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Effect of inorganic carbon source on nitrogen reduction and sedimentation performance of bioflocs

  • Corresponding author: Xugang HE, xgh@mail.hzau.edu.cn
  • Received Date: 2019-04-02
    Accepted Date: 2019-05-21
  • The ectopic biofloc reactor was used to compare the simulated carbon sources (NaHCO3) concentration of 0.0 g/L (control group), 0.5 g/L, 1.0 g/L and 1.5 g/L of simulated aquaculture wastewater which effect the nitrogen reduction and sedimentation performance of the bioflocs in two stages: organic carbon source exist (stage I for 21 d) and organic carbon source loss (stage II for 21 d). The results showed that the effluent ammonia nitrogen concentration in the first-stage control group was significantly higher than that in the other treatment groups (P<0.05), but generally decreased first and then stabilized. The nitrite nitrogen and nitrate nitrogen in each group accumulated a small amount; the biofloc biomass and sedimentation rate of the control group were significantly lower than the treatment groups (P<0.05), and the difference between the treatment groups was not significant. There was no significant difference in the concentration of ammonia nitrogen and nitrite nitrogen in the effluent of each group in stage II (P>0.05). The concentration of nitrate nitrogen in the control group was higher than that in treatment groups, and the concentration of ammonia nitrogen decreased rapidly. At this stage, the biomass and sedimentation rate of the bioflocs decreased, and the 1.0 g/L NaHCO3 treatment group showed better sedimentation effect; the particle size distribution also tends to be uniform. During the whole experimental period, the removal efficiency of ammonia nitrogen reached 97.8% and the nitrite nitrogen did not accumulate significantly under different concentrations of inorganic carbon source. The sedimentation rate and biomass of bioflocs in the treatment groups were significantly higher than those in the control group (P<0.05). The results show that the addition of inorganic carbon source can improve the nitrogen reduction performance of bioflocs and enhance its sedimentation rate. After removing the organic carbon source, the biofloc reactor can maintain the ammonia nitrogen removal capacity, but caused nitrate nitrogen accumulation, biofloc organisms. The amount is reduced when the organic carbon source was missing, the inorganic carbon source (≥0.5 g/L) helps the biofloc reactor to maintain its ammonia nitrogen removal capacity.
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  • [1] Cardona E, Gueguen Y, Magré K, et al. Bacterial community characterization of water and intestine of the shrimp Litopenaeus stylirostris in a biofloc system[J]. BMC Microbiology, 2016, 16: 157. doi: 10.1186/s12866-016-0770-z
    [2] Li J W, Liu G, Li C W, et al. Effects of different solid carbon sources on water quality, biofloc quality and gut microbiota of Nile tilapia (Oreochromis niloticus) larvae[J]. Aquaculture, 2018, 495: 919-931. doi: 10.1016/j.aquaculture.2018.06.078
    [3] Deng M, Chen J Y, Gou J W, et al. The effect of different carbon sources on water quality, microbial community and structure of biofloc systems[J]. Aquaculture, 2018, 482: 103-110. doi: 10.1016/j.aquaculture.2017.09.030
    [4] 卢炳国, 王海英, 谢骏, 等. 不同C/N水平对草鱼池生物絮团的形成及其水质的影响[J]. 水产学报, 2013, 37(8): 1220-1228.Lu B G, Wang H Y, Xie J, et al. Effect of C/N ratio on bioflocs formation and water quality in zero-water exchange grass crap tanks[J]. Journal of Fisheries of China, 2013, 37(8): 1220-1228(in Chinese).
