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Image of the new racks (white) of the desalination plant. SUR
Upgrades to Costa del Sol's main desalination plant could be finished earlier: This is what the new timetable looks like
Drought crisis

Upgrades to Costa del Sol's main desalination plant could be finished earlier: This is what the new timetable looks like

The two phases of the work in Marbella will be carried out by the same contractor, Marea, which will enable the deadlines to be shortened

Chus Heredia

Malaga

Tuesday, 7 May 2024, 13:23

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Upgrading the Marbella desalination plant completely so it can provide much more water to the western strip of the Costa del Sol than it has been producing is almost becoming a reality.

The Junta de Andaluocía's regional ministry of agriculture and water supply company Acosol are working with the idea of starting the autumn at maximum capacity, which would mean shortening the construction period by two or three months. Technical sources confirmed to SUR this is possible largely because the contractor for the first phase (which is now around 50% complete) and the second phase is the same.

The contractor for the seven-million-euro project is Medio Ambiente, Residuos y Agua Marea. The second phase was formalised in March for 3.42 million euros. The first phase has a budget of 3.35 million euros.

If the deadlines are met, the Costa del Sol would begin the next hydrological year in conditions of maximum solvency to face the drought. Already, in fact, projections indicate that, if the limit of 200 litres per inhabitant per day is maintained, it could face the month of October with some 30 cubic hectometres in the La Concepción reservoir (21 if the restrictions were eliminated). In both scenarios, the extra guarantee of having this plant, built in 1997 and operating since 2005, at full capacity is important, as it could provide more than 20% of the annual needs of the coast, estimated at more than 90 hm³.

The plant was designed for a capacity of 20 hm³ per year however its potential is closer to 15 hm³ per year. It was then gradually downgraded to 6hm³ per year. At the end of the work, it will mean an increase to 12 hm³ per year already this summer. That ensures 1hm³ per month, which will become 1.66 hm³ in October if nothing unforeseen happens.

In its almost two decades of operation, the year it produced the most water was 2012, when it desalinated 10 hm³. The real average has been 5.5, given that there is a month in which there is usually a technical stoppage. One condition that must be understood is that the maximum production of the plant when the work is finished will be 650 litres per second. And the coast demands up to 3,500 in high season, which has also sparked ideas to expand the Verde water treatment plant.

The trihalomethanes problem

The plant will not only recover its nominal capacity with the works, but a solution will also be found to a recurring problem that has been causing headaches for Acosol's technicians for some time now. The desalinated water is mixed in a high pipe with the raw water coming from the reservoir and, from there, it is sent to the Verde drinking water treatment plant. When the water from the reservoir comes with high concentrations of organic matter (leaves, soil, mud), a chemical reaction takes place with the desalinated water which generates trihalomethanes, volatile substances which, if they exceed certain established quantities, are potentially carcinogenic.

It can be controlled in real time, so there is no risk to health, but it does require adjustments and partial shutdowns of the desalination plant at times. This is what sparked activating the project by Narval and the first phase of the works, which is now under way.

The cost of desalination is approximately 1.50 euros per cubic metre, which is much higher than the cost of reservoir reserves, whose regulation fee is 0.015 euros per m3.

Where is seawater collected?

The plant's seawater intake is located at the mouth of the Verde river, 2.5 kilometres from the desalination plant and next to the western beach of Puerto Banús. The treatment plant is on the Istán road, very close to the aforementioned DWTP, whose expansion project has just been handed over by Acosol to the Junta (an investment of 30 million euros to treat water equivalent to two million inhabitants).

This is not the first time the desalination plant, built in the times of Jesús Gil and mired in controversy and legal disputes, has been subjected to works. Between 2007 and 2011, emergency works were carried out to improve the filtering and post-treatment system (remineralisation and chlorination).

The total built surface area of the desalination plant is 4,420 m2 on a 19,448 m2 plot of land. The appraised value of the plant is 40 million euros, of which 8 million euros would be for civil works and the rest is the value of the machinery and installations. It is owned by Acuamed (Spanish government), although it is operated by Acosol.

On completion of the works, the plant will produce 56,000 cubic metres per day from 124,445 cubic metres of seawater. The leftover, brine rejects, is returned to the sea 350 metres from the beach line and seven metres deep through an outfall. The outfall is discharged through eight diffusers that protect the marine environment.

Discharge of brine

The raw water is collected 500 metres from the coastal strip and is first pumped by four pumps to a tank, then to a storage tank and then, via an intermediate pumping system, to the above-mentioned facilities.

The sources recognise the difficulty of combining the replacement work with an installation stretched to its limits due to drought problems. This year, for example, the shutdown that is usually carried out every year for a month for maintenance has not taken place.

Once these works are completed, there is no room for further extensions, so Acosol and the Junta are already working on a second desalination plant for the coast to take the place in the planning of the one the central government once awarded to Sacyr, between Mijas and Fuengirola, with a capacity of around 25 hm³ per year.

Second desalination plant and Estepona

A second desalination plant would give extra peace of mind to the coast, which now, due to the current 57 hm³ maximum filling capacity at La Concepción, can never be more than seven or eight months. In any case, the technicians' projections suggest the 11 municipalities located between Torremolinos and Manilva will start the next hydrological year outside in moderate drought, which would mean they would have jumped two steps above the crisis level.

This summer, Estepona will also start producing desalinated water, first from brackish wells and then from seawater. The downstream water concessionaire, Hidralia, has already ordered both portable and containerised plants, which are being manufactured. Thus, 2,000 cubic metres per day will be obtained from the council's boreholes and, in the first phase, 8,000 cubic metres per day from the sea.

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