2018, Vol. 38
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2. 中国科学院大学, 北京 100049
2. University of Chinese Academy of Sciences, Beijing 100049
厌氧氨氧化(Anaerobic ammonium oxidizing, Anammox)工艺是在厌氧或缺氧条件下, 厌氧氨氧化菌利用NO2-为电子受体氧化NH4+为N2的一种化能自养型脱氮工艺(Wr et al., 2007).Anammox工艺因具有脱氮效率高、污泥产量低、无需外加碳源等优势而倍受欢迎, 已被用于实际工程中(Jin et al., 2012a；2012b；Zhang et al., 2013).但Anammox菌具有生长速率慢、倍增时间长、环境敏感度高等缺陷(Jin et al., 2012b；Wr et al., 2007), 增加了Anammox工艺受损后的恢复难度.实际废水, 尤其是工业废水中, 化学成分复杂(He et al., 2016；Li et al., 2017b；Zhang et al., 2013), 氮浓度较高, 其中的NO2--N和NH4+-N虽为Anammox菌的生长基质, 但同时也是毒性物质, 极易影响Anammox菌的生长代谢, 进而威胁Anammox工艺的运行(Li et al., 2017a；2012b).研究表明, NO2--N对Anammox工艺的影响高于NH4+-N(Puyol et al., 2014；Carvajalarroyo et al., 2015), NH4+-N浓度低于1000 mg · L -1时不会抑制Anammox菌活性, 而NO2--N浓度高于280 mg · L -1时便会产生抑制, 因此, 基质抑制尤其是NO2--N抑制是Anammox工艺广泛应用的瓶颈之一(Dapena-Mora et al., 2007；Isaka et al., 2007；Wang et al., 2016；Strous, 1999).因此, 高浓度基质抑制后Anammox菌的活性恢复及其恢复策略研究将有助于Anammox工艺的推广应用.
胞外聚合物(Extracellular Polymeric Substances, EPS)作为微生物新陈代谢和细胞自溶分泌的产物, 是一类附着于细胞壁表面的有机大分子多聚物, 主要由结合型EPS构成, 其又分为紧密型(TB-EPS)和松散型(LB-EPS)两种, 分别由内到外包埋微生物, 以维持细胞结构和功能的完整性(Badireddy et al., 2010；Sheng et al., 2010；Zhu et al., 2009).EPS主要由蛋白质(Protein, PN)和多糖(Polysaccharide, PS)构成, 其中, PS是由中性的和带电的糖苷键构成的异质多糖体, 以各种结合力与基质中的生物分子构成EPS的三维网状结构, 而PN则包含有胞外酶、EPS修饰酶及结构蛋白等, 被固定于PS中, 降解基质中聚合物并修饰EPS结构, 二者相互作用以促进微生物间的物质转换和能量传递, 增强微生物的耐冲击能力并维持其酶活性及功能特性(Flemming et al., 2010).PN和PS浓度易受水质条件、反应器运行方式及优势菌种代谢水平等因素的影响(Hou et al., 2015；Yin et al., 2015；Zhu et al., 2009), 可很好地反映Anammox菌的活性恢复情况.本研究通过考察受基质抑制后的Anammox菌在活性恢复过程中, 其脱氮性能、EPS组分及Anammox菌丰度的变化, 探究升流式厌氧反应器中Anammox菌的活性恢复特性, 以期为Anammox工艺恢复的机制研究及实际应用提供理论与技术支持.
2 材料和方法(Materials and methods) 2.1 试验装置试验采用升流式厌氧氨氧化反应器, 具体如图 1所示.反应器制作材料为有机玻璃, 有效容积1.5 L, 顶部设有三相分离装置和溢流堰, 处理水经溢流堰排出, 反应器内部挂有辫帘式填料, 便于形成生物膜, 上部设有回流装置(回流比为4), 促进反应器内部循环, 并防止进水口堵塞.反应器整体置于恒温(35±2) ℃水浴箱中, 避光运行, 进水pH经0.1 mol · L-1盐酸调节至7.5左右, 维持Anammox菌适宜的生长环境.