    [5] Crab R, Defoirdt T, Bossier P, et al. Biofloc technology in aquaculture: Beneficial effects and future challenges[J]. Aquaculture, 2012, 356-357: 351-357. doi: 10.1016/j.aquaculture.2012.04.046
    [6] 张怖青, 江兴龙, 郑伟刚. 生物絮团技术在水产养殖中的应用研究[J]. 渔业现代化, 2016, 43(6): 33-38. doi: 10.3969/j.issn.1007-9580.2016.06.007Zhang B Q, Jiang X L, Zheng W G. The research progress of biofloc technology in aquaculture[J]. Fishery Modernization, 2016, 43(6): 33-38(in Chinese). doi: 10.3969/j.issn.1007-9580.2016.06.007
    [7] Tidwell J H. Aquaculture Production Systems[M]. Ames, Iowa: Wiley-Blackwell, 2012: 286.
    [8] Avnimelech Y. Biofloc Technology-A Practical Guidebook[M]. Baton Rouge La: World Aquaculture Society, 2012: 50-167.
    [9] De Schryver P, Verstraete W. Nitrogen removal from aquaculture pond water by heterotrophic nitrogen assimilation in lab-scale sequencing batch reactors[J]. Bioresource Technology, 2009, 100(3): 1162-1167. doi: 10.1016/j.biortech.2008.08.043
    [10] Azim M E, Little D C, Bron J E. Microbial protein production in activated suspension tanks manipulating C: N ratio in feed and the implications for fish culture[J]. Bioresource Technology, 2008, 99(9): 3590-3599. doi: 10.1016/j.biortech.2007.07.063
    [11] Vinatea L, Gálvez A O, Venero J, et al. Oxygen consumption of Litopenaeus vannamei juveniles in heterotrophic medium with zero water exchange[J]. Pesquisa Agropecuária Brasileira, 2009, 44(5): 534-538. doi: 10.1590/S0100-204X2009000500014
    [12] Schneider O, Sereti V, Machiels M A M, et al. The potential of producing heterotrophic bacteria biomass on aquaculture waste[J]. Water Research, 2006, 40(14): 2684-2694. doi: 10.1016/j.watres.2006.05.008
    [13] Schneider O, Sereti V, Eding E H, et al. Heterotrophic bacterial production on solid fish waste: TAN and nitrate as nitrogen source under practical RAS conditions[J]. Bioresource Technology, 2007, 98(10): 1924-1930. doi: 10.1016/j.biortech.2006.07.045
    [14] Yue X, Yu G P, Liu Z H, et al. Start-up of the completely autotrophic nitrogen removal over nitrite process with a submerged aerated biological filter and the effect of inorganic carbon on nitrogen removal and microbial activity[J]. Bioresource Technology, 2018, 254: 347-352. doi: 10.1016/j.biortech.2018.01.107
    [15] 国家环境保护总局, 国家质量监督检验检疫总局. GB 3838—2002地表水环境质量标准[S]. 北京: 中国环境科学出版社, 2002.State Environmental Protection Administration, General Administration of Quality Supervision, Inspection and Quarantine of the People’s Republic of China. GB 3838—2002 Environmental quality standards for surface water[S]. Beijing: China Environmental Press, 2002(in Chinese).
    [16] Avnimelech Y. Carbon/nitrogen ratio as a control element in aquaculture systems[J]. Aquaculture, 1999, 176(3-4): 227-235. doi: 10.1016/S0044-8486(99)00085-X
    [17] De Schryver P, Crab R, Defoirdt T, et al. The basics of bio-flocs technology: The added value for aquaculture[J]. Aquaculture, 2008, 277(3-4): 125-137. doi: 10.1016/j.aquaculture.2008.02.019
    [18] Furtado P S, Poersch L H, Wasielesky W Jr. Effect of calcium hydroxide, carbonate and sodium bicarbonate on water quality and zootechnical performance of shrimp Litopenaeus vannamei reared in bio-flocs technology (BFT) systems[J]. Aquaculture, 2011, 321(1-2): 130-135. doi: 10.1016/j.aquaculture.2011.08.034
