Influence of ignited sediments on external phosphorus adsorption and sedimentary phosphorus forms

Phosphorus (P) adsorpted by sediments, when covered by and mixed with ignited sediments from Meiliang Bay in Tai Lake, was analyzed in the laboratory. Potassium dihydrogen phosphate (KH₂PO₄) was added to the parallel experimental units to simulate periodic external P input. Based on the Langmuir model, the sediments after ignition had a greater S_max (maximum P adsorption), a lower equilibrium phosphorus concentration at zero adsorption (EPC₀), and a lower degree of phosphorus saturation in comparison with sediments without ignition. This was confirmed by the variation in the dissolved inorganic phosphorus in the overlying water. When sediments were mixed with or covered by the ignited sediments, 5.985 and 5.978 mg of input P disappeared from the overlying water, respectively. However, when the sediments were mixed with the ignited sediments, 84.18% of the input P was converted to HCl-P, whereas when they were covered by the ignited sediments, sedimentary P was released, mainly from Fe/Al-P (up to 87.50%). This was attributed to differences in the microenvironments where less-intense anaerobic conditions were formed in the mixed sediments than in the sediments covered by the ignited sediments. This suggests that the injection of ignited sediments into existing sediments enhances their P adsorption and retention. It is favor of the control of the eutrophication with a simple technology.