Fabrication Of Modified Moving Bed Biofilm Reactor Carrier And Its Performance Evaluation

Moving bed biofilm reactor as a water treatment equipment is in rapid development through the past30years and is widely used in the sewage treatment plant of various scale. Acting as the core in the moving bed process, the biofilm carrier has a great influence on the operation effects.Currently, the material of moving bed biofilm carrier is mainly based on polyethylene, and the finished product is obtained by extrusion or injection molding process. Polyethylene is in mass production and usage as the dominant engineering material, which is characterized by stable physicochemical properties and ease of processing. However, when used as the biological carrier in the moving bed process, polyethylene material has the following disadvantage:firstly, the hydrophobic surface make it not conducive to microbial attachment; secondly, the material density of polyethylene is slightly lower than that of an optimal carrier; lastly, the low strength of the material can not satisfy a complex environment of the moving bed full of collision and friction at any time.In this paper, high density polyethylene is used as the matrix material to fabricate carrier by means of single screw extruder, after the modification of a variety of modified functional materials and auxiliary materials. Starch and diatomite were added for hydrophilization of the hydrophobic surface of polyethylene. The hydrophilicity is measured by the surface contact angle of the material with water. It is found in the experiment that when the starch additive amount reached5%, the hydrophilicity of the material got a significant improvement, with the contact angle decreasing from92°down to70°, meanwhile, the material property to release nutrients increased:when the carrier is soaked in water for48hours, COD value of the water rised to60.48mg/L. Therefore by adding starch in polyethylene, we can not only improve its surface hydrophilicity, but also can equip the material with ability to release nutrients.We further use nano calcium carbonate to enhance the unnotched impact strength and tensile strength of the high density polyethylene. The compatibility between polyethylene and the applied powders is improved by maleic anhydride grafted polyethylene. We found from the experiment that, with the content of nano calcium carbonate and maleic anhydride grafted polyethylene respectively being1.5%and4%, unnotched impact strength of polyethylene increases from59.4KJ/m2to84.6KJ/m2and the tensile strength increased from24MPa to64Mpa. Thus the strength of high density polyethylene has been greatly improved. In response to the flow state and microbial biomass conditions of the carrier in water, we designed a fan carrier and an uneven pore carrier. The shapes of both carriers facilitate their movement in water, and can enhance the nitrification and denitrification reactions in moving bed bio film reactor as well.In conclusion, the hydrophilicity, biological affinity and mechanical properties of the polyethylene can be improved by modification of high density polyethylene with starch, nano calcium carbonate and maleic anhydride grafted polyethylene. And we have already produced the carriers by industrialization.