    [19] 罗国芝, 陈晓庆, 谭洪新. 水产养殖水体循环利用过程中碱度的变化及调控[J]. 淡水渔业, 2018, 48(2): 100-106. doi: 10.3969/j.issn.1000-6907.2018.02.015Luo G Z, Chen X Q, Tan H X. Changes and control of alkalinity in the process of utilize recycling aquaculture water[J]. Freshwater Fisheries, 2018, 48(2): 100-106(in Chinese). doi: 10.3969/j.issn.1000-6907.2018.02.015
    [20] 夏耘, 郁二蒙, 谢骏, 等. 基于PCR-DGGE技术分析生物絮团的细菌群落结构[J]. 水产学报, 2012, 36(10): 1563-1571.Xia Y, Yu E M, Xie J, et al. Analysis of bacterial community structure of Bio-Floc by PCR-DGGE[J]. Journal of Fisheries of China, 2012, 36(10): 1563-1571(in Chinese).
    [21] 罗国芝, 朱泽闻, 潘云峰, 等. 生物絮凝技术在水产养殖中的应用[J]. 中国水产, 2010(2): 62-63. doi: 10.3969/j.issn.1002-6681.2010.02.029Luo G Z, Zhu Z W, Pan Y F, et al. Application of biofloc technology in Aquaculture[J]. China Fisheries, 2010(2): 62-63(in Chinese). doi: 10.3969/j.issn.1002-6681.2010.02.029
    [22] Luo G Z, Zhang N, Tan H X, et al. Efficiency of producing bioflocs with aquaculture waste by using poly-β-hydroxybutyric acid as a carbon source in suspended growth bioreactors[J]. Aquacultural Engineering, 2017, 76: 34-40. doi: 10.1016/j.aquaeng.2017.01.001
    [23] Ebeling J M, Timmons M B, Bisogni J J. Engineering analysis of the stoichiometry of photoautotrophic, autotrophic, and heterotrophic removal of ammonia-nitrogen in aquaculture systems[J]. Aquaculture, 2006, 257(1-4): 346-358. doi: 10.1016/j.aquaculture.2006.03.019
    [24] 张志, 任洪强, 张蓉蓉, 等. pH值对好氧颗粒污泥同步硝化反硝化过程的影响[J]. 中国环境科学, 2005, 25(6): 650-654. doi: 10.3321/j.issn:1000-6923.2005.06.003Zhang Z, Ren H Q, Zhang R R, et al. Influence of pH value on simultaneous nitrification and denitrification process of aerobic granule sludge[J]. China Environmental Science, 2005, 25(6): 650-654(in Chinese). doi: 10.3321/j.issn:1000-6923.2005.06.003
    [25] Luo G Z, Avnimelech Y, Pan Y F, et al. Inorganic nitrogen dynamics in sequencing batch reactors using biofloc technology to treat aquaculture sludge[J]. Aquacultural Engineering, 2013, 52: 73-79. doi: 10.1016/j.aquaeng.2012.09.003
    [26] 孔得杨. 微生物氮转化途径综述[J]. 西部皮革, 2017, 39(4): 42-47. doi: 10.3969/j.issn.1671-1602.2017.04.034Kong D Y. Review of microbial nitrogen transformation[J]. West Leather, 2017, 39(4): 42-47(in Chinese). doi: 10.3969/j.issn.1671-1602.2017.04.034
    [27] Azim M E, Little D C. The biofloc technology (BFT) in indoor tanks: Water quality, biofloc composition, and growth and welfare of Nile tilapia (Oreochromis niloticus)[J]. Aquaculture, 2008, 283(1-4): 29-35. doi: 10.1016/j.aquaculture.2008.06.036
    [28] Avnimelech Y, Kochba M. Evaluation of nitrogen uptake and excretion by tilapia in bio floc tanks, using 15N tracing[J]. Aquaculture, 2009, 287(1-2): 163-168. doi: 10.1016/j.aquaculture.2008.10.009
    [29] 许宏良. 废水活性污泥生物处理中的丝状细菌[J]. 工业安全与环保, 2006, 32(8): 26-27. doi: 10.3969/j.issn.1001-425X.2006.08.011Xu H L. Brief discussion on filamentous bacteria in the wastewater treatment of active sludge[J]. Industrial Safety and Environmental Protection, 2006, 32(8): 26-27(in Chinese). doi: 10.3969/j.issn.1001-425X.2006.08.011
    [30] 郝晓地, 朱景义, 曹秀芹. 污泥膨胀形成机理及控制措施研究现状和进展[J]. 环境污染治理技术与设备, 2006, 7(5): 1-9.Hao X D, Zhu J Y, Cao X Q. Situation and development of bulking sludge study: General theories and control measures[J]. Techniques and Equipment for Environmental Pollution Control, 2006, 7(5): 1-9(in Chinese).
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Effect of inorganic carbon source on nitrogen reduction and sedimentation performance of bioflocs

