Study On The Removal Of Complex Heavy Metal Wastewater By Constructed Wetlands With Different Substrates

Matrix as a main component of artificial wetland,is the key to improve the ability of artificial wetland purification,so choose a suitable substrate of artificial wetland treatment of heavy metal wastewater has a decisive role,on this basis,this study of compound of heavy metal wastewater by setting the biological carbon and zeolite adsorption experiment,to explore the biological carbon and zeolite adsorption characteristics of a variety of heavy metals and the adsorption ability,be it as a feasibility analysis of artificial wetland substrate packing;Artificial wetland in the actual operation to maintain long-term processing stability is very important,through the simulation experiment of greenhouse,adding zeolite and biochar construct control-constructed wetland,zeolite-constructed wetland,biochar-constructed wetland and zeolite+biochar-constructed wetland（hereinafter referred to as Feisheng-constructed wetland）four groups of artificial wetland system,a long-term water quality determination,this study constructed wetland,many different substrates for long-term treatment effect of compound of heavy metal wastewater and the flow and distribution of heavy metals in the constructed wetland;And by changing the matrix filling ratio,explore the optimization of constructed wetland structure,improve the treatment of complex heavy metal wastewater further methods,by setting different biochar and zeolite ratio,Build control-constructed wetland,10% biochar+90%zeolite-constructed wetland（hereinafter referred to as 10% biochar-constructed wetland）,20% biochar+80%zeolite-constructed wetland（hereinafter referred to as 20% biochar-constructed wetland）,30% biochar+70% zeolite-constructed wetland（hereinafter referred to as 30% biochar-constructed wetland）,40% biochar+60% zeolite-constructed wetland（hereinafter referred to as 40% biochar-constructed wetland）and 50% biochar+50% zeolite-constructed wetland（hereinafter referred to as 50% biochar-constructed wetland）,to explore the different ratio of substrate removal effect of compound of heavy metal wastewater.According to the effluent quality of constructed wetland and the content of heavy metals in plants,substrates and sediments,combined with the adsorption characteristics of biochar and zeolite substrates,the treatment of complex heavy metal wastewater by constructed wetlands with different substrates was studied,which provides theoretical basis for the treatment of complex heavy metal wastewater by constructed wetlands in China.The main results are as follows:1.Adsorption characteristics of zeolite on complex heavy metals（1）At different initial concentrations,the removal rates of zeolite and biochar on the five metals showed a trend of gradually decreasing,while the adsorption amount gradually increased.The maximum removal rates of Cu²⁺,Zn²⁺,Pb²⁺,Cr⁶⁺and Cd²⁺were 90.58%,89.32%,95.46%,90.40%,85.35%respectively.The maximum removal rates of Cu²⁺,Zn²⁺,Pb²⁺,Cd²⁺and Cr⁶⁺by biochar were 99.24%,99.74%,99.70%,85.06%,96.19%respectively.At high concentration,strong competitive adsorption is produced,and the competitive ability of Pb²⁺is stronger,the competitive ability of Zn²⁺and Cd²⁺is the weakest,and the low concentration is more conducive to the removal of Zn²⁺and Cd²⁺.（2）When pH is different,the removal rate and adsorption capacity of zeolite and biochar on five kinds of metals increase with the increase of pH,and the trend of increasing gradually slows down.After equilibrium adsorption,the order of the amount of metals resolved by zeolite and biochar is Pb²⁺>Cu²⁺>Cr⁶⁺>Zn²⁺>Cd²⁺.The adsorption of Cu²⁺,Zn²⁺,Pb²⁺and Cd²⁺by zeolite has a higher fitting degree to Langmuir equation,and the monolayer adsorption indicated by homogeneity is the main adsorption degree,while the adsorption degree of Cr⁶⁺and Freundlich equation is higher,and the multi-layer adsorption is the main adsorption degree.Biochar mainly adsorbed Cu²⁺and Cd²⁺by monolayer,and Zn²⁺,Pb²⁺and Cr⁶⁺by multi-layer adsorption on heterogeneous surface.2.Study on the removal of complex heavy metal wastewater by constructed wetlands with different substrates（1）pH of Feisheng group>Biochar group>Zeolite group,and the three groups were significantly higher than the control group（P<0.01）,which is due to the biochar and zeolite as a matrix,can play a certain neutralization effect;All constructed wetlands were anaerobic,and DO in the effluent was lower than 0.6 mg·L^-1,and there was no significant difference in DO among the four groups（P<0.05）.（2）Among the four groups of constructed wetlands,the removal rates of COD,NH₄⁺-N,TN and TP in Feisheng-constructed wetlands were 95.83%,83.95%,89.91%,64.54%,respectively,and significantly higher than those in other groups（P<0.05）,can maintain a good long-term effluent water quality.The removal rates of five metals in the four groups of wetlands decreased at the later stage of the experiment.For Cu,the removal effect was the best within 69 days,and the effluent concentration of the upper and lower layers was lower than the comprehensive sewage discharge standard（GB8978-1996）(<0.5 mg·L^-1).The effluent of Pb,Cd and Cr in the four groups of constructed wetlands were all lower than the maximum concentration standard for comprehensive sewage discharge（GB8978-1996）,and the removal rates of Cu,Zn,Pb,Cd and Cr in the boiling group were the highest,which were98.72%,98%,98.72%,99.01%and 98.65%,respectively（P<0.05）.3.Distribution of heavy metals in constructed wetlandsThe accumulation of heavy metals in Acorus calamus was mainly concentrated in the underground,but the accumulation of heavy metals in the plant body was relatively low.The accumulation of heavy metals in sediments and substrates,especially substrates,is the main part of heavy metal removal.Among the four parts of effluent,substrate,sediment and plant,the accumulation ratio of heavy metals in substrate was the highest,ranging from 77%to 96%.The accumulation ratio of Cd in five metals was the least.The matrix accumulation ratio of boileotrophic group was significantly higher than that of the other three groups（P<0.05）.4.Study on the removal of complex heavy metal wastewater by constructed wetland with different matrix ratio（1）The pH of constructed wetlands in the five groups with biochar was significantly higher than that of the control group（P<0.01）;The higher the addition amount of biochar,the more conducive to the removal of NO₃^--N,NH₄⁺-N and TN,and the 50%biochar group had the best removal effect（P<0.05）;Three groups of constructed wetlands with more biochar were more conducive to TP removal,and there was no significant difference between 30%,40% and 50%ratio（P>0.05）.（2）The effluent concentration of the five metals is more stable in the first month of stable operation of all devices,and the general rule is the effluent concentration of the lower layer>Upper outlet water（P<0.01）20% biochar group has the best removal effect on metal Cu,Zn,Pb and Cr,but different matrix ratio has no significant effect on metal（P>0.05）;In the six groups of constructed wetlands,the addition of biochar in the heavy metal adsorption capacity of sediments and substrates was higher than that of the control group,but there was no significant difference between different matrix ratios,which confirmed that different matrix ratios had no significant influence on the metal removal effect.