Water quality variation and tubing metal release due to nitrification

Abstract

Metals are released during nitrification in drinking water distribution systems; therefore, the release of metal due to nitrification and the relationship between pipe material and water quality variation have been investigated in this research by rotating disk reactors (RDRs). As a result, the extent of nitrification depended on the pipe material; nitrifiers grown on metal surfaces would be unfavorable relative to inert surfaces because of metal toxicity. Results implicate that nitrification could affect water quality and metal release. In RDR with Cu coupons, copper release was accompanied by a decrease in pH and an increase in the nitrite concentration resulting from nitrification. Fe and Zn ions from galvanized steel followed a pattern similar to that of Cu coupons. Stainless steel was identified as the material that was the least influenced by nitrification. As for other metal ions, metal coupons generally released more metal ion when nitrification existed, moreover, it released more metal than plastic pipe whether nitrification exists or not. Electrochemical reactions and acidic environments that result from nitrification may induce these differences. Surprisingly, iron and manganese released from steel material were found to be highly correlated (R = 0.9373), and iron-to-manganese ratio precisely conform to their composition.