The diagram shows the steps involved in recycling sewage water. Overall, sewage water treatment is a complex process that can be divided into two main stages: primary treatment and secondary treatment. This recycling process also clearly involves six cleaning points and an eventual chemical treatment.
The primary treatment stage involves removing large 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: the comminutor. The subsequent tank is called a ‘grit chamber’ where grit from the sewage water is discharged through the tube located under this chamber. The last piece of equipment in the primary treatment process is the primary clarifier, which functions similarly to the 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 accumulates inside a large aeration tank, which stirs water with an air compressor. Then, the final purifying equipment – the secondary clarifier directs activated sludge in two directions: cleaner water goes back to the aeration tank, whereas contaminations are disposed into the same pipe system as the ones coming out of the primary clarifier. Before going to the secondary effluent from the secondary clarifier, water is treated with disinfectant chemicals. The resultant water can be discharged into surface water, or sent to the tertiary treatment if necessary.