The Effects Of Different C/N And Biological Flocculation Concentration On Bio-flocculation Purification

Microorganisms in biological flocculation?bio-flocs?are mainly consist of heterotrophic bacteria,nitrifying bacteria and denitrifying bacteria.The removal of TAN,NO₂^-and NO₃^-in water mainly depend on bacteria adhering to bio-flocs,such as assimilation of heterotrophic bacteria,nitrification of nitrifying bacteria and denitrification of heterotrophic denitrifying bacteria.The addition of organic carbon sources provide energy for the growth and reproduction of heterotrophic bacteria.When C/N ratio is low,bio-flocs could not provide enough carbon source for heterotrophic bacteria,which can not remove TAN,NO₂^-and NO₃^-efficiently,resulting in the accumulation of TAN,NO₂^-and NO₃^-.Nitrifying bacteria belong to the chemoautotrophic bacteria,even under low C/N conditions,they could also carry out efficiently in water treatment.Therefore,C/N is an important factor determining the effects of assimilation,nitrification and denitrification of bio-flocs.In this experiment,the removal efficiencies of TAN,NO₂^-and NO₃^-,the variation of microbial community and the intensity of nitrification and denitrification under different C/N were studied.The results were as followed:1.Purification effects of Bio-flocs and variations of microbial community under different C/N when TSS was 500 mg/LIn the first,the TSS was adjusted to 500 mg/L,and the bio-flocs which had been cultured for 20 days were divided into fifteen 4L bioflocculation reactors to simulate the aquaculture system.The C/N was set as five gradients?10:1,15:1,20:1,25:1,30:1?.The results showed that the highest removal rate of TAN and NO₂^-were occurred in the C/N=20 group,but there was no significant difference in the concentration variations of TAN and NO₂^-among the five groups?P>0.05?.The removal rate of NO₃^-in group C/N=15 was significantly higher than that in group C/N=10?P<0.05?.The accumulation of NO₃^-in group C/N=10 was significiant higher than in other groups?P<0.05?.Denitrification occurred in all five groups on the first day.The ORP in group C/N=10increased to a positive value on the fifth day of the experiment,which remained negative in the other four groups,but there was no significant difference in the change of ORP among the five groups?P>0.05?.Then,another smaller gradient was set between C/N=10-15?10:1,11:1,12:1,13:1,14:1?and a control group,which added with no glucose.The results showed that the highest removal rates of TAN and NO₂^-were C/N=11,which were 95.00%and 97.57%,respectively,but there was no significant difference in the concentrations of TAN and NO₂^-among the six groups?P>0.05?.The highest removal rate of NO₃^-was in C/N=12,which was 79.31%.The accumulation of NO₃^-in control group was significantly highly than in C/N=10 and 11?P<0.05?,which was also between C/N=10,11 and C/N=12,13,14?P<0.05?.The results of microbial diversity analysis showed that in the control group,C/N=10,12 and 15,the first dominant phylum and class were actinomycetes phylum and actinomycetes class,respectively.At the generic level,only three microorganisms with relative abundance greater than 5%,and the abundance of Bacillus was increased with the increase of C/N.In conclusion,the removal rates of TAN and NO₂^-were very high when C/N was 10,15,20,25 and 30,but the removal efficiency of NO₃^-in C/N=10 group were significantly lower than in other groups?P<0.05?.No significant difference were found in the removal efficiencies of TAN and NO₂-among C/N=10,11,12,13,14 and the control group,but significant differences were found in the removal of efficiently NO₃^-among the control group,C/N=10,11 and C/N=12,13,14?P<0.05?.2.Purification effects of Bio-flocs and variations of microbial community under different C/N when TSS was 200 mg/LTSS was adjusted to 200 mg/L in this experiment.The gradients of C/N were set as10:1,11:1,12:1,13:1,14:1,and the control group was added with no glucose.The results showed that the highest removal rate of TAN was in C/N=12 group?95.43%?,but there was no significant difference in the concentration of TAN and NO₂^-among six groups?P>0.05?.The least accumulation of NO₃^-was in C/N=14,and with the