Application of Combined In Situ Chemical Reduction and Enhanced Bioremediation to Accelerate TCE Treatment in Groundwater

Groundwater at trichloroethylene (TCE)-contaminated sites lacks electron donors, which prolongs TCE’s natural attenuation process and delays treatment. Although adding electron donors, such as emulsified oil, accelerates TCE degradation, it also causes the accumulation of hazardous metabolites such as dichloroethylene (DCE) and vinyl chloride (VC). This study combined in situ chemical reduction using organo-iron compounds with enhanced in situ bioremediation using emulsified oil to accelerate TCE removal and minimize the accumulation of DCE and VC in groundwater. A self-made soybean oil emulsion (SOE) was used as the electron donor and was added to liquid ferrous lactate (FL), the chemical reductant. The combined in situ chemical reduction and enhanced in situ bioremediation achieved favorable results in a laboratory microcosm test and in an in situ biological field pilot test. Both tests revealed that SOE+FL accelerated TCE degradation and minimized the accumulation of DCE and VC to a greater extent than SOE alone after 160 days of observation. When FL was added in the microcosm test, the pH value decreased from 6.0 to 5.5; however, during the in situ biological pilot test, the on-site groundwater pH value did not exhibit obvious changes. Given the geology of the in situ pilot test site, the SOE+FL solution that was injected underground continued to be released for at least 90 days, suggesting that the solution’s radius of influence was at least 5 m.

Utilisation of 2,2DCP by Staphyloccocus aureus ZT and In Silico Analysis of Putative Dehalogenase

Halogenated compound such as 2,2-dichloropropionic acid is known for its toxicity and polluted many areas especially with agricultural activities. This study focused on the isolation and characterization of the bacterium that can utilise 2,2-dichloropropionic acid from palm oil plantation in Lenga, Johor and in silico analysis of putative dehalogenase obtained from NCBI database of the same genus and species. The bacterium was isolated using an enrichment culture media supplemented with 20 mM 2,2-dicholoropropionic acid as a carbon source. The cells were grown at 30ËšC with cells doubling time of 2.00±0.005 hours with the maximum growth at A680nm of 1.047 overnight. The partial biochemical tests and morphological examination concluded that the bacterium belongs to the genus Staphylococcus sp.. This is the first reported studies of  Staphylococcus sp. with the ability to grow on 2,2-dichloropropionic acid. The genomic DNA from NCBI database of the same species was analysed assuming the same genus and has identical genomic sequence. The full genome of Staphylococcus sp. was screened for dehalogenase gene and  haloacid dehalogenase gene was detected in the mobile genetic element of the species revealed that the dehalogenase sequence has little identities to the previously reported dehalogenases.The main outcome of the studies suggesting an in situ bioremediation can be regarded as a natural process to detoxify the contaminated sites provided that the microorganisms contained a specialised gene sequence within its genome that served the nature for many long years. Whether microorganisms will be successful in destroying man-made contaminants entirely rely on what types of organisms play a role in in situ bioremediation and which contaminants are most susceptible to bioremediation.Â

Effect of soil heterogeneity on the optimal design of in-situ groundwater bioremediation systems

<p>The use of optimization approaches for designing in-situ groundwater bioremediation systems has been demonstrated in a number of previous studies under the assumption of homogenous soil. However, in real applications the soil is typically heterogeneous and knowledge of the spatial conductivity distribution is, to some degree, uncertain. Here, a systematic attempt is made to quantify the effect of soil heterogeneity on the optimal design of in-situ bioremediation systems. To determine the optimal placement of injection and extraction wells within the computational domain, the meshless element-free Galerkin method (EFGM) was coupled with particle swarm optimization (PSO), resulting in a simulation-optimization (S/O) model which is referred to as BIOEFGM-PSO. A hypothetical case study is considered where the design of an in-situ bioremediation system is optimized considering different degrees of heterogeneity of the porous medium. Heterogeneous conductivity fields are generated using a pseudo-random field generator with same mean and varying variance and correlation lengths. The BIOEFGM-PSO model was then applied to the different soil scenarios, and the resulting bioremediation costs were compared. Results show that the optimal placement of injection and extraction wells depends on the soil properties and, on average, heterogeneous soils have higher in-situ bioremediation costs compared with a homogeneous soil with the same mean conductivity. This highlights the importance of considering soil heterogeneity in designing cost-effective in-situ bioremediation systems, and further demonstrates the general applicability of the BIOEFGM-PSO model.</p>