Description

Given the average incoming flow and BOD, the average area and depth of the pond and the coldest month average temperature, suggests the area for the pond and calculates the resulting organic superficial load and the maximum superficial load that the pond can bear. Also, calculates the volume of the pond and the recommended volume that should be adopted. The hydraulic detention time is also calculated.

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NOTE

1. Application rates and retention times in optional ponds:

   Application rate, kg BOD/ha.d	Equivalent population/ha	Detention time, days	Local Considerations
   < 10	< 200	> 200	Very cold regions, with sporadic ice coverage, low temperature, variable cloud cover.
   10 - 50	200 - 1000	200 - 100	Cold climate with seasonal ice cover and mild summer temperatures for short periods.
   50 - 150	1000 - 3000	100 - 33	Temperate to non-tropical regions, occasional ice cover, no prolonged cloud cover.
   100 - 350	3000 - 7000	33 - 17	Tropical regions, evenly distributed sun and temperature, no seasonal cloud cover.

2. L/B Ratio: 2 $\le$ L/B $\le$ 5

3. The surface of an optional lake must be less than 15 ha.

4. Depth y: 1.20 m <$\le$ y $\le$ 2.00 m; larger values are recommended.

5. Organic load application rate: $\ge$ 100 g BOD/m³.d; $\le$ 400 g BOD/m³.d. Higher loads are applicable to higher temperature conditions.

6. Mara's criterion leads to values close to limits at which the lagoon starts to behave as anaerobic; must be adopted with discretion.e