# Enhanced Degradation of Petroleum and Chlorinated Hydrocarbons by a Dual-Bacteria System

## TL;DR

A dual-bacteria system was found to effectively degrade mixed pollutants of petroleum and chlorinated hydrocarbons, though less effective on single pollutants.

## Contribution

The study introduces a dual-bacteria system for enhanced degradation of coexisting petroleum and chlorinated hydrocarbons.

## Key findings

- The dual-bacteria system achieved 82.2% degradation of phenanthrene and 89.2% of n-hexadecane in mixed pollutants.
- Degradation rates of single pollutants were lower when using the dual-bacteria system compared to a single strain.
- The system showed 73.1% degradation of p-chlorobenzene and 95.7% of dichloroethane in mixed conditions.

## Abstract

In this study, the gradient pressure enrichment method was first used to screen out an environmental bacterium with the degradation ability of typical petroleum hydrocarbons such as phenanthrene and n-hexadecane, identified as Pseudomonas and named TB-1, from soil samples collected from 9 crude oil-contaminated sites; then, enhanced degradation of mixed organic pollutants, including petroleum and chlorinated hydrocarbons which are commonly coexistent, was achieved by a dual-bacteria system, with the addition of a laboratory storage strain Pseudomonas BL5. The degradation rate of phenanthrene and n-hexadecane by the dual-bacteria system was lower compared with the single bacterium Pseudomonas TB-1 under the tested conditions: phenanthrene degradation decreased from 44.2% to 23.1%, and n-hexadecane degradation decreased from 77.9% to 54.7% at a pollutant concentration of 100 mg/L after 7 days of cultivation. In contrast, the degradation ability of the dual-bacteria system against the mixed pollutants composed of petroleum and chlorinated hydrocarbons was good, with a degradation rate of 82.2% for phenanthrene, 89.2% for n-hexadecane, 73.1% for p-chlorobenzene, and 95.7% for dichloroethane with each concentration of 100 mg/L after 7 days. These results indicate that, although the dual-bacteria system does not enhance degradation under single-hydrocarbon conditions, its performance under chemically complex co-contamination suggests a potential cooperative or complementary interaction between the two strains. Such interactions are proposed here as a working hypothesis rather than a confirmed mechanism. Overall, the defined dual-Pseudomonas system shows promising potential for the treatment of environments co-contaminated with petroleum and chlorinated hydrocarbons.