Regulation 12 of MARPOL Annex I was revised in 2011 prohibiting sludge discharge connections to the oily bilge water tanks, tank top or oily water separators for new vessels delivered after 1 January 2014. The same regulation has again been amended, now making it a retroactive requirement for all vessels irrespective of delivery date, effective form 1 January 2017.
By the new amendments to Annex I of MARPOL, all vessels are required to comply with this requirement not later than the first renewal survey carried out on or after 1 January 2017. It is however anticipated that most vessels constructed after 31 December 1991 already comply as there has been a MARPOL Unified Interpretation ever since, prohibiting interconnections between sludge and bilge systems.
These amendments imply that sludge tanks cannot have any discharge possibilities to the bilge system or tank top, besides the following exemptions:
- Sludge tank(s) may be fitted with drains, with manually operated self-closing valves and arrangements for subsequent visual monitoring of the settled water, that lead to an oily bilge water holding tank or bilge well, or an alternative arrangement, provided such arrangement does not connect directly to the bilge discharge piping system.
- The sludge tank discharge piping and bilge-water piping may be connected to a common piping leading to the standard discharge connection referred to in regulation 13; the connection of both systems to the possible common piping leading to the standard discharge connection referred to in regulation 13 shall not allow for the transfer of sludge to the bilge system.
Visual monitoring should preferably be by a hopper, or alternatively a sight glass; see Figure 1.
A screw down non-return valve in lines connecting to the standard discharge connection, provides an acceptable means for not allowing for the transfer of sludge to the bilge system, see Figure 2.
Ship operators and managers should before the first IOPP renewal survey, ensure that such systems are compliant, and if in doubt contact DNV GL. In the event that modifications are required, system drawings will be subject to approval.