Thermo-digester for Rapid Conversion of Mill Mud to Green Fertiliser
Mill mud presents environmental and economic challenges to sugar industry. Australian sugar mills annually produce two million wet tonnes of mill mud, with Isis Central Sugar Mill contributing over 100,000 tonnes. Currently, most mill mud is sent to local farmers, serving as a soil ameliorant and sometimes a partial substitute for commercial fertilizers. Without proper management, the ongoing application can lead to overfertilization of phosphorus and the long-term accumulation of heavy metals. Moreover, the odour of mill mud presents a health risk and can be a nuisance.
Economically, disposal cost of mill mud emphasises the financial strain of current practices. Converting mill mud into compost or green fertilizer products can be a profitable value-adding strategy, but the conventional composting process, which typically takes 90-180 days, poses a significant challenge and is not feasible for developing mill mud into a commercial product.
Objectives
• Design a thermo-digester for mill mud digestion methodology development, with the capability to (1) regulate the reaction procedure and temperature, (2) deploy in the sugar mill’s operational environment, and (3) optimize mill resource utilization, such as harnessing steam for heating.
• Engineer a pilot, small-scale thermo-digester and validate the thermophilic digestion process.
• Identify suitable thermophilic microbe products, in conjunction with which the digester will efficiently break down mill mud within, ideally, a 24-hour timeframe
• suitable for the effective decomposition of mill mud.
• Investigate the physical, chemical, and biological properties of the mill mud digestate.
• Compare properties of mill mud digestates produced by different procedures and microbe products.
Expected Outputs
The project will deliver following outputs and outcomes:
Pilot Thermo-digester:
Product: A pilot, small-scale thermo-digester engineered to efficiently digest mill mud.
Utilization: The thermo-digester will be deployed in the mill operation environment, heated by waste hot steam to 70-80°C to digest mill mud.
Adoption: The digester will be used to develop valuable products, including potting mix, planting bags (e.g., for capsicum, ginger, eggplant), and green fertilizer from mill mud.
Engineering Skills for Thermo-digesters:
Skills: The project will establish engineering skills related to thermo-digester design and construction in the sugar industry.
Utilization: These skills will be upscaled to engineer larger thermo-digesters for mass production, allowing for the widespread adoption of the technology for efficient waste management in the sugar industry.
Thermophilic Digestion Protocols:
Protocols: Defined parameters for thermophilic digestion, including reaction temperature, microbe products, digesting time, additives, and motor rotation rate.
Utilization: These protocols will establish effective guidelines for digesting mill mud using thermo-digestion, ensuring consistent and optimized results in future applications.
Data on Mill Mud Digestate Properties:
Data: Physical, chemical, and biological properties of mill mud digestate obtained through testing.
Utilization: The data will align with Australian Standard for mature compost (ASS4454-2012), providing valuable insights for product development and quality control.
The timeline for adoption involves immediate application of the thermo-digester in developing products during the project duration. After successful pilot implementation, knowledge and skills will be transferred to develop mill-mud-based products and engineer commercial-scale thermo-digesters. The project outputs will be made available for other mills through knowledge sharing, digester procurement from Isis Central Sugar Mill, and co-adventure. Third-party involvement may include consultations with experts and disseminating information through industry networks, ensuring a broad recognition of the project’s outcomes. The project aims to contribute to reduced waste, enhanced economic returns, and a more sustainable circular economy for the sugar industry.
Expected Outcomes
Upon adopting this project’s outputs, multifaceted benefits will unfold, spanning economic, environmental, and social realms:
Economic Benefits:
Cost Reduction: The project mitigates high disposal costs linked to mill mud. For instance, Isis Central Sugar Mill spending about $8 per ton for over 100,000 tonnes. Transforming mill mud into products will significantly cut disposal expenses.
New Revenue Stream: The conversion of mill mud into high-value products, including locally produced planting bags, represents a lucrative revenue source. For instance, replacing imported coir bags (25-30L) costing $6-8 per bag with alternatives from mill mud generates substantial value.
– Financial Impact: Assuming a 50% conversion rate of Isis Central Sugar Mill’s 100,000 tonnes of mill mud at $100 per ton, it could yield $5 million annually, plus saving $800,000 in disposal costs. This return has high potential to attract investments in mill mud processing factories collaborating with sugar mills.
Environmental Benefits:
– Improved Soil Health: Digested products enhance soil nutrient content and organic carbon, fostering sustainable farmland productivity.
Social Benefits:
Job Creation: Development and adoption of mill mud to agronomic products generates jobs across the supply chain, from digestion factories to packaging, marketing, and distribution, supporting local communities in regions with sugar mills.
Local Supply Chain Support: Local growers will benefit from locally sourced products, reducing risks associated with imported alternatives.
Circular Economy: Full mill mud utilization establishes a sustainable circular economy, enhancing the sugar industry’s reputation for sustainability and low carbon emissions.
Despite these benefits, potential challenges for some mills may include market saturation and high transportation costs. Solutions may involve exploring export markets and implementing in-depth processing, creating high-value products like granulated forms and branded items for home gardening.
SRA PROJECT CONTACT: Muyiwa Olayemi
RESEARCH AGENCY: Charles Darwin University
CHIEF INVESTIGATOR: Prof. Chengyuan (Stephen) Xu
PROJECT NUMBER: 2024/204
END DATE: 01/07/2025
