Marine Sewage Treatment Plant (STP)
The impact of sewage on the marine environment is a significant concern. Seawater can become polluted by a variety of harmful substances, including pathogens, nutrients, detergents, pesticides, and heavy metals. These pollutants pose high environmental and health risks, particularly since communities commonly use seawater for recreation, swimming, and food production. Improperly treated sewage from vessels can have detrimental effects on marine ecosystems. Most vessels have a marine sewage device designed to remove pollutants from sewage water before it is discharged into the sea.
The basic function of marine sewage treatment systems is to speed up the natural processes by which water is purified. Primary sewage treatment is primarily a physical process that removes solids from the sewage. Following this, secondary sewage treatment employs bacteria to decompose organic matter. Finally, chlorination is used to sterilize the effluent before it is released into the environment. However, potential pollutants like heavy metals, nutrients, and non-biodegradable organic chemicals can remain even after secondary treatment.
Advanced sewage treatment (AWT) systems are utilized to address these residual pollutants. These systems are designed to remove substances that are not effectively eliminated by primary and secondary treatments. There are various types of advanced wastewater treatment systems available (such as filtration, carbon adsorption, distillation, or reverse osmosis), each varying in effectiveness, complexity, and cost, depending on their size and design. Some of these systems are better proven than others, making the choice of treatment system crucial for ensuring minimal environmental impact.
What is the difference between Resolution MEPC 159(55) and MEPC 227(64)?
Resolution MEPC 227(64) effectively changed the discharge requirements and test protocols adopted by MEPC 159(55) in 2006. Its specific aim was to reduce nitrogen and phosphorous in the treated water and prevent the acceleration of nitrification of the seas. It states that an approved sewage treatment plant (STP) should not rely solely on dilution of wastewater. While dilution is deemed essential to a treatment process, effluent standards have to meet more stringent criteria stipulated in MEPC.227(64).
Marine Sewage Treatment Plants (STP)
The processing principles of marine sewage treatment plants are naturally occurring (naturally present in the wastewater). Aerobic bacteria are used for biological sewage treatment systems in the majority of municipal applications. This is the chosen process because it has been proven through decades of usage and is more economical than alternate methods. The key feature of the biological wastewater treatment process is the microorganisms (primarily bacteria) that remove the organic pollutants from domestic wastewater. When the wastewater is placed in the proper environment, these microorganisms reduce the organic pollutants of domestic wastewater very effectively and efficiently. The microorganisms utilize (consume) the organic pollutants in the wastewater as their energy source (food) for their cell activity (life).
The preferred microorganisms for the treatment of wastewater are the oxygen-requiring aerobic bacteria. Aerobic bacteria rapidly consume the organic waste material in the sewage and release carbon dioxide and water vapor as byproducts of their respiration and synthesis process. This does not result in an odor or explosive hazard.
If the air supply is cut off for twelve to thirty-six hours, an aerobic sewage treatment process will convert to an anaerobic process. The sewage will become septic and turn black as the solids disintegrate and decompose. The dissolved oxygen levels gradually decrease and produce hydrogen sulfide, causing strong odors to be emitted. However, the process will revert to aerobic within 12 to 24 hours after the air supply has been restored.
The marine sewage treatment plant utilizes an aerobic biological treatment process known as “extended aeration activated sludge” or “extended aeration.” The extended aeration treatment concept requires a large enough sewage treatment unit to retain and aerate the daily average sewage flow for 18-to-24 hours in order to keep the supply (sewage) essentially constant. In this process, the bacterial cell population exceeds the available food supply, causing some bacterial cells to starve to death and become food for the survivors. The result of this process is a minimization of bacterial cell sludge accumulation in the marine sewage treatment unit. In systems that do not employ this process, bacteria are exposed to a steady food supply, causing their population to increase to a point where continuous drain off and disposal of sludge is necessary.
When utilizing the extended aeration process, the microorganism or bacterial cell mass generated by cell reproduction is separated from the liquid being treated prior to discharge and reintroduced with the incoming sewage. This causes the introduction of a dense population of active bacteria that increases the removal rate of organic waste coming into the system. This arrangement is called an “activated sludge” process.
Because aerobic biological wastewater treatment has proven effective, all redFox marine sewage treatment plants utilize this principle.
Membrane Biological Reactors (MBR)
Membrane biological reactors (MBR) systems use ultrafiltration or microfiltration membranes to separate solids and liquids. MBR wastewater treatment systems are suitable for various offshore and on-land building facilities and vessels. The MBR sewage treatment plant is designed to handle all wastewater streams to current standards (black water—sewage, gray water from galleys, sinks, showers, and laundry facilities). Microfiltration membrane filtration effectively removes particles, sediment, algae, protozoa, and bacteria from the effluent. Ultrafiltration membrane filtration goes a step further by eliminating small colloids and viruses in addition to everything microfiltration handles.
