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William W Mohn

Publications and source records attributed to William W Mohn.

22 records · Page 2Linked to original sources
PubMed2003

Reductive dechlorination of weathered Aroclor 1260 during anaerobic biotreatment of Arctic soils.

We investigated the microbial reductive dechlorination of both weathered (aged) and nonweathered (freshly added) Aroclor 1260 in aerobic soil from Resolution Island, Nunavut, Canada. Initial polychlorinated biphenyl (PCB) concentrations were 106 and 100 ppm, respectively. The aerobic soil samples were inoculated with anaerobic sediment, incubated at 30 degrees C until methanogenic, inoculated with a dechlorinating enrichment culture, and incubated a further 8 weeks. The average number of chlorine substituents per biphenyl molecule was biologically reduced from 6.6 to 5.1 and from 6.2 to 4.5 for weathered and nonweathered Aroclor 1260, respectively. Removal of hexa- and heptachlorobiphenyls (CBs), the major homolog groups present, was significantly greater for nonweathered than for weathered Aroclor 1260. Formation of dechlorination products, primarily 2,2',4,4'- and 2,2',4,6'-tetraCBs, was also significantly greater for nonweathered than for weathered Aroclor 1260. We additionally compared the dechlorination at 21 degrees C of weathered Aroclor 1260 in soils from Resolution Island and Saglek, Labrador, Canada. The average number of chlorine substituents per biphenyl molecule was biologically reduced from 6.7 to 5.1 and from 6.5 to 4.6, respectively. This study demonstrated the potential for bioremediation of aerobic soil contaminated with Aroclor 1260 and showed that weathering may limit such treatment to an extent variable among different soils.

Arctic Regions↗
PubMed2002

Sequential anaerobic-aerobic treatment of soil contaminated with weathered Aroclor 1260.

Soil contaminated with weathered Aroclor 1260 was bioremediated by sequential anaerobic and aerobic laboratory-scale treatment. The initial concentration was 59 microg of PCBs/g of soil. Following 4 months of anaerobic treatment with an enrichment culture, all of the major components in Aroclor 1260 were completely or partially transformed to less chlorinated PCB congeners. The major products of reductive dechlorination were 24-24-tetrachlorobiphenyl and 24-26-tetrachlorobiphenyl, and the average chlorine substituents per PCB molecule decreased from 6.4 to 5.2. The molar concentration of PCBs did not decrease during the anaerobic treatment. All of the major products formed during the anaerobic treatmentwere degraded in the subsequent aerobic treatment using Burkholderia sp. strain LB400. After 28 days of the aerobic treatment, the concentration of PCBs was reduced to 20 ug/g of soil. PCBs were not significantly removed in aerobic treatments unless they were bioaugmented with LB400. Also, PCB degradation was not detected in soil bioaugmented with LB400 without prior anaerobic treatment. These results confirm the potential for extensive biological destruction of highly chlorinated, weathered PCB congeners in soil.

Aroclors↗
PubMed2002

Bioaugmentation with the resin acid-degrading bacterium Zoogloea resiniphila DhA-35 to counteract pH stress in an aerated lagoon treating pulp and paper mill effluent.

Efficient and reliable removal of resin acids such as dehydroabietic acid (DhA), which are the major toxicants in pulp and paper mill effluents and form pitch interfering with papermaking, is critically important to prevent toxicity discharge and failure of paper machines. Low- and high-pH stresses sometimes occur in effluent treatment systems due to the use of large amounts of acids and alkalines in the pulping processes. We found that both low- and high-pH stresses (pH 3 and 10, respectively) decreased the removal of total organic carbon and completely inhibited the removal of DhA by the biomass of an aerated lagoon treating pulp mill effluent. The pH stresses caused changes in the bacterial community structure as assessed by ribosomal intergenic spacer length polymorphism. The pH stresses greatly reduced the indigenous DhA-degrading populations in the lagoon community. Bioaugmentation with Zoogloea resiniphila DhA-35, a DhA-degrading bacterium originally isolated from a pulp mill treatment system, restored the DhA removal by both the low- and high-pH-stressed lagoon biomass. This bacterium was persistent after introduction into the lagoon microbial community, and its cellular rRNA:rDNA ratio increased during the period of DhA removal. The introduction of strain DhA-35 changed the microbial community structure, but did not adversely affect the TOC removal by the community. This study suggests that it is feasible and potentially useful to use bioaugmentation with resin-acid-degrading bacteria such as DhA-35 to restore and enhance resin acid removal by aerated lagoon microbial communities.

Biodegradation, Environmental↗