Initial Ammonia Concentration Research Articles

Impact of Diagnosis and Therapy on Cognitive Function in Urea Cycle Disorders.

Individuals with urea cycle disorders (UCDs) often present with intellectual and developmental disabilities. The major aim of this study was to evaluate the impact of diagnostic and therapeutic interventions on cognitive outcomes in UCDs. This prospective, observational, multicenter study includes data from 503 individuals with UCDs who had comprehensive neurocognitive testing with a cumulative follow-up of 702 patient-years. The mean cognitive standard deviation score (cSDS) was lower in symptomatic than in asymptomatic (p < 0.001, t test) individuals with UCDs. Intellectual disability (intellectual quotient < 70, cSDS < -2.0) was associated with the respective subtype of UCD and early disease onset, whereas height of the initial peak plasma ammonium concentration was inversely associated with neurocognitive outcomes in mitochondrial (proximal) rather than cytosolic (distal) UCDs. In ornithine transcarbamylase and argininosuccinate synthetase 1 deficiencies, we did not find evidence that monoscavenger therapy with sodium or glycerol phenylbutyrate was superior to sodium benzoate in providing cognitive protection. Early liver transplantation appears to be beneficial for UCDs. It is noteworthy that individuals with argininosuccinate synthetase 1 and argininosuccinate lyase deficiencies identified by newborn screening had better neurocognitive outcomes than those diagnosed after the manifestation of first symptoms. Cognitive function is related to interventional and non-interventional variables. Early detection by newborn screening and early liver transplantation appear to offer greater cognitive protection, but none of the currently used nitrogen scavengers was superior with regard to long-term neurocognitive outcome. Further confirmation could determine these variables as important clinical indicators of neuroprotection for individuals with UCDs. ANN NEUROL 2019.

A Physiological and Genomic Comparison of Nitrosomonas Cluster 6a and 7 Ammonia-Oxidizing Bacteria.

Ammonia-oxidizing bacteria (AOB) within the genus Nitrosomonas perform the first step in nitrification, ammonia oxidation, and are found in diverse aquatic and terrestrial environments. Nitrosomonas AOB were grouped into six defined clusters, which correlate with physiological characteristics that contribute to adaptations to a variety of abiotic environmental factors. A fundamental physiological trait differentiating Nitrosomonas AOB is the adaptation to either low (cluster 6a) or high (cluster 7) ammonium concentrations. Here, we present physiological growth studies and genome analysis of Nitrosomonas cluster 6a and 7 AOB. Cluster 6a AOB displayed maximum growth rates at ≤ 1mM ammonium, while cluster 7 AOB had maximum growth rates at ≥ 5mM ammonium. In addition, cluster 7 AOB were more tolerant of high initial ammonium and nitrite concentrations than cluster 6a AOB. Cluster 6a AOB were completely inhibited by an initial nitrite concentration of 5mM. Genomic comparisons were used to link genomic traits to observed physiological adaptations. Cluster 7 AOB encode a suite of genes related to nitrogen oxide detoxification and multiple terminal oxidases, which are absent in cluster 6a AOB. Cluster 6a AOB possess two distinct forms of ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO) and select species encode genes for hydrogen or urea utilization. Several, but not all, cluster 6a AOB can utilize urea as a source of ammonium. Hence, although Nitrosomonas cluster 6a and 7 AOB have the capacity to fulfill the same functional role in microbial communities, i.e., ammonia oxidation, differentiating species-specific and cluster-conserved adaptations is crucial in understanding how AOB community succession can affect overall ecosystem function.

Enhanced removal of ammonium from the aqueous solution using a high-gravity rotating packed bed loaded with clinoptilolite

A novel method for efficiently removing low levels of ammonium contamination from the aqueous solution using clinoptilolite in a high-gravity rotating packed bed (HGRPB) was developed. Our batch experiments have shown that irregular clinoptilolite gave better ammonium removal efficiencies due to higher specific surface area, and the adsorption data fitted better using pseudo-second-order adsorption kinetics than pseudo-first-order adsorption kinetics. HGRPB experiments have demonstrated that increasing rotating speeds will improve ammonium removal due to higher mass transfer of ammonium between the liquid and solid phases. The removal efficiency was 90% at the end of the fifth cycle (∼54 min) at a rotating speed of 1500 rpm using irregular clinoptilolite, with an initial ammonium concentration of 12.5 mg-N/L in distilled water and a flow rate of 180 mL/min. However, the removal efficiency was obviously lower in pond water than that in distilled water because of possible competitive adsorption of other cations in the pond water, suggesting modification of clinoptilolite to increase its selectivity for ammonium will be critical. This study has demonstrated the potential of using clinoptilolite in the HGRPB system to remove low levels of ammonium contamination in water and warrants the research need of HGRPB for biphasic liquid–solid adsorption processes.

