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Effects of operating parameters on the biosorption of hexavalent chromium by Tubificidae

基金项目：浙江省自然科学基金 (No.Y12E080076);浙江省高等学校创新团队支持计划(No.T200912);浙江省教育厅项目(No.Y201017078)

摘要：水蚯蚓能通过摄食剩余污泥而使污泥减量,但剩余污泥中常含有各种重金属污染物.本文以颤蚓科蠕虫 (Tubificidae)为研究对象,以六价铬为典型重金属污染物,考察运行工艺参数:初始铬浓度、pH、水蚯蚓投加量和温度对水蚯蚓吸持六价铬的影响.实验结果表明,在研究浓度范围内(0.1~8.0 mg · L^-1),水蚯蚓对六价铬的吸持速率随铬浓度的增大而加快,单位质量吸持量从14.4 mg · kg^-1(以干重计,下同)增加到312.7 mg · kg^-1,但六价铬的吸持率却随Cr⁶⁺初始浓度的增加而降低;pH从6.0增加到8.0,水蚯蚓对六价铬的吸持速率随pH的上升而提高,吸持率和单位质量吸持量先明显增强,pH达到7.5后逐渐趋于平衡,即吸持最佳pH为7.5;水蚯蚓投加量从1.0 g(以湿重计,下同)增加到5.0 g时,吸持速率及吸持率均上升,但单位质量吸持量却随着水蚯蚓投加量的增加而减少;当温度在10~20 ℃范围内时,水蚯蚓对六价铬的吸持速率相对较慢,到25 ℃时,吸持速率明显加快,吸持率和单位质量水蚯蚓的吸持量的变化趋势与吸持速率的变化相一致,但当温度达到30 ℃,水蚯蚓会大量死亡,综合考虑,处理系统最佳温度宜控制在25 ℃.

Abstract：Tubificidae is often used in the wastewater treatment systems to minimize the exess sludge production, but waste sludge always contains various heavy metals. Effects of initial concentrations of Cr⁶⁺, worms quantity, pH and temperature on the biosorption of hexavalent chromium by Tubificidae were investigated in this study. The results indicated that the adsorption rate increased with the increasing initial concentration of Cr⁶⁺. The adsorption amount increased from 14.4 mg · kg^-1(dw) to 312.7 mg · kg^-1(dw), but the adsorption efficiency was reduced. With pH increasing from 6.0 to 8.0, the adsorption rate increased, and the adsorption efficiency and the adsorption amount also increased obviously with pH until reaching equilibrium at pH 7.5. The adsorption rate and the adsorption efficiency increased when the quantity of Tubificidae increased from 1.0 g to 5.0 g, while the adsorption amount decreased. The rate, efficiency and the adsorption amount increased gradually as the temperature rose from 10 ℃ to 20 ℃, and then increased rapidly when the temperature reached 25 ℃. However, large amount of worms died when the temperature was up to 30 ℃. Generally, the results indicated that the optimum conditions for Tubificidae growth were pH 7.5 and temperature 25 ℃.