.0, 1.8–2.0, 2.0–2.8, 2.8–4.0, and 4.0–5.0 mm). The granulometry of the zeolite had no significant effect on its ability to absorb ammonium. Nevertheless, smaller particles (0.71–1.0 mm) exhibited quicker NH4+-N adsorption rates of up to 93.0% in the first 10 min. Maximum ammonium removal efficiency by the zeolite was achieved at ammonium concentrations ranging from 10 to 80 mg/L. Kinetic experiments revealed that chemisorption is the mechanism behind the adsorption process of ammonium on zeolite, while the Freundlich isotherm model fitted the experimental data well. Column sorption experiments under batch operating mode were performed using artificial wastewater and second cheese whey. Column experiments with artificial wastewater showed high NH4+-N removal rates (over 96% in the first 120 min) for all granulometries and initial NH4+-N concentrations tested (200 and 5000 mg/L). Column experiments with second cheese whey revealed that natural zeolite can remove significant organic loads (up to 40%, 14.53 mg COD/g of zeolite) and NH4+-N (about 99%). For PO43−-P, the zeolite appeared to saturate after day 1 of the experiments at a removal capacity of 0.15 mg P/g of zeolite. Desorption experiments with water resulted in low NH4+-N and PO43−-P desorption rates indicating that the zeolite could be used as a substrate for slow nitrogen release in soils.

NH4+-N adsorption behavior of nitrifying sludge immobilized in waterborne polyurethane (WPU) pellets

In this study, the characteristics and mechanism of NH4+-N adsorption by nitrifying sludge (NS) waterborne polyurethane (WPU) immobilized pellets were investigated. The NH4+-N adsorption by WPU immobilized pellets at different initial NH4+-N concentrations, and the influences of temperature, pH, salinity on NH4+-N absorption were respectively studied. Moreover, the adsorption isotherms, kinetics models and intraparticle diffusion model analysis were employed to investigate the adsorption process. The results showed that the NH4+-N adsorption capacity of the nitrifying sludge WPU was higher than that of the pellets without sludge (CK), and it increased with increasing initial NH4+-N concentrations. The optimal pH for NH4+-N adsorption was 7.0; High temperature and high salinity had an inhibitory effect on the NH4+-N adsorption. All the equilibrium data conformed to the Langmuir and Freundlich isotherms. The adsorption kinetics followed the pseudo-second-order kinetic model. The adsorption combined surface and internal diffusion.

Abatement of SF6 in the presence of NH3 by dielectric barrier discharge plasma

In this paper, the degradation rate, energy yield and the degradation by-products of SF6 was studied when different concentrations of NH3 were added. When NH3 concentration increased from 0 to 2%, the degradation rate efficiency(DRE) of SF6 increased from 60% to 97.23% under the flow rate of 50ml/min and 94W input power. The energy yield(EY) reached 4.16g/kWh. In addition, we found that increasing the flow rate to 250ml/min, the DRE decreased to 58.71%, but the EY increased to 12.55g/kWh. The main gas by-products are SOF2, SO2F2, SO2, OF2, HF and NF3. When the concentration of initial NH3 increased, the SO2 concentration increased while the concentrations of SOF2, SO2F2, SOF4 decreased. In addition, we found that a pale yellow film formed on the surface of the reactor wall. XPS analysis showed that the solid products were mainly S, NH3HF and NH4HF2. The emission spectra show that NH3 addition can effectively promote the formation of active particles and increase plasma density.The addition of NH3 can convert some of the sulfur and fluorine into solid products and reduce the production of toxic gases.

Al-Waste-Based Zeolite Adsorbent Used for the Removal of Ammonium from Aqueous Solutions

This work evaluates the use of a synthetic NaP1 zeolite obtained from a hazardous Al-containing waste for the removal of ammonium (NH4+) from aqueous solutions by batch experiments. Experimental parameters, such as pH (6–8), contact time (1–360 min), adsorbent dose (1–15 g/L), and initial NH4+ concentration (10–1500 mg/L), were evaluated. Adsorption kinetic models and equilibrium isotherms were determined by using nonlinear regression. The kinetic was studied by applying both the pseudo-first-order and pseudo-second-order models. The equilibrium isotherms were analyzed according to two-parameter equations (Freundlich, Langmuir, and Temkin) and three-parameter equations (Redlich–Peterson, Sips, and Toth). The results showed that the NH4+ uptake on NaP1 was fast (15 min) leading to a high experimental sorption capacity (37.9 mg/g). The NH4+ removal on NaP1 was a favorable process that followed the pseudo-first-order kinetic model. The NH4+ adsorption was better described by the Sips (54.2 mg/g) and Toth (58.5 mg/g) models. NaP1 zeolite from Al-waste showed good NH4+ sorption properties, becoming a potential adsorbent to be used in the treatment of contaminated aqueous effluents. Thus, a synergic effect on the environmental protection can be achieved: the end of waste condition of a hazardous waste and the water decontamination.

