Remediation Of PAHs Contaminated Soils By Immobilized White-rot Fungi With Biochar As A Carrier And Its Mechanism

Soil is not only the foundation of the whole ecological environment,but also the basic guarantee for the human survival and health.However,as the world becomes more industrialized,soil is increasingly polluted by organic contaminants and heavy metal,which put groundwater and food safety at risk.The widespread occurrence of many persistent toxic organic compounds,such as polycyclic aromatic hydrocarbons (PAHs),in soils and groundwater has become a serious environmental concern,which has led to intensive studies of the transport,bioavailability,fate and potential remediation technology of PAHs in subsurface environment.In this dissertation,pollution status,sorption and bioavailability of organic contaminants,and soil organic pollution remediation were summarized,and the regulation of bioavailability of organic contaminant in soils and its application in the control and remediation of soil organic pollution were reviewed.Biosorption and biodegradation of PAHs to live and heat-killed white-rot fungi were investigated to elucidate the bio-dissipation mechanism,and the relative contributions of biosorption and biodegradation to the total removal of PAHs were also elucidated.Impact of biochar as immobilized carrier on the chemical extraction and plant uptake of PAHs was investigated,and properties of extraction solvent,chafing temperature of biochar, and aging effects on the chemical extraction of PAHs were discussed.Sorption and biodegradation of PAHs by immobilized fungi with biochar as a cartier,its influencing factors and especially control mechanism of bioavaiability were studied.Remediation of 16 PAHs in sewage irrigated soils in Northeast China was also studied.The observations in this work will provide a reference to the use of biochar and immobilized microorganisms for remediation of organic contaminated soils,and offer a theoretical gist for guaranteeing quality of the agricultural products.The main original conclusions of this work are drawn.(1) Biosorption and biodegradation of PAHs by live and heat-killed white-rot fungi were investigated to elucidate the bio-dissipation mechanisms of PAHs.Sorption isotherms of PAHs to heat-killed fungal biomass were linear and non-competitive,and the Freundlich N values approximated to 1,indicating the primary mechanism of biosorption was partition.The carbon-normalized partition coefficients(K_oc) were linearly correlated with octanol-water partition coefficients(K_ow),i.e.,logK_oc= 1.13logK_ow-0.84(n=5,r²=0.996).Biosorption and biodegradation of phenanthrene and pyrene by live white-rot fungi were quantified.In one week,the removal efficiency of phenanthrene(60～80%) and pyrene(90%) by live fungi from aqueous solution were comparable to those by heat-killed fungi.However,approximate 40～65%of phenanthrene and 60～85%of pyrene were still stored in organismal bodies. Biosorption might restrict biodegradation while nutrient limitation and presence of a PAH mixture might stimulate biodegradation.The apparent partition coefficients(K_d^*) in live fungal systems and the K_d of heat-killed fungi without biodegradation were compared,and then the K_d^*/K_d ratios were employed to illustrate the relative contributions of biosorption and biodegradation under different nutrient conditions.(2) Chemical extraction and biological exposure have been utilized for the assessment of sorption of PAHs to biochar as a carrier and their impact on bioavailability.Organic solvent extraction of immobilized naphthalene(Naph), acenanthrene(Acen),phenanthrene(Phen),and pyrene(Pyr) in P100,P300 and P400 biochars were complete.However,the absolute recovery rates of Naph,Acen,Phen and Pyr from P700 biochar were 84.55～100.3%,85.11～106.0%,21.14～61.41%,and 6.56～15.69%,respectively,illustrating strong binding of Phen and Pyr to P700 biochar.As time ongoing,the chemical extractability and bioavailability of biocharsorbed -PAHs decreased.Biochar could significantly reduce bioavailability of PAHs to plant such as rice seedlings,attributed to sorption of PAHs to biochar.Compared with the control solution,with presence of soil,biochar and soil-biochar sorbent,uptake of Phen by rice seedlings were reduced by 23.76%,61.88～94.55%,and 88.61～91.58%; and the decreased in accumulation of Pyr in the plant were 32.35%,53.33～96.08%, and 66.27～93.73%,respectively.Accumulation of PAHs in the root of rice seedlings was related with freely dissolved concentrations of solute in solution,and a linear correlation between shoots and roots concentrations was obtained,suggesting that sorption of PAHs to biochar lowered the freely dissolved concentration and reduced plant uptake and accumulation of PAHs.(3) Sorption and biodegradation of PAHs by immobilized white-rot fungi with biochar as a carrier were described,and remediation of 16 PAHs in sewage irrigated soils in Northeast China with immobilized white-rot fungi was initially studied.PAHs sorbed by immobilized fungi with biocar as a carrier could be degraded,and the degradation of PAHs by immobilized fungi with P300 and P400 were stronger than immobilized fungi with P100 and P700.With addition of biochar immobilized fungi, the concentration and extraction rates of 16 PAHs in sewage irrigated soils in Northeast China were significantly decreased,which was decreased with increasing pyrolytic temperature of biochar as a carrier,and the trends leveled off as time went on,attributed to sorption ofbiochar and biodegradation of immobilized fungi simultaeously.