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Journal of Environmental Quality Abstract -

Mineralization of Nitrogen in Fermentation Residue from Citric Acid Production1


This article in JEQ

  1. Vol. 7 No. 3, p. 315-318
    Received: Dec 5, 1977

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  1. Larry D. King and
  2. Roy L. Vick Jr.2



One of the byproducts of commercial citric acid production is presscake: a mixture of microbial biomass, CaSO4, and a filter aid such as perlite. Large production plants produce this byproduct at rates of over 50 metric tons/day. Since the material is often applied to agricultural land, it is important to know the rate of release of N and other plant nutrients so that appropriate application rates can be determined.

Wafers (1.5 cm diam by 0.6 cm thick) of presscake were incorporated into a loamy sand at rates supplying 223, 446, and 669 ppm N and surface-applied to supply 446 ppm N. Powdered presscake was also incorporated at the 446-ppm-N rate. The mixtures were incubated for 32 weeks.

Nitrate accumulated rather rapidly during the first 8 weeks, with little accumulation thereafter. At the end of the experiment, NO3-N levels at the 446-ppm-N rate were 57% of the applied N with incorporated wafers, 32% with incorporated powder, and 28% with surface-applied wafers. Gaseous N losses were 31% of the applied N with incorporated wafers, 61% with powder, and 55% with surface-applied wafers. Addition of presscake increased levels of extractable P and Ca in most treatments.

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