Study On The Determination Of Hydroxylamine In Short-cut Nitrification Process

Nitrous oxide (N2O) is an important greenhouse gas in the atmosphere, which is called the third major greenhouse gases with carbon dioxide (CO2) and methane (CH4) of the world. The biological treatment of sewage is an important source of N2O,Hydroxylamine (NH2OH) oxidation process, mmonia oxidizing bacteria (AOB)denitrification process and heterotrophic denitrification process can produce N2O. As an intermediate producing in nitrification, NH2OH is directly related to the production of N2O. As NH2OH is an extremely reactvie matter and it can be reacted with many substances, determination of NH2OH in biological wastewater treatment process is not an easy task. Furthermore, the quantitative relationship between NH2OH and the amount of N2O production and effects of NH2OH on the N2O production process have not been cleared.In this study, N2O microelectrode and ammonium ferric sulfate-1, 10 phenanthroline spectrophotometric method were used to determine NH2OH in biological wastewater treatment process. Interference of nitrite nitrogen (NO2-) on N2O microelectrode method and the elimination method was studied. Besdies, the effects of nitrate nitrogen (NO3-)?nitrite nitrogen (NO2-)?orthophosphate (PO43-)?Calcium Ion (Ca2+) and trace elements in biological wastewater treatment processes on the spectrophotometric method was also studied. As PO43- had severe interference on the spectrophotometric method, a numerical method was established for eliminating the interference. The quantative relationships bwtween NH2OH and N2O production under different influent ammonia nitrogen(NH4+-N) concentraitons were obtained by applying the 1, 10 phenanthroline spectrophotometric method to the determination of NH2OH concentations in a short-cut nitrification SBR process.The following conclusions were drawn:(1) The presence of NO2 -N interfered with the determination of NH2OH-N by the N2O microelectrode mothod. When NO2--N concentration was lower than 10.0mg/L in the sample, the interference of N2--N on the method could be eliminated by addition of certain amount of sulfonamide. When the method was used to measure NH2OH in the biological wastewater treatment processes, the lower limit of detection was 0.1 mg NH2OH-N/L.(2) In determination of NH2OH-N by the spectrophotometric method, NH2OH-N concentration in the samples was linearly correlated with the absorbance of the samples without interference. The effects of different interfering substances on the method were not same.(3) NO3- did not interfere with the determination of NH2OH-N by the spectrophotometric method. NO2- and PO43- had different effects on the determination of NH2OH-N by the spectrophotometric method. When the concentration of NO2--N in samples was higher than 15.0 mg/L,the determination NH2OH-N by the spectrophotometric method was interfered severely by NO2--N which could make the determination results of NH2OH-N smaller, and there was no effective method for eliminating the interference. When concentration of NO2--N in samples was lower than 15.0 mg/L, NO2--N did not interfered with the determination of NH2OH-N by the spectrophotometric method, however, it would reduce the determination range of the spectrophotometric method. When concentration of NH2OH-N in samples was higher than 0.1 mg/L, PO43- did not interfere with the determination of NH2OH-N by the spectrophotometric method. When concentration of NH2OH-N in samples was lower than 0.1 mg/L, the determination NH2OH-N by the spectrophotometric method was interfered severely by PO43- which could make the determination results of NH2OH-N smaller. Numerical method established in this study could alleviate the interferences causing by PO43+ in certain extent and ensure the accuracy of the determination results of the spectrophotometric method. When PO43- presented in samples, the determination range of the spectrophotometric method was varied from 0.02 -0.8 mg NH2OH-N/L to 0.05?0.8mg NH2OH-N/L(4) Ca2+ did not interfere with the determination of NH2OH-N by the spectrophotometric method when the concentration of Ca2+ in sample was lower than 8.0 mg/L. When the concentration of Ca2+ in samples was higher than 8.0 mg/L, the determination NH2OH-N by the spectrophotometric method was interfered severely by Ca2+. Common trace elements in biological wastewater treatment processes did not interfere with the determination of NH2OH-N by the spectrophotometric method.(5) The maximum concentrations of dissolved N2O-N in the reactor were 0.11 mg/L and 0.52 mg/L respectively when ammonia concentrations in the influent were 50 mg/L and 70 mg/L. However, NH2OH-N fluctuated around 0.06 mg/L,and didn't vary with the increasing of the influent NH4+-N concentration. According to the determination results of NH2OH-N concentrations, the half-saturation of NH2OH in the bio-chemical conversion process of NH2OH-N to NO2 -N was very small, and 0.05 mg NH2OH-N/L was reasonable.Ammonium ferric sulfate-1, 10 phenanthroline spectrophotometric method could be used for determination of NH2OH in biological wastewater treatment process. An important method was provided in this study, and it was helpful to acertain the the quantitative relationship between NH2OH and N2O production in nitrification process and understand the mechanism of N2O formation under aerobic conditions.