Barcelona Sea Water Desalination Plant, Spain


The Barcelona desalination plant is located next to the mouth of river Llobregat in the municipality of El Prat del Llobregat, Barcelona. With a drinking water output of 200,000m³/day, it is the largest reverse osmosis-based desalination plant in Europe. It was awarded the "Desalination Plant of the Year" award by the Global Water Awards 2010.

The plant was built by Aguas Ter Llobregat (ATLL), the public utility that is responsible for the supply of water to the city of Barcelona and the surrounding eight districts. It was intended to increase the water security and availability in the Barcelona metropolitan region. The plant was officially inaugurated in July 2009. It is currently supplying drinking water to about 1.3m inhabitants in the region, catering to almost 20% of the population.

Background

The project was originally conceived in the Spanish National Hydrological Plan and a strategic plan of Catalonia.

In 2005 the Catalan Government assigned the project to ATLL. In response to the assignment, ATLL awarded a €159m contract to Degramont and Aguas de Barcelona (Agbar) in 2007 to design, construct and operate the plant for two years.

Design

The sea water intake system comprises an open connection involving two intake towers spaced at 30m. The base of the tower is located 2,200m from the shoreline and 31m below sea level.

"In 2005 the Catalan Government assigned the project to ATLL."

Raw water for the pumping station, located about 2,500m from the desalination plant, is supplied through two 1,800mm diameter polyethylene pipes. A fibre-glass-reinforced polyester pipeline of 2,000mm diameter carries it further to the desalination plant.

Over 5,200 photovoltaic modules are installed on the roofs of eight buildings of the plant. They generate approximately 1MW of electricity annually, which can reduce 660t of CO2 emissions.

A windmill is also installed to provide electricity to the plant. It has a tower height of 20m and a turbine of 16m diameter blades.

Pre-treatment

The captured sea water is screened by passing through four automatic 3mm sieves and disinfected using chlorine dioxide, hypochlorite or potassium permanganate depending on its characteristics.

Coagulation of the disinfected water is conducted in two 250m³ coagulation chambers. Sludge is collected at the surface of the float by overflow. The flotation building contains 10 floaters, 78m² in size. Coagulant and coadyuvant are added to the water in post-coagulation chambers.

The clarified water is filtered in three stages to remove non-dissolved particles. In the first stage, water is filtered through 20 open gravity double-layered filters of Mediazur GH type. The second stage of filtration is conducted by using 20 Seaclean closed pressurised double-layered sand filters. The third stage of filtration uses 18 x 5µm cartridge filters.

Finally, a second stage of disinfection is carried out and a dispersant is added to avoid formation of salt crusts during the treatment.

Treatment

The pre-treated water is fed to the reverse osmosis (RO) membranes. The RO process used at the plant is based on a partial dual pass method.

In the first pass, the pre-treated water is pressurised at around 60bar and fed into 16,800 membranes fitted in ten RO racks in a single row. In order to optimise energy consumption and maximise water production concurrently, the membranes are set up in a hybrid system i.e. two membranes arranged in a serial order.

The second pass helps to keep the boron content below the 1mg/l limit (European regulation). It employs two twin-stage RO racks constituted of 1,092 brackish water membranes and has a conversion rate of 85%.

"The plant was built by Aguas Ter Llobregat."

The treated water has a low pH value and reduced salt concentration. To recover the balance of these results and make the water drinkable, it is re-mineralised by lime filters and disinfected by adding chlorine dioxide.

Key players

The project was co-financed by the EU, which contributed €150m. The Spanish Ministry of Environment contributed €52m, while €28m was contributed by ATLL.

Degremont supplied the plant equipment, ERI supplied the energy recovery devices and Hydranautics supplied the membranes.  DRACE medioambiente constructed the photo voltaic system.

The pipes and fittings were manufactured, supplied and erected by Protecciones Plásticas (Protesa).

Grupo ACS was appointed as the civil engineer. Procontrol rendered the control engineering. It was also responsible for programming of functions, screens and the flotation side of the control system.