increase of C/N ratio,the accumulation of NO₃^-was gradually decreased.The accumulation of NO₃^-in control group and C/N=10 were significantly higher than in C/N=14?P<0.05?.The results of 16S RNA sequencing and microbial diversity analysis showed that:in the control group,C/N=10 and 14,the first dominant phylum and the first dominant class were actinomycetes phylum and actinomycetes class,respectively.At the generic level,only three microorganisms with relative abundance greater than 5%were found.The abundance of micropruina and Norank-p-saccharibacteria in C/N=10 was higher than in other two groups.In conclusion,the removal rate of NO₃^-in C/N=14 were significantly higher than in C/N=10 and control group?P<0.05?,and the control group,C/N=10,11,12,13 and 14 groups had good effects on the removal of TAN and NO₂^-?P<0.05?.3.The effects of different C/N on nitrification and denitrification intensity in bio-flocs when TSS was 500 mg/LTSS was adjusted to 500 mg/L in this experiment.The experiment was divided into four groups:no carbon source group,C/N=10,C/N=12 and C/N=15,which were named as A,B,C,D,repectively,corresponding to the control group a,b,c,d.20 mg?5 mg/L?ATU was to groups A,B,C and D,but added no ATU in a,b,c d.The results showed that significant differences was found in the concentration variations of TAN and NO₂^-among groups A,B,C and D?P<0.05?.The concentration variations of NO₂^-among groups a,b,c,d also had significant differences?P<0.05?.The concentration variations of NO₂^-in control groups a,b,c,d were similar to the concentration variations of TAN.The concentrations of TAN and NO₂^-in groups A,B,C and D were higher than in control group,the largest accumulation of NO₃^-was in the group with no carbon source,which was 2.5 times more than in C/N=10,and three times more than in C/N=12.The reduction of total nitrogen in group A,B and C were lower than that in the corresponding control group,which was lower in group D and d.The DOC of A,B,C and D was higher than a,b,c,d.The alkalinity of A,B,C and D was also higher than in a,b,c,d,but alkalinity variation between group A and a was significantly lower than their groups.In conclusion,the nitrification intensity in the experimental group without adding carbon source is 2.5times more than in C/N=10,three times more than in C/N=12,and no nitrification intensity was found in C/N=15.In C/N=15,the intensity of denitrification was stronger than other groups.4.The effects of different C/N on nitrification and denitrification intensity in bio-flocs when TSS was 200 mg/LTSS was adjusted to 200 mg/L.The experiment was divided into three groups:no carbon source group,C/N=10 and C/N=14,named as A,B,C,and the corresponding control groups a,b,c.20 mg?5 mg/L?ATU were added to group A,B,C and added with no ATU in the control groups.The results showed that the concentrations variations of TAN had significiant differences among groups A,B,C?P<0.05?,which was similar with the concentrations variations of NO₂^-.The concentrations variations of TAN was similar with concentrations variations of NO₂^-in groups a,b,c.The accumulation of NO₃^-in the group with no carbon source was similar with group C/N=10,which was about 50 times than group c.The decrease of total nitrogen in groups A,B and C was higher than that in a,b,c,which was highest in group C and C.The increase rate of DOC in group C was significantly faster than that in group A and B,but there was no significant difference in concentration of DOC among group A,B and C?P>0.05?.The DOC concentration in groups A,B and C was significantly higher than in a,b,c?P>0.05?.The alkalinity of groups A,B were always higher than in a,b.However,there was no significant difference in alkalinity between group C and c.The OUR of heterotrophic bacteria in group C was significantly higher than in other two groups?P<0.05?.The OUR of heterotrophic bacteria in group C fluctuated greatly,while the OUR of heterotrophic bacteria in group A and B did not fluctuate too much.In conclusion,the nitrification intensity of the group without carbon source was similair with C/N=10 group,which was about 79 times than in C/N=14group.The denitrification intensity of group C/N=14 was higher than other groups.