Mycorrhizoremediation And Its Enhancement Technology For Farmland Soil Contaminated By Polycyclic Aromatic Hydrocarbons (PAHs)

Abstract: The problem of polycyclic aromatic hydrocarbons (PAHs)-contaminated farmland soil is becoming increasingly serious in some areas of China with the rapid development of economy and the acceleration of industrialization process. PAHs are a group of persistent organic pollutants with the strong carcinogenic, teratogenic, mutagenic potential, which have shown high environmental risks. In this thesis, the mycorrhizoremediation and its enhancement technology for PAHs-contaminated soil were conducted base on the farmland soil that had long been contaminated by PAHs in Wuxi, Jiangsu province. The main contents include effects of AM fungi on phytoremediation of PAHs-contaminated soil, effects of organic wastes on the degradation of PAHs in soil and the study on enhancement of organic wastes in mycorrhizoremediation of PAHs-contaminated soils. The main results were as follows:(1) A greenhouse pot-experiment was carried out to investigate effects of indigenous and exogenous AM fungi on phytoremediation of PAHs-contaminated soil by alfalfa (Medicago sativa L.) and ryegrass (Lolium muhiflorum L.). Inoculation of adventive Glomus caledonium 36 enhanced significantly AM fungi infection rate of alfalfa and ryegrass, and plant biomass as well, while inoculation of indigenous AM fungi alone or together with Glomus caledonium 36 did not show any positive effect on the AM fungi infection and plant biomass, and even decreased AM fungi infection rate at its seeding stage. Planting alfalfa and ryegrass could help PAHs degradation significantly, and the degradation rate could be further elevated when inoculated with Glomus caledonium 36. On D60, the PAHs degradation rates increased from 33.2% and 32.9% in the control treatments to 42.2% and 42.3%, respectively, in the soil planted alfalfa and ryegrass with the inoculation of Glomus caledonium 36. However, inoculation of indigenous AM fungi did not have such effect. Inoculation with indigenous AM fungi and Glomus caledonium 36 together had no significant effect on PAHs degradation in soil planting alfalfa, while enhanced PAHs degradation rate in soil planting ryegrass on D60. A significant positive correlation was observed between PAHs degradation rate in soil and AM fungi infection rate in plant roots (P<0.05), suggesting that AM fungi infection can increase the phytoremediation efficiency of PAHs-contaminated soil.(2) A soil-slurry bioreactor was constructed to investigate effects of 2.5% fermented cow dung (FD) and dry powdered sludge of papermaking waste (PP) on the degradation of PAHs in soil. PAHs contents in soils decreased gradually with incubation time. The addition of FD or PP seemed to stimulate the population size of PAHs-degrading microorganisms, which most likely resulted in the elevated degradation rate of PAHs on D30 up to 37% and 35% compare with 19% in the control treatment (P<0.05), respectively. The number of aromatic rings of PAHs seemed to negatively correlate with the degradation rates of PAHs. For instance, on D30, up to 95% of two-ring PAHs were degraded, while only 50% for three-ring PAHs regardless of all treatments. However, the degradation rates of four to six-ring PAHs were increased significantly (P<0.05) from 7%~13% in the control treatment to 21%~28% in the FD or PP-treated bioreactor, but two to three-rings PAHs did not have such effect. These results suggested that FD and PP could facilitate the propagation and activity of microorganisms specific for the biodegradation of high molecular weight-PAHs in soil.(3) A greenhouse pot-experiment was carried out to investigate effects of fermented cow dung (FD) and dry powdered sludge of papermaking waste (PP) on phytoremediation of PAHs-contaminated farmland soils by AM fungi infected alfalfa (Medicago sativa L.). The addition of 0.5%~2.0% FD had no significant effect on AM fungi infection rate, but could promote growth of alfalfa (P<0.05). PAHs residues in the 1.0% and 2.0% FD treatments were lower than the control treatment. The addition of 0.05% and 0.1% PP enhanced AM fungi infection rate significantly, and plant biomass as well (P<0.05), while the addition of 0.2% PP had negative effect on them (P<0.05). Only 0.05% PP addition significantly decreased PAHs residues (P<0.05), and degradation rates of PAHs with three, four or five-ring were higher than those of the control (P<0.05), respectively. A significant positive correlation was observed between PAHs degradation rate in soil and the AM fungi infection rate in plant roots (P<0.05). These results indicated that proper quantities of FD could increase nutrition to promote plant growth, but had little effect on the degradation of PAHs. However, micro amounts of PP accelerated AM fungi infection to improve plant growth and PAHs degradation, suggested that it could be used as an irritant material in mycorrhizoremediation of PAHs-contaminated soil.