| Since the two industrial revolutions,the society productivity has experienced an exponential surge and structural transformation.However,the high-rapid economic development produce many adverse consequences for the huamans'living environment and the earth's ecology.Given to the sulfur and nitrogen-containing contaminated wastewaters with high chemical oxygen demand?COD?,we proposed a denitrifying sulfide removal process?DSR?to recover elemental sulfur resources maximumlly.However,in a conventional DSR system,the complete removal of sulfur,nitrogen,and carbon was obtained at molar ratio of sulfur/nitrogen?S/N?1:1.Real wastewaters with varying S/N ratios definitely pose a challenge to maintain satisfactory removal efficiencies of sulfur,nitrogen and carbon in DSR reactors.This makes the DSR process very limited in the actual operation process,especially the limitation of the application range caused by the water quality change,so it is urgent to solve or cope with the processing problems caused by different S/N changes,so that the process from the laboratory to the practical application,expand the processing range and processing capacity of the DSR process.Given to this,we attempted to introduce micro-aerobic to supplement the enhanced DSR process to treat different S/N wastewater.The actual extreme high?5:2?and low?5:8?S/N ratios were esimulated separately.Judging from the removal efficiency,whether micro-aerobic condition can be used as an effective means to solve this problem.In order to study why micro-aerobic can be strengthened and how to adapt to different S/N wastewater,the effects of oxygen on the removal of metabolic pathways of S,N and C in the whole DSR were studied in the experiment.For low S/N wastewater treatment,the electron acceptor itself is sufficient.The addition of oxygen leads to the“excess”of electron acceptors in the system.The sulfur-based pollutants are basically completely oxidized to sulfates,making it difficult to recover elemental sulfur,and DSR.The original intention of recovery of elemental sulfur resources is contrary to the original,and the system is relatively simple.Therefore,for the study of metabolic pathways,the author aims to study the high S/N wastewater conditions of the system's own electron acceptor deficiency.Simultaneously,given to the complexity of electron supply and acceptor competition after oxygen intervention,the DSR conditions of oxygen as electron acceptor and acetate as electron donor were simulated in the experiment,and the combined fitting instructions showed different concentrations of oxygen.The effect of the removal route for each substance in the DSR.In addition,the molecular microbiological methods were used to study the response of different oxygen conditions to microbial communities and functional genes.And using the response of the functional gene abundance change ratio,the effect of oxygen on different metabolic pathways is reflected from the gene expression level,and combined with the changes of the above actual removal pathways,the main intermediate processes and products in the DSR system after oxygen intervention are predicted and analyzed.Our works showed oxygen can be used as an effective means to regulate the competition between different electron donors and acceptors,so that the treatment experiments can be adapted to the treatment of different S/N wastewater.However,oxygen concentration is a core regulatory factor in the DSR process.Under low oxygen conditions,oxygen inhibits heterotrophic denitrification and reduces acetate removal efficiency.High concentrations of oxygen cause the two stages of autotrophic and heterotrophic denitrification to be substantially completely inhibited,the rate of nitrate removal is reduced,and the sulfide is primarily converted to thiosulfate,rather than biological elemental sulfur,but acetic acid.Salt can still be removed efficiently.The mass transfer oxygen concentration in the aqueous phase ranges from 0 to0.122 mM.Sulfide,nitrate and acetate can always maintain a high removal rate for efficient removal.This concentration range is defined as the"micro-aerobic condition".While the oxygen concentration is between 0.030 and 0.091 mM,the intervention of oxygen promotes the rapid removal of sulfides and acetates without affecting the nitrates,while greatly improving the synthesis and synthesis of biological elemental sulfur.The rate is therefore defined as the"optimal micro-aerobic condition".From the microbial community,oxygen introduction promoted the abundance of heterotrophic denitrification genus of Azoarcus and aerobic denitrification genus of Alishewanella and Stappia,while inhibiting the abundance of heterotrophic denitrification of Thauera,from the trend of microbial abundance.It is speculated that some microorganisms in the genus Thauera,Azoarus and Alishewanella may be associated with facultative oxidation of acetate and biooxidation of sulfides.From the perspective of functional genes,the addition of oxygen promoted the expression of SQR gene and SoxB gene,but inhibited the expression of narG,nirS,nirK and nosZ genes,but did not have much effect on napA and cnorB genes.And from the change of the abundance ratio of sulfur oxidation gene,it is speculated that there is a potential link between SoxB gene and biooxidation of sulfide to thiosulfate.In addition,from the trend of the abundance ratio of denitrifying functional genes,the predicted system may lead to potential N2O accumulation emissions.Furthermore,the electron balance in the DSR system was studied before and after oxygen intervention and in different oxygen environments.After adding oxygen,the electron imbalance in the system becomes more and more obvious.The number of electron donors in the system is much smaller than the number of electron acceptors.Under the micro-aerobic condition,there are additional electron acceptors in addition to oxygen and nitrate..The electronic imbalance of the system after micro-aerobic intervention promotes a deep understanding of the metabolism and intrinsic electron transport of the DSR process,while expanding sulfur in micro-aerobic or aerobic conditions in wastewater treatment,even in the natural earth ecosystem.A new vision for the understanding of nitrogen-carbon synergistic metabolism.For the prospect of engineering application,the introduction of optimal micro-oxygen to resolve the troubles of sulfur and nitrogen-containing high COD wastewater with actual fluctuations in water quality can indeed regulate electronic competition,alleviate negative inhibition,promote pollutant removal,and eliminate influent S/N fluctuations.The micro-aerobic introduction not only breaks through the technical flaw under the traditional anaerobic conditions,but expand capacity of the DSR process in engineering application. |
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