The ultra-filtration membrane used for wastewater treatment physically separates the smallest particles down to colloids from liquids on the basis of its defined pore size (<0.1 µm). The membrane holds these substances back without changing them either physically or chemically. This means that dangerous substances cannot even be produced. Many membrane biological reactor manufacturers utilize user-friendly flat membranes made of organic polymers, which, combined with the sophisticated filter design, effectively prevent clogging of the filter due to hairs, fibers, or other unhygienic coarse matter.
The proven membrane technology is available in different configurations based on the necessary system capacity. Single filters to be implemented into an existing system are also possible, as are highly complex filtration tank systems with connected aeration and filtration systems.
A marine sewage treatment plant requires a tailored approach to meet your vessel’s unique needs. Contact Separator Spares & Equipment for the right solution for your marine sewage treatment plant. We specialize in providing spare parts, consumables, equipment, and services for marine sanitation devices (MSDs) and marine sewage treatment plants (STPs). Our commitment is to support your maintenance needs throughout your vessel’s lifecycle. For more details on marine sewage treatment plant spare parts or marine sewage treatment plant services, click the link.
Common Marine Sewage Treatment Plant Terms and Definitions:
AEROBIC SEWAGE TREATMENT: Digestion of organic matter when the environment has a presence of oxygen. The byproducts from this process are CO2 and H2O.
ANAEROBIC SEWAGE TREATMENT: Digestion of organic matter when the environment has an absence of oxygen. The byproducts from this treatment process are CH4 and H2S.
BACTERIA: Microscopic one-celled animals that commonly utilize the organic compounds found in soil, sewage, and water as food supply.
BIODEGRADATION: The process of digesting waste through the use of microorganisms in the wastewater to convert unstable materials into stable compounds.
BIOCHEMICAL OXYGEN DEMAND (BOD): A measurement of the dissolved oxygen used by microorganisms in the biochemical oxidation (digestion) of organic matter. The oxygen demand in water is created by (1) organic compounds that act as sources of food for microorganisms and (2) oxidizable nitrogen produced by nitrate, ammonia, and organic nitrogen compounds, which also serve as food for bacteria.
BLACKWATER: The wastewater from toilets and bathrooms that contain urine, feces, sewage, and other contaminants.
BOD5: A standard laboratory test used to evaluate the potential for treated or untreated wastewater to absorb oxygen from the receiving body of water. BOD5 measures the quantity of oxygen used by bacteria in consuming organic matter in a sample of wastewater over a five-day period at a temperature of 68oF under aerobic conditions. The BOD5 test is widely accepted as the measurement of the pollutional strength of wastewater since it gives results in terms of dissolved oxygen that would be consumed if the wastewater were discharged into a natural body of water. The larger the BOD5 value, the greater the pollution.
CAPACITY: Regulations allow the manufacturer to determine the capacity of marine sewage treatment plants or marine sanitation devices.
DISSOLVED OXYGEN: A compound freely available in water and is required to sustain aquatic life in bodies of water, such as rivers, lakes, and oceans. Dissolved oxygen can become depleted by an accumulation of pollutants that draw dissolved oxygen from the water during the natural process of stabilizing pollutants. Dissolved oxygen is essential when biologically treating wastewater aerobically. If the amount of dissolved oxygen in the water is inadequate, the aerobic bacteria will die, allowing the anaerobic bacteria to dominate.
EFFLUENT: Treated or untreated wastewater that flows from a process to the surrounding environment.
FECAL COLIFORM: A type of bacteria found in water pollution that is nonpathogenic (not disease-causing) and is utilized as a guide to the presence of pathogenic (disease) causing bacteria. In wastewater, pathogenic bacteria are fewer in number and much harder to identify compared to fecal coliform. This is why fecal coliform is utilized as the guide to detect the likelihood of pathogenic organisms being present. It is assumed that if the wastewater is free of fecal coliform, then it is free of pathogenic organisms.
FOREIGN VESSELS: Any vessel flagged or registered outside the United States that holds a valid International Sewage Pollution Prevention Certificate (ISPPC) issued by its flag Administration indicating the installed sewage system complies with MARPOL Annex IV as amended by resolutions MEPC.227(64), MEPC.159(55), or MEPC.2(VI) will be accepted by the U.S. Coast Guard as complying with U.S. regulations contained in 33 CFR 159 as it relates to the design, construction, testing, and certification while operating in waters subject to the jurisdiction of the United States.
