碳源对反硝化过程NO2-积累及出水pH值的影响

采用序批式反应器(SBR),考察了以甲醇、乙醇、乙酸钠为碳源的电子供体对反硝化过程中亚硝酸盐积累及出水pH值的影响.结果表明,碳源充足时,亚硝酸盐积累量与碳源类型及污泥负荷有关.进水NO3--N为20mg/L,即低负荷条件下,各碳源系统仅有少量亚硝酸盐积累,比反硝化速率及出水pH值对应碳源依次为乙酸钠>乙醇>甲醇;高负荷条件下,除甲醇系统因反硝化不完全仅有微量亚硝酸盐积累外,乙醇和乙酸钠系统均有大量亚硝酸盐积累,且积累量与出水pH值明显高于低负荷.对以乙酸钠为碳源的研究还发现,不同电子受体投配比的反硝化均出现不同程度的亚硝酸盐积累且反应速率随着NO3--N比例提高而降低,说明亚硝酸盐的还原受到硝酸盐的抑制.pH值监测显示,除了与碳源类型及污泥负荷有关,反硝化过程pH值增量还随COD/N比升高.因此,反硝化过程宜采用乙酸钠与其他碳源混合且适量投加以消除单一碳源造成出水pH值过高或反应速率慢的不利影响.

Effect of carbon source on nitrite accumulation and pH value of effluent during denitrification process

Effects of different carbon sources (including methanol, ethanol and sodium acetate) as electron donors on nitrite accumulation and effluent pH value during denitrification was investigated in a lab scale sequencing batch reactor (SBR). The results showed that nitrite accumulation was correlated with the types of carbon sources and sludge loading employed. Only small amount of nitrite accumulated during denitrification process when nitrate addition was 20 mg/L with low sludge loading. The specific denitrification rate (rDN) and effluent pH value in different systems increased by the order of sodium acetate, ethanol and methanol. Under the condition of high sludge loading, large amount of nitrite accumulation was observed except for methanol system due to the incomplete denitrification. Nitrite accumulation and effluent pH value were higher than those under low sludge loading. It was also observed that nitrite accumulated in mixed electron acceptor systems with different addition ratio using sodium acetate as carbon source. The specific denitrification rate increased with the amount of nitrate added, implying the reduction of nitrite was inhibited by nitrate. The increment of pH during denitrification was also found to increase with COD/N ratio in addition to carbon source and sludge loading through monitoring pH variation. As a result, appropriate addition of sodium acetate combined with other carbon sources was recommended in denitrification to eliminate the adverse effects of high effluent pH value and low denitrification rate caused by single input.