A novel high rate method for the nitrification of sludge liquors containing high levels of ammonia

Abstract

A high rate nitrification system is proposed for the nitrification of digested sludge liquors with N-NH3 levels of between 500 and 1,000 mg/l. Bench and pilot scale studies have established that loading rates of between 1.0 and 2.0 kg N-NH3/m3 of reactor volume/day are achievable by maintaining a constant 30° C reactor temperature. The effluent standard was set at 40 mg/l of N-NH3. Loading rates in excess of 1.0 kg N-NH3/m3 of reactor volume/day required supplementing conventional fine bubble diffusion with pure oxygen. pH and alkalinity control were utilised to maintain the pH in the range 7.2 – 7.6 and total alkalinity in excess of 250 mg/l (as CaCO3) by the use of a feed mixture of NaOH and NaCO3 (20 and 40 g/l respectively). The nitrifying population was fixed and stabilised within the reactor by using reticulated foam blocks (25 mm × 25 mm s× 25 mm) occupying approximately 30% of the reactor volume. Settlement was achieved by conventional clarification with a nominal up flow velocity of 1.0 m/hour.