Evaluation of Nitrate Retention Additives for Developing Environmentally Friendly Manures

Activated carbon is a readily available material that can be added to fertilizers or manures to
reduce nitrate nitrogen (NO3-N) contamination of surface and near-surface groundwater. To test
the nitrate adsorption performance of activated carbon, its absorbance was compared to that of
used wall board (gypsum), sand, carbon, iron filings, wheat litter, wood litter, coffee grounds,
bauxite residue and vermiculite using a nitrate ion selective electrode. Of these adsorbent
candidates, only activated carbon exhibited a significant nitrate adsorption capacity.
A linear adsorption isotherm was observed (r2 = 0.975) over the dosing range 0.77-6.1 mg NO3-
N/g activated carbon using nitrate standards. The adsorption capacity observed using neat
standards was 0.69 mg NO3-N/g carbon. The performance of activated carbon for adsorbing
nitrate under simulated runoff conditions was evaluated for 10, 20, 30, 40 and 50 weight %
mixtures of activated carbon with cow manure. The nitrate adsorption capacity observed for
mixtures of activated carbon and cow manure was 0.47 mg NO3-N/g carbon, which is 68% of the
ideal adsorption capacity observed using neat standards. This shows that activated carbon can be
added to cow manure to significantly reduce NO3-N runoff to water supplies and create an
environmentally friendly manure-based fertilizer.


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