Strengthen the purification of eutrophic water and improve the characteristics of sediment by functional ecological floating bed suspended calcium peroxide and sponge iron jointly.

To overcome the shortcomings of conventional ecological floating bed (CEFB) in purifying landscape water, this study constructed a functional ecological floating bed (FEFB) through the suspension of calcium peroxide (CP) and sponge iron (SI) jointly below the CEFB. The purification effect of water quality and influence of sediment were compared in control check, CEFB, and FEFB systems, which were loaded the same sediment and reclaimed water in a field experiment. Results showed that the FEFB suspended with CP and SI had evident purification effect on the quality of landscape water supplied with reclaimed water and can maintain stably the nutrient status of the water body at mesotrophic levels and low turbidity. The FEFB promoted the degradation of humus, thus eliminating the chroma risk in water body caused by the decay of plants from the CEFB. Moreover, the FEFB can control the sediment mass produced, reduce the total nitrogen (TN) mass of sediment, and decrease the transformable TN (TTN) content in the sediment. The FEFB enhanced the stability of phosphorus (P) in the sediment, where the relative content of Ca-P and stable P reached 42.18% and 64.27%, respectively. To sum up, the FEFB suspended with SI and CP can not only effectively control the eutrophication and sensory index of landscape water but also change the TTN content and P forms in sediment, making the sediment more stable. Thus, the FEFB provides an innovative approach to reduce endogenous nutrient release for landscape water along with recharging with reclaimed water.

Response mechanism of microorganisms to the inhibition of endogenous pollution release by calcium peroxide.

To further explore the response mechanism of microorganisms to the synchronous control of nitrogen and phosphorus release from sediments by CaO2, the spatiotemporal changes in the physical, chemical and biological indicators of the overlying water, interstitial water and sediments in each reactor were measured in the experiment. The experiment results showed that CaO2 could increase the ammonia monooxygenase activity, nitrite oxidase activity and Nitrospira abundance in the sediment near its dosing position, and enhanced the activities of nitrate reductase and nitrite reductase at a certain distance from the dosing position, thereby promoting nitrogen removal in sediments through the alternating process of nitrification and denitrification. At the same time, the increase of alkaline phosphatase activity and Saccharimonadales abundance in the test groups accelerated the hydrolysis of organic phosphorus, and the P immobilization in sediments was realized through the subsequent precipitation reaction of Ca2+ and PO43- under alkaline conditions. In addition, the enhanced activities of dehydrogenase and catalase ensured that CaO2 would not cause great killing effect on microorganisms when improving the hypoxic conditions and inhibiting endogenous release. As a result, the dissolved product of CaO2 such as Ca(OH)2 and H2O2 reduced the nutrients concentration and killed the algae, which kept the algae density and chlorophyll a concentration at a low level throughout the test groups. Therefore, this study systematically clarified the microbial mechanism of CaO2 synchronously controlling the release of nitrogen and phosphorus from sediments, which provided a new idea for the remediation of endogenous pollution in the water system.