Phosphorus forms and extractability in dairy manure: a case study for Wisconsin on-farm anaerobic digesters.
The effect of anaerobic digestion on phosphorus (P) forms and water P extractability was investigated using dairy manure samples from six full-scale on-farm anaerobic digesters in Wisconsin, USA. On an average, total dissolved P (TDP) constituted 12 +/- 4% of total P (TP) in the influent to the anaerobic digesters. Only 7 +/- 2% of the effluent was in a dissolved form. Dissolved unreactive P (DUP), comprising polyphosphates and organic P, dominated the dissolved P component in both the influent and effluent. In most cases, it appeared that the fraction of DUP mineralized during anaerobic digestion became subsequently associated with particulate-bound solids. Geochemical equilibrium modeling with Mineql+ indicated that dicalcium phosphate dihydrate, dicalcium phosphate anhydrous, octacalcium phosphate, newberyite, and struvite were the probable solid phases in both the digester influent and effluent samples. The water-extractable P (WEP) fraction in undigested manure ranged from 45% to 70% of TP, which reduced substantially after anaerobic digestion to 25% to 45% of TP. Anaerobic digestion of dairy manure appears capable of reducing the fraction of P that is immediately available by increasing the stability of the solid phases controlling P solubility.
Güngör
Kerem
K
Biological Systems Engineering Department, University of Wisconsin Madison, Madison, WI 53706, USA.
Karthikeyan
K G
KG
D000693:Anaerobiosis; D000821:Animal Feed; D000818:Animals; D002417:Cattle; D003612:Dairying; D008372:Manure / Q000032:analysis*; D010758:Phosphorus / Q000302:isolation & purification* / Q000378:metabolism*; D013816:Thermodynamics; D014922:Wisconsin
D008372:Manure; D010758:Phosphorus