*2.2.1 The challenge being addressed*

Water quality monitoring within catchments is desirable to maintain the structure and functioning of the land, water bodies and aquatic ecosystem that inhabit the catchment. Problems such as nutrient enrichment, sediment influx and dissolved

#### **Figure 2.**

*(a) (Left): The design tree for the MariaBox centrifugal processing unit (mCPU). In order of development, assay integration was prioritised to generate a proof of concept for testing assay integration. Next, microvalve integration strategies were investigated to automate assay protocol. This was then followed by the development and distribution of calibration and test discs for compatibility troubleshooting with the MariaBox platform. Finally, any compatibility issues were rectified, with two final deployable mCPU variants for the MariaBox platform produced; 3-day, 3-analyte disc (Biological analytes only) and 3-day, 8-analyte disc (all analytes). (b) (Right): Layer-by-layer disc design approach using CAD software for ease of compatibility and rapid modification. Poly(methyl methacrylate) (PMMA) Layers (white), ranging from 0.5–2 mm in thickness, are interlocked with pressure sensitive adhesive (PSA) layers (black), ranging from 80–150 μm in thickness. The thickness dimensions of both the PMMA and PSA make them ideal for μl liquid storage, and capillary action transportation, respectively.*

oxygen depletion are characteristics of stressed water bodies [24]. Excessive riverine nutrient concentrations can have harmful effects on the aquatic ecosystem structure and functioning of a catchment [25].

Phosphorus (P) is an essential nutrient for life. It is a growth-limiting nutrient, which makes it an important parameter to monitor in water [26]. Elevated levels of growth-limiting nutrients lead to algal blooms [27]. Phosphorus exists in many different chemical forms in water [28]. The simplest method for estimating bioavailable phosphorus in water is to analyse for soluble reactive phosphate (SRP). Orthophosphates are the most abundant forms of SRP at pH levels typically encountered in natural waters [29].

The demand for rapid detection methods that provide real-time or near real-time quantification of phosphate levels in freshwater is recognised by both government

## *Water Quality Monitoring Using Innovative Technologies DOI: http://dx.doi.org/10.5772/intechopen.105162*

and legislative bodies [30]. Different methods and technologies for monitoring and detecting phosphate levels in freshwater has been reviewed by Warwick *et al.,* these technologies include: biometric receptors (synthetic receptors and molecular imprinted polymers (MIPs)), electrochemical detection (potentiometric, amperometric, voltametric and conductometric analysis) and optical detection methodologies (colorimetric absorbance and luminescence/fluorescence) [31]. Handheld sensors can be developed for rapid, robust and reliable environmental monitoring. They can provide near real or real-time analysis of environmental water pollution parameters. There is an increase in the demand for cheap, reliable and robust sensing devices that can be used out in the field daily to collect real-time or near real-time data on water quality parameters.

### *2.2.2 The phosphate sensor*

Commonly used assays for optical based detection of phosphate include the Molybdenum blue [32], Vanadomolybdophosphoric acid [33] and Stannous Chloride [34]. These assays have some limitations related to their working complexity, chemical requirements (lifetime and stability) and monitoring duration.

A centrifugal microfluidic disc for this device was fabricated from poly(methyl methacrylate) (PMMA) and pressure sensitive adhesive (PSA) as in **Figure 2b**. Fluid movement for the assay is enabled by rotating the disc at ~8 Hz to generate a centrifugal force that acts from the centre of the disc, radially outwards. [24] The on-board microfluidic architecture, including an air ventilation system for performanceenhanced mixing of samples and reagents, also enables precise fluidic manipulation. In this device all chemical reagents needed in the assay are dried onto the centrifugal disc. This has transformed how the sensor can operate in that the only intervention needed is the addition of the water sample—thus making it an ideal device for taking into the field for rapid and sensitive analysis. A long optical path length of 75 mm was included on the disc design to maximize absorbance signal, achieving the desired sensitivity and limit of detection.

