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A vacuum sewer or pneumatic sewer system is a method of transporting sewage from its source to a sewage treatment plant. It maintains a partial vacuum, with an air pressure below atmospheric pressure inside the pipe network and vacuum station collection vessel. Valves open and reseal automatically when the system is used, so differential pressure can be maintained without expending much energy pumping. A single central vacuum station can collect the wastewater of several thousand individual homes, depending on terrain and the local situation. [1] [ better source needed ]
Vacuum sewers were first installed in Europe in 1882. Dutch engineer Charles Liernur first applied negative pressure drainage to sewers in the second half of the 19th century. [2] [ non-primary source needed ] Technical implementations of vacuum sewerage systems began in 1959 in Sweden.[ citation needed ]
Historically, vacuum sewers have been a niche product, used only in trains, airplanes, and flat areas with sandy soils and high ground water tables. Gravity sewers were used for most applications, because although vacuum sewers were cheaper to install, they were more expensive to maintain. In the 20th century, vacuum sewer technology has improved significantly: fault-locating sensors have reduced operation and maintenance costs, and some operators now consider that vacuum sewers can be cheaper to run than conventional gravity sewers. [3]
The main components of a vacuum sewer system are a collection chambers and vacuum valve parts, sewers, a central vacuum station and monitoring and control components.
Some vacuum systems have vacuum toilets are connected directly to a vacuum line, which requires less water for flushing (less than a quarter of a liter per flush). [4] Others use standard gravity drainage for the first phase of collection; sewage flows by means of gravity from each house, as in a standard system. It discharges into a collection sump that might collect sewage from 2-6 houses and is located in a public area.
Vacuum technology is based on differential air pressure. Rotary vane vacuum pumps generate an operation pressure of -0.4 to -0.6 bar at the vacuum station, which is also the only element of the vacuum sewerage system that must be supplied with electricity.
Interface valves are installed inside the collection chambers. They work pneumatically. After a certain fill level inside this sump is reached, the interface valve opens. The impulse to open the valve is transferred by a pneumatically mechanical controlled controller unit. No electricity is needed to open or close the valve. The energy is provided by the vacuum itself.
While the valve is open, the resulting differential pressure between atmosphere and vacuum becomes the driving force and transports the wastewater and air towards the vacuum station. Besides these collection chambers, no other manholes, neither for changes in direction, nor for inspection or connection of branch lines, are necessary. High flow velocities keep the system free of any blockages or sedimentation.
Large systems with numerous collection chambers benefit from the provision of a monitoring system for remote monitoring of the vacuum valves and sump pits. Such systems allow much faster troubleshooting and easier preventive maintenance of collection chambers and valves. However, monitoring systems are optional systems and not required for operation of vacuum sewer systems.
Vacuum sewer systems are considered to be free of ex- and infiltration which allows their use even in water protection areas. For this reason, vacuum sewer lines may even be laid in the same trench as potable water lines (depending on local guidelines).
In order to ensure reliable transport, the vacuum sewer line is laid in a saw-tooth (length-) profile. [5] The whole vacuum sewers are filled with air at a pressure of -0.4 to -0.6 bar. The most important aspect for a reliable operation is the air-to-liquid ratio. When a system is well designed, the sewers contain only very small amounts of sewage. The air-to-liquid ratio is usually maintained by collecting liquid/air simultaneously or controller units that adjust their opening times according to the pressure in the system.
Sewers can be laid in flat terrain, and parts may flow uphill (within limits). A saw-tooth profile keeps sewer lines shallow; [5] in frost-free climates, trench depth can be about 1.0 – 1.2 m. By contrast, gravity sewers need a monotonically falling slope of at least 0.5 - 1.0%, which can mean that expensive trenching and pumping stations are needed.
Once the wastewater arrives in the vacuum collection tank at the vacuum station, it is pumped to the discharge point, which could be either a gravity sewer or the treatment station. As the dwell time of the wastewater inside the system is very short and the wastewater is continuously mixed with air, the sewage is kept fresh and any fouling inside the system is avoided (less H2S).
Vacuum sewer systems may be the preferred system in the case of particular circumstances, such as:
Trains, aircraft, buses, and many ships with plumbing generally have vacuum systems with vacuum toilets. The lower water usage (less than a quarter of a liter per flush) [4] saves weight, and avoids water slopping out of the toilet bowl in motion. [9] Aircraft toilets may flush with blue disinfectant solution rather than water. [4] A portable collection chamber is used; if it is filled from an intermediate vacuum chamber, it need not be kept under vacuum. [10] [ better source needed ]
Lack of water in many countries and drastic water savings measures have led to difficulties with aging gravity networks with solids blocking in the pipes. Vacuum systems save water.
