Phytoremediation And Regulation Of Heavy Metals In Sludge Nutrient Soil By Turfgrass

The compost of municipal sludge is an economic and environmentally-friendly waste treatment technology of recycling,which can be used as garden soil.In this study,four kinds of turfgrass and their intercropping methods combined with the control of soil and plants for repairing heavy metals pollution?Cu,Zn,Pb,Cd,Ni?in municipal sludge.The three-factor and three-level field experiments were designed:seeding methods?Festuca arundinacea,Zoysia matrella+Lolium perenne,Cynodon dactylon+Lolium perenne?,citric acid?CA?spraying and auxin?IAA and GA₃?spraying.The main results were as follows:?1?Soil organic matter?SOM?in the municipal sludge was up to 204.8 g/kg and the pH was 7.6,which was a high-value greening substrate.The contents of heavy metals Cu,Zn,Pb,Cd and Ni were 48.75 mg/kg,658.2 mg/kg,80.70 mg/kg,3.71 mg/kg and 71.16 mg/kg,respectively.All metals,excepting Cd exceeded the standard value of2 mg/kg,met the requirements of Greening Soil Standards?CJ/T340-2016?.?2?Three factors had significant effects on plant growth,the main influencing factor was CA,followed by grass species and auxin.The largest biomass of the Zoysia matrella+Lolium perenne was 3.632 kg/?a.m²?in T3?400 ppm CA+30 ppm GA₃+5ppm IAA?,the largest biomass of Festuca arundinacea was 3.147 kg/?a.m²?in T6?400ppm CA+60 ppm GA₃?,the largest biomass of Cynodon dactylon+Lolium perenne was 2.885 kg/?a.m²?in T9?400 ppm CA+10 ppm IAA?,the best was T3.?3?Through the analysis of heavy metals in soil,the ratios of Cd and Zn in active states were larger than that of Cu,Pb and Ni.The added CA had the effect of activating heavy metals,which made some stable residual and oxidizable heavy metals transform to the reductive state and the acid extractable state.Meanwhile,the intercropping of turfgrass and the spray of auxin strengthened the effect,with the increase of the acid extractable state of Cu,Pb and Cd,the decrease of the reducible states of Zn and Ni and the increase of the residual state of Zn and Ni.?4?Turfgrass significantly enriched heavy metals.The concentration of heavy metals in the aboveground part of the treatment groups were 0.97¹.23,0.95¹.15,1.03¹.45,0.94¹.55,and 0.99¹.40 times of the control groups.The enrichment of Pb was mainly affected by the grass species,others were CA.The best repair groups of Cu,Zn and Pb were T9,and Cd and Ni were T3.The concentrations of heavy metals in the turfgrass in the underground part were higher than those in the aboveground part.The concentrations of heavy metals in the treatment groups compared with the control groups were Cu:0.92¹.24,Zn:0.97¹.09,Pb:0.96¹.11,Cd:1.00¹.42,Ni:0.89¹.36 times,in which the best combination of Cu,Zn and Ni was T9,and the best combinations of Pb and Cd were T6 and T3,respectively.Meanwhile,the enrichment of Cu,Cd and Ni in the underground part was mainly affected by CA,and the enrichment of Pb and Zn were mainly affected by grass species.?5?The analysis of plant enrichment factor?BCF?and transport coefficient?TF?showed that each treatment increased BCF,which were 1.04¹.52,1.04¹.96,1.05².07,1.10².62,1.03⁶.00 times,respectively.The most significant factor was the effect of CA,in which the best group of Cu and Pb was at T9,and Ni and Zn was at T5?Festuca arundinacea+200 ppm CA+5 ppm IAA+30 ppm GA3?,Cd was at T3.The transport coefficient of each metal was greater than the enrichment coefficient.The three factors affected the grass type>citric acid>auxin.The best group of Cu,Cd and Ni was T1?Zoysia matrella+Lolium perenne+CA 0 ppm+GA₃ 60 ppm?.The highest value of Pb appeared in T8?Cynodon dactylon+Lolium perenne+CA 200ppm+GA₃ 60 ppm?,and Zn was in T3.?6?The physical and chemical properties of soil significantly affected the enrichment of heavy metals in plants.The correlation analysis showed that BCF of each metal was negatively correlated with pH.SOM was negatively correlated with the BCF of heavy metals except Ni,indicating that SOM played an important role of stabilization and reduced heavy metal activity.Soil cation exchange capacity?CEC?showed a positive correlation with heavy metal enrichment,indicating that higher CEC were beneficial for plants to uptake heavy metals.The effect of SOM and pH on the TF of metals were more complex.However,CEC showed a promotion TF of metals,and all metals showed positive correlation with each other.?7?After one year of turfgrass planting,the residual effect of heavy metals in soil was analyzed for evaluating the repairing effect.The results showed that the contents of heavy metals in soil were significantly reduced.The best group for repairing heavy metals was T3,and the repair efficiencies were 36.4%of Cu,74.0%of Zn,34.8%of Pb,62.3%of Cd,27.1%of Ni.Cd met the limit of CJ/T340-2016.Through the potential ecological hazard risk assessment,the risk of heavy metals in soil was significantly reduced,the lowest risk group was T3,and the risk value of Cd was reduced from 265to 79,the total risk value was reduced from 329 to 117,and the repair effect was obvious.In summary,the T3 group was the best group for repairing.It was expected that the heavy metal content in the soil can meet the requirements of CJ/T340-2016 within one year.Through artificial regulation,it can effectively increase the enrichment coefficient and transport coefficient of heavy metals in plants,promoting the migration of heavy metals at the soil/grass interface,and shortening the repair time.This study had great significance for the resource utilization of municipal sludge,and also provided a theoretical basis for the commercialization of turfgrass to repair soil heavy metals.