What happens when feces and urine reach the septic tank?

Feces, urine, and contamination

Feces

The majority of the pathogens in wastewater come from the feces. Urine is mostly sterile but feces contain over 100 varieties of bacteria and viruses. Even though some of the bacteria are harmless, others can cause diseases like dysentery, cholera, typhoid, and Hepatitis A. Additionally, viruses like rotavirus and Norwalk Agent Virus can cause respiratory illnesses. Viruses may not multiply outside the host but they can still survive for weeks as they await a new host. There are five important virus groups that originate from human feces. These are;

• Adenoviruses
• Enteroviruses
• Reoviruses
• Rotaviruses
• Hepatitis A

Of the five classes of viruses listed above, hepatitis A and rotavirus are the ones that are known to spread disease. The human intestine has a huge population of bacteria. Some of these bacteria (e.g. Escherichia coli) play an important role in the digestion of food. Others like salmonella have no benefit to the digestion process but are still harmless while in the colon. However, when they get out of the body through feces, they and can cause illness. The bacteria that can result in sickness include;

• Escherichia coli
• Salmonella
• Vibrio
• Shigella

Urine

Even though urine is sterile and has no serious health ramifications, it largely contributes to nutrient pollution of surface water. When the wastewater is not treated adequately, the nitrates and phosphates get into the rivers and lakes where they encourage the growth of algae. The more these nutrients increase in water, the greater the algal bloom. This ends up upsetting the natural balance in the aquatic ecosystems. Furthermore, as the algae die off, the dissolved oxygen in the water is used up by the microorganisms as they decompose the dead algae. this process by which the river or lake shifts from a clean water body to a lake or river that is oxygen-deficient due to algal bloom is referred to as eutrophication.

What happens to urine and feces in the septic tank?

The wastewater containing urine and feces is referred to as black water. The septic tank was particularly designed for handling blackwater although it also processes greywater. Greywater is the wastewater from the kitchen and shower drains. When blackwater gets into the septic tank, the solid particles from the feces and the tissue drop to the bottom of the tank where bacteria begin to consume them. In a conventional septic tank, the bacteria do not need oxygen and as they eventually convert the solid waste into gas and liquid.

Most of the solid waste is liquefied by the bacteria and the little that is not remains settled at the bottom of the tank to form the sludge layer. Meanwhile, the gas that is produced by the bacteria (mostly hydrogen sulfide, carbon dioxide, and methane) rises to the top of the water where it helps in creating insulation for improving the anaerobic conditions. This is the first stage of processing and it takes 2-4 days. At least 60-70% of the solid waste is typically liquefied at this stage. The semi-processed effluent then flows to the second chamber where the remaining solid waste is acted upon with bacteria. Again, those particles that cannot be broken down by the bacteria settle at the bottom of the tank to form the sludge layer.

From here, effluent leaves the septic tank via a discharge pipe and into a leach field. At this stage, pathogens are removed from the wastewater through the aerobic processes by aerobic bacteria. Nutrients are also removed through a natural filtration system of gravel and then the water will be ready to go back into the water cycle. A conventional system can remove up to 50% of the nutrients from the wastewater. Further filtration of the water will occur as the water percolates through the soil until it reaches the groundwater. If the greater quality of effluent is required, an advanced septic system will need to be installed because it is more efficient in removing nitrogen, phosphorus, and other nutrients from the wastewater before it is finally fed back into the water cycle.

Conclusion

Fecal bacteria and viruses are known to cause many illnesses and that is why wastewater from the house needs to be treated well. When the septic system is working efficiently, all pathogens should successfully be eliminated from the wastewater before it is released into the groundwater. But when the system fails, the ground and surface water might get polluted which exposes humans to communicable diseases. It is, therefore, important to carry out routine checkups and maintenance to avoid this.