Density Functional Theory Study of Marine Polybrominated Diphenyl Ethers in Anaerobic Degradation

Polybrominated diphenyl ethers(PBDEs)are a kind of serious pollutants in the ocean.Biodegradation is considered as an economical and safe way for PBDEs removal and reductive debromination dominates the initial pathway of anaerobic degradation.On the basis of experimental study,Octa-BDE 197,Hepta-BDE 183,Hexa-BDE 153,Penta-BDE 99 and Tetra-BDE 47 were selected as the initial degradation objects,and their debromination degradation were studied using density functional theory.The structures were optimized by Gaussian 09 program.Furthermore,the molecular orbitals and charge distribution were analyzed.All C-Br bond dissociation energies at different positions including ortho,meta and para bromine atoms were calculated and the sequence of debromination was obtained.There is a close relationship between molecular structure,charge,molecular orbital and C-Br bond.All PBDEs exhibited similar debromination pathways with preferential removal of meta and para bromines.

Effects of nature organic matters and hydrated metal oxides on the anaerobic degradation of lindane,p,p'-DDT and HCB in sediments

Effects of natural organic matters(NOM) and hydrated metal oxides(HMO) in sediments on the anaerobic degradation of γ 666, p,p' DDT and HCB were investigated by means of removing NOM and HMO in Liaohe River sediments sequentially. The results showed that the anaerobic degradation of γ 666, p,p' DDT and HCB followed pseudo first order kinetics in different sediments. But, the extents and rates of degradation were different, even the other conditions remained the same. Anaerobic degradation rates of γ 666, p,p' DDT and HCB were 0 020 d -1 , 0 009 d -1 and 0 035 month -1 respectively for the sediments without additional carbon resources. However, with addition of carbon resources, the anaerobic degradation rates of γ 666, p, p ' DDT and HCB were 0 071 d -1 , 0 054 d -1 and 0 088 month -1 in the original sediments respectively. After removing NOM, the rates were decreased to 0 047 d -1 , 0 037 d -1 and 0 066 month -1 ; in the sediments removed NOM and HMO, the rates were increased to 0 067 d -1 , 0 059 d -1 and 0 086 month -1 . These results indicated that NOM in the sediments accelerated the anaerobic degradation of γ 666, p,p' DDT and HCB; the HMO inhibited the anaerobic degradation of γ 666, p,p' DDT and HCB.

Degradation of phenol in an upflow anaerobic sludge blanket(UASB) reactor at ambient temperature

A synthetic wastewater containing phenol as sole substrate was treated in a 2 8 L upflow anaerobic sludge blanket(UASB) reactor at ambient temperature. The operation conditions and phenol removal efficiency were discussed, microbial population in the UASB sludge was identified based on DNA cloning, and pathway of anaerobic phenol degradation was proposed. Phenol in wastewater was degraded in an UASB reactor at loading rate up to 18 gCOD/(L·d), with a 1:1 recycle ratio, at 26±1℃, pH 7 0—7 5. An UASB reactor was able to remove 99% of phenol up to 1226 mg/L in wastewater with 24 h of hydraulic retention time(HRT). For HRT below 24 h, phenol degradation efficiency decreased with HRT, from 95 4% at 16 h to 93 8% at 12 h. It further deteriorated to 88 5% when HRT reached 8 h. When the concentration of influent phenol of the reactor was 1260 mg/L(corresponding COD 3000 mg/L), with the HRT decreasing(from 40 h to 4 h, corresponding COD loading increasing), the biomass yields tended to increase from 0 265 to 3 08 g/(L·d). While at 12 h of HRT, the biomass yield was lower. When HRT was 12 h, the methane yield was 0 308 L/(gCOD removed), which was the highest. Throughout the study, phenol was the sole organic substrate. The effluent contained only residual phenol without any detectable intermediates, such as benzoate, 4 hydrobenzoate or volatile fatty acids(VFAs). Based on DNA cloning analysis, the sludge was composed of five groups of microorganisms. Desulfotomaculum and Clostridium were likely responsible for the conversion of phenol to benzoate, which was further degraded by Syntrophus to acetate and H 2/CO 2. Methanogens lastly converted acetate and H 2/CO 2 to methane. The role of epsilon Proteobacteria was, however, unsure.

Study of 4-t-octylphenol degradation and microbial community in granular sludge

In this study, the authors have investigated the effects of various factors on both aerobic and anaerobic degradation of 4-t-octylphenol （4-t-OP） in granular sludge. In comparison, the aerobic degradation rate was much higher than that of anaerobic degradation. The optimal pH values for 4-t-OP degradation in granular sludge were 9 and 7 under aerobic and anaerobic conditions, respectively. And the degradation rate decreased with an increase in the initial 4-t-OP concentration. Addition of yeast extract or homologous compounds such as phenol also enhanced the 4-t-OP degradation, especially under the aerobic condition. To investigate the bacterial community in this study, the denaturing gradient gel electrophoresis （DGGE） method was applied, based on the primers, for the 16S rDNA V3 region of bacteria, γ-proteobacteria and bacillus were identified as the major species of sludge.

Niche Differentiation of Phenol-Degrading Microorganisms in UASB Granular Sludge as Revealed by Fluorescence in situ Hybridization

A microbial community structure of granules harvested from an anaerobic sludge blanket reactor treating phenolic wastewater was investigated using fluorescence in situ hybridization(FISH)and clone library construction.Clones of Syntrophorhabdaceae and Cryptanaerobacter were observed to be responsible for phenol degradation.For accurate taxonomic assignment of Cryptanaerobacter clones,phylogenetic analysis using nearly full-length 16S ribosomal RNA(rRNA)gene sequences was necessary.Three oligonucleotide probes were designed to detect the following three taxonomic groups:Syntrophorhabdaceae,Cryptanaerobacter,and Syntrophus.FISH analysis of thin sections of anaerobic granules showed a random distribution of bacteria and archaea.However,a well-defined distribution of Syntrophorhabdaceae,Cryptanaerobacter,and Syntrophus was observed.Cryptanaerobacter and Syntrophus were found on the outer layer of the granules and were closely associated with each other,while Syntrophorhabdaceae was located in the deeper part of the granules.Such specific distribution of the bacteria is most likely due to their metabolic association and affinity for the substrate.Phenol degradation in the granular sludge was observed to be carried out in the following way.First,Cryptanaerobacter converts phenol to benzoate,which is then degraded by Syntrophus into acetate.This syntrophic degradation of phenol occurs near the surface of the granule,where the phenol concen-tration is high.In the deeper part of the granule,where the phenol concentration is lower,Syntrophorhabdaceae degrades phenol into acetate.We observed that Syntrophorhabdaceae is less likely to produce benzoate as an intermediate to feed the neighboring organisms,which contradicts the theo-ries presented by previous studies.

Synthesis of 2-[^2H]-2-（1-methylalkyl）succinic acids

We describe a specific procedure for the synthesis of deuterium-labelled 2-（1-methylalkyl）succinate established via alkylation of diethyl malonate, Krapcho decarboxylation reaction with D20 and hydrolysis reaction. Two novel compounds, 2-[^2H]-2-ethylsuccinic acid and 2-[^2H]-2-（1-methylhep- tyl）succinic acid were prepared via this synthetic route and characterized by mass spectrometry and ^1H NMR. The results showed that the 2-（1-methylalkyl）succinic acids were deuterated at the β-position, which is considered as an important reaction centre in the anaerobic degradation of n-alkanes.