Components of floating emergent macrophyte treatment wetlands influencing removal of stormwater pollutants

Floating treatment wetlands planted with emergent macrophytes (FTWs) provide an innovative option for treating urban stormwaters. Emergent plants grow on a mat floating on the water surface, rather than rooted in the bottom sediments. They are therefore able to tolerate the wide fluctuations in water depths that are typical of stormwater ponds. To better understand the treatment capabilities of FTWs, a series of replicated (n = 3) mesocosm experiments (12 × 0.7 m³ tanks using 0.36 m² floating mats) were conducted over seven day periods to examine the influence of constituent components of FTWs (floating mat, soil media, and four different emergent macrophyte species) for removal of copper, zinc, phosphorus and fine suspended solids (FSS) from synthetic stormwater. The presence of a planted floating mat significantly (P < 0.05) improved removal of copper (>6-fold), fine suspended particles (∼3-fold reduction in turbidity) and dissolved reactive P (in the presence of FSS) compared to the control. Living plants provided a large submerged root surface-area (4.6-9.3 m² of primary roots m⁻² mat) for biofilm development and played a key role in the removal of Cu, P and FSS. Uptake of Cu and P into plant tissues during the trials could only account for a small fraction of the additional removal found in the planted FTWs, and non-planted floating mats with artificial roots providing similar surface area generally did not provide equivalent benefits. These responses suggest that release of bioactive compounds from the plant roots, or changes in physico-chemical conditions in the water column and/or soils in the planted FTWs indirectly enhanced removal processes by modifying metal speciation (e.g. stimulating complexation or flocculation of dissolved fractions) and/or the sorption characteristics of biofilms. The removal of dissolved zinc was enhanced by the inclusion of a floating mat containing organic soil media, with reduced removal when vegetated with all except one of the test species. The results indicate that planted FTWs are capable of achieving dissolved Cu and Zn mass removal rates in the order of 5.6-7.7 mg m⁻² d⁻¹ and 25-104 mg m⁻² d⁻¹, respectively, which compare favourably to removal rates reported for conventional surface flow constructed wetlands treating urban stormwaters. Although not directly measured in the present study, the removal of particulate-bound metals is also likely to be high given that the FTWs removed approximately 34-42% of the turbidity associated with very fine suspended particulates within three days. This study illustrates the promise of FTWs for stormwater treatment, and supports the need for larger-scale, longer-term studies to evaluate their sustainable treatment performance.     

Novel insight into the process of nutrients removal using an algal biofilm: The evaluation of mechanism and efficiency

Eutrophication of water by nutrient pollution remains an important environmental issue. The aim of this study was to evaluate the nutrient uptake capacity of an algal biofilm as a means to treat polluted water. In addition, the study investigated the nutrient removal process. The algal biofilm was able to remove 99% of phosphorus within 24 hours of P addition, with the PO₄-P concentration in inflowing water ranging from 3 to 10 mg L^?1. Different patterns of phosphorus and nitrogen removal were observed. Daily quantity of removed NO₃-N ranged from 2 to 25% and was highly dependent on solar irradiance. Precipitation of phosphorus during the removal process was studied using X-ray diffraction analyses and was not confirmed in the biofilm. The biofilm system we constructed has a high efficiency for phosphorus removal and, therefore, has great potential for integration into wastewater treatment processes.     

Polysulfone and polyacrylate-based zwitterionic coatings for the prevention and easy removal of marine biofouling

A series of polysulfone and polyacrylate-based zwitterionic coatings were prepared on epoxy-primed aluminum substrata and characterized for their antifouling (AF) and fouling-release (FR) properties towards marine bacteria, microalgae and barnacles. The zwitterionic polymer coatings provided minimal resistance against bacterial biofilm retention and microalgal cell attachment, but facilitated good removal of attached microbial biomass by exposure to water-jet apparatus generated hydrodynamic shearing forces. Increasing the ion content of the coatings improved the AF properties, but required a stronger adhesive bond to the epoxy-primed aluminum substratum to prevent coating swelling and dissolution. Grafted poly(sulfobetaine) (gpSBMA), the most promising zwitterionic coating identified from microfouling evaluations, enabled the removal of four out of five barnacles reattached to its surface without incurring damage to their baseplates. This significant result indicated that gpSBMA relied predominately on its surface chemistry for its FR properties since it was very thin (~1–2 µm) relative to commercial coating standards (>200 µm).     

