Studies On Immobilization Of Quorum Quenching Bacteria And Its Membrane Antifouling Property

In view of the problem of biofouling in membrane bioreactor(MBR),this paper used quorum quenching(QQ)effect of microorganisms to control membrane biofouling.Rhodococcus sp.BH4 was used as the immobilized object,which has high biodegradability for quorum sensing(QS)signal molecules.Polyvinyl alcohol(PVA)and sodium alginate(SA)were selected as the immobilized matrix,and a small amount of powdered activated carbon(PAC)was added as the immobilized matrix modifier.The mixed matrix was then cross-linked with boric acid calcium chloride and sodium sulfate separately to complete the immobilization of QQ bacteria.The effect of PAC on the gel beads of immobilized QQ bacteria was investigated.The experiment of immobilized QQ bacteria composite gel beads removing QS signal molecule C8-HSL(N-octanoyl-DLhomoserine lactone)was carried out,and the membrane antifouling effects of the immobilized QQ bacteria composite gel beads were explored.The sphericity,mechanical strength,elasticity and dispersity of immobilized QQ bacteria composite gel beads were investigated and the optimum concentration of PVA and SA in the immobilized matrix was 10% and 0.9%(w/v)separately.The mechanical strength of immobilized QQ composite gel beads increased by 11.3% when the concentration of PAC was 1%(w/v).The mass transfer performance increased b y 30% when the concentration of PAC was 1.5%.In addition,when the concentration of PAC was 1%,the removal rate of C8-HSL with immobilized QQ composite gel beads was more than 90%,and the best concentration of PAC was 1%.However,the biological activity of immobilized beads with multi-wall carbon nanotubes(MCNTs)modified has been inhibited by MCNTs,the removal of C8-HSL is not obvious.C8-HSL removal experiments showed that,the removal rate of C8-HSL by immobilized QQ bacteria composite gel beads was significantly higher than that of free QQ bacteria.The optimum temperature for C8-HSL removal is 20~ 30℃,and the optimum pH is about 7.In the first 60 min,the removal rate of C8-HSL is more than 80%.The immobilization of QQ bacteria to a certain extent improved the adaptability of Rhodococcus sp.BH4 to the changes of environmental conditions like temperature and pH,which will help them adapt to the environment of wastewater treatment better.Through a biofilm culture experiment,the membrane antifouling effect of the immobilized QQ bacteria composite gel beads(1% PAC-PVA beads)was studied.The results showed that,compared with the blank control group,the 1% PAC-PVA beads could maintain the membrane flux and reduce the decrease of membrane flux.In addition,the growth of the biofilm was inhibited by the quorum quenching effect of 1% PAC-PVA beads,which showed the same effect on membrane antifouling with the former.During the experimental period,the microbial activity of the 1% PAC-PVA beads decreased in the first 2 days,and the activity gradually recovered to the initial level with the time,and the recovery rate of their activity is faster than that of 0% PACPVA beads,which showed that the 1% PAC-PVA beads had better stability of activity.