Treatment of Domestic Wastewater by Three Plant Species in Constructed Wetlands

Three common Appalachian plant species (Juncus effusus L., Scirpus validus L., and Typha latifolia L.) were planted into small-scale constructed wetlands receivingprimary treated wastewater. The experimental design includedtwo wetland gravel depths (45 and 60 cm) and five plantingtreatments (each species in monoculture, an equal mixture of the three species, and controls without vegetation), with two replicates per depth × planting combination. Inflow rates (19 L day^-1) and frequency (3 times day^-1) were designed to simulate full-scale constructed wetlands as currently used for domestic wastewater treatmentin West Virginia. Influent wastewater and the effluent from each wetland were sampled monthly for ten physical, chemical and biological parameters, and plant demographic measurements were made. After passing through these trough wetlands, the average of all treatments showed a 70% reduction in total suspended solids (TSS) and biochemical oxygen demand (BOD), 50 to 60% reduction in nitrogen (TKN), ammonia and phosphate, anda reduction of fecal coliforms by three orders of magnitude. Depth of gravel (45 or 60 cm) had little effect on wetland treatment ability, but did influence Typha and Scirpus growth patterns. Gravel alone provided significant wastewater treatment, but vegetation further improved many treatment efficiencies. Typha significantly out-performedJuncus and Scirpus both in growth and in effluent quality improvement. There was also some evidence that the species mixture out-performed species monocultures.Typhawas the superior competitor in mixtures, but a decline in Typha growth with distance from the influent pipe suggested that nutrients became limiting or toxicities may have developed.     

Nitrogen And Phosphorus Removal In Substrate-Free Pilot Constructed Wetlands With Horizontal Surface Flow In Uganda

In constructed wetlands (CWs) with horizontal sub-surface flow, nutrient removal, especially phosphorus, is limited because the root biomass fills the pore spaces of the substrate (usually gravel), directing wastewater flow to deeper wetland media; plants are not regularly harvested; the litter formed by decomposing vegetation remains on the surface of the substrate and thus does not interact with the wastewater; and the substrate media often used provide only limited adsorption. Effective nutrient removal including rootzone oxidation, adsorption and plant uptake therefore requires sufficient interaction of wastewater with the treatment media. We assessed the feasibility of biological nutrient removal from wastewater using substrate-free CWs with horizontal flow, planted with two tropical macrophytes namely, Cyperus papyrus and Miscanthidium violaceum. The objectives were to evaluate the system treatment efficiency under semi-natural conditions, and to assess microbial and plant biomass contributions to nutrient removal in the CWs. Results showed high removal efficiencies for biochemical oxygen demand, ammonium-nitrogen (NH₄–N) and phosphorus (P) fractions in papyrus-based CWs (68.6–86.5%) compared to Miscanthidium (46.7–61.1%) and unplanted controls (31.6–54.3%). Ammonium oxidizing bacteria in CW root–mats (10⁸–10⁹ cells/gram dry weight) and residual nitrite and nitrate concentrations in the water phase indicated active system nitrification. Papyrus showed higher biomass production and nutrient uptake, contributing 28.5% and 11.2%, respectively, of the total N and P removed by the system compared to 15% N and 9.3% P removed by Miscanthidium plants. Compared to literature values, nitrification, plant uptake and the overall system treatment efficiency were high, indicating a high potential of this system for biological nutrient removal from wastewaters in the tropics.     

