In Situ Bioremediation in Mixed-culture Inoculated Biological Permeable Reactive Barrier Systems

Cr(VI) reducing bacteria was isolated from dried sludge collected from sand drying beds at a local wastewater treatment plant in Brits (South Africa). The plant received high periodic loadings of Cr(VI) contaminated effluent from an abandoned chrome processing foundry within the chrome mining town of Brits. The isolated bacteria were tolerant to high Cr(VI) loadings with significant chromium removal activity at loadings up to 80 mg(L-1 under continuous flow conditions. The active species in the sludge culture were determined to be predominated by Bacillus thirungiensis, Bacillus cereus, Lycinobacillus sphaerococcus. The isolated consortium culture was introduced as a biocatalyst in a microbial permeable bioreactive barrier for treatment of Cr(VI) contaminated water through soil medium. When tested in continuous flow bench-scale systems, the steady-state condition was attained after the reactor's operation for 25 days. Time course concentration profiles in batch tests fitted well with first- and second-order exponential rate equations yielding first-order rate constants in the range of 0.615 h-1 and 0.0532 L(mg-1(h-1 for Cr(VI) loadings ranging from 50 to 400 mg/L. The laboratory scale studies showed that the biological permeable reactive barrier technology using indigenous microbes has potential application for hexavalent chromium remediation in contaminated environments. Finally, the technology using bacteria in-situ shows that Cr(VI) can be remediated in the environment using a passive system at a low cost with minimum intervention

Microbial Cr(VI) reduction by indigenous activated sludge bacilli and pure culture of escherichia coli ATCC 33456

Cr(VI) reducing microbial species Bacillus thuringiensis, Bacillus cereus and Bacillus mycoides were isolated from dried sludge collected from sand drying beds at a local wastewater treatment plant in Brits (South Africa). The plant received high periodic loadings of Cr(VI) contaminated effluent from an abandoned chrome processing foundry within the chrome mining town of Brits. Other Cr(VI) producing organisms in the sludge sample were identified as Microbacterium foliorum and Lycinobacillus sphaerococcus. Among the five confirmed Cr(VI) reducers, B. thuringiensis was determined to have the highest performance in reducing Cr(VI) to Cr(III). The Cr(VI) reducing capability of organisms isolated at the site has not diminished over a 15 year period (2006- 2021). In the current study, the performance and pathway structures responsible for Cr(VI) reduction are analysed and compared with the activity of a metabolically versatile Escherichia coli ATCC 33456. The observations from this study showcase advanced enzymatic Cr(VI) reductase structures in B. thuringiensis never before observed in other microbial species. Blocking of electron carrier enzymes suggested the involvement of dissolved thioredoxin in the cytosol and bulk media as possible biocatalysis activators for Cr(VI) reduction in resting cells.The National Research Foundation (NRF), Sedibeng Water through a Research Chair in Water Utilisation Engineering and the Rand Water Chair in Water Utilisation.http://www.aidic.it/cetam2023Chemical Engineerin

Biological remediation and removal of radioactive metals and complex aromatic compounds from nuclear and radioactive waste

In pursuing carbon emission free technologies in the energy industry, interest in nuclear energy has grown. However, technology for handling radioactive waste containing organic materials are lacking. Methods are required for biodegradation of often recalcitrant irradiated organic compounds which are persistent in radioactive waste from the nuclear industry. In this study, a bioseparation process for extraction of 14C and de-radiation of nuclear graphite was investigated in a continuous flow sequencing-batch/biofilm reactor. Dehalogenation and mineralisation of aromatic halogenated compounds in the waste stream of a pebble bed manufacturing process was simulated by the photocatalytic/biological hybrid system in the 50 to 1,000 4-CP mg.L-1. The efficiency of degradation of the irradiated compounds was compared to conventional degradation using PAH degrading microorganisms. The Pathway of degradation was established for both systems by evaluating the intermediates of degradation of radiolabelled phenolic compounds with ortho-13C-ortho and para-13C phenol. Phenol degradation under photocatalytic conditions was shown to follow the catechol hydroquinone hydroxyhydroquinone benzene-1,2,3-triol pathway, whereas the degradation in the biological stage followed the meta-cleavage pathway via catechol 2-hydromuconic semialdehyde pyruvate under aerobic conditions. This study demonstrates the potential of efficiently managing the organic component of nuclear waste using a cleaner, environmentally friendly biological process.http://www.aidic.it/cetam2019Chemical Engineerin