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近年来,随着原油轻质化和清洁能源发展趋势盛行,制氢成为石油化工、储能等支柱产业关注的核心焦点;煤焦气化制氢作为当前最为成熟和经济的生产工艺,目前已在全国大规模推广应用。在煤焦制氢工艺中,水煤浆气化产生的粗煤气混合物经脱盐水洗涤后,产生大量富含Ca2+/Mg2+及酚类等有机物的高硬度难降解气化废水,其高效达标处理成为抑制煤焦制氢产业持续发展的瓶颈[1]。
煤焦气化制氢产生的高硬度难降解有机废水处理通常采用以生化为核心的组合工艺,但因生化好氧单元产生的CO2与来水中的Ca2+/Mg2+反应产生大量无机灰分,且常规沉降无法实现无机灰分与活性污泥的持续有效分离,导致生化池中灰分在污泥细胞外集聚并形成隔离保护层,从而对生化系统产生不同程度的抑制作用[2]。生化池生成的无机灰分可能影响其微生物群落结构[3]、优势菌群丰度[4]、微生物代谢途径以及丝状菌生长趋势[5]等;无机灰分也能引起污泥胞外聚合物(EPS)分泌增加[6-7],多糖中相应增加的亲水羧基使得细胞与EPS间的斥力增加[8-9],从而导致活性污泥形态松散、密实度降低直至污泥沉降性降低[10];无机灰分还可能导致污泥微生物细胞在高渗透压下失活死亡,从而显著影响生化系统综合降解效率。
针对来水钙硬在生化系统中生成无机灰分、并从多方面影响生化效能的问题,目前普遍采取化学沉淀[11]、絮凝[12]、电化学[13]等方法从源头大幅降低来水钙硬,但这些方法普遍存在除钙硬不彻底、处理成本高、产生二次污染等问题,无法根本性避免来水硬度在后续生化池中的持续性集聚[14]。通过生化系统排泥来避免生化池中无机灰分集聚是相对合理的选择,但定向排出无机灰分的关键在于先探明活性污泥与灰分的结合形式,并采取经济有效的方法实现泥灰分离。有研究表明,钙镁等无机矿化物与活性污泥的结合作用力主要是静电作用力[15-16],该作用力促使灰分表面层在活性污泥表面或孔道中形成了液桥[17],但无法形成稳固的络合键[18],这为积极探索泥灰原位分离方法实现生化池调节提供了理论支撑。城市污泥中衍生磷与灰分的分离为磷资源化回收提供新思路的同时,也验证了活性污泥与无机灰分之间的作用力为弱结合力[19]。常规的离心分离过程因其流场均匀性,不仅无法实现定向分离,还可能加剧无机灰分在污泥絮体中的渗透[20]。超声过程虽然能利用油相表面属性差异将污泥与带油的无机组分分开,但也无法实现污泥与无机质的直接分离[21]。而旋流器中因流场剪切和边界效应引起的分散相自转运动[22],可适当脱附活性污泥表面或孔道中夹带的颗粒物或胞外聚合物[23],这为实现活性污泥与无机灰分的分离提供了借鉴[24]。
针对高硬度有机废水生化处理过程生成的无机灰分影响其处理效率的问题,目前尚缺乏对生化池中活性污泥与无机灰分的结合形式及分离途径的系统性实验研究。本研究以高硬度难降解有机废水为对象,首先设置并列SBR并测试了不同硬度废水的生化处理效率和所生成的无机灰分对污泥性状的影响,然后采取离线实验测试了生化池活性污泥与无机灰分的结合形式及潜在分离途径,最后考察了旋流处理对泥灰混合物中无机灰分的分离效率,并通过实际工程侧线实验验证无机灰分旋流分离对生化系统综合效能的改善效果,以期为实际高硬度废水生化处理提标改造提供新思路。
高硬度废水处理生化池中泥-灰旋流分离实验
Hydrocyclone separation of activated sludge and inorganic ash in the biological tank treating high hardness wastewater
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摘要: 针对高硬度废水生化处理过程中生成的无机灰分导致污泥活性降低和沉降性差等问题,采用旋流分离方法实现污泥原位脱灰以改善废水综合处理效能。通过离线和在线实验,探究了污泥与无机灰分的结合形式、泥灰混合物旋流分离效率以及旋流处理对高硬度废水生化处理效率的影响。结果表明,6组不同Ca2+浓度的来水经过150 d生化实验,生化池污泥有机质占比从进水Ca2+浓度为0 mg·L−1时的0.75降至Ca2+浓度为2 400 mg·L−1时的0.39,生化系统COD和氨氮去除率也相应降低11%和60%;原子力显微镜测试结果表明,来水含钙条件下生化池污泥表面因无机灰分附着导致其粗糙度从无钙来水下的20.5 nm增至38.2 nm,且活性污泥与无机灰分间的非稳态结合可通过离心等物理法实现分离;来水Ca2+浓度为800 mg·L−1时,泥灰混合液经过最佳结构旋流器10次循环分离,其有机质占比从0.17升高至0.37;依托120 m3·h−1煤制氢废水处理SBR进行旋流脱灰侧线实验,经过3个月连续运行,改造生化池污泥有机质占比较对比样从0.21提升至0.45,且出水平均COD和氨氮分别降低17.1 mg·L−1和14.3 mg·L−1。活性污泥在线旋流分离调理可为高硬度废水生化处理提标改造提供参考。