Application of cowdung and sawdust as biostimulants for enhanced bioremediation of diesel contaminated soil

Abstract

The study was aimed at exploring the use of cow dung (CD) and sawdust (SD) as bio stimulants for enhanced ex-situ bioremediation of diesel fuel contaminated soil. Results of the microbial populations in a gram of soil showed that diesel polluted soil amended with CD had the highest total culturable heterotrophic bacterial (TCHB) population range (1.42 x 10⁶ - 1.56 x 10⁷Cfu/g), total fungal (TF) (1.0 x 10⁶ – 1.60x10⁷Cfu/g), hydrocarbon utilizing bacteria (HUB) (4.5 x 10⁶ – 2.05 x 10⁷Cfu/g) and hydrocarbon utilizing fungi (HUF) (3.5 x 10⁶ – 1.3 x 10⁷Cfu/g) respectively during the study. Diesel polluted soil amended with SD had lower TCHB populations (1.32 x 10⁶ – 2.0 x 10⁷Cfu/g), TF (6.0 x 10⁶ – 3.6 x 10⁷ Cfu/g), HUB (5.4 x 106 – 1.28 x 10⁷Cfu/g) and HUF (1.2 x 10⁶ – 2.0 x 10⁶Cfu/g) respectively, while the microbial populations in option C (control) were TCHB (1.14 x 106 – 1.18 x 10⁷Cfu/g), TF (1.7 x 10⁶ – 7.0 x 10⁶Cfu/g), HUB (4.2 x 10⁶ – 7.8 x 10⁶Cfu/g) and HUF (1.1 x 106 – 5.0 x 10⁷Cfu/g) respectively. Changes in pH values showed reductions in CD (7.10 – 6.20) and SD (5.78 – 4.88) amended soils. Percentage losses in TPH from chromatography results showed diesel polluted soil amended with CD (61.30%), SD (41%) and control (4.11%) respectively. Characterization and identification tests of bacterial isolates revealed that a microbial consortium comprising of the following HUB genera; Bacillus, Pseudomonas, Proteus, Alcaligenes, Klebsiella, Enterobacter, Citrobacter, Corynebacterium and Escherichia coli was implicated in the biodegradation process. Similarly, the HUF encountered were Fusarium, Aspergillus, Microsporium, Penicilium and Mucor. The results suggest that the application of cow dung as biostimulant will enhance the bioremediation of diesel contaminated soil than the application of sawdust.

Keywords: Cowdung, Sawdust, Bioremediation, Biostimulation