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Optimization of Operational Parameters during Anaerobic Co-digestion of Food and Garden Waste

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Abstract

Anaerobic co-digestion (AcoD) is a solution to recover renewable energy, such as methane, from food waste (FW) and garden waste (GW). Methane yield efficiency can be improved through the optimization of the operating conditions, such as mixing ratio of substrates (MRS) and Mixing Ratio of Inocula (MRI). The objective was to optimize the AcoD of FW with GW by combining Artificial Neural Networks (ANN) and Particle Swarm Algorithm (PSO). The AcoD of FW and GW were initially evaluated experimentally at a laboratory scale through a central design composed of two factors, at three levels each: FW:GW MRS at 80:20, 70:30 and 60:40 (w/w) and MRI with sludge mixture Granular (GSL) and Flocculant sludge (FSL) equal to 10:90, 30:70 and 50:50 (GSL:FSL, v/v). The response variables were the biochemical methane potential (BMP), bicarbonate alkalinity (BA), volatile fatty acids (VFA), hydrolysis (kh) and process stability index (If). The optimization identified the best operational conditions, which were later validated with a second experiment. Results of ANN and PSO showed that the maximized methane yield (270 mL CH4/g VS) can occur at the ratios of MRS 64:36 (w/w) and at MRI 44:56 (v/v) that increase the methane yield by 26% compared to mono-digestion of FW (70 mL CH4/g VS), while BA of 1645 mg L−1, 1955 mg L−1 of VFA, kh of 0.32d−1 and a stability (If) of −59 are achieved. The second experiment showed the robustness and applicability of the optimization tools, which resulted in a production of 265 mL CH4/g VS as a maximum yield.

Highlights

• Simultaneous optimization of substrate and inoculum ratios increase methane yields

• A mixing ratio of granular:flocculent sludge (44:56%) increased methane yields by 26%

• The optimal neural network topology was 2-4-1 for predicting response parameters

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Data Availability

The data that support the findings of this study are available from the corresponding author on reasonable request.

Abbreviations

AD:

Anaerobic digestion

AcoD:

Anaerobic Co-digestion

ANN:

Artificial neural networks

BA:

Bicarbonate alkalinity

BMP:

Biochemical methane potential

CODt :

Total chemical oxygen demand

CODS :

Soluble chemical oxygen demand

HA:

Hydrolytic activity

If :

Process stability index

FSL:

Flocculant sludge

\( {\mathcal{F}}_{\left(\uptheta \right)} \) :

Objective function

FW:

Food waste

GSL:

Granular sludge

GW:

Garden waste

k h :

Hydrolysis constant

MLP:

Multi-layered perceptron

MR:

Mixing ratio

MRI:

Mixing Ratio of Inocula

MRS:

Mixing ratio of substrates

MSW:

Municipal solid waste

NET:

Neuronic matrix

OM:

Organic matter

PSO:

Particle swarm optimization

R2 :

Determination coefficient

RMSE :

Root Mean Square Error

SAA:

Specific acidogenic activity

SMA:

Specific methanogenic activity

TA:

Total alkalinity

TN:

Total nitrogen

TOC:

Total organic carbon

TP:

Total phosphorus

VFA:

Volatile fatty acids

VS:

Volatile solids

WWTP:

Wastewater treatment plant

λ:

Lag phase

References

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Acknowledgments

The authors thank Universidad Industrial de Santander (UIS) for the support provided doing the development of this research. Jonathan Soto thank Universidad Industrial de Santander for financing of the postdoctoral research: Convocatoria Programa Vicerrectoria de Investigación y Extensión – Apoyo a la formación de posdoctorados (VIE 2020-II).

Code Availability

The code used was developed on the MatLAB®2020a platform and continues to be improved through its validation in other experiments.

Funding

The authors thank the Universidad Industrial de Santander for funding this research.

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Authors

Contributions

All authors contributed to the study conception and design. Material preparation, data collection and analysis were performed by Miguel Casallas-Ojeda, Jonathan Soto-Paz, Wilfredo Alfonso-Morales, Edgar Ricardo Oviedo-Ocaña and Dimitrios Komilis. The first draft of the manuscript was written by Jonathan Soto-Paz and all authors commented on previous versions of the manuscript. All authors read and approved the final manuscript.

Corresponding author

Correspondence to Dimitrios Komilis.

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The authors declare no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

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The study did not involve humans or animals.

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Casallas-Ojeda, M., Soto-Paz, J., Alfonso-Morales, W. et al. Optimization of Operational Parameters during Anaerobic Co-digestion of Food and Garden Waste. Environ. Process. 8, 769–791 (2021). https://doi.org/10.1007/s40710-021-00506-2

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  • DOI: https://doi.org/10.1007/s40710-021-00506-2

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