Wastewater Calculations - Mathematics and Statistics for the Environment - page 700

Now calculate detention time:

Oxidationditch volume (gal) 160,000 gal

7708 gph

Detentiontime(hr) = = = 0.8hr 2

Flow rate (gph)

24.9 TREATMENT PONDS
The primary goals of wastewater treatment ponds focus on simplicity and flexibility of operation,
protection of the water environment, and protection of public health. Moreover, ponds are relatively
easy to build and manage, they accommodate large fluctuations in flow, and they can also provide
treatment that approaches conventional systems (producing a highly purified effluent) at much lower
cost. It is the cost (the economics) that drives many managers to decide on the pond option of treat-
ment. The actual degree of treatment provided in a pond depends on the type and number of ponds
used. Ponds can be used as the sole type of treatment, or they can be used in conjunction with other
forms of wastewater treatment—that is, other treatment processes followed by a pond or a pond fol-
lowed by other treatment processes. Ponds can be classified based on their location in the system, by
the type of wastes they receive, and by the main biological process occurring in the pond. First, we
look at the types of ponds based on their location and the type of wastes they receive: raw sewage
stabilization ponds, oxidation ponds, and polishing ponds.

24.9.1 t reatment p ond p arameters
Before we discuss process control calculations, it is important first to describe the calculations for
determining the area, volume, and flow rate parameters that are crucial in making treatment pond
calculations.

• Determining pond area in acres:

2
2

Area (ft )
43,560 ft /ac

Area (ac) = (24.74)

• Determining pond volume in acre-feet:

3

Volume (ft )
43,560 ft /ac-ft

Volume (ac-ft) = (24.75)

2

•

Determining flow rate in acre-feet/day:

Flow (ac-ft/day)Flow(MGD) = × 3069 ac-ft/MG (24.76)

Key Point: Acre-feet (ac-ft) is a unit that can cause confusion, especially for those not familiar with
pond or lagoon operations. One ac-ft is the volume of a box with a 1-ac top and 1 ft of depth—but
the top does not have to be an even number of acres in size to use ac-ft.

• Determining low rate in acre-inches/day

Flow (ac-in./day) = Flow (MGD) × 36.8 ac-in./MG (24.77)