Tampa Bay SWRO

ACCIONA has used a pre-coat filtration system in many facilities, such as the Tampa SWRO (Florida).  The pre-coat filters used by ACCIONA are high efficiency pressure filters for retaining suspended solids. They are particularly effective for solutions that require a high level of quality, such as pre-treatment for desalination by reserve osmosis, solutions with low solid content, with SDIs below 3.

The pre-coat filter can add to the filtration and absorption properties, depending on the type of material used to make the pre-coat. They are also used for processing oils and grease, when using other filter types would be unsuitable.

In order to avoid the entry of molluscs and fish that prevent filters from working properly, a biocide product is continuously dosed in conjunction with automatic grilles with 3 millimetre gaps.

The distribution of water to the 250 plus sand filters was modified and a second filtration stage added, much finer than the existing filter. The natural resource of finely ground fossilised shells of single cell algae was used. The chemical products dosing was also modified and the entire system was automated.

All the membranes were replaced, totalling over 10,000, with a new membrane washing system designed and installed with temperature regulation and instruments added

The water resulting from the osmosis process does not contain minerals. In order to add them and meet supply quality requirements, new equipment for dosing chlorine dioxide and calcium hydroxide were installed

The solids removed from the water during the treatment are in a very diluted state. In order to reduce transport costs, a thickening and dehydration line was constructed, which produces solids with a 25 % concentration (which can be transported by lorry), and the water is recovered in the desalination plant

At full capacity, the reverse osmosis process generates around 72 million litres of brine, which is diluted with 5,300 million litres of water used by the neighbouring power plant for cooling, providing a dilution ratio of up to 70:1.

The diluted water then passes through the plant's discharge channel, mixing with more seawater and is returned to Tampa Bay with a salinity level almost equal to the bay's water, meeting every safety requirement.

The major volumes of water that flow close to the Big Bend area help dilute it even further, ensuring that salinity does not build up over the long-term.