Micro-ecological Mechanism Of Nitrogen Transformation Within Sludge Aggregates And Source Identification Of N₂O Emission In Typical Biological Nitrogen And Phosphorus Removal Processes

After the middle of the 20 th century, eutrophication phenomenon becomes increasingly apparent in China and even all over the world, so denitrification and dephosphorization of wastewater becomes a hot topic in water pollution control. In recent years, various research work is developing, which makes people have a deep understanding of the microbial mechanism in biological denitrification. Biological denitrification process belongs to the process of dynamic change, as the consumption of substrate, environmental conditions, such as DO, pH, etc., also will change, at the same time, not only can produce nitrogen gas in biological nitrogen removal process for waste water, but also will lead to produce and release a kind of potent greenhouse gas-N2 O as the change of substrate and environment conditions.In order to deeply analyze the production rule of N2 O in biological denitrification system, self-made microelectrodes of NH4+, NO3-, NO2-, DO, pH and Unisense microelectrode of N2 O were used to measure the change of the concentration of sludge flocs, in order to clarify the mechanism and influence factors of N2 O being released in the experiment from micro level, the results from the experiment were as follow:(1) Microelectrode technology was used to study the producing rule inside the sludge flocs from different biological tanks in A2/O process of municipal sewage treatment plant, the results showed that:①N2O was mainly released in the anoxic and aerobic tank, and the maximum of N2 O emission was at anoxic tank, of which N2 O emission at the front was more than that at the end.② While DO concentration in the aerobic tank was lower, concentration of theproduced N2 O was higher inside the sludge flocs, that was N2 O being released more.③The minimum of N2 O emission was at anaerobic tank, and concentration of the produced N2 O reached only 19 μmol/L inside the sludge flocs.(2) Through 120 days’ running the SBR reactor where the simulation of denitrification and phosphorus removal was made in, stable effect of denitrification and phosphorus removal was obtained.Microelectrode technology was used to study the producing rule inside the sludge flocs from different stages in the system of denitrification and phosphorus removal SBR process,the results showed that:①The maximum of N2 O emission was at anoxic tank.②The second maximum of N2 O emission was at aerobic zone, and N2 O emission became less as aeration time passed.③The minimum of N2 O emission was at anaerobic tank, and concentration of the produced N2 O reached only 14.5 μmol/L inside the sludge flocs. The experimental results was similar with those in six stages of the A2/O process.From the results above, we know that N2 O was mainly released in the anoxic and aerobic tank; while DO concentration in the aerobic tank was lower, concentration of the produced N2 O was higher inside the sludge flocs, that was N2 O being released more.From the experimental results of A2/O process and denitrification and phosphorus removal SBR process, N2 O was produced the most by heterotrophic denitrifying bacteria’s denitrification at anoxic zone and existed the most inside the sludge flocs.