    Corresponding author: Xugang HE, xgh@mail.hzau.edu.cn
  • 1. College of Fisheries, Huazhong Agricultural University, Wuhan 430070, China
  • 2. Hubei Provincial Engineering Laboratory for Pond Aquaculture, Wuhan 430070, China
  • 3. Freshwater Aquaculture Collaborative Innovation Center of Hubei Province, Wuhan 430070, China
  • 4. National Demonstration Center for Experimental Aquaculture Education, Huazhong Agricultural University, Wuhan    430070, China

Abstract: The ectopic biofloc reactor was used to compare the simulated carbon sources (NaHCO3) concentration of 0.0 g/L (control group), 0.5 g/L, 1.0 g/L and 1.5 g/L of simulated aquaculture wastewater which effect the nitrogen reduction and sedimentation performance of the bioflocs in two stages: organic carbon source exist (stage I for 21 d) and organic carbon source loss (stage II for 21 d). The results showed that the effluent ammonia nitrogen concentration in the first-stage control group was significantly higher than that in the other treatment groups (P<0.05), but generally decreased first and then stabilized. The nitrite nitrogen and nitrate nitrogen in each group accumulated a small amount; the biofloc biomass and sedimentation rate of the control group were significantly lower than the treatment groups (P<0.05), and the difference between the treatment groups was not significant. There was no significant difference in the concentration of ammonia nitrogen and nitrite nitrogen in the effluent of each group in stage II (P>0.05). The concentration of nitrate nitrogen in the control group was higher than that in treatment groups, and the concentration of ammonia nitrogen decreased rapidly. At this stage, the biomass and sedimentation rate of the bioflocs decreased, and the 1.0 g/L NaHCO3 treatment group showed better sedimentation effect; the particle size distribution also tends to be uniform. During the whole experimental period, the removal efficiency of ammonia nitrogen reached 97.8% and the nitrite nitrogen did not accumulate significantly under different concentrations of inorganic carbon source. The sedimentation rate and biomass of bioflocs in the treatment groups were significantly higher than those in the control group (P<0.05). The results show that the addition of inorganic carbon source can improve the nitrogen reduction performance of bioflocs and enhance its sedimentation rate. After removing the organic carbon source, the biofloc reactor can maintain the ammonia nitrogen removal capacity, but caused nitrate nitrogen accumulation, biofloc organisms. The amount is reduced when the organic carbon source was missing, the inorganic carbon source (≥0.5 g/L) helps the biofloc reactor to maintain its ammonia nitrogen removal capacity.

  • 近年来,生物絮团技术(Biofloc Technology,BFT)在水产养殖中得到广泛应用,生物絮团能净化养殖水质、降低饵料系数、增强养殖对象免疫力、减少病害发生,尤其是在对虾和滤食性鱼类生产养殖中,取得了良好效果(Cardona等[1],Li等[2],邓闵等[3],卢炳国等[4])。生物絮团的形成需要提供有机碳源,一般通过提高饲料碳氮比或额外添加有机碳源等方式来实现(Crab等[5])。然而有机碳源价格高昂,过高成本限制了生物絮团技术的大规模应用(张怖青等[6])。寻求低廉有机碳源或有机碳源替代品成为生物絮团技术研究的热点之一。无机碳源相对廉价,其不仅是水体酸碱缓冲能力的重要组成部分,同时也为细菌异养同化作用和硝化作用提供碱度,对维持异养细菌和硝化细菌正常功能、降低水体氨氮浓度具有重要作用(Tidwell等[7],Avnimelech[8])。迄今为止,对于无机碳源对生物絮团功能影响的相关研究甚少。生物絮团由微生物、有机碎屑、原生动物和藻类等组成,微生物、原生动物等的呼吸作用需要消耗水中大量溶氧,与养殖对象存在溶氧竞争关系;而且过多的生物絮团聚集成团,会导致水体浑浊,不利于对浊度敏感鱼类的生长(De Schryver等[9],Azim等[10]);在养殖池塘等水体中为保障生物絮团的悬浮需要额外消耗大量电能(Vinateal等[11])。为弥补上述不足,异位生物絮团反应器(biofloc reactor,BR)应运而生。利用异位生物絮团反应器净化养殖废水,再将净化后的水循环到养殖系统中重复利用以节约水资源,产生的生物絮团沉淀收集后部分循环用于反应器,部分作为滤食性动物的补充饲料被资源化再利用(Schneider等[12],Schneider等[13])。异位生物絮团反应器技术具有十分广阔的应用前景。目前,异位生物絮团反应器技术尚不成熟,其中最关键的技术问题就是碳源控制问题。为此,本研究比较研究了有机碳源存在和缺失两种工况下,无机碳源对生物絮团反应器降氮性能、生物絮团生物量积累等重要参数的影响,以期为异位生物絮团反应器技术的完善、无机碳源对生物絮团功能影响机制等问题提供参考资料。

