TBFD are constantly evolving, utilising advances in technology and developing patented techniques to further improve data acquisition and optimise process control.
Typically, the majority of landfill sites are designed and operated to minimise the rate of biological degradation and the corresponding generation of gas and leachate (aqueous liquid) by minimising water ingress.
This is achieved by good water management practices and lining the landfill with impermeable materials such as clay and synthetic plastic liners. This leaves the landfill in what is commonly known as a “dry tomb” state.
In most cases, a dry tomb landfill generally consists of three prominent bands of waste composition, represented below:
Dry tomb landfill: The consequences
It is well known that energy generation rates peak and begin to fall as gas production for the landfill falls in line with the exponential decay curve (12 years).
In practice, the rate of decline in LFG production is occurring at a faster rate than projected due to the impact of the dry tomb conditions. In Western Europe, the industry has now reached a pivotal point as sites exceed the 12 year timeframe, with waste to energy operators now attempting to maintain output to meet financial targets. As a consequence, as LFG production falls, operators will apply additional suction in an attempt to maintain output, causing subterranean fires (hotspots) and these will become more prevalent as LFG production continues to fall.
The solution: R4Energy Site Optimisation
Based on the results of hydro-geological studies, TBFD target dry areas of waste installing vertical impact pin wells directly into the dry putrescible waste.
Leachate recirculation seeks to accelerate the degradation of waste by optimising conditions for anaerobic bacteria. Anaerobic bacteria are responsible for converting organic waste into organic acids and ultimately into methane and carbon dioxide. The moisture conditions that are required to optimise anaerobic degradation requires a field capacity in excess of 40%, equivalent to +40 % moisture. The moisture content in typical dry tomb landfills is around 10-15% water. Moisture is added in the form of leachate through a variety of delivery systems. This leads to an increase in the amount of gas production that is then captured by the gas collection system in the landfill.
During the early stages of landfill operations, the leachate will contain high TDS, BOD, COD, and heavy metals. When leachate is re circulated, biological, physical and chemical reactions will occur and provide treatment for these hazardous by-products. In turn, the recirculation of leachate provides the landfill with various nutrients, which are required for the growth of bacteria that participate in the anaerobic degradation of the waste.
Leachate recirculation will increase a landfill’s moisture content. Moisture is essential for the activities of all microorganisms because it serves as a medium for transporting nutrients and bacteria. During leachate recirculation, the leachate is returned to a lined landfill for re infiltration into the municipal solid waste. This is considered a method of leachate control because as the leachate continues to flow through the landfill it is treated through biological processes, precipitation and sorption.
TBFD has the right tools and expterise, so any site can be transformed from an expensive liability to a valuable commodity.
TBFD systems for leachate extraction and recirculation provide a range of benefits:
- A significant reduction in leachate treatment and disposal costs. This is typically £50,000-£500,000pa, dependent upon the size of the site.
- Rapid waste stabilisation and settlement.
- In situ leachate treatment and control.
- Significantly reduced liability retention period.
- 20-100% uplift in power generation. Representing an increase of 500-5000kw increase annually over a projected 7-10 year period.
- