A Comprehensive Guide to Sewage Treatment Plant on Ship
The impact of marine wastewater treatment plant effluent on the marine environment is a major concern. Seawater can be contaminated with harmful substances, including pathogens, nutrients, detergents, pesticides, and heavy metals. These contaminants pose a high environmental and health risk, especially since communities commonly use seawater for recreation, swimming, and food production. Improper treatment of ship wastewater can hurt marine ecosystems. Most ships have marine sanitation units designed to remove contaminants from wastewater before it is discharged into the sea.
The main function of marine wastewater treatment systems is to accelerate the natural water purification process. Primary wastewater treatment is primarily a physical process that removes solids from wastewater. Next, secondary wastewater treatment utilizes bacteria to break down organic matter. Finally, chlorination is used to disinfect the waste before it is discharged into the environment. However, potential contaminants such as heavy metals, nutrients, and non-biodegradable organic chemicals remain even after secondary treatment.
Advanced wastewater treatment (AWT) systems treat these residual contaminants. These systems are designed to remove improper disposal of materials by primary and secondary treatment. There are different types of advanced wastewater treatment systems (e.g., filtration, carbon absorption, distillation, or reverse osmosis), each with varying effectiveness, complexity, and cost depending on its size and design. Some of these systems are more proven than others, so choosing a treatment system is critical to ensuring minimal environmental impact.
What is the difference between Resolution MEPC 159(55) and Resolution MEPC 227(64)?
Resolution MEPC 227(64) effectively changed the discharge requirements and testing protocols MEPC 159(55) adopted in 2006. Its specific objectives are to reduce nitrogen and phosphorus in treated water and prevent accelerated growth of marine nitrates. The decision states that approved sewage treatment plants should not rely solely on effluent dilution. While dilution is required for the treatment process, waste standards must meet the more stringent standards set out in MEPC.227(64).
Marine sewage treatment plant (STP)
Principle – Marine sewage treatment plant Marine sewage treatment plant principle Naturally occurring (naturally present in wastewater). Most biological wastewater treatment systems in municipal applications use aerobic bacteria. This process was chosen because it has proven successful over decades and is more economical than other methods.
The main advantage of biological wastewater treatment processes is that microorganisms (primarily bacteria) can remove organic pollutants from domestic wastewater. These microorganisms can effectively reduce organic pollutants in domestic wastewater when the wastewater is placed in the right environment. The microorganisms use the organic pollutants in the wastewater as a source of energy (food) for their cellular activities (life).
The preferred microorganisms for wastewater treatment are aerobic bacteria that require oxygen. Aerobic bacteria quickly consume organic matter in the wastewater and release carbon dioxide and water vapor as byproducts of their respiration and synthesis processes. This does not cause odor or explosion risks.
If the air supply is cut off for twelve to thirty-six hours, the aerobic wastewater treatment process will become anaerobic. As the solids break down and decompose, the wastewater becomes sterile and black. The dissolved oxygen content gradually decreases, producing hydrogen sulfide, causing an unpleasant odor. However, after restoring the air supply, the process will return to an aerobic state within 12 to 24 hours.
Marine wastewater treatment plants utilize an aerobic biological treatment process called “extended aerated activated sludge” or “extended aeration”. The extended aeration treatment concept requires a wastewater treatment unit large enough to accommodate the average daily wastewater flow rate and aeration for 18 to 24 hours to maintain a substantially constant (wastewater) supply.
In this process, the number of bacterial cells exceeds the available food supply, causing some bacterial cells to starve and become food for the survivors. This process results in a reduction in the buildup of bacterial cell sludge in marine wastewater treatment units. In systems that do not use this process, bacteria are exposed to a continuous food supply, causing their numbers to increase to the point where sludge discharge and disposal are necessary.
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When the extended aeration process is used, the microorganisms or bacterial cell masses resulting from the cell proliferation are separated from the treated fluid before discharge and reintroduced with the incoming wastewater. This introduces a large population of active bacteria, which increases the removal rate of organic waste entering the system. This arrangement is known as the “activated sludge” process.
Due to the proven effectiveness of aerobic biological wastewater treatment, all redFox marine wastewater treatment plants utilize this principle.
