Strategies for removing lagoon ammonia have become a hot topic over the past few years. Many state environmental agencies have been introducing new ammonia limits for wastewater facilities, including lagoons. This is a problem because most wastewater lagoon systems were not originally designed for ammonia treatment; as a result, most will require some kind of upgrade.
In this episode of Lagoons Do It Better TV, Removing Lagoon Ammonia: 6 Key Factors for Nitrification, lagoon specialists Patrick Hill and Brady O’Leary outline the six conditions that must be optimized to ensure lagoon ammonia removal via nitrification.
Nitrification is the most common way to biologically remove ammonia in wastewater lagoons. In this process, ammonia treatment occurs courtesy of bacteria already present in the water. These bacteria break down the ammonia and eventually promote the release of nitrogen gas into the atmosphere. The end result is that your wastewater lagoon ammonia is nitrified, resulting in lower ammonia levels in your effluent.
Watch the video, then read below for more details on the information presented. Then register for Lagoons Do It Better, our community for lagoon professionals!
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.
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.
Removing lagoon ammonia through nitrification is not an easy process to master, and with stricter effluent requirements, it’s a problem that won’t go away any time soon. By investing in the right infrastructure and treatment system, as well as optimizing the 6 key factors, you can stay ahead of the curve in terms of wastewater lagoon ammonia treatment.
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