| The sources of heavy metal waste water are wide and various, so it is very hard to be removedfrom the environment. After realizing the hazard of the heavy metal on environment especially onhuman being, people have took a great variety of measures, such as Chemical Precipitation Method,Ion Exchange Adsorption Method, Electrolytic Process and Separation Membrane etc, while allthese methods have their own advantages, disadvantages and application scope. With lowinvestment, low energy, low management fees, and strong resistance to impulsive force,Constructed Wetlands is the sewage disposal technology integrated with environmental benefit,economic benefit and social benefit. In recent years, researchers began to use ConstructedWetlands to deal with heavy metal waste water. They all think that Constructed Wetlands with itsspecial ecosystem Matrix-Plant-Microorganism, can play an important role in handling heavymetal waste water.Then this paper retrospect the current situation of heavy metal pollution in environment andthe research progress of Constructed Wetlands in dealing with heavy metal waste water. The objectof study in this paper is the5thseries of Zao River---the model of constructed wetland. The studychooses11sampling point. Sampling point1to6based on sand and soil and the interval amongeach sample is16meters; sampling point7-11based on sand and aluminum mud, its interval is6meters. This paper analysis the content and distribution characteristic of the heavy metals in wastewater in the matrix of constructed wetland both in the horizontal direction and vertical direction.This paper studys the distribution of the heavy metals in waste water in constructed wetland in thehorizontal direction and studys the distribution rules of the heavy metal form in the surface of thematrix in sample region and different levels of matrix. Then through comparing, this paper probeinto the relevance between different forms of heavy metals and the whole content. The conclusionsare as follows:1. The order of the average content of the heavy metals in Zao River constructed wetland(soiland sand)is Zn>Cr>>Cu> Pb>Ni>Cd. From the whole research, we can see that the averagecontent of heavy metals (Cr、Cu、Pb and Zn) is higher than the environmental background value, inwhich the content of Zn and Cr are higher and they exceed339.8%and247.3%separately.2. The order of the average content of the heavy metals in Zao River constructedwetland(sand and aluminum)is Cr>Zn>Cu>Pb>Ni>Cd. From the whole research, we can seethat the average content of heavy metals (Cr、Cu、Pb Zn and Ni) is higher than theenvironmental background value, in which the content of Cr and Zn are higher and they exceed115.7%and178.8%separately.3. As a whole, the heavy metals in soil and sand in the horizontal direction are in afalling trend from high to low. In other words, with the increase of the distance from theentrance in constructed wetland, the content of heavy metals are all decreasing. They arestable when decreased to the level of sample3(48m). The high value of each heavy metal isin the entrance of the constructed wetland also the nearest region of the Zao River waste water.This shows that the content of the heavy metals are very high in Zao River.4. The heavy metals in sand and aluminum in the horizontal direction are rising, whichmeans the content of each heavy metal is rising with the increase of distance from theentrance of the constructed wetland.5. The content of Cu, Pb and Ni in each sampling site in the vertical direction is stable,but the content of Zn, Cd and Cr is changing, in which the content of Cd is increasingobviously.6. The four forms (weak acid soluble, reducible, oxidizable state, the residue state),different changes of heavy metal elements in different sampling points are not the same; theweak acid extractable, all kinds of metal elements (except Pb) content with the distanceincreasing and decreasing. For the reduced state, the contents of Pb and Zn elements was firstincreased and then decreased along with the increase of distance; the content of Cu, Cd and Nielements with an upward trend the increase of distance, but the rise is not big; the content ofelement Cr tends to be stable. The oxidation state, the contents of Pb and Zn elements wasfirst increased and then decreased along with the increase of distance; the contents of Cu andCr elements with an upward trend to increase the distance; the contents of Cd and Ni elementsas the distance decreases, the content from the point1to point at3sharp down, in the sampleafter3of its content tends to be stable. For the residual state, the contents of Pb, Cu and Znelements was first increased and then decreased along with the increase of distance; thecontent of Cd and Cr elements as the distance decreases, but its content is reduced greatly; thecontent of the Ni element with the distance increasing basic stable.7. The regularities of distribution of the six heavy metals in different levels of matrix areas follows: the content of the non-residual state in the superficial of the matrix all exceed10-15cm,15-20cm except Cr. The content of potential available state is bigger than that in thedeep zone. From the point of proportion, the proportion of Cd and Cr in the non-residual statein0-5cm and10-15cm is almost the same, both are higher than15-20cm; the distribution ofnon-residual state in Cr and Ni in different soil layers are similar; the proportion of Cu innon-residual state is in increasing trend with the increasing of the depth of the matrix; thedistribution of the Zn in different soil layers is special, the proportion of non-residual state in 5-10cm is higher than in0-5cm and15-20cm. In general, the residual state in all layers of thematrix is still the main mode of occurrence of the six heavy metals.8.Four forms of six kinds of heavy metals (B1, B2, B3, B4were weak acid soluble,reducible, oxidizable, residue). Between the residual and total showed significant correlation,among them, Pb:rB4-B=0.936(P≤0.01), Zn:rB4-B=0.952(P≤0.01), Cu:rB4-B=0.912(P≤0.01), Cd:rB4-B=0.957(P≤0.01), Cr:rB4-B=0.670(P≤0.01), showed significant correlation;Ni:rB4-B=0.734(P≤0.05) is significantly related to. |
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