Application of computational fluid dynamic to model the hydraulic performance of subsurface flow wetlands

A subsurface flow wetland(SSFW)was simulated using a commercial computational fluid dynamic(CFD)code.The constructed media was simulated using porous media and the liquid resident time distribution(RTD)in the SSFW was obtained using the particle trajectory model.The effect of wetland configuration and operating conditions on the hydraulic performance of the SSFW were investigated.The results indicated that the hydraulic performance of the SSFW was predominantly affected by the wetland configuration.The hydr...

Modeling on Residence Time Distribution in Subsurface Flow Constructed Wetlands by Multi Flow Dispersion Model

As an important design factor for constructed wetlands,hydraulic retention time and its distribution will affect the treatment performance.Instantaneously injected sodium chloride tracers were used to obtain residence time distributions of the lab scale subsurface flow constructed wetland.Considering the presence of trailing and multiple peaks of the tracer breakthrough curve,the multi flow dispersion model(MFDM)was used to fit the experimental tracer breakthrough curves.According to the residual sum of squares and comparison between the experimental values and simulated values of the tracer concentration,MFDM could fit the residence time distribution(RTD)curve satisfactorily,the results of which also reflected the layered structure of wetland cells,thus to give reference for application of MFDM to the same kind of subsurface flow constructed wetlands.

Performance of a subsurface-flow constructed wetland in Southern China

The operational performance of a full scale subsurface flow constructed wetland, which treated the mixed industrial and domestic wastewater with BOD 5/COD mean ratio of 0 33 at Shatian, Shenzhen City was studied. The constructed wetland system consists of screens, sump, pumping station, and primary settling basin, facultative pond, first stage wetland and secondary stage wetland. The designed treatment capacity is 5000 m 3/d, and the actual influent flow is in the range of <2000 to >10000 m 3/d. Under normal operational conditions, the final effluent quality well met the National Integrated Wastewater Discharge Standard(GB 8978\_1996), with the following parameters(mean values): COD 33 90 mg/L, BOD 5 7.65 mg/L, TSS 7.92 mg/L, TN 9.11 mg/L and TP 0 56 mg/L. Seven species of plants were selected to grow in the wetland: Reed, Sweetcane flower Silvergrass, Great Bulrush, Powdery Thalia and Canna of three colours. The growing season is a whole year round. The seasonal discrepancy could be observed and the plants growing in the wetland are vulnerable to lower temperature in winter. The recycling of the effluent in the first stage of the wetland system is an effective measure to improve the performance of the wetland system. The insufficient DO value in the wetland system not only had significant effect on pollutants removal in the wetland, but also was unfavourable to plant growth. The recycling of effluent to the inlet of wetland system and artificial pond to increase DO value of influent to the wetland is key to operate the subsurface constructed wetland steadily and effectively.

Research on Nitrogen Removal and Microorganism in a Subsurface Flow Constructed Wetland System in Sihong County

Experiments in monitoring the removal of organic material and nitrogen and determining the amounts of mi- croorganism at different sites in the subsurface flow constructed wetland in Sihong county were performed. The results show that the removal of CODCr agrees with the kinetic equation of a first order reaction. The removal of pollutants varies with different seasons. The removal rates of CODCr, NH3-N, TN in the spring are 15%–23% higher than those in the autumn. The amount of ammonifier is larger than that of denitrifying bacteria and the amount of denitrifying bacte- ria is larger than that of nitrosomonas. The amount of bacteria around the plant roots is larger than that on the surface of the packing medium. No apparent change is observed for the amount of denitrifying bacteria and nitrosomonas between spring and autumn.

