Research On Influence Mechanism Of Endogenous Sulfur On Nitrogen Reducing Pathways In The Urban Malodorous River

Nitrogen abatement has become the serious problem which is urgently required to be solved in malordorous river treatment.As an important elment in river ecosystem,sulfur plays an unnegligible role in nitrogen reducing pathways.However,influnece of sulfide on nitrogen reduction may be shielded because of its high lability.In order to clarify the influence of endogeous sulfur on nitrogen reducing processes in a malordorous river,interactions between endogenous sulfur and nitrogen were firstly studied under several external regulations.Subsequently,denitrification-and ANAMMOX-assessed incubations were conducted to further inverstigate the role of sulfide on potential denitrification and ANAMMOX activity in this malordorous river sediment.In addition,nitrogen-and sulfur-metabolizing communities were also characteriazed to elucidate the microbial mechanism.This research may help to provide theoretical base for the solution to undesirable total niteogen removal rate.The main results of this study are as follows:?1?Malordorous river simulation with external regulations of overlying-water aeration,sediment aeration and calcium nitrate addition to sediment showed that intermittent overlying-water and sediment aeration were favourable to total nitrogen?TN?removal,the reduction rate aggregating 82.15±3.55%and 67.52±0.6%,respectively.TN contents in the overlying-water were significantly negatively correlated with sulfate for aeration regulated conditions with a coefficiency of-0.882?P<0.01?and-0.856?P<0.01?,respectively.This revealed that intermittent aeration promoted nitrification-denitrification and was unfavorable to sulfate reduction.Bacteria affiliated to genus Pseudomonas were the dominant denitrifiers,with a relative abundance of 5.40%and 5.10%separately for sediment in overlying-water and sediment aerated conditions.Additionally,calcium nirate addition was beneficial to Acid Volatile Sulfide?AVS?removal,its reduction rate aggregating 30.67±2.08%.Denitrying bacteria affiliated to genus Thauera were the dominant sulfur-driven autotrophic denitrifiers in sediment with a relative abundance of 6.20%,which suggested that adding calcium nitrate to the sediment may promote sulfur-dependent autotrophic denitrification process.For all externally regualetd conditions,abundance ratio of nirS to bacterial 16S rDNA?0.11%⁰.16%?and dsrB to bacterial 16S rDNA?0.10%⁰.19%?in sediment samples varied slightly.?2?Research concerning the effects of sulfide on denitrification activity suggested that 8 mg·L^-1 of sulfide had no obvious effect on denitrification.40 mg·L^-1of sulfide could promote sulfur-dependent denitrification with the average potential sulfur-dependent autotrophic denitrification activity(PA_SAD)of 0.016 meq·g^-1 VSS h.In addition,this promoting effect of sulfide at 40 mg·L^-1 slightly decreased with C/N ratio regulation?C/N=8?to 0.011 meq·g^-1 VSS h in average.However,marked inhibition on denitrification activity was observed when the sulfide contents reached 96mg·L^-1.In contrast,no clear effect of iron monosulfide?FeS?and pyrite?FeS₂?on denitrification was shown in this study,which can be explained by that sulfur-dependent denitrifiers may not be able to utilize metal sulfide effectively.For sediment incubations with 40 mg·L^-1 of sulfide,denitrifiers affiliated to genus Thiobacillus,Sulfuritalea and Thauera were the dominant sulfur-dependent denitrifiers.The sediment incubation without C/N ratio regulation was abundant in genus Thiobacillus-and Sulfuritalea-related denitrifers,separately accounting 21.5%and4.85%in all bacteria,while incubation with C/N tatio regulation was rich in geus Thauera accounting for about 1.61%.In addition,abundance ratio of nirS to bacterial16S rDNA?1.42%?for incubations without C/N ratio regulation was higher than that of C/N ratio regulated ones?0.38%?,while its abundance ratio of dsrB to bacterial 16S rDNA was lower.It was postulated that a lower C/N ratio was favorable to sulfur-dependent autotrophic denitrifiers.However,competition between heterotrophic and autotrophic denitrifiers in C/N ratio regulated incubations provided faborable conditions for sulfate reducing bacteria.?3?Research concerning the effects of sulfide on ANAMMOX activity suggested that 40 mg·L^-1 of sulfide had obvious inhibition on ANAMMOX,and average reduction rate of ammonium for ANAMMOX-assessed incubations decreased from50.82%⁵5.25%to approximately 13.36%²9.64%.However,nitrite reduction rate for all sediment inubations remained 98.82%⁹9.75%throughout the time-course incubation,which demonstred that denitrification and ANAMMOX coexisted in the incubated system and denitrification played a predominant role.Genus Pseudomonas-like bacteria were the dominant denitrifying bacteria in incubated sediment without C/N ratio regulation with a relative abuandance of 27.5%,while Thauera-related bacteria were dominnat in the incubation with C/N ratio regulation?18.5%?.While the relative abundance of Planctomyces-like bacteria was both 0.6%for incubations with and without C/N ratio regulation in comparison with ANAMMOX bacteria?0.0%?for the control,which suggested that ANAMMOX bacteria was inhibited by sulfide.In addition,abundance ratio of nirS to bacterial 16S rDNA?1.48%?for incubations without C/N ratio regulation was higher than that of C/N ratio regulated ones?0.29%?and no diffenrece was observed for abundance ratio of dsrB to bacterial 16S rDNA.There was no marked difference between thes two ANAMMOX-assessed incubations in terms of the abundance ratio of anaerobic ammonium oxidizing bacteria?AnAOB?to 16S rDNA gene?0.18%and 0.10%for each group?.In contrast,the abundance ratio was obviously higher for AnAOB in the originally sampled sediment?about 0.45%?.This chould be explained by that sulfide had exhibition on ANAMMOX and therefore the proliferation of AnAOB was inhibited.