Sewage which enters STP from sewage network will combine at incoming sump. Term "wet well" normally used by plant operator to describe the condition of wet area. As the water come in, the flow will be screening for those big/ unwanted material such as stick, wood, diapers, plastic, rags, stone, bottle, clothes, underwear, debris and steel to be removed.
Size of screen for primary is normally 15-20mm bar to bar. It is either static or mechanical screen. For a bigger plant, mechanical screen is the most important however, static screen will be provided in case of mechanical screen failure. Like a small plant (PE<500), static screen is more preferred.
Material of construction to be used for screen is either stainless steel or mild steel. Most plant operator likes to choose mild steel rather stainless steel because it’s more cheaper and low theft frequency. However, stainless steel is last longer.
Purposes for installation are:
1. To prevent loses or faulty to delivery pump (normally called RSP or Raw Sewage Pump)
2. To enhance downstream treatment process
3. To prevent loses to other mechanical equipment and installation
4. To ensure better clarifier look. It is also image of the STP which relevant to operator efficiency.