Performance Characteristics of Pollutants along the Longitudinal Profile of a Subsurface Flow Constructed Wetland Domestic Sewage Treatment Plant in the University of Lagos, Nigeria

The paper reports the findings of a research work carried out to examine the performance and efficiency of a subsurface constructed wetland (SSFCW) for the treatment of domestic sewage in the University of Lagos (Unilag), Nigeria. The removal patterns and efficiencies of the physical, chemical and biological sewage pollutants parameters of domestic waste water generated within Unilag community by the SSFCW were studied. The wastewater was sampled and analysed along the SSFCW from influent (point1) to effluent (point 11). Total Dissolved Solids (TDS) reduced from 471 mg/l to 11.85 mg/l (97.48%), Turbidity reduced from 108.75 HTU to 0.05HTU (99.95%), Manganese reduced from 6.05 mg/l to 0.61 mg/ (89.92%), Nitrate reduced from 27.5 mg/l to 2.0 mg/l (92.73%), Sulphate reduced from 48.5 mg/l to 28 mg/l (42.27%), Iron reduced from 1.13 mg/l to 0.03 mg/l (97.35%), BOD reduced from 73.14 mg/l to 12.8 mg/l (82.5%), and E-coli reduced from 874 MPN/100 ml to 0.15 MPN/100 ml (99.98%). On the other hand, Dissolved Oxygen content increased along the SSFCW from 3.14 mg/l to 7.49 mg/l (138.54%) while the pH improved from slightly acid level of 6.49 to slightly above neutral level of 7.05 (9.3%). All the parameters at effluent point are within the Nigerian Federal Environmental Protection Agency (FEPA) acceptable standard. The study concludes that the SSFCW is a cheap, efficient and appropriate technology for the treatment of domestic sewage under tropical conditions.

Effect of Different Factors on Nitrogen Removal Rate in Constructed Wetlands

Factors affecting total nitrogen(TN) removal rates in constructed wetland were investigated by intermittent operation in the subsurface flow(SSF) constructed wetland system.The results demonstrated that removal rates of TN increased with the rising of TN pollution load(1.40-12.40 g/m2) when the retention time was determined by 60% TN removal efficiency(n=180,p<0.05) in SSF wetlands.The maximum TN removal rate was 1.71 g/(m2·d) in SSF Phragmites australis-soil-slag system.TN removal rates were affected by total phosphorus load in case of higher TN load.TN removal rates in SSF Phragmites australis wetlands were greater than that in SSF Calamagrostis angustifolia wetlands at the same experimental cycle.Effect of wetland substrates on TN removal rates varied with the pollutants loading in SSF constructed wetland system,plant species and plant-growing period.

Study on the Heavy Metals Removal Efficiencies of Constructed Wetlands with Different Substrates

In this study constructed wetlands (CWs) were used to remove three heavy metals (Zn, Cu and Pb). The two tested substrates were made of coke and gravel, respectively. First order dynamic model was appropriate to describe removing of Zn and Cu. The experimental results showed that first dynamic removal rate constants of Zn in CWs with coke and gravel were 0.2326 h-1 and 0.1222 h-1, respectively. And those of Cu in CWs with coke and gravel were 0.2017 h-1 and 0.3739 h-1. However, removal efficiencies of Pb in the coke system and the gravel system were within 95-99%, so the first order dynamic model failed to fit the experimental data because the hydraulic resident times of Pb did not affect outlet concentration of Pb. From the removal rate constants, it is found that the coke and gravel system have different absorption efficiencies of heavy metal pollutants. Therefore, it is suggested that the removal efficiencies of heavy metals are influenced by the choice of substrates to some extent.

Design of Constructed Wetland for Treatment of Tailwater from Wastewater Treatment Plant

In this study, the project of constructed wetland for treatment of tailwater from the wastewater treatment plant in Wudang Mountain was taken as an example, and the technological processes, pollution load, wetland bed structure, bed filler, selection of plants and hydraulic conditions of the subsurface flow constructed wetland were discussed. A subsurface flow constructed wetland, which covered an area of 7 227 m^2 was finally designed. It could treat 7 000 m^3 of tailwater from the wastewater treatment plant a day. In addition, the system could reduce the emission of COD, BODs, TN, TP and NH3-N by 25.55, 25.55, 12.78, 1.28 and 17.89 t respectively a day. The outlet water was proved to reach the Standard A of the first class in Discharge Standard of Pollutants for Municipal Wastewater Treatment Plant （GB 18918-2002）.

