Description
Given the incoming average flow, the number of settling tanks and the geometric characteristics of each one, verifies if it fits the Brazilian standards for domestic sewage treatment plants.
| Number | Purpose |
|---|
| 1 | when preceding a biological filtration process |
| 2 | when preceding an activated sludge process |
| 3 | when the process is a process for chemically assisted primary decantation - CEPT process |
Parameters established by NBR 12209:2011
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6.3.1 The sizing flowrate of the primary clarifier should be the maximum hourly influent flowrate to the unit, except in the case of item (c) of 6.5.1.9.
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6.3.2 The surface overflow rate should be compatible with the desired removal efficiency and not exceed:
- 60 m³/(m².d) when preceding a biological filtration process;
- 90 m³/(m².d) when preceding an activated sludge process;
- 90 m³/(m².d) when the process is chemically enhanced primary sedimentation (CEPT process).
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6.3.3 Wastewater treatment plants with a design flow rate greater than 250 L/s must have more than one primary clarifier.
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6.3.4 The hydraulic detention time for the average flow rate should be less than 3 hours and, for the maximum flow rate, greater than 1 hour.
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6.3.5 The flow rate for the maximum flow through the outlet weir must not exceed 500 m³/(m.d) per weir.
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6.3.6 The sludge removal piping must have a minimum diameter of 150 mm; the sludge transport piping in free-flow conduits must have a minimum slope of 3%; sludge removal from the bottom should preferably be done in a way that allows observation and control of the removed sludge.