MERCER02-14
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Like all new investments in equipment, there are several aspects to consider prior to making a
final decision, including:
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Treatment flow capacity;
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Ease of use (level of expertise/training required);
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Consumables issues including costs, amounts required, risks to user, and storage;
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Initial investment/costs;
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Short and long-termmaintenance time and costs;
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Cost and availability of spare parts;
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Positive or negative effects on the system being treated (e.g., corrosion);
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Power requirements; and
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Permit requirements (in some cases).
This section and the case studies in Section 8, below, review traditional fouling control water
treatment options and present other options being used for ballast water treatment. Themajority
of information for Section 4 was gathered from reviews by Venkatesan and Murthy (2008),
Satpathy et al. (2010), Lloyds Register (2010), and the EPA Science Advisory Board (2011), in
addition to severalwebsite resources.
4.1. Biocides
Biocide treatments introduce either an oxidizing or non-oxidizing chemical into water to
disinfect, inactivate or kill aquatic organisms. In general, oxidizing agents disrupt the organism's
cell structure, while non-oxidizing agents typically disrupt cell functions such as metabolism or
reproduction. The dose and time requirements to kill organisms, and the time required for
chemical degradation, is determined by the specific organisms being treated and local water
quality conditions (i.e., salinity, temperature, pH and organic concentrations).
4.1.1. OxidizingAgents
An oxidizing agent (also called an oxidizer or oxidant) is a chemical compound that readily
transfers oxygen atoms. Oxidizing agents disrupt an organism's cell structure. They are very
effective, but human/environmental hazards and EPA discharge regulations must be considered.
It is important to understand the changing oxidant demand conditions of the water being treated
(e.g., particulate and dissolved organic levels) to optimize dose (i.e., avoid under- and over-
dosing). In some cases, treatments employing oxidants may also need to include chemical
neutralization (e.g., sulphite or bisulphate) prior to discharge tomeet discharge requirements and
avoid environmental impacts.
4.1.1.1. Sodium hypochlorite (inline/onsite electrolysis or liquid injection, commercially
available for fouling prevention)
Chlorine is currently the most common method for controlling biofouling in water and
wastewater treatment facilities, as well as in industrial uses. Sodium hypochlorite is by far the
most common chlorination compound employed. Other forms include chlorine gas and chlorine
dioxide, which are described below. Treatment systems typically use either liquid injection or
electrochlorination (i.e., electrolysis). Like all biocides, the production of disinfectant by-