衰亡期黑藻与生长期菹草交替生长对水体磷迁移的影响

为利用冷暖种交替控制水体磷污染、抑制水体富营养化,揭示湖泊演化规律和机理。研究设置单季植物组(黑藻组、菹草组)和交替生长组(黑藻组+菹草组)进行实验。交替生长组在黑藻衰亡期种植菹草,监测各组上覆水和底泥中各形态磷含量的变化,计算黑藻衰亡释放磷及菹草生长吸收磷的总量,同时测定环境因子指标。分析沉水植物交替生长(黑藻+菹草)过程对衰亡期沉水植物(黑藻组)释放磷所带来的二次污染的消减作用,并分析环境因子变化与磷含量之间的关系。实验结果表明:黑藻+菹草组显著(P<0.05)降低了上覆水中总磷(TP)、溶解性总磷(DTP)和溶解性活性磷(SRP)的浓度;显著(P<0.05)降低了间隙水中DTP和SRP的浓度。底泥TP含量黑藻组呈上升趋势,黑藻+菹草和菹草组呈下降趋势。在采用菹草生物量期望2倍于衰亡植物黑藻生物量的模拟实验条件下,每实验组沉水植物黑藻衰亡分解所释放的磷为1.51 g,沉水植物菹草生长所富集吸收的磷为1.83 g。因此,菹草具备消减黑藻所释放磷的能力,可作为冷暖种交替控制水体富营养化的备选物种。实验组磷的迁移方向分别为:黑藻组磷迁移最终方向为底泥,黑藻+菹草组和菹草组磷的迁移方向为植物。黑藻+菹草组通过提高环境中DO和ORP,使得水相中磷向沉积物相中迁移,从而使得水相中各形态磷浓度保持在相对较低的水平。     

Phosphorus retention in lab and field-scale subsurface-flow wetlands treating plant nursery runoff

Constructed wetland systems built to handle nutrient contaminants are often efficient at removing nitrogen, but ineffective at reducing phosphorus (P) loads. Incorporating a clay-based substrate can enhance P removal in subsurface-flow constructed wetland systems. We evaluated the potential of crushed brick, a recycled building product, and two particle sizes of a palygorskite–bentonite industrial mineral aggregate (calcined clay) to sorb P from simulated nutrient-rich plant nursery effluent. The three substrates were screened for P sorbing behavior using sorption, desorption, and equilibration experiments. We selected one substrate to evaluate in an 8-month field trial to compare field sorption capacity with laboratory sorption capacity. In the laboratory, coarse calcined clay average sorption capacity was 497 mg kg⁻¹ and it sorbed the highest percentage of P supplied (76%), except at exposure concentrations >100 mg L⁻¹ where the increased surface area of fine calcined clay augmented its P sorption capacity. Subsurface-flow mesocosms were filled with coarse calcined clay and exposed to a four and seven day hydraulic retention time treatment. Phosphorus export was reduced by 60 to 74% for both treatments until substrate P-binding sites began to saturate during month seven. During the eight month experiment, the four and seven day treatments fixed 1273 ± 22 mg kg⁻¹ P and 937 ± 16 mg kg⁻¹ P, respectively. Sequential extractions of the P saturated clay indicated that P could desorb slowly over time from various pools within the calcined clay; thus, if the calcined clay were recycled as a soil amendment, most P released would be slowly available for plant uptake and use. This study demonstrated the viability of using coarse calcined clay as a root bed substrate in subsurface-flow treatment wetlands remediating phosphorus from plant nursery runoff.     