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| 图 1 实验装置示意图 Fig. 1 Schematic diagram of the experimental device |
试验用水为人工配制的模拟废水, 具体组成见表 1.其中, 微量元素成分为(g · L-1)：EDTA 20、ZnSO4 · 7H2O 0.43、CoCl2 · 6H2O 0.24、MnCl2 · 4H2O 0.99、CuSO4 · 5H2O 0.25、NaMoO4 · 2H2O 0.043、NiCl2 · 6H2O 0.20、KH2PO4 20、H3BO3 0.014.于进水桶和出水口处, 分别用离心管收集水样, 经0.45 μm滤膜过滤后分别采用纳氏试剂法、N-(1-萘基)乙二胺分光光度法和紫外分光光度法测定样品中的NH4+-N、NO2--N和NO3--N (Hendrickx et al., 2014).pH采用便携式pH计(FG2-FK, METTLER TOLEDO, USA)测定；污泥样品MLSS、MLVSS均按(国家环境保护总局《水和废水监测分析方法》编委会, 2002)的标准方法测定.
| 表 1 模拟废水成分 Table 1 The composition of synthetic wastewater |
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本研究试验前反应器已稳定运行1年, 填料中生长砖红色生物膜, 游离的污泥呈红色松散颗粒状.在进水TN浓度(NH4+-N为350 mg · L-1, NO2--N为350 mg · L-1)为700 mg · L-1, HRT为9 h的条件下, 反应器NH4+-N和NO2--N去除率稳定在94%和83%左右.之后因中断反应器回流, 且仍以TN浓度700 mg · L-1的进水运行, 致使进水区域NO2--N浓度由回流时的20.92 mg · L-1剧增为320.24 mg · L-1, 引起基质抑制, 反应器于之后的1周内脱氮性能骤降, NH4+-N和NO2--N去除率分别降至9.67%和8.75%, 泥色呈灰黑色, 略有臭味, 此时, 反应器中MLSS为7.46 g · L-1, MLVSS为3.96 g · L-1.之后试验采用阶段式提高氮负荷的方法恢复反应器中Anammox菌的活性, 分5个阶段进行, TN浓度分别为160、320、500、700和1000 mg · L-1, 具体运行策略见表 2.
| 表 2 反应器各阶段运行参数 Table 2 Reactor operation parameters of each phase |
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污泥样品中的EPS采用高速离心与超声组合的方式提取(Yu et al., 2009), 即取适量4 ℃下静置1.5 h的污泥, 经缓冲液(Na3PO4 : NaH2PO4 : NaCl : KCl=2 : 4 : 9 : 1, pH=7.0)重悬至初始体积后, 4 ℃下2000 g离心15 min, 弃去上清液, 底部沉淀物再次重悬, 并离心(2000 g, 15 min), 此上清液即为LB-EPS；重复底部沉淀物的重悬步骤, 经20 kHz、480 W超声破碎仪(Scienta-IID, China)超声10 min (工作1 s-停止2 s)后, 4 ℃下2000 g离心20 min, 上清液即为TB-EPS.LB-EPS和TB-EPS经0.45 μm聚四氟乙烯滤膜过滤后进行蛋白质与多糖的测定.EPS中蛋白质采用BCA蛋白浓度测定试剂盒(P0010S, 碧云天, 中国)测定, 以牛血清蛋白为标准物质(欧清梅, 2015)；多糖采用蒽酮-硫酸法测定, 以葡萄糖为标准物质(张俊珂等, 2016).
2.4 DNA提取与实时定量PCR称取500 mg污泥样品, 使用FastDNATM SPIN Kit for Soil(LLC, MP Biomedicals, USA)提取试剂盒按其操作步骤提取污泥样品中总DNA.实时定量PCR实验采用Roche LightCycler®480 Ⅱ(Roche Diagnostics Ltd, Rotkreuz, Swltzerland)实时荧光定量系统进行, 反应采用20 μL体系, 具体配置为：SYBR Green Ⅰ Master(LightCycler®480, mannheim, Germany)10 μL, 前后引物各0.8 μL, 质粒或DNA样品1 μL, 去离子水7.4 μL.其中, 全细菌定量引物为通用引物341F:534R(Hou et al., 2014), 而Anammox菌采用特异性引物Amx808F(5′-ARC YGT AAA CGA TGG GCA CTA A-3′)和Amx1040R (5′-CAG CCA TGC AAC ACC TGT RAT A-3′) (Hou et al., 2014；Meng et al., 2010).实时定量PCR运行程序为三步法：95 ℃预变性5 min；95 ℃变性30 s, 45 ℃退火30 s, 72 ℃延伸30 s, 35个循环；72 ℃终延伸10 min, 最后进行溶解曲线分析.
