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污水地下渗滤系统(subsurface wastewater infiltration system,SWIS)利用土壤与微生物的联合作用,通过物理、化学、生物反应去除污染物[1]。SWIS具有构造简单、操作维护成本低、污染物去除率高等优点[2]。但是,SWIS长期运行会改变土壤渗透性能,影响出水水质。LI等[3]将长期(7年以上)和短期(1年)运行的SWIS进行比较,结果表明,短期运行SWIS的BOD、COD、SS、
$ {\rm{NH}}_{\rm{4}}^{\rm{ + }}$ -N、TP去除率分别为95.0%、89.1%、98.1%、87.6%和98.4%,长期运行SWIS的BOD、COD、SS、$ {\rm{NH}}_{\rm{4}}^{\rm{ + }}$ -N、TP去除率分别降低至89.6%,87.2%,82.6%,69.1%和74.4%,说明长期运行导致的土壤渗透性、孔隙度及代谢气体积累程度的变化将影响SWIS处理性能。土壤渗透性能降低主要由物理、化学、生物和气体4方面因素造成。粒径较小的悬浮物堆积在基质孔道中,降低渗透性。粒径小于6 μm的颗粒是渗透性降低的主要原因[4]。有机悬浮物不会造成明显的渗透性降低,无机悬浮物更易降低土壤渗透性[5]。悬浮物引起的渗透性降低通常无法得到恢复[6]。污水中的离子与SWIS中原有的离子发生化学反应,可产生不溶性沉淀,其中,碳酸盐和铁化合物是主要的沉淀[7-8]。细菌细胞和生物膜会积累在孔隙空间中,导致孔隙减少和水力传导性降低[9]。影响渗透性能的气体包括进水携带空气和生物代谢气体[10]。进水携带空气是随进水进入系统后截留在系统中的空气,生物代谢气体是微生物呼吸产生的气体。一方面,空气可能积累在孔隙中,另一方面,空气中的氧气会影响生物代谢气体的产生,代谢气体也会积累在孔隙中。进水携带空气和生物代谢气体如果不能及时排出系统,会降低体积含水率,导致渗透性能降低。渗透性能适度降低会增加系统内部非饱和流动区,从而导致污染物处理能力增加;而渗透性能大幅降低会使污水难以通过基质层,污染物处理能力降低[5]。
预处理(过滤沉淀)可以减少进入系统的悬浮物,干湿交替可以恢复孔隙度,酸化可以减少化学沉淀产生[11-12]。然而,研究多集中于防治悬浮物、化学物质和微生物导致的渗透性能降低。由于针对气体对土壤渗透性能的影响的研究鲜有报道,实际工程中也没有针对气体的有效防治方法。因此,本研究对气体导致的SWIS渗透性变化及污染物处理效果进行了初步探究,为气体堵塞及其防治奠定基础。对SWIS进水采用了不同曝气处理(不曝气、微曝气、强曝气),研究了不同的曝气量对SWIS渗透系数、体积含水率、代谢气体释放量和污染物(COD、
$ {\rm{NH}}_{\rm{4}}^{\rm{ + }}$ -N、$ {\rm{NO}}_{\rm{3}}^{\rm{ - }}$ -N、$ {\rm{NO}}_{\rm{2}}^{\rm{ - }}$ -N和TP)去除率的影响,以期为研究气体堵塞及其预防提供参考。
曝气对污水地下渗滤系统渗透性及处理性能的影响
Effects of aeration on permeability and treatment performance of subsurface wastewater infiltration system
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摘要: 针对气体影响地下渗滤系统的渗透性及污水处理效果的问题,用地下渗滤系统处理不同曝气程度的生活污水,研究曝气对不同深度基质理化性质(渗透系数、体积含水率、气体类型及浓度)和出水水质的影响。结果表明,曝气增加了−130~−100、−40~−10 cm处的渗透系数,降低了−100~−70 cm处的渗透系数,与−70~−40 cm处的渗透系数不存在相关关系;曝气增加了−70 cm处的体积含水率,降低了−100 cm和−40 cm处的体积含水率,对−10 cm处的体积含水率几乎没有影响;曝气增加了各深度处的CO2、N2O释放浓度,与各深处的CH4释放浓度不存在相关关系;曝气增加了
$ {\rm{NH}}_{\rm{4}}^{\rm{ + }}$ -N和COD去除率,与$ {\rm{NO}}_3^{\rm{ - }}$ -N、$ {\rm{NO}}_2^{\rm{ - }}$ -N和TP去除率不存在相关关系。探明了气体对地下渗滤系统处理性能的影响,为气体堵塞及其预防提供了参考。Abstract: In order to identify the effects of gas on the soil permeability and sewage treatment of subsurface wastewater treatment system (SWIS), domestic wastewater with different aeration treatment was introduced into a set of SWIS to study the effect of aeration on the physicochemical properties (permeability coefficient, volumetric water content, gas types and concentrations) of the matrix at different depths and effluent quality. The results indicated that aeration improved the permeability coefficients at −130~−100 cm and −40~−10 cm, reduced the permeability coefficient at −100~−70 cm, had an insignificant correlation with the permeability coefficient at −70~−40 cm. Meanwhile, the aeration elevated the volumetric water content at −70 cm, reduced