Performance of hybrid constructed wetland systems for treating septic tank effluent

The integrated wetland systems were constructed by combining horizontal-flow and vertical-flow bed, and their purification efficiencies for septic tank effluent were detected when the hydraulic retention time （HRT） was 1 d, 3 d, 5 d under different seasons. The results showed that the removal efficiencies of the organics, phosphorus were steady in the hybrid systems, but the removal efficiency of total nitrogen was not steady due to high total nitrogen concentration in the septic tank effluent. The average removal rates of COD （chemical oxygen demand） were 89%, 87%, 83%, and 86% in summer, autumn, winter and spring, respectively, and it was up to 88%, 85%, 73%, and 74% for BOD5 （5 d biochemical oxygen demand） removal rate in four seasons. The average removal rates of TP （total phosphorous） could reach up to 97%, 98%, 95%, 98% in four seasons, but the removal rate of TN （total nitrogen） was very low. The results of this study also indicated that the capability of purification was the worst in winter. Cultivating with plants could improve the treated effluent quality fTom the hybrid systems. The results of the operation of the horizontal-flow and vertical-flow cells （hybrid systems） showed that the removal efficiencies of the organics, TP and TN in horizontal-flow and vertical-flow cells were improved significantly with the extension of HRT under the same season. The removal rate of 3 d HRT was obviously higher than that of 1 d HRT, and the removal rate of 5 d HRT was better than that of 3 d HRT, but the removal efficiency was not very obvious with the increment of HRT. Therefore, 3 d HRT might be recommended in the actual operation of the hybrid systems for economic and technical reasons.

Relationships between loading rates and nitrogen removal effectiveness in subsurface flow constructed wetlands

Nitrogen removal of wetlands under 40 differ-ent inflow loadings were studied in the field during 15months. The removal efficiency of four different sets ofbeds, namely the reed bed, the Zizania caduciflor bed, themixing planting bed, and the control bed were studied.The outflow loading and total nitrogen (TN) removal rateof these beds under different inflow loadings and pollutionloadings were investigated. The inflow loadings of 4 sub-surface flow systems (SFS) ranged from 400 to 8000 mg·(m^(2) ·d) 21 , while outflow loadings were less than 7000 mg·(m^(2) ·d) 21 . The results showed that the inflow and outflowloading of TN removal rate in SFS presented an obviouslinear relationship. The optical inflow loading to run thesystem was between 2000 to 4000 mg·(m^(2) ·d) 21 . Averageremoval rate was between 1062 and 2007 mg·(m^(2) ·d) 21 .SFS with plant had a better removal rate than the control.TN removal rates of the reed and Zizania caduciflora bedwere 63% and 27% higher than the control bed,respectively. The results regarding the TN absorption ofplants indicated that the absorption amount was verylimited, less than 5% of the total removal. It proved thatplants clearly increase TN removal rates by improving thewater flow, andincreasingthe biomass, as wellas activitiesof microorganisms around the roots. The researchprovided a perspective for understanding the TN removalmechanism and design for SFS.

