N. Christofi

Microbial surfactants and their use in field studies of soil remediation.

The degree of association of organic and inorganic pollutants is governed by the complex physico-chemical interactions at interfaces. This association involves sorption onto soil constituents, sequestration within the soil matrix (micropores) and partitioning in a nonaqueous phase liquid (NAPL) that will, ultimately, control the fate of the contaminants. NAPL represents organic substances that are relatively insoluble in water providing a long-term source of pollutant. They represent a continuous input into the water phase to replace degraded or dissipating concentrations. As a result the bioavailability of contaminants to biodegradation may be reduced (Ogram et al. 1985; Miller and Alexander 1991). The enhancement of natural biological degradation processes, in what is termed bioremediation, can be a preferred cost-effective method of removing contaminants from soil-contaminated and other contaminated environments. The role of microorganisms has been shown to be essential in the remediation of, at least, organic pollution, and the activity of microbial types naturally present can be enhanced by bioremediation techniques which include increased aeration of the polluted material and nutrient additions (Christofi et al. 1998; Ivshina et al. 1998). Supplementing the source of microorganisms capable of degrading particular pollutants (bioaugmentation) and the enhancement of the desorption of pollutants from particulates using surfactants can increase hydrocarbon degradation (Deschenes et al. 1995; Thibault et al. 1996; Christofi et al. 1998; Ivshina et al. 1998). It is only 10–15 years that the use of surfactants in increasing the availability of hydrophobic pollutants in soils and other environments has been considered (Vigon and Rubin 1989). Previous studies have revealed that surfactants can enhance pollutant desorption and availability (Oberbremer et al. 1990; Zang and Miller 1992; Volkering et al. 1995; Rahman et al. 2002). They have been applied in oil washing for secondary oil recovery and to clean oil pipes and oil reservoirs (Osipow 1962). In desorption, both synthetic and natural (biological) surfactants have been used. However, it is not always the case that increasing the bioavailability of nonpolar organic substances through the use of surfactants leads to increased degradation or removal. Synthetic surfactants have also been shown to decrease organic degradation (Bruheim et al. 1999) possibly through, for example, the toxic effects of the surfactant (Rouse et al. 1994). It can also be assumed that increasing bioavailability of a pollutant can lead to an increasing toxicity to degrading microorganisms. It has been shown that sorption of toxicants is one major factor controlling bioavailability and toxicity (Welp

A comparison of five rapid direct toxicity assessment methods to determine toxicity of pollutants to activated sludge

Five rapid direct toxicity assessment methods were used in three European partner countries to determine the toxicity of single toxicants, mixed toxicants and real industrial wastes. The final aim was to protect microbial degradation of organic wastes in biological treatment processes and hence enhance the quality of treated effluents to be discharged to the environment. Nitrification inhibition, Respirometry, Adenosine triphosphate luminescence and Enzyme inhibition were tested utilising activated sludge as the testing matrix. The Vibrio fischeri toxicity test was used as a surrogate to compare the various microbial bioassays. The IC50 (toxicant concentration eliciting a 50% inhibitory effect) was determined for a number of pollutants including single toxicants Cd, Cr, Cu, Zn, 3,5-dichlorophenol, toluene and linear alkylbenzenesulphonate (LAS); a standard mixture of metals and LAS; a standard mixture of organics and LAS, and 16 industrial effluents. The V. fischeri bioassay was also chosen in order to assess quality control of toxicant preparation during testing in the different laboratories of the partner countries. Comparisons of sensitivity, cost of implementation, cost per test, relevance, and ease of use were made. The most sensitive bioassays were V. fischeri and Nitrification inhibition, however, this depended in the main on the pollutant and mixtures tested. It is recommended that during assessment of wastewater toxicity a suite of tests be used rather than reliance on one particular test.

Recovery of Rhodococcus biosurfactants using methyl tertiary-butyl ether extraction.

In the present study, we proposed methyl tertiary-butyl ether (MTBE) as a solvent for extraction of biosurfactants from Rhodococcus bacterial cultures. After comparison with other well known solvent systems used for biosurfactant extraction, it was found that MTBE was able to extract crude surfactant material with high product recovery (10 g/l), efficiency (critical micelle concentration (CMC), 130-170 mg/l) and good functional surfactant characteristics (surface and interfacial tensions, 29 and 0.9 mN/m, respectively). The isolated surfactant complex contained 10% polar lipids, mostly glycolipids possessing maximal surface activity. Ultrasonic treatment of the extraction mixture increased the proportion of polar lipids in crude extract, resulting in increasing surfactant efficiency. Due to certain characteristics of MTBE, such as relatively low toxicity, biodegradability, ease of downstream recovery, low flammability and explosion safety, the use of this solvent as an extraction agent in industrial scale biosurfactant production is feasible.

Alkanotrophic Rhodococcus ruber as a biosurfactant producer

Abstract. In this report we examined the structure and properties of surface-active lipids of Rhodococcus ruber. Most historical interest has been in the glycolipids of Rhodococcus erythropolis, which have been extensively characterised. R. erythropolis has been of interest due to its great metabolic diversity. Only recently has the metabolic potential of R. ruber begun to be explored. One major difference in the two species is that most R. ruber strains are able to oxidise the gaseous alkanes propane and butane. In preparation for investigation of the effects of gas metabolism on biosurfactant production, we set out to characterise the biosurfactants produced during growth on liquid n-alkanes and to compare these with R. erythropolis glycolipids.

