Bioreactor-based Bioremediation of Degreaser-Contaminated Soil: A Study on Microbial Synergy and Nutrient Amendments

Abstract

Aim: The aim of this study is to enhance the bioremediation of degreasers used in upstream sectors of Nigeria Petroleum Industry using Bacteria (Pseudomonas and Bacillus species) grown in Bioreactor. Study Design: This study employs experimental designs, Randomized Block Design Treatment set up, Statistical analysis of data and Interpretation. Place and Duration of Study: The area used for this study is within the Rivers State University Demonstration farmland in Nkpolu-Oroworukwo, Mile 3 Diobu, Port Harcourt, Rivers State. The piece of land is situated at Longitude 4048’18.50’’N and Latitude 6058’39.12’’E measuring 5.486m x 5.1816m with a total area of 28.4283m2. The study was for a period of six months. Methodology: The soil was treated for bioremediation as described by Williams & Inweregbu (2019). In this method, nine (9) setups in triplicate each were made. This bioremediation set up was monitored using microbiological (Total Heterotrophic Bacteria, Fungi, Degreaser Utilizing Bacteria (DUB) and Degreaser Utilizing Fungi (DUF) and physicochemical (total hydrocarbon content (THC), nitrogen, potassium, phosphorus, temperature and pH) parameters from day 1 to 56. This was done at 14 days’ interval. Eighty milliliters (80ml) of sterilized water was added to the set up three times weekly and agitated for proper aeration and adequate distribution of microorganisms.  Results: The baseline microbiological analyses revealed that Total Heterotrophic Bacteria count (THBC) ranged from 5.4±0.57 x 10 6 to 6.3±1.06 x 10 6 CFU/g, Degreaser Utilizing Bacteria (DUB) 2.1±0.07 x 10 3 to 4.1±0.64 x 10 3 CFU/g, Fungal count (FC) 1.6±0.85 x 10 3 to 3.33±0.64 x 10 3 CFU/g, and Degreaser Utilizing Fungal count (DUF) 1.6±0.21 x 10 3 to 2.5±0.35 x 10 3 SFU/g.  The bacterial isolates identified were Bacillus, Pseudomonas, Aeromonas, Escherichia and Micrococcus species while fungal isolates identified were Aspergillus flavus, Aspergillus niger, Penicillium sp and Alternaria sp, Candida sp and Fusarium sp. The results of the physicochemical parameters monitored showed that mean pH value ranged from 5.0 to 7.38, Temperature was between 25 and 30oC, Nitrogen concentration ranged from 3.0 to 9.9 mg/kg, Phosphorus (0.05 to 0.58 mg/kg), Potassium ranged from 0.06 to 3.4 mg/kg and the Total Hydrocarbon Content was between 53.1 and 3983mg/kg. Bioremediation efficiency was estimated from percentage (%) reduction of Total Hydrocarbon Content (THC) from day 1 to the residual hydrocarbon on day 56 of bioaugmented/ bio stimulated plots with the control. Results revealed amount of remediated hydrocarbon and % Bioremediation efficiency after 56 days in the different treatment plots (initial THC value of 3984 mg/kg) in a decreasing order as follows:  CS+FPE (76.6%) > CS+Pse+Bac+FPE (74.6%) > CS+Pse (74.4%) > CS+Bac+FPE (73.8%) > CS+Pse+Bac (73.1%) > CS (71.5%)> CS+Pse+FPE (70.6%) > CS+Bac (68.8%) > CTRL 1 –US (66.4%). where bio stimulating agent, FPE (fish pond effluent), CS (Contaminated soil) and bio-augmenting microorganisms, Pse and Bac (Pseudomonas and Bacillus spp.). Conclusion: The study showed that bioremediation of degreaser contaminated soils with combination of organic nutrients is a better degradative option. Therefore, amendment with organic nutrients like fish pond effluent is recommended for degreaser contaminated soils due to their high nutrient content as substrates for biostimulation of indigenous and augmenting biodegrading microbes. Natural bioremediation of degreaser pollutants by activation of naturally occurring microorganisms will be cost effective in cleaning up and protecting the environment from the hazardous effects of hydrocarbons on our agricultural ecosystem.