Optimization of a wet scrubber with electrolyzed water spray—Part I: Ammonia removal

ABSTRACTElectrolyzed water (EW) is an effective disinfectant with a wide range of pH. EW in acid range was proved to be an ammonia absorbent which make it valuable for wet scrubbers used in animal feeding operations (AFOs). This study aimed to optimize the design and operating parameters of a wet scrubber with EW spray for ammonia removal, based on the size distribution of droplets, the property of EW and the reduction efficiency of ammonia. The optimized parameters included droplet size, nozzle flow rates, pH and available chlorine concentration (ACC) of EW, nozzle number at single stage, stage number, initial ammonia concentration and air speed in the duct. The ammonia removal efficiency increased with the decrease of droplet size and the increase of flow rate. The pH values of EW showed significant influence on ammonia removal efficiency (P ˂ 0.05), while ACC of the EW showed no significant influence (P > 0.05). For inlet ammonia concentration of 70 ppm with one and three spray stages, the wet scrubber with EW (pH = 1.35) spray was able to reduce 55.8 ± 4.3 % and 97.2 ± 3.0 % of ammonia, respectively, when the nozzles with 0.9 mm orifice diameter operated at a flow rate of 1.20 L min-1. Response surface analysis showed that orifice diameter, nozzle flow rate, and their combination were all significant factors impacting ammonia removal efficiency for both pH =1.35 and 5.50 at a 95% confidence level. Optimal ammonia removal efficiency was obtained at orifice diameter 0.9 mm and flow rate 1.20 L min-1 within the selected range. The results of this study demonstrated that wet scrubber with EW spray could be a very effective and feasible ammonia mitigation technology for animal feeding operation.Implications: It is difficult to effectively reduce ammonia emitted from the animal feeding operations (AFOs). Both the acidity and disinfection effects of electrolyzed water (EW) make it a potential absorbent used for spray in wet scrubber to reduce the ammonia and microorganisms. Based on some preliminary field test results, lab tests were conducted to optimize the design and operation parameters of a wet scrubber with EW spray to improve the ammonia removal efficiency. A better understanding of the application and influence factors of the wet scrubber with EW spray can contribute to effective mitigation of ammonia emission from animal houses and improve the atmosphere air quality.

Ammonium removal potential and its conversion pathways by free and immobilized Scenedesmus obliquus from wastewater

In this study, the immobilization with sodium alginate (SA) for cultivating microalgae in entrapped matrix gel beads was conducted for separating it from water. Batch experiments with a period of 5 days were carried out for free and immobilized Scenedesmus obliquus simultaneously under two trophic modes, to compare the removal performances of different initial ammonium (NH4+-N) concentrations. In both free and immobilized form, the positive C-dependent effect in mixotrophy and the negative N-dependent effect in heterotrophy were observed. And the performances of immobilized form were all superior to that of free form, which showed greater tolerance to high concentration, maximally representing 96.6 ± 0.1% removal in 50 mg/L of NH4+-N in mixotrophy. Assimilation of NH4+-N was the main removal pathway resulting the protein synthesis with the dominant component including glutamic acid (Glu), cystine (Cys), arginine (Arg) and proline (Pro). The results demonstrated a systematic understanding for NH4+-N removal in microalgae-based system.

Treating anaerobically digested piggery effluent (ADPE) using microalgae in thin layer reactor and raceway pond

