Initial Nitrate Concentration Research Articles

Characteristics of nutrients removal under partial denitrification initiated by different initial nitrate concentration.

The partial denitrification (PD) is a very promising process developed in the last decade, to study the comprehensive influence of influent carbon to nitrogen (C/N) on the activated sludge system under PD, six sequencing batch reactors (SBRs) were operated in parallel at C/N of 2.75, 3.30, 4.13, 5.50, 8.25 and 16.50, the nitrogen removal, phosphorus removal and sludge settleability of PD were investigated. The results showed that PD was observed treating synthetic wastewater in all the six SBRs, and the nitrite accumulation rate (NAR) was highest at C/N of 5.50 (NAR of 82.30%). However, due to the alternate inhibition of NO2--N and free nitrous acid (FNA) produced by a limited carbon source, both the sludge settleability and phosphorus removal deteriorated. The average SVI at C/N of 8.25 was 130% lower than C/N of 3.30, and the average amount of PO43--P released at C/N of 16.5 was 189% higher than C/N of 2.75. Kinetic analysis showed that the denitrification kinetics of PD and complete denitrification were similar, and the nitrite accumulation was caused by the difference between nitrate reduction rate and nitrite reduction rate. Variations of on-line parameters (pH and ORP) revealed that nitrite accumulation could be indicated by judging the nitrate turning point and nitrite turning point on pH and ORP curves, which provided guidance for the setup of PD.

Nitrate Adsorption capacity of Activated Gamalama Volcanic Ash

<p>The adsorption process of nitrate from an aqueous solution by using activated Gamalama volcanic ash was investigated. Gamalama volcanic ash (VA) was activated with HNO3 2M. The effect of adsorbent mass and initial nitrate concentration on nitrate adsorption were observed in this study. The adsorption process was conducted using a various mass of adsorbent (1 g, 2 g, 4 g, 6 g, and 8 g), various initial concentrations of nitrate (20 mg/L, 30 mg/L,40 mg/L, 50 mg/L, and 60 mg/L). The increasing of adsorbent mass decreased the adsorption capacity was observed. It was also found that the increase in initial concentration increased the adsorption capacity. The highest nitrate adsorption capacity showed by 1 gram adsorbent for 0.167 mg/g, and at nitrate initial concentration 80 mg/L, for 1.831 mg/g. Adsorption isotherm of nitrate on activated VA was determined and figured. These isotherms were modelled according to Freundlich and Langmuir adsorption isotherm.</p>

Synthesis and surface-functionalizing of ordered mesoporous carbon CMK-3 for removal of nitrate from aqueous solution as an effective adsorbent

In this study, the adsorption of nitrate onto ordered mesoporous carbon CMK-3 was investigated. First, CMK-3 was synthesized and then directly amino-functionalized by 3-aminopropyl trimethoxysilane (APTMS). The physicochemical properties of as-prepared adsorbent were characterized by XRD, EDS-SEM, FT-IR and N2 adsorption-desorption. Ultraviolet/visible spectroscopy was used to evaluate the adsorbent ability for nitrate reduction. In batch experiments, the influence of effective parameters such as contact time, adsorbent dosage, solution pH, initial concentration and temperature was investigated on the nitrate adsorption capacity. The obtained results indicated 100% removal efficiency for initial nitrate concentration of 50 mg l−1 and 78% for the concentration of 100 mg l−1, at low adsorbent dosage (3 g l−1) and very fast equilibrium attainment (5 min) without pH dependency (in the range of 2.0–8.0). The maximum nitrate adsorption capacity of Amino-CMK-3 was 48.78 mg g−1 in the concentration range of 50–250 mg g−1. Kinetic studies confirmed that the process followed a pseudo-second-order and that the Langmuir isotherm best fitted the equilibrium adsorption of nitrate. Nitrate desorption occurred after a reasonable time (3 h) and confirmed the adsorbent reusability without further treatment. The higher adsorption capacity of CMK-3 stemmed from its incredible mesoporous structure, including nano-channels that were completely functionalized by amino groups. Grafting aminopropyl groups potentially turned the CMK-3 to a promising adsorbent for nitrate removal.