3 结果与讨论(Results and discussion) 3.1 厌氧氨氧化反应器活性恢复中脱氮性能变化由反应器进出水氮浓度(图 2)和脱氮效率变化(图 3a)可知, 活性恢复中随着进水总氮浓度的阶段性增加, 出水总氮浓度也逐渐增加, 以出水NO3--N浓度增加最为显著, NO2--N次之; 而NH4+-N浓度始终保持在5 mg · L-1以下, 仅在进水氮浓度提高的48 h内, 出水NH4+-N浓度偏高, 但均会迅速趋于稳定.反应器的TN去除率在阶段Ⅰ~Ⅱ逐渐增加, 最高可达91.74%, 在阶段Ⅲ~Ⅴ则逐渐稳定在78.8%左右.而NO2--N去除率相反, 在阶段Ⅰ~Ⅱ稳定于98%左右, 而阶段Ⅲ~Ⅴ则逐渐下降, 阶段Ⅴ去除率平均为83.8%.NH4+-N去除率相对稳定, 始终维持在98%左右.
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| 图 2 活性恢复中反应器进出水氮浓度变化 Fig. 2 Nitrogen variation of influent and effluent during recovery stage of anammox reactor |
由图 3b可知, 活性恢复阶段Ⅰ~Ⅴ中, 氮去除负荷(Nitrogen Removal Rate, NRR)随氮负荷率(Nitrogen Loading Rate, NLR)的增加而逐渐增加, 各阶段NRR分别稳定在0.21、0.64、1.05、1.55和2.21 kg · m-3 · d-1左右, 与Zhang等(2015)报道的重金属铜抑制后Anammox工艺恢复状况相近.因此, 阶段式提高NLR可有效利用菌群的适应性和竞争机制(Sheng et al., 2010), 利于Anammox活性的快速恢复.
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| 图 3 厌氧氨氧化反应器中脱氮效率(a)、氮负荷及去除的不同形式氮素比值(b)的变化 Fig. 3 Nitrogen removal performance of the anammox reactor, including nitrogen removal efficiency(a), nitrogen loading rate, ΔNO2--N/ΔNH4+-N and ΔNO3--N /ΔNH4+-N (b) |
由图 2和图 3可知, 在活性恢复阶段(Ⅰ~Ⅳ), 反应器均可在提高NLR后的24 h内快速适应并稳定运行, 截至阶段Ⅳ, 反应器已恢复至受损前的稳定状态.其中, 阶段Ⅱ第18 d时反应器出现较大波动, 使整体脱氮效率呈现较低状态, 且ΔNO3--N/ΔNH4+-N值低于阶段Ⅲ, 可能是因为HRT由12 h缩短至9 h导致的.而在阶段Ⅴ中, NLR提高后反应器需72 h方可渐渐适应, 且NH4+-N和NO2--N去除率分别较阶段Ⅳ降低了2.44%和10.23%, 可能是高浓度的NO2--N对Anammox菌和异养菌有毒害作用, 细胞死亡自溶使反应器内源性COD增加(Tian et al., 2013), 增加了反硝化菌的竞争力.同时, 在进水NO2--N/NH4+-N为1.32的前提下, 尽管阶段Ⅰ~Ⅴ的NH4+-N去除率均高于96%, 但NO2--N去除率和ΔNO3--N/ΔNH4+-N值却逐渐下降, 且出水NO2--N浓度由起初的0.79 mg · L -1渐增至91.00 mg · L-1, 说明虽然有出水回流的稀释作用, 会一定程度上缓解NO2--N对Anammox菌的毒害, 但高浓度NO2--N仍然会抑制Anammox菌活性(Fernández et al., 2012；Kimura et al., 2010；Tang et al., 2010).有研究指出, 当NO2--N浓度超过750 mg L-1时, 90%的Anammox菌发生可逆性失活(Kimura et al., 2010).研究也表明, 瞬时1000 mg · L -1 TN(NH4+-N+NO2--N)的冲击会引起50%Anammox菌失活(Lotti et al., 2012).
