Preparation Of Positively Charged Red Mud-based Carrier And Its Loading Mechanism Of Anaerobic Ammonia Oxidation Bacteria

Compared with traditional nitrification and denitrification denitrification technology,anaerobic ammonia oxidation（anammox）process is a new biological denitrification technology with wide application prospects and high energy efficiency.However,the slow proliferation of anaerobic ammonia oxidizing bacteria（AnAOB）has severely restricted the engineering application of anammox process.Therefore,how to maintain the abundance of AnAOB in the process is the key to the development of anammox process,in which the immobilization of AnAOB by biological filler is one of the main means to maintain its abundance.Therefore,the development of high enrichment efficiency biopacker for the properties of AnAOB is the key to the problem.Based on the above considerations,this research paper proposes the use of metal salt solution to modify the preparation of charged terracotta-based fillers based on the chargeability of AnAOB for the purpose of enhancing the affinity of AnAOB,and the mechanism of AnAOB adhesion behavior on the surface of the charged terracotta-based filler is investigated.The main conclusions are as follows:（1）After 425 d of start-up and operation of the anaerobic ammonia oxidation reactor TN load was elevated to a maximum of 1.280 kg-N/m³/d.Macrogenomic whole gene sequencing analysis revealed that the reactor formed AnAOB communities dominated by Candidatus Kuenenia and Candidatus Brocadia,which provide a source of inoculum and an enrichment site for positively charged red mud-based fillers loaded with AnAOB.（2）The optimum conditions for the preparation of red mud-based fillers（RMGA）were determined by orthogonal and single-factor experiments:roasting temperature of1080℃,roasting time of 80 min,and the ratio of red mud,wood chips and bentonite of 86:10:4.The non-homogeneous coalescence method was used to prepare iron chloride red mud-based fillers（RMGA-Fe）and microbial promoter modified red mud-based fillers（RMGA-MA）on the basis of RMGA.The zeta potentials of RMGA,RMGA-Fe and RMGA-MA at p H=7 were-0.533 m V,1.86 m V and 9.01 m V,respectively,which completed the charge-positive modification of RMGA;the specific surface areas of BET analysis were 0.373 m²/g,5.038 m²/g and 0.728 m²/g,respectively.The leaching experiments of heavy metals in the simulated packing operation showed that the concentrations of As,Cd,Ni,Pb,Cr and Cr（VI）were lower than the detection limits of the"Comprehensive Wastewater Discharge Standard GB8978-1996"after 20 h leaching.（3）The experimental results of the nitrogen removal rate of the filler showed that the average nitrogen removal rates of RMGA,RMGA-Fe and RMGA-MA fillers prepared in this study were 24.4%,175%and 40.3%higher than those of commercially available K3 fillers,respectively,which showed that the nitrogen removal rates of the red mud-based fillers before and after modification were higher than those of commercially available fillers and had good prospects for engineering applications.Meanwhile,the average nitrogen removal rates of RMGA-Fe and RMGA-MA were increased by 122.8%and 86.6%compared with RMGA,i.e.,the charge-positive modification helped to improve the nitrogen removal rates of the red mud-based fillers.（4）The mechanism of AnAOB loading on positively charged terracotta-based filler is analyzed by combining SEM and laser confocal microscopy results.After attachment,the roughness and specific surface area of the filler surface increased as well as the presence of Fe ions,Ca²⁺and Mg²⁺plasma to enhance the conditions for the subsequent growth of AnAOB,while the leaching of Cr（Ⅵ） promoted the nitrogen removal effect of AnAOB.