Flexible water treatment with CO2
The waterworks of Consorci d’Aigües de Tarragona (CAT) in the north-east of Spain use carbon dioxide in the treatment of drinking water. on air spoke to Josep Ruana, Director of the CAT plant in L’Ampolla, about new water purification methods and the collaboration with Messer.
Clean, pure water – we all depend on it. Today, river water can only be used for our purposes – whether as drinking water or process water – after complex purification procedures. The operators of waterworks also have to use chemicals in this process which are often difficult to dispose of in an environmentally compatible manner. But there is another way, as demonstrated by Consorci d’Aigües de Tarragona. In an interview with on air, Josep Ruana explains how the Spanish waterworks converted their purification process with the help of Messer and the addition of CO2.
on air: What role does CO2 play in the new purification process?
Josep Ruana: Carbon dioxide is added to the untreated water in such a way that when the pH decreases slightly, it is possible to use new flocculants. This allows us to achieve maximum purification results in flocculation, without the formation of by-products which could affect the water quality.
on air: Could you explain that in a little more detail?
Josep Ruana: In order to get rid of suspensions and fine solids in the Ebro water, we had hitherto used aluminum sulfate or iron chloride with polyacrylamides for flocculation. Since the new legal guidelines for drinking water treatment came into force, polyacrylamides may only be added in small quantities which are insufficient for treating the water. In order to achieve maximum water purity, we have to use other flocculants. These new flocculants require the pH of the water to be controlled. Moreover, some flocculants work better within a certain pH range, resulting in tiny suspended particles agglomerating to form flocs.
on air: And you can control the pH with CO2?
Josep Ruana: Yes, the addition of carbon dioxide plays a major role in this. Stronger mineral acids could also be used, but CO2 has the advantage of lower salinity, whereas the stronger mineral acids leave behind chloride and sulfate residues.
on air: Are there any other advantages?
Josep Ruana: Yes, there are. The prevention of corrosion and scale formation is one example. According to the new laws, the water suppliers must ensure that the required water quality standard is maintained all the way to the consumer’s faucet. The key here is to have sufficient alkalinity. Unlike mineral acids, CO2 does not destroy the alkalinity. Furthermore, the addition of CO2 maintains the balance between corrosion-promoting ions such as chlorides and sulfates and the corrosioninhibitinghydrogen carbonate. Carbon dioxide is also more economical as we need less of it compared with mineral acids. What is more, we can control the pH more precisely and easily. Last but not least, the storage and handling of CO2 is simple and less dangerous.
on air: Do you always use the same amount of CO2?
Josep Ruana: No, we inject variable amounts. This means that we can adapt to different situations. For example, should the water flow fluctuate, we can still keep the pH steady. We can also react in the same way to a change in temperature, alkalinity or pH of the untreated water.
on air: Who is responsible for controlling the system?
Josep Ruana: The whole system works fully automatically, with CO2 injection being controlled by an automatic metering device from Messer. From our control room, we only monitor the parameters which also contain information on CO2 levels, temperature and pressure. In addition, an automatic telemetry system from Messer monitors the tank levels and the pressure. It sends the information directly to Messer in Vilaseca. Messer can then automatically replenish the tanks that are on-site here but which belong to Messer. We don’t need to do anything.
on air: So you work together very closely in the operation of the plant. How intensively did you cooperate during the installation of the new system?
Josep Ruana: We worked closely together at every step. Messer was responsible for the design and construction of the entire control system, with the exception of the water flow and pH measuring equipment.