The successful cultivation of microalgae on anaerobically treated wastewaters would not only allow for the bioremediation of the waste stream but also the cost effective production of algal biomass. In this study, the growth and bioremediation ability of a microalgal consortium of Chlorella sp. and Scenedesmus sp. for treating anaerobically digested piggery effluent (ADPE) was assessed and compared using a thin layer reactor (TLR) (0.5-cm depth, 350 L) and a conventional raceway pond (15-cm depth, 1500 L) with an initial ammonium concentration of 110 ± 10 mg N-NH4+ L−1. The ammonium removal rate of microalgae grown in the TLR (19.23 mg N-NH4+ L−1 d−1) was 1.4 times higher than that grown in the raceway pond. The ash-free biomass yield (0.84 g L−1) and the average volumetric biomass productivity (60 mg L−1 d−1) of the algal consortium in the TLR were 2.5 and 2 times higher than that achieved in the raceway pond, respectively. However, considering four times higher culture volume in the raceway pond, the average areal biomass productivity in the raceway pond (4.2 g m−2 s−1) was more than two times higher than the productivity achieved in the TLR (1.9 g m−2 s−1). As a result of this, the areal lipid productivity of the microalgae grown in the raceway pond was also 2.7 times higher than that grown in the TLR. Our results indicated that under the operational conditions evaluated in this study and based on areal biomass productivity, raceway pond performed better than the thin layer reactor for treating ADPE.

Characteristics of Ammonia Adsorption and Kinetics by Nitrifying Sludge Immobilized Pellets

In order to explore the characteristics and mechanisms of ammonia adsorption by both nitrifying sludge waterborne polyurethane (WPU)-immobilized pellets and nitrifying sludge polyvinyl alcohol-sodium alginate (PVA-SA)-immobilized pellets, the ammonia adsorption characteristics of immobilized pellets under different initial ammonia concentrations, and the influences of temperature, pH, and salinity on ammonia adsorption were studied respectively. Moreover, the adsorption isotherms, thermodynamics, and kinetics model analysis were employed to investigate the adsorption process. The adsorption capacity increased as the initial ammonia concentration increased. The optimal pH was 7.0, and salinity and temperature exhibited an inhibitory effect on adsorption. The adsorption capacity for nitrifying sludge-immobilized pellets was higher than the pellets with no sludge; the adsorption capacity of WPU pellets was higher than that of PVA-SA pellets. The thermodynamics demonstrated that the adsorption process was a spontaneous exothermic process and that low temperature favored ammonia adsorption. The process was fitted to the Langmuir and Freundlich isotherm. It exhibited multilevel adsorption at higher energy (Freundlich isotherm) and single adsorption at lower energy by electrostatic force (Langmuir isotherm). Additionally, the process was consistent with the pseudo-second-order kinetic model, as it explained that chemical adsorption was the primary mechanism of ammonia adsorption by immobilized pellets.

Insights into efficient removal and mechanism for ammonium from aqueous solution on tricalcium aluminate

Ammonium (NH4+) has been causing severe environmental pollution while the development of material with high capacity for ammonium removal remains a challenge. Herein, the cement-based material tricalcium aluminate (C3A) was employed to remove NH4+ from digested piggery wastewater. The conditions influencing the removal capacity were investigated, including contact time, initial ammonium concentration, temperature, dosage and initial co-existing phosphate concentration. The physicochemical structure of C3A and the resultant were characterized by X-ray diffraction (XRD), Fourier transformed infrared spectroscopy (FT-IR), scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS) and N2 adsorption–desorption isotherms. The maximum removal capacity of NH4+ by C3A was 155.4 mg·g−1 at 298 K. The characterization revealed that the resultant was CaAl-Cl-LDH. The hydroxyl groups and Al(OH)4− from the C3A hydration played an important role in ammonium removal. High alkalinity could enhance the removal capacity. This work presents an efficient solution for ammonium removal, thus providing new insight into the mechanism of cement-based materials for water pollutant removal.

Differential sensitivity of ammonia oxidising archaea and bacteria to matric and osmotic potential

Microbial oxidation of ammonia controls the rate of nitrification in the majority of soils. Both nitrification rate and the composition of communities of ammonia oxidising archaea (AOA) and ammonia oxidising bacteria (AOB) are influenced by drought, with evidence that AOA are more sensitive to periods of drought than AOB. This has been explained by greater sensitivity of AOA to ammonia concentration, which will increase in soil solution during drought, but an alternative, previously unexplored explanation, is greater sensitivity of AOA to matric and/or osmotic stress. A soil microcosm experiment was designed to distinguish these different explanations in which AOA and AOB abundances (amoA abundance) and nitrification rate were measured over 28 days in nine treatments corresponding to all combinations of three soil matric potentials and three initial ammonia concentrations. Comparison of amoA abundance dynamics suggested that AOA were more susceptible to reduced matric potential than AOB, irrespective of soil ammonia concentration. The greater sensitivity of soil AOA to osmotic stress was also tested in 10-day cultures of representative strains of AOA and AOB in liquid medium containing different concentrations of NaCl and sorbitol as osmo-inducer. AOA were significantly more sensitive to osmotic stress than AOB. These results provide evidence for greater sensitivity of AOA than AOB to both components of water stress, matric and osmotic potential, representing an additional niche differentiation between these two essential groups of ammonia oxidisers.

