Automated determination of ammonium in natural waters with reverse flow injection analysis based on the indophenol blue method with o -phenylphenol

A slow-release fertilizer containing cyhalofop-butyl reduces N2O emissions by slowly releasing nitrogen and down-regulating the relative abundance of nirK

To simplify the process of the application of fertilizers and herbicides for farmers, a slow-release fertilizer containing cyhalofop-butyl (SFC) was developed to prolong the combined effect of the herbicide-fertilizer and achieve a synergistic effect on weeding and reducing N2O emissions. A greenhouse pot experiment was conducted using five treatments: CK (no fertilizer), CF (compound fertilizers), FC (fertilizers combined with cyhalofop-butyl), FF (film-coated compound fertilizers), and SFC (a slow-release fertilizer containing cyhalofop-butyl). The findings indicated that SFC exhibited the lowest N2O emissions, the highest paddy yield, and the highest nitrogen utilization rate among all the treatments. When compared to CF, the nitrogen release was notably delayed, leading to a significant reduction in cumulative N2O emissions under FF and SFC. When compared to CF, N2O emissions under FC were significantly decreased, suggesting that cyhalofop-butyl exerted a reduction role in N2O emissions. The SFC-treated nirK abundance was significantly lower than FF and FC, suggesting that the cyhalofop-butyl of SFC interacted with film of SFC inhibited the denitrification process in the paddy soil. Thus, the SFC reduced N2O emissions by slowing nitrogen release and down-regulating the relative abundance of nirK.

Real-time underway measurement of ammonium in coastal and estuarine waters using an automated flow analyzer with hollow fiber membrane contactor

Ammonium (NH₄⁺) is an important parameter for aquatic ecosystems. To date, continuous and underway acquisition of NH₄⁺ in coastal and estuarine waters has been challenged by the strongly varying salinity and complex matrices in these waters. To address these issues, a hollow fiber membrane contactor (HFMC) was constructed and incorporated in flow injection analysis (FIA) to achieve online separation/preconcentration of NH₄⁺ in water. In the FIA-HFMC system, NH₄⁺ in the water sample was converted into NH₃ under alkaline conditions in the donor channel. The generated NH₃ diffused across the membrane and was absorbed in an acid solution in the acceptor channel. The resultant NH₄⁺ in the acceptor was then quantified based on a modified indophenol blue (IPB) method. Parameters affecting the performance of the FIA-HFMC-IPB system were evaluated and optimized. Under the optimized conditions, the proposed system exhibited a limit of detection of 0.11 μmol L^-1, with relative standard deviations of 1.0-1.9 % (n = 7), and a good linear response (R² = 0.9989) for the calibration in the field with NH₄⁺ standards in the range of 0.40-80 μmol L^-1. The proposed system was applied to a shipboard underway measurement of NH₄⁺ in a two-day cruise in the Jiulong River Estuary-Xiamen Bay, China. A good agreement was observed between measurements from the proposed system and those from manual sampling and laboratory analysis. Both laboratory and field results demonstrated that the system was free of salinity effect and interference from organic nitrogen compounds. The system also showed excellent stability and reliability during a 16-day observation. This work suggests that the proposed FIA-HFMC-IPB system is applicable for the underway measurement of NH₄⁺ in water, especially for estuarine and coastal waters with varying salinity and complex matrices.

Nutrient recovery and valorisation from pig slurry liquid fraction with membrane technologies

Livestock slurry has been reported to be a potential secondary raw material as it contains macronutrients ‑nitrogen, phosphorus and potassium-, which could be valorised as high-quality fertilizers if proper separation and concentration of valuable compounds is performed. In this work, pig slurry liquid fraction was assessed for nutrient recovery and valorisation as fertilizer. Some indicators were used to evaluate the performance of proposed train of technologies within the framework of circular economy. As ammonium and potassium species are highly soluble at the whole pH range, a study based on phosphate speciation at pH from 4 to 8 was assessed to improve the macronutrients recovery from the slurry, resulting in two different treatment trains at acidic and alkaline conditions. The acidic treatment system based on centrifugation, microfiltration and forward osmosis was applied to obtain a nutrient-rich liquid organic fertilizer containing 1.3 % N, 1.3 % P₂O₅ and 1.5 % K₂O. The alkaline path of valorisation was composed by centrifugation and stripping by using membrane contactors to produce an organic solid fertilizer -7.7 % N, 8,0 % P₂O₅ and 2.3 % K₂O-, ammonium sulphate solution -1.4 % N- and irrigation water. In terms of circularity indicators, 45.8 % of the initial water content and <50 % of contained nutrients were recovered - 28.3 % N, 43.5 % P₂O₅ and 46.6 % K₂O - in the acidic treatment resulting in 68.68 g fertilizer per kg of treated slurry. 75.1 % of water was recovered as irrigation water and 80.6 % N, 99.9 % P₂O₅, 83.4 % K₂O was valorised in the alkaline treatment, as 219.60 g fertilizer per kg of treated slurry. Treatment paths at acidic and alkaline conditions yield promising results for nutrients recovery and valorisation as the obtained products (nutrient rich organic fertilizer, solid soil amendment and ammonium sulphate solution) fulfil the European Regulation for fertilizers to be potentially used in crop fields.

