Production of Oxalic Acid from Aspergillus niger and Whey Permeate

When manure is applied to crops on a nitrogen basis, it often creates a buildup of phosphorus (P) in the soil. Phosphorus recovery as struvite is one strategy to capture excess P prior to land application. Dairy cow manure requires an acid pH to break the calcium phosphate bonds present in the manure, and oxalic acid is desirable because, in addition to breaking bonds, its anion binds calcium. The fungus Aspergillus niger is known to produce primarily oxalic acid when utilizing a lactose substrate. Whey permeate is a byproduct of cheese-making and a potential inexpensive source of lactose. An experiment was designed to measure oxalic acid production by Aspergillus niger using two strains of Aspergillus niger (ATCC 6275 and ATCC 9029), whey permeate with varying lactose concentrations of 11 and 20%, and fermentation temperatures of 30 degrees C and room temperature. All fermentations produced oxalic acid; however, concentrations were below 10 mM.