Waste water from ships (black and grey water)
Water is important for ships being used for cleaning and cooling and machinery, hold washing and of course providing the necessities of life for the crew and passengers. The latter use of water produces two distinct streams of waste water commonly referred to as black and grey water. Black water is sewage while grey water is general cooking and cleaning waste.
On a global scale, of these two waste types only sewage is subject to regulation and Annex IV of MARPOL is where the international regulations can be found. In addition to the international standard, some jurisdictions also regulate sewage discharges. In the US, specific waters are designated as no discharge zones (NDZs) where sewage discharges are prohibited. There are no international rules applying to grey water although some contend that the chemicals used in laundry, dishwashing and cleaning can be as hazardous to the marine environment as sewage.
The waste water from cleaning and cooling machinery may be contaminated by oily wastes and its disposal is regulated under MARPOL Annex I and is covered HERE. Not envisaged when MARPOL was first formulated, there is another type of waste water which is not yet regulated and that is the wash water from scrubbers after any hazardous sludge has been removed. Finally there is water used for hold cleaning and tank washing which may or may not be subject to special requirements.
MARPOL Annex IV has been in force since September 2003, and applies to ships of 400gt and above and ships below 400gt that are certified to carry more than 15 persons. It contains a set of regulations regarding the discharge of sewage into the sea, ships’ equipment and systems for the control of sewage discharge and requirements for survey and issuance of the International Sewage Pollution Prevention Certificate (ISPP) that all ships subject to the regulation must carry.
Under MARPOL the discharge of sewage into the sea is prohibited, except when the ship has in operation an approved sewage treatment plant or when the ship is discharging comminuted and disinfected sewage using an approved system at a distance of more than three nautical miles from the nearest land; sewage which is not comminuted or disinfected has to be discharged at a distance of more than 12 nautical miles from the nearest land.
Since Annex IV came into effect it has been altered a number of times introducing more stringent requirements each time and designating some Special Areas where discharge is either prohibited or more controlled. The rules also require a particularly low limit of residual chlorine to protect the marine environment and aquatic life from the side effects of sewage treatment.
In July 2011, IMO adopted the most recent amendments to MARPOL Annex IV which entered into force on 1 January 2013. The amendments introduce the Baltic Sea as a special area under Annex IV and add new discharge requirements for passenger ships while in a special area.
The equipment required on board ships subject to Annex IV is detailed in Regulation 9. Prior to the 2011 amendments, only paragraph 1 was in force with paragraph 2 being added in 2012.
1. Every ship which, in accordance with regulation 2, is required to comply with the provisions of this Annex shall be equipped with one of the following sewage systems:
1. a sewage treatment plant which shall be of a type approved by the Administration, taking into account the standards and test methods developed by the Organization*, or
2. a sewage comminuting and disinfecting system approved by the Administration. Such system shall be fitted with facilities to the satisfaction of the Administration, for the temporary storage of sewage when the ship is less than 3 nautical miles from the nearest land,
or 3. a holding tank of the capacity to the satisfaction of the Administration for the retention of all sewage, having regard to the operation of the ship, the number of persons on board and other relevant factors. The holding tank shall be constructed to the satisfaction of the Administration and shall have a means to indicate visually the amount of its contents.
* Refer to the Recommendation on International effluent standards and guide lines for performance tests for sewage treatment plants adopted by the Organization by resolution MEPC.2(VI). For existing ships national specifications are acceptable.
2. By derogation from paragraph 1, every passenger ship which, in accordance with regulation 2, is required to comply with the provisions of this Annex, and for which regulation 11.3 applies while in a special area, shall be equipped with one of the following sewage systems:
.1 a sewage treatment plant which shall be of a type approved by the Administration, taking into account the standards and test methods developed by the Organization, or
.2 a holding tank of the capacity to the satisfaction of the Administration for the retention of all sewage, having regard to the operation of the ship, the number of persons on board and other relevant factors. The holding tank shall be constructed to the satisfaction of the Administration and shall have a means to indicate visually the amount of its contents.”
