How does a Sewage Treatment Plant work?
Sewage Treatment Plants are in many ways similar to Septic Tanks which is why often their two processes are confused but there are however a number of distinct differences between the two. A Sewage Treatment Plant is primarily designed to take wastewater away from a building and treat it. This process involves removing any contaminants that can be harmful to the environment. The finished water quality is then safe to discharge into a stream or river without posing any danger to the fish or plant life in the surrounding area.
Sewage Treatment Plants use naturally occurring bacteria to treat the wastewater and here we will be breaking down how bacteria behave in each step of this process.
The first stage occurs in the settlement zone which is where the wastewater enters when it arrives in the treatment plant. This zone allows heavier solids within the water to settle at the bottom of the tank and for lighter solids to float to the top. The bacteria which forms within this tank is anaerobic which can survive with very little oxygen present but terms of the breaking down of waste during this process, it does very little. Once the solids have separated, the cleanest part of the water which typically sits a third of the way from the top will be sent to the biological treatment zone.
Biological Treatment Zone
Once the water enters this zone, it should have significantly less solids, but it still contains harmful chemicals such as ammonia which would be dangerous for plant and marine life. It is in this zone that Aerobic bacteria grows and is able to feed on the harmful contaminants in the water. As this type of bacteria needs high levels of oxygen and food to survive and work efficiently, most systems will add oxygen using an air blower. This air blower creates enough oxygen bubbles in the water for the bacteria to survive and any food they require will naturally come from the remaining waste in the water.
Final Settlement Zone
The bacteria should have broken down the majority of the waste at this stage and any remaining small particles of waste will drop to the bottom of the tank. If the solids begin to build up, they will often be a system in place which re-circles it all back to the original zone.
Discharging Into the Environment
At this stage the water should be thoroughly cleaned meaning it is free from any solid waste and should have substantially less ammonia and other contaminants. The water is now safe to be discharged into a river or stream but can still pose a health hazard to humans and therefore should not be reused.