Researched On Effects Of Speciation Of Metals In Liaohe River Estuary Reed Wetland Irrigated By Papermaking Wastewater

The LiaoheRiver estuary wetland is the first largest reed wetland in China.In recent years,due to the lack of natural precipitation in wetlands,the use of papermaking wastewater has become the main way of wetland irrigation.However,there are a variety of metal contaminants in papermaking wastewater,long-term irrigation can cause accumulation of metal in wetland soil.And there is a different speciation for each metal in soil,which decide the metallic biological toxicity,therefore,it is necessary to determine the morphological changes and accumulation mechanism of metals in reed wetland soil under the wastewater irrigation.In this study,the effect of papermaking wastewater irrigation on the morphological distribution of iron,aluminum,zinc,copper and manganese in wetland soil had been studied by simulating LiaoheRiver estuary with experimental device schemes.The redistribution process of different forms of five metals by redistribution model had been identified,and the coupling model of geoaccumulation index with triangular fuzzy number had been used to evaluate the pollution level,this can provide theoretical basis and guidance for regulating metal content in wastewater and wetland.The main findings were as follows:(1)The residual fractions were the main forms of the five metals in wetland.The other three forms had different contents:iron and aluminum were reducible,oxidizable and weak acid fractions from more to less;zinc and copper were oxidizable,reducible and weak acid fractions;while manganese was reducible,weak acid and oxidizable fractions;(2)The residual fractions of metals reduced under irrigation by papermaking wastewater,which indicated that papermaking wastewater could promote the increase of metal activity and promote the absorption of metal to plants.There was an increase of weak acid and reducible fractions for iron and aluminum,while the content of the oxidizable fractions was decreased.The content of the weak acid,reducible and oxidizable fractions for zinc and copper increased;for manganese,the weak acidis increased and the reducible fractions decreased,the oxidizable fractions was almost unchanged.The use of low concentration of wastewater can promote the release of metal activity,but inhibit with the increase of high.(3)With the different growth period of reed,the change trend of different metal forms was different:the weak acid fractions for iron and aluminum increased first and then decreased,while for zinc,it increased slightly,for copper and manganese,it decreased first and then increased.The change trend of reducible fractions was different for different metals:for iron and aluminum,it did not change significantly with the time,and for zinc,copper and manganese,it increased;The change trend of iron,aluminum and zinc oxidation was relatively low,and the change was stable.the change of copper oxidation state was "N" shape,and the oxidation state of manganese increases with time.The residual fractions of five metals gradually increased with time,but there is a slightly decreased in May and June,and decreased after June.(4)Compared with the control soil,the five metals in wetland soil were redistributed after irrigated papermaking wastewater,the greatest impact on redistribution process of zinc and copper,followed by manganese,iron and aluminum.The redistribution of different forms for each metal stabilized gradually with the time.The redistribution coefficient of each metal showed regularity with the change of reed growth period:iron and aluminum were almost no redistribution in May.and the redistribution coefficient was the largest in June and September,indicated that the speciation distribution of the two metals in the two months was the most unstable And the redistribution coefficient of zinc and copper was significantly higher than that of other metals,the down order of the months was basically the same as August,September,June,October and May.The redistribution coefficient of manganese was between the two groups of metals,it was the largest in August,and the distribution of manganese is the most unstable.(5)Irrigation by papermaking wastewater can reduce the strength of metal with soil in wetland,making it more easily absorbed by plants.The irrigation had little effect on the bonding strength of iron and aluminum to soil,but it still had a certain effect on reducing the residual fractions.With the increase of irrigation concentration,the strength of each metal decreases first and then increased.More conducive to reducing the metal in the soil bonding strength of low concentration of wastewater.(6)Based on the index of geoaccumulation and the triangular fuzzy number model,the comprehensive evaluation model of soil metal pollution combined with the double biotoxicity weight coefficient between chemical forms and metal itself can make up the deficiencies in the deterministic evaluation,To comprehensively evaluate the risk of heavy metal enrichment and potential biotoxicity in wetland soil.(7)The comprehensive evaluation model of heavy metal pollution in soils was used to evaluate the metal pollution in LiaoheRiver estuary reed wetland,the results was that:the pollution degree of metals in wetland soil was sorted by high to low order:copper,zinc,manganese,aluminum and iron,it was the highest value for copper,followed by zinc and manganese,aluminum and iron comprehensive evaluation value is relatively low.Irrigation by papermaking wastewater should be appropriate to reduce the content of copper,zinc and manganese in wastewater,to prevent its long-term accumulation of wetland pollution problems.