Anoxic ammonia removal using granulated nanoscale oxyhydroxides of Fe (GNOF) in a SBR

Microbial mediated anoxic ammonia removal in the presence of granulated nanoscale oxyhydroxides of Fe (GNOF) was investigated in a SBR, as a novel alternative to conventional nitrification and denitrification. Activated sludge flocs collected from a SBR treating sewage was used as seed biomass to develop the process. After confirming the feasibility of anoxic ammonia removal, SBR operations were carried out for 267 days in 9 phases by varying the initial NH4+-N concentrations from 100 to 500 mg/L and cycle time from 2 to 0.5 day. Effective anoxic ammonia removal was achieved in 0.5 day cycle time with the removal rates of NH4+-N and TN as 130 mg/L/d and 115 mg/L/d, respectively. Batch studies showed that the optimum COD/NH4+-N ratio for effective NH4+-N removal was less than or equal to 2. The kinetics of NH4+-N removal, confirmation studies for GNOF coupled nitrification-denitrification and Fe redox cycling involved in the process were also performed and discussed. The developed process is economical as there is no need for aeration and alkalinity.

Characterization and prediction of organic nitrogen biodegradability during anaerobic digestion: A bioaccessibility approach

Prediction of organic nitrogen mineralization into ammonium during anaerobic digestion is required for optimizing substitution of mineral fertilizer by digestates. The aim of this study was to understand organic nitrogen biodegradability and to investigate how it can be predicted from carbon biodegradability, and nitrogen bioaccessibility, respectively. Bioaccessibility was assessed using fractionation methods based on sequential extractions. Results showed that organic nitrogen was present in fractions whose bioaccessibility levels differed. Organic nitrogen and carbon biodegradability were also determined and compared. Results highlighted two groups of substrates: the first with an initial NH4+/TKN < 30%, whose carbon and nitrogen biodegradability are similar; the second with an initial NH4+/TKN > 30%, whose carbon and nitrogen biodegradability differ significantly. To enable prediction on all substrates, partial least square (PLS) regressions were carried out to link organic nitrogen bioaccessibility indicators to biodegradability. The models successfully predicted organic nitrogen biodegradability with a maximum prediction error of 10%.

Isotopic evidence for enhanced fossil fuel sources of aerosol ammonium in the urban atmosphere

The sources of aerosol ammonium (NH4+) are of interest because of the potential of NH4+ to impact the Earth's radiative balance, as well as human health and biological diversity. Isotopic source apportionment of aerosol NH4+ is challenging in the urban atmosphere, which has excess ammonia (NH3) and where nitrogen isotopic fractionation commonly occurs. Based on year-round isotopic measurements in urban Beijing, we show the source dependence of the isotopic abundance of aerosol NH4+, with isotopically light (−33.8‰) and heavy (0 to +12.0‰) NH4+ associated with strong northerly winds and sustained southerly winds, respectively. On an annual basis, 37–52% of the initial NH3 concentrations in urban Beijing arises from fossil fuel emissions, which are episodically enhanced by air mass stagnation preceding the passage of cold fronts. These results provide strong evidence for the contribution of non-agricultural sources to NH3 in urban regions and suggest that priority should be given to controlling these emissions for haze regulation. This study presents a carefully executed application of existing stable nitrogen isotope measurement and mass-balance techniques to a very important problem: understanding source contributions to atmospheric NH3 in Beijing. This question is crucial to informing environmental policy on reducing particulate matter concentrations, which are some of the highest in the world. However, the isotopic source attribution results presented here still involve a number of uncertain assumptions and they are limited by the incomplete set of chemical and isotopic measurements of gas NH3 and aerosol NH4+. Further field work and lab experiments are required to adequately characterize endmember isotopic signatures and the subsequent isotopic fractionation process under different air pollution and meteorological conditions.

Effects of Environmental Factors on the Synergy of Functional Bacteria in Completely Autotrophic Granular Sludge

To obtain experimental evidences for optimizing a completely autotrophic nitrogen removal process based on granules, the effects of dissolved oxygen (DO) concentration, temperature (t), initial ammonium (NH4+-N) concentration, and solution pH conditions on the synergy between the aerobic and anaerobic ammonium-oxidizing bacteria (AOB and AMX) were investigated using a single factor batch experiment, while the analysis of the microbial community structure within them was conducted using MiSeq high-throughput pyrosequencing. Results revealed that AOB (genus Nitrosomonas) and AMX (genus Candidatus Kuenenia) dominated in the granules, representing relative abundances of 32.9% and 9.8%, respectively. For the granules, the highest specific nitrogen removal rate of q(TN)=(17.7±1.0) mg·(g·h)-1 was obtained at a DO concentration of 2 mg·L-1, while the initial NH4+-N concentration was set at 100 mg·L-1. And a lower DO level resulted in partial nitritation became the rate-limiting step of process, otherwise, it would be the ANAMMOX reaction instead. According to the free energy of the reactions, the activity of AMX was more sensitive to low temperature than that of AOB. When the reaction temperature was lower than 30℃, nitrite accumulation could be observed in bulk liquid, with the significant decrease of q(TN) for the granules. Under the same oxygen supply conditions, an initial NH4+-N concentration lower than 100 mg·L-1 could inhibit the activity of AMX partly. However, with an initial NH4+-N concentration over 150 mg·L-1, either oxygen-limiting or high free ammonia concentration could lead to the dramatic decrease of q(TN). In addition, the effective synergy of the two types of ammonium oxidizers in granules was always achieved at solution pH in the range of 7.0-8.5.