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我国污水厂进水普遍具有低C/N的水质特征,限制了污水厂的脱氮除磷效率[1-2]。为满足出水氮磷的达标排放,通常选择在污水处理流程中投加有机碳源[3-4]。虽然提升了氮磷脱除效果,但存在碳源药剂费用高昂、污泥产量增加、后续处理处置费用高、大部分有机物转化为CO2 (不符合碳达峰、碳中和的时代发展需求)[5]等诸多问题。因此,急需找寻新的方法或策略以摆脱低C/N污水处理对外加碳源的依赖。
污水处理工艺中好氧区会消耗大量有机物,造成碳源的浪费,控制溶解氧能够节约碳源,提高碳源在缺氧段的脱氮利用率。近几年,较多研究提出通过控制污水处理工艺中好氧区溶解氧(DO)可实现低C/N污水的高效脱氮除磷,无需外加碳源的同时可节省曝气能耗。JIN等在低C/N进水条件下,通过2步控制DO<0.5 mg·L−1,实现87.9%的TN去除率[6]。赵智超等在AAO反应器中通过间歇曝气降低好氧区DO浓度,在无硝化液内回流条件下实现了同步硝化反硝化脱氮除磷,出水TN和TP分别为5.8 mg·L−1和0.3 mg·L−1[7]。此外,低DO控制过程中微生物群落与功能基因的变化,也是实现低C/N进水条件下各工艺高效脱氮除磷的关键原因之一[8-9]。池玉蕾等[10]的研究表明,对于低C/N污水而言,好氧区DO的降低能显著提高系统内反硝化菌和聚磷菌的丰度,从而提高污水处理系统的脱氮除磷效率。
然而,在低C/N进水条件和低DO控制策略下污水处理效能及微生物群落结构的研究大多停留在小试及中试阶段,缺乏针对实际工程的应用研究。对于城镇污水处理厂而言,DO的变化会对整个工艺系统产生较大影响,其准确调控至关重要。因此,有必要针对实际工程研究低DO调控策略下污水处理系统的综合效能。本研究选择山东某城镇污水处理厂(低C/N进水)进行实验,比较在无外加碳源并调控好氧区DO措施实施前后污水厂脱氮除磷效能及微生物种群结构的变化,并综合分析低DO控制策略产生的经济效益。面对碳达峰、碳中和的时代发展目标,本研究通过低DO调控,保障低C/N进水污水厂出水达标的同时,实现药耗(无需外加碳源)和能耗(降低曝气)的同步节省,不仅大大节约了运行费用,也为同类型实际工程的调控及改造提供参考。
低C/N进水城镇污水厂低溶解氧运行效能及微生物变化
The efficiency and microbial community change of urban sewage plant with low C/N influent based on low DO strategy
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摘要: 低C/N进水污水厂通常需要外加碳源以保障脱氮除磷效能,运行费用高。本研究以摆脱低C/N污水处理对外碳源依赖及降低运营成本为目的,依托山东省某城镇污水厂(A2O工艺)开展基于低DO调控策略的污水厂综合效能研究。结果表明,在长期低DO运行策略下,污水厂逐渐停止外加碳源,在硝化液回流比由370%逐渐降至90%的过程中,TN平均去除率由76.3%提升至82.9%,且除磷效率有所提升。对好氧区氮平衡进行分析发现,在低DO运行条件下,好氧区NH4+-N的转化逐渐以短程硝化和同步反硝化作用为主。微生物宏基因组学结果表明,在低DO条件下,NOB丰度由0.15%下降至0.06%,而具备反硝化功能的PAOs与GAOs的总体丰度由2.06%升高至3.57%。长期低DO、无外加碳源运行条件下,脱氮效能的显著提升主要由于好氧区短程硝化和同步反硝化作用的比例升高所致。低DO对AOB抑制作用小,对NOB抑制作用显著,导致NO2−-N的积累,保障了脱氮效能;PAOs与GAOs利用厌氧期储存的内碳源在好氧区反硝化脱氮,提升了脱氮效能;而内碳源利用率的提升又促进了PAOs的生长,提升了除磷效能。此外,污水厂低DO运行策略下,节省了运营成本,吨水处理费用降低了0.3元。Abstract: Low C/N influent wastewater plants usually need additional carbon source to ensure nitrogen and phosphorus removal efficiency, leading to the high operation cost. In order to get rid of external carbon sources for low C/N wastewater treatment and reduce operation cost, a comprehensive efficiency study was carried out in an urban wastewater treatment plant with A2O process in Shandong Province based on low DO regulation strategy. The results showed that under the long-term low DO operation strategy, when the wastewater plant gradually stopped additional carbon sources and decreased the reflux ratio of nitrification liquid from 370% to 90%, TN average removal rate increased from 76.3% to 82.9%, and phosphorus removal effect also increased. The analysis of nitrogen balance in aerobic zone showed that the transformation of NH4+-N in aerobic zone was gradually dominated by partial nitrification and simultaneous denitrification under low DO condition. Microbial metagomenomics results showed that under low DO condition, the abundance of NOB decreased from 0.15% to 0.06%, while the total abundance of PAOs and GAOs with denitrifying function increased from 2.06% to 3.57%. The significant improvement of nitrogen removal efficiency under long-term low DO and no external carbon source was mainly due to the increased proportion of partial nitrification and simultaneous denitrification in aerobic zone. Low DO had slight inhibitory effect on AOB, while inhibited NOB significantly, resulting in NO2−-N accumulation and ensuring TN removal efficiency. PAOs and GAOs used the internal carbon source stored in the anaerobic stage for denitrification in the aerobic zone, which improved the denitrification efficiency. The improvement of internal carbon source utilization rate promoted the growth of PAOs and raised phosphorus removal efficiency. In addition, under the low DO operation strategy of the sewage plant, the operating cost was saved and the wastewater treatment cost was reduced by 0.3 yuan per ton wastewater.
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表 1 工艺构筑物参数
Table 1. Parameters of process structures
构筑物 HRT/h 池体数/个 容积/m3 水深/m 厌氧区 3.6 1 12 000 4.3 缺氧区 2.5 2 8 332 6.0 好氧区 5.0 2 16 664 6.0 二沉池 6.0 4 20 400 4.5 表 2 污水厂2个阶段运行参数
Table 2. Operating parameters of sewage treatment plant in two phases
阶段 乙酸钠投加量/
(mg·L−1)DO/
(mg·L−1)硝化液
回流比/%污泥
回流比/%P1 73~575 2~4 370 100 P2 0~284 0.5~1.4 370~90 100 表 3 污水厂经济效益表
Table 3. The economic benefit calculation of sewage treatment plant
项目 乙酸钠用量/
( t·d−1)曝气电耗/
(kWh·d−1)污泥产量/
( t·d−1)费用/
(万元·d−1)P1阶段 20 9 600 76 4.05 P2阶段 0 3 960 52 1.61 -
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