Microbial Volatile Organic Compounds as Microecological Stability Indicators in Response to Temperature Changes during Anaerobic Digestion

The use of traditional early warning indicators for monitoring anaerobic digestion (AD) is limited, owing to their inability to sensitively reflect microbial performance. Microbial volatile organic compounds (mVOCs) possess distinctive species-specific characteristics, functioning as a communication mechanism between microorganisms at two distinct levels: interspecific and intraspecific, and they can be potential indicators of microbial performance. Therefore, we conducted time-series and comparative nontarget analyses using headspace solid-phase microextraction and high-resolution mass spectrometry to investigate temporal variations in mVOC responses to temperature changes during AD. In total, seventy-six differential mVOCs, playing crucial roles in important material and energy metabolism, signaling, and membrane transport processes throughout AD, were investigated after gradual and pulsed temperature perturbations. These differential mVOCs exhibited high co-occurrences with bacteria and archaea based on 16S rRNA gene sequencing analysis. The study findings suggest that mVOCs can serve as explanatory indicators during AD monitoring, bridging AD process stability, and anaerobic microecology. However, further verification is necessary, owing to the wide range of mVOC types involved.