美人蕉（Canna indica Linn.）和芦苇（Phragmites australis L.）人工湿地对含铬生活污水的净化效果及植物的生理生态变化

选取美人蕉（CannaindicaLinn.）、芦苇（PhragmitesaustralisL.）为植物材料,以不同浓度K2Cr2O（7分别含0、1、20、50mg.L-1Cr6＋）的生活污水作为Cr6＋污染源,研究了不同浓度Cr6＋及处理时间下两种湿地对污水净化效果、植物体Cr6＋积累量及根系活力（TTC）、叶片超氧化歧化酶（SOD）活性、过氧化物酶（POD）活性、净光合速率（Pn）和丙二醛（MDA）等生理指标的影响。结果表明：（1）在试验的初期30d内,随处理时间的延长,两种人工湿地COD、氨氮去除率均呈逐渐上升的趋势,30d后,随着Cr6＋处理时间的延长及Cr6＋浓度的逐渐升高,两种湿地系统对COD、氨氮去除率均逐渐下降。在20、50mg.L-1Cr6＋处理条件下,两种湿地对COD、氨氮的净化效果显著低于对照及1mg.L-1Cr6＋处理,对照与1mg.L-1Cr6＋处理条件下差异不显著。（2）在不同Cr6＋浓度处理下,两种人工湿地对TP净化效果的能力较为稳定,同时随处理时间的延长,美人蕉、芦苇体内Cr6＋积累量逐渐加大。（3）1mg.L-1Cr6＋处理可提高美人蕉和芦苇的TTC、叶片的SOD、POD、Pn,而20、50mg.L-1Cr6＋处理对以上指标均有不同程度的抑制作用,且抑制效果与处理浓度、时间呈正相关。（4）MDA含量随处理时间的延长和浓度升高呈逐渐增加趋势。可见,低浓度Cr6＋能有效促进美人蕉、芦苇生长,使之能够维持正常的净化功能,因此,利用它们作为人工湿地植物来修复Cr6＋污染具有一定的实用价值。     

闽江口湿地沉积物各形态磷分布特征及风险评价

为探究湿地植被、理化性质等对沉积物磷的各赋存形态的影响,评价闽江口湿地污染程度和潜在环境风险。2017年在闽江河口湿地由陆向海选取4个采样点,用SMT法提取各形态磷,测定分析了闽江口湿地沉积物各形态磷变化规律并进行风险评价。结果表明:沉积物中有机磷含量为0.176～0.369mg/g,约占总磷的32.03%;而无机磷含量为0.308～0.666mg/g,占总磷66.49%;总磷含量为0.491～0.998mg/g,其污染指数为0.819～1.618,总体上为轻度污染。各形态磷在不同植被类型沉积物中含量分布不同,其中沉积物有机磷含量芦苇最高,扁穗莎草最低;无机磷中的钙磷含量则是互花米草最少,短叶茳芏和扁穗莎草明显高于其他植被类型;而铁铝磷含量是互花米草远高于其他植物;因总磷受无机磷影响较大,以致无机磷含量与总磷含量分布相似,均是扁穗莎草最高,芦苇最低。沉积物中钙磷与容重呈极显著负相关,与含水率呈极显著正相关,有机磷含量与有机质呈极显著正相关;总磷与含水率呈极显著正相关,与电导率呈显著负相关。以上现象可能由植被类型与生长阶段、理化性质、陆源物质、水文环境、凋落物、人类生产活动等多个因素的综合作用所导致。     

铬对人工湿地净化生活污水的影响及铬积累规律

采用沙培法,研究了不同浓度Cr6＋（0、10、20、40 mg.L-1）对风车草湿地和薏米湿地净化生活污水的影响及铬积累规律。结果表明：（1）COD的去除率在苗期随铬浓度增大而逐渐升高,其余时期在20、40 mg.L-1处理下受到显著抑制（除了花期风车草湿地外）;随铬处理浓度的增大,风车草湿地对TN的去除率变化不明显,薏米湿地对TN的去除率则受到抑制作用（除了花期10 mg.L-1外）;这两种湿地对生活污水中铬的净化效果较好,仅在40 mg.L-1处理的风车草湿地出水中检测出铬。（2）10 mg.L-1铬促进风车草和薏米的生物量增大,较高浓度铬（20、40 mg.L-1）则抑制。（3）基质细沙及植物根系对污水中铬具有较好的吸附及积累作用,铬含量在细沙及植物中均随铬浓度增大而显著升高,其中两种植物对铬的积累量都表现为地下部显著大于地上部,表明风车草和薏米的根部中铬较难转移到其地上部。     

利用极浅型潜流人工湿地修复沙漠化土地的可行性研究

[目的]探讨以城市污水作为植物生长的水源和肥源,以期同步实现沙漠化土地的快速修复和污水净化的可行性。[方法]利用极浅型潜流人工湿地,湿地填料为细沙,栽培植物为高羊茅、黑麦草、狗牙根、芦苇和香蒲进行试验设置。[结果]试验仅4个月,细沙容重减小了20%~23%,有机质至少增加了3.9倍,有效磷、pH值、电导率和孔隙率分别增加了16%~103%,3%~5%,1.7~2.6倍和16%~25%,与原细沙差异性显著(p0.05),而碱解氮、全磷和各湿地细沙理化性质无显著性差异(p0.05)。[结论]极浅型潜流人工湿地能够迅速增加细沙养分含量,改善细沙理化性质,以极浅型潜流人工湿地修复沙漠化土地可行。高羊茅和黑麦草可作为修复沙漠化土地的优选植物。     

