Biological nitrification: heavy metal inhibition and biomass adsorption

The present work deals with an experimentation performed in batch reactors to evaluate copper inhibition in the biological nitrification process. The inhibition was measured both directly, through AUR (ammonia uptake rate) measurement and indirectly, through sOUR (specific oxygen uptake rate) tests. Results show that, due to the essential role of small copper amount for the metabolism of organic matter, nitrifying microorganisms activity was dramatically inhibited only at a copper concentration higher than 1 mg/l. A good fitting of the AUR inhibition data was then obtained by the Kroiss model. Comparing the inhibition data obtained through AUR and sOUR tests, results show that he respirometric tests (sOUR) showed an higher degree of inhibition (up to 50%) with respect to the AUR tests, due to the small oxygen consumption that in the nitrification reaction occurred. In addition, experimental tests performed to evaluate copper distribution between the liquid and solid phases, showed that, up to a concentration of 5 mg/l, the copper amount in solution or adsorbed onto the biomass accounted about for the 98% of the total copper added, while, at higher copper concentration, because of the increasing formation of chelates and the precipitation of copper salts, this amount accounted for the 70%.