    • 单个生物絮团反应器如图1所示,本实验共采用12个生物絮团反应器。反应器材质为聚丙烯,呈圆柱状,高320 mm,底面内径为200 mm,总容量为10 L,实验过程中的有效体积为5 L。反应器被放置在智能人工气候箱(型号HP1500GS,武汉瑞华仪器设备有限公司)中,以达到稳定的生长温度(30.0±0.5 °C)并且满足充分的光照条件(24 h)。此外,每个反应器底部设有一个多孔曝气石,所有多孔曝气石连接到1台电磁式空气泵(功率0.138 kW,型号ACO008,浙江森森集团股份有限公司)上,加装流量计控制溶氧(DO)6.0 mg/L左右,以此提供充足氧气和维持生物絮团在反应器中的悬浮状态。反应器的单个循环周期为48 h,包括人工模拟废水添加阶段10 min,曝气反应阶段,人工充分混合阶段10 min和收集出水阶段5 min。生物絮团反应器的单个循环周期换水量为1 L,占反应器有效体积(5 L)的20%,即收集1 L混合出水后,利用精密蠕动泵(功率35 W,型号LabN1,河北保定申辰泵业有限公司)添加配制的人工模拟废水1 L(保持恒定的有效体积5 L,若水体因曝气等原因挥发,补充至5 L)。反应器出水在经过人工充分混合阶段后,生物絮团呈均匀混合分布,此时收集出水做进一步处理。

      Figure 1.  Schematic diagram of biofloc reactor

    • 本实验一共设置4个实验组,分为对照组和3个处理组,每个实验组设置3个平行。NaHCO3作为模拟废水的唯一无机碳源(Inorganic carbon,IC),4个实验组的NaHCO3浓度分别是0.0 g/L,0.5 g/L,1.0 g/L,1.5 g/L,分别记作对照组,IC=0.5 g/L组,IC=1.0 g/L组和IC=1.5 g/L组。1 L进水的其他组份为585 mg C6H12O6,59.5 mg NH4Cl(相当于20.0 mg N),16 mg KH2PO4,39 mg K2HPO4,2 mg MgSO4·7H2O,4 mg CaCl2。进水由2种磷酸盐组成缓冲系统,有机碳源与氮源的比例为15∶1(w/w,原子质量比)。每个反应器每次添加0.2 mL的微量元素溶液,微量元素溶液的组成参照文献(Yue等[14])。

      生物絮团反应器建立之后,加入天然养殖废水5 L(取自草鱼养殖池塘),随后添加人工模拟废水配伍所需要的药品,使得养殖废水的各组分与人工模拟废水相同。曝气即可启动生物絮团反应器。为探究生物絮团在仅有无机碳源存在条件下的降氮性能的维持,实验又分为2个阶段,第Ⅰ阶段为生物絮团生长稳定阶段(实验为期21 d),第Ⅱ阶段为生物絮团维持阶段(实验为期21 d)。第Ⅰ阶段进水为上述模拟废水,来培养生物絮团;第Ⅱ阶段进水则是移除有机碳源的模拟废水,来维持生物絮团性能。

    • 生物絮团反应器每2天换水一次,每个循环周期的下午14:00准时进行理化指标的监测与测定。DO,pH值和温度在14:00用YSI Pro便携式水质分析仪(Yellow Spring,OH,USA)测量。采集100 mL出水水样随即经过0.45 μm的水系滤膜过滤,用来检测氨氮($ {\rm{NH}}_4^{\rm{ + }}$-N),亚硝态氮($ {\rm{NO}}_2^ - $-N),硝态氮($ {\rm{NO}}_3^ - $-N)和化学需氧量,同时预留过滤后的30 mL水样保存在−20 °C,用来测量总氮(TN)和总磷(TP)。$ {\rm{NH}}_4^{\rm{ + }}$-N,$ {\rm{NO}}_2^ - $-N,$ {\rm{NO}}_3^ - $-N,COD,TN,TP等均采用国家标准方法进行测定(地表水质标准[15])。

      生物絮团沉积量(BFV)使用沉淀漏斗(1000-0010,Nalgene)测定,取1 000 mL的水样经过30 min的沉降,读取沉积物的体积量,每个循环周期测一次。总固体悬浮物(TSS)的测定方法采用水和废水分析的标准方法,使用定量滤纸抽滤1 000 mL水样,然后在105 °C烘箱中烘干称重。污泥体积指数(SVI)是指沉降后1.0 g TSS的体积。生物絮团的粒径则根据颗粒的大小,采用徕卡DM 2500全自动显微镜(连接有数码相机)拍照记录粒径。整个实验过程中,分别在第Ⅰ阶段末和第Ⅱ阶段末收集生物絮团来测定反应器中的TSS,4 mL生物絮团沉降耗时和粒径分布。

    • 用SPSS 19.0对水质数据进行统计分析,其中反应器出水水质指标的组间差异采用单因素方差分析,差异显著水平为P<0.05。用GraphPad Prism 5.0作图。