Treatment of Hydroponics Wastewater Using Constructed Wetlands in Winter Conditions

Hydroponics culture generates large amounts of wastewater that are highly concentrated in nitrate and phosphorus but contains almost no organic carbon. Constructed wetlands (CWs) have been proposed to treat this type of effluent, but little is known about the performance of these systems in treating hydroponic wastewater. In addition, obtaining satisfactory winter performances from CWs operated in cold climates remains a challenge, as biological pathways are often slowed down or inhibited. The main objective of this study was to assess the effect of plant species (Typha sp., Phragmites australis, and Phalaris arundinacea) and the addition of organic carbon on nutrient removal in winter. The experimental setup consisted of 16 subsurface flow CW mesocosms (1 m², HRT of 3 days) fed with 30 L?d¹ of synthetic hydroponics wastewater, with half of the mesocosms fed with an additional source of organic carbon (sucrose). Carbon addition had a significant impact on nitrate and phosphate removal, with removal means of 4.9 g m^-2?d^-1 of NO₃-N and 0.5 g m^-2 d^-1 of PO₄-P. Planted mesocosms were generally more efficient than unplanted controls. Furthermore, we found significant differences among plant treatments for NO₃-N (highest removal with P. arundinacea) and COD (highest removal with P. australis/Typha sp.). Overall, planted wetlands with added organic carbon represent the best combination to treat hydroponics wastewater during the winter.     

Full-Scale Experiment on Domestic Wastewater Treatment by Combining Artificial Aeration Vertical- and Horizontal-Flow Constructed Wetlands System

To improve domestic wastewater treatment for total nitrogen (TN) removal, a full-scale constructed wetlands combining an artificially aerated vertical- (AVCW) and a horizontal-flow constructed wetland (HCW) was completed in July 2007. The system covered a total area of 7,610?m². From 2 July 2007 to 7 August 2008, the treatment capacity was 2,076?m³?day^?1 with an aeration quantity of 7,400?m³?day^?1. The system effectively reduced the average annual output of BOD₅ (52.0?%), NH₄?CN (58.41?%), and TP (41.61?%), although the percentage reductions of other pollutants, including chemical oxygen demand (34.1?%), suspended solid (38.9?%), and TN (31.05?%) were lower. The purpose of the HCW was for denitrification of the effluent from the AVCW, and annual average of 34.27?% of NO₃?CN was removed compared with the reading at the AVCW outlet. With hydraulic loading increased to 4,152?m³?day^?1 from 9 September to 23 November 2007, the removal rate for NO₃?CN from the HCW decreased substantially from 48.80 to 18.86?%. The total removal rates of NH₄?CN showed significant positive correlation with DO content in the AVCW and with total TN removal rates for the combined system (P?<?0.05). The study indicated that, even with limited artificial aeration, nitrification was very effective for NH₄?CN removal.     

Assessing the Impact of Effluents from a Modern Wastewater Treatment Plant on Breakdown of Coarse Particulate Organic Matter and Benthic Macroinvertebrates in a Lowland River

