Functional and molecular approaches for studying and controlling microbial communities in anaerobic digestion of organic waste: a review

Anaerobic digestion (AD) has been studied for centuries, but its operation still mainly relies on physicochemical indicators. Recent advanced molecular biological tools can unveil the nature of the AD process since microbial activity is directly related to digester performance. The paper summarized up-to-date microbiological and molecular biological analysis techniques applied in AD, including PCR-based techniques, electrophoresis, next-generation sequencing, MS-based techniques, and visualization-based techniques. In addition, the paper also reviewed the techniques that link microbial identity and activity to ecological function. Molecular biological techniques can identify microbial activity and AD process disturbance, but research on on-site analysis of microbial communities for a full-scale system is lacking. One of the most suitable methods for studying microbial communities in anaerobic digesters is fluorescence in situ hybridization, which does not require preparative isolation and cultivation. Another very important method is the use of physiological fluorescent probes to reveal the functional characteristics of methanogenic communities by CTC (5-cyano-2,3-ditolyl tetrazolium chloride)/DAPI (4'-6 diamino-2 phenylindole), which is a very rapid, sensitive and informative assay. These methods, together with the application of confocal laser microscopy, and the study of polyphosphate granules and Co-factor 420 of the microbial communities allow us a very effective and targeted functional-molecular control of the processes in anaerobic digesters. Graphical abstract: [Figure not available: see fulltext.].