    2.   结果
    • 整个实验过程在恒温气候箱中进行,且用流量计控制反应器的溶氧供应,因此,各组水温和DO均无显著差异(P>0.05)(表1)。如表1所示,各组反应器内水体均呈弱碱性,但对照组的pH值显著低于处理组(P<0.05),这是由于处理组NaHCO3的添加,导致反应器内的pH值偏高。

      指标 IC=0.0 g/L IC=0.5 g/L IC=1.0 g/L IC=1.5 g/L
      水温 (°C) water temperature 29.8±0.25 29.9±0.26 29.9±0.21 29.8±0.27
      pH值 8.11±0.43a 8.82±0.31b 8.97±0.27b 8.97±0.31b
      溶氧 DO (mg/L) 6.05±0.65 6.01±0.37 6.10±0.40 6.13±0.45
      进水氨氮(mg/L) influent ammonia nitrogen 20.15±0.10 19.97±0.09 20.05±0.06 20.09±0.11
      进水COD(mg/L) (Ⅰ) influent COD 58.8±5.6 65.4±3.3 60.2±2.1 55.9±7.6
      进水COD(mg/L) (Ⅱ) influent COD 10.1±3.5 10.6±2.8 11.5±3.4 9.7±5.0
      a-b The ranges indicated with another superscript are significantly different from each other (mean±standard deviation) according to a One-way ANOVA with Tukey test (P<0.05). Among them, the items marked with (I) and (II) represented theⅠstage and theⅡstage respectively, the data volume was 11, and the others were 21
      a-b 是表明在P<0.05的水平上有显著性差异,根据单因素方差分析的Tukey检验。其中,标注有(Ⅰ)和(Ⅱ)的项目分别代表第Ⅰ阶段和第Ⅱ阶段,数据量为11,其他的为21

      Table 1.  Water physicochemical factors in the biofloc reactors(mean±SD)

      生物反应器启动之后,所有实验组出水中的氨氮浓度显著降低(图2,A)。其中,三个处理组的氨氮浓度在第11天达到最低值,随后一段时间保持在较低水平并趋于稳定。对照组氨氮浓度降低较缓慢,第Ⅰ阶段结束时浓度仍有2.35 mg/L,显著高于处理组(P<0.05)。第Ⅱ阶段,重新调整反应器中初始氨氮浓度为20.00±0.44 mg/L,发现出水氨氮浓度迅速降低,对照组在4个循环周期内就可达到最低浓度,而处理组只需2个周期,且始终稳定维持在最低浓度。第Ⅱ阶段,各实验组氨氮去除效率达到97.8%以上。由图2,B可知,反应器出水亚硝态氮浓度在整个实验周期始终低于0.1 mg/L,无机碳源浓度高的处理组(IC=1.0 g/L组和IC=1.5 g/L组),其出水亚硝态氮浓度出现降低趋势的时段较其他两组有所提前,在第Ⅱ阶段开始的时候,IC=1.5 g/L组就已降到较低水平,随后IC=1.0 g/L组也逐渐降低。实验的第Ⅰ阶段,各组出水中硝态氮缓慢积累,但是各组之间没有显著差异(P>0.05)(图2,C)。在移除有机碳源添加之后,各组出水中的硝态氮浓度迅速增加,并且在实验后期(第31−41天)维持较高浓度,此时,对照组硝态氮浓度显著高于处理组(P<0.05),IC=0.5 g/L组和IC=1.5 g/L组之间差异不显著(P>0.05),IC=1.0 g/L组则显著低于其他实验组(P<0.05)。出水总氮浓度变化如图2,D所示,各实验组第Ⅰ阶段的变化趋势与氨氮浓度变化相似,呈逐渐降低趋势;在第Ⅱ阶段则先降低后逐渐增加,最后保持相对稳定,处理组之间无显著差异(P>0.05),与对照组差异显著(P<0.05)。

      Figure 2.  Changes in ammonia nitrogen ($ {\rm{NH}}_4^{\rm{ + }}$-N) (A), nitrite ($ {\rm{NO}}_2^ - $-N) (B), nitrate ($ {\rm{NO}}_3^ - $-N) (C) andtotal nitrogen (TN) (D) of the biofloc reactors at different inorganic carbon (IC) concentration groups (mean±stand deviation)

