Preparation Of Magnetic Bio-carriers And Their Characteristics On The Cd²⁺/phenol Complex Wastewater Treatment

Biomass materials such as sawdust and straw have good hydrophilic and biological characteristics. As containing a lot of functional groups such as-COOH,-NH2,-OH,-CONH2, these materials can adsorb different heavy metals. But many biological methods can effectively remove organic compounds. Moreover, the weak magnetic field is benefit for microbial growth and can improve degradation effect of pollutant. So in the study, Cd2+/phenol complex wastewater used as the research object, some biomass materials such as sawdust, peanut shells, soybean stem were selected to make magnetic bio-carriers by the chemical coprecipitation method. These magnetic bio-carriers were characterized with special surface area measurement and X-ray diffraction (XRD) and the dosage of dissolution ferrum was measured during application of these maginetic bio-carriers. Adsorption performance of Cd2+on original and magnetic bio-carrier was compared. The removal rate of Cd2+and phenol in the complex wastewater were investigated with original and magnetic sawdust used as biofilm carriers. Otherwise, the treatment effects of these biomass materials were compared with granunal activated carbon during whole experimental process.The main conclusions in this study have been summarized as follows;(1) Magnetic carriers made by chemical coprecipitation method have good magnetic stability characteristic. And modification by magnetization treatment for these carriers can improve specific surface area and pore size of them. Specific surface area of sawdust and peanut shells increased from2.2m2/g to49m2/g and from4.8m2/g to63.0m2/g respectively. Moreover, pore size of them also could achieve16μm and19μm respectively. Based on the analysis results of XRD, the iron oxides formed on the surface of these carriers were mainly Fe3O4and FeaO3.(2) The intial pH had large effect on the absorption of Cd2+. The adsorption velocity will be increased with rising pH in the region of2～6. Moreover, the adsorption velocity was fast and the balance could be achieved in60min. At room temperature, the removal rate of Cd2+adsorbed by these magnetic bio-carriers could achieve similar results with that of granular actived carbon. They all could reach above95%with initial Cd2+concentration and adsorbent dosage of20mg/L and6g/L respectively. The adsorption isothermal data of Cd2+on these magnetic bio-carriers could be interpreted the Langmuir and Freundlich equations. The maximum adsorption capacity of Cd2+on magnetic sawdust, magnetic peanut shells, magnetic soybean stem and magnetic active carbon was12.4mg/g、23.6mg/g、14.5mg/g and14.2mg/g respectively.(3) When biofilm had developed on these biocarriers, the removal rate of phenol on sawdust carrier was almost the same as the granular active carbon and could obtain about95%. Moreover, the removal rate of phenol on sawdust carrier with biofilm could improve above80%comparing with original sawdust carriers without biofilm. The removal rate of Cd2+on sawdust carrier was almost the same as the granular active carbon and could obtain about73～90%. The period of biofilm formed on sawdust carrier could be shorten and biomass could also be improved about8%comparing with granular active carbon carrier.(4) Under the same experimental conditions, compared with original sawdust with biofilm, the removal rate of COD and Cd2+on the magnetic sawdust with biofilm could increase9%and12%respectively. The removal rate of phenol on sawdust and magnetic sawdust all could reach above95%. The period of biofilm formed on magnetic bio-carrier could be shorten and biomass could also be improved about30%comparing with bio-carrier.