NEW TREATMENT OF HARD DRINKING WATER – INFLUENCE ON COPPER CONTENT AND ORGANIC MATTER / Ny dricksvattenbehandling – inverkan på kopparutlösning och organiskt material
Hard drinking waters give problems in several respects. The copper content can be > 2 mg/l after stagnation. The use of detergent is increased and discouloration can occur. Uppsala water work has developed a process to decrease the alkalinity and hardness of the water in a way that does not use special chemicals. The process is described in the report. It is now used in full scale in Malmö. The influence of organic matter in the water is also described.
Hard waters (dH°= 14-23) with pH -7, alkalinity – 300 mg/l and DOC (TOC) =2-13 mg/l can through a treatment using fine sand and water with high velocity at pH -8 be changed to hardness – 5 and alkalinity -100 mg/1. The untreated hard waters have after stagnation 4—12 h in copper plumbing tubes a copper content of 2-3 mg/l. Only 3 % of that is present as Cu-ion. This is found through ISE measurements, pH-HC03 equilibrium calculations and predictions from pH and DOC contents.
The water will after the treatment have much lower copper content, Cu-tot < O. 1 mg/l, with equilibrium copper ion, Cu-ion (equil) < O.Ol mg/l. The copper ion based on DOC content, Cu-ion (DOC), is only 1 % of Cu-tot. It is not possible from the results so far to calculate how much of the Cu-tot that will be bound to DOC. German results show that after 4 h stagnation untreated hard waters with pH >7.1 and TOC < 0.5 mg/l results in Cu-tot < 0.2 mg/l and at TOC > 1 mg/l in Cu-tot > 3.0 mg/l. It is evident that for high Cu-tot that the measured Cu-ion (ISE) come close to the Cu-ion (equil) and Cu-ion (DOC). A DOC content of 4-13 mg/l can bind 2-3 mg/1 Cu.
The treated water has lower hardness and thus lower alkalinity and calcium content. This means that less detergents are needed and discolorations are avoided.