Wastewater treatment plants (WWTP) with insufficient technologies for wastewater purification often cause a distinct nutrient pollution in the receiving streams. The increased concentrations of dissolved nutrients can severely disturb the ecological integrity of streams, which has been recently shown for basic ecosystem processes like mineralization of coarse particulate organic matter (CPOM). The present study investigated the impact of a modern WWTP (Zentralkläranlage Jena) on breakdown rates of CPOM exposed in net bags (1 mm mesh size) to the effluent of a large municipal WWTP and an upstream control site in the Saale River (Thuringia, Germany) from April to October 2005. Control and effluent site differed significantly in water chemistry with increased concentrations of dissolved organic carbon (DOC), ammonium, sulfate, and chloride at the effluent site, while the control site displayed higher concentrations of nitrate. However, breakdown rates of toothpickers and small twigs were not significantly different between the sites, whereas breakdown rate of leaf litter was significantly higher at the effluent site (k?=?0.0124 day^?1) than at the control site (k?=?0.0095 day^?1). Benthic invertebrate assemblages inhabiting the sandy stream bed at both sites were dominated by Chironomidae and Oligochaeta, typical inhabitants of fine sediments. Although the Shannon diversity of the benthic invertebrates was slightly higher at the effluent site (0.85) than at the control site (0.63), no significant difference could be detected. Bacterial numbers in water samples and surface biofilms on glass slides also displayed no significant differences between the two sites. This study showed that the effluents of a WWTP with modern technologies for wastewater purification did not directly affect breakdown rates of CPOM, bacteria numbers in epibenthic biofilms and the water column, and the community composition of sediment inhabiting aquatic macroinvertebrates in an effluent-receiving river with already increased concentrations of dissolved nutrients.     

极浅型潜流人工湿地用于污水处理和风沙土改良的中试研究

[目的]就利用极浅型潜流人工湿地同步处理污水和改良风沙土的可行性进行中试,为后续相关工程的设计、建设和运行提供科学依据。[方法]以污水处理厂初沉池出水为原水,以取自毛乌素沙漠的风沙土为湿地填料,以高羊茅、黑麦草和狗牙根为湿地栽培植物,研究并分析湿地对水中污染物的去除效果和在风沙土的富集特征。[结果]经过15个月的运行,各湿地对污水中COD,TN以及TP的平均去除率分别高于原土68.75%,70.09%和62.74%。运行完毕后,各湿地风沙土较原土有机质、全氮含量显著增加(p0.05),全磷含量虽呈增加趋势但增幅不显著(p0.05),其中风沙土有机质、全氮及全磷含量分别较原土增加了10.64~18.77,8.74~13.98,0.34~0.55倍。[结论]利用极浅型潜流人工湿地同步处理污水和改良风沙土可行。它既能高效净化污水,又可快速提升风沙土的生产力。     

Nitrous oxide emission from simulated overland flow wastewater treatment systems

Nitrous oxide evolution was measured from overland flow models receiving daily applications of municipal wastewater with NH₄⁺-N concentration in the wastewater of 10 or 47 μgN ml^?1. The amount of N₂O evolved from the system ranged from 0.07 to 1.3 mg N day^?1, or 1.5–25.5 kg N ha^?1yr^?1, respectively. Liming the soil or increasing the NH₄⁺-N in the wastewater increased the emission of N₂O from the system. The N evolved as N₂O did not exceed 1.2% of the applied NH₄⁺-N, indicating N₂ to be the major denitrification end product in the overland flow wastewater-treatment system.     

Phosphorus Mass Balance and Internal Load in an Impacted Subtropical Isolated Wetland

Internal loading is a critical component of the phosphorus (P) budget of aquatic systems that can control trophic conditions. While diffusion across the soil?Cwater interface is generally considered the dominant process controlling P load to the water column, advection due to water table fluctuations can also be significant. Our objective was to evaluate the role of diffusive and advective fluxes in relation to the total P (TP) loads entering and exiting an impacted wetland in the Lake Okeechobee drainage basin. The average diffusive flux of TP was 0.32?±?0.14 mg?m^?2?day^?1 and occurred for 240 days out of 314, while advective flux was 1.31?±?4.03 mg?m^?2?day^?1 and occurred for only 57 days. Phosphorus load to the wetland via internal modes was estimated to be 2.3 and 4.0 g?day^?1 from diffusion and advection respectively, accounting for 18% of the total P input, while overland flow (51%) was the major input pathway to the wetland. Ditch flow and groundwater outflow accounted for 49% (18.0 g?day^?1) and 14% (5.0 g?day^?1) of the total P output, respectively. This study shows the importance of advective flux in addition to diffusive flux and that the former should not be neglected when estimating internal P load of transiently flooded isolated wetlands. The monthly P budget-based retention and release patterns were consistent with previous findings, showing that intermittent flooding and drying cycling significantly reduces the P retention capacity of a wetland.     

