Effect Of Black Carbon (BC) On The Microbial Degradation Of Pentachlorophenol (PCP) In Sediment

Black carbon (BC) has a strong affinity for hydrophobic organic compounds (HOCs), leading to limited bioavailability of HOCs in sediment. However, there are few systematic study on the effect of BCs on microbial degradation of HOCs in sediment. In this paper, the flow cytometry was used to analyze the ecotoxicological effect of fly ash (FP) and rice-straw (RP), together with their demineralized product (FC and RC), on Microcystis aeruginosa. Furthermore, the effect of RC with different doses on the microbial degradation of pentachlorophenol (PCP) in sediment was studied. At the same time, in order to investigate the functional mechanism of RC on microbial degradation of PCP, the microbial community structure was conducted with PCR-DGGE technique. The main conclusions are as follows:(1) The properties of BCs changed a lot after acid treatment, especially for RC. The acid demineralisation process greatly increased C content, surface area, porosity and acid functional groups, such as carboxyl and lactone.(2) The inhibition effect on Microcystis aeruginosa increased with the increase of BCs’dosage. The cell density and esterase activity are more sensitive than chlorophyll a fluorescence. It was found that BCs had little negative effect on cyanobacteria, when the content of BCs was lower than1mg/mL. However, higher doses of BCs (>2mg/mL) had negative effects on cyanobacteria in different degrees. The negative effect of non-acid-treated BCs on cell density and esterase activity may be caused by their high pH. However, the acid-treated BCs had little negative effect on esterase activity, but had great inhibition on cell density, owing to their strong adsorptivity.(3) The microbial degradation of PCP in sediment could be stimulated by RC at low doses, while inhibited at high doses. In the sediment with20mg/kg PCP, the addition of0.1%and0.2%RC could greatly stimulate the degradation of PCP, which occurred at35days after the addition, and finished at60days. However, PCP in sediment without RC or with higher RC content started to degrade at60days or even90days. (4) The results of PCP degradation and PCR-DGGE showed that the degradation efficiency was in good correlation with microbial growth in sediment. What’s more, the addition of RC had great influence on the microbial diversity in sediment. In the sediment with low RC content (0.1%-0.5%), the concentration of PCP in pore water was reduced, together with its acute toxicity. It also improved the growth of microorganisms in sediment, resulting in high microbial diversity and new dominant bacteria bands in good homology with PCP degrader. However, for sediment with higher RC content (>0.5%), the influence of RC on PCP degradation was dominated by the inhibition effect on bioavailability of PCP. The results of clone and sequencing showed that the Beta proteobacterium and Pseudomonas sp. were dominant bacteria, which played main roles in the degradation of PCP in sediment.