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
Before our presentation,I will introuduce you some new words.
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.
Now？I 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) 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:
including soil 、sands、rocks 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.
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
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 wetland？it cost some
residence time to get purified.
1. Meanwhile？the plants will absorb nutritions such as N and P to
2. The microorganisms will decompose some organics from the
wastewater to live.
3. the suspended solids of wastewater would be primary removed？and
few metallic elements；such as Fe 、Zn？within substrate can absorb
+N、P、NH-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 processes？most of the pollutants have been
removed ,the water is purified.
Application and examples
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.
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，
3、 low-energy option
4、 beautiful landscape
1、a great area
2、be suited for low concentration wastewater
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
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 time，the
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.