DARWIN has participated in a project aimed at improving the productivity of a biogas production plant located in Jena, Germany. In this project, it was applied a third-generation portable sequencer that allowed real-time monitoring of the microbial communities involved in the biogas generation process.

Anaerobic digestion is a well-established technology that enables microbial conversion of the biomass present in wastewater sludges into methane and carbon dioxide. This work utilized liquid and solid fractions of grass biomass as co-substrates for anaerobic co-digestion with sewage sludge.

The amount of grass biomass was gradually increased, and the underlying methanogenic microbiome was evaluated using cell counting based on microscopy and high-throughput sequencing of full-length 16S rRNA gene. This demonstrated, for the first time, the suitability of nanopore-based portable sequencers as a monitoring tool for anaerobic digestion systems.

Problem

The production of a biogas plant depends on the microorganisms inside it, which are typically studied using techniques that are slow. Therefore, until now, analysis of anaerobic microbiomes was only known once the production had concluded.

Additionally, common cultivation or sequencing methods make it difficult to access the underlying microbial diversity. Often, 16S rRNA sequence reads are short and do not allow classification into more specific taxonomic levels.

Solution

For the first time, intervention in the process was achieved almost in real time through the application of a third-generation portable sequencer. The results presented show that the feeding strategy of the digesters greatly influences the success of the process, as the successful adaptation of sewage sludge microorganisms to higher loading rates depends on their feeding.

High-throughput sequencing allows the obtention of sufficient sequences to cover most of the species housed in the sludge. The MinION tool provides sequencing of the plant’s archaea within hours, enabling classification into more specific taxonomic levels. This facilitates making changes in the digester and thus improving production in time, before the process concludes. Altogether, this has reduced the response time from weeks to hours.

Completion Year: 2018

Success

Although the microbial communities were very different between batches fed with solids and liquids, in both cases, co-fermentation resulted in a greater number of methanogenic bacteria and archaea. However, batches fed with liquid developed a more stable microbiome, enriched in Methanosarcina spp., and resulted in higher methanogenic yield. In contrast, batches fed with solids were highly unstable at higher substrate concentrations and remained enriched in Methanosaeta spp., typically associated with sewage sludge.

Following these results, the microbiome of reactors fed with liquid was reformed, shifting from a community dominated by Methanosaeta spp. to one enriched with Methanosarcina spp. This work concludes that the addition of liquid co-substrates resulted in a more effective methanogenic microbiome and allowed for increased biogas production.

The results confirm the high potential to increase the efficiency of wastewater treatment plant sludge digesters. Specifically, the technology applied enables improvement of the microbial community present in the digesters and increases daily biogas production from wastewater by between 50% and 60%.

Press

• The company Darwin increases the productivity of a biogas plant by 50%. – La Vanguardia
• The company Darwin increases the productivity of a biogas plant by at least 50% – PCUV

Papers

• J. Hardegen, A. Latorre-Pérez, C. Vilanova, T. Günther, M. Porcar, O. Luschnig, C. Simeonov, C. Abendroth. Methanogenic community shifts during the transition from sewage mono-digestion to co-digestion of grass biomass. Bioresour. Technol., 265 (2018), pp. 275-281, 10.1016/j.biortech.2018.06.005