S.Y. Yuan

Anaerobic biodegradation of polycyclic aromatic hydrocarbon in soil

Known concentrations of phenanthrene, pyrene, anthracene, fluorene and acenapthene were added to soil samples to investigate the anaerobic degradation potential of polycyclic aromatic hydrocarbon (PAH). Consortia-treated river sediments taken from known sites of long-term pollution were added as inoculum. Mixtures of soil, consortia, and PAH (individually or combined) were amended with nutrients and batch incubated. High-to-low degradation rates for both soil types were phenanthrene > pyrene > anthracene > fluorene > acenaphthene. Degradation rates were faster in Taida soil than in Guishan soil. Faster individual PAH degradation rates were also observed in cultures containing a mixture of PAH substrates compared to the presence of a single substrate. Optimal incubation conditions were noted as pH 8.0 and 30 degrees C. Degradation was enhanced for PAH by the addition of acetate, lactate, or pyruvate. The addition of municipal sewage or oil refinery sludge to the soil samples stimulated PAH degradation. Biodegradation was also measured under three anaerobic conditions; results show the high-to-low order of biodegradation rates to be sulfate-reducing conditions > methanogenic conditions > nitrate-reducing conditions. The results show that sulfate-reducing bacteria, methanogen, and eubacteria are involved in the PAH degradation; sulfate-reducing bacteria constitute a major component of the PAH-adapted consortia.

Effects of alternative electron donors, acceptors and inhibitors on pentachlorophenol dechlorination in soil

Abstract The potential dechlorination of pentachlorophenol (PCP) in soil by a DCP-adapted consortium was investigated Results show that PCP dechlorination was enhanced under sulfate reduction and methanogenic conditions, but inhibited under denitrifying conditions within a 20-day incubation period. Under those same three conditions we also found that PCP dechlorination was enhanced by the addition of lactate, pyruvate, and acetate, but delayed by the addition of manganese oxide and inhibited by the addition of ferric chloride. In addition, our results failed to show any relationship between PCP dechlorination and oxidation-reduction potential (ORP) or changes in pH values. Treatment with lactate caused the greatest increase in methane production, the highest rates of sulfate or nitrate consumption; adding manganese oxide led to the second greatest increase, and the addition of ferric chloride the least. The addition of methylphenols and nitrophenols were found to inhibit PCP dechlorination. Methanogen may have constituted the major dechlorination population in our experimental consortium.

Biodegradation of phthalate esters in compost-amended soil

In this study, we investigated the biodegradation of the phthalate acid esters (PAEs) di-n-butyl phthalate (DBP) and di-(2-ethyl hexyl) phthalate (DEHP) in compost and compost-amended soil. DBP (50 mg kg(-1)) and DEHP (50 mg kg(-1)) were added to the two types of compost (straw and animal manure) and subsequently added to the soil; they were tested as a single compound and in combination. Optimal PAE degradation in soil was at pH 7 and 30 degrees C. The degradation of PAE was enhanced when DBP and DEHP were simultaneously present in the soil. The addition of either of the two types of compost individually also improved the rate of PAE degradation. Compost samples were separated into fractions with various particle size ranges, which spanned from 0.1-0.45 to 500-2000 microm. We observed that the compost fractions with smaller particle sizes demonstrated higher PAE degradation rates. When the different compost fractions were added to soil, however, compost particle size had no significant effect on the rate of PAE degradation.

Anaerobic Degradation of Phenanthrene and Pyrene in Mangrove Sediment

This study investigated the anaerobic degradation of the polycyclic aromatic hydrocarbons (PAHs) phenanthrene and pyrene in mangrove sediment from Taiwan. The anaerobic degradation of PAH was enhanced by the addition of acetate, lactate, pyruvate, sodium chloride, cellulose, or zero-valent iron. However, it was inhibited by the addition of humic acid, di-(2-ethylhexyl) phthalate (DEHP), nonylphenol, or heavy metals. Of the microorganism strains isolated from the sediment samples, we found that strain MSA3 (Clostridium pascui), expressed the best ability to biodegrade PAH. The inoculation of sediment with the strain MSA3 could enhance PAH degradation.

Microbial hexachlorobenzene dechlorination under three reducing conditions

The potential dechlorination of hexachlorobenzene (HCB) in medium by 1,2,3-trichlorobenzene (TCB)-adapted mixed culture under three reducing conditions was investigated. It was found that strongest to weakest HCB dechlorination occurred in the order of methanogenic conditions > sulfate-reducing conditions > denitrifying conditions. Under denitrifying conditions, no dechlorination was observed during the first 20 days of incubation. Biotransformation occurred in this order: HCB-->pentachlorobenzene (PCB)-->1,2,3,5-tetrachlorobenzene (TeCB)-->1,3,5-TCB + 1,2,4-TCB-->1,3-dichlorobenzene (DCB), HCB dechlorination was delayed following treatment with ferric chloride and manganese dioxide, but enhanced by the addition of lactate and pyruvate under methanogenic or sulfate-reducing conditions, the addition of acetate had no significant effect on HCB dechlorination under any of the three reducing conditions. Sequential dechlorination was observed at concentrations of 2-50 mg/L, but at a significantly slower rate at the highest concentrations.