Abstract: The generated inorganic ash in biological reactor treating high hardness wastewater decreased the activity and settleability of activated sludge. Hydrocyclone application was expected to in-situ separate the inorganic ash from the activated sludge and increase its biological treatment efficiency. The attachment pattern and separation efficiency between inorganic ash and activated sludge were investigated by offline and online experiments, as well as the effect of inorganic ash removal on the biological treatment efficiency of simulated high hardness wastewater. The results showed that the organics ratio decreased from 0.75 in SBR reactor without calcium ion to 0.39 with influent calcium ion concentration of 2 400 mg·L−1 after 150 d continuous biological treatment of 6 groups of influent with different Ca2+ concentrations, COD and NH4-N removal efficiencies also decreased by 11% and 60%, respectively. The atomic force microscope (AFM) images illustrated that the generated inorganic ash increased the surface roughness of activated sludge from 20.5 nm for Ca2+-free influent to 38.2 nm for Ca2+-containing influent. The surface-attached inorganic ash can be removed from the activated sludge by centrifuge. The mixture of inorganic ash and activated sludge in SBR with influent calcium ion concentration of 800 mg·L−1 was circularly separated for 10 times by hydrocyclone with the optimum structure, and the organics ratio in SBR increased from 0.17 to 0.37. The side-flow hydrocyclone separation experiments were conducted for 120 m3·h−1 SBR in a coal-to-hydrogen gasification wastewater treatment plant, three months running caused the increase of the organics ratio from 0.21 in control SBR to 0.45 in modified SBR, the effluent COD and NH4-N decreased by 17.1 mg·L−1 and 14.3 mg·L−1, respectively. The new approach of online hydrocyclone separation conditioning provides a reference for the upgrade of the biological treatment efficiency of high hardness wastewater.
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Key words:
- high hardness wastewater /
- biological process /
- inorganic ash /
- hydrocyclone separation /
- MLVSS/MLSS
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表 1 泥灰混合液旋流分离效率
Table 1. Hydrocyclone separation efficiency of the mixture of activated sludge and inorganic ash
旋流器结构 旋流溢流泥灰单次分离 旋流溢流泥灰10次循环分离 旋流底流泥灰单次分离 固体灰分质量
浓度/(mg·L−1)有机质
占比固体灰分质量
浓度/(mg·L−1)有机质
占比固体灰分质量
浓度/(mg·L−1)有机质
占比6°旋流器 438 0.21 205 0.27 559 0.13 10°旋流器 409 0.24 171 0.37 581 0.10 20°旋流器 394 0.26 85 0.31 672 0.05 -
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