Enhancing treatment efficiency of swine wastewater by effluent recirculation in vertical-flow constructed wetland

Livestock wastewater has been a major contributor to Chinese cultural eutrophication of surface waters. Constructed wetlands are under study as a best management practice to treat wastewater from dairy and swine operations, but the removal efficiency of pollutants is relatively low. Enhancing the treatment efficiency of livestock wastewater by effluent recirculation was investigated in a pilot-scale vertical-flow constructed wetland. The wetland system was composed of downflow and upflow stages, on which narrow-leaf Phragmites communis and common reed Phragraites Typhia are planted, respectively; each stage has a dimension of 4 m^2 （2 m × 2 m）. Wastewater from facultative pond was fed into the system intermittently at a flow rate of 0.4 m^3/d. Recirculation rates of 0, 25%, 50%, 100% and 150% were adopted to evaluate the effect of the recirculation rate on pollutants removal. It shows that with effluent recirculation the average removal efficiencies of NH4-N, biological oxygen demand （BOD5） and suspended solids（SS） obviously increase to 61.7%, 81.3%, and 77.1%, respectively, in comparison with the values of 35.6%, 50.2%, and 49.3% without effluent recirculation. But the improvement of TP removal is slight, only from 42.3% to 48.9%. The variations of NH4-N, dissolved oxygen（DO） and oxidation-reduction potential（ORP） of inflow and outflow reveal that the adoption of effluent recirculation is benefi- cial to the formation of oxide environment in wetland. The exponential relationships with excellent correlation coefficients （R2 〉0.93） are found between the removal rates of NH4-N and BOD5 and the recirculation rates. With recirculation the pH value of the outflow decreases as the alkalinity is consumed by gradually enhanced nitrification process. When recirculation rate is kept constant 100%, the ambient temperature appears to affect NH4-N removal, but does not have significant influence on BOD5 removal.

Effects of Cd^(2+) and Pb^(2+) on the substrate biofilms in the integrated vertical-flow constructed wetland

The effects of single Cd^(2+)and Pb^(2+),and combined Cd^(2+)and Pb^(2+)on dehydrogenase activity and polysaccharide content of the substrate biofilms in the integrated vertical-flow constructed wetland(IVCW)were studied.Dehydrogenase activities decreased linearly with the increasing concentrations of Cd^(2+)and Pb^(2+)at different times(6,24,72,and 120 h).The activities at both 6 and 24 h were significantly higher than that at 72 and 120 h in the case of single and combined treatments.The single Cd^(2+)and...

Spacial Distribution Characteristics, Activity and Degradation Capability of the Biofilm in Integrated Vertical-flow Constructed Wetland

The spacial distribution characteristics, activity and degradation capability of the biofilm in integrated vertical-flow constructed wetland were investigated. Results showed that the biofilm widely distributed in the substrate of integrated vertical-flow constructed wetland and mainly in the 0-10 cm top layer where the activity ofdehydrogenase of the biofilm was also higher than that of other layers. The water quality could also affect the activity of the biofilm, for the TF（1,3,5-Triphenylformazan） amount reduced by the biofim incubated in water of the higher eutrophication was larger, too. The PCP （pentachlorophenol） removal rate by the substrate with biofilm was 1.5 times that without biofilm. In total, the biofilm of the down-flow chamber appeared larger biomass, higher dehydrogenase activity and stronger degradation capability of organic contamination than that in up-flow chamber and it was the major place for removal of the organic matters in waste water.

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.

Toxic effect of perfluorooctane sulfonate on plants in vertical-flow constructed wetlands

Per-and polyfluoroalkyl substances(PFASs)can be taken up and bioaccumulated in plants,but the toxic mechanisms of PFASs on wetland plants are still unclear.In present study,the toxic influences of perfluorooctane sulfonate(PFOS)on Eichhornia crassipes(E.crassipes)and Cy perus alternifolius(C.alternifolius)in a vertical-sub surface-flow constructed wetland were evaluated.The results showed that E.crassipes was more tolerant to PFOS stress than C.alternifolius,and the growth and chlorophyll synthesis of the two plants were promoted by low concentration(<0.1 mg/L)of PFOS,and the chlorophyll synthesis was inhibited by high concentration(10 mg/L)of PFOS but the growth did not change obviously.The catalase activity and malondialdehyde content in the leaves of the two plants increased,peroxidase activity decreased under exposure to high concentrations of PFOS,and superoxide dismutase activity did not change.Under PFOS stress,the membrane of plant leaves and the cell structure of the two wetland plants were destroyed,and the mitochondrial contour of root cells became incomplete.Tanscriptomic analysis showed that the expression levels of genes related to cell wall formation,the cell apoptosis pathway,material synthesis,and metabolism in the plants were changed by PFOS.Analysis in fluorogenic quantitative real time polymerase chain reaction(RT-qPCR)also confirmed that the photosynthesis system of E.crassipes was inhibited,while that of C.alternifolius was promoted.

