flange. Threaded or flanged connections shall be provided for the
upper and lower hanger pipes. Bearings with O-ring seals shall be
as specified for the upper pivot joint. The intermediate pivot
joint shall have a locking device to allow positive locking in any
position. Spacing of diffuser assemblies in the tank and
diffusers on the header shall be as recommended by the diffuser
manufacturer. The drilling and tapping of the horizontal portion
of drop pipe shall be such as to give the diffuser the correct
horizontal alignment without being skewed either upwards or
downwards. Horizontal portion of drop pipe shall incorporate an
adjustable stop on the wall side to prevent the diffuser from
coming on contact with the wall. A portable hoist shall be
provided to raise and lower the diffuser assembly. Hoist shall be
expressly designed to be compatible with the diffuser holder
assembly and shall be provided by the same manufacturer. Hoist
shall be engine- or motor-driven hydraulically operated,
pneumatically operated or manual, with quick clamping arrangement
to securely engage upper hanger pipe. The hoist shall be
adequately powered to raise the assembly from a dry tank. The
hoist shall provide means of locking the diffuser header in a
raised position over the tank or the walkway.
2.8.2.3
Air Diffusers in Aerobic Digester
Drop-pipe with air diffusers shall be provided in the tank with placement
of diffusers near the bottom. Air control valve shall be of the needle
valve or globe valve type and shall have indicator markings for throttling
and complete shut-off; globe valve shall conform to MSS SP-80. The amount
of air supplied to the tank shall be sufficient to allow aerobic
stabilization of solids and in no case less than 0.25 cubic meter per
second of air per 1,000 cubic meters 15 CFM of air per 1,000 cubic feet of
tank volume.
2.8.2.4
Air Blower Assembly
Air blower assembly shall be as specified in paragraph entitled "Air Blower
Assembly."
2.8.2.5
Piping
Piping shall include piping from air blower assembly to aeration tank and
aerobic digester, air header piping and drop piping (piping from air header
to diffusers). Materials for piping and gate and plug valves shall be as
specified in paragraph entitled "Piping."
2.8.3
Mechanical Aeration Equipment
**************************************************************************
NOTE: Delete paragraph and subparagraph thereto
when step aeration type or complete mixing type is
specified, or when mechanical aerator is not allowed
for extended aeration type. Mechanical aerator may
not be suitable for use in areas having prolonged
periods of sub-freezing temperatures when spray may
form accumulation of ice. Consideration should be
given to temperature and detention time of the
liquid and freeboard in the tank in determining
temperatures that may be tolerated. Mechanical
aerator is not suitable for extended aeration type
SECTION 11375N
Page 38
Previous Page