Formation and evolution of brown carbon during aqueous-phase nitrate-mediated photooxidation of guaiacol and 5-nitroguaiacol

Light absorbing organic aerosols, which are commonly referred to as brown carbon (BrC), have important climate impacts. Phenolic compounds are a class of aromatic compounds that are known BrC precursors. Inorganic nitrate is a ubiquitous component of atmospheric aerosols, clouds, and fog. The photolysis of inorganic nitrate in atmospheric aqueous phases generates a variety of reactive oxygen species and reactive nitrogen species that can facilitate the photooxidation of organic compounds to form BrC. In this study, we investigated the formation and evolution of BrC from the aqueous-phase photooxidation of guaiacol and 5-nitroguaiacol initiated by inorganic nitrate photolysis. Guaiacol and 5-nitroguaiacol are two water-soluble phenolic compounds that are commonly found in fossil fuel and biomass burning emissions. Upon illumination in the presence of sodium nitrate, guaiacol and 5-nitroguaiacol reacted rapidly to form BrC. The reaction rates and quantities of BrC formed depended on the initial sodium nitrate concentration. The reaction rates of guaiacol were substantially faster than those of 5-nitroguaiacol. The electron-withdrawing nitro functional group on 5-nitroguaiacol's aromatic ring likely had a deactivating effect on the ring's reactivity, which contributed to 5-nitroguaiacol's lower reactivity compared to guaiacol. The major products produced during the initial stages of photooxidation were formed by the addition of nitro and/or nitroso groups to guaiacol and 5-nitroguaiacol. These products likely strongly absorbed near-UV and/or visible light, which led to an observed increase in light absorption (i.e., photo-enhancement) in the near-UV and visible range. Greater photo-enhancement was observed during the nitrate-mediated photooxidation of guaiacol. This indicated that the presence of nitro functional group(s) on the aromatic ring of phenolic compounds will impact the extent of photo-enhancement during BrC formation. Further photooxidation caused the initial products to fragment into smaller molecules that do not absorb near-UV and visible light. This resulted in an observed decrease in light absorption (i.e., photo-bleaching). These results highlight how aqueous-phase inorganic nitrate photolysis can drive the formation of BrC by facilitating the photooxidation of organic compounds.

Nitrate Removal from Groundwater by Electrocoagulation: Process Optimization through Response Surface Method

This study will investigate the removal of nitrate from groundwater by aluminum–aluminum (Al–Al) electrocoagulation (EC) using response surface methodology. Box–Behnken design (BBD) will be used to investigate the mutual interaction effect of important process parameters, such as current density (A), electrolysis time (C), and spacing (B) on nitrate removal efficiency (NRE %) from four groundwater samples with different initial nitrate concentrations. Experiments will be performed according to the BBD matrix and the data obtained fitted well to a quadratic model that demonstrated a good association between the predicted and experimental values with >R2 = 0.97 for all samples. In ANOVA studies, a p-value of <0.00001 was obtained, which confirmed the suitability of the regression models (p-value <0.05). In addition, a small value for the coefficient of variation (3.95%, 1.65%, 2.90%, and 3.84%) for all the samples indicated a higher degree of accuracy and the reliability of the experiments. ANOVA results and three-dimensional (3D) plots suggested that A and C were the main process parameters in this study and B had a negative effect on NRE %. Maximum NREs (%) of 92.5 (106 mg/L), 91.5 (133 mg/L), 83.5 (148 mg/L), and 71 (231 mg/L) were obtained at C = 1.6–2.78 h, A = 0.065 A/cm2, and B = 1 cm. In addition, for the feasibility of EC at an industrial scale, the management of the generated sludge was explained by its characterization using scanning electron transmission microscopy (SEM). This study concluded that the EC approach might be a promising technique for application to nitrate removal from groundwater.

