# Reducing spontaneous combustion propensity of lignite through functional group regulation by microbial flame retardant

## TL;DR

This study shows that treating lignite with a specific bacterium can reduce its tendency to spontaneously combust by altering its chemical structure.

## Contribution

The novel contribution is using Pseudomonas putida to modify lignite's functional groups and reduce its spontaneous combustion risk through microbial biotechnology.

## Key findings

- Microbial treatment increased lignite's ignition temperature by 23.95°C and reduced its maximum weight loss rate by 53.75%.
- Oxygen-containing functional groups decreased from 41% to 36%, while aromatic groups increased from 17% to 30%.
- Extracellular enzymes like catalase and esterase peaked at 24 hours, correlating with functional group changes.

## Abstract

This study investigated the effects of microbial treatment on lignite functional group structure and thermal oxidation characteristics using Pseudomonas putida (CICC21884) through Fourier transform infrared spectroscopy (FTIR), thermogravimetry-differential scanning calorimetry (TG-DTG-DSC), spontaneous combustion propensity testing, and enzymatic activity assays. After 72 h of treatment, initial weight loss temperature increased from 140.99 °C to 162.12 °C (+21.13 °C), maximum weight loss rate decreased from 1.6%/min to 0.74%/min (−53.75%), and ignition temperature increased from 270.34 °C to 294.29 °C (+23.95 °C). Oxygen-containing functional groups decreased from 41% to 36%, aromatic groups increased from 17% to 30%, and hydroxyl content decreased from 39% to 31%. The spontaneous combustion propensity index peaked at 540.15 after 24 h (+28.71% vs. raw coal). Three extracellular enzymes—aromatic acid monooxygenase (22.0 U/mL), esterase (68.5 U/mL), and catalase (125.5 U/mg protein)—peaked at 24 h, showing temporal correlation with functional group modifications. Linear regression analysis across seven treatment conditions revealed general trends between functional group composition and thermal stability parameters, with weak to moderate correlations (R2 = 0.11–0.26) influenced by limited sample size and outlier effects. This study suggests that P. putida may degrade the oxygen-containing functional groups and promote coal aromatization, thereby inhibiting the low-temperature oxidation process of lignite and potentially providing an environmentally friendly biotechnological approach for lignite spontaneous combustion prevention.