The behaviour of nitrilotriacetic acid during upflow sludge blanket clarification

The removal of nitrilotriacetic acid (NTA), a synthetic detergent builder, was investigated in a pilot‐scale upflow sludge‐blanket clarification process. Initial studies involved dosing influent water with 1 mgl−1 and 2.5 mgl−1 NTA for 32 and 34 d respectively at a surface load of 0.55 mh−1. Nitrilotriacetic acid removals during these periods were 62.6% and 41.9% respectively. At a surface loading of 1.82 mh−1 when the influent NTA was 2.5 mgl−1 NTA removal decreased to 26.4%. A transient increase in influent NTA concentrations from 2.5 to 5.0 mgl−1 resulted in a significant reduction in NTA removal. A combined transient increase in NTA concentration and surface loading caused a substantial decrease in NTA removal. The heavy metals chromium, iron, manganese and nickel were unaffected by the presence of NTA during steady state operation. However, during the transient increase in influent NTA a significant decrease in nickel removal occurred.