Flat terrain, unfavorable soil (rocky or swampy ground), or a high groundwater table (which requires dewatering trenches) can make gravity sewerage systems much more expensive. Vacuum sewers are small in diameter and leak inwards, and in frost-free areas, they can be laid close to the surface in small trenches.
Vacuum sewers can pass through water protection areas and areas with sensitive high ground water tables, because there is no danger of spoiling groundwater resources (vacuum sewers have a high leak tightness due to their material; and if they leak, they leak inwards). Vacuum systems are used in many environmentally sensitive areas such as the Couran Cove Eco Resort close to the Barrier Reef in Australia. They've also been used to replace septic tanks to reduce nitrogen levels in ground/surface water. [11]
Vacuum systems have also been applied to collect toxic wastewater from the environment.
If the temperatures in an area dip below freezing in winter, the vacuum line is buried below the frost line, in ground that stays unfrozen year-round (as are conventional gravity sewers). Valves, collection pits, intake vents, and control systems need to be designed to keep functioning despite cold, snow and ice. Temperature-monitoring sensors are also standard, so problems can be noticed early.
In the case of Plum Island (Massachusetts), the island was prone to freezing temperature and excessive snowfall that initially made it difficult to locate a potential problem. Changes to their Pit setup and monitoring at the valve pit has helped with maintenance.
Many Nordic Countries utilize vacuum sewers, it is helpful to have some type of marker or monitoring to locate valves when they are buried under the snow for extended periods.
With lower population densities, the costs for the collection chambers and vacuum stations are less important than the costs of installing pipe and, for gravity sewers, pumping stations, etc.. Pneumatic pipes are generally smaller than gravity-drained hydraulic ones [ citation needed ] In frost-free climates, the pipes for a vacuum system can also be buried more shallowly than a gravity system.
High specific conduit lengths, where the required pipe length is longer than ~4 metres per inhabitant[ citation needed ], will tend to make a vacuum system cheaper.
In seasonal settlements (recreation areas, camping sites etc.) with conventional gravity sewer systems, sedimentation problems can easily occur as automatic flushing by daily waste water does not take place. High flow velocities within vacuum sewers prevent such sedimentation problems. The Formula 1 race tracks in Shanghai and Abu Dhabi are using a vacuum sewer system for that reason.[ citation needed ]
Historic sites may have old buildings, narrow streets, and steep terrain. Tourism may also cause strong seasonal fluctuations in population density. Vacuum sewer systems may be selected for their fast (avoiding conflicts with traffic and tourism), cost-effective and flexible installation. Examples include Flavigny-sur-Ozerain, France, and Khasab and Al Seeb in Oman.
Vacuum sewer systems can be set up so that they collect concentrated blackwater (toilet wastewater) only, with the greywater from sinks and baths being collected separately (it is much easier to treat greywater than blackwater). The biosolids from a vacuum system need not be diluted with flushing water.
Sewage systems usually thermophilically compost biosolids which have been separated and dewatered from a standard gravity sewer. [12] [13] This process is simpler if the biosolids are never watered.
Composting at high temperatures kills pathogens and seeds. [13] [14] Biosolids compost is required to be composted at high temperatures. [15]
Sewage can also be treated in an anaerobic process with the production of biogas. This design has the potential to increase sustainability of water infrastructures. [16]
Sewerage is the infrastructure that conveys sewage or surface runoff using sewers. It encompasses components such as receiving drains, manholes, pumping stations, storm overflows, and screening chambers of the combined sewer or sanitary sewer. Sewerage ends at the entry to a sewage treatment plant or at the point of discharge into the environment. It is the system of pipes, chambers, manholes, etc. that conveys the sewage or storm water.
A septic tank is an underground chamber made of concrete, fiberglass, or plastic through which domestic wastewater (sewage) flows for basic sewage treatment. Settling and anaerobic digestion processes reduce solids and organics, but the treatment efficiency is only moderate. Septic tank systems are a type of simple onsite sewage facility. They can be used in areas that are not connected to a sewerage system, such as rural areas. The treated liquid effluent is commonly disposed in a septic drain field, which provides further treatment. Nonetheless, groundwater pollution may occur and can be a problem.
