Effects of Chemical Sludge Recycling on the Removal of Phosphate from Water

• Main Authors: Ling-Ching Hsiao, 蕭玲菁
• Other Authors: Wei-Chin Chang
• Format: Others
• Language: zh-TW
• Published: 2007
• Online Access: http://ndltd.ncl.edu.tw/handle/25417262485754779975

碩士 === 國立雲林科技大學 === 環境與安全工程系碩士班 === 95 === This research evaluated the effect of recycling the precipitated sludge on chemical phosphorus removal system, by using adsorptive capacity of the aluminum hydroxide (Al(OH)3) sludge on phosphate. The influence of recycling chemical sludge on phosphate removal was investigated by conducting a sevies of batch and continuous adsorption experiments in laboratory to simulate the post-precipitation process. The batch experiment results showed that recycling precipitated sludge in the phosphorus removal system can promote the efficiency of phosphate removal under the same PAC dose, owing to the phosphate adsorption by aluminum hydroxide in returned sludge. The suspended solid and COD was also reduced in the same tests. Besides, the process performance of using PAC was better than that of using the aluminum sulfate. The results of adsorption isotherm experiments showed that increasing sludge dosage elevated the adsorption rate and the adsorption kinetics followed the Pseudo-Second-Order Model. Besides, the Freundlich equation was fitted better than the Langmuir equation, the Freundlich constant K was 12.62, n was 0.97. The results of the continuous adsorption experiment showed that the efficiency of phosphate removal was increased from 84% to 94%, the residual phosphate was reduced to 0.5 mg/L from 1.6 mg/L when the chemical dosage is Al3+/P = 1.5. It was also found that returning the sludge produced by dosage of Al3+/P = 2.0, can obtained about 13﹪of the phosphate of removal in adsorption tank. Furthermore, if increased the recycling sludge concentration to two times of precipitated chemical sludge, the efficiency of phosphate removal can be upgraded to 36.9%. The results of column adsorption experiments, operated by using spent aluminum sludge from water purification plant, showed that increasing the height of bed packed aluminum sludge extended the breakthrough time. The correlation coefficients were calculated for selected breakthrough point from BDST graph. The correlation coefficients were all more than 0.99; revealing that the BDST equation could be fitted well for these experimental data. The value of N0 showed that the adsorptive capacity of PO43- was increased from 20.4 mg/L to 36.2 mg/L (flow rate, 6 ml/min); 40.8 mg/L increased to 52.1 mg/L (flow rate, 9 ml/min); 21.8 mg/L increased to 73.4 mg/L (flow rate,12 ml/min) with the bed-depth height increase. It also implied that the PO43- could be successfully removed by aluminum sludge through the column adsorption. However, because the particle of aluminum sludge was too fine, it was not easily fixed on bed. This question should be overcome by using the spent aluminum sludge as adsorbent for phosphate removal from column adsorption process.