刘 春,王聪聪,刘 颖,张瑞娜,陈晓轩,张 静,张 磊



生物膜反应器-单宁酸铁处理低C/N废水的脱氮性能

刘 春*,王聪聪,刘 颖,张瑞娜,陈晓轩,张 静,张 磊

(河北科技大学环境科学与工程学院,河北省污染防治生物技术重点实验室,河北 石家庄 050018)

采用生物膜反应器耦合包埋型单宁酸铁处理低C/N比废水,考察其脱氮性能,分析了生物脱氮过程功能菌群的变化,以及单宁酸铁强化脱氮的作用机制.结果表明,生物膜反应器耦合包埋型单宁酸铁,具有低C/N比废水高效脱氮性能.进水C/N比为1:2.7时,TN平均去除率可达80.0%,TN平均去除负荷为1.38kg/(m3·d).生物膜反应器内随着进水C/N比降低,优势脱氮过程从同步硝化-反硝化过程向同步短程硝化-厌氧氨氧化-反硝化(SNAD)过程转变,厌氧氨氧化过程对TN去除的贡献率逐渐升高至76.2%,亚硝化菌群和厌氧氨氧化菌群成为优势生物脱氮功能菌群.包埋型单宁酸铁在生化处理后,通过吸附-催化氨氧化作用同步去除氨氮和亚硝酸盐氮,进一步提高TN去除性能.因此,耦合单宁酸铁强化生物膜反应器SNAD脱氮过程,是实现低C/N比废水高效脱氮新的有效途径.

生物膜反应器；包埋型单宁酸铁；脱氮；SNAD过程；催化氨氧化

生物脱氮是废水处理研究领域的热点[1].传统硝化-反硝化生物脱氮过程能耗高、碳源需求量大,不适于低氮碳比(C/N)废水脱氮处理[2-3].同步短程硝化-厌氧氨氧化-反硝化(SNAD)过程是一种新型生物脱氮工艺[4-6],可在单个反应器内利用短程硝化、厌氧氨氧化和反硝化过程同时去除总氮(TN)和有机物[7-8],为低C/N比废水生物脱氮提供了高效低耗的新途径[9-10].

厌氧氨氧化是SNAD过程的关键环节[11],但厌氧氨氧化菌群的形成和工艺稳定运行较为困难[13],成为SNAD脱氮过程应用的主要限制因素.研究表明,由单宁酸与铁离子络合形成的金属-有机骨架材料单宁酸铁,能够同步吸附氨氮和亚硝酸盐氮[14],并将氨氮和亚硝酸盐氮通过催化氨氧化转化为氮气,从而实现氨氮和亚硝酸盐氮吸附-催化氨氧化脱氮过程[15].因此,在实现SNAD过程的生物反应器中耦合单宁酸铁,形成厌氧氨氧化和催化氨氧化的协同作用,有助于获得更为稳定高效的脱氮效率.

生物膜反应器可在生物膜内形成氧浓度梯度,为亚硝化细菌、厌氧氨氧化细菌和反硝化细菌的生长提供适宜的生长环境,能够实现SNAD脱氮过程[13,16].本研究运行生物膜反应器处理低C/N比废水,使其逐渐实现SNAD脱氮过程;在此基础上耦合包埋型单宁酸铁,进一步强化SAND脱氮过程以获得更高的脱氮能力.同时,通过高通量测序分析生物膜内脱氮功能菌群变化,并对包埋型单宁酸铁脱氮过程和机制加以探究,从而为低C/N比废水脱氮处理提供新的解决途径.

1 材料与方法

1.1 实验装置

实验装置如图1所示,包括生物膜反应器(R1)和生物膜/单宁酸铁复合反应器(R2). R1有效容积为16.6L,底部设有微孔曝气盘,反应器内填充10L环状碳纤维填料(直径10mm,高8mm,流化态),作为生物膜生长载体.R2有效容积2.5L,底部填充1.5L环状碳纤维填料(运行至一定阶段后由R1移入,固定床),上部填充0.4L包埋型单宁酸铁(固定床).废水经过进水计量泵1进入R1底部,处理后由上部溢流出水至中间水箱,而后经过进水计量泵2由底部进入R2,处理后由上部溢流出水.