Effect of Magnetic Chitosan Hydrogel Beads with Immobilized Feammox Bacteria on the Removal of Ammonium from Wastewater

The bacterial reaction of ammonium oxidation coupling with iron reduction (Feammox) has been discovered recently. To improve the ammonium removal efficiency from wastewater of Feammox bacteria, magnetic chitosan hydrogel beads (MCHBs) were prepared via sodium hydroxide co-precipitating-sol-gel method, Feammox bacteria were immobilized to 1-5 mm MCHBs, and the ammonium removal efficiency by MCHBs-Feammox bacteria was compared to free-Feammox bacteria. In addition, the influences of initial ammonium concentration, pH and temperature were assessed. The results showed that the MCHBs were ferromagnetic and exhibited high crystallinity, with the magnetization of saturation of 29.46 emu·g-1. The average rates of ammonia oxidation and iron reduction increased by 42.96% and 20.75% after Feammox bacteria immobilization, respectively, and the most significant effect was observed on 1-2 mm MCHBs-Feammox bacteria (P<0.05). Furthermore, 1-2 mm MCHBs immobilized bacteria worked in less favorable matrix concentrations, temperatures, and pH. Particularly, it could maintain high ammonium removal efficiency with 60.00 mg·L-1 initial ammonium concentration, 25℃ temperature and 4.50 pH. In addition, nitrate and ferrous ions were detected in the system. The highest ammonium removal rate occurred on day 16, reaching 53.62%. These results indicated that MCHBs immobilization can improve the ammonium removal efficiency of Feammox.

Enhanced ammonium removal efficiency by ion exchange process of synthetic zeolite after Na+ and heat pretreatment.

In this study, the optimum ammonium removal by activation of synthetic zeolite in the aqueous phase was investigated by batch ion exchange adsorption assay, and its surface changes due to activation modification was elucidated accordingly. Among the adsorbents examined, modified synthetic zeolite A-4 was the most effective at ammonium removal. The best activation condition of zeolite A-4 was established by Na+ and 300 °C heat treatment at pH around 6 to 7. Besides, the removal efficiency was investigated under various reaction conditions of pH, adsorbent dosage, stirring speed, and initial ammonium concentration. Finally, the adsorptive capacity Qe of synthetic zeolite A-4 activated by Na+ and heat treatment was determined as 31.9 mg/g at 1,000 mg-N/L of ammonium, whereas that of natural zeolite was measured as 16.0 mg/g. The obtained adsorption data was fitted to both Langmuir and Freundlich isotherm models, and the Langmuir isotherm model provided a better correspondence than the Freundlich isotherm. Finally, regeneration cycles for synthetic zeolite A-4 was determined for further industrial applications and efficient ammonium removal.

The Adaptive Neuro-Fuzzy Inference System (ANFIS) Application for the Ammonium Removal from Aqueous Solution Predicting by Biochar

The adaptive neuro-fuzzy inference system (ANFIS) model was developed to predict the removal of ammonium () from wastewater. The ANFIS model was developed and validated with a data set from a pilot-scale of adsorption system treating aqueous solutions and wastewater from fish farms. The data sets consist of four parameters, which include pH, temperature, an initial concentration of ammonium and amount of adsorbent. The adsorbent was biochar obtained from rice straw. The ANFIS models performance was assessed through the root mean absolute error (RMSE) and was validated by testing data. The results of the study show that the adaptive neuro-fuzzy inference system (ANFIS) is able to predict the percentage of ammonium removal from adsorption column according to the input variables with acceptable accuracy, suggesting that the adaptive neuro-fuzzy inference system model is a valuable tool for estimating the quality of fish farms water. This model of ANFIS leads to cost reduction because prediction can be done without resorting to efforts that require cost and time.

