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磷是生物生长的重要营养元素,也是农业肥料中不可替代的养分[1]。然而,磷作为不可再生资源,预计将在2035年达到磷产量峰值后面临供不应求的风险,影响着全球粮食供应[2]。另一方面,工业、农业和生活废水中过量排入水体的磷不仅未能有效回收,反而导致水中藻类等水生生物过度生长,引起水体富营养化,造成水体水质恶化等严重问题[3-4]。因此,如何实现磷的去除与资源回收成为水处理行业的研究重点。常用的除磷技术有化学沉淀法、生物法、吸附法等[5]。其中,化学沉淀法一般是利用铝盐、铁盐和钙盐等化学药剂形成不溶性磷酸盐沉淀,并通过固液分离除磷的传统技术[6]。该方法操作简单、占地面积小、除磷效率高,但生成的化学污泥产量大且成分复杂,导致磷资源回收困难,污泥处置成本增加,还可能造成二次污染[6-8]。生物法是利用聚磷菌在厌氧和好氧交替的条件下过量吸收磷,并通过排泥除磷的方法[9]。生物除磷无需添加化学药剂,产生的污泥可直接用作肥料,具有磷资源回收的潜力,但对环境条件要求高,除磷后的出水稳定性较差,工艺运行成本高[8-10]。相比之下,吸附法因操作简单、效率高、能耗低、无二次污染、磷资源可回收等优点而受到广泛关注[11]。目前用于水体除磷的吸附材料主要有生物炭、双层氢氧化物、水凝胶等[12],但生物炭吸附量低,双层氢氧化物、水凝胶等材料成本较高,因此,寻求高效低成本的吸附材料成为废水除磷的关键[13]。
给水厂污泥(drinking water treatment residues,DWTR)是饮用水生产过程中相对清洁安全的副产品,对PO43−-P具有选择性吸附,被认为是一种有前景的廉价除磷材料[14]。DWTR主要含有铝、铁等元素,并以无定型的非晶形态存在,具有较大的比表面积和孔隙率,能够通过表面官能团与PO43−-P发生配体交换吸附水中的磷,可以作为人工湿地的除磷填料[14-17]。另外,提高DWTR吸附性能的改性技术也受到研究者的关注[18-20]。譬如,镧的负载可以显著提高DWTR对PO43−-P的吸附量[21],但镧属于稀土金属,价格较高;铁是一种来源广泛、价格相对较低的金属,其对PO43−-P的吸附能力较弱[22]。
为了发挥镧和铁的协同作用,本研究采用共沉淀法制备出一种镧铁复合给水厂污泥吸附材料(LaFe-DWTR)。目前,DWTR的除磷研究一般采用静态吸附和固定床吸附模式进行,采用完全混合式反应器(continuous stirred tank reactor,CSTR)的研究相对较少[23-24]。由于CSTR可以提供充足的反应空间和运行时间,能够实现较高的传质速率和连续稳定运行[25],因此,本研究采用自主设计的CSTR实验装置,研究了LaFe-DWTR在CSTR中对模拟废水和城市污水处理厂二沉池出水的除磷效果,探讨了停留时间(hydraulic retention time,HRT)、LaFe-DWTR投加量和水力学条件对CSTR运行效果的影响,以期为LaFe-DWTR应用于水体富营养化控制提供参考。
镧铁负载给水厂污泥复合材料在完全混合式反应器中的动态吸附除磷特征
Dynamic phosphorus removal from aqueous solutions by lanthanum/iron-loaded drinking water treatment residues in a continuous stirred tank reactor
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摘要: 采用共沉淀法制备出一种镧铁负载给水厂污泥复合材料(LaFe-DWTR),研究其在完全混合式反应器(CSTR)中对模拟废水和城市污水处理厂二沉池出水的除磷效果以及水力停留时间(HRT)、LaFe-DWTR投加量和水力学条件的影响。结果表明,当CSTR进水PO43−-P质量浓度为50 mg·L−1,HRT为3 h,LaFe-DWTR投加量为2 g·L−1,反应区采用搅拌时,LaFe-DWTR对PO43--P的去除率稳定在99%以上,吸附量可达24.82 mg·g−1。对于CSTR进水初始PO43−-P质量浓度为2 mg·L−1的城市污水处理厂二沉池出水,在3 h HRT,0.14 g·L−1投加量时,CSTR出水的PO43−-P质量浓度稳定在0.2 mg·L−1左右,已达到《城市污水处理厂污染物排放标准》(GB 18918–2002)一级A标准的要求。Abstract: A lanthanum/iron-loaded drinking water treatment residues (LaFe-DWTR) composite material was prepared by the co-precipitation method, and its performance on phosphorus removal from the simulated wastewater and the secondary effluent of municipal wastewater treatment plant(WWTP) in a continuous stirred tank reactor (CSTR) was studied. The effects of hydraulic retention time (HRT), LaFe-DWTR dosage and hydraulic conditions on PO43−-P removal were also discussed. The results indicated that PO43−-P removal efficiency in the CSTR with stirring at the reaction zone was over 99%, and the corresponding adsorption capacity of LaFe-DWTR toward PO43−-P reached 24.82 mg·g−1 at the initial PO43−-P concentration of 50 mg·L−1, HRT of 3 h and LaFe-DWTR dosage of 2 g·L−1. For the secondary effluent of municipal WWTP with an initial PO43−-P concentration of 2 mg·L−1 as the influent of CSTR, when the HRT was 3 h and LaFe-DWTR dosage was 0.14 g·L−1, the concentration of PO43−-P in CSTR effluent stably maintained about 0.2 mg·L−1, which could meet the requirements of the Class A Standard of the Discharge Standard of Pollutants for Municipal Wastewater Treatment Plant (GB 18918-2002).
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Key words:
- lanthanum/iron loading /
- drinking water treatment residues /
- phosphorus adsorption /
- dynamic /
- CSTR
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表 1 CSTR系统运行参数
Table 1. Operational parameters of CSTR system
控制变量 进水PO43−-P
浓度/
(mg·L−1)LaFe-DWTR
投加量/
(g·L−1)HRT/
h水力学
条件运行
时长/hHRT 50.00 2 1/2/3 无搅拌 220 投加量 50.00 1/2/3 3 无搅拌 220 水力学条件 50.00 2 3 无/有搅拌 220 表 2 动态条件下LaFe-DWTR与其他吸附剂对PO43--P吸附性能的比较
Table 2. Comparison of phosphate adsorption capacities onto LaFe-DWTR with other adsorbents under dynamic conditions
吸附材料 CSTR反应区
体积/L初始PO43−-P
质量浓度/(mg·L−1)HRT/h 材料投加量/
(g·L−1)磷吸附量/
(mg·g−1)磷去除率/% 参考文献 海草纤维(POF) 1.2 50 0.5 5 3.03 80 [28] 磷矿废石(PMS) 1.2 50 0.5 5 5.63 81 [25] 大理石粉末(PMW) 1.2 100 8.8 12 17.0 88.3 [27] 羟基磷灰石(HAP) — 72.9 2 — — 52.4 [30] 给水厂污泥(DWTR) 1.0 10 2 10 0.95 95 [24] 粉煤灰/钢渣复合材料(PSPRC) 375 0.5 3 10 — 84 [31] 酸矿排水污泥(AMD) 2.0 1.8 1 1 1.79 99.3 [5] LaFe-DWTR 1.85 50 3 2 24.82 99 本研究 -
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