Preparation Of The Ceramsite Substrate For Phosphorus Immobilization In Constructed Wetland

Constructed wetland was a water purification system with good ecological appreciation. In order to improve phosphorus removal rate in constructed wetland to meet the relevant requirements, preparing a good absorbent material with stable property as wetland substrate is significant. Different with traditional clay ceramsite and biological ceramsite filter used in waste water treatment, coal fly ash and waterworks sludge were used as the main materials and oyster shell as additives to make a calcined ceramsite for phosphorus immobilization in the paper. During experiment, the nature of the raw materials, the ceramsite preparation condition and the capability of the ceramsite for phosphorus immobilization had been studied.The preparation parameters influence of ceramsite composed of coal fly ash and waterworks sludge was studied. The influent degree of parameters could be ranked as calcination temperature, the ratio of materials, preheating time, calcination time and preheating temperature with descending order through the orthogonal experiment with five factors and four levels and its range analysis. Besides, with the calcination of 800℃ and 2 hours, the phosphorus adsorption of oyster shell modified was largely improved, and the adsorption capacity could reach 476.19 mg/g.The bulk density, apparent density, compressive strength of particles and phosphorus adsorption capacity were used for evaluating the adding of oyster shell influencing on ceramsite properties, the optimal preparation parameters of single factor experiment, were that the ratio of coal fly ash, waterworks sludge and oyster shell being 6:4:0.8, calcination temperature being 1050℃, calcination time being 8 min, preheating temperature being 600℃ and preheating time being 30 min. The SEM and XRD analysis showed that the ceramic contained more microporous structure, some active calcium and strength crystal composition. By the heavy metals leaching analysis, the leaching concentration of the ceramsite in solution is far below the thresholds required by Hazardous Wastes Distinction Standard-Leaching Toxicity Distinction(GB 5085.3-2007, China).The batch experiment demonstrated that the phosphorus adsorption of ceramsite could be better to some extent in neutral or alkaline environment and at higher ambient temperature. The Langmuir equation fitted showed that the theoretical phosphorus adsorption capacity was 4.51 mg/g at temperature of 35℃. In the other hand, the ceramsite packed adsorption column with continue influent secondary treatment water of urban sewage treatment plant was investigated. With the hydraulic retention time of influent being 12 hours, the phosphorus removal rate was 90%.