Optimization And Performance Of Granular Activated Carbon And Dynamic Membrane Bioreactor Hybrid Process For Domestic Wastewater Treatment

Membrane bioreactor reactor（MBR）is limited in application due to the disadvantages of severe membrane fouling,and high costs including management and maintance,while dynamic membrane bioreactor（DMBR）is widely concerned for its low cost,high flux and easy cleaning method.In this study,the granular activated carbon（GAC）was added to the DMBR to treat the real domestic wastewater.Based on the optimization of GAC-DMBR process by batch experiments,the effects of GAC on the efficiency of domestic wastewater treatment,the properties of activated sludge and dynamic membrane layers,and the distribution of microbial community under the long-term conditions were studied,providing reference for the practical application of GAC-DMBR technology.The main research contents and results are as follow:（1）The batch experiments were conducted to study the effect of pore size of supporting material（200,300,500 meshes）and GAC dosage（0.5,1,2,3 g/L）on GAC-DMBR process.Results show that there is no significant difference in pollutant removal when using nylon meshes with different pore size in DMBRs,but a higher flux was obtained using the 200 mesh nylon mesh,and the flux is 65 L/m²·h after 120 min;The batch experiments with different GAC dosages were carried out,it was found that the treatment efficiency and filtration performance were the best with GAC dosage as 2g/L.（2）In the long-term experiments,two groups of DMBR（C-DMBR and GAC-DMBR）with 0 and 2 g/L GAC were constructed for comparison.The constant gravity head（20 cm）filtration mode showed that:In the first 25 days,for each operation cycle,it was found that the effluent turbidity of GAC-DMBR was lower than that of C-DMBR.When running 5 min later,the turbidity of C-DMBR dropped below 5NTU,while the effluent turbidity of GAC-DMBR dropped below 3 NTU and with a stable turbidity around 1 NTU at the end of running cycle.The flux of C-DMBR and GAC-DMBR were maintained at 4-22 L/m²·h and 13-35 L/m²·h,respectively,indicating GAC could increase the effluent flux.After 25 days,there was no significant change in the effluent turbidity,and the flux of GAC-DMBR decreased but still higher than that of C-DMBR at the end of single cycle operation compared with 25 days ago.In a word,GAC addition strengthed the pollutant removal of the system.The dynamic membrane had a certain interception effect on COD and TP,but had a poor interception effect on NH₄⁺-N、UV₂₅₄ and other soluble substances.（3）In the long-term experiments,the effects of GAC on the properties of bulk sludge and dynamic membrane layer,filtration behavior and microbial community distribution were mainly studied.The results of PSD analysis show that the volume fraction of bulk sludge in GAC-DMBR was significantly higher than that in C-DMBR in the range of 256-1512μm,indicating that GAC could acted a framework to form larger sludge flocs.The analysis of extracellular polymeric substances（EPS）and dissolved organic matter（DOM）showed that GAC reduced the soluble EPS（SEPS）content in the bulk sludge and improved the properties of bulk sludge.By analyzing the morphology,inorganic and organic components of the dynamic membrane layer,it was found that the dynamic membrane surface of GAC-DMBR is relatively more rough,the relative content of C element is increased,while the content of SEPS is reduced compared with C-DMBR,suggesting that the deposition of GAC on the dynamic membrane improved the dynamic membrane structure and effectively reduced the pollution caused by organic components.Classical filtration model for constant pressure operation mode show that the intermediate filtration model could reflect the dynamic membrane filtration behavior best for C-DMBR and the cake filtration model reflect the dynamic membrane filtration behavior properly for GAC-DMBR,which further clarified that GAC plays an important role in improving the structure and filtration performance of dynamic membrane layer.Microbial community analysis revealed that after GAC addition,the relative abundance of phylum Proteobacteria decreased,while the relative abundance of phylum Bacteroides increased,which may ruduce membrane pollution and improve dynamic membrane layer properties.Moreover,as a carrier,GAC provides an aerobic/anaerobic living environment for microorganisms,which is beneficial to the removal of pollutants.