PubMed · 13599003
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H MANN. Comparative study of vasodilators by objective method.. https://pubmed.ncbi.nlm.nih.gov/13599003/
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In order to study the nitrogen removal via nitrite at normal temperature in anoxic/oxic (A/O) process for treating domestic wastewater, the influence of pH, free ammonia (FA), dissolved oxygen (DO), and hydraulic retention time (HRT) were studied. Results indicated that it was possible to remove nitrogen via nitrite in A/O process, if the temperature was between 18 and 25 degrees C and pH was below 7.5. Even if FA was as low as 0.06 mg NH3-N/L, it would inhibit the nitrobacteria. However, FA could not be the sole factor. Whether denitrification went thoroughly or not could affect the nitrification pathway. If denitrification went well, nitrite accumulation could recover in a short while. Nitritification lagged nitratification, so that short HRT would help nitrite accumulation. On the other hand, extended aeration would reduce nitrite accumulation.
With control of the concentration of free ammonia (FA), shortened nitrification-denitrification was accomplished in SBR to achieve enhanced nitrogen removal from the sewage containing seawater. Several parameters which included salinity, temperature, pH and NH4(+)-N load were studied to evaluate their effects. The results of experiences indicated that shortened nitrification-denitrification can be accomplished in sewage containing seawater with relatively high salinity. With various salinity, the nitrogen removal efficiency had relationship with the NH4(+)-N load, there should be a lower NH4(+)-N load when the salinity was high. The nitrogen removal efficiency reached above 90% when the NH4(+)-N load was not exceed 0.15 kg/(kg.d). Elevation of the temperature availed to higher nitrogen removal efficiency, this efficiency doubled when the reaction temperature was changed from 20 degrees C to 30 degrees C. Relatively high value of pH, in the range of 7.5 and 8.5 had advantage to achieve effective shortened nitrification-denitrification which caused by the selective inhibition of free ammonia(FA).
A new fluorescence quenching method has been developed to determine nitrite in water samples. The method is based on the diazo-reaction between nitrite ion and safranine T in hydrochloric acid medium. The fluorescence intensity was measured at excitation and emission wavelengths of 525.0 and 556.0 nm, respectively. The optimum experimental conditions have been confirmed and the concentration of hydrochloric acid was 0.096 mol.L-1; the reaction time was 10 min. Under the selected conditions, the relationship was obtained between the fluorescence intensity and nitrite concentration in the range 4-200 x 10(-9) g.mL-1 NO2-. The detection limit was 4 x 10(-9) g.mL-1 NO2-. The method was applied to determine trace nitrite in water samples. The mechanism involved in the reaction was discussed.