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重金属是造成我国水环境污染的主要因素之一[1]。传统处理重金属污水的方法包括物理化学技术和微生物法均存在一定的局限性[1-3]。人工湿地(constructed wetlands, CWs)是人为建造和管控的污水处理系统[4-5],投资少、污水净化效果好,近年来受到大量关注[6-8]。
研究发现,基质吸附是CWs去除重金属的主要途径[9-10]。碎石、河砂、砾石等传统基质具有来源广、造价低等特点受到广泛关注。陈银萍等[11]为期10 d的实验发现粉煤灰对Cd去除效果较好但不利于植物生长;余关龙等[12]发现短期内,碎石基人工湿地对营养物及Cd2+、Zn2+ 去除率较高好。但传统基质在长期运行下对重金属的去除能力仍有限[9]。因此,需要对人工湿地基质配置进行优化,以实现长期最佳的污水处理效果。沸石与生物炭因具有多孔的结构、丰富的官能团[13-15]以及较强的静电效应和吸附性能[16],在污水处理中具有较高的应用价值[17-19],但目前关于添加生物炭能否提高含重金属污水的去除率存在一定的争议。CHEN[20]与CHANG等[21]认为生物炭基CWs具有较好的重金属固定能力并能促进植物生长,而FENG[22]认为添加生物炭会增加重金属对β-变形菌、甲型变形菌纲的毒性导致脱氮效率下降。
多种基质组合使用能发生协同作用,从而提高净化效果[9]。张晓斌等[18]研究发现沸石与炉渣组合添加对电镀废水中Cr、Zn的去除效果优于单独添加;ABEDI等[13]采用响应面分析评估了沸石-生物炭基人工湿地处理模拟污水的效果,发现3个月运行期内Pb、Mn的去除效果优于对照。目前,关于不同基质配置对复合重金属污水长期处理效果的研究较少。鉴于此,本研究构建以沸石+砾石、生物炭+砾石、沸石+生物炭+砾石为基质的CWs,探究其对含有机物、氮磷营养物、多种重金属的复合污水的长期处理效果及重金属的去除途径,以期为CWs处理复合重金属污水提供一定的数据支撑。
人工湿地不同基质配置对复合重金属污水的长期处理效果
Long term treatment effect of combined heavy metal wastewater by the constructed wetlands with different substrates
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摘要: 为探究不同基质对含有复合重金属污水的长期处理效果及重金属在人工湿地中的分布特征,通过温室内构建基质分别为砾石(CK)、沸石(F)、生物炭(S)和沸石-生物炭(FS)的4组垂直潜流人工湿地污水处理模拟装置,连续运行161 d,观测出水水质变化并研究湿地各系统中重金属的浓度分布特征。结果表明,所有装置出水均呈低溶解氧状态,pH呈中性或弱碱性;4组人工湿地均具有良好的脱氮除磷及重金属去除效果,有机物、TN、NO3--N、NH4+-N和TP的平均去除率分别为91.93%~95.85%、86.08%~89.80%、94.99%~97.60%、75.22%~83.58%和60.35%~64.61%,Cu、Zn、Pb、Cd和Cr 5种重金属的去除率均在90%以上;菖蒲体内重金属的质量浓度表现为地下部分>地上部分,但菖蒲体内富集的重金属总量相对较少,整个系统中重金属主要富集在基质中(77%~96%);与湿地CK相比,沸石与生物炭的联合添加显著提高了污水的净化能力(P<0.01),但运行后期,装置对复合污水的去除率呈一定的下降趋势。Abstract: In order to explore the long term treatment effect of combined heavy metal wastewater by the constructed wetlands with different substrates and the distribution characteristics of heavy metals in constructed wetlands, four wastewater treatment simulators of vertical submerged constructed wetlands with gravel(CK), zeolite(F), biochar(S) and zeolite-biochar(FS) substrate were constructed in the greenhouse and ran continuously for 161 days. The changes in effluent quality were tested and the concentrations distribution of heavy metals in each part of the wetland were analyzed. The results showed that the dissolved oxygen contents in the effluent of all devices were low, and pH values were neutral or weakly alkaline. Four wetlands had good removal performance on N, P and heavy metals, the average removal rates of organics, TN, NO3--N, NH4+-N and TP were 91.93%~95.85%, 86.08%~89.80%, 94.99%~97.60%, 75.22%~83.58% and 60.35%~64.61%, respectively. And the removal rates of Cu Zn, Pb, Cd and Cr were all above 90%. The accumulation of heavy metals in the underground part of acorus calamus L. was higher than that overground part, but the total amounts of heavy metals accumulated in acorus calamus L. was relatively low, the heavy metals were mainly accumulated in the substrates(77%~96%). The combined addition of zeolite and biochar increased the purification ability of the wetlands extremely significantly compared to CK(P<0.01), but the removal rate showed a certain downward trend at the later stages of the experiment.
