Anaerobic biodegradation of PAHs in mangrove sediment with amendment of NaHCO_3

Mangrove sediment is unique in chemical and biological properties. Many of them suffer polycyclic aromatic hydrocarbon（PAH） contamination. However, the study on PAH biological remediation for mangrove sediment is deficient. Enriched PAH-degrading microbial consortium and electron acceptor amendment are considered as two effective measures. Compared to other electron acceptors, the study on CO2, which is used by methanogens, is still seldom. This study investigated the effect of Na HCO3 amendment on the anaerobic biodegradation of four mixed PAHs, namely fluorene（Fl）, phenanthrene（Phe）,fluoranthene（Flua） and pyrene（Pyr）, with or without enriched PAH-degrading microbial consortium in mangrove sediment slurry. The trends of various parameters, including PAH concentrations, microbial population size, electron-transport system activities, electron acceptor and anaerobic gas production were monitored. The results revealed that the inoculation of enriched PAH-degrading consortium had a significant effect with half lives shortened by 7–13 days for 3-ring PAHs and 11–24 days for 4-ring PAHs. While Na HCO3 amendment did not have a significant effect on the biodegradation of PAHs and other parameters, except that CO2 gas in the headspace of experimental flasks was increased.One of the possible reasons is that mangrove sediment contains high concentrations of other electron acceptors which are easier to be utilized by anaerobic bacteria, the other one is that the anaerobes in mangrove sediment can produce enough CO2 gas even without adding Na HCO3.

Stabilization of heavy metals in sediments:A bioavailability-based assessment of carbon adsorbent efficacy using diffusive gradients in thin films

This study investigated the effectiveness of carbon adsorbents as remediation material for sediments contaminated with heavy metals and the feasibility of utilizing diffusive gradients in thin films(DGT)as a biomimetic tool to estimate the accumulation of heavy metals in Venerupis philippinaram(Manila clam).The results showed that carbon materials had significant inhibitory effects(14.0-53.0%)on the enrichment of heavy metals in organisms and the order of increasing overall inhibitory effect was:charcoal,peat,activated carbon,and biochar.There were significant correlations(P<0.0001)between the four heavy metals accumulated in Venerupis philippinaram and those accumulated in DGT devices after 28 days in the laboratory.Observed concentrations of heavy metals enriched in DGT(5.4-42.0%)were less than accumulations in Venerupis philippinaram.The results of in situ DGT applications showed significant correlations between the amount accumulated in DGT and the acid-soluble portion in sediments for both Cu and Pb,with positive linear correlations and R-squares of 0.97 and 0.92,respectively.These results supported the notion that a DGT device can be used as a biomimetic tool that predicts and monitors the accumulation of heavy metals in aquaculture ponds.Future studies should focus on improving the stabilization of heavy metals in sediments using different types of carbon sorbents,as well as minimizing simulation deviations using DGT.