Initial Urea Concentration Research Articles

Simultaneous removal of SO2 and NOx from flue gas by wet scrubbing using a urea solution

ABSTRACTNitrogen oxides (NOx) and sulfur dioxide (SO2) are major air pollutants, so simultaneously removing them from gases emitted during fossil fuel combustion in stationary systems is important. Wet denitrification using urea is used for a wide range of systems. Additives have strong effects on wet denitrification using urea, and different mechanisms are involved and different effects found using different additives. In this study, the effects of different additives, initial urea concentrations, reaction temperatures, initial pH values, gas flow rates, and reaction times on the simultaneous desulfurization and denitrification efficiencies achieved using wet denitrification using urea were studied in single factor experiment. The optimum reaction conditions for desulfurization and denitrification were found. Desulfurization and denitrification efficiencies of 97.5% and 96.3%, respectively, were achieved at a KMnO4 concentration 5 mmol/L, a reaction temperature of 70°C, initial urea solution pH 8, a urea concentration of 9%, and a gas flow rate of 40 L/h. The concentrations of the desulfurization and denitrification reaction products in the solution were determined. NOx was mainly transformed into N2, and the and concentrations in the solution became very low. The reactions involved in SO2 and NOx removal using urea were analyzed from the thermodynamic viewpoint. Increasing the temperature was not conducive to the reactions but increased the rate constant, so an optimum temperature was determined. The simultaneous desulfurization and denitrification kinetics were calculated. The urea consumption and , , and generation reactions were all zero order. The generation rate was greater than the generation rate. The simultaneous desulfurization and denitrification process and mechanism were studied. The results provide reference data for performing flue gas desulfurization and denitrification in factories.

Urease activity in an autotrophic bacteria Thiobacillus thiooxidans

Urease activity was found in the fermented liquid of Thiobacillus thiooxidans. It was found that initial concentration of sulfur and urea, and initial pH influenced urease activity in Thiobacillus thiooxidans, and the maximum urease activity was noted after 96h of fermentation with 24g/L initial concentration of sulfur and 0.1g/L of urea, and nature pH 5.82. The experiment found that urease activity showed a steady change which follow along with the growth of Thiobacillus thiooxidans. It shows a possibility to determine the Thiobacillus thiooxidans attached on the sulfide surface.

Effects of Preparation Conditions and Environmental Conditions on Rice-straw-biochar Adsorption of Urea

To investigate the feasibility of using biochars to adsorb urea in aqueous solution, we extracted biochar which was generated at pyrolysis temperature of 400℃, 600℃ and 800℃ respectively from rice-straw combustion residues. In this study we evaluated the effect of adsorption time, the pH of environment, the contents of urea and biochar yield on the ability of adsorption for urea using a solution adsorption method. The results showed that all biochars could sorb the higher amounts of urea at pyrolysis temperature of 800℃, which was larger than 600℃ and 400℃ successively with prolonging adsorption time, increasing environmental pH, larger amounts of urea and greater the addition of biochars. However, biochars particle size of 1.91mm and 0.38mm had no significant effect. We conclude that rice-straw derived biochars can be used for adsorbing urea under the conditions where the pyrolysis temperature of 800℃, adsorption time of 3 hours, environmental pH of 7, biochar particle size of 2.0mm, initial urea concentration of 3mol/L and lesser usage of biochars.

Preparation of Oxidized and Grafted Chitosan Superabsorbents for Urea Delivery

Different hydrogels based on chitosan were prepared by two environmentally friendly approaches: (i) oxidation under mild conditions and (ii) grafting of itaconic acid. Both procedures guide to it success modification leading hydrogels with adequate crosslinked degree. The hydrogels were structurally and chemically characterized and their swelling behavior was evaluated in water, NaCl and buffer solutions at different pHs. In all the cases, the increase of ionic strength decreases the equilibrium swelling. It was also demonstrated a superior swelling percentage at acidic pH. This percentage of swelling is significantly higher in grafted films than in the oxidized chitosans. Besides, the ability as fertilizers and water controlled-release superabsorbent hydrogels was evaluated. Consequently, the absorption and delivery of urea fertilizer was investigated as a function of initial concentration of urea in the media and the pH. These materials can be used in the agriculture as controlled fertilizer delivery as well as water regulators. Hydrogels based-chitosan were prepared by non-environmentally aggressive approaches. Chitosan was modified by mild oxidation and grafting reaction with itaconic acid. The hydrogels present adequate crosslinked degree and worthy swelling behavior. Hydrogels were evaluated as superabsorbent for urea and water controlled- release.