2-Chlorophenol consumption by cometabolism in nitrifying SBR reactors

Cometabolic consumption of 2-chlorophenol (2-CP) by a nitrifying sludge was evaluated in two SBR reactors fed with 60 mg 2-CP-C/L and different initial ammonium concentrations (100, 200, 300, 400, and 500 mg NH4+-N/L). Irrespectively to the increase in ammonium concentration and throughout the operational cycles, the sludge achieved a complete nitrification in 14 days, accounting for ammonium consumption efficiencies close to 99% and nitrate production yields between 0.93 and 0.99. The sludge was able to completely consume 2-CP within 7 days. The increase in ammonium concentration provoked an increment in the specific rates of both ammonium (qNH4+-N) and 2-CP (q2-CP-C) consumption up to 5.2 and 3.1 times, respectively. The cometabolic effect of the increase in ammonium concentration on 2-CP consumption was supported by a direct and significant relationship between the qNH4+-N and q2-CP-C (r = 0.83). Moreover, batch assays conducted with ammonium, 2-CP, allylthiourea as specific inhibitor of the ammonium monooxygenase (AMO) enzyme, and the sludge inoculated into the reactors, resulted in a decrease of 34% in q2-CP-C, evidencing the participation of the AMO in the consumption of 2-CP. When the same assays were carried out with the sludge obtained from the SBR reactors after 13 operating cycles, a higher participation of the AMO in 2-CP consumption was noticed with a decrease of 53% in q2-CP-C. According to these results, the use of nitrifying sludge and high ammonium concentrations in SBR systems can be a suitable alternative for increasing the cometabolic consumption of recalcitrant compounds like 2-CP.

Coming Late for Dinner: Localized Digestate Depot Fertilization for Extensive Cultivation of Marginal Soil With Sida hermaphrodita.

Improving fertility of marginal soils for the sustainable production of biomass is a strategy for reducing land use conflicts between food and energy crops. Digestates can be used as fertilizer and for soil amelioration. In order to promote plant growth and reduce potential adverse effects on roots because of broadcast digestate fertilization, we propose to apply local digestate depots placed into the rhizosphere. We grew Sida hermaphrodita in large mesocosms outdoors for three growing seasons and in rhizotrons in the greenhouse for 3 months both filled with marginal substrate, including multiple sampling dates. We compared digestate broadcast application with digestate depot fertilization and a mineral fertilizer control. We show that depot fertilization promotes a deep reaching root system of S. hermaphrodita seedlings followed by the formation of a dense root cluster around the depot-fertilized zone, resulting in a fivefold increased biomass yield. Temporal adverse effects on root growth were linked to high initial concentrations of ammonium and nitrite in the rhizosphere in either fertilizer application, followed by a high biomass increase after its microbial conversion to nitrate. We conclude that digestate depot fertilization can contribute to an improved cultivation of perennial energy-crops on marginal soils.

Solubility of ammonium paratungstate in aqueous diammonium phosphate and ammonia solution and its implications for a scheelite leaching process

ABSTRACTScheelite could be digested with an aqueous diammonium phosphate and ammonia solution in an autoclave. However, unexpected ammonium paratungstate (APT) crystallisation and tungstophosphoric acid formation occasionally occurred. In order to provide a theoretical basis for the scheelite leaching process, the solubility of APT in solution was determined by the isothermal solution equilibrium method. The effects of initial ammonia and diammonium phosphate concentration as well as temperature on APT solubility and tungstophosphoric acid formation were investigated. Results showed that APT solubility increased with increasing ammonia concentration, diammonium phosphate concentration and temperature, while tungstophosphoric acid concentration in the leaching solution increased with decreasing ammonia concentration and increasing diammonium phosphate concentration. In order to verify the effects of these factors on the leaching of scheelite, scheelite digestion experiments using diammonium phosphate and ammonia solution were also carried out.

Recovering ammonia from municipal wastewater by flow-electrode capacitive deionization

This work investigated ammonia pre-concentration from low-strength municipal wastewater by flow-electrode capacitive deionization (FCDI) cell. A variety of operating conditions, including applied voltage, flow rate, graphite powder dosage, pH value and initial ammonia concentration, were investigated systematically. The results indicated that removal efficiency was greatly improved by increasing the working voltage (from 0.2 V to 1.2 V) and flow rate (from 5.00 to 7.75 mL/min), adding 1.5 wt% graphite powders and decreasing pH to 4. The maximum ammonia removal efficiency (87.00 ± 0.79%) was obtained with adsorption capacity of 1.43 ± 0.01 mg NH4Cl/g. Based on these optimum operation conditions, enrichment experiments were conducted with the desired concentration multiple times of 20 and an initial ammonia concentration of 20 mg N/L, which led to a final ammonia concentration of 322.06 mg N/L in the aqueous phase of flow electrodes. Additionally, valence, initial concentration, hydrate radius and diffusion efficiency also notably affected the alternative electro-performance of the FCDI cell because of co-existing cations. The study provides new insights into the emerging FCDI technology, which is expected to improve the methods of performing cost-effective ammonia removal and pre-concentration from low-strength municipal wastewater with moderate ion selectivity and wide ranging influent quality.