Oil desorption from mineral and organic materials using biosurfactant complexes produced by Rhodococcus species

Rhodococcus strains from the culture collection at the Institute of Ecology and Genetics of Microorganisms, Perm, Russia were examined for biosurfactant production during growth on n-alkanes and the ability to remove oil associated with contaminated sands and oil shale cuttings. Members of the genus, particularly R. ruber, were shown to produce low toxicity surfactants effective in removing oil from surfaces. The extent of desorption was inversely related to the concentration of high molecular weight hydrocarbons, namely asphaltenes and resins. In addition, crude surfactant complexes enhanced the degradation of crude oil, in the short term, when added to contaminated agricultural soil during bioremediation studies utilizing biopiling technology.

Comparison of alternative treatments for 4-chlorophenol removal from aqueous solutions: Use of free and immobilized soybean peroxidase and KrCl excilamp

The removal of 4-chlorophenol (4-CP) from industrial wastewater continues to be an important environmental issue and some interesting results have been obtained using oxidoreductive enzymes such as peroxidases and UV, generated by novel excilamps. In this study enzyme (free and immobilized soybean peroxidase) and UV (produced by a KrCl excilamp) were used to treat 4-CP solutions at concentrations ranging from 50 to 500 mg L(-1). It was shown that the excilamp can facilitate higher removal efficiencies in all cases with complete 4-CP elimination taking place between 5 and 90 min. The enzyme removed approximately 80% of the 4-CP concentrations in both the free and immobilized state up to concentrations of 250 mg L(-1). At 500 mg L(-1) the immobilized system shows much higher removal efficiency due to increased enzyme stability in the presence of higher formation of by-products.

An ATP luminescence method for direct toxicity assessment of pollutants impacting on the activated sewage sludge process

An ATP luminescence method was used to determine the toxicity of three reference toxicants to two sources of domestic activated sludge, and an activated sludge from a laboratory model plant. Repeatability in the ATP test was demonstrated for Cr (as K2Cr2O7), Zn (as ZnSO4 x 7H2O), and 3,5-dichlorophenol (3,5-DCP) using each source of activated sludge. The three sources of sludge showed sensitivity to Cr and 3,5-DCP, and insensitivity to Zn using the ATP luminescence method. Sludge source did not appear to effect test response. The toxic response to 3,5-DCP in model and domestic activated sludge was shown to be dependent on sludge solid concentration (measured as total suspended solids, gTSS(-1). It is recommended that a standard solids concentration is used during toxicity evaluation.

Bioremediation of Crude Oil-Contaminated Soil Using Slurry-Phase Biological Treatment and Land Farming Techniques

Field-scale experiments on bioremediation of soil heavily contaminated with crude oil were undertaken on the territory of the Kokuyskoye oil field (Perm region, West Urals, Russia) owned by the LUKOIL Company. The pollution consisted of the contents of a oil waste storage pit, which mostly received soils contaminated after accidental oil spills and also the solid n-alkane (paraffin) wastes removed from the surface of drilling equipment. Laboratory analyses of soil samples indicated contamination levels up to 200 g/kg of total recoverable petroleum hydrocarbons (TRPH). Average oil composition consisted of 64% aliphatics, 25% aromatics, 8% heterocyclics, and 3% of tars/asphaltenes. Ex situ bioremediation techniques involved the successive treatment of contaminated soil using a bioslurry reactor and land farming cells. An oleophilic biofertilizer based on Rhodococcus surfactant complexes was used in both treatment systems. An aerobic slurry bioreactor was designed, and the biofertilizer applied weekly. Slurry-phase biotreatment of the contaminated soil resulted in an 88% reduction in oil concentration after 2 months. The resulting reactor product, containing approximately 25 g/kg of TRPH, was then loaded into land farming cells for further decontamination. To enhance bioremediation, different treatments (e.g., soil tilling, bulking with woodchips, watering, and biofertilizer addition) were used. The rates of oil biodegradation were 300 to 600 ppm/day. As a result, contamination levels dropped to 1.0 to 1.5 g/kg of TRPH after 5 to 7 weeks. Tertiary soil management involved phytoremediation where land farming cells were seeded with a mixture of three species of perennial grass. The effect of phytoremediation on the residual decontamination and rehabilitation of soil fertility is being evaluated.

Disinfection by-product formation after biologically assisted GAC treatment of water supplies with different bromide and DOC content

Abstract Chlorination of drinking water in the presence of bromide and dissolved organic carbon (DOC) leads to the formation of brominated and chlorinated disinfection by-products (DBP). The concentration of bromide ions in the raw water is a significant factor in the speciation of DBP formed, and causes shifts in trihalomethane (THM) formation from chlorinated to brominated species. Drinking water treatment techniques that remove organic contaminants without affecting bromide ion concentrations cause increases in the brominated THM. For the present study, three water supplies containing different DOC and ambient bromide concentrations were filtered through biologically assisted granular activated carbon (BGAC). Similar to adsorption and coagulation treatment, this treatment does not remove bromide from drinking water; also, THMFP (trihalomethane formation potential) analysis indicated that the chlorinated effluent contained higher concentrations of brominated THM in comparison to the influent. Although BGAC may increase the brominated THM, which may be more toxic than the chlorinated THM, the overall reduction of THMFP by DOC removal far exceeds this negative change, thereby producing a much less toxic finished drinking water. This work is part of a study to make high DOC surface waters on the Canadian prairie safe and palatable for small volume users (individuals or small communities).

Efficiency of KrCl excilamp (222 nm) for inactivation of bacteria in suspension

Aims:  To examine the killing efficiency of UV KrCl excilamp against Gram‐positive and Gram‐negative bacteria.