Continuous urea–nitrogen recycling from human urine: A step towards creating a human excreta based bio–economy

The present study argues that human excreta are vital, renewable biological resources (nutrients) which must be considered an important subset of a bio–based economy. A human excreta based bio–economy can be defined as a set of circular and sustainable approaches that promote closed–loop flows of resources and nutrients from sanitation to agriculture. To this effect, from a technological perspective, this study presents a pathway for recovering, concentrating, and reusing fertilizer products from human urine. The development and implementation of urine diversion technologies have facilitated large–scale separation and storage of human urine independent of the faeces; however, processes that help harness the fertilization potential of source–separated urine in an effective, simple, yet efficient manner remain to be found. Hence, this study demonstrates a simple approach to selectively strip urea (a value–added product) from human urine in a continuously operated column packed with activated carbon prepared from agricultural wastes (coconut shells). Investigations were performed to determine the effect of carbon bed height, urine flow rate and concentration on efficiency of urea recovery. In order to model the column breakthrough and understand interactive influence of process parameters, experimental data was modelled against four well–known breakthrough equations. Optimal operating conditions were identified through an objective of simultaneous maximization of column capacity and urea removal efficiency of the activated carbon as well as minimization of sorption time. An initial urea concentration of 60%, urine flow of 6 L h−1 and carbon bed height of 30 cm resulted in 80% urea removal and an equilibrium uptake capacity of 94.03 mg g−1. For quantitative recovery of the adsorbed urea and reuse of the saturated column, regeneration experiments were performed using deionised water as the desorption media pumped in up flow mode at 3 L h−1. Considering the average annual nutrient composition of human urine, this approach could allow production of ∼4.5 kg urea per person per year. The reutilization of human wastes through ecologically–conscious sanitation practices could therefore blur the difference in the cognition of two human constructs, ‘resources’ and ‘wastes’.

Short communication: Urea hydrolysis in dairy cattle manure under different temperature, urea, and pH conditions

The objective of the study was to quantify the rate of urea hydrolysis in dairy cattle manure under different initial urea concentration, temperature, and pH conditions. In particular, by varying all 3 factors simultaneously, the interactions between them could also be determined. Fresh feces and artificial urine solutions were combined into a slurry to characterize the rate of urea hydrolysis under 2 temperatures (15°C and 35°C), 3 urea concentrations in urine solutions (500, 1,000, and 1,500 mg of urea-N/dL), and 3 pH levels (6, 7, and 8). Urea N concentration in slurry was analyzed at 0.0167, 1, 2, 4, 6, 8, 12, 16, 20, and 24 h after initial mixing. A nonlinear mixed effects model was used to determine the effects of urea concentration, pH, and temperature treatments on the exponential rate of urea hydrolysis and to predict the hydrolysis rate for each treatment combination. We detected a significant interaction between pH and initial urea level. Increasing urea concentration from 1,000 to 1,500 mg of urea-N/dL decreased the rate of urea hydrolysis across all pH levels. Across all pH and initial urea levels, the rate of urea hydrolysis increased with temperature, but the effect of pH was only observed for pH 6 versus pH 8 at the intermediate initial urea concentration. The fast rates of urea hydrolysis indicate that urea was almost completely hydrolyzed within a few hours of urine mixing with feces. The estimated urea hydrolysis rates from this study are likely maximum rates because of the thorough mixing before each sampling. Although considerable mixing of feces and urine occurs on the barn floor of commercial dairy operations from cattle walking through the manure, such mixing may be not as quick and thorough as in this study. Consequently, the urea hydrolysis rates from this study indicate the maximum loss of urea and should be accounted for in management aimed at mitigating ammonia emissions from dairy cattle manure under similar urea concentration, pH, and temperature conditions reported in this experiment.

