Kilometers of pipe beneath the sand

Les Sables-d’Olonne, a well-known seaside resort frequented by large numbers of tourists once the days start getting warmer again, is part of the municipality which decided to do something about its aged sewer network and to equip itself with a sewer system that would fulfill the most stringent requirements. To achieve this, it was decided to create a new wastewater treatment plant with a substantially increased capacity, a brand new and extremely effective sewer main and a new sea outlet. The ambitious program worth over 42 million Euros was launched in 2005, with the completion of the pipe network scheduled for 2006 and the wastewater treatment plant is expected to be completed during 2007.

Maximum capacities achieved

The community’s old sewage plant started to show signs of weakness since it was regularly overloaded due to its insufficient capacity. Discharges threatened to enter the marina and, depending on the shifting currents, end up on Sables d’Olonne`s beaches or may have polluted the nearby saltwater wetlands.

A study was initiated in 1998 to find a solution to the problem that would also not disturb the large numbers of tourists going to the seaside to relax and recuperate and to enjoy the picturesque landscape during the summer season. Several ideas were proposed and the solution finally agreed upon involved three phases of construction:

• the establishment of a new treatment plant with a far greater capacity than the existing located in the future Olonne development zone;
• a 14.2 km pressure transfer network;
• and a 4 km sea outlet.

Calculations showed that future effluents would this way not come anywhere near the bathing areas.

The pressure network

A problem that came with the solution adopted by the municipality is the difference in altitude between the current and future treatment plant, the latter lying 34 m higher. There was no other choice to transfer the wastewater but to set up a main pumping station at the beginning of the new transfer network. 8.7 km of HOBAS CC-GRP Pipe Systems dimensioned DN 800, PN 10 were completed with further pumping stations plus another 5.5 km of HOBAS^® CC-GRP SewerLine^® DN 250 and DN 400, PN 10 which consequently withstand the required pressure of 6 to 8 bar. While this difference in altitude created a few constraints, the new geographic location enables the construction of a far larger, high performance biological treatment plant to keep operating problems at a minimum. The treated water coming from the plant’s outlet is pumped into a new 4 km long HOBAS^® CC-GRP DN 800, PN 10 Line, with a head created by the gravity-based flow to the sea outlet. The wastewater system must maintain its head in order to avoid operating problems, e.g. produced by air pockets, with the sea outfall system. To ensure this, the pressure and the flow rate are regulated with a valve system. No manholes are needed since the whole network is pressurized. Only the Tees are installed in shafts.

The new wastewater treatment plant

While the old plant’s capacity sufficed for a population of 87,200 the new construction is capable to serve for 125,000 and later even for 145,000 because the local authority asked for certain networks to be connected directly to the transfer network as well.

Safe design – quick laying

While the study for finding the best sanitary solution for the municipality Olonne dates back to 1998, it was in 2004 that the project engineers were appointed: Sogreah Consultants for the networks and Merlin Bourgois for the wastewater treatment plant. The operation can therefore be completed in record time as the networks will be completed during the year and the sewage plant can go into operation within less than 18 months. The efficiency and professionalism of the partners associated with this massive operation should be emphasized at this point; particularly the Community Board, the Consultants, the DDE from the Ministry for Public Works as the project leader, the 4 laying companies DLE (a subsidiary of Eiffage), Cise TP (a subsidiary of Saur) and EHTP, a subsidiary of Guintoli, and Demathieu et Bard, as well as the CC-GRP Pipe supplier HOBAS France.

HOBAS^® CC-GRP Pipe Systems lent themselves naturally for their high resistance against aggressive substances in the transported effluents. Apart from this they easily handle the maximum working pressure of 6 bar plus another 2 bar for the surge. The mirror-like finish of the inner Pipe surface guarantees an optimal flow and is at the same time extremely abrasion resistant which is important considering the sea sand that is constantly washed through the pipes with the wastewater. Only pH1 cast iron could live up to these requirements but was ultimately ruled out as CC-GRP is totally unaffected by stray currents - a precious advantage in an out-of-town zone. While the inside of the Pipes will be subject to very harsh effluents, their external surface of around 20 % of the linear length has to deal with harsh environment and even saltwater wetlands, ergo a challenge for which HOBAS CC-GRP Pipe Systems are practically made for.

Once the project is completed, the current sewage plant will be taken down. The vacant lot will then be returned to the municipality, except for some space for the creation of a retention tank.

As soon as the issue of sludge treatment is settled (being processed either on site or via an external service provider), the last remaining problem to be dealt with is to establish full separation for the town of Sables d’Olonne in order to eliminate diffuse discharges. All this is done to ensure ideal treatment for all the urbanized zones in the municipality of Boroughs and to have beaches and bathing water of optimal quality.

The HOBAS group

HOBAS has been standing for high quality and innovative ideas in the pipe system segment for 50 years. Today HOBAS is a successful international organization and the leading supplier of flexible, high-performance pipe systems. The enterprise manufactures and markets HOBAS^® CC-GRP Pipes Systems and supplies advanced production technology and management know-how to a steadily growing customer base.

At present, HOBAS^® CC-GRP Pipe Systems are produced in 16 locations around the globe. The worldwide HOBAS Network includes 35 HOBAS Group owned production facilities and sales organizations in Europe and America as well as Joint Ventures and License Partners all over the world.

Products

HOBAS^® CC-GRP Pipe Systems are composed of a thermoset composite material. Comprised of fiber glass and unsaturated polyester resin as well as minerals for structural reinforcement in optimal grain-size distribution the product is manufactured by means of the HOBAS Centrifugal Casting Process. This method is patented by HOBAS and allows the production of compact pipes with programmable characteristics. Therefore, HOBAS can provide individual solutions for a wide range of applications such as sewage, potable water, raw water and irrigation, drainage, thermal cooling, industry and hydro power.

HOBAS^® CC-GRP Pipe Systems distinguish themselves by a number of highly advantageous product qualities:

• Long operational lifetime
• Leak tightness
• High level of corrosion resistance
• Product flexibility
• Transport efficiency
• Low weight
• Easy handling
• Simple installation
• Low energy costs
• Low roughness coefficient

HOBAS Pipes are available in diameters ranging from DN 150 to DN 2900, they are produced in pressure classes from PN 1 – PN 32 and show stiffness classes up to SN 1000000. The standard length of Pipes is 6 m and they are delivered with a HOBAS Sealtight^® Coupling already mounted on one end. With the use of an ordinary angle grinder the Pipes can be easily cut on site and joined by simply pushing them together. Impracticable terrain which allows only narrow pipe trenches are no problem for the installation of HOBAS Pipes thanks to their easy assembly.

However, HOBAS does not manufacture pipes alone but a wide range of supplementary products are produced alongside in order to offer complete system solutions to clients. Couplings, custom made Fittings such as Tees and Bends as well as Manholes and Water Tanks, etc. compile an assortment fit for almost any need.