| (a) This section applies to the traditional approach
for sizing an aeration basin and clarifier, and is based on empirically-derived
design values that have been used historically as standard engineering
practice.
(b) Aeration Basin Sizing.
(1) An aeration system must be designed to maintain
a minimum dissolved oxygen concentration of 2.0 milligrams per liter
(mg/l) throughout the aeration basin at the maximum diurnal organic
loading rate determined in §217.32(a)(3) and Figure: 30 TAC §217.32(a)(3)
of this title (relating to Organic Loading and Flows for New Wastewater
Treatment Facilities). The executive director may consider alternative
dissolved oxygen specifications for designs that include biological
nutrient removal or tapered aeration for energy conservation, which
must be approved in writing.
(2) Based on the calculated organic load, the aeration
basin volume must be designed to ensure that the organic loading on
the aeration basin does not exceed the organic loading rates in the
following table:
Attached Graphic
(3) When identifying the aeration basin temperature
for the process design in Table F.1. in Figure: 30 TAC §217.154(b)(2),
the owner must use the average of the lowest consecutive seven-day
mean aeration basin temperature from a wastewater treatment facility
with similar characteristics. For purposes of this subsection, a similar
wastewater treatment facility:
(A) is located within 50 miles of the wastewater treatment
facility where the planned aeration basin or system will be installed;
(B) uses the same placement of the aeration basin (in-ground
or above-ground); and
(C) has any other characteristics required by the executive
director in writing.
(c) Clarifier Sizing.
(1) The following table establishes the maximum surface
loading rates and the minimum detention times that must be used to
determine the size of a clarifier:
Attached Graphic
(2) A clarifier must meet both the detention time and
weir overflow rate criteria in Table F.2. in Figure: 30 TAC §217.154(c)(1).
(A) When calculating weir overflow rates for a clarifier,
return activated sludge flow must not be used in the calculation of
the maximum weir overflow rate, in compliance with Table F.2. in Figure:
30 TAC §217.154(c)(1).
(B) When calculating the weir overflow rate for a clarifier,
the surface area of the stilling well may be included as part of the
clarifier surface area.
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