Study On Distribution And Regulation Of Cyclic Diguanylate In Membrane Bioreactor

Membrane bioreactor(MBR)is an efficient wastewater biological treatment process which integrates biodegradation and membrane efficient separation.Compared with the traditional wastewater treatment process,MBR is very active in research and engineering application.But membrane fouling is still one of the important factors that hinder MBR large-scale application.It is because microorganisms can adhere to the membrane surface and have a tendency to constantly multiply on the membrane surface to form biofilms,which inevitably leads to the occurrence of membrane pollution.In recent years,the understanding of the mechanism of membrane fouling in terms of biofilm formation mechanism,and the research on the mitigation or control of membrane fouling through corresponding methods have been widely concerned.This study focused on the distribution and regulation of cyclic diguanylate in MBR with the aim of reducing membrane fouling.The main results are shown as follows:(1)To investigate the dynamic distribution of c-di-GMP in MBR.The results showed that the variation of c-di-GMP content in sludge mixed liquor with different time and transmembrane pressure(TMP)fluctuated little,ranging from 3.35 to 4.47μg/g SS,and there was no correlation between TMP and c-di-GMP(p=0.153>0.05).c-di-GMP content in the membrane fouling layer increased significantly with different time and TMP.And there was a significant correlation between TMP and c-di-GMP(p<0.01).When TMP increased from 3.2 kPa to 30.9 kPa,c-di-GMP content increased from 3.85 to 9.89 μg/g SS.(2)Study on Mn2+regulation of c-di-GMP.The results showed that c-di-GMP contents of 0 h and 48 h are 1,88 and 0.24μg/g SS,respectively.This is due to the fact that Mn2+ ions have already diffused into the cell and activated the synthesis of phosphodiesterase at 48 h,resulting in the decomposition of c-di-GMP into two GMP molecules in the cell,followed by a decrease in the content of c-di-GMP.The content of polysaccharides(PS)and protein(PN)decreased significantly due to the addition of Mn2+.The decrease of PS was significantly correlated with the decrease of c-di-GMP(p<0.01).PN is hydrolyzed and degraded into amino acids,resulting in a decrease in its content.Mn2+regulates the production of EPS by regulating the content of c-di-GMP,thus controlling the formation of biofilm.(3)To investigate the comprehensive effects of c-di-GMP regulated by Mn2+in MBR.The results showed that the membrane fouling was significantly controlled by Mn2+regulation,and the membrane fouling cycle was prolonged by 12-15 days.After Mn2+ regulation,the membrane fouling rate in the last two cycles remained mostly at 0-1 kPa/d,indicating that the regulation of Mn2+ on membrane fouling was mainly shown in the early stage of membrane fouling.The c-di-GMP content in activated sludge decreased gradually from 3.79 μg/g SS to 1.21 μg/g SS after 30 days.The content of c-di-GMP in the membrane fouling layer was more stable,ranging from 8.68-8.84 μg/g SS,which indicated that although Mn2+could regulate the content of c-di-GMP in activated sludge,for the membrane fouling layer with TMP up to 30 kPa,the regulation effect of Mn2+was not obvious.