Statistical optimization and kinetic studies of enhanced bioremediation of crude oil - contaminated marine water using combined adsorption-biostimulation strategy

Samuel E Agarry

doi:10.4314/jasem.v21i1.7

Abstract

The objectives of this study were to investigate and evaluate through Taguchi orthogonal experimental design the effects of amendment agents as well as the optimization and kinetics of enhanced bioremediation of crude oil-contaminated marine water using combined adsorption-biostimulation strategy. The amendment agents are organic fertilizer, slow release inorganic NPK fertilizer, commercial activated carbon and Tween 80. Bioremediation of weathered Escravos crude oil (WECO)-contaminated marine water was studied for four weeks in ten plastic buckets open system. The oil-contaminated marine water in nine of the buckets was each amended with the amendment agents according to Taguchi’s (L9) orthogonal array of four factors and three levels and the tenth un-amended bucket served as control (natural bioattenuation). Results showed that the amendment agents had relative significant influence on the enhancement of WECO-marine water bioremediation. The optimum amendment agent conditions were determined as follows: organic fertilizer 30 g, inorganic slow release NPK fertilizer 4 g, activated carbon 30 g, and Tween 80, 1.5 g. Under these optimum conditions, the optimum percentage of crude oil biodegradation achieved was 98.25%. Bioremediation kinetic data of WECO fitted well to the first-order kinetic model. The combined adsorptionbiostimulation strategy (using the amendment agents) resulted in higher biodegradation rate constant, k (0.0443 - 0.1183 day -1 ) and lower biodegradation half-life, t 1/2 (5.86 – 15.6 days) of the WECO biodegradation than the natural bioattenuation with lower k (0.0144 day -1 ) and higher t 1/2 (48.8 days). Therefore, the amendment agents have effective potential application as a tool for combined adsorption-biostimulation strategy in the remediation of crude oilcontaminated aquatic environment. Keywords: Biodegradation; Bioremediation; Amendment agents; Crude oil; Kinetics; Optimization

Highlights

Marine oil pollution has elicited more public concern than any other waste or spilt material
These results indicated that the combined addition of nutrients, adsorptive/biocarrier agent and surfactants (Tween 80) enhanced the rate of crude oil biodegradation
The results indicated that the biodegradation half-life time of crude oil subjected to natural bioattenuation was more than 40 days and this was reduced to very low half-life time using the combined adsorption-biostimulation strategy

Summary

Introduction

Marine oil pollution has elicited more public concern than any other waste or spilt material. Taguchi method being one of the powerful optimization techniques, is a simple mathematical and statistical tool involving a system of tabulated designs (arrays) that allows a maximum number of main effects to be estimated in an unbiased (orthogonal) fashion with a minimum number of experimental runs (CastorenaCortes, 2009). This method establishes the relationship between variables and operational conditions (Roy 2001). The amendment agents are organic fertilizer (fertilizer composed or compounded of cattle dung, pig dung and poultry droppings), slow release inorganic NPK fertilizer, commercial activated carbon (adsorbent/biocarrier) and Tween 80 (non-ionic surfactant)

Objectives

Methods

Findings

Conclusion