Floating treatment wetlands as biological buoyant filters for wastewater reclamation

Abstract

Floating treatment wetlands (FTWs) are an innovative product of ecological engineering that can play a promising role in wastewater treatment. It provides low-cost, eco-friendly, and sustainable solutions for the treatment of wastewater, particularly in regions with economic constraints. Generally, FTWs comprise rooted plants that grow on the surface of water with their roots extending down into the pelagic zone rather than being embedded into the sediments. This drooping structure helps develop (1) a hydraulic flow between the root network and the bottom of the treatment system and (2) a large biologically active surface area for the physical entrapment (filtration) of contaminants, as well as their biochemical transformation and degradation. Furthermore, the rooted network allows proliferation of microorganisms that form biofilms and enhance pollutant degradation while promoting plant growth. The augmentation of bacteria in FTWs has been proven to be the most effective approach for reclamation of wastewater. This article discusses the operational parameters of FTWs for maximal remediation of wastewater and highlights the importance of plant-bacteria partnerships in a typical FTW system for enhanced cleanup of wastewater. We propose that this technology is preferable over other methods that require high energy, costs, and area to install or operate machinery.     

Long-distance dispersal of the coconut palm by migration within the coral atoll ecosystem

Background

The location of the original home of the coconut palm, Cocos nucifera, and the extent of its natural dispersal are not known. Proponents of a South American origin must explain why it is not indigenous there and why it shows greatest diversity in southern Asia. Conversely, proponents of an Asian origin must explain why there are no Asian Cocoseae and why the closest botanical relative to Cocos is in South America. Both hypotheses share the common problems of how, when, where and in what directions long-distance dispersal occurred.

Hypothesis

These difficulties are resolved by accepting that C. nucifera originated and dispersed by populating emerging islands of the coral atoll ecosystem, where establishment conditions impose high selection pressures for survival. When lifted by wave action onto virtually sterile, soilless coralline rocks just above sea level and exposed to the full impact of the sun, seednuts must germinate, root and establish vigorous populations. The cavity within the nut augments the buoyancy provided by the thick husk, which in turn protects the embryo and, by delaying germination, simultaneously extends viability while floating and provides a moisture-retentive rooting medium for the young seedling. These adaptations allow coconuts to disperse widely through the coral atoll ecosystem.

Conclusions

The monthly production of fruit and the long floating duration ensure that viable seednuts are always available in the lagoon to replace those destroyed by hurricanes and tsunamis, or to populate newly emerged coral atolls elsewhere. Long-distance dispersal is secondary, because it was the spontaneous, independent migration of coral polyps on a prolonged geological time scale that generated new coral atolls in new areas where the coconuts would be amongst the earliest inhabitants. The coconut palm became an intermittent, itinerant, pioneer endemic there, and also on suitable beaches on volcanic or large islands and continental coastlines.     

Formulation and Evaluation of Gastroretentive Dosage Forms of Clarithromycin

The purpose of this research was to develop the hydrodynamically balanced delivery system of Clarithromycin (CLA) which, after oral administration should have the ability to prolong gastric residence time with the desired in vitro release profile for the localized action in the stomach, in the treatment of Helicobacter pylori (H.pylori) mediated peptic ulcer. By applying wet granulation technique floating tablets of Clarithromycin were prepared. The proportion of sodium bicarbonate was varied to get the least possible lag time, also the polymer part varied to get the desired release. In vivo radiographic studies were performed with Barium sulphate loaded formulation to justify the increased gastric residence time of the dosage form in the stomach, based on the floating principle. The formulation developed using 66.2% Clarithromycin, 12% HPMC K4M polymer, 8% sodium bicarbonate gave floating lag time less than 3 min with a floating time of 12 h, and an in vitro release profile very near to the desired release. X-ray studies showed the enhanced gastric residence time of the tablet to 220 ± 30 min. The mechanism of release of Clarithromycin from the floating tablets is anomalous diffusion transport and follows zero order kinetics. In vivo radiographic studies suggest that the tablet has increased gastric residence time for the effective localized action of the antibiotic (Clarithromycin) in the treatment of H.pylori mediated peptic ulcer.     