Hybrid constructed wetlands for highly polluted river water treatment and comparison of surface-and subsurface-flow cells

A series of large pilot constructed wetland （CW） systems were constructed near the confluence of an urban stream to a larger fiver in Xi＇an, a northwestern megacity in China, for treating polluted stream water before it entered the receiving water body. Each CW system is a combination of surface- and subsurface-flow cells with local gravel, sand or slag as substrates and Phragmites australis and Typha orientalis as plants. During a one-year operation with an average surface loading of 0.053 m3/（m2.day）, the overall COD, BOD, NH3-N, total nitrogen （TN） and total phosphorus （TP） removals were 72.7% ~ 4.5%, 93.4% ＋ 2.1%, 54.0% ＋ 6.3%, 53.9% ~ 6.0% and 69.4% ：t： 4.6%, respectively, which brought about an effective improvement of the fiver water quality. Surface-flow cells showed better NH3-N removal than their TN removal while subsurface-flow cells showed better TN removal than their NH3-N removal. Using local slag as the substrate, the organic and phosphorus removal could be much improved. Seasonal variation was also found in the removal of all the pollutants and autumn seemed to be the best season for pollutant removal due to the moderate water temperature and well grown plants in the CWs.

Analysis of pollutant removal effect usinginnovative ridge-shaped constructed wetland

In this paper,a new type of ridge-shaped constructed wetland which combines surface flow and horizontal subsurface flow was proposed.The proposed wetland had simple structure,low construction and operating cost,less human interference and good pollution removal effect.The combination of surface flow and subsurface flow provided an aerobic and anaerobic alternating environment for the entire wetland.The performance of the proposed wetland was compared with a traditional horizontal subsurface flow wetland.The comparison results showed that the removal rates of BOD(biochemical oxygen demand),TN(total nitrogen),and TP(total phosphorus)in the ridge-shaped wetland increased up to 20.3%,17.0%,and 9.1%,respectively.The proposed wetland structure could be widely applied for treatment of rural and urban domestic sewage pollution or agricultural point and nonpoint source water pollution.

生物接触氧化-潜流型人工湿地组合工艺处理农村生活污水的应用案例研究

以浙江省永康市某农村的生活污水处理及灌溉回用工程为例,对“生物接触氧化-潜流人工湿地”组合工艺处理农村生活污水的设计参数、运行效果和工程效益等进行了分析。该工程设计规模为30 m^(3)/d,研究期间实际处理规模12~20 m^(3)/d,出水中TP、NH_(3)-N、COD、BOD5、SS、粪大肠菌群等11项主要指标灌溉期(4月至10月)满足《农田灌溉水质标准》,作为该村苗木基地灌溉用水,非灌溉期(11月至次年3月)出水满足《浙江省农村生活污水处理设施水污染物排放标准》,作为该村荷花种植塘的用水。工程运行期间对TP、NH_(3)-N、COD、BOD_(5)、粪大肠菌群、阴离子表面活性剂、色度、SS和浊度的平均去除率分别为44.3%、65.3%、63.8%、61.7%、76.2%、65.7%、74.2%、54.3%和50.5%。

潜流人工湿地脱氮除磷基质的应用研究及展望

基质的选择直接影响着潜流人工湿地全生命周期及污水处理效果,不同类型的基质对脱氮除磷具有差异性效果。综述了不同类型潜流人工湿地基质的研究现状,分析了其脱氮除磷机理,总结了各类基质的应用效果,展望了天然矿石基质、固体废弃物基质和人工合成基质研究方向和研究重点,以期为潜流人工湿地脱氮除磷基质的研发提供参考。

垂直潜流人工湿地净化水中镉、氮、磷效果及机理

矿山区域因降雨形成含镉(Cd)、氮(N)和磷(P)混合废水,对生态和人类构成威胁,本文探求一种高效人工湿地净化装置并进行机理研究。设置“生物炭(BC)+土壤+菖蒲”试验装置(CWSPB),选择“土壤+菖蒲”(CWSP)与“BC+土壤”(CWSB)装置对照。结果表明,CWSPB对Cd、NH_(4)^(+)-N和TP去除效果最好,平均去除率分别为98.65%±1.90%、72.77%±19.35%和74.46%±16.06%。CaCl_(2)和Tessier提取法表明CWSPB土壤中Cd稳定性最好。FTIR和XPS分析表明,BC表面官能团-COOH、-OH和-C=O以及离子HPO_(4)^(2-)、PO_(4)^(3-)、OH^(-)、CO_(3)^(2-)参与Cd去除。微生物群落分析表明门水平细菌变形菌、拟杆菌、厚壁菌和真菌担子菌、毛霉菌及属水平细菌普雷沃氏菌、不动杆菌和真菌青霉菌、曲霉菌、木霉菌、紫球菌相对丰度增加明显。研究显示由BC、土壤和菖蒲组成的人工湿地在处理Cd、N、P废水有较好效果与潜力。