As can be seen from Regulation 9, the approval of sewage treatment plants is left to the flag state. The new paragraph 2 removed one of the previous sewage treatment options permitted to ships operating in the Baltic and also introduced new performance standards for treatment plants. In October 2012, The MEPC adopted the 2012 Guidelines on implementation of effluent standards and performance tests for sewage treatment plants.
The new standards were intended apply to new passenger ships from 1 January 2016 and for existing passenger vessels from January 2018. However a study conducted in 2014 on the provision of reception facilities in the Baltic Sea region concluded that the situation was inadequate and that compliance would be extremely difficult. As a consequence the IMO decided at MEPC 68 to postpone the ban on discharge at sea. The new dates are 1 January 2019 for new ships and 1 January 2021 for existing vessels although existing vessels transiting the area and not calling at ports within it are allowed a further extension to 2023.
In the special area, the discharge of sewage from passenger ships will generally be prohibited unless the ship has in operation an approved sewage treatment plant that meets the applicable additional effluent standards for nitrogen and phosphorus in accordance with the 2012 Guidelines on implementation of effluent standards and performance tests for sewage treatment plants (resolution MEPC.227(64)).
An MEPC resolution adopting the effective dates encourages member governments (port and flag states), industry groups and other stakeholders to comply immediately on a voluntary basis with the Special Area requirements for the Baltic Sea Special Area. Treatment options
Concurrent with the development of MARPOL, the US was introducing its own regulations in the form of the Clean Water Act (CWA) passed by the US Congress in 1972 and covering cleaning up the territorial waters of the US. This was done through the National Pollutant Discharge Elimination System (NPDES) permit programme which controls water pollution by regulating sources that discharge pollutants into the nation’s waters. In most cases, the NPDES permit program is administered by individual states but for matters extending beyond individual states, the Environment Protection Agency (EPA) is the governing body.
Section 301(a) of the CWA prohibits the discharge of any “pollutant” unless authorised by an NPDES permit. Shortly after the enactment of the CWA, the EPA issued a regulation that exempted from NPDES permitting “any discharge of sewage from vessels, effluent from properly functioning marine engines, laundry, shower, and galley sink wastes, or any other discharge incidental to the normal operation of a vessel”.
After the turn of the century, environmentalists began legal actions in some states demanding ships should not be exempted from the regulations. In December 2003, the California federal district and appeals courts ruled that the EPA had exceeded its authority when it excluded ships’ discharges from the NPDES permitting system.
As a consequence EPA had to implement a permit system for a wide variety of vessel discharges which would affect all US-flagged vessel and foreign-flagged vessels trading to the US. This resulted in the introduction in 2008 of the Vessel General Permit (VGP) that would apply to all affected vessels whose owners filed a Notice of Intent.
A VGP provides ‘NPDES permit coverage nationwide for discharges incidental to the normal operation of commercial vessels greater than 79 feet (24m) in length’. In 2013, a new version of the VGP was introduced which will run until 18 December 2018. This permit regulates 27 specific discharge categories and also provides for improvements to the efficiency of the permit process, and clarifies discharge requirements.
The following links to the US EPA website will allow readers to investigate the requirements of the current VGP https://www.epa.gov/npdes/over... and https://www.epa.gov/npdes/vess... EPA has also amended several of the VGP’s administrative requirements, including allowing electronic recordkeeping, requiring an annual report in lieu of the one-time report and annual non-compliance report, allowing combined annual reports for some vessel operators.
Under US regulations, sewage treatment plants are referred to as Marine Sanitation Devices and as with MARPOL it is the results that matter and not the method of treatment. However, the US rules do recognise three basic MSD types of which one is only permitted for small vessels.
Blackwater choices and technology
There is plenty of choice both in numbers of suppliers and in the technologies and treatment methods used. Systems for treating sewage employ methods ranging from those based on physical or chemical separation to biological and electrolytic treatment systems.