Coal fly ash for the recovery of nitrogenous compounds from wastewater: Parametric considerations and system design

The use of coal fly ash for nutrient recovery in wastewater treatment offers a potential win–win scenario as it simultaneously utilizes and re-channels two wastes – coal fly ash and wastewater. This study investigated the adsorptive recovery of urea from synthetic urine using fly ash. Equilibrium experiments revealed that 1.5g ash loading, initial urea concentration of13.5gL−1, urine pH=6.0, sorption temperature=30°C and 150rpm shaker speed were the optimal process parameters and maximum adsorption capacity was 410mgg−1. Proof of concept to the use of synthetic urine was conducted by performing adsorption with real human urine which validated the experimental findings. Comparative analysis and non–linear optimization of nine isotherm models through comprehensive error analysis revealed that Flory–Huggins and Redlich–Peterson equations best described the adsorption. Process thermodynamics suggested that Van der Waal’s and electrostatic interactions occur between urea molecules and the surface of fly ash particles; besides, the sorption was found to be exothermic, spontaneous and physical in nature. Kinetic studies pointed toward a pseudo–second–order kinetic fit with contributions from intra–particle diffusion. Further, the rate of mass transfer was seen to be controlled and limited by film diffusion of urea which featured stronger than its pore diffusion. To design a multistage batch adsorber, a mathematical model unique to the sorption system was derived that minimized the total amount of fly ash required for 90% removal of urea from different volumes of influent synthetic urine solutions.

Simultaneous resource recovery and ammonia volatilization minimization in animal husbandry and agriculture

The study demonstrates that the minimization of ammonia volatilization and urea recovery could be coupled through the use of physical adsorption processes in continuous packed-bed columns. The potential of using microwave activated coconut shell based activated carbon toward the recovery of urea from cattle urine was investigated. The prepared carbon was immobilized onto etched glass beads to investigate the effect ofinitial concentration, flow rate and size of carbon support in a continuous, down-flow mode packed column. Further, to describe the sorption behavior, the experimental data were tested against different kinetic models. The analysis of the breakthrough curves allowed identification of the favorable operating parameters as: sorbate flow (8 L·h−1), initial urea concentration (60%) and glass bead support size (ϕ 1.5 cm). An equilibriumsorption of 802.8 mg·g−1 and up to 80% urea recovery was observed. Regeneration studies allowed for nearly 95% urea recovery with sorbent capacity decreasing by 5% over seven cycles of sorption/desorption.

Simultaneous resource recovery and ammonia volatilization minimization in animal husbandry and agriculture

Abstract The study demonstrates that the minimization of ammonia volatilization and urea recovery could be coupled through the use of physical adsorption processes in continuous packed-bed columns. The potential of using microwave activated coconut shell based activated carbon toward the recovery of urea from cattle urine was investigated. The prepared carbon was immobilized onto etched glass beads to investigate the effect of initial concentration, flow rate and size of carbon support in a continuous, down-flow mode packed column. Further, to describe the sorption behavior, the experimental data were tested against different kinetic models. The analysis of the breakthrough curves allowed identification of the favorable operating parameters as: sorbate flow (8 L⋅h −1 ), initial urea concentration (60%) and glass bead support size (ϕ 1.5 cm). An equilibrium sorption of 802.8 mg⋅g −1 and up to 80% urea recovery was observed. Regeneration studies allowed for nearly 95% urea recovery with sorbent capacity decreasing by 5% over seven cycles of sorption/desorption.

