The conclusion of most of the researches about building’s water and sewage systems around the world, always shown that the toilet is the sanitary fixture that uses more water than any other else in residential and commercial buildings. Buildings were a big number of persons circulates every day, like transportation terminals, as train and bus stations and airports are very interesting points for application of high efficiency water savings technologies, in a way to reduce water consumption, good practices as world’s environment and water resources situation require. One technology that appears with the high efficiency is the vacuum toilet systems, using fixtures that consumes just 1.2 Lpf and shows an enhanced performance on collection and transportation of human waste. As a requirement of a public building, like an airport, this two primary conditions must be accomplished: use the minimum amount of natural resources, while the service is improved. The objective of this article is to show the application of a vacuum toilet system on a Brazilian airport (Santos Dumont, downtown Rio de Janeiro), identifying the benefits and features of this system.
Vacuum system; vacuum toilet; water conservation.
Over the last decades, water consumption per capita had increased by several reasons, at the same time population also increased in number. The population concentration in big metropolitan areas is today in a level never seen before. Those factors together are
taking water resources to conditions of scarcity, leading for a challenge of finding better and more reasonable and efficient ways of using water.
Because of this, one of the major concerns of authorities, researches, as well of all technical community involved with water and sewage building systems is to reduce water consumption and sewage generation, keeping performance and quality in the same levels of the existing services, if not improving then.
Several studies show the toilet to be the fixture that consumes the largest quantity of water in both residential, commercial and public buildings, thus any action toward saving water in this type of fixture should be welcome , . It’s important also to notice that modifications in this type of fixture does not necessarily need to be accompanied by changes in user’s behaviour, facilitating the implementation of water saving programs based on new toilet technology.
With these thoughts in mind, the authors of this article decided to collect information to show eventual benefits of a vacuum toilet system installed in an airport in Brazil.
2 Vacuum system description
Facing the problems and needs before written, an alternative technological application is the use of a vacuum toilet system. Considering two aspects of a sewage system performance, sewage transport and removal and water savings, vacuum sewage systems can show important improvements comparing to gravitational sewage systems.
Vacuum systems use difference in air pressure between the toilet environment and inside the vacuum pipe to collect and transport the sewage. During flush cycle, a vacuum toilet receives surrounding air that gets inside the pipe (permanently under pressure lower than atmospheric) through the bowl, toward the vacuum central, where vacuum is generated and therefore where is the lower pressure in the whole system. The airflow through the bowl forces the sewage to get inside the pipe and water is used only to clean the bowl (a total of 1.2 liters of water per flush), not for sewage transport. Since air that transport the sewage and water is used only for cleaning, a better understanding of the water savings potential of a vacuum toilet system is given. Many standards cover the design and installation of a vacuum toilet system , .
A Stevens Institute of Technology report shows tests made with vacuum toilets and they meet or exceed the North American Codes for sewage removal .
Vacuum sewage systems are not exactly new. There are indications that around 1870 in Germany and France some municipal vacuum sewage systems installations happened. Technological development of engineering at that time probably made things difficult to continue with the idea and is not until late 1950 new mentions of vacuum sewage systems appear again.
In Sweden, 1956 to 1958, a new concept of vacuum sewage systems equipped with vacuum toilet fixtures is presented in some installations in this country and others. This same basic concept have been developed over the years and this Swedish technology of late 50’s is the basis of vacuum toilets systems we see today, with applications in land based projects and others fields like marine.
The idea was to generate low pressure in one centralized point (the vacuum central unit) built a vacuum pipe network with some special features and install in the extremities of this pipe network toilets operated by vacuum and that could hold the vacuum inside the pipe when not in operation.
During flush, a special design valve in the toilet opens and allows the content of the bowl to get inside the pipe in direction of the vacuum central unit. While this “flush valve” is open, another valve put some water to clean the bowl. All this operation is controlled by another pilot valve, activated by a push button. The bowl itself is made of vitreous china and because there is no siphon in the toilet, the space normally occupied by it now gives room to install all these valves.
One simplified scheme of the system can be seen in the Figure 1. This figure shows: the vacuum central unit (number 1 in the figure), responsible for vacuum generation, through vacuum pumps, and responsible also for collecting the sewage and temporarily storing it; the vacuum pipe network (simplified here with only one point of collection) (number 2); and the vacuum toilet itself (number 3).
