Resilience of the wastewater biocoenosis
Microbial communities determine the stability and performance of biological wastewater treatment plants. The diversity and analysis of indicator organisms can be monitored using molecular biological methods and disruptions can be detected and rectified at an early stage.
Biocoenosis as a central control variable
The wastewater biocenosis comprises the entirety of all microorganisms in the respective plant section. Its composition determines to a large extent whether biological purification performance is stable. Diversity is crucial: the wider the functional and taxonomic spread, the higher the probability that failures of individual groups will be compensated for. Conversely, low diversity increases the risk of a tipping point with a rapid loss of function.
Every plant has home populations. Although there are similarities within communal and industrial systems, the specific interaction between the groups is site-specific. The greater the diversity, the higher the resilience. Resilience here means the resistance of the biocoenosis to external influences.
The biocenoses are dynamic and regulate themselves within a buffer zone. However, the balance can still be permanently shifted in the event of strong external influences. It is therefore important to measure resilience.
Measuring resilience via diversity
Resilience can be determined as a trend variable of diversity. The number of taxonomic units (OTUs) is determined using 16S rDNA amplicon sequence analyses. The focus here is also on temporal development: resilience usually changes over weeks and is therefore suitable for more extensive monitoring. However, the quantification of individual species based solely on amplicon data is only of limited value in wastewater treatment plants due to technology-related biases. Above all, it provides indications for the classification of changes. VIT® gene probe technology should be used for exact quantification.
Evaluate function using indicators
Functionality is what counts for operational control. This is tracked using specifically selected indicator organisms - positive-acting, problem-causing or accompanying groups. VIT® gene probe technology is used for this purpose: specific probes bind to ribosomal target structures, make the cell glow and thus allow identification, quantification and visualization in the sample. The visualization provides additional context, for example on the association and interaction of functional populations. In this way, changes in functionality can be mapped closely and close to the cause.
Two practical examples
Example 1: In an industrial plant, the average diversity over months was just under 100 OTUs - an area of maximum resilience. External influences (toxic discharges due to overproduction) gradually reduced the diversity; the biocoenosis collapsed at the end of August 2023. Based on a VIT®-supported population comparison with other plants, a sludge was inoculated at the beginning of September with a profile that came closest to the target state.
Example 2: In an anaerobic pellet sludge reactor , the monitoring of Chloroflexi, which are conducive to pellet integrity, and contraindicated KSB3 filaments served as a functional indicator. The increasing pellet decay could be clearly traced along these indicators: an early warning signal for operational management.
Consequences for operation
The combined view of diversity (resilience) and indicator organisms (function) creates a reliable basis for control and prevention. Continuous monitoring makes it possible to react before limit values are exceeded and to avoid cost-intensive remediation.
Sequence data is particularly suitable for stability trends, as specific in situ evidence of the relevant microorganisms is required for targeted intervention in the system. This results in a practical, targeted operating concept for municipal and industrial plants.
