/pdf/treatment-wetlands-second-edition-4pf3o7i6u6.pdf

Treatment Wetlands, Second Edition

It has been estimated that wetlands occupy approximately 6% of the earth’s land surfaces (Maltby 1991). They comprise fresh, brackish and salt-water marshes, inland and coastal swamps, flood plains, and lowland and upland mires (fen, bogs), as well as agricultural wetlands such as rice paddy. On a smaller scale there are constructed wetlands valued for their role in the purification of domestic, agricultural and industrial effluents (Cooper & Findlater 1990). In addition to these examples, occasional soil flooding and even a degree of submergence can be a common though unwelcome feature of non-wetland agriculture. Wetlands are usually characterized by permanent or long-term soil flooding, but often the vegetation may be wholly or partly submerged; in the lower reaches of coastal marshes this may be a daily or twice daily occurrence. Indeed, since wetlands are found world-wide and at most altitudes, flooding regimes can vary enormously; not only do the seasonal timing, duration and depth of flooding differ, but so too do light and temperature regimes and sediment type—factors which strongly interact with flooding to influence vegetation. The large numbers and wide variety of vascular plants indigenous to wetlands reflect this variety in habitat features; species range from wholly submerged aquatics of pools, rivers, coastal and lake margins through to the large tree species of the flood plain forests of the Americas and Africa. In view of this variety in both plant and habitat, a whole spectrum of flood-related stresses might be anticipated; similarly one might expect to find a number of flood-tolerance strategies.

/pdf/mechanisms-of-flood-tolerance-in-plants-49u929yrvv.pdf

Mechanisms of flood tolerance in plants

The presence of macrophytes is one of the most conspicuous features of wetlands and their presence distinguishes constructed wetlands from unplanted soil filters or lagoons The macrophytes growing in constructed wetlands have several properties in relation to the treatment process that make them an essential component of the design However, only several roles of macrophytes apply to constructed wetlands with horizontal subsurface flow (HF CWs) The plants used in HF CWs designed for wastewater treatment should therefore: (1) be tolerant of high organic and nutrient loadings, (2) have rich belowground organs (ie roots and rhizomes) in order to provide substrate for attached bacteria and oxygenation (even very limited) of areas adjacent to roots and rhizomes and (3) have high aboveground biomass for winter insulation in cold and temperate regions and for nutrient removal via harvesting The comparison of treatment efficiency of vegetated HF CWs and unplanted filters is not unanimous but most studies have shown that systems with plants achieve higher treatment efficiency The vegetation has mostly a positive effect, ie supports higher treatment efficiency, for organics and nutrients like nitrogen and phosphorus By far the most frequently used plant around the globe is Phragmites australis (Common reed) Species of the genera Typha (latifolia, angustifolia, domingensis, orientalis and glauca) and Scirpus (eg lacustris, validus, californicus and acutus) spp are other commonly used species In many countries, and especially in the tropics and subtropics, local plants including ornamental species are used for HF CWs

Plants used in constructed wetlands with horizontal subsurface flow: a review

The use constructed wetlands with horizontal sub-surface flow for various types of wastewater

Phytoremediation of soils contaminated with organic pollutants.

Elimination of sulphur compounds from wastewater by the root zone process—I. Performance of a large-scale purification plant at a textile finishing industry

Elimination of sulphur compounds from wastewater by the root zone process—II. Mode of formation of sulphur deposits

The sulphur content of domestic waste water is similar to its phosphorus and nitrogen content. In conventional treatment processes sulphur compounds are converted to sulphate, thus all reaching the recipients and the oceans. In the aquatic metabolic cycle sulphate then acts as a catalyst towards anaerobiosis. Therefore, besides its efforts for removal of other nutrients, waste water technology should look for possibilities of minimizing the discharge of sulphurous effluents into the water course. Here, a new treatment process for sulphur elimination is introduced, the Root Zone method.

Margarita Winter

Papers

Elimination of sulphur compounds from wastewater by the root zone process—I. Performance of a large-scale purification plant at a textile finishing industry

Elimination of sulphur compounds from wastewater by the root zone process—II. Mode of formation of sulphur deposits

Sulphur compounds—their environmental aspect and their elimination from waste water