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Constructed wetland

By Frank Jones,2014-04-22 23:37
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Constructed wetland

Helloeveryone. ;蓝色部分为解释内容?

    My name is ~~~I come from group1.I am so glad to be here . Today we are going to learn about Constructed wetlands for wastewater

    treatment.

    Before our presentation,I will introuduce you some new words.

     Introduction

    When we think of wetlands, we usually envision a picture about a natural wetland?a great area with shallow water where full of exuberant aquatic plants and sometimes you will see serval waterfowls walking on it to seek foods.

    NowI will show you some pictures about the real natural wetland

    Nowadays, using constructed wetland to treat wastewater has become more and more popular. Our team’s work is to introduce this process to all of you

    Constructed wetland(CW)

    Constructed wetland (CW) is a biogeochemical and highly efficient system to treat wastewater generating from different sources such as domestic ,highways ,mining and industrial sectors.

    In general, CWs can be grouped into two categories as of freewater surface and of subsurface-flow. The subsurface-flow CW can be further divided as of horizontal subsurface-flow and of vertical subsurface-flow based on detail fluent characteristics.

Three elements of CW:

    Substrate:

    including soil sandsrocks et la. It can filtrate and absorb pollutants. Wetland plants:

    Wetland plants play an important role for the functions of the total CW system, absorbing pollutants and

    creating favorable environments for bacteria.

    Microorganism:

    Mechanism

    Water cleaning by constructed wetland is particularly suited for wastewater which contains not so high concentration pollutants such

    as domestic wastewater municipal wastewater stormwater and so

    on.

    The process of water purification is mainly replys on the combination action of hytoaccumulation?植物吸收: biodegradation?生物降

    解:、physisorption?物理吸附:and chemical reaction?化学反应:.

    When wastewater flows into the constructed wetlandit cost some

    residence time to get purified.

    1. Meanwhilethe plants will absorb nutritions such as N and P to

    grow up.

    2. The microorganisms will decompose some organics from the

    wastewater to live.

3. the suspended solids of wastewater would be primary removedand

    few metallic elementssuch as Fe Znwithin substrate can absorb

    +NPNH-N at the same time. Other substances could be removed 4

    or its concentration(COD) decrease through the interaction of

    microorganism and plants.

    4. After the above processesmost of the pollutants have been

    removed ,the water is purified.

    Application and examples

    Example1:

    CW offers an effective alternative to traditional wastewater treatment system.

    This picture can simply explain the mechanism of a continuous free surface flow wetland which is used to remove the heavy metals from

industrial wastewater, in Swabi, Pakistan.

    Industrial wastewater flows into its in-let, then have close contact with substrate, it finally comes out from out-let.

    Thanks to the Z shaped path, the microorganism have enough time to cut down the concentration of the pollutants,so that the pollutants can be removed efficiently.

    The removal of heavy metals from industrial wastewater and its removal performance was in order of Cd>Cr>Fe>Pb>Cu>Ni. The removal efficiencies of the CW for Pb,Cd,Fe,Ni,Cr,andCuwere 50%,91.9%,74.1%,40.9%,89%,and48.3%,respectively.

    Example2:

    This picture is about a vertical subsurface-flow constructed wetland in Beijing which consists of membrane, substrate, plants, pumps and pipes.

    With the treating capacity of 200 m3/d, the average treatment cost in the Longdao River CW is summed up to 0.230 RMB/m3. ADVANTAGES

    A constructed wetland offers us a comparatively low-cost, low-maintenance, and low-energy option for wastewater treatment. The plants also make a significant contribution to the constructed wetland which becomes a beautiful landscape.

    So the advantages can be refer to

    1 low-cost

    2 low-maintenance

    3 low-energy option

    4 beautiful landscape

    DISADVANTAGES:

    1a great area

    2be suited for low concentration wastewater

    3limited capacity

    4substrate’s saturation

1. Building a constructed wetland always requires a great area

    and it is very difficult to get in an crowed city. 2. The constructed wetland is just suited for low concentration

    wastewater it can’t purify some high concentration industry

    wastewater.

    3. The process of purification needs a proper residence time

    so the handling capacity of wastewater has been limited. 4. After the constructed wetland applied for a period of timethe

    substrate would become saturated so that it can’t absorb

    pollutants of the wastewater. The situation becomes even

    worse when they may have the opportunity to release

    pollutants outward so that cause pollution again.

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