Ammonium determination by merging-zone flow injection analysis and a naphthalene-based fluorescent probe

This paper discusses the first-time study of a naphthalene-based fluorescent probe-naphthalene-2,3-dicarboxaldehyde (NDA), in combination with merging-zone flow injection analysis for the automated fluorescence determination of ammonium. The determination was contingent on detecting the fluorescent product of NDA-SO₃^2--NH₄⁺, which has maximum excitation and emission wavelengths of 508 nm and 564 nm, respectively. And the possible sensing mechanism of NDA-NH₄⁺ was proposed. The effects of the reaction parameters, including reagent concentrations, reaction flow rate, coil length, reaction temperature, and pH were optimized. Under optimal conditions, this method afforded a sampling rate of 8 h^-1, a limit of detection of 0.045 μmol L^-1, and RSD of 3.68% (n = 14) with 1.50 μmol L^-1 ammonium, and the calibration range was 0.045-6.00 μmol L^-1. Examination of the organic nitrogen interference confirmed that the method attracts minimal interference from organic nitrogen, and the stability of the NDA reagent facilitates its field application. Other exhibited advantages include low reagent consumption and high automation; the method has been utilized in the successful determination of ammonium in freshwater and rainwater. The development of NDA applications for ammonium determination also provides more options for fluorometric determination of ammonium.

Flow-Injection Methods in Water Analysis-Recent Developments

Widespread demand for the analysis and control of water quality and supply for human activity and ecosystem sustainability has necessitated the continuous improvement of water analysis methods in terms of their reliability, efficiency, and costs. To satisfy these requirements, flow-injection analysis using different detection methods has successfully been developed in recent decades. This review, based on about 100 original research papers, presents the achievements in this field over the past ten years. Various methodologies for establishing flow-injection measurements are reviewed, together with microfluidics and portable systems. The developed applications mostly concern not only the determination of inorganic analytes but also the speciation analysis of different elements, and the determination of several total indices of water quality. Examples of the determination of organic residues (e.g., pesticides, phenolic compounds, and surfactants) in natural surface waters, seawater, groundwater, and drinking water have also been identified. Usually, changes in the format of manual procedures for flow-injection determination results in the improvement of various operational parameters, such as the limits of detection, the sampling rate, or selectivity in different matrices.

Determination of ammonium in natural water using a quinoline-based o-dialdehyde fluorescent reagent with visible excitation wavelength

In this paper, a novel and stable fluorescent reagent, quinoline-2,3-dicarbaldehyde (QDA), is synthesized as a probe to detect ammonium in natural water. Ammonium reacts with QDA in the presence of SO₃^2- and Ca²⁺ to form a fluorescence product, which has maximum excitation and emission wavelengths at 429 nm and 518 nm. The concentration of reagents, the reaction temperature, the reaction time, and the pH in the final solution are investigated and optimized. The interferences of typical organic nitrogen and inorganic compounds are evaluated, and results prove that most volatile amines have little or negligible effect. Under the optimized conditions, this method provides a limit of detection of 0.065 μmol L^-1, a calibration range of 0.216-9 μmol L^-1, and reproducibility (with a relative standard deviation) of 1.9% for 1.5 μmol L^-1 ammonium. For water sample analysis, the proposed method provides comparable results to those of the conventional o-phthalaldehyde method but has longer reagent stability (42 days).