Heterotrophic aerobic denitrification by novel bacterium Georgenia daeguensis ARB2 for treatment of nitrate contaminated waters

Denitrification is a potential strategy for nitrate removal from wastewater. This study reports the isolation of a novel bacterium Georgenia daeguensis ARB2 which has not been earlier reported for treatment of wastewater. ARB2 was isolated from pharmaceutical wastewater and optimized for growth and nitrate removal under conditions of 10 mM nitrate stress (140 mgL−1 $${{\text{NO}}_{3}^{ - }} - {\text{N}}$$ ). It can utilize nitrate as a sole source of nitrogen, exhibits highest growth and aerobic denitrification using glycogen + maltose as a carbon source at pH 7.0, carbon-to-nitrogen ratio of 34, temperature 30 °C, and shaking speed of 100 rpm. ARB2 removes 20% of the initial nitrate concentration of 10 mM in 56 h, and 40% of the initial nitrate concentration of 1 mM in 52 h. Further, the efficacy of strain ARB2 was tested on real contaminated waters and was found to successfully reduce nitrate levels in them. The findings suggest that Georgenia daeguensis ARB2 has a potential application for the alleviation of nitrate under aerobic conditions.

Synthesis of polyoxometalates (POM)/TiO2/Cu and removal of nitrate nitrogen in water by photocatalysis

Nitrate nitrogen is one of the vital issues needed to be addressed in the water purification process utilizing groundwater as a drinking water source. In this study, a sandwich-type polyoxometalate Na [α-SiW9O34] has been synthesized and SiW9/TiO2/Cu composite has been prepared by sol-gel method. Samples have been characterized by XRD, BET, FTIR, SEM, ED-Mapping, UV–Vis, XPS. The catalytic reduction of nitrate was performed in the presence of SiW9/TiO2/Cu composite as photocatalyst. The effects of catalyst loading, initial nitrate concentration, sandwich-type polyoxometalate loading, dissolved O2, and concentration of formic acid on nitrate removal have been investigated. The results showed that the prepared composite catalyst had better photocatalytic activity than the TiO2. 76.53% of nitrate removal with 82.09% of N2 selectivity was obtained under the following conditions: catalyst dosage 0.8 g/L, initial nitrate concentration of 30 mg/L, SiW9/Cu loading percentage of 10%, 30 mmol/L of formic acid, in presence of N2, and 6 h reaction time.

Aerobic denitrification using Bacillus pumilus, Arthrobacter sp., and Streptomyces lusitanus: Novel aerobic denitrifying bacteria

Aerobic denitrification capacity of some strains is not yet shown. Consequently, this study aimed to isolate new aerobic denitrifying strains, to identify them, and finally to test their aerobic denitrifying potential. Three strains were isolated and they have shown a high aerobic denitrification capacity. These strains were identified as Bacillus pumilus, Arthrobacter sp., and Streptomyces lusitanus. After 48 h, the nitrate removal achieved 99.7%, 98.98%, and 99.81% respectively for Bacillus pumilus, Arthrobacter sp., Streptomyces lusitanus, and their consortium. These removals were occurred using a bacterial concentration of 6%, an initial nitrate concentration of 70 mg/L, sodium acetate as carbon source, a temperature of 37 °C, and shaking at 150 rpm. In conclusion, these isolated strains can be considered as a future solution for removing nitrate from contaminant resources, or they can be added to various biological processes to eliminate nitrate from the wastewater.

Kinetic, isotherm, and mechanism investigations of the removal of nitrate and nitrite from water by the synthesized hydrotalcite Mg–Al

The objective of this work is to test the effectiveness of hydrotalcite as an adsorbent for the retention of nitrate and nitrite ions and to study the influence of various reaction parameters such as pH, adsorbent dose, contact time and initial ion concentration. Hydrotalcites (HTx) of different Mg/Al ratios (x was Mg/Al ratio; 2, 3, 4) were synthesized by the co-precipitation method at constant pH and characterized by X-ray diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR). The results obtained indicate that hydrotalcite (HT3) allows good retention of nitrate and nitrite ions with no pH adjustment. Adsorption increases with decreasing mass of the adsorbent and increases with increasing initial concentration of nitrate and nitrite ions. When the Mg/Al ratio changes from 2 to 4; the electrical charge density between layers weakens; the inter-layer spacing increases and the material shows greater adsorption capacity. The equilibrium isotherm showed that the Langmuir model provided a better fit to the experimental data than the Freundlich model for nitrates and nitrites. The adsorption capacity of HT3 for nitrates and nitrites was found to be 6.92 mg/g and 9.26 mg/g, respectively. The XRD analysis after adsorption showed that materials that had undergone nitrate and nitrite ions adsorption, maintain the hydrotalcite structure.

