磁絮凝高效处理高浊度废水的性能及机理研究

Study on the performance and mechanism of magnetic flocculation for the efficient treatment of high turbidity wastewater

自来水供水厂在运行过程会产生大量高浊度废水,其中富集了许多微生物、有机物及无机杂质,若直接排放会严重污染河流水体及周边土壤.采用磁絮凝工艺处理自来水厂供水过程中产生的高浊度废水,通过单因素和正交试验考察了聚合氯化铝(PAC)投加量、磁种(Fe_(3)O_(4))投加量、废水初始pH值和沉降时间对废水中浊度、COD和UV_(254)去除效果的影响.结果表明,在PAC投加量为5 mg·L^(-1),Fe_(3)O_(4)投加量为20 mg·L^(-1),沉降时间为5 min,pH为7~9条件下,废水中浊度由140.8 NTU降低至5 NTU,COD由66.7 mg·L^(-1)降低至14.2 mg·L^(-1),UV_(254)由0.0430 cm^(-1)降低至0.0311 cm^(-1),去除率分别达到96.4%、78.7%和27.7%.采用扫描电子显微镜(SEM)、X-射线衍射仪(XRD)和振动样品磁强计(VSM)对絮体的形态结构、物相组成及磁性能进行表征,并对絮体分形维数及磁絮凝过程Zeta电位变化进行分析,以揭示磁絮凝作用机理.结果表明,磁种作为絮体核心,通过化学键和分子间作用力与废水中胶体颗粒形成复合磁性絮体,有利于提高絮体的分形维数,增强结构密实度,在絮凝过程中可有效促进胶体颗粒脱稳絮凝.同时,复合磁性絮体附有磁性,可通过外加磁场进一步缩短絮体沉降时间,使该工艺具有进一步扩大和工业化应用的前景.

In water supply factory,a large amount of high turbidity wastewater would be produced with many microorganisms,organic matters and inorganic impurities,bringing serious pollution if discharged directly.In this study,a magnetic flocculation was adopted to treat the high turbidity wastewater.The effects of dosage of polyaluminum chloride(PAC),dosage of magnetic seed(Fe_(3)O_(4)),initial pH and sedimentation time on the removal of turbidity,chemical oxygen demand and UV_(254)of the wastewater were systematically investigated according to single factor and orthogonal experiment.Results showed that under the optimal condition with 5 mg·L^(-1) of PAC,20 mg·L^(-1) of Fe_(3)O_(4),5 min of sedimentation time,and at initial pH 7~9,the turbidity decreased from 140.8 NTU to 5 NTU,COD was reduced from 66.7 mg·L^(-1) to 14.2 mg·L^(-1),UV_(254)decreased from 0.0430 cm^(-1) to 0.0311 cm^(-1),with the removal efficiencies of 96.4%,78.7%and 27.7%,respectively.Moreover,Scanning electron microscopy(SEM),X-ray diffractometer(XRD)and vibrating sample magnetometer(VSM),fractal dimensions and the Zeta potential were used to characterize the morphological structure,phase composition and magnetic properties of the flocs,respectively,in order to reveal the mechanism of magnetic flocculation.results indicated that magnetic seeds in the flocculation process could promote the destabilization and flocculation of colloidal particles.Magnetic seeds could form composite magnetic flocs with colloidal particles in wastewater by the chemical bond and intermolecular force,which was beneficial to improve the fractal dimension of the flocs and enhance the structure density.Owing to the magnetics of the composite flocs,magnetic flocculation could shorten the sedimentation time by external magnetic field,indicating a prospect technology for industrial application.