| With the inclusion of ammonia nitrogen into the "The quota of total control system" of the "Twelfth Five-Year Guideline", biological nitrogen removal of the wastewater has become an important research area for the water pollution control. Because of the low C/N ratio of municipal sewage, deficiency of carbon source became the main inhibiting factor for the biological nitrogen removal. A sewage treatment plant in Shanxi, which adopted the SBR process, could hardly achieve the TN requirement of Class A standard of Grade I of the "Discharge standard of pollutants for municipal wastewater treatment plant (GB18918-2002)". To guarantee the success of the upgrading and reconstruction, a in situ experiment was performed to study the influencing factors on nitrogen removal of SBR and the benefit effects of addition of different carbon sources.This experiment mainly studied the interaction between organic matter degradation and nitrification during the aeration in the pre and post denitrification program, the practicability of the shortcut nitrification-denitrification at low temperature and short SRT, the effects of the endogenous denitrification after elongating the stirring period and the enhanced denitrification effects of different added carbon resources such as sodium acetate and sludge low-temperature carbonization lysate.The study of the interaction between organic matter degradation and nitrification during the aeration in the pre and post denitrification program indicated that the organic matter degradation and the nitrification can take place simultaneously. The degradation of COD and the oxidation of NH4+-N took place simultaneously right after the aeration. The NO3-N concentration rose from nearly0mg/L to12mg/L (18mg/L after3.5h). The nitrification rate was further accelerated during the period from0.5h to1h while the COD was less than40mg/L. That means the presence of organic matter can affect nitrification but is not decisive to the nitrification. If the oxygen transfer rate is sufficient to the consuming rate of both degradation of organic matter and oxidation of ammonia, the two reactions can take place simultaneously and the reaction rates decrease gradually with the decreasing of the NH4+-N concentration. During early period of commissioning, the blocking of the aerator reduced the oxygen supply thus the DO was less than1mg/L. Then the nitrification ceased abruptly but the degradation of organic matter continued. The hypothesis that the heterotrophic bacteria which degrades organic matter competing with the nitrobacteria for oxygen inhibits the nitrification is the most possible one for the oxygen supplying speed plays a decisive role on nitrification.At temperature of18～22℃and SRT of15d, nitrosobacteria were not screened out thus the shortcut nitrification and denitrification process was not realized in this experiment. At the end of the pre aeration of shortcut nitrification and denitrification experiment, the NO3-N was10.14mg/L and the NO2-N was2.96mg/L. Since the NO2-N concentration was lower than NO3-N, the nitrobacteria were supposed to be predominant bacteria. The nitrisofication bacteria did not washout successfully meanwhile the effluent TN remained between16-20mg/L. At the end of the pre aeration the COD was57.8mg/L, but it rose to73.2mg/L after post stirring. During the1h pre aeration period, the COD reduction may not totally due to the oxidation and partly because of the sludge adsorption. The adsorbed organic matter was released during the stirring period.Before the addition of the sodium acetate, the removal rate of TN in the SBR was68.63%～72.18%and the effluent TN was16.02-20.02mg/L. After the addition of sodium acetate and when the dosage was100mg/L, the removal rate of TN was74.13%～77.98%, the effluent TN was14.17～16.84mg/L; When the dosage was150mg/L, the removal rate of TN was81.25%～84.77%, the effluent TN was9.18～13.47mg/L; When the dosage was200mg/L, the removal rate of TN was88.45%～90.45%, the effluent TN was5.62～8.12mg/L. When the dosage was200mg/L, carbon source was sufficient, so the denitrification demonstrated a zero order reaction, the denitrification rate was5.2mgNO3-N/gMLSS·h. The optimum ratio of sodium acetate COD/NO3-N was2.04. After the addition of lysate and the dosage were800mL and400mL respectively, the effluent appeared to be yellow brown and the odor was irritating. The undesirable color and odor faded with the decreasing of the dosage. Lysate also influenced on activated sludge greatly. After the addition800mL of the lysate, the SV30increased from40%to70%meanwhile the settling property deteriorated. After the addition of lysate and when the dosage was800mL, denitrification during the post stirring period was strengthened. The amount of reduced NO3-N by denitrification was9.85mg/L, but the NH3-N increased by10.40mg/L at the same time. The TN did not change apparently and the TN of effluent remained between17.67-20.87mg/L. It could not achieve the Class A standard of Grade I. After the addition of lysate and when the dosage was400mL, the amount of reduced NO3-N by denitrification was5.68mg/L but the NH3-N increased by3.82mg/L at the same time. The TN of effluent remained between18.97-21.78mg/L. It could not achieve the Class A standard of Grade I yet. Although the COD concentration was high in the lysate, unfortunately not all of them were degradable thus could not be fully utilized. |