Effect of nutrient loading and retention time on performance of high rate algal ponds

Small pilot ponds in a glasshouse at the Scottish Agricultural College (Auchincruive) were used to investigate the effects of changing C:N:P loading rate and retention time on pond performance as measured by nutrient removal and dry matter biomass. One experiment investigated ponds operated at two C:N:P ratios: low (9:7:1) and high (104:10:1) and two retention times (4 and 7 days θ. Increasing retention time from 4 to 7 days increased the concentration of total (dry matter) and algal (chlorophyll a) biomass and the degree of nitrification. It also increased removal of phosphorus, but had no effect on nitrogen or COD removal. Cyanobacteria predominated in ponds operated at both 4 and 7 days, and the density of cyanobacteria increased with increased retention time. Nitrogen removal was independent of C:N:P ratio; indeed the lower C:N:P ratio favoured increased nitrification. A high C:N:P ratio increased phosphorus and COD removal and increased the concentration of algal biomass (chlorophyll a), but had little effect on total biomass (dry matter). A second experiment varied COD loading rate (600, 350 and 100 kg COD ha-¹ d-¹) while maintaining a constant retention time (either 5 or 7 days θ). Species composition was independent of retention time. The longer retention time increased both total and algal biomass concentration and also percentage of nitrogen removed. Nitrification was independent of retention time. Increasing loading rate increased dry matter production and resulted in a predominance of cyanobacteria over Chlorophyceae. Increased loading rate was related to increase in nitrogen removal, however more complete nitrification occurred at low COD loading rates. Phosphorus removal in the pond with 5-day (θ) remained constant independent of loading rate, but in the pond with 7-day θ phosphorus removal increased with increased COD loading. COD removal was independent of both retention time and loading rate. This revised version was published online in August 2006 with corrections to the Cover Date.     

Creating riverine wetlands: Ecological succession, nutrient retention, and pulsing effects

Successional patterns, water quality changes, and effects of hydrologic pulsing are documented for a whole-ecosystem experiment involving two created wetlands that have been subjected to continuous inflow of pumped river water for more than 10 years. At the beginning of the growing season in the first year of the experiment (1994), 2400 individuals representing 13 macrophyte species were introduced to one of the wetland basins. The other basin was an unplanted control. Patterns of succession are illustrated by macrophyte community diversity and net aboveground primary productivity, soil development, water quality changes, and nutrient retention for the two basins. The planted wetland continued to be more diverse in plant cover 10 years after planting and the unplanted wetland appeared to be more productive but more susceptible to stress. Soil color and organic content continued to change after wetland creation and wetlands had robust features of hydric soils within a few years of flooding. Organic matter content in surface soils in the wetlands increased by approximately 1% per 3-year period. Plant diversity and species differences led to some differences in the basins in macrophyte productivity, carbon sequestration, water quality changes and nutrient retention. The wetlands continued to retain nitrate–nitrogen and soluble reactive phosphorus 10 years after their creation. There are some signs that sediment and total phosphorus retention are diminishing after 10 years of river flow. Preliminary results from the beginnings of a flood pulsing experiment in the two basins in 2003–2004 are described for water quality, nutrient retention, aboveground productivity, and methane and nitrous oxide gaseous fluxes.     

Aquatic Macrophytes Alter Metabolism and Nutrient Cycling in Lowland Streams

Macrophytes influence the physical, chemical, and biological characteristics of lowland streams, so may be critically important in stream management. We investigated the role of macrophytes in regulating metabolism and nutrient cycling in three lowland, agricultural streams. We measured stream metabolism over the growing season and following experimental macrophyte removal, and used short-term nutrient additions of phosphate (P) and ammonium to assess macrophyte influences on nutrient uptake. Primary production was closely correlated with macrophyte cover across all streams and dates, and decreased greatly with macrophyte removal, whereas ecosystem respiration was not correlated with macrophyte cover and was not altered by macrophyte removal. Phosphate uptake velocity was negatively related to primary production, suggesting that macrophyte activity actually slowed P uptake. Ammonium uptake was not correlated with macrophyte cover or metabolism metrics. Stream nitrate concentrations typically exceeded concentrations of incoming groundwater, suggesting little net nitrate retention in these macrophyte-dominated streams. Phosphorous demand by macrophytes was 10-fold lower than observed uptake rates, indicating that macrophyte P demand was much lower than that of other stream biota. Nitrogen demand by macrophytes was nearly equal to ammonium uptake and was not sufficient to affect the high nitrate flux. These results indicate that macrophytes drive ecosystem metabolism but have limited influence on water column nutrient concentrations because macrophyte demand is much lower than the supply available from the water column. Thus macrophytes in our streams had a large impact on stream trophic state, but offered little potential to influence nutrient removal via management.     