Adsorptive Resource Recovery from Human Urine: System Design, Parametric Considerations and Response Surface Optimization

Despite its high concentration, potential availability and hence, potential reusability of nutrients, human urine continues to be flushed away in our toilets. The poor management of nutrients in our built environment in lieu of the representative failures in our systems to safely handle, treat and assimilate these ‘waste’ resources has resulted in considerable environmental externalities. Adsorption systems that utilize agro–waste sourced carbon as an adsorption media have shown promise in recovering plant–required nutrients from urine. This study details the applicability of two continuously operated columns for stripping urea from urine for subsequent use as fertilizers. The first column was packed with prepared carbon at various bed heights (10–50cm) and the second column had carbon immobilized over etched glass beads of various support sizes (1.5–2.5cm). By using a Box–Behnken design and Response Surface Methodology (RSM), the system was optimized with the objective of maximizing column capacities. For the packed bed, maximum sorption of 0.116g.g–1 occurs at inlet flow rate of 6 L.h–1, concentration of 100% and carbon bed depth of 30cm; in the immobilized bed, the optimal parameters were identified as flow rate of 10 L.h–1, 100% initial urea concentration and support size of 1.5cm to yield capacity of 0.328g.g–1. Immobilization as a pre–treatment in column design was significantly advantageous in recovering higher amount of urea at lesser activated carbon input relative to the packed bed. RSM was found to be an effective tool for selecting the process parametric inputs, in describing their effects on the operation of the column and in maximizing the urea recovery.

Sensitivity analysis of mechanistic models for estimating ammonia emission from dairy cow urine puddles

Ammonia (NH3) emission can cause acidification and eutrophication of the environment, is an indirect source of nitrous oxide, and is a precursor of fine dust. The current mechanistic NH3 emission base model for explaining and predicting NH3 emissions from dairy cow houses with cubicles, a floor and slurry pit is based on measured data from a limited number of studies. It requires input values for numerous variables, but the empirical equations for the model parameters in the literature vary. Furthermore, many of the input variables cannot be assessed accurately, and their actual influence on the prediction is unknown. We aimed to improve NH3 emission modelling, by assessing the contribution to the variation in NH3 emission of each input variable and each model parameter related to a single urine puddle. We did so for 27 candidate models, created by each possible combination of three equations per model parameter: the acid dissociation constant, Henry's law constant, and the mass transfer coefficient. After analysing each candidate model with a Global Sensitivity Analysis we found that at least 71% of the model variation in NH3 emission for each candidate model was explained by five puddle related input variables: pH, depth, area, initial urea concentration and temperature. NH3 emission was not sensitive to the other four variables: air temperature, air velocity, maximum rate of urea conversion and the Michaelis–Menten constant for urea conversion. Based on these results we recommend simplifying the model structurally and reducing the number of input variables.

Evaluation of NO<sub>X</sub> Removal from Simulated Flue Gas by "Absorption-Oxidation-Reduction" Method

This paper presented a new method of absorption-oxidation-reduction which used ferrous sulfate solution as absorbent, oxygen as oxidizer and urea as reducer to remove NOX from flue gas based on the properties of Fe2+, NO, [Fe (NO)]2+ and urea. These properties included that Fe2+ and NO could produce [Fe (NO)]2+, furthermore [Fe (NO)]2+ was easy to be oxidized by O2, as well as urea can reduce HNO2 and HNO3 in the absorption liquid. This research was to discuss its absorption and removal mechanism with the influence of the initial urea concentration, pH value, initial NOX concentration and gas flow rate on the NOX removal efficiency. The results showed that the removal efficiency of NOX would increase when the initial concentration of urea and NOX increased, while the pH value and gas flow rate decreased.

Controlled Release of Urea Through Mesoporous Methylcellulose Films Derived From N, N Dimethyl Formamide

The controlled release of urea through mesoporous methylcellulose (MPMC) films with varying concentration of urea (10, 20, 40, and 50 wt%) was studied. It was found that the release of urea from methyl cellulose (MC) films take place through pores as well as through bulk of the MC matrix. The release of urea through MPMC film is independent of the initial concentration of urea. The mass of diffused urea is well fitted to the transport equations. The transport of urea is pseudo-Fickian. The optical study exhibits the compactness of the MC film at the high percentage of urea.

