IoT Septic Tank Gas and Sludge-Level Monitor with Safety Dashboard

Septic tanks generate methane as waste decomposes, and the gas accumulates in the sealed headspace — manual inspection without testing the atmosphere has caused asphyxiation accidents. Separately, nobody knows a tank needs desludging until it overflows or backs up. Both problems are sensing problems: continuous gas and level measurement with automatic ventilation when gas crosses a threshold. This project builds that on an ESP32 with an MQ-4 methane sensor, an ultrasonic level sensor and a relay-driven exhaust fan, demonstrated on a sealed model tank with a live safety dashboard showing gas trends and fan state.

1. The MQ-4 sensor in the sealed tank's headspace is read by the ESP32, converted to an indicative ppm value against the calibrated baseline.
2. The ultrasonic sensor measures the distance to the sludge surface and converts it to a level percentage of the known tank depth.
3. Every 10 seconds the node publishes methane ppm, level percentage, temperature and fan state to the companion dashboard over Wi-Fi.
4. When methane reaches 5,000 ppm (10% LEL, a design-target action threshold), the relay starts the exhaust fan and the dashboard banner switches to the ventilation-active state.
5. The fan runs until gas falls below the 3,500 ppm reset band, with every start and stop timestamped in the event log.
6. The dashboard's desludge estimate divides the remaining capacity by the measured fill rate; the calibration procedure documents baseline setting and fan-trigger verification.

Tech stack:

• ESP32 (monitor node)
• MQ-4 methane gas sensor
• HC-SR04 ultrasonic level sensor
• DS18B20 temperature sensor
• Relay-driven 12 V exhaust fan
• HTML/CSS/JavaScript safety dashboard
• Arduino IDE (C/C++ firmware)
• Sealed demo tank rig

• [Methane sensing] MQ-4 sensor in the tank headspace tracks methane continuously; readings are shown in ppm on the dashboard with a 6-hour trend chart.
• [Automatic exhaust fan] Crossing 5,000 ppm (10% of methane's lower explosive limit) starts the exhaust fan automatically; it stops when gas falls back below the reset band.
• [Sludge-level measurement] Ultrasonic sensor reports the sludge level as a percentage of tank capacity with a visual tank gauge on the dashboard.
• [Desludge estimate] The dashboard extrapolates the fill trend into an estimated days-to-desludge figure, turning a level reading into a maintenance plan.
• [Safety dashboard] Live gas gauge, level gauge, fan state, 24-hour peak reading and a timestamped event log of every fan start/stop and threshold crossing.
• [Headspace temperature] DS18B20 temperature reading included, since gas sensor response and decomposition rate both vary with temperature.
• [Buyer-run calibration] MQ sensors are indicative devices; the kit includes a calibration procedure so the student sets the clean-air baseline and verifies the fan trigger on their own build.

• Working ESP32 monitor node (MQ-4, ultrasonic, temperature, relay/fan stage)
• Sealed demo tank rig with sensor and fan mounting
• Companion safety dashboard web app (gas gauge, trend chart, tank gauge, fan state, event log)
• Arduino firmware source with documented threshold constants
• Wiring diagram and rig assembly notes
• Buyer-run gas sensor calibration and fan-trigger verification procedure
• Project report PDF (septic gas hazards, sensor theory, LEL thresholds, methodology, results)
• PPT presentation for final review
• Viva Q&A preparation document (MQ sensor working, LEL concept, ultrasonic ranging, relay control)

• The MQ-4 is an indicative semiconductor sensor, not a certified gas detector — readings are approximate and the buyer calibrates the baseline; it must never be presented as a calibrated safety instrument.
• Demonstrated on a sealed model tank; real septic installations require certified equipment and professional installation, which this student build does not claim to be.
• Ultrasonic level accuracy depends on a calm sludge surface; foam or crust affects readings.
• The 5,000 ppm fan trigger is a design target verified by the buyer's own procedure, not a measured certified trip point.
• MQ sensors need a warm-up period (approximately 24 hours for stable baseline per the procedure) before trustworthy readings.