Such a portable sensor that can be transported around the catchment and detect the levels of specific nutrients in real-time will give more information about the quality of water in the overall catchment, not just one point (as in a spot sample or a single *in-situ* sensor), improving the temporal and spatial resolution of the data is obtained. These devices are easily transported around a catchment, therefore can increase the temporal and spatial data collection, filling in data gaps from the use of standard *insitu* monitoring and remote sensing. **Figure 3** illustrates the sensor unit, the measurement disc, optical detection unit and control panel. This system has been tested in the field and demonstrates the potential for low-cost potable nutrient sensors in water quality monitoring.

## **2.3 Bacterial** *E. coli* **sensing for bathing water**

### *2.3.1 The challenge being addressed*

The biological contamination of water is a major concern for public health reasons. The COVID-19 pandemic has meant that more people are turning to sea swimming as a form of exercise and for general wellbeing. The current approach to monitoring bathing water quality requires a sample to be collected and returned to the laboratory for analysis. The time to result is generally 24-72 hours after sample collection.

#### **Figure 3.**

*Image showing the use of the phosphate analyser onboard a boat—showing the keypad below the centrifugal platform and the read-out to the right.*

The determination of microbial water quality is a key requirement for water safety management The microbial contamination of water is associated mainly with faecal coliforms (FC) such as mainly *Escherichia coli* (*E. coli*) and Enterococcus. Although FC has traditionally been regarded as good indicators of faecal contamination of waters, recent reviews suggest *E. coli* be a better, more specific indicator. [35] Both *E. coli* and *Enterococcus* can be classified as indicator organisms for faecal contamination and can be used to assess the hygienic quality of water. The EU Water Framework Directive's (WFD) bathing water directive is based on the classification and quality of bathing waters as 'poor', 'sufficient', good' or 'excellent' based on the presence of intestinal Enterococcus and *E. coli*. The EU Bathing Water Directive (https://eur-lex. europa.eu/legal-content/EN/TXT/?uri=CELEX:31976L0160) provides specific limits, in Colony Forming Units (CFU), of *E. coli* and *Enterococcus*, as a guide for acceptable water quality for both inland and bathing waters, reported in **Figure 4** [37, 38].

#### *2.3.2 The sensing technology*

The high contribution of faecal coliforms, particularly *E. coli*, to the microbiological contamination of water is of growing concern. The standard method for *E. coli* detection is time consuming as it focuses on culture-based methods. A method for the rapid identification of *E. coli* is the optical detection of β-Glucuronidase (GUD) activity using a soluble fluorescent molecule as a marker. GUD is a fluorometrically detectable enzyme that cleaves the glycosidic bond of glucuronides in living organisms. GUD is used widely as a marker enzyme for *E. coli* and can be exploited by incorporating chromogenic and fluorogenic substrates into growing mediums. Another method is the direct extraction of GUD from *E. coli* cells and measuring its activity. These methods eliminate any


## **Figure 4.**

*Schematic illustrating the elements of a bathing water monitoring sensor (i) the legislation driving the development; (ii) bacterial target species; and (iii) sample collection to measurement with the Colisense fluorimeter [36].*

time-consuming culturing steps, providing a rapid monitoring system for the detection of *E. coli*. **Figure 4** shows the steps involved in the Colisense measurement system. This sensor developed in DCU provides for a sample collection to answer in 75 minutes [39]. The process involves sample collection, filtering to trap the bacteria, lysis to release the GUD enzyme and then addition of a fluorogenic substrate for detection using a mini fluorimeter as shown in **Figure 4**. The slope of the fluorescence response relates to the concentration of enzyme present and thus the level of bacterial contamination. This sensor methodology has been demonstrated during bathing seasons and it has been shown to correlate well with the standard culture-based method. The robust methodology can be further developed and commercialized to provide an early warning device for bathing water applications. This type of simple, robust technology has the potential to transform how information can be provided to sea swimmers and policy makers. The challenge in scaling this technology relates to the current legislation which relies on standard culture methods. A mind-set change is needed if low-cost sensor technology is to be adopted for routine environmental monitoring to protect human health.
