With FILTRALITE®, the Pedraza drinking water production plant improved the elimination of Iron and Manganese, while increasing production
The drinking water production plant for the community of Villa and Tierra de Pedraza, in Segovia (Spain), was built by the Ministry of Agriculture, Fisheries and Food in 2012. Raw water comes from the Céguilla river; whose source is a high mountain torrent.
However, the flow of this small stream is insufficient to supply the population of the area during the summer months. Thus, raw water is withdrawn and stored to be redistributed during the months of deficit. This new process highlighted the presence of Iron and Manganese in connection with the geology of the area. These compounds are mainly present in cationic forms and also partially complexed with organic matter. The concentrations vary between 0.15 mg/l and 0.7 mg/l for Iron, and between 0.07 mg/l and 0.2 mg/l for Manganese.
Until 2021, Iron and Manganese were removed in their cationic forms using the conventional approach of oxidation – with a strong oxidant – and sand and anthracite filtration. This method has limitations and undesirable effects. At high concentrations, it is necessary to use strong oxidants such as potassium or sodium permanganate and to do so in proportion of the concentrations of each cation. Which is difficult to adjust in real time. Furthermore, this oxidation leads to rapid clogging of sand filters in connection with an increase in the quantity of particulate matter. Conventional sand filters filter on the surface and clog quickly, requiring frequent washing and notably reducing production capacity. This process can also lead to water coloring problems in the event of overdosing, and the generation of oxidation by-products.
ACUAES, in collaboration with Elecnor SyP, has defined an action plan to improve water treatment. In 2019, a first phase of column tests was carried out with Filtralite® Pure to measure the gain in performance by replacing the sand-anthracite filter bed. The results for the removal of the cationic part of Iron and Manganese have been very positive; the decision was therefore made to change all the filtering media of the plant filters.
At the beginning of 2021, the operating company Elecnor SyP replaced the existing filter media, anthracite and sand, of its four filters with Filtralite® Pure. Throughout 2021, filter performance has been monitored. The improvement has been substantial. In summer, the plant went from a production capacity of 220 m3/h with sand-anthracite to 300 m3/h with Filtralite® Pure, which represents a 36% increase. This has made it possible to reduce the number of operating hours of the plant in summer from 18 hours to 13,5 hours.
Similarly, the frequency of backwashing in summer has drastically decreased thanks to the highest retention capacity of Filtralite®. The permanganate dosage has also been reduced to a minimum. The water savings associated with the reduction in backwashing are estimated at approximately 140 m3 of water per day, the consumption of water for backwash compared to the water production has therefore fallen from 4.4% to only 0.9 %. From an economic point of view, the reduced use of washing water translates into a return on investment of the substitution from sand-anthracite to Filtralite® of one year.
At the same time, the use of oxidation treatment has been considerably reduced and the plant produces filtered water with an average turbidity of less than 0.3 NTU.
In conclusion, Filtralite® Pure has enabled the Pedraza drinking water production plant to increase production capacity by more than 30%, reduce OPEX and the associated backwashing water and energy losses by more than 75%, and easily achieve the Iron and Manganese removal goal, limiting the use of permanganate.