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14.- WSP Design Summary (3)

# 001eaf mean of inflow qi minimum retention time

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Unformatted text preview: where Qm Facultative ponds: = θf = AfD/Qm ∴ θf = AfD/[(Qi + Qe)/2] ∴ Qe = Qi – 0.001eAf mean of inflow Qi Minimum retention time Minimum • Min θf = 4 days Min • If calculated value of θf is <4 days, then take θf = 4 days, and recalculate the area from: Af = (Q × 4)/Df 4) • Take Df = 1.5 m B O D Le = Li 1 + k1(V/Q) (V/Q) Le = V/Q is the mean hydraulic time, days (symbol: θ) Li Le = unfiltered BOD 1 + k1θ Filtered BOD = 0.3Le For secondary facultative ponds k1 for BOD secondary removal varies with temperature as follows: k1(T) = 0.1(1.05)T−20 NB: 20 °C 20 °C Facultative ponds: Facultative So far we’ve calculated the area, chosen the depth, and calculated the retention time & effluent BOD Now check suitability of effluent for restricted irrigation: • ≤105 E. coli per 100 ml, and • ≤1 egg per litre (assume no children under 15 exposed) 1. E. coli removal removal • General equation is: Ne = Ni / [(1+...
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