Decontamination efficiency and root structure change in the plant-intercropping model in vertical-flow constructed wetlands

Subtropical climatic conditions can contribute to the death of the aerial parts of constructed wetland plants in winter. This presents a barrier to the widespread application of constructed wetland and is an issue that urgently needs to be solved. Three contrasting experi- ments, the plant-intercropping model （A）, the warm- seasonal plant model （B）, and the non-plant model （C）, were studied in terms of their efficiency in removing pollutants, and the change in root structure of plants in the plant-intercropping model within the vertical-flow con- structed wetlands. The results indicate that model A was able to solve the aforementioned problem. Overall, average removal rates of three pollutants （CODcr, total nitrogen （TN） and total phosphorous （TP）） using model A were significantly higher than those obtained using models B and C （P 〈 0.01）. Moreover, no significant differences in removal rates of the three pollutants were detected between A and B during the higher temperature part of the year （P〉 0.05）. Conversely, removal rates of the three pollutants were found to be significantly higher using model A than those observed using model B during the lower temperature part of the year （P 〈 0.01）. Furthermore, the morphologies and internal structures of plant roots further demonstrate that numerous white roots, whose distribution in soil was generally shallow, extend further under model A. The roots of these aquatic plants have an aerenchyma structure composed of parenchyma cells, therefore, roots of the cold-seasonal plants with major growth advantages used in A were capable of creating a more favorable vertical-flow constructed wetlands media- microenvironment. In conclusion, the plant-intercropping model （A） is more suitable for use in the cold environment experienced by constructed wetland during winter.

Effect of artificial aeration on the performance of vertical-flow constructed wetland treating heavily polluted river water

Three lab-scale vertical-flow constructed wetlands （VFCWs）, including the non-aerated （NA）, intermittently aerated （IA） and continuously aerated （CA） ones, were operated at different hydraulic loading rates （HLRs） to evaluate the effect of artificial aeration on the treatment efficiency of heavily polluted river water. Results indicated that artificial aeration increased the dissolved oxygen （DO） concentrations in IA and CA, which significantly favored the removal of organic matter and NH4＋-N. The DO grads caused by intermittent aeration formed aerobic and anoxic regions in IA and thus promoted the removal of total nitrogen （TN）. Although the removal efficiencies of CODEr, NH4＋-N and TN in the three VFCWs all decreased with an increase in HLR, artificial aeration enhanced the reactor resistance to the fluctuation of pollutant loadings. The maximal removal efficiencies of CODEr, NH4＋-N and total phosphorus （TP） （i.e., 81%, 87% and 37%, respectively） were observed in CA at 19 cm/day HLR, while the maximal TN removal （i.e., 57%） was achieved in IA. Although the improvement of artificial aeration on TP removal was limited, this study has demonstrated the feasibility of applying artificial aeration to VFCWs treating polluted river water, particularly at a high HLR.

Treatment Efficiency of Integrated Vertical-Flow Constructed Wetland for Saline Wastewater

The integrated vertical-flow constructed wetland（IVCW） was simulated with three suits of designed experiment columns planted with Kandelia candel.Units A,B and C were irrigated with sewage of different salinity（A：10‰ B：20‰,C：30‰）,respectively.The removal rates of dissolved organic carbon（DOC）,NH3-N and NO3--N dropped 90.4%-48.6%,80.2%-40.3% and 84.8%-60.9%,respectively,when salinity increases from 10‰ to 30‰.The removal rate of TP increased 14%-31.2%,oppositely.A 20-day inflow salinity drastic change shock affective trial was done on units D and E.Unit D was used as a control and irrigated with saline sewage（20‰）.Unit E was irrigated with sewage with low salinity（5‰） as a salinity drastic change shock on the third and fourth days.DOC,NH3-N and NO3--N removal efficiency of unit E showed a three-stage process of change,＂rapidly decrease,increase beyond the normal standard,and then back to the normal standard＂.TP removal value was negative during the 2-day shock period.

