Mechanical biological treatment

Mechanical biological treatment flowchart

MBT sorting

MBT anaerobicdigesters

Mechanical Biological Treatment (MBT) is a waste processing technique that combines mechanical and biological processes to manage and treat municipal solid waste before disposal. This method is designed to minimize the environmental impact of waste by reducing the volume of waste sent to landfills, recovering materials for recycling, and producing a biologically stabilized material that can be used in various applications, such as in land reclamation or as a fuel substitute.

Overview

MBT plants are facilities where mixed municipal solid waste is subjected to a series of mechanical and biological treatments. The mechanical phase typically involves the separation of recyclable materials (such as metals, plastics, and paper) from the waste stream, using technologies like conveyor belts, shredders, air classifiers, and magnetic separators. The biological treatment usually follows, where the organic fraction of the waste is decomposed using either aerobic (composting) or anaerobic (digestion) processes. The end products of MBT can include recyclables, a biologically stabilized material, and residues destined for disposal.

Process

The MBT process can be divided into several stages:

Pre-treatment

The waste is collected and transported to the MBT facility, where it undergoes initial sorting to remove large items and hazardous waste. This stage prepares the waste for further processing and ensures the safety and efficiency of the facility.

Mechanical Treatment

The waste is then subjected to mechanical separation processes. This stage aims to extract valuable materials for recycling and to prepare the organic fraction for biological treatment. Technologies used in this phase include screens, magnets, and eddy current separators.

Biological Treatment

The biodegradable component of the waste is treated biologically to reduce its volume and to stabilize it. This can be done through:

• Composting: Aerobic decomposition of organic waste into compost.
• Anaerobic Digestion: Anaerobic breakdown of organic material to produce biogas (a renewable energy source) and digestate (a nutrient-rich substance).

Refinement and Disposal

Following biological treatment, the material may undergo further processing, such as maturation of compost or refinement of digestate. Residual waste materials that cannot be recycled or biologically treated are then sent to landfill or incineration facilities.

Benefits

MBT offers several environmental and economic benefits:

• Reduces the volume of waste sent to landfills, thereby extending landfill life and reducing methane emissions.
• Recovers materials for recycling, contributing to the circular economy.
• Produces renewable energy (in the case of anaerobic digestion) and soil conditioners, promoting sustainable agriculture.
• Can significantly reduce the carbon footprint of waste management.

Challenges

Despite its benefits, MBT faces several challenges:

• High initial capital and operational costs.
• The quality of recovered materials can be lower than that of source-separated recyclables.
• The need for sophisticated technology and skilled personnel for operation and maintenance.
• Regulatory and public acceptance issues, particularly concerning the siting of facilities.

Conclusion

Mechanical Biological Treatment represents a promising approach to managing municipal solid waste, offering a way to recover resources and reduce environmental impact. However, its success depends on overcoming technical, economic, and social challenges. As waste generation continues to grow globally, the development and optimization of MBT and other waste management technologies will be crucial in achieving sustainable waste management practices.