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Biodegradation performed by indigenous bacteria is one of the major technologies that can effectively remove organic pollution from the environment. The success of the bioremediation process depends on the ability to set up and maintain the optimal conditions for the contaminant biodegradation. Soil excavation followed by ex situ bioremediation is mostly applied to accelerate the site clean-up efficiency of the contaminated soil. An overview of various bioremediation techniques for soil treatment will be provided in this chapter. Basic information on the optimal conditions, the biodegradable contaminants, and the different kinds of bioremediation stimulants with their efficiency will be presented in comparison with the application of allochthonous bacteria. This chapter is especially devoted to the petroleum hydrocarbons, which still represent the main pollutants that are removable by bioremediation in real applications. The topic of bioremediation of persistent organic pollutants will be mentioned only marginally as it will be discussed in detail in the following chapters.

In this chapter, a field study from an oil field in Kazakhstan is described. This study ranges from lab- and pilot-scale tests to the application of a new on-site technology. Although it is related to biodegradation only marginally, this study shows a new approach to the remediation of sites with enormous oil contamination. The dense medium separation technology is based on the physical pretreatment (gravity separation in heavy suspensions), followed by bioremediation. Contaminated soil heavily polluted with petroleum substances, including macroscopic petroleum conglomerates with a fraction ≥1 mm, is initially treated by grading. The fine-grained fraction is decontaminated by biodegradation. The coarse-grained fraction is divided by the heavy-suspension separation into a heavy product and a light product. The light product consists of large and light petroleum conglomerates, which are treated by combustion or other processing. The heavy product made up of soil with other petroleum substances is treated by crushing and biodegradation together with the fine-grain fraction. Part of the process comprises recycling of process water and heavy suspension, where the process water is also used to wet the material during biodegradation.

In situ bioremediation (ISB) using reductive dechlorination is a widely accepted but relatively slow approach compared to other technologies for the treatment of groundwater contaminated by chlorinated ethenes (CVOCs). Due to the known positive kinetic effect on microbial metabolism, thermal enhancement may be a viable means of accelerating ISB. We tested thermally enhanced ISB in aquifers situated in sandy saprolite and underlying fractured granite. The system comprised pumping, heating and subsequent injection of contaminated groundwater aiming at an aquifer temperature of 20-30°C. A fermentable substrate (whey) was injected in separate batches. The test was monitored using hydrochemical and molecular tools (qPCR and NGS). The addition of the substrate and increase in temperature resulted in a rapid increase in the abundance of reductive dechlorinators (e.g., Dehalococcoides mccartyi, Dehalobacter sp. and functional genes vcrA and bvcA) and a strong increase in CVOC degradation. On day 34, the CVOC concentrations decreased by 87% to 96% in groundwater from the wells most affected by the heating and substrate. On day 103, the CVOC concentrations were below the LOQ resulting in degradation half-lives of 5 to 6days. Neither an increase in biomarkers nor a distinct decrease in the CVOC concentrations was observed in a deep well affected by the heating but not by the substrate. NGS analysis detected Chloroflexi dechlorinating genera (Dehalogenimonas and GIF9 and MSBL5 clades) and other genera capable of anaerobic metabolic degradation of CVOCs. Of these, bacteria of the genera Acetobacterium, Desulfomonile, Geobacter, Sulfurospirillum, Methanosarcina and Methanobacterium were stimulated by the substrate and heating. In contrast, groundwater from the deep well (affected by heating only) hosted representatives of aerobic metabolic and aerobic cometabolic CVOC degraders. The test results document that heating of the treated aquifer significantly accelerated the treatment process but only in the case of an abundant substrate.

The present report describes a 13month pilot remediation study that consists of a combination of Cr(VI) (4.4 to 57mg/l) geofixation and dechlorination of chlorinated ethenes (400 to 6526μg/l), achieved by the sequential use of nanoscale zerovalent iron (nZVI) particles and in situ biotic reduction supported by whey injection. The remediation process was monitored using numerous techniques, including physical-chemical analyses and molecular biology approaches which enabled both the characterization of the mechanisms involved in pollutant transformation and the description of the overall background processes of the treatment. The results revealed that nZVI was efficient toward Cr(VI) by itself and completely removed it from the groundwater (LOQ 0.05mg/l) and the subsequent application of whey resulted in a high removal of chlorinated ethenes (97 to 99%). The persistence of the reducing conditions, even after the depletion of the organic substrates, indicated a complementarity between nZVI and the whey phases in the combined technology as the subsequent application of whey phase partially assisted the microbial regeneration of the spent nZVI by promoting its reduction into Fe(II), which further supported remediation conditions at the site. Illumina sequencing and the detection of functional vcrA and bvcA genes documented a development in the reducing microbes (iron-reducing, sulfate-reducing and chlororespiring bacteria) that benefited under the conditions of the site and that was probably responsible for the high dechlorination and/or Cr(VI) reduction. The results of this study demonstrate the feasibility and high efficiency of the combined nano-biotechnological approach of nZVI and whey application in-situ for the removal of Cr(VI) and chlorinated ethenes from the groundwater of the contaminated site.

Floristic composition in three industrial areas with soils contaminated by heavy metals (As, Cd, Cu, Hg, Pb, Zn) and organic pollutants (polychlorinated biphenyls) was studied. The content of Pb was only significantly correlated with the floristic composition and explained 13.8% of its variability considering spatial dependency of the sites. No correlation was found for PCBs. Altogether, 237 plant vascular species were found at three study sites (117, 133 and 105, respectively). The three study areas differed in their species composition represented by their own characteristic species. The gradient in the content of natives/non-natives, species number, prevailing life forms and indicator values for plant species investigated was revealed. Based on our results, for phytoremediation purposes we can select productive plant species with high biomass and ability to accumulate large amounts of heavy metals or organic compounds and surviving on soils with low mineral content.