Heavy Metal Immobilization In Groundwater By In Situ Bioprecipitation: Comments And Questions About Efficiency And Sustainability Of The Process

About 45% of the contaminated sites are dealing with heavy metal problems. Metals are spread in the environment by mining activities, surface treatment and non ferrous processing. As heavy metals can not be degraded, removal or immobilization (leading to bioavailability reduction) are the only risk reducing measures that exist. Next to the often used but expensive pump an treat technologies, heavy metals can be immobilized by inducing sulfate reducing bacteria (SRB) to transform the sulfates, that are very often present in the same groundwater (due to the metal mining or processing activities), into sulfides. These sulfides will precipitate the metals as insoluble metal sulfides. At the moment several studies have demonstrated the feasibility of this In Situ Bioprecipitation Process (ISBP) for the removal of heavy metals from groundwater as well at lab scale (batch and column tests) as at field scale. However, some questions arise concerning the continuation of the process, the efficiency and the sustainability of the precipitates. The presented study will try to answer these questions. The study is based on more than 10 different studies, all done by the same authors, on different groundwaters and aquifer samples. The presentation will give an overview of the guidelines necessary for a correct and successful bioprecipitation process with stable metal sulfide precipitates. It will pay attention to the influence of the carbon source on the complexing of the metals and the efficiency of the induction of the bioprecipitation process, the possible negative influence of acetate inhibition, the influence on the competence between sulfate reducers and methanogenic bacteria and the influence of low pH on the ISBP. These results will allow the correct implementation of the ISBP with an eye on longevity and sustainability of the process and present the ISBP as a much more sustainable alternative to the pump and treat technology as measure for heavy metals contaminated groundwaters

Acinetobacter diversity in environmental samples assessed by 16S rRNA gene PCR-DGGE fingerprinting

A primer pair was designed to selectively amplify a fragment of the Acinetobacter 16S rRNA gene from environmental samples by PCR. 16S rRNA gene products were only obtained in PCRs with DNA from members of the genus Acinetobacter and not with DNA from other bacterial species. Denaturing gradient gel electrophoresis (DGGE) of the Acinetobacter 16S rRNA gene amplicons enabled discrimination between different Acinetobacter species. PCR using the Acinetobacter primer pair allowed detection of Acinetobacter in soil with a detection limit of 10(4) cells g(-1) soil, but attachment of the GC-clamp to the forward primer resulted in a 100-fold decrease in sensitivity. Using a nested PCR approach, the detection limit could be lowered to at least 10 cells g(-1) of soil. The method was applied to assess Acinetobacter diversity in soil samples originating from different historically hydrocarbon -contaminated sites. In addition, for one oil-contaminated soil, the dynamics of the Acinetobacter community in response to different treatments was monitored over time in a laboratory biostimulation experimental set-up. In all cases, bands in the DGGE fingerprints were cloned and sequenced. Environmental samples taken from a mineral oil-contaminated site and from a kerosene-contaminated site demonstrated relatively simple Acinetobacter 16S rRNA gene fingerprints with A. lwoffii and A. johnsonii as dominant members. In contrast, soils derived from MTBE- and BTEX-contaminated sites did not harbor detectable Acinetobacter populations. Although Acinetobacter was detected in the soil employed for the biostimulation experiment prior to treatment, substantial changes in its populations were observed depending on the treatment. (C) 2004 Federation of European Microbiological Societies. Published by Elsevier B.V. All rights reserved