Removal,distribution and plant uptake of perfluorooctane sulfonate(PFOS)in a simulated constructed wetland system

A vertical-flow constructed wetland(VFCW)was used to treat simulated domestic sewage containing perfluorooctane sulfonate(PFOS).The removal rate of PFOS in the domestic sewage was 93%–98%,through soil adsorption and plant uptake,suggesting that VFCWs can remove PFOS efficiently from wastewater.The removal of PFOS in the VFCW was dependent on soil adsorption and plant uptake;moreover,the percentage of soil adsorption was 61%–89%,and was higher than that of the plants uptake(5%–31%).The absorption capacity of Eichhornia crassipes(E.crassipes)(1186.71 mg/kg)was higher than that of Cyperus alternifolius(C.alternifolius)(162.77 mg/kg)under 10 mg/L PFOS,and the transfer factor of PFOS in E.crassipes and C.alternifolius was 0.04 and 0.58,respectively,indicating that PFOS is not easily translocated to leaves from roots of wetland plants;moreover,uptake of PFOS by E.crassipes was more than that of C.alternifolius because the biomass of E.crassipes was more than that of C.alternifolius and the roots of E.crassipes can take up PFOS directly from wastewater while C.alternifolius needs to do so via its roots in the soil.The concentration of 10 mg/L PFOS had an obvious inhibitory effect on the removal rate of total nitrogen,total phosphorus,chemical oxygen demand,and ammonia nitrogen in the VFCW,which decreased by 15%,10%,10%and 12%,respectively.Dosing with PFOS in the wastewater reduced the bacterial richness but increased the diversity in soil because PFOS stimulated the growth of PFOS-tolerant strains.

多级串联表面流人工湿地净化生活污水效果

农村生活污水已经成为农业面源污染的主要来源之一。为了研究如何在经济发展水平不高的农村建立能有效治理农村生活污水,且建设成本低、运行维护简单的人工湿地系统,该文通过在桂林市青狮潭灌区构建了多级串联的表面流人工湿地系统,研究分析了不同子系统的水质净化效果及相关检测指标浓度的沿程变化规律。研究结果表明,湿地系统对氮磷的去除效率总体呈现出随时间推移逐渐下降的趋势,同时湿地的表面积越大,其对氮磷的去除率越高。研究还发现,该湿地系统对高浓度进水具有快速、稳定的去除效果,而对低浓度进水的营养盐去除则表现得较为平缓和持久。通过对湿地系统沿程氮磷浓度衰减的拟合及回归分析,建立了与湿地系统进口浓度有关的TN、NH4+-N和TP浓度的沿程衰减模型,相关分析表明其最佳的拟合模型均为指数衰减模型。该湿地系统在整个试验时期内均表现出了良好的净化效果,有效地减轻了农村生活污水对外界水环境的破坏,指数衰减模型的建立也为后续湿地设计及排水水质预测提供了理论分析依据。

串联垂直流人工湿地去除河水中磷的效果

利用在温室内构建的串联垂直流人工湿地模拟装置，以芦苇为湿地植物，填充砾石，研究两种水力负荷（0．2和0．4m／d）、3个串联级数、有，无植物等对处理北京市清河河水磷去除的影响，试验共持续144d．结果表明：①在进水P（TP）为0．50～1．77mg／L（平均值为1．15mg／L）、P（DTP）为0．41～1．53mg／L（平均值为0．9mg／L）的条件下，TP去除率随进水P（TP）的升高而升高．②水力负荷为0．2m／d时，有、无植物3级串联系统磷的去除率分别为38．36％、26．85％；水力负荷为0．4m／d时，分别为32．42％，23．99％，说明低水力负荷与有植物的条件利于除磷．③有植物3级串联系统TP去除率平均值为38．36％，大于2级串联系统（28．30％）；无植物3级串联系TP去除率平均值为26．85％，大于2级串联系统（21．81％）和1级串联系统（14．98％），串联级数增加，磷去除率升高．研究显示，水力负荷为0．2m／d时，有植物3级串联系统的TP去除率最高．

复合垂直流湿地反应动力学及水流流态的研究

提出一种新型的复合垂直流湿地系统(IVCW),并对其反应动力学和系统的实际流态进行了研究.经过中试的运行试验,得到了系统对COD去除的反应速率方程,由示踪剂试验确定了系统中水流的停留时间分布(RTD),提出RTD的不同是湿地处理效率差异的主要原因,进而运用串联反应器模型和离散流模型两种非理想流态模型,模拟IVCW的实际水流流态,经过比较发现离散流模型模拟的效果较好.

