Improving phosphorus fixation in constructed wetland soil using three amendments

• Main Authors: Yi-Ling Tsai, 蔡宜伶
• Other Authors: Zeng-Yei Hseu
• Format: Others
• Language: zh-TW
• Published: 2005
• Online Access: http://ndltd.ncl.edu.tw/handle/08935874715893254719

碩士 === 國立屏東科技大學 === 環境工程與科學系 === 93 === Different strategies of contaminant removal in wastewater had been conducted by constructed wetland. However, the soil proiperties of constructed wetland is crucial in the above processes. Past studies always showed low efficiencies in P removal from constructed wetland for wastewater. Three amendments enriched with Al, Fe or Ca, including waterwater treatment residues (WTR, that is alum sludge), oyster shell (shell) and carbonate crystal derived from softening tap water (crystal), were used to fix P in the constructed wetland soil. The three amendments are nonhazardous wastes but with greatly annual production in Taiwan. The purposes of this study are to explore the fixation capacity of the three amendments, to increase the removal efficiency of P for the constructed wetland and to reuse the wastes as resource. The Chungpin soil series was selected as as the constructed wetland soil which is an acidic sandy loam and contains large amounts of quartz with low fixation capacity of P (FCP). Therefore we adjusts its pH value and improves its FCP by the amendments. Different application rates of each amendment were used based on the change of pH in the study soil, and the optimum application rate was determined and carried on the isotherm adsorption experiments of P for laboratory-scale incubation. Total phosphorus concentration of the inflow wastewater with 200 mg/L and the hydraulic retention time with 2 weeks were designed. Total P and cation and anion ions were monitored during the period. The soil pH was clearly increased by adding various proportions of amendments from the moderately acid to weakly acid, however, the crystal as well as the oyster-shell powder had much better effects in pH change than WTR. Additionally, the isothermal adsorption shows that FCP had been promoted significantly by adding the amendments to the soil. Phosphorus sorption maxima of the soil is 1.97 g/kg, and the optimum proportion of each amendment was 10% for WTR, 2% for oyster-shell powder, and 6% for crystal, that phosphorus sorption maxima is 3.78 g/kg, 2.71 g/kg and 2.75 g/kg, respectively. The mean removal (%) of total phosphorus was 58.3% for the WTR, 71.3% for the oyster-shell powder, and 75.6% for the crystal, respectively. The FCPs in the oyster-shell powder and crystal incubated soils were mainly controlled by Ca concentration. The major inorganic phosphorus fraction of the original soil was Fe-/Al-P (NaOH-Pi), however the proportion of the easily soluble phosphorus (NH4Cl-Pi) was as high as above 25%. After us9ing the amendments, the NaOH-Pi and Ca-P (HCl-Pi) in each incubated soil increased significantly, and the NH4Cl-Pi falled to below 12%. The inorganic phosphorus fractions of each incubated soil were mainly in NaOH-Pi, but with the less extent in HCl-Pi.