Wax-incorporated Emulsion Gel Beads of Calcium Pectinate for Intragastric Floating Drug Delivery

The purpose of this study was to prepare wax-incorporated pectin-based emulsion gel beads using a modified emulsion-gelation method. The waxes in pectin–olive oil mixtures containing a model drug, metronidazole, were hot-melted, homogenized and then extruded into calcium chloride solution. The beads formed were separated, washed with distilled water and dried for 12 h. The influence of various types and amounts of wax on floating and drug release behavior of emulsion gel beads of calcium pectinate was investigated. The drug-loaded gel beads were found to float on simulated gastric fluid if the sufficient amount of oil was used. Incorporation of wax into the emulsion gel beads affected the drug release. Water-soluble wax (i.e. polyethylene glycol) increased the drug release while other water-insoluble waxes (i.e. glyceryl monostearate, stearyl alcohol, carnauba wax, spermaceti wax and white wax) significantly retarded the drug release. Different waxes had a slight effect on the drug release. However, the increased amount of incorporated wax in the formulations significantly sustained the drug release while the beads remained floating. The results suggest that wax-incorporated emulsion gel beads could be used as a carrier for intragastric floating drug delivery.     

Everglades tree island restoration: testing a simple tree planting technique patterned after a natural process

Tree islands in the Everglades are critical landscape features, but anthropogenic modification of the Everglades during the past century has led to the degradation and loss of many of the tree islands that originally dotted the Everglades landscape. Many of the tree islands have lost elevation and the majority of their woody species such that they are now covered with emergent plants such as sawgrass (Cladium jamaicense). A simple, cost‐effective tree planting technique is needed for restoring degraded Everglades tree islands. We patterned our design after a natural Everglades process that creates floating islands, which promotes tree survival and growth in both flooded and dry conditions and may lead to the development of fixed islands. Commercial peat bags were tested as a means to provide the medium for the growth and establishment of potted tree saplings native to Everglades tree islands. Three tree species (Annona glabra, Ficus aurea, and Acer rubrum) and five treatments were evaluated. The results indicate that the preferred deployed peat‐bag configuration should provide the greatest additional elevation to minimize inundation and be planted with a single Everglades tree island species sapling, with a single commercial tree fertilizer spike inserted for nutrients. Although most plants survived and many thrived for the two‐year period of this study, determining whether the trees planted using this technique can become established will require longer‐term studies and extensive field tests.     

上海乡土水生植物资源及其在水生态恢复与水景观建设中的应用潜力

水生植物作为水生生态系统的主体, 对发挥水生生态系统的自维持、自循环功能有重要作用。研究通过相关资料的查阅, 建立上海地区乡土水生植物名录, 并对其科属组成、区系特征、生活型、生长型等进行统计分析。结果表明上海地区乡土水生植物共计35 科83 属160 种(含变种), 单属科、单种属的比例较高, 均达65%以上; 植物区系组成丰富、成分复杂, 以热带成分占优势, 达64.6%; 生活型以挺水植物为主, 沉水植物次之, 浮水植物最少; 生长型类型丰富, 以草本型、禾草型居多, 20 种生长型可进一步归为表征相似生态学特征和功能地位的6 个生长型组。在水生态恢复与水景观建设中, 仅有68.8%的景观水体有水生植物应用,且应用种类在2 种以下的占79.2%。乡土水生植物应用不足, 一半以上为观赏性强的外来物种, 应用频率较高的为挺水植物, 对具有良好净化效果的沉水植物重视不够。因此, 在水生态恢复与水景观建设中, 建议加强乡土水生植物资源的繁育栽培, 在充分利用乡土水生植物资源配置群落的基础上, 根据水质的富营养及基底状况, 通过不同生长型组水生植物的应用, 构建沉水-浮水-挺水植物群落复合体, 并通过近自然型护岸的营造, 形成水生-湿生复合生态系统。运用植被工程学的原理和方法, 采用生态浮岛、生态沉岛等技术营造水生植被, 将强人工化的水景观建成具生命的水生生态系统。