Biofilm formation by Pseudoalteromonas ruthenica and its removal by chlorine

The distribution of a recently described marine bacterium, SBT 033 GenBank Accession No. AY723742), Pseudoalteromonas ruthenica, at the seawater intake point, outfall and mixing point of an atomic power plant is described, and its ability to form biofilm was investigated. The effectiveness of the antifouling biocide chlorine in the inactivation of planktonic as well as biofilm cells of P. ruthenica was studied in the laboratory. The results show that the planktonic cells were more readily inactivated than the cells enclosed in a biofilm matrix. Viable counting showed that P. ruthenica cells in biofilms were up to 10 times more resistant to chlorine than those in liquid suspension. Using confocal laser scanning microscopy it was shown that significant detachment of P. ruthenica biofilm developed on a glass substratum could be accomplished by treatment with a dose of 1 mg l-1 chlorine. Chlorine-induced detachment led to a significant reduction in biofilm thickness (up to 69%) and substratum coverage (up to 61%), after 5-min contact time. The results show that P. ruthenica has a remarkable ability to form biofilms but chlorine, a common biocide, can be used to effectively kill and detach these biofilms.     

Variability in adsorptive phosphorus removal by structural stormwater best management practices

Various best management practices (BMPs) utilizing sorption processes (SP) have demonstrated effectiveness for phosphorus (P) management in stormwater. However, the widespread use of these BMPs in urban areas has been limited by large land requirements and limited P removal capacity. Central to this study is the development of the urban wetland filter (UWF), a concept intended to overcome these limitations and provide a low-cost, easily implemented BMP that can meet urban P-management goals. Performance variation along with finite sorption capacity has limited the reliability of SP as a primary removal strategy. However, if variability were better understood and capacity made renewable, sorption of P to substrates could provide the option of a more rapid and (with less required retention time) more space-efficient sustainable removal strategy than biological uptake. The goal of this study was to identify and model major sources of variability in P removal by sorption, enabling better prediction and optimization of sorption performance and ultimately the development of a small-footprint stormwater BMP with efficient P removal ability. Experiments were conducted in bench-scale reactors with an iron-oxide sand substrate. Results included a physical-process model developed by considering the thermodynamic and kinetic properties of SP. Significant sources of variability included, by order of importance, magnitude of a solution/substrate concentration gradient, length of the “antecedent dry period” between loadings, and pH. Most importantly, results indicate the critical importance of a thermodynamic gradient between solution P and previously adsorbed P to achieve continued removal.     

Filter bed systems treating domestic wastewater in the Nordic countries – Performance and reuse of filter media

Nine filter beds have been constructed in the Nordic countries, Denmark, Finland, Norway and Sweden. Filter beds consist of a septic tank followed by an aerobic pre-treatment biofilter and a subsequent saturated flow grass-covered filter. Thus, filter beds are similar to subsurface flow constructed wetlands with pre-treatment biofilters, but do not have wetland plants with roots submerged into the saturated filter. All saturated filters contain Filtralite^®P, a light-weight expanded clay aggregate possessing high phosphorus sorption capacity. The filter bed systems showed stable and consistent performance during the testing period of 3 years. Removal of organic matter measured as biochemical oxygen demand (BOD) was >80%, total phosphorus (TP) >94% and total nitrogen (TN) ranged from 32 to 66%. Effluent concentrations of fecal indicator bacteria met the European bathing water quality criteria in all systems. One system was investigated for virus removal and somatic viruses were not detected in the effluent. The investigations revealed that the majority of the BOD and nitrogen removal occurred in the pre-treatment filters and the phosphorus and bacteria removal was more prominent in the saturated filters. The saturated filters could be built substantially smaller than the current design guidelines without sacrificing treatment performance. The used filter material met the Norwegian regulations for reuse in agriculture with respect to heavy metals, bacteria and parasites. When saturated with phosphorus, the light-weight aggregate, Filtralite^®P used in the saturated bed is a suitable phosphorus fertilizer and additionally has a liming effect.     