Membrane Bioreactor (MBR)
Marine-membrane-biological-reactors Membrane bioreactor (MBR) systems use ultrafiltration or microfiltration membranes to separate solids from liquids. MBR wastewater treatment systems suit many building facilities and marine and land vessels. By current standards, MBR wastewater treatment plants are designed to treat all wastewater streams (black water – sewage and grey water from kitchens, sinks, showers, and laundry facilities). Microfiltration membrane filtration effectively removes particles, sediments, algae, protozoa, and bacteria from wastewater. Ultrafiltration technology goes a step further and eliminates colloidal particles and small viruses in addition to everything else treated by microfiltration.
Ultrafiltration membranes for wastewater treatment separate the smallest particles from liquids to colloids based on a specific pore size (<0.1 µm). The membrane captures these substances without changing their physical or chemical properties. This means that it cannot even produce hazardous materials. Many membrane bioreactor manufacturers use easy-to-use flat membranes made of organic polymers and advanced filter designs that prevent hair, fibers, or other unclean coarse matter from clogging the filter.
Proven membrane technology is available in different configurations depending on the required system capacity. Installing individual filters into existing and complex filter tank systems that connect aeration and filtration systems is also possible.
Marine wastewater treatment plants require a customized approach to meet the unique needs of your vessel. Contact Separator Spares & Equipment for the right marine wastewater treatment plant solution.
We specialize in spare parts, consumables, equipment, and services for Marine Sewage Treatment Devices (MSDs) and Marine Sewage Treatment Plants (STPs). Our commitment is to support your maintenance needs throughout the life of your vessel.
Common Terms and Definitions for Marine Wastewater Treatment Plants:
Activated Sludge: Activated sludge is a clumping biological culture formed in an aeration tank under controlled conditions and is usually brown. Activated sludge is also called waste-activated biosolids or waste-activated solids.
Aeration Tanks: Aeration tanks provide the required retention time and thoroughly mix the incoming activated sludge and wastewater.
Aerobic Wastewater Treatment: The digestion of organic matter when oxygen is in the environment. The byproducts of the process are carbon dioxide and water.
Anaerobic wastewater treatment: The digestion of organic matter without oxygen. The byproducts of the treatment process are CH4 and H2S.
Bacteria: Tiny, single-celled animals that use organic compounds found in soil, sewage, and water as a food source.
Biodegradation: The process by which microorganisms in wastewater digest waste and convert unstable substances into stable compounds.
Biochemical oxygen demand (BOD): A measurement of dissolved oxygen used by microorganisms during organic matter’s biochemical oxidation (digestion). Oxygen demand in water is generated by (1) organic compounds that serve as food sources for the microorganisms and (2) oxidizable nitrogen produced by nitrates, ammonia, and organic nitrogen compounds, which also serve as food for the bacteria.
Blackwater: Wastewater from toilets and showers that contains urine, feces, sewage, and other pollutants.
Biochemical oxygen demand (BOD5): A standard laboratory test to assess the potential of treated or untreated wastewater to absorb oxygen from a receiving body of water. BOD5 measures the oxygen bacteria consume over five days at 68°F under aerobic conditions to consume organic matter in a wastewater sample. The BOD5 test is widely accepted as a measure of the intensity of wastewater pollution because it results from the dissolved oxygen the wastewater consumes when discharged into a natural body of water. The higher the BOD5 value, the greater the degree of pollution.
Capacity: Regulations allow manufacturers to specify the capacity of a marine wastewater treatment plant or marine sewage unit.
Dissolved oxygen: A compound that occurs freely in water and is necessary to sustain aquatic life in water bodies such as rivers, lakes, and oceans. Dissolved oxygen may be depleted due to the accumulation of pollutants drawn from the water in the natural process of stabilizing the pollutants. Dissolved oxygen is essential in the aerobic biological treatment of wastewater. If the amount of dissolved oxygen in the water is insufficient, aerobic bacteria die, and anaerobic bacteria become dominant.
Wastewater: Treated or untreated wastewater that flows from a process (septic tank or wastewater treatment plant) into the surrounding environment.
Fecal coliform: A class of non-pathogenic (non-pathogenic) bacteria found in water pollution that can be used as evidence of the presence of pathogenic bacteria. Pathogenic bacteria are present in smaller numbers in wastewater and are more difficult to identify than fecal coliforms. Therefore, fecal coliforms are used as clues to detect the presence of pathogenic microorganisms. It is assumed that the wastewater does not contain pathogenic microorganisms if fecal coliforms are absent in the wastewater.
