Application of biofilm reactors to improve ammonia oxidation in low nitrogen loaded wastewater

An airlift reactor using zeolite particles as carrier material was used for the nitrification of effluents from the aquaculture industry. During the start-up the nitrogen concentration was kept around 100 mg NH₄ ⁺-N/L to develop the nitrifying population. Later it was decreased down to around 3 mg NH₄⁺-N/L and the dilution rate was increased up to 4.8 d^-1 in order to simulate the conditions in a an aquaculture waster treatment system. A nitrogen loading rate (NLR) of 535 mg NH₄⁺-N/m² d was fully oxidized to nitrate. Higher values of NLRs caused nitrite accumulation. A second biofilm reactor was fed with a synthetic medium containing 50 mg NH₄⁺-N/L which simulated the effluents from anaerobic units treating domestic wastewater. A nitrogen loading rate of 400 mg NH₄⁺-N/L d was oxidized into nitrate with an efficiency of 60% at a dilution rate of 8 d^-1. Both biofilm systems allowed the development of a nitrifying population to treat the studied types of wastewaters.