The efforts involved in creating the landmark Palm Jumeirah in Dubai are well publicised, from the 94 million cubic metres of sand needed to build the 560-hectare man-made island to the 25-metre deep subsea tunnel that connects it to the mainland. But less well known is that the Palm Jumeirah is currently a world leader in the field of vacuum sewage technology. According to Germany’s Roediger Vacuum, which delivered the network in partnership with local wastewater firm Concorde Corodex, the island’s vacuum station is the largest in the world.

Suction is generated within vacuum stations to pull sewage from the collection sumps where it gathers after gravitating away from the source. In the case of Palm Jumeirah, a single vacuum station removes sewage from more than 2,500 villas, using 1,200 collection pits.

Sewage suction systems

“Negative pressure is generated in the central vacuum station with vacuum pumps,” says Marc-Andre Lyachenko, regional manager for the Middle East and Asia at Roediger Vacuum, which is part of German facilities provider Bilfinger Berger. “From the vacuum station, collected wastewater is usually pumped directly into a treatment plant or transferred into existing gravity sewer networks.”

Removal of the sewage by suction is what differentiates the system from traditional sewers, which either use gravity or pump sewage away from the source and transfer it into treatment works or holding tanks. Because gravity is not required to move the flows in the vacuum system’s collection pipes, it can be laid at a relatively shallow depth of 1-1.5 metres below ground level.

This is one of the primary drivers behind the technology’s increased takeup in the Middle East. Regional topography includes flat areas with high groundwater that makes it desirable to install shallow collection systems and bypass the perils of deep excavation, which can require dewatering.

“In the Middle East, typical applications are gated communities consisting of town houses and villas. However, vacuum systems have been used even for industrial and commercial projects,” says Lyachenko. “The Qatalum aluminium plant in Qatar uses a vacuum sewer system, as does the Yas Marina Formula 1 circuit in Abu Dhabi.”

Another issue regional wastewater authorities must tackle is groundwater ingress into the collection systems, which are often designed to absorb stormwater and municipal wastewater. Combined stormwater and sewage systems are vulnerable to groundwater seeping in and the high salinity of this water means that increasingly sophisticated treatment processes are required, especially if the effluent is to be reused for irrigation or industrial purposes.

Vacuum systems are sealed and take only sewage, not stormwater, so neither ingress nor groundwater contamination from leakage out of the system is a problem. On the other hand, the relatively small pipelines and carefully optimised system designs mean that vacuum systems are inappropriate for combined sewage and stormwater collection.

In the past, operations and maintenance (O&M) requirements have deterred some investors from using the systems. “Maintenance of vacuum sewer systems was sometimes a challenge 20 years ago,” says Lyachenko. “However, there has been a technical evolution to make O&M a lot easier.”

Efficiency gains 

Over the past two decades, vacuum providers have been improving the performance of their systems by upgrading components. Contractors have also been gaining more experience in implementing and operating the systems, leading to more efficient networks.

As a result, maintenance requirements have reduced greatly and today mainly focus on the central vacuum station, which operators say has similar maintenance needs to a traditional pumping station. “There is a growing demand for vacuum sewer systems in the UAE and particularly Saudi Arabia. We are also looking at Qatar,” says Lyachenko. “The region is one of our main target markets.”

VACUUM SEWER SYSTEM SAW-TOOTH CONFIGURATION

To keep the pipes close to ground level, vacuum sewer systems are often installed in a stepped arrangement known as a saw-tooth configuration. The pipes slope towards the vacuum station typically in 100-metre sections. After each section, the pipe is lifted up again in a 45-degree angle by 20-45 centimetres. This forms the saw-tooth-shape. In this arrangement, the pipes can stay at constant installation depths or can be lifted to overcome obstacles.

Source: Roediger Vacuum