3.2 活性恢复阶段厌氧氨氧化菌的EPS组分变化由图 4可知, 反应器活性恢复中EPS含量随NLR提高呈先下降后上升的趋势, 阶段Ⅰ~Ⅴ的EPS含量分别为150.56、33.51、8.42、10.05和10.21 mg · g-1(以VSS计), 各阶段TB-EPS含量均高于LB-EPS含量, 且TB-EPS较LB-EPS对环境敏感度高, 其PN含量均高于PS含量, 这与Jia等(2017)和Pellicernàcher等(2013)的研究结果一致.阶段Ⅰ~Ⅲ中, EPS含量逐渐下降, 阶段Ⅰ中EPS含量远高于阶段Ⅱ和Ⅲ, 其TB-EPS约为LB-EPS的90.25倍, 且TB-PN/PS和LB-PN/PS值分别为21.02和2.21左右, 说明高浓度基质冲击时, 反应器内部分微生物发生了菌体自溶(Tian et al., 2013), 释放出了细胞内部的PN, 使TB-EPS中PN含量剧增, 而PN中荷负电氨基酸较多, 疏水性强(Raszka et al., 2010；Zhang et al., 2007), 利于絮体聚集, 加速了Anammox菌恢复稳定, 同时, TB-EPS紧附于细胞壁上不易脱落(Li et al., 2007；Yang et al., 2009), 导致TB-EPS中PN滞留, 使阶段Ⅰ的TB-EPS含量较高.
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| 图 4 活性恢复中反应器内EPS组分变化 Fig. 4 Variation of the EPS composition during recovery stage of anammox reactor |
阶段Ⅰ~Ⅲ, TB-EPS和LB-EPS中PS含量逐渐增加, 易于形成三维网状结构, 利于PN和PS的相互协作及细胞间物质转换和能量传递, 同时, 增加Anammox菌和TB-EPS中EPS修饰酶活性, 使EPS分层更加趋于稳定(Flemming et al., 2010).阶段Ⅳ和Ⅴ, TB-PN/PS和LB-PN/PS值稳定于0.84左右, 此结果与Jia等(2017)报道的Anammox菌稳定时的结果相近, 说明Anammox系统已处于稳态.另外, 阶段Ⅳ和Ⅴ中EPS含量较阶段Ⅲ分别增加了19.36%和21.26%, 是因为TN浓度超过了Anammox菌的合适阈值使其产生一定程度的应激性, 加速了EPS的分泌, 以增强对外界环境变化的耐受性(Hou et al., 2015；Neyens et al., 2004).
3.3 活性恢复阶段Anammox菌的丰度变化从图 5中Anammox菌丰度变化可知, 反应器活性恢复阶段Ⅰ~Ⅴ中细菌总数逐渐上升, 而Anammox菌丰度为7.7×109~2.4×1010 copies · g-1(以VSS计), 介于高梦佳等(2016)和王衫允等(2016)报道的数据之间.Anammox菌的相对丰度与其绝对丰度变化趋势相同, 阶段Ⅰ~Ⅴ分别为7.78%、5.73%、4.14%、12.59%和7.46%.阶段Ⅰ~Ⅲ中, Anammox菌丰度相当, 这说明中断回流1周后Anammox菌数量并没有显著变化, 而其活性受损才是脱氮性能降低的主要原因.在阶段Ⅳ中Anammox菌丰度最高, 为2.4×1010 copies · g-1(以VSS计), 这显示Anammox菌重新适应了反应器的运行条件, 活性得到恢复(Ma et al., 2012；Molin et al., 2003).随后的阶段Ⅴ中, Anammox菌丰度略有下降, 可能与过高的进水NH4+-N和NO2--N浓度的抑制作用有关(Dapena-Mora et al., 2007；Isaka et al., 2007；Raudkivi et al., 2017；Strous et al., 1999；Yang et al., 2011).
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| 图 5 活性恢复中反应器内Anammox菌丰度变化 Fig. 5 Changes in abundance of anammox bacteria during recovery stage of anammox reactor |
综合反应器活性恢复过程各阶段的脱氮性能、EPS组分及Anammox菌丰度变化可知, 逐步提高氮负荷, 受损反应器中Anammox菌的活性逐步恢复.TN浓度为700 mg · L-1时, 脱氮效率和Anammox菌丰度较高, 且EPS组分含量适宜.而过高的TN浓度(1000 mg · L-1)条件下, 反应器虽然仍有良好的脱氮效率, 但EPS组分含量及Anammox菌丰度均呈现一定程度恶化(Hou et al., 2015；Lotti et al., 2012), 随着时间延长, 有可能导致其脱氮效率下降.
4 结论(Conclusions)Anammox菌对废水中氮浓度变化敏感.高于700 mg · L-1的TN浓度会导致Anammox菌产生基质抑制, 使Anammox污泥中EPS、TB-PN/PS和LB-PN/PS显著增高.采用阶段式提高负荷有利于Anammox菌的活性恢复, 最终平均氮去除负荷达2.21 kg · m-3 · d-1.TN浓度为700 mg · L-1时反应器运行效果最佳, TN去除率最高为79.74%, 且Anammox菌丰度最高.
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