# Augmentation of psychrophilic anaerobic digestion with psychrotolerant Serratia marcescens, calcium phosphate (CaHPO4·2H2O) and hematite (α-Fe2O3) nano-additives

## TL;DR

This study shows that adding a specific bacteria and nano-additives improves methane production in cold anaerobic digestion of organic waste.

## Contribution

The novel approach combines psychrotolerant Serratia marcescens with calcium phosphate and hematite nanoparticles to enhance psychrophilic anaerobic digestion.

## Key findings

- The highest methane yield was achieved with Serratia marcescens and both nano-additives.
- Nano-additives reduced the lag phase and biostimulated digestion without altering microbial communities.
- Methanosarcina was a dominant methanogen across all treatments.

## Abstract

Psychrophilic anaerobic digestion (PAD) requires optimization to improve methane production at low temperatures (<20 °C). This study aimed to improve methane production via bioaugmentation with psychrotolerant Serratia marcescens (SM) and biostimulation with nano-additives, comprising calcium phosphate (CaP) and hematite (α-Fe2O3) nanoparticles (NPs), during batch PAD of cattle manure and food waste at 15 °C. The highest methane yields were obtained from treatment with SM and both NPs (163.9 ± 18.0 mL CH4 g−1 VS), thereafter with the combination of CaP and α-Fe2O3 NPs (143.9 ± 50.2 mL CH4 g−1 VS). The lowest yield was observed in the control (70.2 ± 4.9 mL CH4 g−1 VS) followed by treatment with SM alone (124.6 ± 20.3 mL CH4 g−1 VS). Treatment with CaP and α-Fe2O3 NPs reduced the lag phase more than the other treatments. Moreover, the addition of nano-additives biostimulated PAD without significantly altering the microbial community composition. The dominant genera included Bacteroides, Acinetobacter, and Methanosarcina (a mixotrophic methanogen) after batch PAD across all treatments. This research provides new insights on the augmentative effect of SM, CaP and α-Fe2O3 NPs on methane production and microbial community dynamics during PAD.