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Key words:
- vertical subsurface flow constructed wetland /
- zeolite /
- biochar /
- heavy metals removal
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表 1 人工湿地进水水质
Table 1. Water quality of CWs inlet water
成分 质量浓度/(mg·L−1) 成分 质量浓度/(mg·L−1) COD 183.69±12.73 CuSO4 10.05±0.66 TP 5.02±0.17 ZnSO4 15.26±0.66 TN 47.52±0.64 CdCl2 5.16±0.14 NH4+-N 24.30±1.20 Cr(NO3)3 7.56±0.11 NO3−-N 23.08±0.42 Pb(NO3)2 8.23±0.19 表 2 人工湿地出水水质
Table 2. Effluent quality of CWs
处理 COD/(mg·L−1) pH DO/(mg·L−1) NO3−-N/(mg·L−1) NH4+-N/(mg·L−1) TN/(mg·L−1) TP/(mg·L−1) CK 14.83±4.37a 6.69±0.20c 0.59±0.33a 0.55±0.37c 5.91±3.18a 6.34±2.88a 1.99±1.33a F 12.58±4.15b 6.65±0.22d 0.57±0.37a 0.87±1.25c 5.14±4.50b 5.96±4.21a 1.97±1.48a S 11.15±5.12c 6.77±0.13b 0.46±0.36a 1.15±1.20a 5.66±4.80a 6.60±4.90a 1.92±1.11a FS 7.60±6.01d 6.83±0.14a 0.51±0.55a 0.89±0.75b 3.90±3.30c 4.84±3.43b 1.78±0.96b 注:表中不同小写字母表示同一指标在不同CWs间的差异性(P<0.05) 表 3 出水水质指标平均去除率
Table 3. Average removal rate of water quality indices in effluent
% 处理 COD NO3−-N NH4+-N TN TP CK 91.93 97.60 75.22 86.63 60.35 F 93.15 96.21 78.30 87.42 60.57 S 93.93 94.99 76.15 86.08 61.83 FS 95.85 96.12 83.58 89.80 64.61 表 4 菖蒲不同部位重金属含量
Table 4. Enrichment of heavy metals in different parts of acorus calamus L.
处理 部位 Cu/(mg·kg−1) Zn/(mg·kg−1) Pb/(mg·kg−1) Cd/(mg·kg−1) Cr/(mg·kg−1) CK 地上 358.75±15.910 439.25±13.08 111.25±13.79 49.75±6.72 106.00±7.70 地下 1 281.00±216.38 1 673.25±375.83 813.75±269.76 370.50±70.71 729.00±8.49 F 地上 245.25±37.12 352.75±90.86 65.75±21.57 36.25±6.72 90.75±11.67 地下 744.75±19.45 1 147.00±41.01 460.00±50.91 348.75±1.06 540.00±22.63 S 地上 374.50±70.71 465.00±11.31 111.25±3.18 59.75±1.06 127.00±13.31 地下 944.75±270.47 1 203.50±142.84 435.50±82.02 276.00±57.89 491.25±19.45 FS 地上 326.50±14.14 390.00±16.97 106.25±2.48 50.75±1.77 116.25±2.48 地下 1 176.25±182.79 1 448.00±258.09 540.75±86.62 387.50±74.95 588.25±12.37 注:小写字母a、b表示同一装置某种重金属地上部分与地下部分的显著差异性(P<0.05) 表 5 不同基质中重金属的吸附量
Table 5. Heavy metals adsorption in different substrates
处理 Cu/(mg·kg−1) Zn/(mg·kg−1) Pb/(mg·kg−1) Cd/(mg·kg−1) Cr/(mg·kg−1) CK 113.38±3.63c 176.88±0.88d 53.50±2.75a 24.13±0.38b 46.00±0.25b F 167.63±0.88b 252.63±13.88c 62.13±0.13a 45.50±1.75a 70.88±5.38a S 204.38±4.38b 271.88±19.13b 82.13±3.38a 37.13±0.13a 72.35±2.15a FS 242.65±3.53a 285.13±16.75a 72.81±1.19a 48.33±2.05a 77.813±1.44a 注:不同小写字母表示同一种金属在不同基质CW间的差异性(P<0.05) -
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