Foreign Vessels: Any vessel flying or registered outside the United States and holding a valid International Sewage Pollution Prevention Certificate issued by the government of its flag state indicating that the installed sewage system complies with Annex IV of MARPOL as amended by MEPC.227(64), MEPC.159 (55), or MEPC.2(VI) will be deemed by the U.S. Coast Guard to comply with U.S. regulations for design, construction, testing, and certification in 33 CFR 159. Operating in waters subject to U.S. jurisdiction.
Free Chlorine: Chlorine is commonly used in disinfection after wastewater treatment and before discharge into the environment. A free chlorine reading in the waste indicates that pathogens have been completely killed. All the chlorine required to disinfect the waste has been converted to another substance, leaving only “free chlorine” molecules.
Grey Water: Wastewater from dishwater, bathrooms, laundry rooms, sinks, showers, washing machines, etc. Non-biodegradable: Material that will not break down through natural processes.
Grease Trap: A grease trap (also called a grease trap) is a plumbing device that separates most grease and solids before they enter the wastewater treatment system. Kitchen water must pass through a grease trap before entering any wastewater tanks because fats, oils, and grease (FOG) can negatively impact plumbing and wastewater treatment plants.
Marine Sanitation Devices (MSDs): The Clean Water Act (CWA) is the cornerstone of the federal effort to combat pollution in U.S. waters. A key aspect of this legislation, under Section 312, involves controlling wastewater discharge from vessels. This is accomplished by regulating the use and maintenance of marine sanitation devices (MSDs), specialized devices designed to treat or retain wastewater from vessels.
Type I Marine Sanitation Device: A U.S. Coast Guard MSD that may only be installed on vessels 65 feet or less long. A Type 1 MSD is a sewage treatment device that uses immersion and disinfection to treat wastewater. Type I sanitation facilities must ensure that the waste produced does not contain visible floating solids and that the fecal coliform count does not exceed 1,000 per 100 milliliters.
Type II Marine Sanitation Device – A U.S. Coast Guard MSD that can be installed on vessels of any length. A Type II MSD is a continuous flow treatment device that uses biological treatment and disinfection (some Type II MSDs can use immersion and disinfection). Type II devices are required to produce wastewater that meets the following standards: not more than 200 fecal coliforms per 100 milliliters and not more than 150 milligrams of total suspended solids per liter.
Type III Marine Sanitation Device – A U.S. Coast Guard MSD that can be installed on vessels of any length. The second type of MSD generally consists of a tank where wastewater is stored until it can be discharged to shore or into the sea (more than three miles from shore). There are no specific performance standards; however, they must be “designed to prevent the discharge of treated or untreated wastewater or any wastewater derived residues,” as defined in 33 CFR 159.53(c) (PDF)(2 p. 163k).
Pathogens: Bacteria carried in feces that can cause disease in humans, animals, and plants.
pH: A value used to indicate the acidity or alkalinity of a solution. The pH scale ranges from 1 to 14. A value of 1 is the maximum reading for an acidic solution. A value of 14 is the maximum reading for an alkaline solution, while a reference value of 7 is a neutral solution. If the environment in a biological system becomes too acidic or alkaline, aerobic bacteria will begin to die. The permissible pH range for aerobic biological septic systems is 6.5 to 9.0.
PPM (parts per million): The units ppm and mg/l (milligrams per liter) are used interchangeably.
Raw wastewater: Raw wastewater is untreated wastewater.
Sludge: A homogeneous mass in a biological wastewater treatment unit consisting primarily of microorganisms, non-degradable solids, and organic waste.
Wastewater: Wastewater collected from toilets, urinals, sinks, troughs in medical facilities (pharmacy, infirmary, etc.), drainage from live animal breeding facilities, and any other wastewater that remains after mixing with the elements mentioned in this definition.
Total Suspended Solids (TSS): TSS is the total particulate matter suspended in a liquid. High dissolved solids in wastewater can cause harmful environmental effects, such as blocking the light needed for algae growth and clogging fish gills. High values generally indicate high BOD5 levels due to the retention of organic sludge in suspension. TSS values are determined through laboratory testing.
U.S. Flagged Vessels: U.S. flagged vessels must comply with the Clean Water Act and be equipped with a Marine Sanitation Device (MSD) approved by the U.S. Coast Guard.
Vacuum Collection Systems (VCHT): Vacuum collection systems use air pressure differentials to move wastewater from toilets, sinks, and other sanitary facilities to marine wastewater treatment plants or separate collection tanks.