Denitrification characteristics of subtropical soils in China affected by soil parent material and land use

Forty‐five soil samples were collected from rice paddy land (R), tea garden land (T), forestland (F), brush land (B), and upland (U) in Jiangxi province, a subtropical region of China. These soils were derived from Quaternary red earth (Q), Tertiary red sandstone (S), and granite (G). Their denitrification capacities were determined after treatment with 200 mg NO₃⁻‐N kg⁻¹ soil by measuring changes in NO₃⁻‐N content during a 28‐day anaerobic incubation under N₂ gas in the headspace, at 30°C. The subtropical soils studied here were characterized by generally small denitrification capacities, ranging from no denitrification capacity to complete disappearance of added NO₃⁻‐N within 11 days of incubation. With few exceptions, NO₃⁻‐N reduction with incubation time followed a first‐order relationship with reaction constants of 0 – 0.271 day⁻¹, but the data could be simulated better by a logarithmic relationship. Thus, denitrification capacity was determined by the reaction constant of the first‐order reaction, the slope of the logarithmic relationship, and the averaged NO₃⁻‐N reduction rate in the first 7 days of anaerobic incubation (ranging from 0 to 28.5 mg kg⁻¹day⁻¹), and was significantly larger in the soils derived from G than from Q and S for all land uses except for rice paddy land. Soil organic carbon and nitrogen availability are the key factors that determine differences in denitrification capacity among the three soil parent materials. Rice cultivation significantly promoted denitrification capacity compared with the other four land uses and masked the effect of soil parent materials on denitrification capacity. This is most likely due to increases in organic carbon and total N content in the soil, which promoted the population and biological activities of microorganisms which are able to respire anaerobically when the rice soil is flooded. Neither the increased pH of upland soil caused by the addition of lime for upland crop production, nor the decreased pH of the tea garden soil by the acidification effect of tea plants altered soil denitrification capacity. Our results suggest that land use and management practices favour soil carbon and/or nitrogen accumulation and anaerobic microorganism activities enhance soil denitrification capacity.     

Greenhouse gas emissions from a wastewater sludge-amended soil cultivated with wheat (Triticum spp. L.) as affected by different application rates of charcoal

Applying biochar to soil is an easy way to sequester carbon in soil, while it might reduce greenhouse gas (GHG) emissions and stimulate plant growth. The effect of charcoal application (0, 1.5, 3.0 and 4.5%) on GHG emission was studied in a wastewater sludge-amended arable soil (Typic Fragiudepts) cultivated with wheat (Triticum spp. L.) in a greenhouse. The application of charcoal at ≥1.5% reduced the CO₂ emission rate significantly ≥37% compared to unamended soil (135.3 g CO₂ ha⁻¹ day⁻¹) in the first two weeks, while the N₂O emission rate decreased 44% when 4.5% charcoal was added (0.72 g N₂O ha⁻¹ day⁻¹). The cumulative GHG emission over 45 days was 2% lower when 1.5% charcoal, 34% lower when 3.0% charcoal and 39% lower when 4.5% charcoal was applied to the sludge-amended soil cultivated with wheat. Wheat growth was inhibited in the charcoal-amended soil compared to the unamended soil, but not yields after 135 days. It was found that charcoal addition reduced the emissions of N₂O and CO₂, and the cumulative GHG emissions over 45 days, without altering wheat yield.     

Performance of the Giant Reed (<Emphasis Type="Italic">Arundo donax</Emphasis>) in Experimental Wetlands Receiving Variable Loads of Industrial Stormwater

