IoT Biogas Digester Monitor with Methane, Pressure and Temperature Sensing

Small biogas digesters are usually built and then ignored: a bottle of slurry with a tube, producing gas nobody measures. Without instruments the student cannot tell whether the digester is healthy, stalled, or leaking — methane is odourless and invisible, pressure build-up is hidden, and temperature swings silently kill the methanogens. This project instruments a bottle-scale digester with an ESP32: an MQ-4 sensor watches methane concentration, a pressure sensor tracks gas build-up in the headspace, and a DHT22 reports digester temperature, with all three shown live on a 20x4 LCD alongside a status line. A balloon on the gas outlet makes production visible and gives the pressure reading something tangible to correlate with. The build is honest about its limits — the MQ-4 gives indicative readings that need calibration, and this is a teaching demo, not a certified gas-safety instrument.

1. The bottle digester is charged with slurry and sealed; the gas outlet feeds a collection balloon.
2. The MQ-4 methane sensor, pressure sensor and DHT22 report to the ESP32 on a timed sampling cycle.
3. Firmware compares each reading against configured bands and sets the LCD status line (e.g. OK vs check-digester).
4. The LCD refreshes each cycle with temperature, humidity, methane indication and pressure trend.
5. The student logs readings against balloon inflation over days, building the production curve for the report.
6. All thresholds are documented firmware constants, retunable for the student's feedstock.

Tech stack:

• ESP32 DevKit (Arduino/C++ firmware)
• MQ-4 methane gas sensor
• Pressure sensor module
• DHT22 temperature/humidity sensor
• 20x4 character LCD
• Bottle digester + balloon gas collector

• [Methane sensing] An MQ-4 sensor monitors methane concentration near the digester headspace, with the reading shown live on the LCD.
• [Gas pressure tracking] A pressure sensor follows headspace pressure as gas accumulates, correlated with the visible inflation of the collection balloon.
• [Digester temperature monitoring] A DHT22 tracks the slurry temperature that the methanogens depend on.
• [Live LCD status] A 20x4 LCD shows temperature, humidity, methane reading and a plain-language status line.
• [Visible gas collection] The demo digester uses a bottle reactor with a balloon collector, so gas production is observable and measurable.
• [Leak-awareness design] The methane channel exists to make invisible gas visible in the demo; the report teaches the limits of semiconductor gas sensing honestly.
• [Viva-ready documentation] Report, PPT and Q&A cover anaerobic digestion basics, sensor interfacing and calibration limits.

• Working monitor prototype (ESP32, MQ-4, pressure sensor, DHT22, 20x4 LCD)
• Bottle-scale demo digester rig with balloon gas collector
• Arduino firmware with bands and status logic
• Wiring diagram and connection list
• Digester charging and logging procedure
• Project report PDF, PPT presentation and viva Q&A document

• The MQ-4 is a semiconductor sensor: its readings are indicative and drift with humidity, temperature and age — calibration against a known reference is required for anything beyond trend observation, and the report states this.
• This is a teaching demo at bottle scale, NOT a certified gas-safety instrument; it must never be relied on for leak protection in a real installation.
• Methane is flammable: the demo uses tiny quantities, no ignition sources are permitted near the rig, and the safety procedure in the report is mandatory reading.
• Digester output depends on feedstock, temperature and time — gas production figures are the student's own logged observations, never pre-claimed.
• The pressure sensor measures headspace pressure qualitatively for the demo; it is not a calibrated industrial gauge.