Adsorption capacity of nitrate from artificial fertilizers and soil on pyrophyllite

The study at hand presents for the first time the use of pyrophyllite as adsorbent for nitrate removal from soil and artificial fertilizers. A series of column and batch adsorption experiments were conducted to examine the effects of the adsorbent’s various parameters, the contact time, pH of the solution, the initial concentration of nitrate, concentration and adsorbent granulometry. Pyrophyllite fractions of 0.25, 0.50 and 1.00 mm had very similar pH values of aqueous suspensions and were in the weakly basic range. Nitrate adsorption capacity on pyrophyllite expressed by recovery factor values ranges from 93.14 to 99.77%. High recovery factor values from 90.44 to 97.45% for 1, 3, 5 and 8 mL min−1 flow rates were obtained using all pyrophyllite fractions. Nitrate removal was very effective by the contact time of 1 and 2 h, and the recovery factor values were in the range of 90.38–91.47% and 92.15–93.18% for a contact time of 1 h and 2 h, respectively. In addition, elution of nitrate from pyrophyllite was performed using the following solution with different pH values: 1.70 (synthetic gastric juice), 6.40 (rainwater), 7.70 (distilled water), 9.30 and 12.50 (NaOH solution). Elution was very low for all used solutions and was the highest at the pH 9.30. The results show that the use of pyrophyllite for removal of nitrate from artificial fertilizers and soil was an adequate approach because it has a high nitrate adsorption capacity, while the nitrate elution from the pyrophyllite was very low.

Investigation on the removal of nitrate from water using different types of biosorbents

Eutrophication due to excessive leaching of dissolved nitrogen is a principal cause of water quality degradation. Among different types of removal methods, adsorption is contemporarily deemed favourable due to its simplicity, efficiency and reusability. In this study, six biosorbent candidates, namely rambutan skin (RS), passion fruit skin (PFS), longan seeds (LS), chia seeds (CS), papaya seeds (PS), and luffa (L) were investigated for nitrate removal from water at pH 3.0, room temperature, initial nitrate concentration of 50 mg/L, biosorbent particle size of 425 μm, contact duration of 4 h, shaking speed of 120 rpm, and biosorbent dosage of 0.1 g. Shake flask method was carried out in the adsorption experiments to investigate the effect of heat treatment and acid treatment on the uptake of nitrate from water. The results showed that acid- and heat-treated passion fruit skin biosorbent (biochar, PFSBC) has the best biosorption performance for nitrate uptake of 5.179 mg/g. This biochar possessed high porosity, and abundant surface functional groups for nitrate adsorption.

Response surface methodology for the removal of nitrate ions by adsorption onto copper oxide nanoparticles

Nitrate ions (NO3−) enter water sources through sewage and can cause (in high concentrations) methemoglobinemia, cancer of the lymphatic and blood systems. Therefore, the level of NO3− in water must be controlled and effectively reduced. In the present work, copper oxide nanoparticles (CuONPs) were synthesized by chemical deposition method and their physicochemical properties have been determined by SEM, FTIR, XRD techniques. CuONPs have been used as adsorbents to remove nitrate ions from synthetic effluents. The optimization of nitrate ions removal was performed using response surface modeling (RSM) with parameters (input): initial nitrate concentration (20, 45, 70 mg/L), CuONPs concentration (0.03, 0.06, 0.08 g/L), pH (3, 7, 11) and reaction time (40, 80, 120 min). The optimum conditions found were 70 mg/L as nanoparticles dose, 0.08 g/L as NO3− concentration, pH=3, and 120 min contact time. The analysis of variance for this model confirmed that the model was fitted successfully (R2=0.9987, R2adj=0.9974). The adsorption fitted to Langmuir isotherm (R2L=0.9822) and second-order kinetics (R2s2=0.9999).

