The effects of aerobic pH on nitrification in a single-sludge pre-anoxic system treating high ammonia leachate

Gerard Ian Juan Charlette
The Environmental Engineering group in the Civil Engineering Department has, for the past two decades, been studying high ammonia leachate that is usually produced during both the early and late stages of sanitary landfills. This research makes use of these past achievements to study the effects of pH on the nitrification process in the aerobic tank at 20°C. The main objective was to understand how nitrification reacted to two series of pH changes, each involving a step up from 7.5 to 8.0, and
more » ... ack to 7.5 and then finally to 7.0. Each of the steps lasted around 10 to 15 days. The aerobic production of nitrous oxide (N₂O) was also monitored. N₂O is a greenhouse gas and is more potent and persistent than carbon dioxide. The pre-anoxic set-up (Modified Ludzack Ettinger process), that was used was made up of a 5L anoxic tank, 10L aerobic and a 4L clarifier. The hydraulic retention time in the anoxic, aerobic and clarifier was 1.9 hours, 3.7 hours and 1.5 hours, respectively. Leachate from the Burns Bog Landfill in the Delta Municipality was fed at 9L/day and supplemented by ammonium chloride to reach a target of 1,200 mg N/L or a load of 10kg N/day. The clarifier recycle ratio was adjusted to 6:1. The aerobic pH was maintained at 7.5 during the acclimatization period by the addition of 80g/L sodium bicarbonate. Upon reaching steady state, the system had an MLSS of around 6,000mg/L, a VSS of 5,500mg/L, and an airflow of 2L/min. The COD loading of 40 to 44g COD/day into the anoxic tank reduced the anoxic NOx to less than 5mg N/L. The ratio of nitrite to nitrates in the aerobic tank was less than 1. As the pH was lowered, it consistently led to lower nitrate concentration in the effluent, but a slightly higher nitrite concentration after 10 days. The nitrite accumulation is consistent with the suggestion that nitrite is taken to the cellular exterior, after it is formed from the oxidation of hydroxylamine. The decrease in nitrate concentration is believed to be due to the lower amount of nitrite be [...]
doi:10.14288/1.0063302 fatcat:7nvlz2xy5jethbkuwjvyutcduu