the volumetric water content at −100 cm and −40 cm, had slight influence on the volumetric water content at −10 cm. Aeration improved the releasing concentrations of CO2 and N2O at different depths, and had an insignificant correlation with CH4 releasing concentrations. Aeration treatment of raw water improved the removal rates of$ {\rm{NH}}_{\rm{4}}^{\rm{ + }}$ -N, COD and TP, reduced$ {\rm{NO}}_3^{\rm{ - }}$ -N removal rate, and had no correlation with$ {\rm{NO}}_2^{\rm{ - }}$ -N removal. The effects of gas on SWIS were preliminarily identified, which provided references for further research on gas clogging and its prevention. -
图 5 不同曝气处理下出水
$ {{\bf{NH}}_{\rm{4}}^{\rm{ + }}{\text{-}}\bf{N}} $ 、$ {{\bf{NO}}_{\rm{3}}^{\rm{ - }}{\text{-}}\bf{N}}$ 、$ { {\bf{NO}}_{\rm{2}}^{\rm{ - }}{\text{-}}\bf{N}}$ 、COD和TP去除率随时间的变化Figure 5. Change in
$ { {\rm{NH}}_{\rm{4}}^{\rm{ + }}{\text{-}}\text{N}}$ ,${ {\rm{NO}}_{\rm{3}}^{\rm{ - }}{\text{-}}\text{N}}$ ,$ {{\rm{NO}}_{\rm{2}}^{\rm{ - }}{\text{-}}\text{N}}$ , COD and TP removal with time at different aeration表 1 曝气量与渗透系数的相关分析
Table 1. Correlation analysis of aeration andpermeability coefficient
深度/cm 相关系数 P −130~−100 0.536 0 −100~−70 −0.887 0 −70~−40 0.071 0.413 −40~−10 0.951 0 表 2 曝气量与体积含水率的相关分析
Table 2. Correlation analysis of aeration andvolume water content
深度/cm 相关系数 P −100 −0.745 0 −70 0.629 0 −40 −0.747 0 −10 0.082 0.347 表 3 曝气量与气体浓度的相关分析
Table 3. Correlation analysis of aerationand gas concentrations
深度/cm CO2浓度 CH4浓度 N2O浓度 相关系数 P 相关系数 P 相关系数 P −130 0.572 0 −0.235 0.174 0.489 0.003 −100 0.578 0 0.12 0.492 0.511 0.002 −70 0.624 0 0.261 0.131 0.555 0.001 −40 0.628 0 0.185 0.287 0.572 0 −10 0.576 0 0.171 0.327 0.473 0.004 表 4 曝气量与污染物去除率的相关分析
Table 4. Correlation analysis of aeration andpollutants removal
污染物 相关系数 P $ {\rm{NH}}_{\rm{4}}^{\rm{ + }}$ -N0.854 0 $ {\rm{NO}}_{\rm{3}}^{\rm{ - }}$ -N−0.384 0.094 $ {\rm{NO}}_{\rm{2}}^{\rm{ - }}$ -N0.095 0.689 COD 0.88 0 TP 0.414 0.07 -
[1] JIANG Y, SUN Y, PAN J, et al. Use of dewatered sludge as microbial inoculum of a subsurface wastewater infiltration system: Effect on start-up and pollutant removal[J]. Water SA, 2017, 43(4): 595-601. doi: 10.4314/wsa.v43i4.07 [2] QIN W, DOU J, DING A, et al. A study of subsurface wastewater infiltration systems for distributed rural sewage treatment[J]. Environmental Technology, 2014, 35(16): 2115-2121. doi: 10.1080/09593330.2014.894579 [3] LI Y H, LI H B, PAN J, et al. Performance evaluation of subsurface wastewater infiltration system in treating domestic sewage[J]. Water Science and Technology, 2012, 65(4): 713-720. doi: 10.2166/wst.2012.905 [4] SIRIWARDENE N, DELETIC A, FLETCHER T. Clogging of stormwater gravel infiltration systems and filters: Insights from a laboratory study[J]. Water Research, 2007, 41(7): 1433-1440. doi: 10.1016/j.watres.2006.12.040 [5] 张建, 邵长飞, 黄霞, 等. 