The elemental compositions of P-accumulating microbial granules developed in sequencing batch reactors

The effects of substrate P/COD ratios on the elemental compositions of P-accumulating microbial granules were investigated. Results showed that the substrate P/COD ratio had a significant effect on the elemental compositions of P-accumulating microbial granules. The P content in granules fell into a range of 1.9–9.3% by weight and increased with the increase of substrate P/COD ratio. Chemical precipitation-related P in granules accounted for less than 10% of the total P accumulation, i.e. biological storage was mainly responsible for the observed P accumulation in granules. These indicate that microbial granules cultivated had an excellent ability to uptake phosphorus from liquid solution. According to the elemental analyses, the empirical formulae of P-accumulating granules developed at different substrate P/COD ratios were generated. Significant difference in the elemental compositions between P-accumulating and non-P-accumulating granules was observed, indicating a shift in microbial association. A substantial accumulation of calcium and magnesium ions was found in the P-accumulating granules, and was closely related to the poly-phosphate accumulated in granules. The present results show potential application of microbial granules in enhanced biological phosphorus removal process.