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.

Ammonium removal by a novel magnetically modified excess sludge

Disposal of nitrogen nutrient and excess sludge is a keen concern in wastewater treatment plants. This study describes a simple method of preparing an economical adsorbent, i.e., magnetic excess sludge (MES) by compounding the excess sludge with Fe3O4 nanoparticles. Ammonia–nitrogen removal from simulated wastewater was investigated by using the MES as an adsorbent. The MES had an adsorption efficiency of up to 90% for ammonium removal. Highly efficient separation of adsorbed ammonium on the MES could be magnetically separated from wastewater within 30 s. The operating conditions for ammonium adsorption were optimized at MES dose of 20 g/L, initial ammonium concentration of 45 mg/L and operating temperature of 298–308 K. The equilibrium data of ammonium adsorption on the MES showed a good agreement with the Langmuir isotherm, while the kinetic data were best fitted by the pseudo-second-order model. FTIR analysis indicated that various functional groups, such as hydroxyl and carboxyl groups, existed on the surface of the MES and contributed to the excellent capability for ammonium adsorption. These results suggest that the MES is a promising candidate for removing ammonium from wastewater and recycling excess sludge to ease its disposal at low cost.

Ammonium Transformation in 14 Lakes along a Trophic Gradient

Ammonia is a widespread pollutant in aquatic ecosystems originating directly and indirectly from human activities, which can strongly affect the structure and functioning of the aquatic foodweb. The biological oxidation of NH4+ to nitrite, and then nitrate is a key part of the complex nitrogen cycle and a fundamental process in aquatic environments, having a profound influence on ecosystem stability and functionality. Environmental studies have shown that our current knowledge of physical and chemical factors that control this process and the abundance and function of involved microorganisms are not entirely understood. In this paper, the efficiency and the transformation velocity of ammonium into oxidised compounds in 14 south-alpine lakes in northern Italy, with a similar origin, but different trophic levels, are compared with lab-scale experimentations (20 °C, dark, oxygen saturation) that are performed in artificial microcosms (4 L). The water samples were collected in different months to highlight the possible effect of seasonality on the development of the ammonium oxidation process. In four-liter microcosms, concentrations were increased by 1 mg/L NH4+ and the process of ammonium oxidation was constantly monitored. The time elapsed for the decrease of 25% and 95% of the initial ion ammonium concentration and the rate for that ammonium oxidation were evaluated. Principal Component Analysis and General Linear Model, performed on 56 observations and several chemical and physical parameters, highlighted the important roles of total phosphorus and nitrogen concentrations on the commencement of the oxidation process. Meanwhile, the natural concentration of ammonium influenced the rate of nitrification (µg NH4+/L day). Seasonality did not seem to significantly affect the ammonium transformation. The results highlight the different vulnerabilities of lakes with different trophic statuses.

The Performance of a Self-Flocculating Microalga Chlorococcum sp. GD in Wastewater with Different Ammonia Concentrations

The performance of a self-flocculating microalga Chlorococcum sp. GD on the flocculation, growth, and lipid accumulation in wastewater with different ammonia nitrogen concentrations was investigated. It was revealed that relative high ammonia nitrogen concentration (20–50 mg·L−1) was beneficial to the flocculation of Chlorococcum sp. GD, and the highest flocculating efficiency was up to 84.4%. It was also found that the highest flocculating efficiency occurred in the middle of the culture (4–5 days) regardless of initial ammonia concentration in wastewater. It was speculated that high flocculating efficiency was likely related to the production of extracellular proteins. 20 mg·L−1 of ammonia was found to be a preferred concentration for both biomass production and lipid accumulation. 92.8% COD, 98.8% ammonia, and 69.4% phosphorus were removed when Chlorococcum sp. GD was cultivated in wastewater with 20 mg·L−1 ammonia. The novelty and significance of the investigation was the integration of flocculation, biomass production, wastewater treatment, and lipid accumulation, simultaneously, which made Chlorococcum sp. GD a potential candidate for wastewater treatment and biodiesel production if harvested in wastewater with suitable ammonia nitrogen concentration.