Austrian Science Fund project: Temp4AD
Firing up anaerobic digestion – a high-res temperature assay

Start of the project
January 2025

Principal Investigator
Sabine M. Podmirseg

Research Context

The project addresses the increasing global energy demand and the need to reduce greenhouse gas emissions to meet UN climate goals and the European Green Deal strategy. In this context, anaerobic digestion (AD) is a promising renewable energy source due to its ability to produce biogas consistently or on demand, utilizing organic wastes from various sources. The project aims to optimize the AD process by meticulously assessing the effects of temperature on a fed-batch lab-scale AD system, also considering the importance of inoculum in influencing the system’s functionality and efficiency.

Hypotheses

There are three main hypotheses:

1. Small changes in process temperature affect biogas and methane yields, with the best-performing reactors expected between 40°C and 50°C. The microbial community structure is hypothesized to change gradually from 34°C to 61°C, with different temperature optima for each of the three starting inocula.
2. AD systems can tolerate moderate organic loading rate (OLR) peaks, but extreme peaks may lead to volatile fatty acids (VFA) accumulation and unstable fermentation. The robustness of the system against OLR shocks is expected to vary with temperature and inoculum, with reactors operated between 40°C and 50°C being more stable.
3. While minor temperature fluctuations can be tolerated by well-adapted AD systems, higher amplitudes may lead to severe process disruption. Reactors between 40°C and 50°C are expected to be more robust due to high microbial versatility in both directions.

Objectives & Methods

The main objective is to assess the effects of temperature on a fed-batch lab-scale AD system across a broad temperature range (34°C to 61°C) with high resolution (3°C steps). The project aims to determine the temperature optima for biogas production, evaluate the robustness of AD systems against unstable or extreme OLRs, and investigate the resilience of AD systems towards fluctuating reactor temperatures applying a plethora of microbial community investigation tools.

These methods include a continuous monitoring of physico-chemical, biogas-yield and -quality related parameters during the experiments, DNA-based quantification and investigation of prevailing microorganisms through 16S rRNA amplicon sequencing and droplet digital PCR and microbial function evaluation via meta-proteomics, and meta-genomics.

Originality

The project is innovative in its comprehensive assessment of the entire temperature range from 34°C to 61°C at high resolution, which has not been done before. It also uniquely considers the influence of different inocula on AD systems, evaluates tolerance towards feeding stress and extreme OLRs, and investigates the impact of regular and irregular temperature fluctuations on AD processes.