Formation of nitrite and ammonium during the irradiation of nitrate-containing water by VUV/UV

Vacuum ultraviolet/ultraviolet (VUV/UV) has been regarded as an efficient chemical-free advanced oxidation process for degradation of micropollutants, but hazardous byproducts, e.g. nitrite, can be formed during the irradiation of nitrate-containing water by VUV/UV. This study investigated the kinetics of nitrite and ammonium formation by VUV/UV irradiation of nitrate. The results indicate that the formation of nitrite and ammonium followed pseudo zero-order reaction kinetics at an initial nitrate concentration of 10 mg L−1. Direct UV photolysis, VUV photolysis, and indirect VUV photolysis contributed to 24.6 %, 44.6 %, and 30.8 % of nitrite formation, and 0%, 65.0 % and 35.0 % of ammonium formation, respectively, in VUV/UV process. Initial nitrate concentration strongly affected not only the final concentrations of nitrite and ammonium but also the kinetics of their formation by VUV/UV. The presence of nitrate inhibited the degradation of alachlor, a typical herbicide, while alachlor had various influence on the formation of nitrite and ammonium depending on its initial concentration. Inorganic anions inhibited nitrate reduction by competing for VUV, while dissolved oxygen inhibited nitrate reduction by scavenging H and eaq−. The surface water had higher rate constants for the formation of nitrite and ammonium than those of the ground water because the former had lower content of inorganic ions but higher content of natural organic matter. When applying the VUV/UV process for water treatment, the formation of nitrite and ammonium should be taken seriously, especially at the presence of nitrate with high concentration.

Synthesis and characterization of Ce(III) decorated Duolite resin and its removal performance of toxic anions from aqueous solutions

Nitrate and phosphate are major threats for water/ wastewater which grounds eutrophication's and methemoglobinemia diseases, respectively and also severely hazards the safety of aquatic beings and public health's. To deal with the purging of aqueous nitrate and phosphate contamination, a low-cost Ce(III) decorated Duolite A 368 Plus resins (Ce-DA) were used. The influence of various adsorption factors was studied, such as adsorbent dosage, shaking time, pH, initial concentrations of nitrate and phosphate ions, competitive co-ions, isotherms and kinetic studies at different experimental temperatures etc. Ce-DA resin formed complexation with target nitrate and phosphate ions by adsorption via ion exchange and electrostatic attractions. Results from nitrate and phosphate adsorption showed that Ce-DA was greatly pH adjustable with an optimum pH of 3 to 7. The kinetic study revealed the pseudo-second-order and the Langmuir isotherm assessed a maximum adsorption efficiency of 138.67 and 156.26 mg/g for nitrate and phosphate ions respectively, which was higher than unloaded DA resin. The adsorption-desorption operations, demonstrating a great recovering performance of the adsorbent upto five successive cycles. This work highlights the cost-effective method to prepare promising adsorbent for efficient removal of toxic ions nitrate and phosphate from water. • Ce(III) decorated Duolite resins were fabricated and applied for the removal of toxic ions from water. • Electrostatic interaction, ion exchange and complexation are main mechanisms. • Ce-DA resin obeyed for pseudo-second-order kinetic and Freundlich isotherms. • Field studies were opted to analyze the performance of the Ce-DA resin.

Effects of Initial Nitrate Concentrations and Photocatalyst Dosages on Ammonium Ion in Synthetic Wastewater Treated by Photocatalytic Reduction

Ammonium ( NH 4 + ) is an undesirable by-product of photocatalytic nitrate ( NO 3 − ) reduction since it is harmful to aquatic life once it converts into ammonia (NH3). This research investigated the removal efficiency of NO 3 − and for the first time quantified the relationships of initial nitrate concentrations ([ NO 3 − ]0) and photocatalyst dosages on the remaining ammonium ( NH 4 + ) in synthetic wastewater using photocatalytic reduction process with either nanoparticle titanium dioxide (TiO2) or 1.0%Ag-TiO2 under Ultraviolet A (UVA). The experiments were systematically carried out under various combinations of [ NO 3 − ]0 (10, 25, 50, 80, and 100 mg-N/L) and photocatalyst dosages (0.1, 0.5, 1.0, and 2.0 g). The NO 3 − removal efficiency of both photocatalysts was 98.96-99.98%, and the catalytic selectivity products were nitrogen gas (N2), nitrite ( NO 2 − ), and NH 4 + . Of the two photocatalysts under comparable experimental conditions, 1.0%Ag-TiO2 provided better NO 3 − removal efficiency. For both photocatalysts, the remaining NH 4 + was predominantly determined by [ NO 3 − ]0; higher [ NO 3 − ]0 led to higher NH 4 + . Multiple linear regression analysis confirmed the dominant role of [ NO 3 − ]0 in the remaining NH 4 + . The photocatalyst dosage could play an essential role in limiting NH 4 + in the treated wastewater, with large variation in [ NO 3 − ]0 from different sources.

