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TRO (Total Residual Oxidants) in Ballast Water Treatment

Total Residual Oxidants (TRO) refer to the amount of chlorine and other oxidants in treated ballast water. TRO sensors ensure Ballast Water Treatment Systems (BWTS) meet IMO and Vessel General Permit (VGP) discharge standards, measuring residuals in mg/L of chlorine as Cl₂.

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TRO Monitoring & Calibration

TRO sensors play a key role in oxidant-based BWTS by:

• Monitoring dosage levels for proper treatment.

• Measuring discharge concentrations to ensure compliance.

• Preventing excess residual oxidants that require neutralization.

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The EPA mandates a maximum TRO discharge of ≤ 0.1 mg/L, with variations in some states. TRO reagent kits, used for accurate measurement, require replacement every 90 days and full replenishment annually.

TRO calibration ensures sensor accuracy by comparing readings with a standard solution. Proper calibration prevents compliance failures and ensures operational reliability.

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Regulatory Requirements

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VGP (2013) and IMO guidelines require:

• Annual calibration of all BWTS sensors, with more frequent checks for TRO, pH, and DO probes.

• Onboard or manufacturer-conducted calibration, depending on the system.

• Mandatory TRO sensor functionality—if sensors fail, ballast discharge is prohibited.

• Annual functional tests for automated BWTS shutdown systems.

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Articob – Your Global TRO Calibration Partner​

At Articob, we provide TRO and BWTS calibration for all major brands, ensuring compliance with IMO, EPA, and VGP regulations.

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Why choose ARTICOB?

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• Ensure compliance & environmental safety

• Prevent costly fines & violations

• Extend BWTS lifespan with proactive maintenance

• Optimize system efficiency

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For expert TRO calibration, contact Articob today to schedule a service at your next port of call!