CENPES/PDISO/BIO - Biotechnology

The effectiveness of cell-free rhamnolipid biosurfactant, derived from the culture medium at the end of fermentation was investigated for the removal of two different kinds of oil from contaminated sandy soils. The crude cultivation medium, containing 13.2 g L −1 of rhamnolipids, had a surface tension, interfacial tension and critical micellar concentration of 30 mN m −1 , 2 mN m −1 and 60 mg L −1 , respectively. The evaluation of biosurfactant in the culture medium (BM) and oil concentrations in the removal of oil from different contaminated sandy soil was performed using a statistical experimental design tool. Oil in sandy soil, containing predominantly aromatic or paraffinic hydrocarbons (5 to 10% w/w), was removed by as much as 91 and 78%, respectively, in the presence of reduced amounts of BM (6.3 to 7.9 g L −1 ). The progress of oil removal was monitored for 101 days and results indicated that removal efficiency in sandy soil with aromatic characteristics was relatively stable over the entire period. Based on these studies, it is concluded that use of a BM was effective in reducing oil concentrations in contaminated sandy soil.

BACKGROUND: Oil spills are a frequent source of environmental contamination. As a consequence, remediation of soils, waters and sediments is a great challenge in this area of research. This study aims at using a new type of soil bioreactor (13 L bench-scale and 800 L pilot-scale) to treat tropical soil contaminated with petroleum. Additionally, it includes the evaluation of the effectiveness of two auxiliary techniques: bulking agent addition (sawdust) and biostimulation using two different nitrogen sources (sodium nitrate and urea).

A biorremediação é uma alternativa atraente para o tratamento de solos contaminados com hidrocarbonetos de petróleo. No entanto, a efetividade do processo pode ser limitada não só pelas características do contaminante, mas também pela sua biodisponibilidade. Este trabalho tem como meta o estabelecimento de procedimento preliminar para identificar o fator principal (recalcitrância ou biodisponibilidade) que interfere negativamente na biodegradação, resultando em baixas eficiências. Foram realizados testes em microcosmos contendo solo aplicando as técnicas de bioestímulo e bioaumento. Experimentos semelhantes foram conduzidos em meio líquido contendo óleo cru e microorganismos extraídos do solo contaminado, nutrientes e inóculo microbiano (Rhodoturula glutinis e Nocardia nova). Após 30 dias, o maior nível de biodegradação (98.8%) foi obtido na condição com bioaumento em meio líquido, indicando que o problema principal de biodegradação de hidrocarbonetos de petróleo pode estar associado à baixa biodisponibilidade destes no solo e não apenas a recalcitrância intrínseca do poluente residual.

Low solubility and adsorption on soil matrix are the two major features of high molecular weight hydrocarbons that limit their availability to microorganisms. Consequently, the use of surfactants in contaminated soils is an interesting strategy to enhance contaminant solubility and their removal from the environment. With this aim, an experimental design technique was adopted involving 4 variables and 2 levels.

Bioremediation processes are being applied nowadays for treatment of contaminated soils by petroleum products. However, only chemical analyses are used for efficiency verification, without taking into account a biological indicator. The aim of this work was the application of two ecotoxicological tests for the evaluation of a soil contaminated by crude oil, after treatment on a bioreactor, in different conditions. Sample A was treated with biostimulation (pH, nutrients and moisture control), while samples B and C, besides biostimulation was applied bulking material (sawdust; 10% w/w) also. The ecotoxicological tests chosen were luminescent bacteria Vibrio fischeri (ISO 11348-3:1998) and an avoidance behavior test with Eisenia fetida earthworms (still in a draft form). This test consists in the exposition of the organisms to contaminated soil and control soil samples, simultaneously, to evaluate the percentage of organisms that goes from the center of the recipient to the control sample sector. The results of avoidance behavior tests of samples A, B and C were, respectively, 52%, 29% and 50%. Those results indicate no toxicity, once the criteria for a sample be considered toxic is that more than 80% of the total exposed organisms are in the control soil at the end of the test. However, the test with Vibrio fischeri indicated toxicity for sample B (CE 50 13.8%), probably because of the recent contamination. Those results indicate that, although the importance of ecotoxicological tests inclusion for the complementation of bioremediation processes evaluation, at least two tests, using different organisms must be performed for a better consideration.