[Phosphorus Enrichment Efficiency of CaO2@FA Composites and the Effect of Its Recovered Material on Soil Improvement].

To explore the resource utilization of phosphorus (P) in wastewater and industrial waste fly ash, we used an efficient composite material (CaO2@FA) for phosphorus removal by loading nano-CaO2 on the surface of fly ash as well as in the pores using the surface precipitation method. The results showed that the material had a larger specific surface area and porosity after loading CaO2 on the fly ash surface. The specific surface area increased to 4.641 m2·g-1, and the total pore volume was up to 0.025 cm3·g-1. The adsorption process of CaO2@FA on P could be described using the Langmuir isothermal adsorption model, and its maximum adsorption capacity was 185.776 mg·g-1(20℃). The adsorption mechanism was attributed to chemical precipitation, mainly the formation of calcium hydroxyphosphate. The enrichment efficiency of CaO2@FA composites on P was significantly higher than that of fly ash, and the efficiency was increasing with the increase in the dosage added. HCO3- and CO32- in the coexisting ions had a negative effect on P adsorption by the composites. The enrichment rate of P in domestic wastewater was up to 93% when the dosage of CaO2@FA composites was 2.0 g·L-1. The content of biological P in the recovered precipitates reached 1.658 mg·g-1. The soil improvement test showed that the biological P content in soil increased by 102.9% when the recovered precipitates were added into the soil. This indicated that the operating cost of recovering 100 mg of P by this composite was as low as 0.76 yuan.

[Effect of Oxidation Strengthening on In-situ Phosphorus Immobilization of Calcium Hydroxide].

In this research, calcium hydroxide[Ca(OH)2] and hydrogen peroxide (H2O2) were injected into the bottom mud in the form of plum blossom scatterers to investigate the effect on the control of endogenous phosphorus. The results showed that Ca(OH)2 used singly effectively immobilized in the order of 90% of endogenous phosphorus approximately 20 mm below the sediment-water interface (SWI); however, at the same time, the anaerobic environment was enhanced, resulting in the transformation of stable phosphorus to easily released phosphorus and the accumulation of potential active phosphorus. Nevertheless, the addition of H2O2 greatly reduced the amount of potential active phosphorus in deep sediments after adding Ca(OH)2. The vertical diffusion depth of Ca(OH)2 in the sediments was significantly increased, having an influence across the depth range of 0-40mm below the SWI; the improvement at depths greater than 40 mm was not notable, which was mainly attributed to an 18-fold increase of redox potential due to the addition of the oxidant. The change of phosphorus forms in the sediment also demonstrated the excellent immobilization effect of the oxidant on phosphorus. In the 0-20 mm layer, the content of readily released phosphorus decreased significantly, while compared with a control test, Ca-P increased by approximately 10%. However, at greater depths, the amount of easily released phosphorus decreased and the rate of Ca-P increase gradually slowed.