Removing Lagoon Ammonia via Nitrification Requires:
- Healthy levels of dissolved oxygen (DO) in your lagoon—Wastewater lagoon nitrification consumes large quantities of oxygen. Just for reference, every pound of BOD oxidized consumes 1.5 lbs of O2. On the other hand, according to Metcalf & Eddy, every pound of ammonia oxidized consumes 4.57 lbs of O2. In order for lagoon nitrification to occur, a minimum working DO level of 2.0 mg/L is required and a DO level of 5 mg/L is optimal. Therefore, you must ensure that your lagoon aeration system is properly sized, and working efficiently and effectively enough to provide the necessary oxygen.
- BOD reduction—Nitrifying bacteria do not compete well against BOD-removing heterotrophic bacteria. For nitrification to take place, BOD levels must be sufficiently reduced in order to eliminate competition. Generally a BOD level of 20–30 mg/L is required before lagoon ammonia removal can begin.
- Lagoon pH of 7.5–8.0—Lagoon nitrification is pH-sensitive, and ammonia treatment rates decline significantly at pH values below 6.8. Optimal lagoon nitrification rates occur at pH values in the 7.5 to 8.0 range. Most municipal wastewater lagoons will naturally have a pH in this range. However, industrial wastewater lagoons may vary, so be sure to monitor these levels closely.
- Sufficient lagoon water temperature—Similar to many other wastewater lagoon treatment processes, nitrification slows as water temperature decreases. Optimal temperature range for lagoon nitrification is 82 to 97° Fahrenheit. This is clearly unrealistic for most wastewater lagoons, but acceptable rates of lagoon nitrification can also be achieved at or above 68° F. Triplepoint’s NitrOx® system optimizes temperature when needed to ensure nitrification year round, even in cold climates.
- Adequate mixing—Ammonia can be released as a result of the anaerobic digestion of sludge at the bottom of the lagoon. As a result, without mixing to prevent sludge buildup, ammonia effluent levels can actually end up being higher than that of influent. Ideally, it is recommended that sludge depths remain below 2 feet. Another adverse effect of a poorly mixed lagoon is short circuiting. This occurs when a basin becomes stratified, allowing influent flows to take a “short cut” through it by only moving through the top layer (or stratum) of the water. This lack of homogeneity results in reduced retention time for the water, and generally leads to poor overall treatment, including poor BOD and ammonia treatment.
- Biomass—Nitrifying bacteria are attached-growth organisms, so the more surface available for them to attach to, the more will grow.