One option for achieving this related to the cost of water,” Mr Costi says.

“A vacuum sewerage system with over 200 toilets would use only 1.2L (1/3 gallon) of water per flush compared to 6-12L (1½ - 3 gallons) with conventional toilets, but the investment would be higher.

“Finally, we arrived at a mixed solution: to use a vacuum system for toilets, as well as a gravity sewerage system for other fixtures such as urinals and wash basins.

“This also allowed us to program the installation as an independent phase of the construction process, and resulted in the same cashflow situation as if we had installed a conventional sewerage system.

“The more expensive parts, such as the central vacuum unit and the actual toilets, could be purchased within the planned supply and cashflow schedule.

“Other key issues such as close supervision also had to be addressed. Because there are few examples of installation of EVAC systems in large commercial buildings, the installation was done by workers who did not have specific technical experience in this type of project.

“Also, we were not sure how the new vacuum toilets would be received by the public, and whether there would be problems with vandalism and the cost of maintenance.

“The investing group, the construction contractor, and Procion, had indeed agreed to proceed with what could have been regarded at the time as a high-risk solution.

“However, the main reason that we proceeded was that one parameter was assured – while the price of water in Brazil was very low compared with other countries, it was going to increase.”

Operation

Vacuum systems operate on the difference in air pressure between the atmospheric pressure in the toilet bowl and the lower pressure created by the vacuum in the collection pipe.

When the toilet is flushed suction is created which draws the sewage from the bowl into the pipe. Air pressure is used to transport the sewage, and water is only used for cleaning the bowl.

The vacuum sewerage system installed in the Sao Paulo project consists of two main sewerage stacks for concentrated male and female toilets. There are around 170 toilets in the Mall and Convention Centre and the remainder are installed in the theatre and administration areas.

By connecting toilets to the stacks, a toilet can be isolated for repairs or maintenance without affecting the normal operation of the others.

The central vacuum sewage pumping room has two completely independent systems with four pumps and a tank each, and the public electricity supply is backed up with a diesel generator in case of a power outage.

Successful payback

According to Luiz Costi, today the mall is a successful enterprise – this year the investors are planning a 20,000m2 (215,000ft2) expansion.

“After almost five years the system is operating effectively, the economic result is positive and public acceptance is good,” Mr Costi says.

“There were virtually no problems in assembling the system. Installation was quick and there was minimal interference with other systems within the dry wall. A major benefit of the vacuum system proved to be the ability to move sewage vertically up the system, thereby providing added installation flexibility.

“However, the most outstanding advantage of all is the payback. Given higher water prices, the system has been completely paid for on the basis of reduced water consumption.

Overcoming problems

“One problem which the maintenance technicians have needed to confront is the number of strange objects discharged by the public into the system, including underwear and plastic bags.

“This has caused intermittent pipe blockages, so a small rooter machine with seven metres of flexible cord is now used to clear pipes once obstruction sites have been identified by tapping the pipes.