人工湿地强化运行措施研究

人工湿地是一项水质净化效果好,建造、运行费用低的生态污水处理技术。目前缺少对湿地强化条件下净化特性和氧状态的研究,制约了湿地净化效率的提高。研究了串联型人工湿地、美人蕉湿地曝气、湿地多点进水和湿地出水回流对人工湿地氧环境的改善及净化效果;结果表明湿地出水回流净化效果最明显。

二级串联人工湿地处理稠油污水的季节变化

选取不同材料做基质,芦苇为湿地植物,构建了1#和2#二级串联潜流式人工湿地系统,对稠油采出污水进行现场处理试验研究。考察了水力负荷分别为0.18和0.09m3/(m2.d)的1#和2#湿地,不同季节(夏季和冬季)情况下的运行效果。结果表明,夏季人工湿地对石油类、COD、BOD5、TN、SS的去除率分别为79.22%、81.20%、89.67%、87.61%和89.47%;冬季则达到77.57%、78.98%、79.05%、71.35%、89.88%。

多级串联潜流人工湿地净化城市地面径流的试验研究

在室外露天试验场按不同水流方式设计和建造2组多级串联潜流人工湿地,通过中型试验测试其在不同运行方式下对西安市地面径流中COD、NH4+-N、TN、TP的净化效果。结果表明:2组人工湿地系统出水水质均达到GB 3838-2002《地表水环境质量标准》Ⅳ类标准;在湿地净化过程中,填料起主要作用,可吸附40%～50%的污染物,植物和微生物的协同作用可将净化效果提高20%～30%;2种人工湿地系统HRT为36～48h,运行间隔时间为7～15d的运行效果最佳;改变水流方式的复合流人工湿地系统净化效果优于水平潜流人工湿地系统,净化效果高出5%左右。研究设计的2种人工湿地均可用于城市地面径流污染的控制和雨水利用。

串式垂直流湿地去除河水COD_(Mn)效果的模拟研究

为揭示湿地对污染河水的去除效果,用温室内3级、2级、1级下行流人工湿地模拟系统去除北京清河河水中的化学需氧量(COD)。结果表明,有植物2级柱系统(水力负荷为0.2m3·m-2·d-1,水力停留时间为1.72d)的去除效果最佳,运行期CODMn的平均去除率为59.71%,平均出水浓度可达地表水Ⅱ类标准。串联级数对CODMn去除的影响较大,1级柱系统对CODMn去除率与多级柱系统间均呈显著差异(P<0.05),但多级柱系统间对CODMn去除率无显著差异(P>0.05)。植物对CODMn去除有显著影响,无-有植物各级对应系统间CODMn去除率均呈显著差异(P<0.05),运行期有植物各级柱系统及多级系统的沿程各柱均具更好的CODMn去除效果。综合考虑去除效果及构成成本,推荐有植物2级串联系统。

三级串联垂直潜流人工湿地的脱氮性能及微生物学特征

探究了3种水力负荷(HLR)下三级串联垂直潜流人工湿地(T-VFCWs)对农村生活污水的处理效果,并解析了系统中的氮素转化机制。结果表明:当系统HLR由0.10增至0.20 m^(3)·m^(-2)·d-1时,T-VFCWs始终保持着对农村生活污水高效的处理效果,系统出水水质满足《城镇污水处理厂污染物排放标准》(GB 18918—2002)一级A标准。T-VFCWs中顺次连接的3个VFCW单元(标记为V-1、V-2和V-3)在限氧环境下因其进水水质的差异可形成各自不同的氮素转化途径,并通过协同作用实现系统的高效脱氮。当T-VFCWs在试验期间连续运行时,V-1、V-2和V-3中主要的脱氮途径分别为短程硝化/反硝化作用、基于亚硝化的全程自养脱氮(CANON)作用和反硝化作用,上述3单元对进水中总氮(TN)和NH_(4)^(+)-N去除的贡献率分别为(51.3±4.4)%和(63.7±2.6)%、(30.9±4.8)%和(35.5±4.5)%、(17.8±5.0)%和(0.8±0.1)%。该研究可为组合式人工湿地的研发及工程化应用提供科学依据和技术支撑。