图1 耦合工艺系统实验装置示意

1.2 包埋型单宁酸铁的制备

在常温下,将单宁酸(0.01mol/L)溶液和FeCl3(0.2mol/L)溶液按体积比1:1混合,而后滴加NaHCO3(0.65mol/L)溶液调节pH值至7左右,静置至出现黑色沉淀即为单宁酸铁.用去离子水将单宁酸铁洗涤后,离心(8000r/min,2min)并冷冻干燥(-70℃)40h左右,得到单宁酸铁粉末(图2A).

将制得的单宁酸铁粉末按照1g单宁酸铁与50mL海藻酸钠溶液(2%,/)比例混合,然后将混合液滴加到氯化钙溶液(2%,/)中,迅速形成凝胶球,静置12h使其充分包埋,从而得到海藻酸钠包埋型单宁酸铁(图2B).

图2 单宁酸铁粉末(A)和海藻酸钠包埋单宁酸铁(B)

1.3 实验方法

向生物膜反应器内接种某城镇污水处理厂二沉池回流污泥,初始接种污泥浓度(MLSS)约为0.8g/L,闷曝48h后将悬浮污泥排出,投加人工模拟生活污水,以葡萄糖为碳源,以NH4Cl为氮源,调节葡萄糖和NH4Cl投加量以控制C/N,同时添加P、Ca、Mg、Fe、Mn等微量元素,添加NaHCO3调节pH值并提供无机碳源[17].按照设定条件连续运行.运行温度为(30±2)℃,进出水pH值范围保持在7.4~8.2.

表1 运行条件

系统连续运行过程可分为4个阶段,启动阶段~Phase2阶段仅运行R1,运行过程中,调节空气流量控制生物膜反应器内溶解氧(DO)浓度逐渐低于1.0mg/L,并提高氨氮负荷及C/N比.Phase3阶段串联运行R1和R2,生物填料总量不变(R1向R2移入1.5L生物填料,R1出水经过R2内生物填料层消耗DO,为包埋型单宁酸铁催化氨氧化创造低DO条件).各阶段运行条件见表1.

运行过程中,测定进出水COD、氨氮、TN、亚硝酸盐氮、硝酸盐氮、DO浓度和生物膜生物量变化,并在Phase2阶段结束时检测分析生物膜细脱氮功能菌群及丰度.

1.4 分析方法

水质指标COD、氨氮、硝酸盐氮、亚硝酸盐氮、TN等,均采用国标方法测定.DO浓度采用溶解氧测定仪(cell Oxi330,德国WTW)测定.

运行过程中,每周从反应器中取一定量填料进行超声清洗,使生物膜脱落并悬浮于液相中,并测定其SS和VSS,根据所取填料占反应器内总填料的比例核算反应器内生物膜生物量(以SS和VSS浓度计)[19-20].在Phase2阶段结束时,按同样方法收集生物膜样品,进行高通量测序(上海派森诺生物科技股份有限公司),获得生物膜样品属水平细菌种群构成和相对丰度数据,分析其中的脱氮功能菌群,包括亚硝化菌群(AOB)、硝化菌群(NOB)、厌氧氨氧化菌群(AnAOB)和反硝化菌群(DNB),并计算其丰度[21].

2 结果与讨论

2.1 处理系统运行性能

2.1.1 生物膜生物量变化 运行各阶段处理系统中生物量变化如图3所示.可以看到,R1单独运行时,启动阶段生物膜生物量逐渐升高,至启动阶段运行结束时SS达到1.50g/L,VSS达到1.15g/L,VSS/SS为0.77,完成挂膜.Phase1~Phase2阶段生物膜生物量波动上升并趋于稳定,两个阶段平均SS分别为1.40, 1.66g/L,平均VSS分别为1.03,1.29g/L,平均VSS/SS分别为0.74,0.78.Phase3阶段R1、R2耦合运行后,系统中平均SS为1.67g/L,平均VSS为1.35g/L, VSS/SS为0.81,与Phase2阶段基本相当.

2.1.2 COD去除性能 运行各阶段COD进出水浓度及去除率变化如图4所示.可以看到,R1单独运行时,启动阶段~Phase2阶段进水COD平均浓度分别为54.4,58.5,56.1mg/L,出水COD平均浓度分别为30.8,27.1,16.5mg/L,COD平均去除率分别为43.0%、53.4%、70.3%.COD平均去除负荷分别为0.28,0.38, 0.48kg/(m3·d).COD去除率不断提高,COD去除负荷也随之升高.