3种水生植物潜流人工湿地模拟处理池塘养殖尾水的研究

为了解潜流人工湿地对养殖尾水的处理效果,比较蕹菜、凤眼莲、喜旱莲子草三种水生植物潜流人工湿地对草鱼养殖池塘尾水的净化效果,并探讨潜流人工湿地在不同水力负荷、排停水和排水转换对池塘养殖尾水的处理效果,以及潜流人工湿地微生物群落多样性和组成。结果显示:蕹菜、凤眼莲和喜旱莲子草分别对总磷(TP)、氨氮(NH_(4)^(+)-N)和化学需氧量(COD_(Mn))去除率最高,为24.7%、25.1%和25%。停水时,蕹菜、凤眼莲和喜旱莲子草均对NH_(4)^(+)-N去除率最低,分别为-526.07%、-871.08%和-1196.46%。水力负荷为低(5.76 m^(3)/d)时,蕹菜、凤眼莲和喜旱莲子草分别对COD_(Mn)、NH_(4)^(+)-N和TP去除率最高,为30.4%、42.5%和22.1%。蕹菜Shannon、Ace和Chao 1均最高,喜旱莲子草Simpson最高。3组样本共分析出5131个OTU,注释为45个门,293个目和974个属;蕹菜停水前、中和后共分析出5021个OTU,注释为47个门,294个目和953个属。研究表明,水生植物潜流人工湿地对养殖尾水具有一定的净化效果,运行期间停水会降低净化效果,水力负荷低的净化效果大于中和高,微生物群落多样性和组成的差别影响了人工潜流湿地对养殖池塘尾水的净化效果。

潜流人工湿地处理农田退水的温室气体排放特征研究

人工湿地作为一种生态、低耗的污水处理技术,在去除污染物的同时,也产生和排放温室气体。本研究基于处理农田退水的中型人工湿地系统,探讨了不同运行方式、湿地构型和水力停留时间等因素对温室气体排放的影响。结果表明:运行方式对温室气体排放的影响受到水力停留时间的制约。水力停留时间1d时,连续运行的潜流湿地的CH4排放通量[-0.062mg/(m^(2)·h)]显著高于间歇运行的潜流湿地[-0.225mg/(m^(2)·h)](P<0.01),间歇运行的潜流湿地N_(2)O排放通量略高于连续运行的潜流湿地。水力停留时间1—3d时,水平潜流湿地的CH4排放通量和N_(2)O排放通量均显著高于垂直潜流湿地的CH4排放通量和N_(2)O排放通量(P<0.01);水力停留时间与温室气体排放通量呈正相关。研究结果可为降低人工湿地的温室气体排放提供参考。

不同化学药剂对人工湿地基质堵塞的缓解效果与机理

以水平潜流人工湿地为研究对象,探究十二烷基硫酸钠(SDS)、次氯酸钠(NaClO)和过氧化氢(H_(2)O_(2))对基质堵塞的缓解效果与机理,并分析其工程应用可行性.结果表明,经过3种化学药剂处理后,基质层渗透系数分别提高53.3%、27.5%、210.7%.此外,H_(2)O_(2)对反应器污染物去除效率影响最小,并提高了NH_(4)+-N及TP的去除效果.3种药剂的投加对植物造成轻微伤害,但这种负面影响短期内(14d)可弹性恢复(93.8%、84.4%、84.4%).在微生物群落结构方面,化学药剂处理可以通过抑制生物膜形成细菌(如Pleomorphomonas属和norank_f__norank_o__Saccharimonadales属)的生长来缓解堵塞,并通过改善反应器厌氧环境促进脱氮除磷功能细菌(如反硝化细菌unclassified_f__Comamonadaceae)的生长来恢复反应器性能.结合堵塞缓解效果和工程应用可行性比较认为,3种药剂中H_(2)O_(2)为缓解人工湿地基质堵塞的最佳药剂.

