Process Description:

Pomelo peel: Collect samples of pomelo peel after juice extraction from street-side juice vendors in the city (Ninh Kieu District, Can Tho City).

Grinding and Cutting:
The raw pomelo peel samples are ground to a size of about 0.5–1 cm.

Sun Drying:

• Dry the pomelo peel until moisture reaches 50–60%. Weigh samples before and after drying to determine relative moisture content.
• Simultaneously, coconut coir and rice husk charcoal (ash) are soaked in water for 7–10 days to remove tannins from the coconut coir and mineral salts from the rice husk charcoal. The pH is maintained at 5.6–6.5 with moisture at 50–60%.

Mixing:
Add UREA fertilizer at a rate of 2.205 g per kg of pomelo peel to adjust the Carbon/Nitrogen (C/N) ratio to approximately 30.
Add treated rice husk ash and coconut coir at a pomelo peel:rice husk ash:coconut coir ratio of 5:2:1 (w/w/w). Then adjust the mixture pH to about 6.5 using lime.
To accelerate composting, add Trichoderma bio-agent at 5% (w/w).

Aeration:
The compost pile is thoroughly mixed and aerobically fermented with an airflow adjusted to an average of 195 L/min to provide stable aeration. The aeration cycle is 15 minutes on and 45 minutes off.
The compost pile is placed in a sheltered area with limited sunlight to stabilize the fermentation process.

Composting:
The pile is composted for 51 days, with mixing every 7 days. Water is sprayed regularly to maintain moisture at 50–60%. Tribat 10% is added to supplement nutrients during composting.

Final Product:
After production, the microbial organic fertilizer is analyzed and evaluated for quality indicators according to the national standard TCVN 7185:2002, including moisture content, pH, microbial density, total organic matter, total nitrogen content, etc.

Conclusion:
Production of 500 g scale microbial organic fertilizer samples showed good results across all evaluation criteria. The process has been effectively transferred and applied in practice, and it can be scaled up for medium and small enterprises.
This indicates great potential for utilizing pomelo peel in organic fertilizer production, reducing pollution from pomelo peel waste. Moreover, it adds value to pomelo fruit in the market by converting by-products into valuable products.