污水土地处理工艺中的土壤堵塞问题[J]. 中国给水排水, 2003, 19(3): 17-20. doi: 10.3321/j.issn:1000-4602.2003.03.006 [6] 赖兰萍. 土地渗滤系统处理村镇生活污水的实验研究[D]. 南昌: 江西理工大学, 2009. [7] LARROQUE F, FRANCESCHI M. Impact of chemical clogging on de-watering well productivity: Numerical assessment[J]. Environmental Earth Sciences, 2011, 64(1): 119-131. doi: 10.1007/s12665-010-0823-9 [8] 许增光, 杨雪敏, 柴军瑞. 考虑化学淤堵作用的尾矿砂渗透系数变化规律研究[J]. 水文地质工程地质, 2016, 43(4): 26-29. [9] AAL G Z A, ATEKWANA E A, ATEKWANA E A. Effect of bioclogging in porous media on complex conductivity signatures[J]. Journal of Geophysical Research Biogeosciences, 2015, 115(3): 65-65. [10] HEILWEIL V M, SOLOMON D K, PERKINS K S, et al. Gas-partitioning tracer test to quantify trapped gas during recharge[J]. Groundwater, 2004, 42(4): 589-600. doi: 10.1111/j.1745-6584.2004.tb02627.x [11] 路莹. 北京平谷地区雨洪水地下回灌堵塞机理分析与模拟研究[D]. 长春: 吉林大学, 2009. [12] HUA G, ZENG Y, ZHAO Z, et al. Applying a resting operation to alleviate bioclogging in vertical flow constructed wetlands: An experimental lab evaluation[J]. Journal of Environmental Management, 2014, 136(8): 47-53. [13] 杜磊. 含水层回灌过程中的气相堵塞实验研究[D]. 济南: 济南大学, 2016. [14] 国家环境保护总局. 水和废水监测分析方法[M]. 4版. 北京: 中国环境科学出版社, 2002. [15] REDDI L N, XIAO M, HAJRA M G, et al. Physical clogging of soil filters under constant flow rate versus constant head[J]. Canadian Geotechnical Journal, 2005, 42(3): 804-811. doi: 10.1139/t05-018 [16] 孙铁珩, 李宪法. 城市污水自然生态处理与资源化利用技术[M]. 北京: 化学工业出版社, 2006. [17] PAN J, YU L. Characteristics of subsurface wastewater infiltration systems fed with dissolved or particulate organic matter[J]. International Journal of Environmental Science and Technology, 2015, 12(2): 479-488. doi: 10.1007/s13762-013-0408-8 [18] BECKWITH C W, BAIRD A J. Effect of biogenic gas bubbles on water flow through poorly decomposed blanket peat[J]. Water Resources Research, 2001, 37(3): 551-558. doi: 10.1029/2000WR900303 [19] SPOTT O, FLORIAN STANGE C. Formation of hybrid N2O in a suspended soil due to co-denitrification of NH2OH[J]. Journal of Plant Nutrition and Soil Science, 2011, 174(4): 554-567. doi: 10.1002/jpln.201000200 [20] 李英华, 李海波, 王鑫, 等. 生物填料地下渗滤系统对生活污水的脱氮[J]. 环境工程学报, 2013, 7(9): 3369-3374. [21] ONG S A, UCHIYAMA K, INADAMA D, et al. Performance evaluation of laboratory scale up-flow constructed wetlands with different designs and emergent plants[J]. Bioresource Technology, 2010, 101(19): 7239-7244. doi: 10.1016/j.biortech.2010.04.032 [22] BROOKS A S, ROZENWALD M N, GEOHRING L D, et al. Phosphorus removal by wollastonite: A constructed wetland substrate[J]. Ecological Engineering, 2000, 15(1): 121-132.