Template-Free Hydrothermal Synthesis of β-FeOOH Nanorods and Their Catalytic Activity in the Degradation of Methyl Orange by a Photo-Fenton-Like Process

The rod-shaped form of crystalline β-FeOOH (akaganeite) was prepared by the template-free hydrothermal method with urea as the homogeneous precipitant. X-ray diffraction, field-emission scanning electron microscope and Fourier transform infrared spectrum were used to characterize the resulting products. The degradation of methyl orange (MO) was studied using the prepared nanostructure materials in a photo-Fenton-like process. MO degradation was effectively achieved by hydroxyl radicals that were generated in the heterogeneous catalysis process. Specific surface area of the prepared β-FeOOH was an important factor affecting the efficiency of MO degradation, which depended on the synthesis conditions such as the reaction temperature, the initial concentration of urea and FeCl3.6H2O as well as the n(urea)/n(Fe3+) ratio. The photodegradation efficiencies slightly decreased with the increase of initial pH in the range of 4.5 - 9.5, which indicated the prepared β-FeOOH catalyst can well overcome the drawback of a narrow pH range of homogeneous Fenton reaction. β-FeOOH catalysts loading and H2O2 concentration also play important effect on the degradation efficiency of MO. The prepared β-FeOOH showed good ability of reuse for multiple trials.

Preparation and Kinetic Modeling of Cross-Linked Chitosan Microspheres Immobilized Zn(II) for Urea Adsorption

The preparation of Zn(II)-immobilized glutaraldehyde-crosslinked chitosan microspheres which was modified with epichlorohydrin, tetraethylenepentamine, and bromoacetic acid was presented in this work. The Zn(II)-immobilized value of the microspheres (Ac-TEPA-CS) is 43.6 mg g−1, which is higher than the blank microspheres. The adsorption of urea onto Zn-Ac-TEPA-CS was studied in a batch system. Langmuir and Freundlich adsorption models were applied to describe the experimental isotherm and isotherm constant, and the kinetic of adsorption process were estimated. These data fits well with Langmuir isotherm and also indicated that the adsorption process is exothermic and follow the pseudo-second-order kinetics. The adsorption capacity depends upon the pH, the temperature and the initial concentration of urea. It observed that Zn-Ac-TEPA-CS could be repeatedly used by elution and regeneration without significant loss of adsorption capacity.

Modeling urea biodegradation in activated sludge using combined respirometric–titrimetric measurements

Urea biodegradation kinetics determination has been performed in the literature using a two-step nitrification model that was calibrated using on-line respirometric measurements. However, the model neglected the initial hydrolysis step that converts urea to carbon dioxide and ammonia nitrogen, and assumed constant carbon dioxide transfer rate (CTR), though it is inherently a non-linear process which has an impact on the titrimetric modeling. Hence, in this paper, it is aimed to propose a complete two-step nitrification model for urea biodegradation paying attention to urea degradation pathway along with due consideration given for non-linear CTR process occurring in activated sludge system. Experiments were performed in a simple batch reactor equipped with respirometric and titrimetric set-up. Three different initial urea concentrations were added to the reactor for investigating the process kinetics. Proposed model was successfully calibrated with respirometric, titrimetric and combined respirometric–titrimetric measurements; and the estimated parameters were compared for model evaluation. Furthermore, the proposed model was validated with off-line ammonium, nitrite and nitrate measurements. The study revealed that urea was hydrolyzed at a faster rate in liquid phase. The maximum growth rates of the Nitrosomonas species and the Nitrobacter species were found to be 0.065–0.1 d–1 and 0.006–0.008 d–1 respectively.

Synthesis of zirconium tungstate–zirconia core–shell composite particles

In this work, ZrW 2O 8–ZrO 2 core–shell composite particles were synthesized. ZrW 2O 8 that was used in the core is a material with negative coefficient of thermal expansion, and it was synthesized from a high-pH precursor based on use of tungstic acid and zirconium acetate. Shell layer was composed of ZrO 2 nanocrystallites and precipitated from an aqueous solution by urea hydrolysis. While volume of the shell was effectively controlled by the initial zirconium ion concentration in the solutions, the rate of precipitation was a function of the ratio of initial concentrations of urea to zirconium ions. It is hypothesized that isolation of the ZrW 2O 8 within a layer of ZrO 2, will be a key element in solving problems associated with reactivity of ZrW 2O 8 towards other components in sintering of ceramic–ceramic composites with tuned or zero thermal expansion coefficient.