FREE CHLORINE: Chlorine is often used in the disinfection process after the treatment of the wastewater but before it is discharged into the environment. A reading of free chlorine in the effluent exhibits a complete kill of pathogenic bacteria. This is because all the chlorine required to disinfect the effluent has been converted to another substance, leaving only “free chlorine” molecules.
GRAYWATER: The wastewater from dishwater, bath, laundry, sinks, showers, washing machines, etc. NONBIODEGRADABLE: Substances that do not degrade using natural processes.
MARINE SANITATION DEVICE (MSD): The Clean Water Act (CWA) is the cornerstone of USA federal efforts to combat pollution in U.S. waters. A crucial aspect of this legislation, outlined in Section 312, involves controlling sewage discharges from vessels. This is achieved by regulating the use and maintenance of marine sanitation devices (MSDs), which are specialized equipment designed to treat or hold sewage on board vessels.
MARINE SANITATION DEVICE TYPE I: US Coast Guard MSD that may be installed only on vessels less than or equal to 65 feet in length. The MSD Type I device is a flow-through sanitation treatment device that typically uses maceration and disinfection to treat sewage. A Type I sanitation device must ensure that the effluent produced contains no visible floating solids and has a fecal coliform bacterial count not exceeding 1,000 per 100 milliliters.
MARINE SANITATION DEVICE TYPE II: US Coast Guard MSD that may be installed on vessels of any length. The MSD Type II is a flow-through treatment device that may utilize biological treatment and disinfection (with some Type II MSDs possibly employing maceration and disinfection). A Type II device is required to produce an effluent that meets the following standards: a fecal coliform bacterial count not exceeding 200 per 100 milliliters and no more than 150 milligrams of total suspended solids per liter.
MARINE SANITATION DEVICE TYPE III: US Coast Guard MSD that may be installed on vessels of any length. The MSD Type II typically consists of a holding tank, where sewage is stored until it can be discharged either shore-side or at sea (beyond three miles from shore). There is no specific performance standard; however, they must “be designed to prevent the overboard discharge of treated or untreated sewage or any waste derived from sewage,” as specified in 33 CFR 159.53(c) (PDF)(2 pp, 163 K).
PATHOGENIC BACTERIA: Those bacteria carried by feces can produce diseases in man, animals, and plants.
pH: A value used to indicate the acidity or alkalinity of a solution. The range of values for pH is 1-14. A value of 1 is the extreme reading of an acid solution. A value of 14 would be the extreme reading for a caustic solution, while an indication of 7 is a neutral solution. Aerobic bacteria in a biological system will begin to die if their environment becomes too acidic or too caustic. The allowable pH range for an aerobic biological sewage system is 6.5-9.0.
PPM (PARTS PER MILLION): The units ppm and mg/l (milligrams per liter) can be used interchangeably.
RAW SEWAGE: Raw sewage is untreated sewage.
SLUDGE: A homogenous matter in a biological sewage treatment unit consisting primarily of microorganisms, non-biodegradable solids, and organic waste material.
SEWAGE: The wastewater collected through the drainage of toilets and urinals, medical premises (dispensary, sick bay, etc.) via wash basins, tubs, scuppers located in such premises, spaces containing living animals, and any other wastewater drainage when mixed with items mentioned in this definition.
TSS (TOTAL SUSPENDED SOLIDS): TSS is the total amount of particulate matter suspended in the fluid. A high TSS in the effluent can cause detrimental environmental effects, such as blocking light essential for the growth of algae and clogging fish gills. A high value usually indicates high BOD5 because of suspended organic sludge carry-over. The value of TSS is determined by laboratory testing.
US FLAGGED VESSELS: US-flagged vessels are obliged to comply with the Clean Water Act and must install a US Coast Guard approved Marine Sanitation Device (MSD).
VACUUM COLLECTION SYSTEMS (VCHT): Vacuum collection systems use differential air pressure to transport sewage from toilets, washbasins, and other sanitary fittings to the marine sewage treatment plant or independent collection tank.
Relentless Pursuit of Excellence!
Need an approved system? A marine sewage treatment plant requires a tailored approach to meet your vessel’s unique needs. Contact Separator Spares & Equipment for the right solution for your marine sewage treatment plant. We specialize in providing spare parts, consumables, equipment, and services for marine sanitation devices (MSDs) and marine sewage treatment plants (STPs). Our commitment is to support your maintenance needs throughout your vessel’s lifecycle. For more details on marine sewage treatment plant spare parts or marine sewage treatment plant services, click the link.