两种不同基质的垂直潜流人工湿地对尾水的处理效果研究

为提高人工湿地对污水处理厂尾水的处理效率,采用以黄铁矿和砾石为基质的两种垂直潜流人工湿地处理武汉某污水处理厂尾水,研究了不同水力负荷下人工湿地去除污染物的效果,并分析了基质的微生物群落结构。结果表明,在低水力负荷(0.4~0.7 m^(3)/(m^(2)·d))下,两种人工湿地对尾水化学需氧量(COD)、总氮(TN)、NO_(3)^(-)和总磷(TP)具有较好的去除效果;在高水力负荷(1.0~1.3 m^(3)/(m^(2)·d))下,对氨氮去除效果较好。黄铁矿人工湿地对尾水COD、TN、NO_(3)^(-)和TP的去除效果好于砾石,分析基质微生物发现,黄铁矿人工湿地中反硝化脱氮菌属主要为硫杆菌属(Thiobacillus)和硫氧化菌属(Sulfurifustis),相对丰度分别为16.68%和4.62%,且硫杆菌属具有提高磷去除能力的功能;而砾石人工湿地中反硝化脱氮菌属主要为类固醇杆菌属(Steroidobacter),相对丰度为4.56%,采用黄铁矿为基质后,人工湿地中的脱氮除磷菌丰度和多样性升高,有利于人工湿地对尾水的脱氮除磷。黄铁矿人工湿地出水存在SO_(4)^(2-)含量偏高的现象,建议工程应用中在人工湿地底部填充黄铁矿以达到出水SO_(4)^(2-)含量降低的目的。

铁碳强化潮汐流-潜流复合人工湿地处理模拟养殖尾水的启动运行效果

为探究潮汐流-潜流复合人工湿地对含四环素养殖废水处理效果的影响,本研究构建陶粒(一级系统)和铁碳+陶粒(二级CCW系统)基潮汐流-潜流复合人工湿地(TC组),以及陶粒(一级系统)和陶粒(二级PCW系统)基潮汐流-潜流复合人工湿地(对照组),研究其对模拟养殖尾水的启动运行效果及微生物群落结构特性.结果表明:①加入0.2 mg/L的四环素在一定程度上会抑制人工湿地启动期对污染物的去除,尤其对一级系统的抑制作用更加明显,CODCr、TP、NH_(4)^(+)-N和TN平均去除率分别降低0.59%、1.51%、9.57%和1.97%;②二级CCW系统去除率均高于二级PCW系统,且四环素实验组(TC组)中促进作用更为明显.CODCr、TP、NH_(4)^(+)-N、TN在TC组中平均去除率分别增加5.81%、2.47%、0.91%、1.02%,铁碳填料的加入强化了常规污染物的去除;③TC组和对照组填料表面生物膜差异较小,二级CCW系统较二级PCW系统生物膜附着更为明显,铁碳填料的加入有利于微生物的生长繁殖;④二级CCW系统物种丰富度及生物多样性高于二级PCW系统.变形菌门(Proteobacteria)和拟杆菌门(Bacteroidetes)作为人工湿地典型菌落,铁碳填料的加入使二者丰富度明显增加,对氮的去除产生积极作用.研究显示,铁碳填料的加入强化了潮汐流-潜流复合人工湿地系统对氮磷的去除,该结果可为养殖尾水的净化处理提供数据支持和一定的理论支撑.