Study On Effects Of Exogenous Quinoid Redox Mediators On Activity Of Anammox Biomass

Anaerobic ammonium oxidation (anammox) process is now widely recognized as a novel and important process in biological nitrogen removal, which can directly convert NH4+to N2gas with NO2-as electron acceptor under anaerobic conditions. Compared with the conventional nitrification-denitrification process, anammox process offers significant advantages, such as no demand for oxygen and organic carbon, low sludge production and no greenhouse gas like N2O and CO2emissions. However, the long term of startup period and high requirements for the wastewater are still the main limitations of anammox process for industrial application. The purpose of this thesis was to investigate whether the redox mediators enhancing technology could be applied in anammox process to enhance the anammox biomass activity and cell division, and as a result, to shorten the startup term of anammox reactors finally.This study first explored the relationship between the activity of anammox biomass/key enzymes and exogenous quinoid redox mediators, which were anthraquinone-2,6-disulfonate (AQDS),2-hydroxy-1,4-napthoquinone (LAW) and anthraquinone-2-carboxylic acid (AQC). Batch experimental results demonstrated that the total nitrogen removal performance showed a downward trend with all three redox mediators (RMs) dosage increasing. For instance, when the AQC addition increased to0.8mM, the TN removal rate sharply reduced to17.2mg-N/g-VSS/h, only about20%of the control. This phenomenon might be caused by the microbial poisoning effect of the exogenous RMs.Nevertheless, the crude hydrazine dehydrogenase, nitrate reductase and nitrite reductase activities were enhanced about0.6to3folds with additional RMs in comparison with the control experiment. The specific ladderane membrane structure could block the contacting between RMs and the key enzymes inside the anammoxosome, which was inferred to be the main reason for the contrary effects of RMs on anammox biomass and the key enzymes.The catalyzing mechanism of RMs on hydrazine dehydrogenase activity of anammox biomass was also studied. The results demonstrated that the coenzyme Q (CoQ) could get involved in the electron transport pathway in the anammox process. As60%of the total CoQ extracted from the crude enzyme, the hydrazine dehydrogenase activity decreased to0.88uM cyto-c/mg-pro/min, which was about60%of the activity of the unextracted enzyme. When0.06mM CoQ was added back into the enzymatic reaction system, the enzyme activity could be almost restored. The same dosage of exogenous quinoid redox mediators’ addition (anthraquinone-2,6-disulfonat, AQDS and2-methyl-1,4-naphthaquinone, MQ) could also restore the enzyme activity. Moreover, the hydrazine dehydrogenase activity was significantly enhanced by RMs than CoQ. The standard redox potential of the RMs played an important role in the electron transport pathway. Thus, it was clearly that the exogenous quinoid redox mediators could replace the coenzyme Q in the electron transfer pathway of anammox process.