Nitrogen and phosphorus removal from wastewater by subsurface wetlands planted with Iris pseudacorus

Subsurface horizontal flow constructed wetlands are being evaluated for nitrogen (N) and phosphorus (P) removal from wastewater in this study through different gravel sizes, plant densities (Iris pseudacorus), effects of retention times (1 to 10 days) on N and P removal in continuously fed gravel wetland. The inlet and outlet samples were analyzed for TKN, NH₄-N, and NO₃-N, as standard methods. The planted wetland reactor with fine (SG) and coarse (BG) gravels removed 49.4% and 31.4% TKN, respectively, while unplanted reactors removed 43.4% and 26.8% TKN. Also, the efficiencies for NH₄-N were 36.7–43% and 21.6–25.4% for SG and BG planted reactors, respectively. The efficiencies for NO₃-N were 53.5–62.5% and 21.6–25.4% for SG and BG planted reactors, respectively. Roles of plants in SG reactors for O-PO₄ were 5–12% and 3–8% in BG. Also, the roles of plants in the reactors for TP were 9% and 7.4%. The minimum effective detention time for the removal of NO₃-N was 4–5 days. The subsurface constructed wetlands planted with I. pseudacorus can be an appropriate alternative in wastewater treatment natural system in small communities.     

Dynamics of nitrogen and phosphorus retention during wetland ecosystem succession

We compared the mechanisms of nitrogen (N) and phosphorus (P) removal in four young (<15 years old) constructed estuarine marshes with paired mature natural marshes to determine how nutrient retention changes during wetland ecosystem succession. In constructed wetlands, N retention begins as soon as emergent vegetation becomes established and soil organic matter starts to accumulate, which is usually within the first 1–3 years. Accumulation of organic carbon in the soil sets the stage for denitrification which, after 5–10 years, removes approximately the same amount of N as accumulating organic matter, 5–10 g/m²/yr each, under conditions of low N loadings. Under high N loadings, the amount of N stored in accumulating organic matter doubles while N removal from denitrification may increase by an order of magnitude or more. Both organic N accumulation and denitrification provide for long-term reliable N removal regardless of N loading rates. Phosphorus removal, on the other hand, is greatest during the first 1–3 years of succession when sediment deposition and sorption/precipitation of P are greatest. During this time, constructed marshes may retain from 3 g P/m²/yr under low P loadings to as much as 30 g P/m²/yr under high loadings. However, as sedimentation decreases and sorption sites become saturated, P retention decreases to levels supported by organic P accumulation (1–2 g P/m²/yr) and sorption/precipitation with incoming aqueous and particulate Fe, Al and Ca. Phosphorus cycling in wetlands differs from forest and other terrestrial ecosystems in that conservation of P is greatest during the early years of succession, not during the middle or late stages. Conservation of P by wetlands is largely regulated by geochemical processes (sorption, precipitation) which operate independently of succession. In contrast, the conservation of N is controlled by biological processes (organic matter accumulation, denitrification) that change as succession proceeds.     

Phosphorus dynamics in shallow eutrophic lakes: an example from Zeekoevlei,South Africa

Zeekoevlei is the largest freshwater lake in South Africa and has been suffering from hyper-eutrophic conditions since last few decades. We have used total P (TP), dissolved phosphate (PO₄ ³⁻), organic P (OP), calcium (Ca) and iron (Fe) bound P fractions to investigate the relevant physical, chemical and biological processes responsible for sedimentation and retention of P and to study phosphorus (P) dynamics in this shallow lake. In addition, redox proxies (V/Cr and Th/U ratios) are used to study the prevailing redox conditions in sediments. Adsorption by CaCO₃ and planktonic assimilation of P are found to control P sedimentation in Zeekoevlei. Low concentration of the labile OP fraction in surface sediments restricts the release of P by bacterial remineralisation. Low molar Ca/P and Fe/P ratios indicate low P retention capacity of sediments, and P is most likely released by desorption from wind-induced resuspended sediments and mixing of pore water with the overlying water column. Handling editor: J. Saros     

