Biological Control - Baltimore Aircoil Company 3000 Series Operating And Maintenance Instructions Manual

1. The chemicals must be compatible with the unit
construction (zinc coated) steel as well as all other
materials used in the system (pipe, heat exchanger, etc.)
2. Chemicals to inhibit scale and corrosion should be
added to the re-circulating water by an automatic feed
system on a continuously metered basis. This will pre-
vent localized high concentrations of chemicals, which
may cause corrosion. It is recommended the chemicals
be fed into the system at the discharge of the

Biological Control

Bleed-off with or without chemical treatment for scale and
corrosion control is not adequate for control of biological
contamination. The growth of algaes, slimes and other
micro-organisms, if unchecked, will reduce system effi-
ciency and may contribute to the growth of potentially
harmful micro-organisms, including Legionella, in the
recirculating water system.
Accordingly, a biocide treatment program specifically
designed to address biological control should be initiated
when the system is first filled with water and administered
on a regular basis thereafter in accordance with the sup-
plier's instructions. Liquid biocides may be added to the
basin of the cooling tower in dilute form. If a solid form of
biocide is used, it should be added to the system via a
pot feeder. If ozone water treatment is used, ozone
concentrations should not exceed 0.1–0.5 ppm in
order to ensure maximum equipment life.
B.A.C. offers a simple, easily applied, low maintenance
form of biological control, the IOBIO
Algae Control. The control is easy to use and requires
little maintenance. By delivering low concentrations of
iodine through the make-up water line, the IOBIO
Control automatically controls unwanted microbiological
contaminants in the open wet system. Contact your local
B.A.C. Representative for more information.
Start-up Following a Shut-Down Period
To minimize the risk from biological contamination fol-
lowing a shut-down period, it is strongly recommend-
ed that the entire system (cooling tower, system pip-
ing, heat exchangers, etc.) be drained when the sys-
tem is to be shutdown for more than 3 days. To
resume operation of a drained system, clean all debris,
such as leaves and dirt from the cooling tower and re-fill
the system with fresh water. While operating the circulat-
ing pump(s) and prior to operating the cooling tower
fans, execute one of the following two alternative biocide
treatment programs:
® Bacteria, Slime and
®
re-circulating pump. They should not be batch fed
directly into the cold water basin.
3. Acid water treatment is not recommended unless
the unit(s) have been furnished with the BALTIBOND
Corrosion Protection System or is constructed of
stainless steel — in which cases acid treatment can be
used provided the requirements of paragraph 1 and 2
above are maintained.
1. Resume treatment with the biocide, which had been
used prior to shutdown. Maintain the maximum recom-
mended biocide residual (for the specific biocide) for a
sufficient period of time (residual and time will vary with
the biocide) as recommended by the water treatment sup-
plier to bring the system under good biological control.
2. Check the pH of the circulating water and, if necessary,
adjust it to 7.0 to 7.6. Then treat the system with sodium
hypochlorite to maintain a level of 4 to 5 mg/l (ppm) free
chlorine over a six (6) hour period. Test kits that can be
used to measure the free residual of chlorine are commer-
cially available.
When it is not practical to drain the system during shut-
down periods, a by-pass line with shut-off valves should
be installed to permit the cooling water to be circulated
throughout the system, including the tower basin, while
by-passing the tower fill. Then, after each shut-down of
three (3) days or more, the system should be treated prior
to restarting the tower using one of the two methods
described above. However, while circulating the treated
cooling tower water through the entire system, the
cooling tower fill should be by-passed and the tower
fans kept inoperative. After the biocide residual has been
maintained at the required level for at least six (6) hours,
the water can be directed over the fill and the tower
returned to service. The standard water treatment program
(including the biological treatment) should be resumed at
this time.
For specific recommendations on treatment for scale,
corrosion, or biological control, consult a qualified
water treatment consultant.
®
11