Many systems require chemical additions to provide alkalinity needed for ammonia removal. Often I get questions on what is the "best" source of alkalinity. And, how much is needed to stabilize the system. In response to question frequency, I decided to post the following bullet points.
- Remember pH and alkalinity are not the same thing and are not correlated. Alkalinity is the buffering or resistance to pH change of the water. For example, it takes more acid to lower the pH of a water with higher alkalinity than a low alkalinity (low hardness) water.
- Alkalinity is needed in wastewater as most beneficial microbes operate best in the 6.5 - 8.5 pH range. More specifically, ammonia removing nitrfiers function best between 7.2 - 8.0.
- Usually we need a minimum 40 - 50 mg/L effluent alkalinity as calcium carbonate of biological treatment to ensure adequate buffering in the system.
- Common Sources of Alkalinity (miliequivalent weight of calcium carbonate)
Caustic (sodium hydroxide) - 40 mg/meq
Lime - 37 mg/meq
Mag Lime - 29 mg/meq
Soda Ash (sodium bicarbonate) - 53 mg/meq - What Decreases Alkalinity
1. Anaerobic acid formation (fermentation) - produces organic acids
2. Nitrification (ammonia removal) 7.14 mg of alkalinity consumed per mg ammonia nitrogen oxidized to nitrate. - What Increases Alkalinity
1. Denitrification (NO3/NO2 conversion to N2 gas) releases 3.6 mg of alkalinity.
2. Methane production in anaerobic digesters - low pH in digester indicates organic acid buildup and low methane production. (methanogens use H+ to form CH4 gas)
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