Two emergent macrophytes, Arundo donax and Phragmites australis, were established in experimental subsurface flow, gravel-based constructed wetlands (CWs) and challenged by untreated stormwater collected from the hard-pan and other surfaces of a dairy processing factory in south-west Victoria, Australia. The hydraulic loading rate was tested at two levels, sequentially, 3.75 and 7.5 cm day⁻¹. Some of the monitored variables were removed more efficiently by the planted beds in comparison to unplanted CWs (biochemical oxygen demand (BOD), total nitrogen (TN) and total phosphorus (TP); p < 0.007) but there was no significant difference between the A. donax and P. australis CWs in removal of BOD, suspended solids (SS) and TN (p > 0.007) at 3.75 cm day⁻¹ or SS and TN at 7.5 cm day⁻¹. At 3.75 cm day⁻¹, BOD, SS, TN and TP removal in the A. donax and P. australis CWs was 71%, 61%, 78% and 75% and 65%, 60%, 73% and 41%, respectively. Nutrient removal at 7.5 cm day⁻¹ in the A. donax and P. australis beds was 87%, 91%, 84% and 71% and 96%, 94%, 87% and 55%, respectively. As expected, the A. donax CWs produced considerably more biomass (10 ± 1.2 kg wet weight) than the P. australis CWs (2.7 ± 1.2 kg wet weight). This equates to approximately 107 and 36 tonnes ha⁻¹ year⁻¹ biomass (dry weight) for A. donax and P. australis, respectively (assuming 250 days of growing season and single-cut harvest). The performance similarity of the A. donax- and P. australis-planted CWs indicates that either may be used in HSSF wetlands treating dairy factory stormwater, although the planting of A. donax provides additional opportunities for secondary income streams through utilisation of the biomass produced.     

莱州湾南岸滨海湿地的氮、磷循环过程及调控对策

在莱州湾南岸滨海湿地的生物地球化学循环过程中,N、P元素主要来源于通过河流输入的工业废水、城市生活污水、农田地表径流、灌溉余水和海水养殖池养殖废水,通过潮上带、潮间带湿地最终被输送到潮下带近海湿地,引起潮下带近海湿地水体N、P含量的不断升高,2000年通过河流输入到莱州湾南岸的N总量为46271.1t,P总量为2092.1t.潮上带、潮间带自然湿地的底质、土壤和植物对N、P元素有显著的吸收、净化作用.以2000年为例,若不考虑自然湿地的吸收、净化作用,仅靠水体交换、扩散稀释,输送到潮下带近海湿地的N、P在海水中的含量为6.74mg·L-1、0.299mg·L-1,而当年潮下带近海湿地水体N、P含量实测值分别为0.086mg·L-1、0.029mg·L-1,计算值分别是实测值的78.4倍、10.3倍;说明自然湿地对输入的N、P有明显的吸收净化效应.为降低莱州湾南岸潮下带近海湿地海水中的N、P含量,提出了发展循环经济,减小莱州湾南岸滨海湿地的N、P输入通量,对自然湿地进行有效的保护和生态恢复,建设人工湿地、提高湿地的环境净化功能等调控措施.     

Effect of labile and recalcitrant carbon on heterotrophic nitrification in a subtropical forest soil

Carbon (C) is an important factor controlling heterotrophic nitrification in soil, but the effect of individual C components (e.g., labile and recalcitrant C) is largely unclear. We carried out a C amendment experiment in which either labile C (glucose) or a recalcitrant C (cellulose and biochar) was added to a subtropical forest soil. A ¹⁵N-, ¹³C-tracing and MiSeq sequencing study was performed to investigate soil gross heterotrophic nitrification rates, carbon utilization for soil respiration and microbial biomass production and microbial composition, respectively. After 2 days, results showed a significant increase of gross heterotrophic nitrification rate in glucose (GLU) (on average 3.34 mg N kg⁻¹ day⁻¹), cellulose (CEL) (on average 0.21 mg N kg⁻¹ day⁻¹) and biochar (BIO) (on average 0.13 mg N kg⁻¹ day⁻¹) amendment in comparison with the unamended soil (CK) (on average 0.01 mg N kg⁻¹ day⁻¹; p < 0.05). The contribution of heterotrophic nitrification to total soil nitrification was significantly larger in GLU (average 85.86%), CEL (average 98.52%) and BIO (average 81.25%) treatments compared with CK (average 33.33%; p < 0.01). After 2-month amendment, the gross rates remarkably decreased in GLU (average 0.02 mg N kg⁻¹ day⁻¹), and the contribution to total nitrification (average 8.73%) were significantly lower than that in CK (p < 0.05). A decrease in the proportion of heterotrophic nitrification to total nitrification in soil was also observed in CEL (average 38.40%) and BIO (6.74%) treatments. Nevertheless, BIO amendment (compared to CK, GLU and CEL) showed the highest gross heterotrophic nitrification rate, accompanied by a notably higher abundance of specific heterotrophic nitrifiers, i.e. Trichoderma, Aspergillus and Penicillium. These results point to a stimulatory effect of C addition on soil heterotrophic nitrification in the short term, while the stimulatory impact of C amendment diminishes with the decline in easily available C. In addition, a shift of the microbial composition in the long term can possibly be sustained for longer if additional recalcitrant C is available to heterotrophic nitrifiers. The dynamic response of heterotrophic nitrification to labile and recalcitrant C in this study offered an explanation for the positive effect of plantation and plant root exudation on the process.     

