城镇生活污水处理厂出水硝酸盐浓度及同位素组成的影响因素

Factors Affecting Nitrate Concentrations and Nitrogen and Oxygen Isotope Values of Effluents from Waste Water Treatment Plant

城镇生活污水是地表水硝酸盐(NO_(3)^(-))的重要来源,但其NO_(3)^(-)浓度和同位素组成(δ^(15)N-NO_(3)^(-)和δ^(18)O-NO_(3)^(-))仍不明确,特别是污水处理工艺对出水NO_(3)^(-)浓度、δ^(15)N-NO_(3)^(-)和δ^(18)O-NO_(3)^(-)影响仍不清楚.选择焦作市污水处理厂作为研究载体,每隔8 h收集污水厂进水、二沉池出水以及总排口出水样品,连续收集3 d,分析NH_(4)^(+)浓度、NO_(3)^(-)浓度以及δ^(15)N-NO_(3)^(-)和δ^(18)O-NO_(3)^(-)组成变化,说明处理工艺对氮转化、出水NO_(3)^(-)浓度及δ^(15)N-NO_(3)^(-)和δ^(18)O-NO_(3)^(-)组成的影响过程.结果发现:(1)ρ(NH_(4)^(+))均值在进水口为(22.86±2.16)mg·L^(-1),二沉池出水降低至(3.78±1.98)mg·L^(-1),总排口出水减小到(2.70±1.98)mg·L^(-1);进水ρ(NO_(3)^(-))中间值为0.62 mg·L^(-1),二沉池出水ρ(NO_(3)^(-))均值升高至(33.48±3.10)mg·L^(-1),总排口出水ρ(NO_(3)^(-))均值增加到(37.20±4.34)mg·L^(-1);(2)进水δ^(15)N-NO_(3)^(-)和δ^(18)O-NO_(3)^(-)均值分别为(17.1±10.7)‰和(19.2±2.2)‰,二沉池出水δ^(15)N-NO_(3)^(-)和δ^(18)O-NO_(3)^(-)中间值分别为11.9‰和6.4‰,总排口出水δ^(15)N-NO_(3)^(-)和δ^(18)O-NO_(3)^(-)均值分别为(12.6±1.9)‰和(5.7±0.8)‰;(3)进水NH_(4)^(+)浓度与二沉池出水和总排口出水NH_(4)^(+)浓度存在显著差异(P<0.05),二沉池出水NH_(4)^(+)浓度降低与好氧处理工艺中NH_(4)^(+)发生硝化作用有关,二沉池出水NH_(4)^(+)浓度与总排口出水NH_(4)^(+)浓度不存在显著差异(P>0.05);(4)进水NO_(3)^(-)浓度与二沉池出水和总排口出水NO_(3)^(-)浓度存在显著差异(P<0.05),进水NO_(3)^(-)浓度极低,但δ^(15)N-NO_(3)^(-)和δ^(18)O-NO_(3)^(-)均值较高,可能与生活污水在管道运输过程中发生反硝化作用有关;二沉池和总排口出水NO_(3)^(-)浓度显著升高(P<0.05),但δ^(18)O-NO_(3)^(-)均值显著降低(P<0.05),与NH_(4)^(+)硝化过程中水的参与有关.研究结果说明污水处理厂好氧和厌氧处理过程对出水NO_(3)^(-)浓度和同位素组成的影响,为借助δ^(15)N-NO_(3)^(-)和δ^(18)O-NO_(3)^(-)均值辨识生活污水对地表水硝酸盐的贡献提供科学依据.

Urban domestic sewage is one of the important nitrate(NO_(3)^(-))sources for surface water;however,their NO_(3)^(-) concentrations and nitrogen and oxygen isotope values(δ^(15)N-NO_(3)^(-) and δ^(18)O-NO_(3)^(-))remain unclear,and the factors affecting NO_(3)^(-) concentrations and δ^(15)N-NO_(3)^(-) and δ^(18)O-NO_(3)^(-) values of effluents in the waste water treatment plant(WWTP)are still unknown.Water samples in the Jiaozuo WWTP were collected to illustrate this question.Influents,clarified water in the secondary sedimentation tank(SST),and effluents of the WWTP were sampled every 8 h.The ammonia(NH_(4)^(+))concentrations,NO_(3)^(-) concentrations,and δ^(15)N-NO_(3)^(-) and δ^(18)O-NO_(3)^(-) values were analyzed to elucidate the nitrogen transfers through different treatment sections and illustrate the factors affecting the effluent NO_(3)^(-) concentrations and isotope ratios.The results indicated that(1)the mean NH_(4)^(+) concentration was(22.86±2.16)mg·L^(-1)in the influent and decreased to(3.78±1.98)mg·L^(-1)in the SST and continuously reduced to(2.70±1.98)mg·L^(-1)in the effluent of the WWTP.The median NO_(3)^(-) concentration was 0.62 mg·L^(-1)in the influent,and the average NO_(3)^(-) concentration increased to(33.48±3.10)mg·L^(-1)in the SST and gradually increased to(37.20±4.34)mg·L^(-1)in the effluent of the WWTP.(2)The mean values of δ^(15)N-NO_(3)^(-) and δ^(18)O-NO_(3)^(-) were(17.1±10.7)‰ and(19.2±2.2)‰ in the influent of the WWTP,the median values of δ^(15)N-NO_(3)^(-) and δ^(18)O-NO_(3)^(-) were 11.9‰ and 6.4‰ in the SST,and the average values were(12.6±1.9)‰and(5.7±0.8)‰ in the effluent of the WWTP.(3)The NH_(4)^(+) concentrations of influent had significant differences compared to those in the SST and the effluent(P<0.05).The reduction of NH_(4)^(+) concentrations in the SST was due to the above nitrification during the aerobic treatment process,which transferred NH_(4)^(+) to NO_(3)^(-).The NH_(4)^(+) concentrations in the SST had no significant differences with that in the effluent of the WWTP(P<0.05).(4)The NO_(3)^(-) concentrations in the influent had significant differences with those in the SST and the effluent(P<0.05),and minor NO_(3)^(-) concentrations but relatively high δ^(15)N-NO_(3)^(-) and δ^(18)O-NO_(3)^(-) values in the influent were probably due to denitrification during the pipe sewage transportation.The obviously increased NO_(3)^(-) concentrations(P<0.05)but decreased δ^(18)O-NO_(3)^(-) values(P<0.05)in the SST and the effluent resulted from water oxygen incorporation during the nitrification.The above results confirmed the impacts of aerobic and anaerobic treatment processes on NO_(3)^(-) concentrations and isotope ratios of effluent from the WWTP and provided scientific basis for the identification of sewage contributions to surface water nitrate via average δ^(15)N-NO_(3)^(-) and δ^(18)O-NO_(3)^(-) values.