Rapid removal of nitrate from liquid dairy manure by cationic poly (vinyl alcohol-co-ethylene) nanofiber membrane

Elevated levels of nitrate in surface water is a leading concern, which impacts human and animal health, and controlling it requires improved and sustainable methods capable of removing nitrate anions from source waste water to reduce nitrate anions transport to environment. In liquid dairy manure, nitrogen content can vary from 200 to 600 ppm and the transport of manure nitrogen into ambient water through hydrologic processes has a potential to exceed the maximum contaminant level limit (10 ppm) of nitrate nitrogen for regulated public water systems. Dairy manure is considered as a reservoir of nitrate. This research investigates on the determination of optimal designing of nanofiber membrane to remove nitrate anions from liquid dairy manure. A cationic poly (vinyl alcohol-co-ethylene) nanofiber membrane (EVOH) NFM was grafted via UV with 2-(methacryloyloxy) ethyl trimethylammonium chloride (DMAC) monomers. The adsorption efficiency of nitrate by the membrane was determined on liquid manure of dairy lagoons located in Central Valley of California. Initial nitrate concentrations in dairy manure varied from 75 to 100 ppm. Results showed that nitrate in dairy water was removed by 70% in 40 min. Tortuous structure and chemical stability of membrane resulted in nitrate dynamic binding capacity of 40 mg g−1. Furthermore, it exhibits efficient reusability without significant changes in its performance using 0.5 M sodium hydroxide solution for nitrate desorption. Results showed that change in pH, and multi-anion conditions had limited effects on nitrate removal efficiency, and EVOH NFM can be a viable option to remove nitrate of liquid manure. This could be used for mitigating transport of excess nitrate from manure to environment. Overall, the results suggest that EVOH-g-DMAC NFM is efficient, low-cost (13 USD/m3) and recyclable material for sustainable removal of nitrate from dairy manure wastewater without requiring any ionic strength or pH adjustment.

A novel strategy for sequential reduction of nitrate into nitrogen by CO2 anion radical: Experimental study and DFT calculation

In order to expand the application of CO2 anion radical (CO2−), as a novel green reductant in the control of environmental pollution, CO2− radical was induced into the reduction of nitrate. The reduction efficiency, products and mechanism of nitrate or nitrite by CO2− radical were investigated based on the results of batch experiments and theoretical calculation using density functional theory (DFT) methods, respectively. It was found that: (1) the efficiency of nitrate reduction by CO2− radical from the HCOOH/UV system was far lower than that of nitrite under the same reaction conditions, (2) the rate-control step of nitrate reduction by CO2− radical was the transformation process of nitrate into nitrite with an activation energy of 23.9 kcal/mol, (3) the final products of nitrate reduction were mainly composed of nitrogen (N2). On this basis, a novel strategy of rapid reduction of nitrate into N2 using CO2− radical was proposed. Specifically, nitrate was firstly reduced into nitrite with the assistance of Zn/Ag bimetal, and then nitrite was further reduced into N2 by CO2− radical. In this way, the removal efficiency of nitrate was all achieved nearly 100% in the initial nitrate concentration ranging from 25 to 100 mg (N)/L, while the highest N2 selectivity could reach 97.5%. This work provided a promising approach for the reduction of nitrate into nitrogen with high efficiency and high N2 selectivity by CO2− radical.

Nitrate removal from aqueous solutions by cobalt ferrite nanoparticles synthesized by co-precipitation method: isotherm, kinetic and thermodynamic studies.

