Ammonia biofiltration

Ammonia biofiltration is the process of converting ammonia into nitrates by filtering it through an active aerated compost system. This is often referred to as nitrification, the conversion of organic or ammoniacal nitrogen to oxides of nitrogen.

Measurements

Process efficiency

Process efficiency is calculated in three ways.

1. The nitrogen uptake rate (units: grams/m³/hr) This represents the scale of the system, the amount of input and output material that can be processed.
   

   grams of ammonia absorbed

   ---

   cubic meter of biofilter • hour

2. The efficiency (units: moles/m³/hr) This represents how efficient the system is. Nitrogen can leave the system in a variety of waste forms (ammonia, nitrite, nitrogen gas) but conversion to nitrate is usually what is desired.
   

   NH₄ converted to NO₃

   ---

   cubic meter of biofilter • hour

3. The latency (units: time, days-to-weeks) which defines the amount of time for the ammonia to be converted to nitrate. Smaller is better. A normal unenhanced latency might be 30 days.

Conversions

1kg of nitrogen produces

• 1.2kg of ammonia
• 5.85kg of calcium nitrate
• 7.2kg of saltpeter

So 1kg of ammonia produces roughly 6kg of saltpeter.

Other limitations

• maximum nitrate sequestration (per m³ of biofilter) before absorption or conversion are affected
• reaction temperature
• physical dimentional scaling

Process

Posmanik

Four authors including Posmanik wrote an excellent paper goes into some great detail on the matter.

This paper gives evaluation metrics of 40 (g/m³/hr), 96-100% conversion rate, and a latency of ten days.

The apparatus is six 120cm tall x 15cm diameter (21.2L) silos containing a mixture of 10L of "mature dairy manure compost" and 10L inert aeration balls, giving a system-wide total of 0.120 m³ of biofilter. Through these columns a mixture containing 15L of fresh air and 5L of ammoniated gas are pushed per minute. Approximately 0.016g of ammonia per liter of ammoniated gas would result in the measured 40g per cubic meter per hour. For the apparatus described, this would result in 115g of NH₃ (95g N) being converted into 556g of calcium nitrate per day, with an unknown latency between absorption and nitrate formation.

See Also

• compost
• nitrogen fixation
• saltpeter
• Gross, Amit; Guy, Ofer; Posmanik, Roy; Fine, Pinchas; Nejidat, Ali (2012) "A Novel Method for Combined Biowaste Stabilization and Production of Nitrate-Rich Liquid Fertilizer for Use in Organic Horticulture".
  Water, Air, & Soil Pollution 223(3); pp1205-1214. Springer Netherlands
  DOI:10.1007/s11270-011-0938-y
• Posmanik, Roy; Gross, Amit; Nejidat, Ali (2014) "Effect of high ammonia loads emitted from poultry-manure digestion on nitrification activity and nitrifier-community structure in a compost biofilter" (local copy)
  Ecological Engineering 
  DOI:10.1016/j.ecoleng.2013.10.033