图3 处理系统中生物膜生物量变化

图4 处理系统COD去除性能

Phase3阶段R1、R2耦合运行后,平均COD进出水浓度、去除率和去除负荷分别为56.3mg/L、11.5mg/L、79.4%和0.54kg/(m3·d),COD去除性能进一步提高.

2.1.3 氨氮去除性能 运行各阶段氨氮进出水浓度及去除率变化如图5所示.可以看到, R1单独运行时,启动阶段~Phase2阶段进水氨氮平均浓度分别为54.4,105.2,152.1mg/L,出水氨氮平均浓度分别为24.3,33.8,47.0mg/L,氨氮平均去除率分别为55.2%、67.6%、68.9%,氨氮平均去除负荷分别为0.36,0.86, 1.26kg/(m3·d).可见,启动阶段~Phase2阶段氨氮去除率持续升高并趋于稳定,氨氮去除负荷亦随之升高.Phase3阶段R1、R2耦合运行后,平均氨氮出水浓度、去除率和去除负荷分别为27.3mg/L、80.9%和1.39kg/(m3·d),去除性能高于Phase2阶段,表明耦合包埋型单宁酸铁能够促进氨氮去除.

2.1.4 TN去除性能 运行各阶段TN进出水浓度及去除率变化如图6所示.可以看到,R1单独运行时,启动阶段~Phase2阶段进水TN平均浓度分别为54.4,105.2,152.1mg/L,出水TN平均浓度分别为28.6, 37.7,51.7mg/L,TN平均去除率分别为47.5%、63.7%、66.0%,TN平均去除负荷分别为0.31,0.81,1.20kg/ (m3·d).TN去除过程与氨氮去除过程类似,启动阶段TN去除率逐渐升高,Phase1~Phase2阶段TN去除率继续升高并趋于稳定.同时,随着进水TN负荷升高, TN去除负荷随之升高.

图5 处理系统氨氮去除性能

图6 处理系统总氮(TN)去除性能

Phase3阶段R1、R2耦合运行后,平均TN进出水浓度、去除率和去除负荷分别为150.8mg/L、27.6mg/L、80.0%和1.38kg/(m3·d),TN去除性能比Phase2阶段有明显提高,表明耦合包埋型单宁酸铁能够促进TN去除.

2.1.5 亚硝酸盐氮和硝酸盐氮累积 进水中氮的存在形式仅有氨氮,各运行阶段亚硝酸盐氮和硝酸盐氮出水浓度即为累积程度,其变化如图7所示. R1单独运行时,启动阶段出水中硝酸盐氮平均浓度为3.54mg/L,亚硝酸盐氮平均浓度为0.73mg/L.Phase1~ Phase 2阶段亚硝酸盐氮累积显著增加,平均浓度分别为3.31,4.44mg/L,而硝酸盐氮累积降低,平均浓度分别为0.65,0.28mg/L. 启动阶段~Phase2阶段亚硝酸盐氮、硝酸盐氮累积量的变化,表明随着提高TN负荷逐渐形成低C/N比进水条件,并控制DO浓度低于1.0mg/L,可能使得R1中TN去除由硝化-反硝化过程向SNAD过程转变.

图7 处理系统出水亚硝酸盐和硝酸盐浓度变化

Phase3阶段R1、R2耦合运行后,亚硝酸盐氮累积明显减少,平均浓度降至1.16mg/L,同时氨氮和TN去除亦明显增加,表明包埋型单宁酸铁可以加速亚硝酸盐氮和氨氮去除,从而提高TN去除效率.

已有研究表明,SNAD过程获得较高的氨氮和TN去除效率通常所需HRT较长(>24h)[13,22].本研究中生物膜反应器Phase 2阶段HRT仅为2h时,即可获得基本相当的氨氮和TN去除效率,氨氮和TN去除负荷可达1.26,1.20kg/(m3·d),显著高于已有研究中普遍达到的TN去除负荷(0.2~1.0)kg/(m3·d)[9]. Phase3阶段生物膜反应器耦合单宁酸铁后,整体氨氮和TN去除负荷进一步提高至1.39,1.38kg/(m3·d).