Figure 1 – Simplified scheme of a vacuum toilet system. Image: Courtesy of EVAC
2.2 Vacuum central
The vacuum central unit is built with tanks, vacuum pumps, valves, electrical control panel and other instrumentation and control devices. The vacuum pumps take out the air that exists inside the tanks and pipe until about a maximum of 1/3 of atmospheric pressure. Vacuum switches are permanently making readings of the pressure in the system and feed the Programmable Logic Controller (PLC), installed inside the electrical control panel. With this information, the PLC determines witch, when, how long and how many vacuum pumps will run. Inside the tanks float level switches are installed and they also feed the PLC with information. When one tank is partially filled
and the sewage reaches one of these float level switches, a sign is given to dump the tank. This dumping is made in some cases by breaking the vacuum inside the tank (bringing the specific tank to atmospheric pressure) and leaving the sewage flowing by gravity. While one tank is dumping, the other, still under vacuum, receives the sewage generated during this period, making the availability of vacuum to the whole systems continuous. Tanks may dump to municipal sewer system or to a sewage treatment plant. Depending on the type of vacuum central unit technology and specific project needs, the tanks may dump by action of sewage pumps. The vacuum central unit is the only point where electrical energy is needed in the whole system.
2.3 Vacuum toilet (water closet)
Vacuum toilets have a special design. The vacuum toilet bowl is manufactured in vitreous china and externally they look just like a normal toilet. Inside of the fixture is different, since there is no siphon inside the bowl. In its location, a kit of valves is installed: the discharge valve, the water valve, the control valve, hoses and a metal plate that holds all these valves, all of then pneumatic operated. The discharge valve, when not in operation, holds a little amount of water inside the bowl and vacuum inside the pipe.
Figure 2 – Vacuum toilet fixture. Floor mounted model. Image: Courtesy of EVAC
When pressing the flush push button, witch is just an air below that forces a little bit of air inside an specific chamber of the control valve, a flush cycle is initiated. At that time, the control valve sends a pneumatic sign to both, water valve and discharge valve, and they are at that time opened.
When the discharge valve is opened, air at atmospheric pressure forces the content inside the bowl toward the vacuum pipe, at the same time the water valve rinses the bowl, cleaning it. After collecting the sewage and water that was inside the bowl, the discharge valve closes and the water valve remains open for one more instant, to re- establish the pool of water inside the bowl. The whole cycle takes a few seconds and consumes 1.2 liters of water and from 60 to 100 liters of air. The energy required for the valves to operate comes from the vacuum existing on the pipe
2.4 Pipe system
The vacuum pipe is normally built in PVC. Because of the difference in pressure, a bigger wall thickness is needed. Normally a pipe that resists to a 7,5 kgf/cm2 pressure in service can resist to vacuum levels that a typical vacuum sewage system is subject to. Some particular pipe profiles and special pipe arrangements were specifically developed to improve the performance and give better functionality of vacuum sewage systems and they are shown in system’s manufactures technical manuals.
Three features of vacuum pipes are especially interesting. Most of the cases the pipe diameter are much smaller the gravitational pipes would show (usually half of the size), there is no need of constant slope on the pipe and the ability of lifting the sewage. These features make, in many cases, retrofits and renovations easier with vacuum toilets systems.
3 Case of study: research development and data discussion
The Santos-Dumont Airport is located in Rio de Janeiro, the second largest Brazilian city, in down town area. First civil airport in Brazil had opened its runway in 1936, with the name “Santos-Dumont”: the Brazilian who was the first person to take-off and fly a self-propulsion aircraft in 1906. It is not until 1947 that the airport’s passenger terminal start it’s operations, with the same basic shape it has today.
Figure 3 – Aerial view of the Santos-Dumont Airport complex, Rio de Janeiro and Internal view (lobby) of the Santos-Dumont Airport, Rio de Janeiro.
In Feb 2001 a vacuum toilet system was installed in the public restrooms of the main airport terminal, replacing regular gravity toilets with flush valves. After and before the new toilets system start-up, the toilet’s use of water was measured and recorded. The collected data is the basis of this study.
The Santos-Dumont Airport had during the period of the vacuum toilet system evaluation an average of 13.000 people passing through it every day, not all of then were actually passengers, since this number includes people that works there and also
because the airport’s very central location, down town Rio de Janeiro, many non- passenger visitors goes there for many reasons.
The system installed in the airport consists of 21 vacuum toilets located in the main terminal lobby restrooms, 10 of then in men’s restrooms and 11 in the women’s one, the vacuum sewage collection unit and the vacuum pipe.
The material used to build the vacuum pipe was Brazilian class 15 (similar to American schedule 40 PVC) solvent-welded PVC in diameters varying from 1 1/2” to 2 1/2”. In Brazil this type of pipe is normally used for cold-water installations. The small pipe diameter in the toilet outlet (1 1/2”) and its direction (toward the wall), associated with the ability of elevation (up to 20 ft) of the sewage provided by the vacuum toilet system contributed for the system to be installed with minor disturb of the airport daily activities.
