# Anaerobic Codigestion of Municipal Wastewater, Landfill Leachate, and Crude Glycerin: Process Stability and Methane Yield Assessment Using a Screening Design

## TL;DR

This study shows that combining wastewater, landfill leachate, and glycerin in anaerobic digestion can produce high methane yields, but requires careful balancing of ingredients.

## Contribution

The study identifies optimal proportions of landfill leachate and crude glycerin for anaerobic codigestion to maximize methane yield.

## Key findings

- A 2% landfill leachate and 1% crude glycerin mix achieved near-theoretical methane yields.
- Higher crude glycerin content reduced methane yield, indicating a dosing threshold.
- Microbial adaptation was robust, with short lag phases despite leachate toxicity.

## Abstract

Water resource recovery facilities often receive landfill leachate (LL), which can disrupt biological processes due to its toxicity and low biodegradability. This study evaluates the anaerobic codigestion (AcoD) of municipal wastewater (MWW), LL, and crude glycerin (CG) as a strategy to enhance organic matter removal and methane yield. Batch reactors were operated under varying conditions defined by a Plackett–Burman screening design, and methane production kinetics were modeled using modified Gompertz and Cone equations. Soluble chemical oxygen demand (sCOD) removal ranged from 67.4% to 94.3%, whereas methane yield varied between 0.076 and 0.349 L NCH4/g tCODadd (liters of normalized methane per gram of total COD added). The highest yield was achieved with 2% LL and 1% CG, approaching the theoretical maximum. Statistical analysis revealed that increasing CG content reduced methane yield, and extending the digestion time to 40 days offered limited performance gains. Despite the presence of inhibitory compounds, most conditions showed stable digestion, with short latency phases and effective microbial adaptation. These findings demonstrate the feasibility of codigesting MWW, LL, and CG, especially under optimized proportions, and highlight the potential for energy recovery in wastewater treatment plants using biodiesel by‐products.

Leachate codigestion feasibility: Anaerobic codigestion of LL with MWW and CG is viable.CG impact: The addition of CG, a biodegradable carbon source, reduced methane yield, suggesting an optimal dosing threshold.Microbial adaptation: The inoculum adapted well to the substrate, with short lag phases estimated by modified Gompertz, indicating robust biological activity despite leachate toxicity concerns.Methane yield kinetics: Reverse L‐shaped curves indicated rapid initial methane production, likely due to glycerol. Elongated S‐shaped curves suggested slower hydrolysis, linked to lower CG content and potentially more complex substrates.

Leachate codigestion feasibility: Anaerobic codigestion of LL with MWW and CG is viable.

CG impact: The addition of CG, a biodegradable carbon source, reduced methane yield, suggesting an optimal dosing threshold.

Microbial adaptation: The inoculum adapted well to the substrate, with short lag phases estimated by modified Gompertz, indicating robust biological activity despite leachate toxicity concerns.

Methane yield kinetics: Reverse L‐shaped curves indicated rapid initial methane production, likely due to glycerol. Elongated S‐shaped curves suggested slower hydrolysis, linked to lower CG content and potentially more complex substrates.

Anaerobic codigestion of municipal wastewater with landfill leachate and crude glycerin can achieve near‐theoretical methane yields (0.349 L NCH4/g tCODadd). An optimal mixture of 2% leachate and 1% glycerin was identified, as higher glycerin content negatively impacted performance, highlighting the criticality of substrate balance for energy recovery.