Section 139.18 - Exhaust gas emission control systems(a)Applicability. The requirements in paragraphs (b) through (d) of this section apply to discharges from the operation and cleaning of any exhaust gas cleaning system (EGCS) and exhaust gas recirculation (EGR) system.(b)Discharge requirements. Unless excluded in paragraph (c) of this section, any discharge identified in paragraph (a) of this section must meet the following discharge requirements.(1)pH.(i) The discharge must meet one of the following requirements:(A) The discharge must have a pH of no less than 6.5 as measured at the vessel's overboard discharge point with the exception that during maneuvering and transit, the maximum difference of two pH units is allowed between inlet water and overboard discharge values; or(B) The pH discharge limit is the value that will achieve a minimum pH of 6.5 at 4 meters from the overboard discharge point with the vessel stationary. This overboard pH discharge limit is to be determined at the overboard discharge monitoring point and is to be recorded as the vessel's discharge limit. The overboard pH limit can be determined either by means of direct measurement, or by using a calculation-based methodology (computational fluid dynamics or other equally scientifically established empirical formulas).(ii) The pH numeric discharge standard may be exceeded for up to 15 minutes in any 12-hour period.(2)PAHs (Polycyclic Aromatic Hydrocarbons).(i) The maximum continuous PAH concentration in the discharge must be no greater than 50 [MICRO]g/L PAHphe (phenanthrene equivalents) above the inlet water PAH concentration. This standard applies downstream of any washwater treatment equipment including any reactant dosing unit but upstream of any seawater addition for control of pH prior to discharge.(ii) The 50 [MICRO]g/L numeric discharge standard is normalized for a discharge flow rate, before any seawater neutralization for pH control, of 45 tons (t)/megawatt-hour (MWh) where the mega-watt (MW) refers to the Maximum Continuous Rating (MCR) or 80% of the power rating of the fuel oil combustion units whose EGCS discharge water PAH is being monitored at that point. In cases where sensors are installed in a separate measurement cell, the PAH limit applies to the flow in the main discharge pipe from which the water is bypassed. This numeric discharge standard is adjusted upward or downward for different discharge flow rates, pursuant to table 1 to paragraph (b)(2)(ii) of this section. Table 1 to Paragraph (b)(2)(ii)
| Discharge water flowrate before any seawater addition for pH control (t/MWh) | Numeric discharge standard ([MICRO]g/L PAHphe equivalents) | Measurement technology |
| 0-1 | 2,250 | Ultraviolet light |
| 2.5 | 900 | - ' - |
| 5 | 450 | Fluorescence a |
| 11.25 | 200 | - ' - |
| 22.5 | 100 | - ' - |
| 45 | 50 | - ' - |
| 90 | 25 | - ' - |
a For any Flow Rate greater than 2.5 t/MWh, Fluorescence technology must be used.
(iii) The continuous PAHphe numeric discharge standard may be exceeded by 100% for up to 15 minutes in any 12-hour period.(3)Turbidity/suspended particulate matter.(i) The washwater treatment system must be designed to minimize suspended particulate matter, including but not limited to heavy metals and ash.(ii) The maximum continuous turbidity in the discharge must be no greater than 25 FNU (formazin nephlometric units) or 25 NTU (nephlometric turbidity units) or equivalent units above the inlet water turbidity. However, to account for periods of high inlet turbidity, readings must be a rolling average over a 15-minute period to a maximum of 25 FNU or NTU. This standard applies downstream of any washwater treatment equipment including any reactant dosing unit but upstream of any seawater addition for control of pH prior to discharge.(iii) For an aggregated 15-minute period in any rolling 12-hour period, the continuous turbidity discharge limit may be exceeded by 20%.(4)Nitrates plus nitrites:(i) The washwater treatment system must prevent the discharge of nitrates plus nitrites beyond that associated with a 12% removal of NOX from the exhaust, or beyond 60 mg/L normalized for a discharge rate of 45 tons/MWh, whichever is greater, where the MW refers to the MCR or 80% of the power rating of all those fuel oil combustion units whose EGCS discharge water nitrates plus nitrites are being monitored at that point. This standard applies downstream of any washwater treatment equipment including any reactant dosing unit but upstream of any seawater addition for control of pH prior to discharge. The 60-mg/L limit is adjusted upward for lower washwater flow rates per MWh, and vice-versa, and the applicable permit limits are contained in table 2 to paragraph (b)(4)(i) of this section. Table 2 to Paragraph (b)(4)(i)
| Discharge water flowrate before any seawater addition for pH control (t/MWh) | Numeric discharge standard (mg/L nitrate + nitrite) |
| 0-1 | 2,700 |
| 2.5 | 1,080 |
| 5 | 540 |
| 11.25 | 240 |
| 22.5 | 120 |
| 45 | 60 |
(5)Discharge water from temporary storage:(i) pH. See § 139.18(b)(1).(ii) PAH. Maximum of 50 [MICRO]g/L PAHphe before any addition of seawater (or similar) for control of pH.(iii) Turbidity. Not greater than 25 FNU or 25 NTU or equivalent units, before any addition of seawater (or similar) for pH control.(6)Treatment Residuals: Discharges of sludge or residues generated from treatment of EGCS or EGR washwater or bleed-off water are prohibited.(c)Exclusion. For a vessel operating on fuel that meets the sulfur content limits specified in Regulation 14 of MARPOL Annex VI, discharge of EGR bleed-off water is excluded from paragraph (b) of this section if the vessel: (1) Does not retain the EGR bleed-off onboard in a holding tank prior to discharge, and(d)Prohibition. For a vessel not operating on fuel that meets the sulfur content limits specified in Regulation 14 of MARPOL Annex VI, discharge of EGR bleed-off water which is retained in a holding tank is prohibited unless the vessel: (3) In compliance with the discharge standard in paragraph (b) of this section.