    • 生物絮团沉积量(BFV)的测定结果见图3,第Ⅰ阶段,各组的BFV先增加后减少,IC=1.5 g/L组显著低于其他处理组(P<0.05)。实验中后期(第15—35天)对照组与IC=1.5 g/L组的BFV低于其他两组。移除有机碳源的添加后,BFV逐渐减少,在实验后期趋于稳定,对照组的BFV显著低于处理组(P<0.05)。如图4,A所示,第Ⅰ阶段末期,处理组的TSS浓度显著高于对照组(P<0.05),IC=1.0 g/L组的最高。第Ⅱ阶段末期,各组的TSS浓度差异减小,但IC=1.0 g/L组的仍保持较高水平,且显著高于对照组(P<0.05)。SVI的测定结果显示对照组的SVI指数显著高于处理组(P<0.05),IC=1.5 g/L组的最低,显著低于其他组(P<0.05)(图4,B)。但是在第Ⅱ阶段末期,各组之间的SVI指数无明显差异(P>0.05),均保持在40−100 mL/g范围内。

      Figure 3.  The biofloc volume at different inorganic carbon (IC) concentration groups

      Figure 4.  Total suspended solids concentration (TSS) (A) and sludge volume index (SVI) (B) under different carbon (IC) concentration groups at the end of the two stages

      等量生物絮团耗时(实验后期生物絮团沉积量不足4 mL/L,故取2 L反应器出水进行沉降,以获得足够沉积量)结果如图5所示,对照组在整个实验阶段,4 mL生物絮团沉降耗时远高于处理组(P<0.05),处理组中IC=1.0 g/L组沉降耗时在各个阶段均保持较低水准,沉降性能良好。IC=0.5 g/L组和IC=1.5 g/L组的沉降耗时相似,两组之间无显著差异(P>0.05)。用显微镜观察生物絮团大概的颗粒粒径,结果如图6所示。第Ⅰ阶段对照组生物絮团颗粒整体较小,低于450 μm的占比高达99%,IC=1.0 g/L组中大颗粒生物絮团比例较高,小颗粒的占比最少,只有32%。第Ⅱ阶段中所有实验组的生物絮团粒径都有很大的提升,其中IC=0.5 g/L组变化明显,大于150 μm的颗粒比例达到71%以上。

      Figure 5.  Duration of 4 mL of biofloc (volume) in different inorganic carbon (IC) concentration groups at the end of the two stages

      Figure 6.  Particle size abundance distribution of bioflocs at the end of two stage

    3.   讨论
    • 研究表明,生物絮团技术是通过提高碳氮比,促进异养微生物的生长,利用水体中的残饵以及粪便转化为菌体蛋白,从而显著降低氨氮水平,起到净化水质的作用(Azim等[10],Avnimelech[16],De Schryver[17])。而应运而生的异位生物絮团反应器,在降低水体氨氮水平的同时,还能够有效避免生物絮团在水产养殖系统中产生的的消极影响(Crab等[5],De Schryver等[9])。昂贵的有机碳源限制了生物絮团技术的发展,需要降低碳源成本以利于生物絮团技术推广应用。本实验结果证明,添加无机碳源补充因氨氮同化和部分自养硝化所消耗的碱度,对促进生物絮团生成,维持反应器的降氮性能起到了积极作用(Furtado等[18],罗国芝等[19])。

    • 实验的第Ⅰ阶段,启动生物絮团反应器后,出水的氨氮迅速降低,随后保持相对稳定,这一现象已被证明(卢炳国等[4],De Schryver等[9])。此阶段的进水包含有机碳源,并使碳氮比保持在15∶1,水体中的异养细菌利用充足的有机碳源,通过异养微生物的同化作用,生成微生物菌体蛋白,达到去除氨氮的目的(Azim等[10],Avnimelech[16],夏耘等[20])。对照组的氨氮浓度高于处理组,原因是对照组中无机碳源不足引起水体内碱度较低,不利于异养同化的进行(罗国芝等[21]),反应器中氨氮不能有效去除,碱度是此阶段的限制因素。反应器中的亚硝态氮的少量积累,可能是反应器中存在的硝化作用或者是反硝化作用进行的不彻底导致的(Luo等[22],Ebeling等[23])。IC=1.0 g/L组和IC=1.5 g/L组出水中亚硝态氮较低,说明增加碱度提高了硝化细菌的活性,从而对生物絮团反应器中亚硝态氮的去除起到积极作用(张志等[24])。硝态氮没有明显的积累,这与邓闵等[3]的研究相似,一些异养的反硝化菌存在于生物絮团中,利用硝态氮或者是发生了反硝化作用(Luo等[25])。各组总氮去除率达到90%以上,说明了生物絮团反应器的高效的除氮性能。