Impact of Prior Physico-Chemical Treatment on the Clogging Process of Subsurface Flow Constructed Wetlands: Model-Based Evaluation

The objective of this study was to check the effect of the use of a physico-chemical treatment on the clogging process of horizontal subsurface flow constructed wetlands by means of dynamic modelling. The hydraulic submodel was based on series as well as parallel branched complete stirred tanks of equal volume. The model was validated with data obtained from 2 identical experimental wetlands, which had a surface area of 0.54 m² and a water depth of 0.30 m, and that were monitored over a period of 5 months. One of the wetlands was fed with settled urban wastewater, whereas the other with the same wastewater, but previously treated with a physico-chemical treatment. In the model, pore volume reduction depends on the growth of bacteria and on solids retained. The effluent concentrations of COD and ammonium in both experimental wetlands were very similar in all the conditions tested, and therefore the physico-chemical treatment did not improve the removal efficiency. The model indicated that after 120 days of operation in some regions of the wetland fed with settled wastewater the porosity decreased in a 17%, whereas in the other wetlands it only decreased as much as 6%. The use of a prior physico-chemical treatment is a good alternative for avoiding an anticipated clogging of subsurface flow constructed wetlands.     

Insights on the role of vegetation on nitrogen cycling in effluent irrigated lands

This work investigated the effect of plant species (Eucalyptus camaldulensis vs Arundo donax) on N-turnover during land application of pre-treated municipal wastewater. The study was carried out in 40-L pots under field conditions and revealed strong effects of plant species on N uptake, potential nitrification rate (PNR), and gaseous losses of N. E. camaldulensis accumulated 38% more N in its biomass than A. donax. With regard to the soil N, there was no effect of plant species on total Kjeldahl N content. The lower PNR measured in pots planted with A. donax could not be explained by differences in archaeal or bacterial amoA gene copies; suggesting that plant species affected the activity of nitrifiers.The loads of NH₄⁺-N applied were not found to have delayed the oxidation of NH₄⁺-N, despite the differences in PNR, as indicated by soil solution and soil NH₄⁺-N concentrations in the rhizosphere of the two plant species throughout the period of the study. However, decreased concentrations of NO₃⁻-N were measured in the pots planted with A. donax from the end of June onwards. This finding implies increased losses of N through denitrification and reveals a direct effect of plant species on the activity of denitrifiers since differences in copy numbers of denitrification genes (nirK, nirS, nosZ) were observed only early in the season. Our findings reveal a critical role of plant species on N cycling in terrestrial environments with important implications for the management/restoration of N-polluted areas, such as riparian zones, and for land treatment systems and constructed wetlands.     

几种植物去除污染水体中养分效果研究

对城市尾水和人工模拟富营养化水体进行了静态培养试验.通过比较不同植物对城市尾水中氮、磷去除效果,以及它们在不同磷浓度条件下对不同形态氮素去除效果研究,目的在于筛选出适合治理富养分污染水体的植物品种.研究结果表明,空心菜(Ipomiea aquatica)、酸模(Rumex acetosa)、莎草(Cyperus glomeratus)3种植物都能很好地吸收尾水中的营养物质,且生长状况良好.经3种植物处理的城市尾水,其氮、磷浓度随水培时间的增加而降低.莎草、酸模对污水中TN的去除率达90%以上,其中莎草最高,达93.4%;空心菜对全磷的去除率最高达76.9%.NH_4~+-N在处理前期变化显著,且莎草的净化效果最好达94.4%;污水中NO_3~--N含量随着水培时间的增加而逐渐下降,但在试验后期NO_3~--N又有所增加.酸模去除NO_3~--N效果最好,达65.4%.另外3种植物对NH4+-N和NO_3~--N都具有一定的吸收作用,并且优先吸收NH_4~+-N.且从对于NH_4~+-N和NO_3~--N净化效果看,莎草>酸模>空心菜.