Performance Of Anaerobic Ammonium Oxidation

Nitrogenous pollution has posed hazardous effects on human health and ecological safety.Environmentalists have tried their best to develop several novel nitrogen removal technologies to solve the problem.Anaerobic ammonium oxidation(anammox) has attracted much attention because it was highly efficient,stable and cost-effective. However,the long start-up period of the process due to extremely slow growth rate of anammox bacteria retards its application.Anammox process can be categoried into two kinds,including nitrite-dependent anammox(N-anammox) and sulfate-dependent anammox(S-anammox) based on different electron receptors.As for N-anammox process,endevours were made to enhance bacteria growth and cell retention in by medium optimization and reactor configuration improvement.As for S-anammox,the experiment was conducted in autotrophic conditions,and the existence of autotrophic S-anammox process was confirmed.The study provided new knowledge for biogeochemical cycle of nitrogenous and sulfurous compounds.Major research results are as follows:1) A new N-anammox expanded-bed reactor was invented.It was discovered that:â‘ The start-up course of N-anammox process inoculated with denitrifying sludge could be divided into three stages including autolysis phase,activity lag phase and activity elevation phase.â‘¡The maximum total nitrogen removal rate reached 3.02kg N·m^-3·d^-1.â‘¢The seeding sludge in the reactor turned from khaki flocs to sandybrown granules and finally to red granules.â‘£The predominant N-anammox bacteria in red granules was "Candidatus Brocadia", which was the major contributor to the N-anammox process in the reactor.2) The effects of ferrous and ferric ion on N-anammox bacteria were investigated. It was found that:â‘ Ferrous and ferric ion stimulated substrate removal of N-anammox bacteria and the stimulatory effect was enhanced with increased ferrous or ferric ion concentration.NH₄⁺-N and NO₂^--N removal rates in the test reactor were 1.95- and 1.71-fold of those in the control reactor when ferrous ion concentration was 4.60mg·L^-1;NH₄⁺-N and NO₂^--N removal rates in the test reactor were 2.18- and 2.84-fold of those in the control reactor when ferric ion concentration was 4.60mg·L^-1.â‘¡The inhibitory effect of substrate NO₂^--N to N-anammox bacteria could be relieved by ferrous and ferric ion.â‘¢The fequently used medium for N-anammox bacteria was lack of iron.The growth of N-anammox bacteria was enhanced by increment of ferrous or ferric ion in the medium.The VS and ATP of the test reactor in ferrous ion experiment was 2.16- and 3.53-fold of those in the control reactor;the VS and ATP of the test reactor in ferric ion experiment was 4.15- and 3.37-fold of those in the control reactor.â‘£Conversion of total dissolved iron was increased by extra addition of ferrous or ferric ion.Ferrous ion addition resulted in iron and Heme C content increment,and ferric ion addition lead to iron content increment but Heme C decrease.⑤Long-term effect of ferrous-ion-replete condition resulted in cellular structure alteration of N-anammox bacteria.An unknown grey area appeared,but no similar area appeared in N-anammox bacteria under ferric-ion-replete condition.â‘¥The microbial community altered with extra addition of ferrous or ferric ion.Most of the microorganisms were uncultred bacteria,which implies that the potential microbial resource is abundant.3) The existence of autotrophic S-anammox was confirmed.The results showed that both SO₄^2- and NH₄⁺ were chemically stable.They did not react with each other in the absence of biological catalyst(sludge).Anaerobic digested sludge cultivated in an anaerobic reactor for three years took on the ability of oxidizing ammonium with sulfate anaerobically.The average reduction of NH₄⁺-N and SO₄^2--S were 71.67mg·L^-1 and 18.94mg·L^-1 at high subtrate concentrations. The experiment demonstrated that high substrate concentrations and low oxidation-reduction potential(ORP) were favourable for the biological reaction.