Removal Of Heavy Metals From Sludge By Bdellovibrio And Improvement Of Dewatering Performance

In the sewage treatment process,a large amount of heavy metals are enriched in the sludge.The sludge of the sewage treatment plant is directly stacked or landfilled,the heavy metals enriched in the sludge will not only harm the ecological environment,but also affect the health and safety of human beings through the circulation accumulation of food chain.Traditional heavy metal removal methods have some disadvantages.Therefore,it is particularly necessary to find a low-cost,low-hazard method to remove heavy metals and improve the performance of sludge dewatering.Bdellovibrio is a kind of parasitic bacteria that can lyse most of Gram-negative bacteria and a small amount of Gram-positive bacteria,which has very good research significance,however,the application of Bdellovibrio in removing heavy metals in the remaining sludge has not been reported yet.Therefore,in this study,we use activated sludge to separate and enrich the Budovibrio with high efficiency lysis effect,and carry out the experiment of lysing sludge,obtain the best reaction conditions for the lysis of sludge and the best removal rate of heavy metals and the improvement effect of sludge dewatering.On this basis,discuss the mechanism of the removal of heavy metals and the key factors affecting the dewaterability by Bdellovibrio lyse sludge.The experimental results are as follows(1)A host strain capable of efficiently accumulating Bdellovibrio is selected from the activated sludge,and 28 Budovibrium strains are screened out on double-layer agar plates,and by measuring the decrease rate of the absorbance(OD600)of the supernatant of the liquid medium and the removal rate of heavy metals when the host bacteria are lysed by Bdellovibrio to select the No.24 strain with the best lysis effect as the experimental strain for this experiment.And it is identified that the similarity between No.24 strain and the known Bacteriovorax sp.HEA is 95%.(2)Sludge cracking experiments were carried out by setting different environmental conditions.The best reaction conditions are: reaction time 24 h,p H value 7,sludge concentration(MLVSS)range of 20000mg/L?25000mg/L,dissolved oxygen(DO)concentration of 3.5mg/L,the dosage of bacteria is 108PFU/m L,and the reaction temperature is 30?.Under the optimal conditions,the removal rates of Cu and Zn in the sludge are 45.1% and 49.8%,respectively,and the reduction rates of the sludge specific resistance(SRF)and capillary water absorption time(CST)are 32.78%and 25.81%.Bdellovibrio bacteria can effectively lyse sludge to release heavy metals enriched in it and improve the dewatering performance of sludge.(3)The analysis of sludge wall breaking index showed that in the process of sludge cracking by Budovibrus,the sludge dissolved chemical oxygen demand(SCOD),dissolution rate(DDSCOD)and heavy metal removal rate change trends are consistent,all at 24 h get the maximum value.At this time,SCOD and DDSCOD are1.5 times and 8 times of the initial sludge.The proportion of protein(PN)and polysaccharide(PS)in soluble extracellular polymer(S-EPS)increase significantly at24 h,it shows that when the sludge is lysed by Budovibrus,the bound EPS in the sludge is dissolved into the liquid phase,which causes the heavy metals complexed on the EPS to fall off,with the conversion of bound EPS to S-EPS and the dissolution of microbial cells in the sludge,a large amount of intracellular organic compounds are dissolved,which increases the content of SCOD(4)Analyze the correlation between the dewaterability of sludge and PN and PS in EPS during the lysis of Bdellovibrio,and discuss the key factors affecting the dewaterability of the sludge,the results show that,SRF and CST of sludge are negatively correlated with the content of dissolved PN and PS,the lysis of Budovibrus changes the dissolved PN and PS in the sludge,which affects the dewatering performance of the sludge.It is speculated that both PN and PS have hydrophilic groups,when the PN and PS in the bound EPS continuously fall off from the sludge,the content of PN and PS in the liquid phase of the sludge increases greatly,and Increase the number of hydrophilic groups in S-EPS,and the water is more concentrated in S-EPS,thereby improving the performance of sludge dewatering(5)By analyzing the diversity of microorganisms in the sludge during the lysis process of Bdellovibrio,it was found that with the lysis of the sludge by Bdellovibrio,the Shannon index and Simpson index of the flora in the sludge decreased significantly.At 24 h,the uniformity and diversity of the microbial flora in the sludge reached the lowest value.The bacterial flora contained in the sludge mainly includes Proteobacteria,Actinobacteria,Bacteroidetes,Chloroflexi,Firmicutes,Acidobacteria and Verrucomicrobia.Sludge in the Proteobacteria Gammaproteobacteria,Betaproteobacteria,Deltaproteobacteria,Bacteroidetes Sphingobacterium,Chryseobacterio,Porphyromonas and Ethanoligenens along with the effect of Budovibrio on the sludge Cracked and dropped sharply,reach the lowest value in 24 h,it shows that Bdellovibrio is mainly used to lyse such bacteria to achieve the purpose of removing heavy metals and improving dehydration performance.In the process of lysing the sludge by Bdellovibrio,the contents of Actinobacteria,Chloroflexi,Acidobacteria,and Verrucomicrobia in the sludge did not decrease significantly,it shows that the lysis effect of Bdellovibrio on this kind of bacteria is not obvious.