Aggressive drinking water and treatment with film-forming protection in Europe
asked 8 March 2017 asked by Loïc-R (540 points)
First of all, water at equilibrium does not foul the networks. If that happens, it is because the water chemistry is not under control. On the other hand, if there is exposure to air during transport, especially in tanks and basins, the water may leave lime scale deposits. In that case, you should avoid cascades of water at the basin inlet. Regarding film-forming products, they are being used less and less, in particular because the increase in phosphates promotes the formation of biofilm. Wherever these products were traditionally used, they have now been replaced. These days we achieve equilibrium most of the time by means of caustic soda. Unfortunately I don't know what other European countries do.
It is interesting to see the different approaches depending on the country. Indeed, in North America (Canada, but also in the United States), there seems to be more interest in film-forming products since these allow for operating at lower pH—and make chlorination more efficient. In addition, in some cases, the pH of saturation is above the regulatory limit (6.5-8.5), which means that even by adjusting the pH to around 8.5, the waters remain aggressive. However, regarding the formation of biofilm, to my knowledge, there is no recrudescence of bacteria growth with the use of film-forming products in a drinking water system, knowing that some cities have used this process for many years.
In the US, they chlorinate their drinking water as much as we do our pools in France (1 to 2 mg/L of free chlorine!). That might explain why there is no bacteria development.
I don't know about the States, but here in Quebec, the average level of chlorine in the distribution network of towns and cities has to be in the order of 0.6 mg/l of residual free chlorine. In fact, in Quebec, the regulations require a minimum of 0.30 mg/l of free chlorine at tank outlet (in the treatment facility), and there is no such obligation in the network, although it is strongly recommended to maintain trace levels of chlorine throughout the network. In other Canadian provinces the minimum is 0.5 mg/L of chlorine in the overall network.
Hello, In some cases, a film-forming solution is useful to avoid occurrences of "red" water: it allows you to eliminate the unwanted color within a few days or weeks. That's what I did here in France recently, and it did not generate any bacterial proliferation.
Actually, that is the main reason we use corrosion inhibitors here in Canada. And it works very well, without causing a proliferation of bacteria in the distribution network. It seems to me that in France you are allowed to use corrosion inhibitors to protect lead pipe networks. But as for iron corrosion (red water), if calco-carbonic equilibrium is mandatory, then you probably experience fewer instances of discolored water in your networks?
Sometimes, even water at equilibrium can be corrosive (high Larson index) or have low mineral content (so aggressive or even corrosive), and this generates problems on the network, especially if the cast iron is not coated. In France, phosphate use is subject to specific authorization.