Novel Ceramsite Substrate of Constructed Wetland: Preparation and Study on Phosphorus Removal.

Ceramsite substrate was prepared by crushing, screening, mixing, pelletizing, preheating and calcining using polyaluminium chloride residue (PACR) as the main raw materials. Through orthogonal design-range analysis, the best preparation condition of ceramsite substrate determined was: the ratio of PACR: bentonite was 14 g:6 g; amount of eggshell 0.6 g, calcination temperature 600 °C, and calcination time 60 min; and SEM-EDS and XRD were used to characterize the micromorphology, element changes and crystal structure of the ceramsite substrate before and after phosphorus adsorption. Furthermore, static adsorption experiment was conducted, which indicated that the prepared ceramsite substrate possessed good phosphorus adsorption characteristics, with the removal rate of 99.74% and the adsorption capacity of 4.12 mg/g; the adsorption process conformed to the quasi-second-order kinetic model and was controlled by physical and chemical processes; the adsorption isotherm fairly fit the Langmuir and Freundlich models, indicating that ceramsite substrate could provide homogeneous monolayer and heterogeneous multilayer active sites for phosphorus adsorption; and the speciation analysis for the adsorbed phosphorus revealed that the chemisorption by aluminum, calcium and iron in ceramsite substrate was the dominant adsorption mechanism. Finally, the laboratory dynamic column experiment conducted revealed that the Thomas and Yoon-Nelson models could used to well simulate the dynamic adsorption data of ceramsite substrate: the higher the phosphorus concentration in the influent, the shorter the penetration time of the adsorption column of ceramsite matrix. In general, the ceramsite made from PACR could be used in constructed wetland as a potential substrate for removing phosphorus in sewage; besides, the headache problems of solid waste such as PACR in Gongyi area of Henan Province would find a way to tackle. In summary, the aim of turning waste into treasure and green environmental protection could be expected to attain. [ABSTRACT FROM AUTHOR]