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NewsroomUpcoming Ammonia Limits for Wastewater Treatment Lagoons
According to the Kansas Department of Health and Environment (KDHE), the EPA is proposing a limit of 0.4 milligrams per liter for ammonia. This is achievable for a well-operated lagoon in the summer, but will be difficult for most discharging systems to meet in the winter. There are two main pathways for ammonia removal from wastewater – off-gassing and nitrification – and both of these processes drastically slow down during cold weather. Ice covering the pond limits the amount of oxygen absorbed, which is essential for nitrification. KDHE realizes that improvements to the lagoons specifically to remove ammonia may be unaffordable, so most systems will be granted a waiver.
Off-gassing is more effective in the summer, since ammonia is less soluble in warm water with a high pH. Algae growth during warm, sunny days drives the pH up. During the winter, ice cover and longer nights kill off algae. As the algae sinks, it decomposes and releases ammonia.
Since ammonia is less soluble when the pH is greater than 9, adding lime (calcium hydroxide) to the water is an option. This may be a good solution for some systems, but most treatment systems have a high buffering capacity (ability to resist pH change) and adding enough lime might not be cost-effective.
The easiest way to comply with the new permit would be a seasonal discharge, if the lagoons are large enough. Operators could draw the water level down by two or three feet in the summer and fall, when the effluent is in compliance, and hold water during the winter.
Adding aeration in the primary treatment cell and just before discharge will help with ammonia levels, it’s just a question of whether or not it will help enough to meet permit requirements. For every pound of Total Kjeldahl Nitrogen (TKN, the sum of organic nitrogen and ammonia nitrogen), 4.6 pounds of oxygen are required to convert it into nitrate – nitrogen. Organic nitrogen can readily be converted to ammonia, so it’s important to include it in the calculation. If it’s cold, aerobic bacteria will not consume much oxygen and ammonia regardless of how much oxygen is added.
The most foolproof and lowest maintenance solution is to build an additional unlined cell so that effluent can be entirely disposed of via evaporation and seepage. Reeds and cattails are allowed to grow in the cell bottom, which provides additional nutrient removal. This is the solution most favored by KDHE, since the operator would need only a state permit and not a National Pollutant Discharge Elimination System (NPDES) Permit from the EPA.
Richard Ammel, PE
Richard Ammel, PE, EBH Engineer, is a licensed professional engineer who has designed and inspected the construction of sewers, pump stations, and wastewater treatment systems for several small towns in Kansas. He received his Bachelor of Science (B.S.), Civil Engineering degree from Colorado School of Mines. Contact Richard if you would like to discuss your municipality’s waste water treatment challenges at 620-793-8411.
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