The diagram illustrates how sewage water is recycled. Overall, sewage water treatment goes through a complex process which can be divided into two main stages: primary treatment and secondary treatment. It is also clear this recycling process involves six cleaning points and an eventual chemical treatment.
The primary treatment stage involves removing larger impurities from the sewage water. Once sewage water has come out of the raw sewage system, it passes through several layers of screens before going into the next cleaning device: comminutor. The subsequent tank is called ‘grit chamber’ where grit from the sewage water is discharged from the tube located under this chamber. The last equipment in the primary treatment process is called primary clarifier, which has a similar function with grit chamber: while primary sludge goes out of the lower pipe, cleaner water is sent to the next stage.
At the initial point of the secondary treatment, water accummulates inside a large aeration tank, which stirs water with an air compressor. Then, the final purifying equipment – secondary clarifier directs activated sludge to two directions: cleaner water goes back to the aeration tank whereas contaminations are disposed into the same pipe system with the ones coming out of the primary clarifier. Before going to the secondry affluent from the secondary clarifier, water is treated with disinfectant chemicals. The resultant water can be discharged into surface water sources, or sent to the tertiary treatment if necessary.