Anaerobic degradation of nonylphenol in subtropical mangrove sediments

Nonylphenol (NP) is known as an endocrine disruptor and has consequently drawn much environmental concern. We investigated the effects of various factors on the anaerobic degradation of NP and characterized the structures of microbial communities in mangrove sediments collected at five sites along the Tanshui River in northern Taiwan. NP anaerobic degradation rate constants (k(1)) and half-lives (t(1/2)) ranged from 0.008 to 0.0131/day and 53.3 to 86.6 days, respectively. The addition of NaCl (1%, 2%), zero-valent iron (10 g/L), humic acid (0.5 g/L), cellulose (0.96 mg/L), brij 30 (55 microM) and brij 35 (91 microM) enhanced NP anaerobic degradation. However, the addition of NaCl (3%), acetate (20mM), lactate (20mM), pyruvate (20mM), and humic acid (5 g/L) inhibited NP anaerobic degradation. Sulfate-reducing bacteria, methanogen, and eubacteria are involved in the degradation of NP, sulfate-reducing bacteria being a major component of the sediment. Our results also show that the addition of various substrates changed the microbial community in mangrove sediments. Also noted was the presence of 2-butyl-1-octanol, an intermediate product resulting from the anaerobic degradation of NP accumulated in the sediments.

Biodegradation of benzene, toluene; and other aromatic compounds by Pseudmonas sp. D8

Pseudomonas sp. D8 strain, which has the potential to utilize toluene as a sole carbon source, was isolated. At a concentration of 100 mg/l, this strain was found to efficiently degrade toluene and benzene (both individually and in mixture) in culture medium at 30 degrees C and pH7. Following a two-hour lag phase, complete biodegradation of 100 mg/l toluene or benzene occurred within 6 to 8 hours. The addition of nitrate, phosphate, or sulfate at various concentrations were found to have significant influence on both toluene and benzene degradation. In addition, results show that the D8 strain has the ability to degrade monochlorophenols, nitrophenols, and phenol, but not aliphatic compounds. Inoculation of groundwater samples containing 100 mg/l toluene or benzene with Pseudmonas sp. D8 resulted in rapid degradation within 24-33 hours.

Dechlorination of pentachlorophenol in anaerobic sewage sludge

Abstract Dechlorination of pentachlorophenol (PCP) in municipal sewage sludge by a chlorophenols (CPs)-adapted consortium was investigated. Results of a batch experiment showed no significant differences in PCP dechlorination following treatment with inoculum at densities ranging from 10% to 50%, but a significant delay following treatment with inoculum at 5% density. Results also show that the higher the PCP concentration, the slower the dechlorination rate. PCP dechlorimation was not significantly altered by the addition of acetate, lactate, pyruvate, vitamin B 12 or manganese dioxide. Results from a bioreactor experiment show optimal pH for dechlorination at 7.0 and optimal total solid concentration at 10 g/L. Dechlorination rates were also found to decrease significantly at higher agitation speeds. Finally, it was found that methanogenic conditions enhanced PCP dechlorination, but denitrifying and sulfidogenic conditions inhibited the dechlorination process.

Reductive Dechlorination of Hexachlorobenzene by an Anaerobic Mixed Culture

The potential for reductive dechlorination of hexachlorobenzene (HCB) by a 1,2,3-trichlorobenzene (TCB)-adapted mixed culture was investigated. Optimal dechlorination conditions were assessed at 29 °C ∼ 37 °C and pH 6.1 ∼ 6.9. The observed transformation pathway was HCB → pentachlorobenzene (PCB) → 1,2,3,5-tetrachlorobenzene (TeCB) → 1,3,5-TCB. The dechlorination of HCB was delayed by the addition of ferric chloride and manganese dioxide as electron acceptors, but enhanced by the addition of lactate and pyruvate as electron donors. However, we found that the addition of acetate had no significant effect on HCB dechlorination. Following treatment with bromoethanesulfonic acid (BESA) and vancomycin, it was suggested that the methane-producing bacteria was involved in the dechlorination of CBs.

Microbial dechlorination of polychlorinated biphenyls in anaerobic sewage sludge.

The potential of a chlorophenol (CP)-adapted consortium to dechlorinate polychlorinated biphenyls (PCBs) in sewage sludge was investigated. Results show that dechlorination rates differed significantly depending on sludge source and PCB congener. Higher total solid concentrations in sewage sludge and higher concentrations of chlorine in PCB resulted in slower dechlorination rates. No significant difference was found for 2,3,4,5-CB dechlorination from pH 6.0 to pH 8.0; however, dechlorination did not occur at pH 9.0 during a 41-day incubation period. Results show that at concentrations of 1 to 10 mg/L, the higher the PCB concentration, the faster the dechlorination rate. In addition, dechlorination rates were in the following order: methanogenic conditions > sulfate-reducing conditions > denitrifying conditions. The addition of acetate, lactate, pyruvate, and ferric chloride decreased lag times and enhanced dechlorination; however, the addition of manganese dioxide had an inhibitory effect. Dechlorination rates were also enhanced by the addition of PCB congeners, including 2,3,4-CB, 2,3,4,5-CB and 2,3,4,5,6-CB in mixture. Overall results show that the CP-adapted consortium has the potential to enhance PCB dechlorination. The optimal dechlorination conditions presented in this paper may be used as a reference for feasibility studies of PCB removal from sludge.