Not surprisingly because the objective is to destroy harmful bacteria in sewage many of the treatment methods employed are the same as those used in ballast water treatment systems. As well as biological treatment, hypochlorination and UV are commonly employed. Some systems do not rely on a single method but combine methods to increase effectiveness. Membrane bio-reactors are also popular.
Biological treatment involves the breakdown of sewage in an organic process. The following is a description of the RWO CleanSewage system:
As a first step the sewage is separated from heavier solids and particles causing clogging or damages in further process steps. In the Moving-Bed Biofilm Reactor (MBBR) organic matter is degraded into carbon dioxide and water by microbial activity. Biofilm carriers inside are clustered in cages, which significantly eases handling and maintenance. Aeration stabilises the biomass and prevents harmful and dangerous gases from forming.
In the Clarifier residual solids and suspended activated sludge are separated by sedimentation and turned back into the MBBR.
The clean sewage flows into the Disinfection chamber. Here a chlorine-based disinfection chemical is added. The clean water is then pumped overboard. To meet the limit values set for the chlorine content, a special neutralising agent, LC35, is dosed prior to the discharge pump.
Treated excess sludge, reduced in volume, can be discharged or collected in an external tank. Due to the biomass retained by the MBBR process, sludge discharge does not interfere with the performance of the plant.
A development of the biological process is the membrane bio reactor (MBR). These systems combine conventional biological treatment processes with membrane filtration to provide an advanced level of organic and suspended solids removal. In an MBR system, the membranes are submerged in an aerated biological reactor. The membranes have porosities ranging from 0.035 microns to 0.4 microns (depending on the manufacturer), which is considered between micro and ultrafiltration.
This level of filtration allows for high quality effluent to be drawn through the membranes and eliminates the sedimentation and filtration processes typically used for wastewater treatment. This reduces the process tankage required.
Greywater – unregulated but still an issue
Greywater issues have remained largely absent from the maritime conscience, perhaps due to the rather more obvious and immediate effects of blackwater. But greywater can pose equally difficult challenges, particularly if a dangerous chemical finds its way into a sink, laundry or shower system. Greywater has managed to creep under the regulatory radar, mostly because it has a tenth of the levels of nitrogen and pathogens that appear in sewage and decomposes more rapidly.
But due to the high volume of untreated greywater produced by the ever-increasing number of passenger cruise ships and ferries, manufacturers have developed systems aimed at greywater treatment. The development of greywater-oriented systems has also come about because of the need to establish ways to effect the complete degradation of organic matter found in greywater, including fat and grease. Many manufacturers are active in the sector and again a variety of technologies are employed. In order to remove fat and grease, some systems make use of separation technology similar to that used for treating oily bilge water and described in more detail in the following chapter.
It is not unknown for black and grey water to become mixed due to operational reasons such as use of wrong tanks or when one tank becomes full and the only space available is in the other system’s holding tank. In 2012 at IMO MEPC 64, the delegation of the Netherlands informed the Committee of some preliminary results on a survey conducted on the performance status of the sewage treatment plants installed on board ships, which indicated that a vast majority of the equipment did not meet the existing sewage treatment standards due to improper use of detergent, lack of maintenance or not following the operational instructions. Revelations such as this can mean a concerted inspection campaign will be initiated by PSC regimes.
Although MARPOL does not regulate grey water, some other national and state bodies do. Regional rules vary and change frequently. In Alaska, stringent limits regarding cruise ship discharges were introduced in 2000 (33CFR159 sub-part E) with grey water regulated for the first time.
In addition to Alaska’s clean-up efforts, the Great Lakes, US waters (EPA Vessel General Permit, 2013), and inland waterways in Europe (2012/49/EU) have also regulated grey water treatment in various shapes and forms, each affecting certain shipping sectors. There are already four sets of different type approval specifications and at least five different compliancy regimes for operators and equipment makers to contend with. Some equipment makers have developed treatment systems that can handle both black and grey water. These systems ensure compliance with regulations and also save space as there is no need to duplicate equipment.