Turbidity is a measure of the degree to which the water looses its transparency due to the presence of suspended particulates. The more total suspended solids in the water, the hazier it seems and the higher the turbidity [11].

There are various parameters influencing the turbidity of water, including: [11]

• Phytoplankton (microscopic algae)
• Algal blooms
• Sediments from erosion
• Re-suspended sediments from the bottom
• Waste discharge
• Urban runoff

When combined with PAH, turbidity measurement is an effective means of continuously monitoring online the effective performance of the wash water treatment plant.

IMO has set turbidity limits for wash water [10], however because the measurement may be affected by the turbidity of the water entering an exhaust gas cleaning system, a rolling 15-minute average of the difference between the water at inlet and discharge (before any dilution for pH correction) is allowed. A typical reason for the turbidity at inlet being high is sediment disturbance during shallow water manoeuvring.

Turbidity must be continuously measured online and data securely logged to confirm compliance with the IMO EGCS Guidelines.