The system was installed without any interruption of the restrooms operation. The vacuum pipe was installed during the day in all areas where the installation work would not disturb the regular operation of the services of the airport.
At the same time, the vacuum central was installed and put ready to work, sharing the room space of an existing pumping lift station area. The vacuum central unit installed was equipped with 3 vacuum pumps of 1.5 kilowatts producing 48m3 of vacuum per hour each one. The pumps are started depending on the demand of use of the system and they rotate the use to equalize the usage of each one of the pumps. To collect the sewage there are 2 tanks of 60 gallons of capacity each one. These tanks drain (by gravity) their content when they are 40% full, by means of venting the tank (they are normally under vacuum). When one tank is draining, the other, still under vacuum, receives the sewage generated during the cycle. The unit contains also instrumentation and control to all the operation of the system
Figure 4 – Vacuum central unit and vacuum toilet installed
Inside the restrooms, the vacuum pipe branches had been installed in small sections that could be accomplished between 11 PM and 6 AM, when the airport was closed. There
was no need of floor penetration, since the new pipe was installed on top of the floor surface, behind the toilet.
Because of the distance between the existing wall and the new toilet, created to accommodate the new vacuum pipe, Formica covered plywood and marble stone top cabinets were installed to give the job a good finish, as the airport’s restrooms deserve. Underneath the cabinet, the old water flush valves that used to feed the gravitational toilets were hidden, and the same water valve connection was used to feed the new vacuum toilet of water. The cabinet was also helpful to install the new vacuum toilet flush push button.
As each one of these small sections of vacuum pipe branches were ready, the regular gravity toilet was removed, the gravity pipe connection in the floor was caped (typically gravity toilets in Brazil has their outlet toward the floor), the new vacuum toilet was installed and connected to the already existing vacuum pipe connection in that position.
Since the vacuum central unit was already in conditions to work, as well the main vacuum pipe between the braches and the vacuum central and the not ready to use vacuum pipe branches had isolation valves, the toilets could be put to work one by one, during the night.
The result was that in only two days the vacuum fixtures replaced all the gravitational toilets. This explains why the water consumption felt dramatically, as shown in the charts.
Two months before the installation of the vacuum toilet system in the airport, an authorization was given from Infraero (Brazilian airport authority, responsible for the airports operations) to install water flow meters in these specific restroom’s water supply pipes.
Two 2 1/2” flow meters were installed in two lines, these pipes are exclusively used to feed the toilets, not been used to feed any other fixtures in these restrooms; sinks and urinals had a different water supply that were not object of any water consumption measurement.
These two water pipes are used, one for feeding water to the ten men’s toilets and other for the eleven women’s toilets. Fifty five days prior to the beginning of the operation of the vacuum toilets system in airport, daily readings in the flow meters were taken, and these readings continued for more almost fifty days, while the vacuum toilets system was already working, making a total of 100 days with flow meters daily readings. The data are shown in the Figure 5.
18.00 16.00 14.00 12.00 10.00
8.00 6.00 4.00 2.00
Water Consuption in Toilets Santos Dumont Airport – RJ – Brazil
Figure 5 – Water consumption in the toilets.
During the first fifty five days of the evaluation, the average daily water consumption for the 21 toilets of the airport’s terminal restrooms was 25,58 m3, achieving peaks of 16,63m3 only in the men’s restroom in January 18th and 14,93m3 in the women’s restroom in December 19th, but also having low consumption in some days, like January 29th, when the women’s restroom consumed only 9,21m3, and January 10th when only 10m3 of water were consumed in the men’s toilets.
In the other hand, after the vacuum toilets installation and begin of operation, 4,31m3 were measured, in average, of water consumption per day in the same toilets. The biggest daily consumption was 2,91m3 in March 12th and the smallest was 1,41 in the women’s restroom in the last day of our measurements, the March 20th.
In average, the calculate savings in water consumption was 83% in the toilets.
Considering that the vacuum toilets nominally uses only 1.2 liters per flush, the gravitational toilets should be using about 7 liters per flush to give 83% savings. This number, 7 liters per flush for a regular gravitational toilet, is very small, since they are not the latest style 6 LPF toilets but old style toilets, designed to perform with 9 to 12 liters per flush.
This discrepancy could be explained, somehow, with most of uses of the fixtures taking place to flush liquid sewage rather than solids, as mentioned at . In this situation, the siphon effect of the gravity toilets would happen easier, leading people to keep the flush valve open for less time comparing to the situation where solids would be flushed.
