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MERC STDN Test Plan
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2. Treatment to be Evaluated
The STDN Ballast Water Treatment System (BWTS) applies established chlorination
technology to oxidize and disinfect aquatic invasive species (AIS). The BALPURE® BWTS ia
an electrolytic process for the on-site generation of dilute hypochlorite on demand without
storage during the ballasting operation and the neutralization of residual oxidants during the de-
ballasting operation. Sodium hypochlorite is generated by means of electrolysis of seawater. In
this process, seawater flows through the electrolytic cells in a ratio of 1 part for every 100 parts
of ballast water. The system can operate effectively in brackish water to 15 PSU. Because the
amount of seawater required to effectively treat ballast water is small even fresh water ballast
can be treated by BALPURE® BWT with supplemental salt or stored seawater in designated
ballast tanks such as aft peak tanks. The current passing through the seawater causes the salt
(NaCl) and water (H
2
O) to form sodium hypochlorite (NaOCl) and hydrogen (H
2
) as a secondary
by-product. Hypochlorite solution and Hydrogen are produced and separated immediately upon
exit from the electrolytic cells. The weak hypochlorite solution (1 g/L) is injected back into the
ballast stream. Hydrogen that is separated from the hypochlorite is immediately diluted to less
than 1% hydrogen by forced air blowers and discharged to a safe location. The hypochlorite is
generated automatically on demand and is matched to the ballast flow rate and the oxidant
demand of the ballast water. Initial oxidant concentration is dosed at 1.5 times the TOC
concentration which remains effective for several days. To minimize potential regrowth of
(micro) organisms a background level of chlorine is maintained (1 mg/L) until discharge. This
will affect toxicity and by-product concentrations at compulsory sampling at day 1 and day 3 of
the tests. To reduce potential toxic effects of the chlorine at discharge sodium sulfite or bisulfite
is added prior to discharge. Sulfite when reacted forms sulfate which is present in seawater at
concentrations 4,000 times stronger than the treated ballast water.
For this land based test, the water is filtered through a 40 micron BallastSafe™ BSFc
Automatic Electric Filter, Model BSFc-H-1.6 prior to treatment. The sintered stainless steel
screen technology enables it to remove zooplankton. BallastSafe’s filter features continuous
cleaning of large volumes of dirt during ballasting without interruption, and a reversible screw
system for smooth, reliable and rapid cleaning of the entire screen surface.
3. Overview of Test Facilities
Basic Approach:
The specific protocols described below are based on the IMO G8 guidelines and the US
Coast Guard supported ETV protocols under development. The fundamental approach of MERC
is to conduct independent, scientifically-sound, rigorous, and quality assured evaluations of
ballast water treatment systems. Therefore, MERC relies on challenging ambient conditions
found in the Chesapeake Bay, and does not artificially augment test waters in most evaluations,
to avoid artifacts and the potential to overestimation of system performance (see Table 1). For
example, rapid changes in physical conditions (such as salinity or total suspended solids) as
ambient organisms are being brought in with ballast water may cause significant mortality,