Monitoring of bioreactors for microalgae
The requirements called for a monitoring and control system based on Arduino or a similar platform, ensuring easy maintenance, integration with unbranded peripherals, and simple replicability. Two experimental systems for cultivating microalgae, in a broth derived from waste from other productions, are compared under identical operating conditions.
The first system, called Thin Layer, consists of a 20-meter-long slide where water containing algae flows freely.
The second system, called Flat Panel, is made up of two vertical reactors, each with a surface area of 1 square meter, enclosed by glass walls and holding 100 liters of liquid each.
The parameters monitored in both systems are partly the same:
pH, D.O. (dissolved oxygen), and T (temperature). In the first system, additional monitoring includes rain detection, automatic level control to compensate for evaporation losses, and indirect measurement of solar radiation.
The control mechanisms differ: recirculation and sampling pumps in the first system; solenoid valves for sampling and refill pumps in the second.
Both systems are equipped with temperature regulation through a heater and a cooling heat exchanger.
Within a project for the study and testing of experimental systems for the treatment of wastewater from dairy production, we designed and built small monitoring and process control units based on the Arduino platform.
These systems use bioreactors in which the wastewater feeds algal cultures.
The parameters controlled include pH, dissolved oxygen, temperature, recirculation pump flow, CO2 delivery for acidity correction, air delivery in the bioreactors, and solar radiation.
For the open system, the “rain” event is also managed, with segregation of the liquid containing algae and nutrients and exclusion of rainwater input.
The initial requirements included the use of “open” tools and software, which could be adapted to the needs of the project and later repurposed to support its evolution.
The initial requirements called for the use of “open” tools and software, which could be adapted to the needs of the project and later repurposed to support its evolution.
The platform chosen for development was an industrialized version of Arduino, known as Industruino.
This was paired with a server-side system to manage communication with actuators, operation logging, and the automation and alerting processes.
The server-side solution selected was Node-RED, an environment that allows devices, sensors, and services to be connected through a highly flexible and intuitive graphical interface.
In our case, Node-RED runs on a virtual server, ensuring minimal operating costs and high reliability.
As actuators for electrical commands, we selected Itead remote controls distributed under the name SonOff, based on the ESP8266 processor, which were made agnostic by updating them with Tasmota firmware.
This allowed the use of CE-certified devices in all phases of the project with maximum modularity.
The entire command/feedback line was implemented using MQTT (Message Queuing Telemetry Transport) messages, with the station/peripherals connected via a Wi-Fi access point and a 3G field line.
The device connection chain has a single access point to the internet through the 3G modem, from which an Ethernet network branches out to a 5-port switch, which in turn connects to:
Control and Communication Infrastructure
The technological heart behind the monitoring of the reactors
Local network and connected devices
- the Industruino of the Flat Panel system and the 2.4GHz Access Point.
- Conel UR5i v2 3G modem with MIMO antennas, 12VDC power supply,
- 1 Ethernet port with SIM card
- Netgear 5-port 10/100/1000 switch powered at 12VDC
- Ubiquity 2.4 GHz Access Point powered via PoE. Wireless devices connect to the Access Point as clients, obtaining a dynamic IP from the integrated DHCP server.
- SONOFF 4CH remote control with 4x10A relays, remotely controllable via the Node-RED server dedicated to the installation and locally via 433MHz remote control.
- SONOFF 1CH 16A with input for temperature and humidity probe, remotely controllable through the dedicated Node-RED server.
Inkbird ITC-308-WIFI thermostats with temperature probe. Dedicated to temperature control of the Flat Panel devices. Remotely controllable through the proprietary InkbirdSmart app.
Main actuators
- 1/2″ solenoid valves 220VAC control
- 1/2″ solenoid valves 12VDC control
- 220V pumps with recessed impeller
- Peristaltic pump for Thin Layer refill
- Data storage
Storing the output values from the probes through the Cayenne service of Mydevices.com at this link - Control logic
- Industruino with ethernet module
