# Enhanced Biomethane Conversion and Microbial Community Shift Using Anaerobic/Mesophilic Co-Digestion of Dragon Fruit Peel and Chicken Manure

## TL;DR

Adding dragon fruit peel to chicken manure during anaerobic digestion boosts methane production and stabilizes the process.

## Contribution

Demonstrates that co-digesting chicken manure with dragon fruit peel at a 25:75 ratio significantly enhances methane yield and microbial stability.

## Key findings

- Co-digestion with dragon fruit peel increased methane yield up to 180.3 mL/g VS at a 25:75 ratio.
- The optimal ratio reduced acidification and improved process stability with low volatile fatty acid accumulation.
- Microbial communities like Bacteroidetes, Bacillota, and acetoclastic methanogens were enriched, aiding methane production.

## Abstract

The traditional perspective of waste disposal is no longer appropriate, as the circular economy recognizes organic waste as a key potential for both nutrition and energy recovery. Anaerobic digestion has proved high efficacy as a sustainable technique for acquiring energy from organic wastes with fewer adverse environmental effects. Chicken manure rich in organic matter is a significant agricultural pollutant associated with greenhouse gas emissions and water pollution. Due to the low carbon-nitrogen ratio of chicken manure, acidification could quickly occur in the anaerobic digestion process, reducing anaerobic digestion efficiency. Therefore, the application of chicken manure for anaerobic digestion has become a hot topic. The study was designed to improve the biogas/methane production and enhance the core microbial interaction of anaerobic digestion. The addition of dragon fruit peel as a co-substrate was suggested to determine the optimal ratio that reduces the low carbon nitrogen ratio and improves methane potential. The co-substrate dragon fruit peel at an optimal ratio maximizes the biogas/methane yields up to 411.1 and 180.2 mL/g VS, respectively. The study findings contribute to a deeper understanding and the approach of dragon fruit peel as a co-substrate for methane recovery from anaerobic digestion of chicken manure.

Biogas and methane generated from the anaerobic digestion (AD) of organic waste present a highly effective alternative to fossil fuels. The study assessed using dragon fruit peel (DFP) as a co-substrate to enhance chicken manure (CM) biodegradability and stabilize the AD process for methane during co-digestion. The biochemical methane potential assays were conducted at mono-controls (CM and DFP) and co-digestion at CM-75:DFP-25, CM-50:DFP-50, and CM-25:DFP-75. Compared to the controls, mono-digestion produced 103.3 mL/g of volatile solids (VSs) of CM and 34.6 mL/g VS of DFP, while all treatment groups of co-digestion exhibited an increase in methane production. The highest yield was 180.3 mL/g VS at CM-25:DFP-75 (74.6% and 421.1% increase relative to mono-digestions of CM and DFP, respectively), followed by 148.3 mL/g VS at CM-50:DFP-50 (43.6% higher than CM) and 116.7 mL/g VS at CM-75:DFP-25 (13% higher than CM). Process stability at the optimal DFP co-substrate ratio (CM-25:DFP-75) was confirmed by total volatile fatty acid (VFA) conversion, as below 0.5 g/L VFAs were observed at the end of incubation, indicating highly acceptable performance. The relative abundance of Bacteroidetes and Bacillota in the treatment groups was higher as compared to the control reactors, correlating with enhanced substrate hydrolysis and VFA production. Moreover, the enrichment of acetoclastic methanogens Methanosarcina and Methanosaeta in co-digesters at CM-25:DFP-75 was associated with the efficient degradation of acetic acid and propionic acid, which aligns with the observed increase in methane yield. The study enhances the understanding of DFP as a co-substrate for optimizing methane recovery from AD of CM.