[Effect of Different Adding Means of Ignited Water Purification Sludge on Phosphorus Adsorption and Forms]

The adsorption of external phosphorus (P) and the distribution of dissolved inorganic P (DIP) in the sediment interstitial water and sedimentary P forms were researched under the ignited water purification sludge (IWPS) addition (mixing and capping). The results showed that the adsorption ability of the IWPS increased obviously, compared with the water purification sludge (WPS). It indicated that the S_max increased by 43.7%, the EPC₀ decreased by 69.1% and the DPS decreased by 54.4%. The contribution of P disappearance in the overlying water had almost no difference between the mixing and capping with IWPS, but it was obviously higher than the control in both cases. Under the mixing condition, the adsorption of external P by unit IWPS was 2.3 times of that under the capping condition, if the contacting probability between the IWPS and the overlying water was considered. Under the capping condition, the DIP in the sediment interstitial water (1-2 cm) was 33.17 times (average) of that under the mixing condition. It was attributed to the decrease of the dissolved oxygen penetration due to capping. Under the mixing condition, the external P tended to form Ca-P, while the percentages of NH₄Cl-P and Fe/Al-P to Tot-P were bigger under the capping condition. It was suggested that the improvement of the sedimentary microenvironment by mixing with the IWPS was favorable for the adsorption of the external P and the immobilization of the internal P.