Journal of Hazardous Materials 197 (2011) 80–87 Contents lists available at SciVerse ScienceDirect Journal of Hazardous Materials j ourna l ho me p ag e: www.elsevier.com/l o cate/jhazmat Aerobic remediation of petroleum sludge through soil supplementation: Microbial community analysis M. Venkateswar Reddy, M. Prathima Devi, K. Chandrasekhar, R. Kannaiah Goud, S. Venkata Mohan ∗ Bioengineering and Environmental Centre (BEEC), Indian Institute of Chemical Technology CSIR-IICT, Hyderabad 500 607, India a r t i c l e i n f o Article history: Received 28 April 2011 Received in revised form 8 August 2011 Accepted 15 September 2011 Available online 21 September 2011 Keywords: Surry phase reactor Dehydrogenase activity Polycyclic aromatic hydrocarbons Proteobacterium Phylogenetic tree a b s t r a c t The effect of soil concentration on the aerobic degradation of real-field petroleum sludge was studied in slurry phase reactor. Total petroleum hydrocarbons (TPH) and polycyclic aromatic hydrocarbons (PAHs) showed effective removal but found to depend on the soil concentration. Aromatic fraction (48.12%) doc- umented effective degradation compared to aliphatics (47.31%), NSO (28.69%) and asphaltenes (26.66%). PAHs profile showed efficient degradation of twelve individual aromatic compounds where lower ring compounds showed relatively higher degradation efficiency compared to the higher ring compounds. The redox behaviour and dehydrogenase activity showed a linear increment with the degradation pattern. Microbial community composition and changes during bioremediation were studied using denaturing gradient gel electrophoresis (DGGE). Among the 12 organisms identified, Proteobacteria was found to be dominant representing 50% of the total population (25% of  -proteobacteria; 16.6% of ˇ-proteobacteria; 8.3% of ˛-proteobacteria), while 33.3% were of uncultured bacteria and 16.6% were of firmicutes. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Petroleum industry unavoidably generates large quantities of oily and viscous residue, i.e., the petroleum based oily sludge formed during various productions, transportation and refin- ing processes. The safe disposal of oily waste generated during the processing of crude oil is one of the major problems faced by the oil industry as, improper disposal pollutes environment which includes freshwater, marine and terrestrial habitats. Crude petroleum oil is a complex mixture of hydrocarbons and other organic compounds generally classified into four fractions: aliphat- ics, aromatics, nitrogen sulphur oxygen containing compounds (NSO) and asphaltenes. Aromatic and polar constituents are less biodegradable than aliphatics, while asphaltenes are regarded as non biodegradable that can bring up serious environmental prob- lems when spills occur [1]. There are many techniques available to remediate hydrocarbon polluted soil including in situ meth- ods, such as soil vapour extraction and ex-situ methods such as soil removal and disposal, incineration and chemical treatment [2]. One in situ technique for the remediation of hydrocarbon contaminated soil is bioremediation, which is the application of biological remediation for the treatment of hazardous materials [2,3]. However bioremediation is recognized as an efficient, eco- nomic and versatile alternative to physicochemical treatment of oil ∗ Corresponding author. Tel.: +91 40 27191664; fax: +91 40 27193159. E-mail addresses: vmohan s@yahoo.com, svmohan@iict.res.in (S.V. Mohan). contaminants. Aerobic microbial degradation is the main process, where microorganisms play an important role in the degrada- tion of PAHs. As crude oil contains various compounds, a single strain might not be able to degrade all components. In general, the combined bacterial consortium show better results due to their synergistic effects [4]. Soil slurry bioremediation is a tech- nique used to optimize abiotic conditions for biodegradation. It consists of a mixture of soil and water in various ratios and greatly enhances degradation rates over solid treatment systems by maximizing the contact between microorganisms, hydrocarbons, nutrients and oxygen [2,5]. In slurry bioreactors, the increase in soil moisture results in a larger amount of soluble contaminant, therefore increasing the bioavailability [6]. A better understanding of the microbial communities diversity inhabiting PAHs contami- nated soils and their response to biostimulation strategies could provide clues about the type of bacteria that are able to adapt to exploit such habitats [7]. It is well known that majority of microbes in environmental samples cannot be cultured at present in laboratory media, which are biased for the growth of specific microorganisms [8]. In light of this, molecular biological techniques viz., denaturing gradient gel electrophoresis (DGGE) offers new opportunities and allows us to directly determine the presence and relative levels of different 16S rRNA gene amplicons both qualita- tively and semi quantitatively to perform a community analysis [9]. The present investigation provides an insight in to the aerobic remediation of real field petroleum sludge and the functional role of soil supplementation on the bioremediation efficiency. The study was performed in slurry phase system. Degradation pattern of TPH 0304-3894/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.jhazmat.2011.09.061