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TRO stands for Total Residual Oxidants. The TRO sensor measures the amount of free chlorine or chlorine residual compounds present in the ballast water after it has been treated by the Ballast Water Treatment System (BWTS). The TRO sensor is used to evaluate the efficiency of the treatment process and to ensure that it meets the standards set by the International Maritime Organization (IMO) and VGP (Vessel General Permit) for ballast water discharge. TRO levels are measured in milligrams per litre (mg/L) of chlorine as Cl2.
TRO instruments are often used as part of the control systems for BWMS that employ oxidant-based treatments. Such TRO instruments are used to monitor dosage (to validate it meets treatment design requirements) and water discharge concentrations (to activate a neutralization step and/or ensure environmental safety). For example, the EPA requires a daily maximum TRO discharge concentration of ≤ 0.1 mg L-1, varying in some states. Accurate, precise and reliable measurements of TRO are therefore critical to verify the performance of oxidant-based BWMS and to assure ballast water discharge into the environment does not exceed the regulatory or target residual concentrations. If the residual concentration exceeds the limits, the ballast water requires additional testing.
Indicator reagents, generally known as TRO reagent kits, react with any oxidant, generally chlorine, to create a colour that the instrument measures and compares with a sample of water without reagents. The buffer reagent is required to control the sample pH to bring the sample to neutral. Such reagents are generally pre-hydrated and require little operator preparation. The reagents are usually packaged in plastic boxes and are sold as complete TRO kit products. Each 125 mL indicator requires the addition and mixing of a DPD powder contained in a separate bottle. This activates the reagent. The reagents should be replaced every 90 days even if they are not fully used. After one year all reagents should have been consumed and a replacement TRO reagent kit will be required. In this way, the accuracy of the information on the residuals in the water discharge is maintained.
TRO calibration refers to the process of adjusting and verifying the accuracy of a TRO sensor or meter in a BWTS. TRO calibration monitors that the sensor or meter measures the correct level of TRO in the ballast water and that the readings are accurate and reliably reflect the type-approved specification.
Calibration of the TRO sensor or meter is done by comparing its readings with a standard solution of known TRO concentration to adjust any discrepancies that may exist. The manufacturer or supplier of the sensor or meter usually provides this standard solution. The precision of the TRO sensor is essential in informing about the standard operation of the BWTS.
To comply with the latest Ballast Water Treatment regulations, it is important to guarantee your system is performing optimally. This is achieved by monitoring that your crew correctly operates the system according to the manufacturer’s instructions and that your BWTS is calibrated annually.
According to 184.108.40.206.1.1.2 Ballast Water Monitoring Equipment Calibration from Vessel General Permit Factsheet (2013): “All applicable sensors and other control equipment must be calibrated as recommended by sensor and equipment manufacturers, or by ballast water treatment system manufacturers or when warranted based on device drift from a standard or calibrated setting. At a minimum, all applicable sensors and equipment must be calibrated annually, however, EPA fully expects many sensor types (e.g., pH probes, TRO sensors, DO probes) will need to be calibrated on a more frequent basis.
The vessel owner/operator must do so if specified by the probe or ballast water treatment system manufacturer. Calibration of the sensors and equipment can be conducted onboard the vessel or they can be removed and shipped to the manufacturer for calibration. For some probes, vessel owners/operators may want to switch out electrodes more frequently, once every four months, to maximize the accuracy of their probes. During any period when the sensors are not installed and operating on the ballast water treatment system, the vessel must not discharge ballast water. Ballast water treatment systems that are equipped with automated control systems that initiate a sequence to stop the overboard discharge of the effluent in the event of alarm conditions must be subjected to an annual functional test. The detailed program for a functional test of such equipment is typically developed by the manufacturer, taking into account the features and functions of the specific design of the equipment and the operating and discharge conditions monitored. A copy of the functional test protocol must be carried aboard the vessel at all times.”
Mr. Marine Ballast performs both TRO and complete system calibration services for all leading brands and BWTS types. Such services are offered for individual vessels and complete fleets, depending on your requirements and the features of the BWTS. By ensuring the correct operation of your system, you minimize the risk of environmental damage through the discharge of water with high residual concentration and comply with the latest terms and regulations set forth. Furthermore, regular calibration and maintenance services can help prolong the life of your system and facilitate its operation at optimal levels. This can ultimately save you money in the long run by reducing the need for costly repairs or replacements. Additionally, it contributes to the optimal performance of the system.
Another important aspect of TRO monitoring is data management and analysis. The real-time information provided by TRO instruments can help to identify any issues or problems with the system early on, allowing for prompt and effective maintenance or repairs. Furthermore, TRO instruments can be integrated with information management systems, which can provide a historical record of the system’s performance, enabling the analysis of trends and patterns and providing valuable insights for future maintenance and upgrades.
Mr. Marine Ballast is your trusted global partner for TRO Calibration. Our certified technicians can calibrate any type of BWTS to facilitate your vessel’s compliance with the applied rules and limit the potential harmful water discharge. With a proven record of performance and worldwide experience, our team is your solution for TRO Calibration.
Contact our team for additional information. You can also review our FAQ blogpost about TRO.
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Mr. Marine trades under Mr. Marine Elevator, Mr. Marine Ballast and Mr. Marine Instruments & Controls. Our dynamic company aims at keeping vessels safe and compliant, anywhere in the world. With technical know-how, unparalleled spare part sourcing and 24/7 responsiveness, we are your global beacon.
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