The carboxylate platform offers a sustainable bioconversion strategy for biorefineries, utilizing anaerobic mixed cultures to produce carboxylate mixtures, including medium-chain fatty acids (MCFAs), as valuable intermediates. The effects of carbon sources (glucose, glycerol, casein) and exogenous supplied electron donors (ethanol, methanol, propanol, pyruvate) on MCFA production via chain elongation were investigated to elucidate the role of external electron donors and assess the feasibility of self-sufficient MCFA production in their absence. For this purpose, all experimental sets included corresponding control conditions without external electron donor addition. Batch experiments were conducted without active pH control, allowing pH to evolve dynamically in response to substrate type and metabolic activity. Results showed that the carbon source significantly affected carboxylic acid production and composition. Glucose primarily yielded propionate, independent of the electron donor. Casein resulted in the lowest carboxylic acid and gas production but uniquely produced the highest MCFA. Acidic pH conditions (5.0–5.5), which developed primarily in glucose- and glycerol-fed systems, favoured short-chain fatty acid production, whereas near-neutral pH conditions (6.0–6.7), observed in casein-fed systems, enhanced MCFA formation. Electron donors significantly influenced the degradation rate of glycerol. Methane production was observed in glucose and glycerol sets but was absent in casein sets. Microbial community analysis revealed methanogen dominance across most sets, irrespective of substrate. These findings highlight the complex interactions between pH, electron donor/acceptor availability, and microbial community dynamics in anaerobic digestion. Future multi-omics and flux analyses are needed to elucidate the metabolic pathways governing chain elongation and anaerobic digestion.

In recent years, there has been growing interest in harnessing anaerobic digestion technology for resource recovery from waste streams. This approach has evolved beyond its traditional role in energy generation to encompass the production of valuable carboxylic acids, especially volatile fatty acids (VFAs) like acetic acid, propionic acid, and butyric acid. VFAs hold great potential for various industries and biobased applications due to their versatile properties. Despite increasing global demand, over 90% of VFAs are currently produced synthetically from petrochemicals. Realizing the potential of large-scale biobased VFA production from waste streams offers significant eco-friendly opportunities but comes with several key challenges. These include low VFA production yields, unstable acid compositions, complex and expensive purification methods, and post-processing needs. Among these, production yield and acid composition stand out as the most critical obstacles impacting economic viability and competitiveness. This paper seeks to offer a comprehensive view of combining complementary modeling approaches, including kinetic and microbial modeling, to understand the workings of microbial communities and metabolic pathways in VFA production, enhance production efficiency, and regulate acid profiles through the integration of omics and bioreactor data.

Shifting the concept of municipal wastewater treatment to recover resources is one of the key factors contributing to a sustainable society. A novel concept based on research is proposed to recover four main bio-based products from municipal wastewater while reaching the necessary regulatory standards. The main resource recovery units of the proposed system include upflow anaerobic sludge blanket reactor for the recovery of biogas (as product 1) from mainstream municipal wastewater after primary sedimentation. Sewage sludge is co-fermented with external organic waste such as food waste for volatile fatty acids (VFAs) production as precursors for other bio-based production. A portion of the VFA mixture (product 2) is used as carbon sources in the denitrification step of the nitrification/denitrification process as an alternative for nitrogen removal. The other alternative for nitrogen removal is the partial nitrification/anammx process. The VFA mixture is separated with nanofiltration/reverse osmosis membrane technology into low-carbon VFAs and high-carbon VFAs. Polyhydroxyalkanoate (as product 3) is produced from the low-carbon VFAs. Using membrane contactor-based processes and ion-exchange techniques, high-carbon VFAs are recovered as one-type VFA (pure VFA) and in ester forms (product 4). The nutrient-rich fermented and dewatered biosolid is applied as a fertilizer. The proposed units are seen as individual resource recovery systems as well as a concept of an integrated system. A qualitative environmental assessment of the proposed resource recovery units confirms the positive environmental impacts of the proposed system.

An approach based on wastewater epidemiology can be used to monitor the COVID-19 pandemic by assessing the gene copy number of SARS-CoV-2 in wastewater. In the present study, we statistically analyzed such data from six inlets of three wastewater treatment plants, covering six regions of Stockholm, Sweden, collected over an approximate year period (week 16 of 2020 to week 22 of 2021). SARS-CoV-2 gene copy number and population-based biomarker PMMoV, as well as clinical data, such as the number of positive cases, intensive care unit numbers, and deaths, were analyzed statistically using correlations and principal component analysis (PCA). Despite the population differences, the PCA for the Stockholm dataset showed that the case numbers are well grouped across wastewater treatment plants. Furthermore, when considering the data from the whole of Stockholm, the wastewater characteristics (flow rate m³/day, PMMoV Ct value, and SARS-CoV gene copy number) were significantly correlated with the public health agency’s report of SARS-CoV-2 infection rates (0.419 to 0.95, p-value < 0.01). However, while the PCA results showed that the case numbers for each wastewater treatment plant were well grouped concerning PC1 (37.3%) and PC2 (19.67%), the results from the correlation analysis for the individual wastewater treatment plants showed varied trends. SARS-CoV-2 fluctuations can be accurately predicted through statistical analyses of wastewater-based epidemiology, as demonstrated in this study.