A flush toilet is a toilet that disposes of human waste by using the force of water to flush it through a drainpipe to another location for treatment, either nearby or at a communal facility, thus maintaining a separation between humans and their waste. Flush toilets can be designed for sitting or squatting, in the case of squat toilets. Most modern sewage treatment systems are also designed to process specially designed toilet paper. The opposite of a flush toilet is a dry toilet, which uses no water for flushing.
A sanitary sewer is an underground pipe or tunnel system for transporting sewage from houses and commercial buildings to a sewage treatment plant or disposal. Sanitary sewers are a type of gravity sewer and are part of an overall system called a "sewage system" or sewerage. Sanitary sewers serving industrial areas may also carry industrial wastewater. In municipalities served by sanitary sewers, separate storm drains may convey surface runoff directly to surface waters. An advantage of sanitary sewer systems is that they avoid combined sewer overflows. Sanitary sewers are typically much smaller in diameter than combined sewers which also transport urban runoff. Backups of raw sewage can occur if excessive stormwater inflow or groundwater infiltration occurs due to leaking joints, defective pipes etc. in aging infrastructure.
The London sewer system is part of the water infrastructure serving London, England. The modern system was developed during the late 19th century, and as London has grown the system has been expanded. It is currently owned and operated by Thames Water and serves almost all of Greater London.
In modern plumbing, a drain-waste-vent is a system that allows air to enter the plumbing system to maintain proper air pressure to enable the removal of sewage and greywater from a dwelling. Drain refers to water produced at fixtures such as sinks, and showers; waste refers to water from toilets. As the water runs down, proper venting is required to allow water to flow freely, and avoid a vacuum from being created. As the water runs down air must be allowed into the waste pipe either through a roof vent (external), or an internal vent.
A composting toilet is a type of dry toilet that treats human waste by a biological process called composting. This process leads to the decomposition of organic matter and turns human waste into compost-like material. Composting is carried out by microorganisms under controlled aerobic conditions. Most composting toilets use no water for flushing and are therefore called "dry toilets".
Milorganite is a brand of biosolids fertilizer produced by treating sewage sludge by the Milwaukee Metropolitan Sewerage District. The term is a portmanteau of the term Milwaukee Organic Nitrogen. The sewer system of the District collects municipal wastewater from the Milwaukee metropolitan area. After settling, wastewater is treated with microbes to break down organic matter at the Jones Island Water Reclamation Facility in Milwaukee, Wisconsin. The byproduct sewage sludge is produced. This is heat-dried with hot air in the range of 900–1,200 °F (482–649 °C), which heats the sewage sludge to at least 176 °F (80 °C) to kill pathogens. The material is then pelletized and marketed throughout the United States under the name Milorganite. The result is recycling of the nitrogen and phosphorus from the waste-stream as fertilizer. The treated wastewater is discharged to Lake Michigan.
Sewage sludge treatment describes the processes used to manage and dispose of sewage sludge produced during sewage treatment. Sludge treatment is focused on reducing sludge weight and volume to reduce transportation and disposal costs, and on reducing potential health risks of disposal options. Water removal is the primary means of weight and volume reduction, while pathogen destruction is frequently accomplished through heating during thermophilic digestion, composting, or incineration. The choice of a sludge treatment method depends on the volume of sludge generated, and comparison of treatment costs required for available disposal options. Air-drying and composting may be attractive to rural communities, while limited land availability may make aerobic digestion and mechanical dewatering preferable for cities, and economies of scale may encourage energy recovery alternatives in metropolitan areas.
Sewage treatment is a type of wastewater treatment which aims to remove contaminants from sewage to produce an effluent that is suitable to discharge to the surrounding environment or an intended reuse application, thereby preventing water pollution from raw sewage discharges. Sewage contains wastewater from households and businesses and possibly pre-treated industrial wastewater. There are a high number of sewage treatment processes to choose from. These can range from decentralized systems to large centralized systems involving a network of pipes and pump stations which convey the sewage to a treatment plant. For cities that have a combined sewer, the sewers will also carry urban runoff (stormwater) to the sewage treatment plant. Sewage treatment often involves two main stages, called primary and secondary treatment, while advanced treatment also incorporates a tertiary treatment stage with polishing processes and nutrient removal. Secondary treatment can reduce organic matter from sewage, using aerobic or anaerobic biological processes.
