Septic tanks are essential for properties not connected to mains sewer systems. These systems, when correctly designed and maintained, offer an effective way to manage wastewater. This article will guide you through the processes, design considerations, and best practices for septic tanks, ensuring your construction projects in Bali meet environmental and functional standards.

How Septic Tanks Work

A septic tank is a small-scale sewage treatment system that effectively breaks down waste. In a typical household setting, the output from the toilet is known as sewage. This waste is directed to a two-chamber septic tank where it is processed through a natural bacterial process.

The Bacterial Process

1. First Stage (Anaerobic): Raw sewage enters the first chamber, and solid particles sink to the bottom. Here, naturally occurring bacteria begin to consume the solid waste. This is an anaerobic process, meaning it doesn’t require oxygen. These bacteria convert the waste into liquid and gas.
   • Most solid waste is broken down, leaving a small amount of sludge at the bottom and a crusty scum on the surface. This stage generally takes three to four days.
   • At this stage, the waste is approximately 60% to 70% processed.
2. Second Stage (Further Breakdown): The semi-processed liquid moves to the second chamber. Further settling and bacterial action occur here, with additional sludge settling at the bottom.
3. Final Stage (Discharge): The almost fully processed liquid is discharged from the second chamber through a pipe. This discharge is often directed to a leach field for final processing.

The Leach Field

The discharge from the septic tank is typically directed to a leach field, a network of buried pipes with seepage holes. Here, an aerobic process occurs where microbes and UV light break down the remaining contaminants, and the septic tank bacteria die off, resulting in fairly pure water that safely percolates into the ground.

Important Design Considerations

• Two-Chamber System: Septic tanks utilize two chambers to create a two-stage purification process. Raw sewage entering the first chamber displaces partially processed water into the second, separating the raw sewage from partially purified water.
• Minimizing Turbulence: To ensure smooth processing, the design should minimize turbulence as sewage enters the tank and moves between chambers. This is achieved by using tee pieces or baffles on inlet, transfer, and outlet pipes.
• Proper Sizing: The septic tank must be adequately sized to hold the wastewater long enough for proper processing.
• Material and Construction: Septic tanks should be built strongly to prevent cracking due to earth movement and must not leak.

Maintaining Septic Tank Efficiency

1. Avoid Disinfectants: Do not put disinfectants into your toilet, as they can kill the essential bacteria.
2. No Additives: Septic tanks don’t need additives; naturally occurring bacteria are sufficient. Additives may contain different bacterial strains that may unbalance the system.
3. Yeast is not Suitable: Avoid putting yeast into the septic tank as yeast are not bacteria and they may inhibit the action of the good bacteria.
4. Only Black Water: Ensure that only black water (sewage) enters the septic tank. Greywater from washing should be kept separate.
5. Prevent Water Intrusion: Do not allow rainwater or groundwater to enter the tank.
6. Regular Sludge Removal: Pump out the sludge periodically to maintain the tank’s capacity.
7. Proper Waste Disposal: Avoid flushing anything that bacteria cannot break down, such as sanitary napkins, as they may clog pipes and fill the septic tank.

Environmental Considerations

• Groundwater Contamination: In areas without proper drainage, septic tanks can contaminate groundwater if not managed correctly. This can lead to health issues.
• Piped Sewerage Systems: Piped sewage systems are crucial for improving public health, especially in densely populated areas.

Maximizing Purification

• Third Chamber: Adding a third chamber can provide an additional level of purification.

Conclusion

A well-designed and properly maintained septic tank is a highly effective system for managing wastewater. By adhering to these guidelines, you can ensure that your septic system operates efficiently, protects the environment, and avoids common issues such as odors or rapid fill-up. Remember, the key is to foster a healthy bacterial environment, avoid harmful chemicals and ensure correct water flow within the system.