Biological and chemical phosphorus fractionalization in swine manure under aeration

Abstract

In this work, the dynamic responses of different phosphorous factions in swine manure to aeration treatment were investigated and profiled to provide insight on potential ways to improve the biological phosphorus removal process. Batch reactors fabricated from clear acrylic columns were filled with fresh swine manure containing a 4.6 % solids content, which was aerated continuously for 15 days at an airflow rate of 2 L/min. The results indicate that the treatment can reduce soluble phosphorus (P) by about 78 % after only one-day aeration due largely to chemical precipitations. At the end of the experiment, the average soluble inorganic P level was reduced by 12 % (from 91 down to 79 %), while the average soluble organic P was increased by 13 % (from 9 to 22 %). The biomass P (DNA/RNA/poly-P) was increased by 24 % in the first three days, but only by 14 % in the rest 12 days of aeration. Also increased by aeration was the lipid P (47 %) but not the protein P. The data reveal that the current aeration rate cannot maintain a stable oxygen level [represented by the oxidation-reduction potential (ORP)] in the treated manure, evidenced by the decrease in ORP from 250 mV at the beginning to almost zero at the conclusion of the experiment, which is considered the major factor hindering the growth of aerobes, including the phosphorus-accumulating organisms (PAOs). Therefore, it may be concluded that continuous aeration of swine manure at a constant rate will not guarantee the supply of sufficient oxygen to the growth of PAOs. On another front, it was observed that too much aeration might negatively impact the overall P removal by increasing the release of soluble organic P from dead cells.