Water quality is one of the most critical indicators of environmental pollution and it affects all of us. Water contamination can be accidental or intentional and the consequences are drastic unless the appropriate measures are adopted on the spot. This review provides a critical assessment of the applicability of various technologies for real-time water quality monitoring, focusing on those that have been reportedly tested in real-life scenarios. Specifically, the performance of sensors based on molecularly imprinted polymers is evaluated in detail, also giving insights into their principle of operation, stability in real on-site applications and mass production options. Such characteristics as sensing range and limit of detection are given for the most promising systems, that were verified outside of laboratory conditions. Then, novel trends of using microwave spectroscopy and chemical materials integration for achieving a higher sensitivity to and selectivity of pollutants in water are described.

Thousands of pollutants are threatening our water supply, putting at risk human and environmental health. Between them, trace metals are of significant concern, due to their high toxicity at low concentrations. Abandoned mining areas are globally one of the major sources of toxic metals. Nowadays, no method can guarantee an immediate response for quantifying these pollutants. In this work, a novel technique based on microwave spectroscopy and planar sensors for in situ real-time monitoring of water quality is described. The sensors were developed to directly probe water samples, and in situ trial measurements were performed in freshwater in four polluted mining areas in the UK. Planar microwave sensors were able to detect the water pollution level with an immediate response specifically depicted at three resonant peaks in the GHz range. To the authors’ best knowledge, this is the first time that planar microwave sensors were tested in situ, demonstrating the ability to use this method for classifying more and less polluted water using a multiple-peak approach.

The feasibility of using novel electromagnetic wave sensors for real-time monitoring of metal pollution in water was assessed. Five solutions with different concentrations of lead (0, 1, 10, 50, 100 mg/L) were measured using several sensing methods: UV–Vis spectroscopy, low frequency capacitance and resistance measurements, and two sensing systems based on microwave technology. With this last approach, two sensing devices were used: a resonant cavity and a planar sensor with gold interdigitated electrode design printed on a PTFE substrate with a protective PCB lacquer coating. Results confirmed the ability of these systems to quantify the lead concentration as changes in spectrum signal at specific frequencies of the electromagnetic spectrum. Spectra were unique, with clearly observed shifts in the resonant frequencies of the sensors when placed in direct contact with different lead solutions, demonstrating the possibility of continuous monitoring with great sensitivity, selectivity, and high spatial and temporal resolution. Consequently, determination of trace and toxic metals using microwave spectroscopy is a promising alternative to traditional grab-sampling and laboratory based analyses. On-line and continuous monitoring of real-time metal concentrations offers the potential for a more effective emergency response and the platform for better scientific understanding and remediation of contaminated mine drainage. 文章评价一种利用电磁波传感器实时监测水中金属污染新型方法。使用几种传感方法,包括紫外可见吸收光谱、低频电容电阻测量和双传感微波装置,测量了五种已知铅浓度溶液(分别为0、1、10、50和100 mg/L)。最后一种方法采用双传感系统:一个谐振腔和一个平面传感器,金指状交叉电极印制于聚四氟乙烯(PTFE)底片,覆盖保护性印制电路板(PCB)膝涂层。结果证实:该系统可依据特定电磁波谱频段内的波谱信号变化来量化铅浓度。波谱是唯一的,当谐振传感器被直接放入不同铅浓度溶液时,可清楚观察到谐振频率迁移,表明该方法具有高敏感性、选择性和高时空分辨率的连续监测能力。因此,除传统取样和实验室测试金属浓度以外,微波频谱是另一种有潜力的测量微量元素或有毒元素浓度的方法。在线和连续实时监测金属浓度为高效应急响应、高水平科研平台搭建和矿井废水处理提供了更广的发展前景。 Die Anwendbarkeit von elektromagnetischen Sensoren zur Echtzeitüberwachung der Metallbelastung von Wässern wurde überprüft. Fünf Lösung mit verschiedenen Bleikonzentrationen (0, 1, 10, 50, 100 mg/L) wurden mit verschiedenen Methoden gemessen: UV-Vis-Spektroskopie, Niederfrequenzkapazitäts- und Widerstandsmessungen und zwei auf Mikrowellentechnologie basierende Sensorsysteme. Für letztere wurden zwei Messgeräte genutzt: ein Resonanzhohlraumsensor und ein Flächensensor mit Gold-Interdigitalstruktur, aufgedampft auf ein PTFE-Substrat mit einer PCB-Schutzschicht. Die Ergebnisse bestätigten die Eignung dieser Systeme, die Bleikonzentration als Änderungen des Spektrumsignals bei spezifischen Frequenzen quantitativ zu bestimmen. Im direkten Kontakt mit verschiedenen Bleilösungen zeigten die Sensoren eindeutige sowie deutliche Ausschläge der Resonanzfrequenzen. Damit bieten diese die Möglichkeit der kontinuierlichen Überwachung mit einer großen Empfindlichkeit, Selektivität und einer hohen räumlichen und zeitlichen Auflösung. Die Bestimmung von Spurenmetallen und toxischen Metallen mittels Mikrowellenspektroskopie stellt damit eine vielversprechende Alternative zur herkömmlichen Probenahme mit anschließender Laboranalyse dar. Die Online- und Echtzeitüberwachung von Metallkonzentrationen bietet die Möglichkeit eines effektiveren Notfallschutzes sowie die Plattform für ein besseres wissenschaftliches Verständnis und die Behandlung von belasteten Grubenwässern. Se analizó la factibilidad de utilizar sensores electromagnéticos para el monitoreo en tiempo real de la polución del agua por metales. Cinco soluciones con diferentes concentraciones de plomo (0, 1, 10, 50, 100 mg/L) se midieron usando varios métodos: espectroscopía UV-Vis, capacitancia de baja frecuencia y mediciones de resistencia y dos sensores basados en tecnología de microondas. Con esta última aproximación, se usaron dos instrumentos distintos: una cavidad resonante y un sensor plano con electrodo de oro interdigitado impreso en un sustrato PTFE con un revestimiento protector de laca PCB. Los resultados confirmaron la capacidad de estos sistemas para cuantificar la concentración de plomo como cambios en la señal espectral a frecuencias específicas del espectro electromagnético. Los espectros fueron únicos con picos claros en las frecuencias resonantes de los sensores cuando se ubican en contacto directo con las soluciones de diferentes concentración en plomo, demostrando la posibilidad de un continuo monitoreo con buena sensibilidad, selectividad y alta resolución espacial y temporal. Consecuentemente, la determinación de metales tóxicos usando espectroscopía de microondas es una alternativa promisoria a la toma de muestra y el análisis de laboratorio. El monitoreo continuo y en línea ofrece la potencialidad de una respuesta más efectiva en emergencias y la plataforma para una mejor comprensión y remediación de los drenajes de mina contaminados.