      第Ⅱ阶段,有机碳源被移除之后,氨氮浓度迅猛降低并稳定在较低水平,亚硝态氮也持续减少,这与生物絮团中存在的自养硝化细菌有关,其能够在无机条件下,将氨氮转化为硝态氮,并且不产生亚硝态氮的积累(孔得杨[26])。这说明生物絮团反应器在仅有无机碳源存在的条件下,是可以维持其降低氨氮性能的。但是,硝态氮出现了显著地积累,其主要原因是有机碳源的移除,反硝化作用受到抑制,从而导致硝态氮的积累(卢炳国等[4],Luo等[25],Azim等[27])。对照组由于缺少无机碳源,pH值较处理组低,这降低了反应器中反硝化菌的活性(张志等[24]),从而导致硝态氮浓度的显著积累。在此阶段,总氮变化与硝态氮变化趋势相似,但其去除效率仅有20−30%,效率较低。

    • 生物絮团反应器中生物量的增加可用TSS浓度来表示。本实验中,TSS浓度始终维持在100 mg/L以下,略低于形成良好生物絮团的要求(Avnimelech等[28]),可能是本实验单循环周期换水量过多(20%)引起的,研究表明,生物絮团在零或低水交换率的条件下就能够改善养殖水体水质(Crab等[5],Avnimelech[16],Avnimelech等[28])。第Ⅰ阶段对照组的TSS浓度低于实验组,源于无机碳提供的充分碱度,促进异养生物同化产生菌体蛋白,同时降低氨氮浓度(张怖青等[6],Tidwell等[7])。第Ⅱ阶段,处理组TSS浓度均有所降低,这是由于生物絮团中异养细菌的同化受到一定程度的抑制,部分生物絮团分解以供异养细菌维持生物活性,BFV的变化也佐证了TSS浓度降低的事实。对照组的TSS浓度在第Ⅱ阶段末期有所增加,可能是换水过程中,对照组的生物絮团流失较少,取样时部分生物絮团沉淀没有搅拌均匀引起的。另外,实验的第Ⅰ阶段末期,无机碳源浓度与SVI指数呈反比,但第Ⅱ阶段则无差异,也支持TSS浓度变化特征。

      为了更深入地了解生物絮团的物理沉降性能以及其原理,探讨如何快速收集到生物絮团固体物,等量生物絮团沉降耗时和生物絮团颗粒粒径分布情况得到了进一步的探索。生物絮团沉降4 mL结果表明,对照组的生物絮团沉降性能差,实验组沉降性能良好,收集等量的生物絮团实验组耗时更短,更有利于收集生物絮团固体物。实验发现,第Ⅱ阶段末期显微镜下观察生物絮团时,发现大量丝状菌,有研究表明,丝状菌的快速增殖会引起污泥絮凝体的沉降性能变差(许宏良等[29])。生物絮团的粒径分布结果显示,无机碳源的添加会明显增加絮体的体积。生物絮团技术是活性污泥法的延续,其生成过程中也会发生类似于污泥膨胀的现象,对照组的絮体体积较小,絮体之间联系不紧密,原因可能是发生了丝状菌污泥膨胀(许宏良等[29],郝晓地等[30])。实验过程中,第Ⅱ阶段的生物絮团粒径比第Ⅰ阶段的普遍有所增加,是由于生物絮团颗粒形成后,其质量有所增加,故曝气产生的悬浮作用不能使絮体悬浮,从而进一步沉降,絮体粒径也趋向均匀。无机碳源的加入能够提高生物絮团的沉降速度,这对生物絮团的快速收集、重复利用有着重要意义。

      本研究表明,利用异位生物絮团反应器,在短时间内高效处理高氨氮废水的同时,也回收一定数量的生物絮团。回收的生物絮团可资源化再利用,如作为水产饲料的替代品或添加剂等。无机碳源的存在,不仅提升了反应器废水处理能力、维持反应器pH值和碱度稳定,也有利于生物絮团的回收。尤其是在有机碳源缺失时,无机碳源(≥0.5 g/L)可帮助生物絮团反应器保持其氨氮去除能力,有助于有机碳源的节约使用。当有机碳源用量不足时,为达到理想的综合降氮效果,至少有以下两条途径:1. 利用植物优先利用硝态氮的特性,生物絮团反应器可配合使用浮游植物等水生植物,以利用积累的硝态氮;2. 在生物絮团成熟后,可适当降低碳氮比,而不是完全移除有机碳源,以维持总氮较高去除率。

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