Optimizing contaminant desorption and bioavailability in dense slurry systems. 1. Rheology, mechanical mixing, and PAH desorption

A highly efficient method with low energy and water consumption in biodegradation of total petroleum hydrocarbons of oily sludge

The hydrocarbons in petroleum sludge are environmental pollutants. It is crucial to eliminate this type of pollution. In this study, a comprehensive and operational study has been conducted on the total petroleum hydrocarbons (TPH) biodegradation in oily sludge. The experiments were performed in a semi-solid phase by two degrader bacterium, Arthrobacter citreus and Rhodococcus jostii, and they were compared with the slurry phase. Solid samples were prepared in three mixing modes of oily sludge with clay. Experiments were conducted by semi-solid bioreactors and other methods on samples contaminated with petroleum hydrocarbons. The performance of the semi-solid bioreactor for the removal of clay-free oily sludge samples showed the best results, in which biodegradation of TPH was 90.33%. GC analyses were conducted on samples before and after biodegradation. It was observed that the contaminants were decomposed uniformly by the microorganisms, except for a combination with a large peak in 12 min. For the best case, the GC-MS test was performed before and after biodegradation. Compounds with a high concentration in the sludge were significantly reduced. Only one heavy aromatic compound was detected in 51.628 min, which decomposed quite slowly and produced a large peak. It was found that 78.2% of the compounds were removed completely.

Effects of RAMEB and/or mechanical mixing on the bioavailability and biodegradation of PCBs in soil/slurry

Microbial remediation is preferred as a clean and cost-effective method for restoring environments polluted by organics. But the biodegradation rates of hydrophobic organic contaminants (HOCs) are usually extremely restricted by their low bioavailability, especially in soil. Here, a physical method (mechanical mixing) and a chemical method (randomly methylated-β-cyclodextrins, RAMEB) were adopted to improve the bioavailability and biodegradation of polychlorinated biphenyls (PCBs) of an aged soil. The bioavailability of tri-CBs was increased by adding RAMEB in soil/slurry or assisting mechanical mixing in slurry, but these methods had no effects on the bioavailability of tetra-CBs and high chlorinated PCBs (Cl > 4). The degradation rate of tri-CBs could be obviously enhanced by adding RAMEB in soil or assisting mechanical mixing in slurry. The highest removal amount of tri-CBs reached 43.8% in 100 d with a first-order decay kinetics constant of 0.0059 d(-1). But the removal of tetra-CBs and high chlorinated PCBs (Cl > 4) were not significant in all mesocosms, possibly due to the lack or weakness of the native degrading microflora. Based on the analysis of the richness and diversity of bacterial communities, the characteristics of the heatmap and the variation of bphC copy numbers in the soil/slurry mesocosms, it could be inferred that there was no obvious corresponding relationship between the variation of the bacterial communities and the physical/chemical measures.

Biodegradation of heptadecane in hydrocarbon polluted dune sands using a newly-isolated thermophilic bacterium, Brevibacillus borstelensis TMU30: statistical evaluation and process optimization

An enrichment culture was established to isolate a thermophilic hydrocarbon-degrading bacterium from contaminated soil samples from the Tehran Petroleum Refinery.

Recent development in the treatment of oily sludge from petroleum industry: a review

Oily sludge is one of the most significant solid wastes generated in the petroleum industry. It is a complex emulsion of various petroleum hydrocarbons (PHCs), water, heavy metals, and solid particles. Due to its hazardous nature and increased generation quantities around the world, the effective treatment of oily sludge has attracted widespread attention. In this review, the origin, characteristics, and environmental impacts of oily sludge were introduced. Many methods have been investigated for dealing with PHCs in oily sludge either through oil recovery or sludge disposal, but little attention has been paid to handle its various heavy metals. These methods were discussed by dividing them into oil recovery and sludge disposal approaches. It was recognized that no single specific process can be considered as a panacea since each method is associated with different advantages and limitations. Future efforts should focus on the improvement of current technologies and the combination of oil recovery with sludge disposal in order to comply with both resource reuse recommendations and environmental regulations. The comprehensive examination of oily sludge treatment methods will help researchers and practitioners to have a good understanding of both recent developments and future research directions.

Carbon content reduction in a model reluctant clayey soil: slurry phase n-hexadecane bioremediation

Clayey soils contaminated with organic pollutants are nowadays one of the important environmental issues as they are highly reluctant to conventional bioremediation techniques. In this study, biodegradability of n-hexadecane as a model contaminant in oil polluted clayey soil by an indigenous bacterium was investigated. Maximal bacterial growth was achieved at 8% (v/v) n-hexadecane as sole carbon and energy sources in aqueous phase. The predominant n-hexadecane uptake mechanism was identified to be biosurfactant-mediated using bacterial adhesion to hydrocarbon (BATH) test and surface tension measurements. The effect of n-hexadecane concentration, soil to water ratio, inoculum concentration and pH on total organic carbon (TOC) reduction from kaolin soil in slurry phase was investigated at two levels in shake flasks using full factorial experimental design method where 10,000 (mg n-hexadecane)(kg soil)(-1), soil-water ratio of 1:3, 10% (v/w) inoculum and pH of 7 resulted in the highest TOC reduction of 70% within 20 days. Additionally, slurry bioreactor experiments were performed to study the effect of various aeration rates on n-hexadecane biodegradation during 9 days where 2.5 vvm was found as an appropriate aeration rate leading to 54% TOC reduction. Slurry phase bioremediation is shown to be a successful method for remediation of clayey reluctant soils.

Impacts of microbial redox conditions on the phase distribution of pyrene in soil-water systems

Variations in the soil/sediment organic matter (SOM)-hydrophobic organic contaminant (HOC) bindings upon microbially mediated redox conditions were examined. While the extractability of pyrene associated with soil declined after its biodegradation began during aerobic incubation, its variations were almost constant (+/-3.0-4.4%) during anoxic/anaerobic incubations. The dissolved organic matter released from the soil incubated under highly reduced conditions became more humified and aromatic, had a higher average molecular weight, and was more polydispersed compared to that obtained from oxic incubation, similar to the SOM alterations in the early stage of diagenesis (humification). The concentrations of pyrene in the aqueous phase increased significantly during the soil incubations under highly reduced conditions due to its favorable interaction with the altered DOM. Our results suggest that the microbially mediated redox conditions have significant impacts on SOM and should be considered for the transport, fate, bioavailability, and exposure risk of HOCs in the geo-environments.

Slurry-phase biodegradation of weathered oily sludge waste

We assessed the biodegradation of a typical oily sludge waste (PB401) in Mexico using several regimes of indigenous microbial consortium and relevant bioremediation strategies in slurry-phase system. Abiotic loss of total petroleum hydrocarbons (TPH) in the PB401 was insignificant, and degradation rates under the various treatment conditions ranged between 666.9 and 2168.7 mg kg(-1) day(-1) over a 15 days reaction period, while viable cell count peaked at between log(10)5.7 and log(10)7.4 cfu g(-1). Biostimulation with a commercial fertilizer resulted in 24% biodegradation of the TPH in the oily waste and a corresponding peak cell density of log(10)7.4 cfu g(-1). Addition of non-indigenous adapted consortium did not appear to enhance the removal of TPH from the oily waste. It would appear that the complexities of the components of the alkylaromatic fraction of the waste limited biodegradation rate even in a slurry system.