抚仙湖窑泥沟人工湿地的除磷效果研究

为了减缓和控制抚仙湖局部湖湾水体富营养化趋势,在抚仙湖北岸建设了净化面积1 hm²的人工湿地.综合利用生物氧化塘、水平潜流人工湿地和表面流人工湿地治理技术,对入湖河道窑泥沟污水中磷的去除效果进行了试验研究.结果表明,该人工湿地系统对磷具有较强的去除能力.总磷去除率在57.7%～81.10%之间,平均去除率为54.9%.单位面积磷滞留量平均为26 mg·m^-2·d^-1,其中,湿地植物同化作用磷滞留量为26.1 mg·m^-2·d^-1,约占磷滞留总量的10%,大部分磷去除是通过基质吸附和沉降作用,但主要湿地植物水芹的季节变化对相应功能区的除磷效果会产生一定影响.试验期间,各功能区单位面积磷滞留量依次为水平潜流人工湿地＞生物氧化塘＞沉淀池＞表面流人工湿地.     

Benthic sediment influence on dissolved phosphorus concentrations in a headwater stream

Phosphate interacts with inorganic sediment particles through sorption reactions in streams. Collectively, this phosphorus (P) buffering mechanism can be an important determinant of soluble reactive P (SRP) concentrations. If sorption reactions control SRP concentrations in a stream, then differences in sediment characteristics may cause spatial differences in SRP concentrations. This prediction was tested by examining sediment-buffering characteristics and spatial variation in SRP among reaches with distinct sediment composition (i.e., fine versus coarse particles) in two tributaries of Boulder Creek, a headwater stream in central Wisconsin. SRP concentrations were significantly lower and algal available P and P sorption capacity were significantly higher in the reach dominated by fine sediments. Although fine particles such as sand had the greatest P sorption capacity, no retention could be attributed to biotic processes, whereas over 50% of P retention in coarse particles such as gravel could be linked to biotic uptake. Equilibrium P concentration (EPC₀) assays from different sediment fractions also indicate that biotic uptake is relatively unimportant in sand particles (EPC_live 10 μg/L: EPC_killed 10 μg/L) but very important in gravel or larger particles (EPC_live 10 μg/L: EPC_killed 80 μg/L). Thus, sediment influence on stream water P concentrations can shift predictably from abiotic sorption in reaches with fine particles to biotic retention in areas dominated by coarse sediments. Consequently, changes in sediment composition due to natural or anthropogenic disturbance have the potential to alter the type and strength of sediment-associated processes determining ambient stream P concentrations.     

Influence of Submerged Plants on Phosphorus Fractions and Profiles of Sediments in Gucheng Lake

To understand the effect of submerged macrophytes on P in sediment, P fractions in the surface sediments (0–20 cm) of Potamogeton crispus, Potamogeton maackianus and non-vegetated areas were investigated. In the submerged macrophytes areas, the concentrations of HCl-P, NaOH-P, IP, OP and BD-P were significantly lower than in the non-vegetated area. NH₄Cl-P did not differ significantly among areas.

In the submerged macrophyte distribution areas, TP was significantly correlated with IP and OP. However, in the non-vegetated area, TP was significantly correlated with NH₄Cl-P and OP. In all of the areas sampled, IP was the major phosphorus fraction in the sediments, which consists largely of NAOH-P and HCl-P. The decreasing order of P fractions was: IP > HCl-P > NaOH-P > OP > BD-P > NH₄Cl-P. These results show that submerged macrophytes can decrease the concentrations of all P fractions and imply that submerged macrophytes play a key role in the retention of P nutrients.     

