Study On The Mechanism Of Sulfite-Dependent Anaerobic Ammonium Oxidation Process

SO₂ is one of the major air pollutants in China,which not only directly damages human health,but also causes acid deposition,endangers aquatic ecosystem and affects human production and life.The combustion of coal and other fossil fuels are the main sources of SO₂.A variety of technologies are adopted to reduce the emission of SO₂.Among them,the wet ammonia flue gas desulfurization technology with its superiority of product recycling and high desulfurization efficiency is extensively used.NH₄HSO₃,which is the main products of the wet ammonia flue gas desulfurization process,are exported from absorption system firstly,then neutralized by ammonia to?NH₄?₂SO₃,oxidized to?NH₄?₂SO₄ fertilizer finally.But the oxidation process have some defects,such as the low oxidation efficiency and high requirements for equipment,therefore,to explore effective?NH₄?₂SO₃ oxidation or other ways at the same time removing NH₄⁺and SO₃^2-in absorbing liquid is of great significance.At the beginning of this century,it was reported that the mixed culture of anammox could catalyze the ammonia oxidation under anaerobic conditions with SO₄^2-as the electron acceptor.Based on thermodynamic analysis,the ammonia oxidation with SO₃^2-as electron acceptor is more favorable.In this study,firstly,nitrite-depedent anammox sludge was inoculated in an expanded granular sludge bed?EGSB?reactor,sulfite-depedent anammox reaction was started up and acclimated with sulfite as the only electron acceptor.Secondly,nitrite-depedent anammox sludge was inoculated in the microbial fuel cell?MFC?to confirm the existence of ammonia oxidation catalyzed by electroactive microorganisms in the sludge,and the effect of Fe???concentration on sulfite-depedent anammox reactor denitrification performance was explored.Finally,16S rRNA gene high-throughput sequencing technology was used to detect the changes of microbial community structure in the EGSB reactor,the potential biology mechanisms on transformation of nitrogen and sulfur was analyzed,so as to provide a reference for the development of an alternative technology of wet ammonia flue gas desulfurization production?NH₄?₂SO₄.The main conclusions are as follows:?1?The NO₂^-in anammox reactor influent was directly replaced by SO₃^2-,synchronous conversion of NH₄⁺and SO₃^2-was achieved.After the substrate was replaced,the ammonium salt was basically removed in the form of N₂,and the removal rate was basically stable at 300mgN/?L·d?,but thereafter the removal amount of NH₄⁺was no longer increased with the increase of the concentration of SO₃^2-in influent.SO₃^2-were converted to SO₄^2-largely,and a small quantity of sulfide,but no sulfur.?2?The concentration of Fe???was adjusted to explore changes of the reactor performance.Results showed that,the removal rate of total nitrogen could reach more than 400mgN/?L·d?when the concentration of Fe???was 6mg/L,?NH₄⁺-N/?SO₃^2--S ranged from 1.02 to 2.01.The experiment of single-chamber air cathode MFC reactor proves the existence of denitrification pathway via extracellular electron transfer in the anammox system.It is believed that increasing the concentration of Fe???not only can precipitate sulfide,supply trace elements,but also strengthen the extracellular electron transfer in the anammox system.?3?Candidatus Kuenenia and Candidatus Jettenia with the function of anammox were detected in two sludge samples,but their relative abundance changed a lot.However,the sum of relative abundance of the two still accounts for a large proportion,indicating that the anammox bacteria always maintain good activity during domestication,but whether the anammox bacteria can use SO₃^2-needs further verification.After the anammox sludge was domesticated by SO₃^2-,the relative abundance of Thiobacillus was up to 2.79%in sample 1-2,suggesting that there might be a process of sulfur autotrophic denitrification in the system.In addition,the dominant bacterium Bacillus benzoevorans of the sulfate anammox system was not detected in two sludge samples,indicating that there were significant differences between the SO₃^2-anammox system and the SO₄^2-anammox system.