1、 The gases that need to be monitored in septic tank projects

Organic matter in septic tanks can produce various harmful, flammable, and explosive gases during anaerobic fermentation. The main monitoring objectives include:

1. Main hazardous gases (must be monitored):

• Methane (CH ₄): Primary monitoring objectFlammable and explosive gases, with an explosion limit (LEL) of 5% -15% by volume. When the concentration reaches 10% of the lower explosive limit (i.e. around 0.5% LEL or 5000ppm), an alarm must be triggered. It is the core of security monitoring.

• Hydrogen sulfide (H ₂ S): Highly toxic and flammableAt low concentrations, there is a foul egg odor, while at high concentrations, it can quickly paralyze the olfactory nerve. Short term exposure to higher concentrations can lead to "electrocution like" poisoning. The occupational exposure limit is usually very low (e.g. 10ppm). It is also the main cause of poisoning among workers during underground operations.
  

• 2. Secondary/related hazardous gases (to be monitored according to specific circumstances):

• Oxygen (O ₂):monitorHypoxic environmentMicroorganisms in septic tanks consume oxygen, which can easily form hypoxic spaces (O ₂<19.5%), leading to suffocation of those entering. At the same time, monitoring oxygen concentration can also help determine the ventilation status and explosion risk of the space (sufficient oxygen is one of the conditions for combustion).

• Carbon monoxide (CO):If there is a backflow of combustion exhaust gas or equipment operation nearby, it needs to be monitored. Toxic, can bind with hemoglobin and cause hypoxia.

• Ammonia gas (NH3):Stimulating gases have strong irritation to the eyes and respiratory tract, and high concentrations also pose a risk of explosion.

• Volatile Organic Compounds (VOCs):Reflect the overall concentration of organic volatile gases.

Summary of monitoring plan:

• Configuration/Core Configuration: Methane (CH ₄)andHydrogen sulfide (H ₂ S).

• Recommended configuration (more secure): Four in one gas detector, monitoringCH ₄ (or LEL), H ₂ S, O ₂ COThis is crucial for scenarios that require entering a confined space for work.

• Advanced/environmentally friendly configuration:According to environmental requirements, there may be an increase inNH₃andVOCsThe monitoring.
  

• 2、 Precautions for installing an online monitoring system

• The installation of online systems is to achieve continuous and real-time monitoring and prevent accidents from occurring.

• 1. Preliminary design and planning:

• Clear monitoring objectives:It focuses onwork safety(Explosion proof, Poison proof), orEnvironmental emissions(Monitoring odor or VOCs emissions)? Sensor selection and installation position vary greatly with different objectives.

• Layout strategy:

• Key monitoring points:septic tankWellhead, ventilation opening, gas collection hood/collection pipelineThese are the points where gases are most likely to accumulate and leak.

• Layered monitoring:Due to methane having a lower density than air and hydrogen sulfide having a higher density than air, it is recommended toTop (monitoring CH ₄)andBottom (monitoring H ₂ S)Install sensors.

• Explosion proof and protection level:The septic tank area usually belongs toExplosive hazard zone (Zone 1 or Zone 2)All online devices must be selected to meet the standardsExplosion-proof typeThe protection level of sensors and host enclosures should not be lower thanIP65(Dustproof and waterproof).

2. Equipment selection:

• Sensor technology:

• Catalytic combustion sensor:Used for detecting combustibles (LEL), with high cost-effectiveness, but requires the presence of oxygen and is prone to poisoning and failure in hydrogen sulfide environments.

• Infrared (NDIR) sensor:Used for detecting methane, it has high accuracy, long lifespan, and is not affected by hypoxic environments, making it a better choice, but the cost is relatively high.

• Electrochemical sensors:Used for detecting H ₂ S, O ₂, CO, etc.

• Sampling method:

• Diffusion type:Simple economy, relying on natural air flow, will result in delayed reactions.

• Pump suction:Active gas extraction, fast response speed, suitable for monitoring points that are far away or have obstacles, can detect leaks faster.

• Data transmission and alarm:system support4G/LoRaUpload data in real-time to the monitoring platform or central control room using various methods. The site must be equipped withaudible and visual alarmThe alarm value should be graded (low alarm, high alarm).
  
  3. Installation and construction:

• Safety:Installation must be done onUnder the condition of ensuring safetyIt may require forced ventilation and gas detection. Construction personnel are required to wear portable gas detectors and personal protective equipment.

• Firmly installed:Sensors should be installed in representative areas with stable airflow, avoiding blind spots and locations with severe vibrations.

• Easy to maintain:Consider sensorsCalibration, cleaning, and replacementConvenience and reserved maintenance space.

Summary suggestion:
For septic tank projects, it is strongly recommended to install“CH₄ + H₂S + O₂”As the coreExplosion proof pump suction extraction online monitoring system.