Portable sensor for pathogen monitoring in domestic wastewater treatment processes

The presented sensor uses a measurement approach relying on the intrinsic fluorescence of the E. coli based on their tryptophan content (CUMBERLAND et al. 2012). The light produced by a Light Emitting Diode (LED), centred at excitation peak value for tryptophan, illuminates the sample deposited in a quartz cuvette. The emitted fluorescent light is then measured, at an angle of 90º from the light source, by a photomultiplier (PMT), which produces a signal. The voltage of this signal is directly correlated with the colony-forming units (CFU) number of E. coli present in the water according with several calibrations performed in laboratory.

The schematic below (Figure 1) shows the measurement cavity, excitation illumination and the PMT detector. This configuration shows a flow-through cuvette water slowly runs through while being tested.

Figure 1. Schematic of a flow-through cuvette. Source: Own illustration (2023a)

The liquid phase design is based on spectroscopy absorption measurements in a glass cuvette. Ultraviolet/visible (UV/VIS) light from a Deuterium/Halogen lamp is guided through fibre to the glass cuvette, where absorption takes place, then collimated back into a fibre and guided back to a UV/VIS spectrometer. The value peak of the absorption is directly correlated with the VFA concentration (this has been demonstrated for laboratory synthetic samples).

The VFA sensor is put in a portable suitcase and measurements can be carried out by a trained operator, who collects the sample and deposits on the device.

Figure 2. Exploded view of the sensor’s CAD blueprint. Source: Own illustration (2023b)

The pathogen sensor is embedded in a portable suitcase with the purpose of obtaining a portable sensor which is able to provide a concentration of E. coli in different decentralized wastewater treatment system, water reclamation technologies or disinfection water units. Figure 3 shows the design of the suitcase with the sensor integrated.

Figure 3. Suitcase image with sensor integrated. Source: Own illustration (2023c)

Figure 4 below shows the assembled suitcase with the sensor ready for use.

Figure 4. Suitcase completed and prepared to measure. Source: Own illustration (2023d)

This pathogen sensor is employed to determine single-observation measurements in the field. Samples are drawn manually and prepared for the analysis by being filtered with a syringe filter of 0,45 µm (micrometre) to remover solid particles which could cause interferences.

For user-friendly operation, the sensor is equipped with a touchscreen with an intuitive interface that allows to work in two different modes:

• Maintenance mode which enables to adapt calibration and operation parameters.
• Operator’s mode in which the system only allows to run the measurements program and start the measurement.

The obtained results are an average of 20 consecutive measurements carried out by the sensor and displayed on the screen in less than 60 seconds.

This sensor is prepared to connect to a communication module which sends data to a network gateway and allows upload to a cloud via GPRS (General Packet Radio Service). Also, there is an in-built storage module in the sensor that stores the last measurements and allows to export data to an USB (Universal Serial Bus) pen drive for off-line analysis of the data.

The sensor was designed to in-situ measurement in wastewater treatment- and drinking water plants. The system contains a battery that enables several hours of off-grid operation, which is ideal for measuring at remote places or as a portable device. As the measurements require only a few seconds, the autonomy of the sensors will allow measurements to be taken for weeks without recharging the battery.

The sensor is designed as a straight-forward device, which can be used by a non-expert operator who has received basic training. Every component was selected to work with a minimum number of consumables.

The measurement process is automated, except for the sampling. The operator needs to collect, prepare, and place the sample on the designated cuvette inside the suitcase sensor and launch the measurement. The measurement process, the data analysis, the results display and the data upload to the cloud will run automatically without further instructions.

Maintenance requirements are minimal, with the main activity being the disinfection and rinsing of the measurement cavity after each measurement. Recalibration is also contemplated, and operators need to be trained for it in case any malfunction is detected.

This device has been designed and tested as part of the PAVITR project and prior to that has not been deployed anywhere else in India.

First experiences in India made during the validation and dissemination activities have indicated its relevancy and potential for applications in a country like India: the sensor offers a possibility to reduce laboratory dependence and costs for pathogen measurements, which is among others of great interest for remote and decentralised treatments plants.

This device has been designed and tested as part of the PAVITR project and prior to that has not been deployed anywhere else.