Study On Enhanced Purification Technology Of Pyrene And Indeno (1,2,3-cd) Pyrene In Liaohe Estuarine Reed Wetlands

The Liaohe estuarine wetland has the largest reed (Phragmites communis Trin) population in Asia and provides habitat for many rare plants and animals. However, the wetland has inadvertently suffered PAHs contamination during long-term crude exploitation. The high molecular weight (HMW) PAHs (4-6 rings) that resist biological degradation account for nearly 50% of total PAHs, and the distribution has no obvious change within the whole growing season of reed. This shows that the activity of the degraders of PAHs was weak in natural wetlands and the aging of PAHs has lower bioavailability.Therefore, we chose pyrene and indeno(1,2,3-cd)pyrene as targeted PAHs because they were the most abundant HMW PAHs in Liaohe estuarine reed wetlands contaminated with oils. Therefore, plant-immobilized microbe is needed to strengthen the microbial community degrading PAHs based on enhanced quantities and activities of rhizosphere microorganism.In this study, two PAHs-degrading isolates (PYR1 and INP1) were used as the objective strains of microorganism immobilization, and coal cinder, industrial and life waste was chose as carrier material. The cells of isolates were entrapped in cinder beads. Then the cinder beads immobilizing bacteria were added into rhizosphere soil of reeds in Liaohe wetland simulator to study the removal efficiency of PAHs. Additionally, microbial analysis after adding immobilized microorganism into soils was conducted with high-throughput sequencing. The results are as follows:(1) Most pyrene-degrading and indeho(1,2,3-cd)pyrene-degrading isolates selected from Liaohe estuarine wetlands were identified as Pseudomonas putida PYR1 and Acinetobacter baumannii INP1. The PAH degradation abilities of strain PYR1, strain INP1 and a mix of the two in equal proportions were evaluated in basal salt medium containing PAHs. An enhanced pyrene-degradation was observed when pyrene and indeno(1.2.3-cd)pyrene were supplied as cometabolic substrate, while indeno(1.2,3-cd)pyrene-degradation was not enhanced. Degradation rates of pyrene and indeno(1,2,3-cd)pyrene were 83.3% and 59.8% respectively by mixed strains.(2) The physical properties of the cinder beads were enhanced upon a ratio of 100:5:2.5(g:mL:mL). The rate is that the cinders were mixed with modified polyvinyl alcohol and gelling solution of calcium chloride (4%). And the interspace of the carrier material structure is relatively large and provides good growth of strains after immobilization on the cinder beads. Biodegradation of pyrene and indeno(1,2,3-cd)pyrene in rhizosphere soil of reeds was carried out in pots using cells of PYR1 and INP1 that were free as well as those immobilized on cinder beads to ascertain the role of the carrier material. Only cinder beads or free bacteria were able to degrade PAHs but not as efficiently as immobilized cells. The enhanced depletion of pyrene and indeno(1,2,3-cd)pyrene after 30 days was 70.7%, and 80.9%, respectively.(3) A small-scale wetland simulator divided into two sets with different concentrations of polycyclic aromatic hydrocarbons (PAHs) was bioaugmented with immobilized PYR1 and INP1 strains and reeds under natural environmental conditions. Depletion rates of pyrene and indeno(1,2,3-cd)pyrene were more than 59% and 80%, respectively, in 40 days by immobilized cells and reeds. This shows that the combined purification system can serve as a model study for effective degradation of PAHs. The effect on purifying PAHs using plant-immobilized microorganism technology under the conditions of different initial concentrations of PAHs is different. In a certain concentration of pollution range, the higher the concentration of PAHs pollutants is, the higher the removal rate is.(4) The diversity of the microbial community before cinder beads were embedded in soil was higher with a Shannon index of about 9.3, while the diversity of the microbial community lessened obviously and Shannon index was only about 5.3 after mixed bacteria-entrapped cinder beads were embedded in soil. Gammaproteobacteria was absolutely dominant which accounted for approximately 60% of all bacteria based on the class-level analysis. Dominant genera such as Acinetobacter sp.(12.68%). Pseudomonas sp.(7.4%), and Dysgonomonas sp.(3.78%) based on the genus-level analysis and all of them can degrade PAHs.