Cost-effective and sensitive anthocyanin-based paper sensors for rapid ammonia detection in aqueous solutions

In this work, we developed a cost-effective and environmentally friendly anthocyanin-based paper sensor with high sensitivity and optical visibility for the rapid detection of ammonia in aqueous solutions. The detection principle is based on a color change upon ammonia exposure to an anthocyanin-containing paper, which can be recorded simply via a smartphone. The paper sensors were fabricated by extracting anthocyanin from different sources (i.e., red cabbage, blueberry, and blackberry) and immersing pre-cut paper in anthocyanin extracts. Anthocyanin was extracted from different sources into water and aqueous ethanolic solution (80%) using solid-liquid extraction (SLE) and sonication assisted extraction (SAE) methods. The sensor sensitivity and optical visibility were improved by selecting a suitable combination of anthocyanin source, extraction technique, and solvent and controlling the ammonia release from the samples via alkalinization using a suitable base. Sensors fabricated with anthocyanin extracted from red cabbage (Red-C) into water using the SLE method and samples alkalinized with NaOH showed higher sensor sensitivity and better optical visibility. The Red-C anthocyanin sensors also exhibited a visible color change from dark to light blue for ammonia samples with concentrations as low as 2 mg NH₃-N/L. Moreover, the spike recovery results of the sensors (101.9-109.4%) were in good agreement with those of the standard spectrophotometry method (105.4-112.2%), which suggest that these biosensors are a promising analytical tool as a replacement for time-consuming and environmentally unfriendly standard spectrophotometry methods for the on-site screening of ammonia.

An environmentally-benign flow-batch system for headspace single-drop microextraction and on-drop conductometric detecting ammonium

This work presents a lab-made automatic flow-batch system for headspace single-drop microextraction and on-drop conductometric sensing ammonium. Sample and NaOH solution are simultaneously pumped into a reaction chamber (RC), where ammonium is converted to ammonia by raising pH. The converted ammonia then diffuses into the headspace of the RC, and reacts with a 100 mM boric acid drop. The conductivity of the drop is measured by an on-drop conductivity probe, which is made by two stainless-steel contacting electrodes. The result shows that the increasing rate of conductivity has a linear relationship to the ammonium concentration in sample (R² = 0.9945). This method has a linear range up to 400 μM, a limit of detection 2.8 μM, a relative standard deviation of 3.0% (200 μM, n = 10) and carryover coefficient 0.028. Measurements of river waters, lake waters and wastewaters have been demonstrated. The recoveries have achieved from 99.0 to 114%. This method avoids using of harmful or odorous reagents and follows the concept of green chemistry.

Combined SPRi Sensor for Simultaneous Detection of Nitrate and Ammonium in Wastewater

Water pollution is a serious problem in modern society. Agriculture, being responsible for the discharge of agrochemicals, organic matter, or drug residues, produces a huge amount of wastewater. Aquaponics has the potential to reduce both water consumption and the impact of water pollution on fish farming and plant production. In the aquatic environment, inorganic nitrogen is mostly present in the form of nitrate and ammonium ions. Nitrate, as a final product of ammonia mineralization, is the most common chemical contaminant in aquifers around the world. For continuous monitoring of nitrogen compounds in wastewater, we propose a sensor for the simultaneous detection of nitrate and ammonium. A surface plasmon resonance imaging method with enzyme-mediated detection was used. Active layers of nitrate reductase and glutamine synthetase were created on the gold surface of a biochip and tested for the sensing of nitrate and ammonium in water from an aquaponic system. The proposed sensor was applied in water samples with a concentration of NO3- and NH4+ in a range between 24-780 mg·L-1 and 0.26-120 mg·L-1, respectively, with minimal pretreatment of a sample by its dilution with a buffer prior to contact on a biochip surface.

Development of an Integrated Syringe-Pump-Based Environmental-Water Analyzer ( iSEA) and Application of It for Fully Automated Real-Time Determination of Ammonium in Fresh Water

The development of a multipurpose integrated syringe-pump-based environmental-water analyzer ( iSEA) and its application for spectrophotometric determination of ammonium is presented. The iSEA consists of a mini-syringe pump equipped with a selection valve and laboratory-programmed software written by LabVIEW. The chemistry is based on a modified indophenol method using o-phenylphenol. The effect of reagent concentrations and sample temperatures was evaluated. This fully automated analyzer had a detection limit of 0.12 μM with sample throughput of 12 h^-1. Relative standard deviations at different concentrations (0-20 μM) were 0.23-3.36% ( n = 3-11) and 1.0% ( n = 144, in 24 h of continuous measurement, ∼5 μM). Calibration curves were linear ( R² = 0.9998) over the range of 0-20 and 0-70 μM for the detection at 700 and 600 nm, respectively. The iSEA was applied in continuous real-time monitoring of ammonium variations in a river for 24 h and 14 days. A total of 1802 samples were measured, and only 0.4% was outlier data (≥3 sigma residuals). Measurements of reference materials and different aqueous samples ( n = 26) showed no significant difference between results obtained by reference and present methods. The system is compact (18 cm × 22 cm × 24 cm), portable (4.8 kg), and robust (high-resolution real-time monitoring in harsh environments) and consumes a small amount of chemicals (20-30 μL/run) and sample/standards (2.9 mL/run).