| (ii) Imhoff tank or clarification as primary treatment
method.
Attached Graphic
(B) Advanced secondary treatment. The detention times
given in Table Number 4 are based on the fraction of BOD5 remaining after secondary treatment. Table
Number 4 assumes a wastewater treatment plant influent BOD5 of 200 mg/liter. For percentages that fall
between the listed quantities, linear interpolation is permissible.
Attached Graphic
(C) Vector control. The presence of mosquitos and other
vectors has been associated with open water. Since the FWS systems
will have open water surfaces, vector control must be a priority.
Vector control mechanisms using natural controlling agents such as
introduction of Gambusia spp. (mosquito fish) have been proven effective.
However, if the predatory fish are used to control vectors, provisions
must be made within the basin for designated open water areas so the
fish can surface for oxygen. At least 20% of the basin's surface should
be open to the atmosphere. Other methods of vector control may be
considered. However, the introduction of chemicals (such as pesticides)
should be carefully evaluated so that there are no adverse effects
on vegetation or on effluent water quality.
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