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城市排水系统是指收集和处理城市污水和雨水的市政设施,主要由排水管网和污水处理厂组成。随着城市化进程的推进,城市排水系统规模不断扩大。截至2019年底,我国城市排水管道总长度达74.4×104km,建成区排水管道密度为9.27 km·km−2,城市污水日处理能力为19 171×104 m3[1]。加之水环境问题日益严峻,水行业中各种标准也随之提高,城市排水系统的运行面临“体量大、标准严”的挑战,随之造成排水管网运行维护成本的增加、污水处理环节药耗加大等问题。
混凝是饮用水处理中的重要环节[2]。硫酸盐系絮凝剂是全球饮用水处理领域主要使用的药剂[3]。饮用水生产中使用硫酸铝为絮凝剂,会导致饮用水中含有较高浓度的
${\rm{SO}}_4^{2-} $ ,并间接造成生活污水中${\rm{SO}}_4^{2-} $ 浓度的升高[3]。而城市排水管道属于相对封闭的空间,易形成厌氧环境。在厌氧条件下,管壁生物膜和管道沉积物中的硫酸盐还原菌(sulfate-reducing bacteria,SRB)可将${\rm{SO}}_4^{2-} $ 还原成S2−,进而水解形成HS−和H2S[4-7]。气相H2S扩散到排水管道壁面后会被硫化物氧化菌(sulfide-oxidizing bacteria,SOB)氧化成H2SO4,最终导致管道腐蚀[8-10]。化学药剂的投加是控制排水管道内硫化物的常用方法,但普遍药耗量巨大,且控制效果不一[11-12]。仅在美国,每年因硫化物引起排水管道腐蚀而投入的维护费用就高达上百亿美元[13]。污水处理厂作为城市排水系统末端的设施,日渐严格的排放标准造成厂内化学药剂使用量陡增,从而极大地增加了运行成本。铁盐作为一种常见的絮凝剂可用于排水管道腐蚀和异味管理[11, 14]、污水处理厂化学除磷[15-17],以及污泥厌氧消化中H2S的去除[18]。以前针对铁盐絮凝剂在城市排水系统中的应用及研究主要集中于优化投加点处目标污染物的去除效率,并同时减少投加量,其研究范围仅局限在孤立单元中,并未综合考虑投加的絮凝剂对整个系统造成的影响。随着厂网一体化运营理念的推广,部分学者研究了铁盐在城市排水系统中的迁移转化路径及其给下游单元带来的影响和二次效益。
本文综述了铁盐在城市排水系统中综合使用的研究进展,介绍了一种既减少用量又实现多种管理效益的铁盐使用策略,重点阐述了铁盐在各个阶段的作用机制和末端铁盐的回收利用,最后根据目前的研究现状,总结了铁盐综合使用中存在的不足和可进一步优化的方向。
铁盐在城市排水系统中的综合使用研究进展
Research progress of comprehensive use of iron salt in urban drainage system
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摘要: 对排水管网和污水处理厂的一体化管理,可极大提升城市排水系统运行的高效性和安全性。作为厂网一体化运营理念的一部分,铁盐的综合使用愈发受到关注。在城市排水系统中,铁盐可在污水输送、污水处理及污泥处理过程中发挥作用。围绕铁盐的迁移转化路径、铁盐在污水输送和污水处理厂中的作用机制,以及系统末端铁盐的回收这4个方面,综述了城市排水系统中铁盐综合使用的研究进展。最后根据当前的研究现状,总结了铁盐综合使用中面临的挑战并给出了相关建议,并从厂网一体化铁盐自动加药控制和末端铁盐的进一步回收两方面进行了展望。Abstract: The integrated management of drainage network and sewage treatment plant has greatly improved the efficiency and safety of urban drainage system. As a part of plant-network integrated operation concept, the comprehensive use of iron salt has attracted more and more attention. In urban drainage systems, iron salt can play a role in sewage conveyance, sewage treatment and sludge treatment. This paper summarizes the research progress of comprehensive use of iron salt in urban drainage system from four aspects: the migration and transformation path of iron salt, the action mechanism of iron salt in sewage conveyance and sewage treatment plant, and the recovery of iron salt at the end of the system. Finally, according to the current research status, the challenges faced in the comprehensive use of iron salt are summarized, and the usage suggestions are given,and the research prospects are put forward on plant-network integrated automatic dosing control and terminal further recovery of iron salt.
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Key words:
- iron salt /
- comprehensive use /
- plant-network integration /
- sewage conveyance /
- sewage treatment /
- sludge treatment
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表 1 不同化学药剂的硫化物控制成本
Table 1. Cost of s ulfide control by different chemicals
化学药剂 剂量水平 药剂单价 质量分数 控制成本/
(10−6澳元·L−1)参考文献 氧气 15.8~91.5 mg·L−1 1.15澳元·m−3 0.995 12.8~74.0 [33] 硝酸盐 1.33~15.5 mg·L−1 1 010澳元·m−3 0.5 41.3~483.6 [33] 氢氧化钠 11.4~28.6 μL·L−1 3.46澳元·L−1 0.5 39.6~99.1 [33] 氢氧化镁 47.9~156.6 mg·L−1 590澳元·t−1 0.58 48.7~159.3 [33] 铁盐 3~47 mg·L−1 526澳元·t−1 0.42 10.9~170.6 [33] 电化学氧化铁 (40~82) × 10−6 kWh·L−1 0.15澳元·(kWh)−1
(电极成本19~37澳元·(kWh)−1)− 25.0~49.3 [42] 高铁酸盐 180 mg·L−1
(实验室反应器试验,每隔4.5 d投加一次)4澳元·kg−1 0.99 20 [43] 表 2 实验室模拟城市排水系统中各种反应器内铁的质量平衡
Table 2. Iron mass balance in the laboratory-scale urban drainage system
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