With vacuum toilets, it does not make difference if there is solids or liquids to be flushed: the operation of the fixture does not depend on holding or not a flush valve that will put more or less water in the bowl. Vacuum toilets are activated by pressing a flush button, and after that, an internal mechanism controls the amount of water that will be used during the cycle.
Water – m3
During the data period collect, the amount of water used in the vacuum toilets was measured and none of the toilets was using more then 1.2 liters per flush.
Considering also the situation of the toilet not been flushed every time it is used by someone, there is no reason to believe that vacuum toilets would be more frequently activated comparing to gravitational ones, except for curiosity of the user of seen a different type of flush. So, the tendency is to believe that if the fixtures are not flushed every time they are used, that would happen with both type of fixtures, the vacuum ones and the gravitational also, not explaining again the calculated 7 liters per flush of the gravitational toilets.
During this period other aspects of the system operation were also analyzed. Because of the type use these toilets are subject to, a big number of blockages took place everyday. It’s not unusual to find enormous amounts of paper towel, T-shirts, underwear and other strange objects clogging toilets in an open traffic facility’s public restroom like the one studied.
An average of 1 vacuum toilet blockage every 2 days has been computed. Apparently is a high number, but checking the logbook of the airport’s maintenance department, an average of 3 blockages per day of gravitational toilets was found. In both cases, the procedure was closing the toilet booth and waiting until the airport is closed to fix the problem.
This is a good indication for the vacuum toilets system, especially when comparing to other water saving toilets, like the regular 6 liters per flush gravity toilets, since a recent study showed an increase in services calls after installing this type of fixture in Denver airport , and the present study points to a decrease in services call after the vacuum system was installed.
Unless with 100% occupancy of the toilets, witch may be the case in some peak hours but not all the time, and, in this situation, because of big lines forming to use the toilets, people could quit waiting for using then, and then, the higher availability of the vacuum toilets would lead to higher use of the fixtures. Only in this situation, 100% occupancy, we could explain why such low volume per flush in the gravitational toilets when calculating the volume per flush based on average savings.
Another aspect of this installation is the electricity consumption. Vacuum toilets systems to operate needs electricity to run vacuum pumps or any other vacuum generation device. In any place where there is elevated water reservoir that can’t be fed by the public water system pressure, electricity is also needed to pump water into this reservoir.
When we compare the electricity consumption of vacuum toilets systems with regular gravitational ones, we have to consider these two elements: pumping water and generating vacuum. In one side vacuum systems need energy to generate vacuum, in the other needs lees water to work, gravitational systems needs more water to be pumped but is only that. Therefore, depending on the height of the water reservoir, vacuum
toilets systems with vacuum pumps are more electrical efficient, because generating vacuum with vacuum pumps, in this particular situation and with the current technology, is a more efficient process than pumping water, making a positive balance to the vacuum technology.
It was not be able to precisely calculate the electrical energy consumption in this study, but preliminary considerations based on air volume consumed by the vacuum toilets during flushes, water volume consumed by both gravity toilets and vacuum ones, power and capacity of vacuum pumps, height of the water reservoir and power and capacity of water pumps showed us possible electrical energy savings of about 30% by the use of vacuum toilets. Accurate calculations in one other study were made showing electrical savings in a vacuum toilet application. 
The use of new technologies focusing water savings is becoming a really need. In several geographical regions and metropolitan areas in Brazil and other countries, potable water is getting very scarce. By saving water in fixtures like toilets, where potable water will become sewage in order to put away, for hygiene reasons, human excrement, a better use of this resource can be given such as drinking and cooking.
Water used by toilets, especially in public and high population non residential buildings, is one of the biggest consumer of this natural resource. Actions taken by public authorities, sanitary fixtures manufacturers, research and education institutes in order to develop better products and policies aiming lowering water consumption with better overall performance are important to face a situation, that can became dramatically bad, that is the availability of water, particularly in high densely populated urban areas.
As some studies show, the use of regular gravity 6 LPF low flush toilets in similar applications can lead to an increase number of services call because of blockages, nevertheless they can potentially decrease the water consumption.
When changing a regular gravity toilet system in an airport, putting in its place a vacuum toilet system, the saving presented was really of big amount, and having in mind the toilets are, in most of the cases, the biggest consumer of water in a public building like the one this study took place, is difficult to image any other action that could lead to better results.
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 CEN (Comité European de Normalisation), Vacuum drainage systems inside buildings. An European Stardand (prEN 12109:1997), Brussels, Belgium, March 1997.
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Post time: 22-07-2021