Nutrient limitation as a strategy for increasing starch accumulation in microalgae

Increasing microalgal starch content by nutrient limitation has been regarded as an affordable approach for the production of third generation bioethanol. This work evaluated starch accumulation in Chlorella vulgaris P12 under different initial concentrations of nitrogen (0–2.2 g urea L −1) and iron (0–0.08 g FeNa-EDTA L −1) sources, using a central composite design (CCD) for two factors. The obtained model: Starch content (%) = 8.220 − 16.133 X 1 + 13.850 X 1 2 , relating starch accumulation in microalgae with the coded level for initial urea concentration in the growth medium ( X 1) presented a good concordance between the predicted and experimental values ( R 2 = 0.94). Since accumulation of starch occurred at nitrogen depletion conditions under which the cell growth was much slower than that observed during nitrogen supplemented cultivations, a two-stage cultivation process for high starch accumulation (>40%) and cell growth of C. vulgaris was proposed: a first cultivation stage using nitrogen- and iron-supplemented medium (initial urea and FeNa-EDTA concentrations of 1.1 and 0.08 g L −1, respectively), followed by a second cultivation stage in a nitrogen- and iron-free medium. The high starch content obtained suggests C. vulgaris P12 as a very promising feedstock for bioethanol production.

A Novel Route to Prepare ZnO-SnO<sub>2</sub> Nanocomposite with High Photocatalytic Activity

A nanometer coupled oxide ZnO-SnO2 was prepared by the fractional homogeneous co-precipitation route using urea as the latent precipitant under boiling reflux condition. The samples prepared from different initial concentrations of urea or at different calcination temperatures were characterized by X-ray diffration (XRD) or transmission electron microscopy (TEM). It was found that the coupled oxides ZnO-SnO2 mainly consist of nanosized ZnO and SnO2, the calcination temperature had obvious effect on the phase composition and the crystal size of the samples obtained, and the precipitant concentration also had obvious effect on the oxide particles size and the production rate of ZnO. Moreover, their photocatalytic activity was investigated for the liquids-phase photocatalytic degradation of methyl orange (MO) in water under UV light irradiation.The coupled oxides showed better photocatalytic activity for the degradation of MO than the pure ZnO or SnO2.

Optimum conditions for microbial carbonate precipitation

The type of bacteria, bacterial cell concentration, initial urea concentration, reaction temperature, the initial Ca 2+ concentration, ionic strength, and the pH of the media are some factors that control the activity of the urease enzyme, and may have a significant impact on microbial carbonate precipitation (MCP). Factorial experiments were designed based on these factors to determine the optimum conditions that take into consideration economic advantage while at the same time giving quality results. Sporosarcina pasteurii strain ATCC 11859 was used at constant temperature (25 °C) and ionic strength with varying amounts of urea, Ca 2+, and bacterial cell concentration. The results indicate that the rate of ureolysis ( k urea) increases with bacterial cell concentration, and the bacterial cell concentration had a greater influence on k urea than initial urea concentration. At 25 mM Ca 2+ concentration, increasing bacterial cell concentration from 10 6 to 10 8 cells mL −1 increased the CaCO 3 precipitated and CO 2 sequestrated by over 30%. However, when the Ca 2+ concentration was increased 10-fold to 250 mM Ca 2+, the amount of CaCO 3 precipitated and CO 2 sequestrated increased by over 100% irrespective of initial urea concentration. Consequently, the optimum conditions for MCP under our experimental conditions were 666 mM urea and 250 mM Ca 2+ at 2.3 × 10 8 cells mL −1 bacterial cell concentration. However, a greater CaCO 3 deposition is achievable with higher concentrations of urea, Ca 2+, and bacterial cells so long as the respective quantities are within their economic advantage. X-ray Diffraction, Scanning Electron Microscopy and Energy Dispersive X-ray analyzes confirmed that the precipitate formed was CaCO 3 and composed of predominantly calcite crystals with little vaterite crystals.