A sewerage drain field and a septic tank make up a small scale sewage treatment system. A septic tank is basically a rectangular shaped underground receptacle for wastewater. It is watertight, made of concrete, and consists of tanks that are divided into chambers. The first chamber has twice the volume as the second and the majority of the organic solid matter, referred to as sludge, gets settled here. The second chamber further purifies the wastewater.
The septic tank collects wastewater from toilets, showers, sinks, etc. Due to the absence of a current the sludge quickly settles down to the tank floor. Anaerobic bacterial digestive activity on the sludge leads to the generation of methane and carbon dioxide; the sludge is stabilized and does not rot anymore. Particles of stabilized sludge stay settled, some may float to the top as scum.
A septic tank should be constructed such that there is maximum contact time with the microorganisms so as to enable swifter digestion of the sludge. This is achieved by placing the inlet, overflow, and outlet diagonal to each other and by making the streams flow in vertically placed pipes.
The semi-purified water moves...