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基于污水源分离技术,生活污水按其来源和水质的不同可被分为灰水(grey water)和黑水(black water),灰水由厨房和卫生间的洗涤、洗浴水组成;黑水包括大小便和冲厕水等,约占生活污水总量的30%,化学需氧量(chemical oxygen demand, COD)、总氮(total nitrogen, TN)、悬浮固体(suspended solid, SS)、总磷(total phosphorus, TP)等污染物质量浓度高,处理难度大,同时具备资源化条件[1-3]。另外,黑水的高效处理与资源化对“厕所革命”的推进、农村人居卫生条件的改善等也至关重要[4]。黑水经化学强化高负荷活性污泥法(chemical enhance high-rate activated sludge, CEHRAS)捕获碳源后,虽然NH4+-N质量浓度可达100~300 mg·L−1,但各种氮回收技术仍不具有经济性[5],且碳氮比较低(COD/NH4+-N< 3)[6],传统硝化/反硝化工艺无法实现有效脱氮[7]。近年来,基于NO2−-N的高效低耗脱氮工艺如短程硝化-反硝化(partial nitrification-denitrification, PN/D)、短程硝化-厌氧氨氧化(partial nitrification-anammox, PN/A)等新型脱氮技术受到了广泛关注[8]。
长期稳定的短程硝化是实现PN/A等新型脱氮技术的前提与难点,其关键在于富集并促进氨氧化菌(ammonia-oxidizing bacteria, AOB)的同时有效抑制和淘汰亚硝酸盐氧化菌(nitrite-oxidizing bacteria, NOB)。目前已报道的短程硝化控制策略包括游离氨(free ammonia, FA)[9]、游离亚硝酸(free nitrous acid, FNA)[10]、碳氮比(C/N)[11]、温度[12]、进水氨氮负荷[13]、溶解氧(dissolved oxygen, DO)[14]、间歇曝气[15]、不同停曝比[16]等。采用单一的控制手段难以实现稳定的短程硝化,将多种控制策略组合应用能进一步提高短程硝化效果[17]。XU等[18]在移动床生物膜反应器(moving bed biofilm reactor, MBBR)中,通过控制DO、FA和FNA的质量浓度,实现了高效、稳定的短程硝化。WEN等[19]利用序批式反应器(sequential batch reactor, SBR),通过实时控制进水温度、pH、DO、FA等参数,在反应器运行的第16个周期成功启动短程硝化,并稳定运行了32 d。
在实际应用中,进水中的FA、FNA、C/N等参数难以实现灵活控制,而曝气模式和DO值较容易控制[20]。曝气控制相对于其它控制策略而言,具有操作简单、成本低廉等优点,有研究[21]认为,曝气控制是黑水实现短程硝化较为合适的策略。高氧持续曝气、间歇曝气和低氧持续曝气是3种常见的曝气方式,当前国内外研究中,有关3种曝气方式实现碳捕获预处理黑水部分亚硝化及其稳定性的文献报道较少。为此,本文采用SBR,对比研究了高氧持续曝气、间歇曝气和低氧持续曝气3种曝气方式实现碳捕获预处理黑水短程硝化的效果差异,剖析了不同曝气方式对微生物种群结构的影响,提出了实现长期稳定短程硝化的调控策略,以期为后续短程硝化与Anammox工艺的耦合奠定基础。
基于曝气方式控制的碳捕获预处理黑水部分亚硝化工艺
Partial nitritation based on aeration control strategies for carbon-captured blackwater pretreatment
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摘要: 短程硝化是短程生物脱氮工艺的前提与难点,通过曝气控制实现短程硝化具有操作灵活、成本低等优点。本文采用序批式活性污泥反应器,对比分析了高氧持续曝气、间歇曝气和低氧持续曝气3种曝气方式实现碳捕获预处理黑水短程硝化的效果和微生物群落结构的差异。结果表明:相对于高氧持续曝气和间歇曝气,低氧持续曝气工况亚硝态氮累积率(NAR)更高,出水NO2−-N/NH4+-N更接近厌氧氨氧化进水的水质要求;高氧持续曝气工况能逐步洗脱Nitrospira,同时提高AOB和Nitrobacter的相对丰度;低氧持续曝气工况显著降低了Nitrobacter的相对丰度,但低DO条件下AOB丰度降低并出现了Nitrospira。以上研究结果表明,针对碳捕获后的黑水,采用高氧持续曝气与低氧持续曝气交替组合运行的控制策略有助于实现更好的短程硝化效果和运行稳定性。