Sewage is a type of wastewater that is produced by a community of people. It is typically transported through a sewer system. Sewage consists of wastewater discharged from residences and from commercial, institutional and public facilities that exist in the locality. Sub-types of sewage are greywater and blackwater. Sewage also contains soaps and detergents. Food waste may be present from dishwashing, and food quantities may be increased where garbage disposal units are used. In regions where toilet paper is used rather than bidets, that paper is also added to the sewage. Sewage contains macro-pollutants and micro-pollutants, and may also incorporate some municipal solid waste and pollutants from industrial wastewater.
A vacuum truck, vacuum tanker, vactor truck, vactor, vac-con truck, vac-con is a tank truck that has a pump and a tank. The pump is designed to pneumatically suck liquids, sludges, slurries, or the like from a location into the tank of the truck. The objective is to enable transport of the liquid material via road to another location. Vacuum trucks transport the collected material to a treatment or disposal site, for example a sewage treatment plant.
Effluent sewer systems, also called septic tank effluent gravity (STEG), solids-free sewer (SFS), or septic tank effluent drainage (STED) systems, have septic tanks that collect sewage from residences and businesses, and the liquid fraction of sewage that comes out of the tank is conveyed to a downstream receiving body such as either a centralized sewage treatment plant or a distributed treatment system for further treatment or disposal away from the community generating the sewage. Most of the solids are removed by the interceptor tanks, so the treatment plant can be much smaller than a typical plant and any pumping for the supernatant can be simpler without grinders.
Infiltration/Inflow causes dilution in sanitary sewers. Dilution of sewage decreases the efficiency of treatment, and may cause sewage volumes to exceed design capacity. Although inflow is technically different from infiltration, it may be difficult to determine which is causing dilution problems in inaccessible sewers. The United States Environmental Protection Agency defines the term infiltration/inflow as combined contributions from both.
A urine-diverting dry toilet (UDDT) is a type of dry toilet with urine diversion that can be used to provide safe, affordable sanitation in a variety of contexts worldwide. The separate collection of feces and urine without any flush water has many advantages, such as odor-free operation and pathogen reduction by drying. While dried feces and urine harvested from UDDTs can be and routinely are used in agriculture, many UDDT installations do not apply any sort of recovery scheme. The UDDT is an example of a technology that can be used to achieve a sustainable sanitation system. This dry excreta management system is an alternative to pit latrines and flush toilets, especially where water is scarce, a connection to a sewer system and centralized wastewater treatment plant is not feasible or desired, fertilizer and soil conditioner are needed for agriculture, or groundwater pollution should be minimized.
Fecal sludge management (FSM) is the storage, collection, transport, treatment and safe end use or disposal of fecal sludge. Together, the collection, transport, treatment and end use of fecal sludge constitute the "value chain" or "service chain" of fecal sludge management. Fecal sludge is defined very broadly as what accumulates in onsite sanitation systems and specifically is not transported through a sewer. It is composed of human excreta, but also anything else that may go into an onsite containment technology, such as flushwater, cleansing materials, menstrual hygiene products, grey water, and solid waste. Fecal sludge that is removed from septic tanks is called septage.
The Great Lakes Water Authority (GLWA) is a regional water authority in the U.S. state of Michigan. It provides drinking water treatment, drinking water distribution, wastewater collection, and wastewater treatment services for the Southeast Michigan communities, including Wayne, Oakland, and Macomb counties, among others. GLWA overlays a majority of the water and sewer assets which were formerly operated and maintained by the Detroit Water Sewer District (DWSD) prior to the bankruptcy of the City of Detroit, Michigan.
The Thomas P. Smith Water Reclamation Facility (TPS) is owned and operated by the city of Tallahassee, Florida. The facility provides sewage treatment services for Tallahassee, Florida and the surrounding areas.
A gravity sewer is a conduit utilizing the energy resulting from a difference in elevation to remove unwanted water. The term sewer implies removal of sewage or surface runoff rather than water intended for use; and the term gravity excludes water movement induced through force mains or vacuum sewers. Most sewers are gravity sewers; because gravity offers reliable water movement with no energy costs wherever grades are favorable. Gravity sewers may drain to sumps where pumping is required to either force sewage to a distant location or lift sewage to a higher elevation for entry into another gravity sewer, and lift stations are often required to lift sewage into sewage treatment plants. Gravity sewers can be either sanitary sewers, combined sewers, storm sewers or effluent sewers.
A pressure sewer provides a method of discharging sewage from properties into a conventional gravity sewer or directly to a sewage treatment plant. Pressure sewers are typically used where properties are located below the level of the nearest gravity sewer or are located on difficult terrain.