Overland Flow Systems

The area required for an overland flow (OF) site depends on the length of the operating season. The recommended storage days for an overland flow system for planning purposes can be estimated from Figure 2.1. The effective flow to the OF site can then be estimated using Equation 2.8:

where

Qm = Average monthly design flow to the overland flow site (gal/mo; m3/mo). q = Average monthly flow from pretreatment (gal/mo; m3/mo). ts = Number of months storage is required. ta = Number of months in the operating season.

The OF process can produce advanced secondary effluent from a primary effluent or equivalent. The expected effluent quality is BOD = 10 mg/L, TSS = 10 mg/L, total N < 10 mg/L, and total P < 6 mg/L. The site area given by Equation 2.9

where

FIGURE 2.1 Recommended storage days for overland flow systems.

I i 2 to 5 days storage for 1: ■ - ■■■L operational flexibility

FIGURE 2.1 Recommended storage days for overland flow systems.

includes an allowance for a 1-day aeration cell and for winter wastewater storage (if needed), as well as the actual treatment area, with an assumed hydraulic loading of 6 in./wk (15-cm/wk):

where

A0f = Overland flow project area (ac; ha).

Qm = Average monthly design flow to the overland flow site, gal/mo (m3/mo).

q = Average monthly flow from pretreatment, gal/mo (m3/mo).

ts = Number of months storage is required.

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