Abstract: Nitritation is the precondition and difficulty of biological nitrogen removal process via nitrite pathway, meanwhile, its occurrence through aeration control has the advantages of flexible operation, lower cost and so on. Therefore, a sequencing batch activated sludge reactor (SBR) was used in this study, the partial nitritation effects and bacterial communities of three aeration control strategies for carbon-captured blackwater pretreatment were compared and analyzed, including high oxygen continuous aeration, intermittent aeration and low oxygen continuous aeration. The results show that, compared with high oxygen continuous aeration and intermittent aeration, the nitrite accumulation rate (NAR) for the working condition of low oxygen continuous aeration was higher, and the NO2−-N/NH4+-N ratio of effluent could better meet the influent quality of anammox. High oxygen continuous aeration could gradually elute Nitrospira and increase the relative abundance of AOB and Nitrobacter. Under low oxygen continuous aeration condition, the relative abundance of Nitrobacter decreased significantly, but under low DO condition, the abundance of AOB decreased and Nitrospira appeared. The results show that for the carbon-captured blackwater, the control strategy of alternating combination of high oxygen continuous aeration and low oxygen continuous aeration is helpful to achieve better nitritation and operation stability.
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表 1 各工况的进水水质特征
Table 1. Wastewater quality characteristics of influent at different phases
工况 pH 质量浓度/(mg·L−1) COD NH4+-N NO2−-N NO3−-N 碱度(以CaCO3计) Ⅰ 8.2±0.1 352±129 194±38 <0.5 0.9±0.6 792±173 Ⅱ 8.0±0.2 162±118 146±49 ND 1.1±0.9 550±270 Ⅲ 8.1±0.1 213±90 187±48 ND 0.3±0.2 628±192 注:ND表示未检出。 表 2 3种曝气控制策略的具体工况条件
Table 2. Specific operational conditions of three aeration control strategies
工况 SRT/d SBR程序 曝气策略 Ⅰ 10 总周期12 h;VER=50%;进水15 min;反应600 min;排泥5 min;沉淀60 min;排水15 min;闲置25 min DO=2~7 mg·L-1
曝气时长固定Ⅱ 40 总周期12 h;VER=50%;进水15 min;反应600 min;排泥5 min;沉淀60 min;排水15 min;闲置25 min 交替曝气20 min/不曝气10 min
pH<6.2停止曝气Ⅲ 40 总周期12 h;VER=50%;进水15 min;反应600 min;排泥5 min;沉淀60 min;排水15 min;闲置25 min DO=0.3 mg·L−1
pH<6.2停止曝气注:VER表示SBR体积交换比(volume exchange rate);尽管高氧持续曝气未采用pH实时判别曝气终点,但由于污泥龄(sluge retention time, SRT)短、生物量低,在固定曝气时长反应末期(600 min)pH接近6.2,与间歇曝气和低氧持续曝气终点pH判定功能相差
不大。表 3 接种污泥和不同工况污泥中AOB和NOB的相对丰度
Table 3. Relative abundances of AOB and NOB in inoculum sludge and sludge at different phases
污泥样品
来源AOB/% NOB/% AOB/NOB
相对丰度比Nitrosomonas Nitrospira Nitrobacter 接种污泥[27] 0.089 0.39 0.15 0.16 工况Ⅰ 1.99 — 1.02 1.95 工况Ⅱ 1.02 — 2.42 0.42 工况Ⅲ 0.38 0.01 0.07 4.75 注:“—”表示无法检出或相对丰度低于0.01%。 -
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