MARPOL restrictions on waste oil from bilges and tank washings being discharged into the sea are mostly covered by two resolutions emanating from MEPC 49 held in June 2003. These are 107(49) covering bilge waste on most ship types and 108(49) covering tank washings from oil tankers of 150gt and above. The latter was amended by MEPC resolution 240(65) to take account of the specific characteristics of some cargoes containing biofuels.
The equipment used for treating the oily waste is basically the same but whereas the oil content limit for discharging bilge water for non-tankers is set at 15ppm to be monitored and measured using an oil content monitor (OCM), tankers must install more sophisticated equipment generally referred to as ODME (oil discharge monitoring equipment)
An ODME will use the same technologies for measuring oil content as an ODME but as well as monitoring oil content in the discharge flow, it must also ensure that the rate of discharge of oil is limited to 30 litres of oil per nautical mile regardless of ship size and the total quantity of discharge must not exceed 1/30000 of the total quantity of the cargo from which the residue was formed. The additional requirements mean that as well as the OCM, an ODME will need:
- a flow meter to measure the rate of discharge,
- a computing unit to calculate the oil discharge in litres/nautical miles and the total quantity, along with the date and time identification and
- a control valve to stop discharge when the permissible limit has been reached.
There are other restrictions on discharge beyond those mentioned above and these require that the vessel must be underway, it should not be in any special area where discharge is prohibited, and it must be 50 nautical miles away from any land. These restrictions should be monitored and recorded utilizing a GPS input to the data and the record of ODME operation must be retained on board for a minimum of three years.
The limit on discharge rate does mean that vessels which are slow moving may reach the 30l/NM limit frequently and have to interrupt treatment. Furthermore, if the waste is particularly high in oil content, the limit of 1/30,000 of the cargo might also be reached and any excess either retained on board and treated after discharging a subsequent cargo or else discharged ashore.
IMO guidelines require that the accuracy of the oil content monitoring element of ODMEs should be verified at IOPP renewal surveys and a calibration certificate attesting to that should be retained on board for inspection purposes. Most system makers have facilities for recalibrating their products with some offering better services than others.
There are some differences in interpretation of the guidelines but many cargo owners and charterers are strict on ships carrying their cargoes ensuring that equipment is always fully compliant and functional.
As a leading manufacturer of ODME equipment, Rivertrace offers a flexible bespoke solution to suit operator needs. This includes the following value-added services:
- Calibration Check Certificates issued by approved representatives
- Free to use RT Connected Portal to track monitors and automate reminders
- Calibrated SMART CELL exchange schemes
- Fixed annual maintenance charges so no hidden costs
Biofuel increase needs care
The MEPC 240(65) amendment to 108(49) was required because of the new biofuels being carried in product tankers. To meet these new requirements which became effective on 1 January 2016, ODMEs needed to be type-approved to the new standard for affected ships. Ships that were not intending to carry any of the five bio-fuel blends identified in MEPC 240(65) could continue with their existing ODME equipment. As ODME makers reacted to the new requirement most systems available now are type approved to meet the newer requirement.
Today the use of biofuels is accelerating in many industries and in recent months reports of ships trialling new biofuels have appeared with growing regularity. Biofuel use ashore for automotive and power production is nothing new but as it is now considered by many countries as a renewable and carbon neutral source of energy its use is bound to grow further.
The energy crisis that began in 2021 has actually resulted in an increase in crude oil cargoes being moved around the globe but the trend does appear to be for biofuels to take an increasing role in the future. If as expected, crude cargoes decline in quantity it would not be unreasonable to expect that some ships currently engaged in carrying crude will switch to carrying biofuels.
This would potentially mean that existing ships that do not have an ODME type-approved to MEPC 240(65) would need to upgrade. In addition, as grades of biofuels change over time, it might be expected that IMO guidelines and rules around their carriage will need to be amended. It could be that such changes will require modifications to ODMEs. If and when such changes occur it would be a wise precaution for ships with older equipment to seek advice from the maker of the ODME to ensure that it remains compliant with MARPOL regulations.