2.2 生物脱氮机制分析

2.2.1 生物脱氮过程 R1单独运行时,TN去除依赖于硝化-反硝化过程和SNAD过程及同化作用.在同化作用中,假设典型的微生物细胞分子式为C5H7O2N,则N在微生物细胞(以VSS计)中所占质量比约为12.4%(干重);由此,根据VSS增长量(图3)可粗略估算启动阶段~ Phase2阶段同化作用去除TN贡献率分别为: 0.63%、0.12%、0%.可见,启动阶段和Phase1阶段,生物膜VSS增长明显,同化作用对去除TN略有贡献;Phase2阶段生物膜VSS总体稳定,因而同化作用对TN去除贡献率几乎为0.因此,微生物增殖的同化作用对TN去除量相对于反应器内TN的去除总量而言可以忽略.

不考虑同化作用,硝化-反硝化过程和SNAD过程主要脱氮反应方程式如式(1)~(5)所示.其中,硝化-反硝化过程包括反应方程式(1)、(2)、(4)和(5),SNAD过程包括反应方程式(1)、(3)、(4)和(5).

图8 脱氮过程氮平衡估算模型(Phase 2)

依据脱氮反应方程式(1)~(5)所反映的化学计量关系,同时根据生物膜反应器运行各阶段进出水COD、氨氮、TN、亚硝酸盐氮和硝酸盐氮浓度变化,进行氮平衡模型计算[22],以反映各生物脱氮过程,特别是厌氨氧化过程和反硝化过程对TN去除的贡献率,结果如图8所示(以Phase 2阶段为例).可以看到,Phase 2阶段厌氧氨氧化过程对TN去除的贡献率为76.2%,反硝化过程对TN去除的贡献率为23.8%,可见Phase 2阶段SNAD过程为TN去除的主要途径.

启动阶段~Phase 2阶段厌氧氨氧化过程和反硝化过程对TN去除的贡献率如表2所示.可以看到,厌氧氨氧化过程对TN去除的贡献率由启动阶段的30.7%提高至Phase 2阶段的76.2%;反硝化过程对TN去除的贡献率由启动阶段的69.3%下降至Phase 2阶段的23.8%.可见,启动阶段~Phase 2阶段R1内,厌氧氨氧化过程在TN去除作用逐渐提高并占据优势,是实现生物脱氮过程由硝化-反硝化过程向SNAD过程转变的关键.

表2 厌氧氨氧化和反硝化过程对TN去除的贡献率

2.2.2 生物脱氮功能菌群分析 R1运行至Phase2阶段实现了SNAD脱氮过程,对Phase2阶段SNAD生物脱氮过程相关功能菌群进行分析,结果如表3所示.可以看到,生物膜样品中AOB菌群为(亚硝化单胞菌属)和(亚硝化叶菌属);NOB菌群为(硝化杆菌属)和(硝化螺旋菌属); AnAOB菌群为和; DNB菌群为、(假单胞菌属)、(脱氯单胞菌属)、(索氏菌属)以及(黄杆菌属)[21-24].

表3 生物膜内生物脱氮功能菌群(Phase 2)

计算Phase2阶段生物脱氮功能菌群的平均相对丰度,结果如表3所示.可以看到,Phase2阶段AOB、NOB、AnAOB和DNB平均相对丰度分别为23.7%、11.6%、39.9%和14.4%.可见, Phase2阶段AOB和AnAOB成为优势生物脱氮功能菌群,因而实现了SNAD脱氮过程.

2.3 包埋型单宁酸铁脱氮机制分析

如前所述,Phase3阶段R1、R2耦合运行时,氨氮和TN去除性能均有明显提高,表明包埋型单宁酸铁对脱氮性能具有强化作用.Phase3阶段对R2反应器生化处理后(R2取样口)和包埋型单宁酸铁处理后(R2出水口2)出水氨氮和亚硝酸盐氮浓度进行测定.结果表明,生化处理后再经过包埋型单宁酸铁处理,氨氮平均浓度由40.5mg/L降至27.3mg/L,亚硝酸盐氮平均浓度由15.6mg/L降至1.2mg/L,而TN平均去除率分由60.8%升至80.0%.可见,包埋型单宁酸铁可以同步去除氨氮和亚硝酸盐氮,从而提高TN去除性能.

