Sustainable cleaning strategies for naval tanks and traceability of wastewater according to international regulations

by Marco Arezio

The sea is not only the primary transportation route for goods and raw materials but also a complex ecosystem that must be protected with all available resources. In this context, cleaning naval tanks becomes a crucial step for both environmental protection and the safety of onboard operators. When oil tankers, chemical carriers, or other cargo ships are unloaded, carrying substances such as oily residues, chemicals, biological remnants, or industrial sludge, the internal walls may retain potentially polluting or hazardous traces. Cleaning these surfaces and disposing of the resulting waste in compliance with legal requirements is not a luxury but a necessity.

International regulations, including the IMO's MARPOL 73/78 Convention, strictly govern the treatment of onboard waste, imposing stringent procedures to minimize impacts on the marine environment. Under MARPOL Annexes I and II, shipowners and operators are required to follow specific standards for cleaning holds and tanks while ensuring that the effluents resulting from the cleaning process are properly traced and disposed of. Additionally, each state can impose further regulations aligned with European and national directives on hazardous waste management, including coding systems (CER) and documentation requirements.

Characteristics of Residues and Risk Assessment

Inside the tanks, even after a complete discharge of the cargo, residues and encrustations of various types can remain: petroleum or fuel oils, chemical solvents, contaminated aqueous emulsions, and solid sludge. These materials pose specific risks to health (toxic vapors, irritants), safety (potentially explosive atmospheres), and the environment (threats to marine biodiversity in case of spills).

Before initiating any cleaning activities, the type and associated hazards of the substances must be assessed by collecting safety data sheets and technical details of the previous cargo. This preliminary phase determines the cleaning method and protective equipment to be used. Additionally, air monitoring in the tank is conducted to measure oxygen levels and concentrations of flammable or toxic gases (e.g., H₂S, benzene).

Preparing the Intervention: Ventilation, Inerting, and Safety

One of the most delicate operations is ensuring the safety of the work environment. Since naval tanks are confined spaces, forced ventilation is carried out before personnel entry to reduce harmful vapors and bring oxygen levels to acceptable values. In high-risk situations, inerting, which involves introducing an inert gas (usually nitrogen), is performed to eliminate the risk of explosions.

At the same time, operators prepare by equipping themselves with suitable Personal Protective Equipment (PPE): respiratory masks with specific filters or self-contained breathing apparatus (SCBA), disposable suits resistant to aggressive chemicals, suitable gloves, and anti-slip, anti-static footwear. These meticulous precautions significantly reduce the risks of intoxication, chemical burns, or accidents caused by flammable vapors.

Cleaning Methods: Hot Water, Detergents, and Robotic Technologies

The choice of cleaning technology depends on the nature of the residues and the size of the tank. High-pressure hot water is the most common solution for removing oily encrustations and surface deposits. In some cases, detergents or emulsifying solvents are used to dissolve particularly stubborn substances that water alone cannot eliminate.

In certain operations, especially on oil tankers with large tanks, rotating heads that evenly distribute pressurized jets are installed. In other contexts, robotic systems or mechanical arms are employed. These automated solutions reduce direct exposure for operators while increasing the speed and precision of the cleaning process.

Managing Liquid and Solid Waste: Storage, Transport, and Disposal

The most critical phase, in terms of environmental impact and regulatory compliance, is waste management. Washing water mixed with hydrocarbon residues or chemical substances becomes a potentially hazardous liquid waste, classified under CER codes or MARPOL Annexes. After cleaning, this mixture is collected in temporary tanks or certified drums, labeled with the content and the date of collection.

If the ship is equipped with water/oil separators, part of the distinction between aqueous and oily fractions occurs onboard, reducing the volume of waste sent to onshore facilities. However, the decisive step occurs in port, where specialized companies handle the transportation of waste to authorized incineration or recovery centers.

The oily fraction can sometimes be regenerated into new lubricating bases or industrial fuels. Similarly, contaminated waters are treated in physico-chemical or biological purifiers until they meet parameters suitable for potential reuse. Solid waste, such as removed encrustations, absorbent cloths, and protective filters, follows a documented path of storage and disposal. Some materials, once stripped of their most polluting components, can even re-enter recycling or recovery processes, fostering a circular economy.

Traceability and Certifications: From the Garbage Record Book to Final Analyses

To prevent illegal dumping or discharge of waste into the sea, traceability remains a fundamental requirement. Ships subject to MARPOL must maintain a Garbage Record Book, documenting the type, quantity, and destination of all discharged waste. Every step, from tank collection to disposal facility, is formalized with recognized forms and periodic inspections by maritime and environmental authorities.

Specialized operators and contractors then provide shipowners with certificates of proper disposal, certifying that the waste was managed in compliance with legal obligations. For particularly hazardous materials, chemical analyses are conducted before and after the treatment process to ensure maximum environmental safety.

Conclusions: Circular Economy and Innovative Perspectives

Implementing precise cleaning procedures and a transparent system for managing maritime waste is not just about compliance with stringent regulations; it represents a concrete commitment to protecting the marine ecosystem. Beyond minimizing immediate risks to the health of operators, it opens up opportunities to valorize waste as a resource—turning spent oils into recovered products, treating contaminated waters for reuse, and reintegrating solid materials into recycling circuits.

Robotic technologies and the use of advanced sensors for continuous monitoring of gases and environmental parameters optimize intervention times and reduce human exposure. The adoption of innovative solutions, combined with continuous training of onboard personnel, paves the way for sustainable evolution in the maritime sector. Only in this way can we secure a future where the global economy does not further burden marine resources and those who work daily in this environment.

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