# Advancing Circular Bioeconomy through a Systems-Level Assessment of Food Waste and Industrial Sludge Codigestion

## TL;DR

This study shows that combining food waste with paper mill sludge in digestion processes can produce more methane and reduce waste disposal costs and emissions.

## Contribution

The novel approach of codigesting food waste and pulp and paper mill sludge is shown to enhance methane yield and sustainability.

## Key findings

- Codigestion of food waste and paper mill sludge increased methane yield by 36% compared to sludge alone.
- Codigestion achieved 92% COD removal, significantly higher than 80% in monodigestion.
- Codigestion reduced costs and emissions compared to landfilling food waste.

## Abstract

Disposal of food waste (FW) in landfills remains an unsustainable
practice for organic waste management. Simultaneously, pulp and paper
mills produce significant amounts of recalcitrant organic waste that
is difficult to decompose due to its high lignocellulosic content.
In this study, we developed an innovative approach to improve the
digestion of pulp and paper mill sludge (PPMS) by amending FW to produce
a low chemical oxygen demand (COD) sludge while recovering methane
in the process. This codigestion process was evaluated through lab-scale
biogas production experiments coupled with a comprehensive economic
and environmental sustainability assessment. Biomethane production
results revealed that the FW-PPMS codigestion methane yield was 36%
higher on average than the PPMS monodigestion. Additionally, metagenomic
analysis revealed that microbial communities for both systems transitioned
from highly heterogeneous to more adapted uniform communities after
digestion. Improved microbial communities contributed to higher COD
removal (92%) in the FW-PPMS system compared to monodigestion (80%
removal). The sustainability analysis revealed that the codigestion
of FW-PPMS had median costs of 236.64 USD·tonne–1·day–1 and emissions of 228.30 kg CO2 eq·tonne–1·day–1,
a significant reduction compared to directly disposing the FW in landfills
(median costs of 405.13 USD·tonne–1·day–1 and emissions of 556.27 kg CO2 eq·tonne–1·day–1). A nationwide contextual
analysis revealed that out of six regions, the US Northeast had the
lowest median costs and emissions, while the Mountain Plains region
had the highest, highlighting the importance of geographical and infrastructural
factors in implementation. Overall, codigesting FW with PPMS is revealed
to be a sustainable waste management option to decrease landfill disposal
of valuable organic waste.