图9 单宁酸铁处理中亚硝酸盐氮与氨氮去除量比值(Phase 3)

进一步计算Phase3阶段包埋型单宁酸铁处理中亚硝酸盐氮去除量与氨氮去除量的比值(),结果如图9所示.可以看到,开始运行阶段值较低,而后逐渐升高,接近并稳定在1.32左右.造成这一变化趋势的原因是:开始运行阶段,单宁酸铁吸附对亚硝酸盐氮和氨氮去除具有重要作用,而单宁酸铁对氨氮的吸附能力更强[14],因此氨氮去除量相对较高,值较低;随着运行时间延长,单宁酸铁逐渐吸附饱和,亚硝酸盐氮和氨氮主要通过催化氨氧化作用去除,因此值逐渐接近并稳定在催化氨氧化的理论值1.32.可见,单宁酸铁通过吸附-催化氨氧化作用同步去除亚硝酸盐氮和氨氮.因此,在生物膜反应器中实现SNAD脱氮过程,并耦合单宁酸铁吸附-催化氨氧化作用加以强化,是实现低C/N比废水高效脱氮的新的有效途径.

3 结论

3.1 生物膜反应器耦合包埋型单宁酸铁,可获得低C/N比废水高效脱氮性能.进水C/N比为1:2.7时,TN平均去除率可达到80.0%,TN平均去除负荷为1.38kg/(m3·d).

3.2 生物膜反应器内控制DO浓度并降低进水C/N比,脱氮过程从硝化-反硝化向SNAD过程转变,厌氧氨氧化过程对TN去除的贡献率逐渐升高至76.2%,亚硝化菌群和厌氧氨氧化菌群成为优势生物脱氮功能菌群,SNAD过程成为生物脱氮的主要途径.

3.3 包埋型单宁酸铁在生化处理后,通过吸附-催化氨氧化作用同步去除氨氮和亚硝酸盐氮, 进一步提高TN去除性能.

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Nitrogen removal process in low C/N ratio wastewater treatment using a biofilm reactor coupled with embedded ferric tannate.

LIU Chun*, WANG Cong-cong, LIU Ying, ZHANG Rui-na, CHEN Xiao-xuan, ZHANG Jing, ZHANG Lei

(Pollution Prevention Biotechnology Laboratory of Hebei Province, School of Environmental Science and Engineering, Hebei University of Science and Technology, Shijiazhuang 050018, China)., 2019,39(5)：1993~1999

A biofilm reactor coupled with embedded ferric tannate was used to treat low C/N ratio wastewater and its nitrogen removal performance was investigated. The biological nitrogen removal process and the corresponding functional bacterial populations in the biofilm were also analyzed. The enhanced nitrogen removal by ferric tannate and its mechanism were also discussed. The results showed that the efficient nitrogen removal for low C/N ratio wastewater could be achieved in the biofilm reactor coupled with embedded ferric tannate. When the influent C/N ratio was 1:2.7, the average total nitrogen (TN) removal efficiency was 80.0%, and the average TN loading rate removed was 1.38kg/(m3·d). The dominant biological nitrogen removal process was converted from simultaneous nitrification-denitrification to simultaneous partial nitrification, ANAMMOX and denitrification (SNAD) process in the biofilm reactor when the influent C/N ratio decreased. As a result, the contribution of ANAMMOX process to TN removal increased up to 76.2% in the biofilm reactor. The populations of nitrosate bacteria and anammox bacteria became dominant for biological nitrogen removal. The ammonia nitrogen and nitrite nitrogen could be removed simultaneously by embedded ferric tannate due to the adsorption-catalytic ammonia oxidation process after biological treatment, resulting in further improvement of TN removal. Therefore, the enhancement of SNAD process by ferric tannate in a biofilm reactor is a new and effective solution for efficient nitrogen removal of low C/N ratio wastewater.

biofilm reactor；embedded ferric tannate；nitrogen removal；SNAD process；catalytic ammonia oxidation

X703

A

1000-6923(2019)05-1993-07

刘 春(1976-),男,河南安阳人,教授,博士,主要从事废水处理理论与技术研究工作.发表论文80余篇.

2018-10-27

国家自然科学基金资助项目(51808186)

*责任作者, 教授, liuchun@hebust.edu.cn