DISTRIBUTION OF PHOSPHORUS FORMS IN CHILEAN SOILS AND SEWAGE SLUDGE BY CHEMICAL FRACTIONATION AND 31P-NMR

The disposal of sewage sludge from domestic wastewater treatment plants is a growing problem worldwide. Because of the total P content and other characteristics, it is highly probable that in Chile important amounts of the sewage sludge will be disposed of on agricultural lands. The distribution of P forms in Chilean soils and sewage sludge was studied by chemical fractionation and 31P-NMR spectroscopy. The 0-15 cm depth of soils derived from volcanic materials (one Ultisol and two Andisols), alluvial materials (Mollisol), and sewage sludge from a domestic wastewater treatment plant located in Santiago were considered. The total P concentration is 6 to 18 times higher in the sewage sludge than in soils, but a similar 31P-NMR pattern was found in all samples. The most important signals correspond to inorganic orthophosphate and monoester P, with small signals assigned to pyrophosphate and diester P. The disposal of sewage sludge might not succeed as soil P fertilizer, contributing to an increase in the accumulation of P in volcanic soils, and it might be a potential pollutant in soils and water