Modification And Enhancement Of Artificial Microbial Particle Carrier And Its Application In Wastewater Treatment

In recent years,the biological treatment technology of sewage based on immobilization of microorganisms has been paid more attention.As the core of microbial immobilization technology,the performance of biological carrier directly affects the processing ability of the technology.Commonly used biological carriers are made of organic materials（such as polyvinyl alcohol and polyurethane foam）,but they still have the following problems in the application process:（1）polyvinyl alcohol-sodium alginate（PVA-SA）particle carriers have dense internal structure and poor mass transfer performance,which is not conducive to the internal and external transport of gas and nutrients,and are difficult to be applied in aerobic denitrification;（2）Polyurethane foam from liquefied citric acid residue prepared from waste biomass has smooth surface,poor hydrophilicity and low surface positive charge,resulting in poor biological affinity,low microbial biomass,slow film hanging speed and low sewage treatment efficiency.In view of the above problems,this paper through the modification of polyvinyl alcohol-sodium alginate particle carrier and polyurethane foam from liquefied citric acid residue prepared a new type of microbial particle carrier with high mass transfer efficiency,good biological affinity,easy film hanging,large biomass and high pollutant treatment ability.The main research conclusions are as follows:（1）The carrier prepared with modified conditions of 0.30%Na HCO₃,8.0%polyvinyl alcohol（PVA）and 1.0%sodium alginate（SA）has the best apparent characteristics.Compared with the modified carrier,the average pore size is increased by 3.39 times,the connectivity between pores is higher,and the mass transfer efficiency is increased by 12.8%.After fixing the aerobic denitrifying bacteria,the removal efficiency of NO₃^--N of the modified carrier is 99.06%,which is 21.39%higher than that of the modified carrier.The optimal denitrification conditions after fixing denitrifying bacteria by modified carrier were investigated.The experimental results showed that the denitrification ability of modified carrier was the best when bacteria concentration was 15%,carrier dosage was 10%and C/N=25:1.The removal efficiency of NO₃^--N and TN were 94.28%and 98.87%,respectively.（2）The surface of polyurethane foam based on citric acid residue was modified by calcium ion deposition method,chitosan-Halloysite nanotube layer coating method and dopamine coating method.Calcium ion modified foam carrier（Ca-PUF）,chitosan-halloysite nanotube modified foam carrier（CS/HNT-PUF）and dopamine modified foam carrier（PDA-PUF）were successfully prepared.The experimental results showed that compared with other modified foams,PDA-PUF had the highest hydrophilicity,surface charge and bioaffinity,the water holding ratio and activated sludge fixed amount were 17.57%and 94.67%higher than those of modified foams,respectively,and the surface negative potential of foam soaking solution was5.77 times higher than that of PUF.The introduction of Ca²⁺on the foam surface also improved the biocompatibility of the foam.Although there was no significant difference in the amount of fixation of the foam modified by different concentrations of calcium ions,it was 36%higher than that of PUF.In addition,the stability of PDA-PUF and Ca-PUF is significantly better than that of CS/HNT-PUF,which is more conducive to the application of carrier in wastewater treatment technology.（3）Ca-PUF,PDA-PUF and PUF were filled into SBR reactor for culture.The biomass content of Ca-PUF and PDA-PUF was 41.11%and 56.80%higher than that of PUF respectively.The surface modification also improved the wastewater treatment capacity of the foam carrier,and the removal efficiency of COD,NH₄⁺-N,TN and TP were 0.28%,1.84%,3.72%and13.6%higher than those of the original carrier,respectively.High throughput sequencing results showed that PDA-PUF had higher bacterial diversity.Macellibacteroides,Sphingopyxis,Flavobacterium,Acidovorax,Azospira and other organic degradation and denitrification bacteria relative abundance is higher,the removal of pollutants is the best.