湿地植物供碳功能与优化

尾水湿地氮的反硝化去除往往受限于碳缺乏。综述了湿地植物供碳促反硝化的主要途径与影响因素,构建了华东地区典型冷、暖季型湿地植物供碳的一般性季节动态模式,以期为发挥湿地植物稳定高效供碳功能、缓解尾水湿地碳缺乏问题提供解决思路。湿地植物的主要供碳途径包括根系分泌、地下有机质分解和地上有机质分解(淋溶)等,湿地植物的供碳动态是物种和环境因子综合影响的结果,存在极大的时空异质性。湿地植物具有很强的供碳促反硝化潜力,地上最大生物量为5 kg/m~2的芦苇全年脱氮潜力可高达0.57 kg N/m~2。在构建的湿地植物生物质积累量和供碳量的一般性模式中,冷、暖季型湿地植物无论是生物质积累量(总生物量)和还是供碳量(分解部分+根系分泌物)均存在显著的季节性差异,以及季节间的互补特征。因此,冷、暖季型湿地植物间进行合理的配置,是发挥湿地植物供碳功能且避免生物质分解引起二次污染的可行性措施。今后在湿地植物供碳定量化研究方法、多种供碳途径的定量化监测、供碳功能调控策略,以及稳定高效供碳促反硝化人工湿地构建等方向需做进一步研究。     

Municipal wastewater treatment with vertical flow constructed wetlands for irrigation reuse

The treatment effect of two pilot-scale vertical flow constructed wetlands (VFCWs) on municipal wastewaters and their suitability for irrigation reuse were evaluated in a 2-year (2002–2003) experiment. One VFCW was planted with Typha latifolia and the other with Phragmites australis. VFCW efficiency was evaluated in terms of both mass removal and water quality improvement, considering the following parameters: pH, electrical conductivity (EC_w), total suspended solids (TSS), chemical oxygen demand (COD) and biochemical oxygen demand (BOD), total nitrogen (TN) and nitrate (NO₃^?), total phosphorus (TP) and orthophosphate (PO₄^3?), sodium (Na), potassium (K), magnesium (Mg) and calcium (Ca). The accumulation of the elements in the plant organs and VFCW sandy surface layer and their offtake with the macrophyte harvest were also measured.In quantitative terms the established VFCWs showed higher removal efficiencies (>86%) for COD, BOD, N and K, while lower efficiencies (<47%) were observed for Na and Mg. The direct contribution (offtake) of the macrophytes in N, P and K removal processes was particularly high (>65%) due to the massive growth. The results were less favourable in terms of water quality, because the high evapotranspiration losses counteracted the depuration process by concentrating the elements in the outflow water. Higher concentrations were found in outflow than inflow, especially of Na (relative increase of 89%) and Mg (relative increase of 74%). Only parameters with high removal efficiencies fulfilled the Italian guidelines for irrigation reuse whereas parameters with lower efficiencies (e.g., TSS, TP) limited the potential water reuse. Efficient pre-cleaning systems or innovative integrated systems are thus necessary to obtain high removal efficiencies that reduce the effect of ET on water quality.     

Use of dewatered alum sludge as main substrate in treatment reed bed receiving agricultural wastewater: long-term trial

This study aims to explore a novel application of dewatered alum sludge cakes (DASC) as the main medium in a single model reed bed to treat phosphorus-rich animal farm wastewater under "tidal flow" operation on a long-term basis. It is expected that the cakes act as the carrier for developing biofilm and also serve as adsorbent to enhance phosphorus (P) immobilization. Results have demonstrated that average removal efficiencies of 73.3+/-15.9% for COD, 82.9+/-12.3% for BOD(5), 86.4+/-6.0% for RP (reactive P), 88.6+/-7.2% for soluble reactive P (SRP) and 77.6+/-17.5% for SS can be achieved during the two year's operation. More significantly, the "P-adsorption proportion" by DASC in the reed bed is 42% of the overall P removal. The remaining removal of P may be contributed by the trapping and filtration process of DASC. Therefore, the lifetime of the DASC in reed bed is reasonably longer than that determined from the batch isotherm test.