An open source ultrasonic flowmeter for monitoring the input/output flow rates of wastewater treatment plants

Abstract

Sensors play an important role in both the continuous monitoring and intermittent analyses, which are essential for the study of wastewater treatment plant management and conducting related research. Given the significant environmental impact of the issues involved, accurate measurement of the volume of water flowing into and out of treatment plants is a key parameter for plant management, ecotoxicological studies and academic research programs. Traditionally, flow measurements have been based on calibrated weirs or venturi flumes, using water level measurements for conversion into flow, according to established relationships. In this article, the authors propose an innovative approach to explore the feasibility of developing an open-source, reparable and cost-effective data logger for flow monitoring using ultrasonic technology. By leveraging Arduino modules and a complementary Grove shield, the proposed data logger offers seamless integration and affordability. In particular, it features an on-board web server to facilitate data collection and device testing, offering accessibility through Wi-Fi connectivity with smartphones or computers. The authors demonstrate the effectiveness of their flowmeter by comparing its performance with that of a commercial reference flowmeter, yielding a maximum permissible measurement error of 0.6 mm on the water level measurement. Furthermore, they demonstrate the durability and reliability of the developed data logger through extensive field-testing over a 9-month period.

Keywords: Low-tech; Monitoring; Treatment plant; Ultrasonic sensor; Wastewater; Water level.

Graphical abstract

Fig. 1

Operating principle of the ultrasonic sensor (ultrasonic waves shown in green).

Fig. 2

Schematic design of the flowmeter.

Fig. 3

The flowmeter prototype.

Fig. 4

Assembly of Arduino boards, a) Assembly method of the MKR Connector Carrier, MKR SD Proto Shield and Arduino MKR Wi-Fi 1010 boards, b) Final result of the board assembly steps.

Fig. 5

Installation of the Grove RS485 module, in order to communicate with the water-level sensor.

Fig. 6

Installation of the Grove RTC module for time management purposes.

Fig. 7

Installation of the Grove voltage divider module for downward scaling.

Fig. 8

Installation of the Grove LED module for visual indication.

Fig. 9

Installation of the Grove terminal screw module.

Fig. 10

Preparation of the data logger enclosure: a) polycarbonate enclosure, b) PVC plate and template for cutting the plate and drilling, c) identification of drilling diameters, d) drilling of the PVC plate.

Fig. 11

Installing spacers on the PVC plate: a) spacer M2 with a height of 2 cm, b) spacer M3 with a height of 2 cm.

Fig. 12

The holes are drilled on the data logger enclosure: a) 12  mm diameter holes on the long side, b) 20 and 12  mm diameter holes on the short side.

Fig. 13

Installation of the PVC plate with spacers in the data logger box (this installation is the same for the 3D print support plate).

Fig. 14

Mounting of the data logger in the enclosure: a) secure the Arduino MKR Connector Carrier in the enclosure using the M3 x 8  mm screw, b) install the RTC module onto the spacers with M2 x 8  mm screw and M2 x 20  mm spacers, c) install the Grove Screw Terminal module with M2 x 8  mm screws, d) install the pushbutton, e) screw the pushbutton seal and nut.

Fig. 15

Connection of the pushbutton to the Grove Screw Terminal module: a) cut the wires to the appropriate length, b) strip the wires by 5 mm, c) fasten the wires to the two central screws of the Grove Screw Terminal.

Fig. 16

Installation of the Ultrasonic Sensor URM14 SEN0358: a) attaching the gland and installing the sensor wire, b) presenting the wires, c) connecting the RS485 module, d) attaching the RS485 module to the housing.

Fig. 17

Installation of a) the voltage divider, b) the red LED grove module, c) the power supply female connector, d) Tightening of the nut to ensure connector attachment.

Fig. 18

Connecting the power cables: a) preparing the cables, b) connecting the cables to the female connector, c) fitting the length of the cables, d) connecting the cables to the Grove Voltage Divider module.

Fig. 19

The final implementation step for the data logger: a) connect the red and black 1-mm² cables to the Arduino MKR Carrier connection, b) introduce the CR1225 battery in order to power the Grove RTC module, c) screw the external nut of the gland, d) insert the SD card into the Arduino SD proto shield.

Fig. 20

Flowmeter data logger enclosure.

Fig. 21

Preparation of the power supply system: a) power supply and connector, b) identification of the polarity of the power supply wires, c) opening of the connector and positioning of the cables, d) connection of the cables to the screw terminal block of the connector.

Fig. 22

Finalisation of the power supply: a) installation of the clamping ring, b) installation of the body and nuts, c) assembly of the power supply and connector, d) adjustment of the power supply system to the 12  V position.

Fig. 23

Connecting the power supply to the data logger.

Fig. 24

Flowmeter program flowchart.

Fig. 25

Comparison of the open source flowmeter with the reference flowmeter: a) water head measurement for the two flowmeters, b) correlation between both flowmeters.

Fig. 26

Long-term installation of an ultrasonic flowmeter on a wastewater treatment plant outlet: a) photo of the installation, b) results of water level monitoring, c) precipitation measured near the wastewater treatment plant.