The purpose of this study was to examine the nitrate adsorption by cobalt ferrite (CFO) nanoparticles. The adsorbent was synthesized by co-precipitation method and its structure was characterized using scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, X-ray diffraction and vibrating-sample magnetometry. In batch adsorption studies, the effects of various parameters like pH (3-11), adsorbent dose (0.2-0.8 g/L), contact time (5-120 min), initial nitrate concentration (50-200 mg/L), and temperature (283-313 K) on the adsorption process were examined. The results of this study indicated that the maximum adsorption capacity was 107.8 mg/g (optimum condition pH = 3, adsorbent dosage: 0.2 g/L, nitrate concentration: 200 mg/L, contact time: 20 min and temperature: 313 K). The adsorption isotherm had a proper match with Langmuir (R2 = 0.99) and Freundlich (R2 = 0.99) models. The adsorption of nitrate by CFO followed pseudo-second-order kinetics. The results of the thermodynamics of the nitrate adsorption process by CFO showed that all the values of Gibbs free energy change, enthalpy change and entropy change were positive. Therefore, this process was endothermic and non-spontaneous.

Effect of low temperature on abiotic and biotic nitrate reduction by zero-valent Iron

The effect of low temperatures on abiotic and biotic nitrate (NO3−) reduction by zero-valent iron (ZVI) were examined at temperatures below 25 °C. The extent and rate of nitrate removal in batch ZVI reactors were determined in the presence and absence of microorganisms at 3.5, 10, 17, and 25 °C. Under anoxic conditions, NO3− reduction rates in both ZVI-only and ZVI-cell reactors declined as temperature decreased. In ZVI-only reactor, 62% and 17% of initial nitrate concentration were reduced in 6 days at 25 and 3.5 °C, respectively. The reduced nitrate was completely recovered as ammonium ions (NH4+) at both temperatures. The temperature-dependent abiotic reduction rates enabled us to calculate the activation energy (Ea) using the Arrhenius relationship, which was 50 kJ/mol. Nitrate in ZVI-cell reactors was completely removed within 1–2 days at 25 and 10 °C, and 67% of reduction was achieved at 3.5 °C. Only 18–25% of the reduced nitrate was recovered as NH4+ in the ZVI-cell reactors. Soluble iron concentrations (Fe2+ and Fe3+) in the ZVI reactors were also measured as the indicators of anaerobic corrosion. In the ZVI-cell reactors, soluble iron concentrations were 1.7 times higher than that in ZVI-only reactors at 25 °C, suggesting that the enhanced nitrate reduction in the ZVI-cell reactors may be partly due to increased redox activity (i.e., corrosion) on iron surfaces. Anaerobic corrosion of ZVI was also temperature-dependent as substantially lower concentrations of corrosion product were detected at lower incubation temperatures; however, microbially induced corrosion (MIC) of ZVI was much less impacted at lower temperatures than abiotic ZVI corrosion. This study demonstrated that ZVI-supported microbial denitrification is not only more sustainable at lower temperatures, but it becomes more dominant reaction for nitrate removal in microbial-ZVI systems at low temperatures.

Scale-Up Cultivation of Phaeodactylum tricornutum to Produce Biocrude by Hydrothermal Liquefaction

Phaeodactylum tricornutum is an interesting source of biomass to produce biocrude by hydrothermal liquefaction (HTL). Its biochemical composition, along with its biomass productivity, can be modulated according to this specific application by varying the photoperiod, the addition of CO2 or the variation of the initial nitrate concentration. The lab-scale culture allowed the production of a P. tricornutum biomass with high biomass and lipid productivities using a 18:6 h light:dark photoperiod and a specific CO2 injection. An initial concentration of nitrates (11.8 mM) in the culture was also essential for the growth of this species at the lab scale. The biomass generated in the scale-up photoreactor had acceptable biomass and lipid productivities, although the values were higher in the biomass cultivated at the lab scale because of the difficulty for the light to reach all cells, making the cells unable to develop and hindering their growth. The biocrudes from a 90-L cultivated microalga (B-90L) showed lower yields than the ones obtained from the biomass cultivated at the lab scale (B-1L) because of the lower lipid and high ash contents in this biomass. However, the culture scaling-up did not affect significantly the heteroatom concentrations in the biocrudes. A larger-scale culture is recommended to produce a biocrude to be used as biofuel after a post-hydrotreatment stage.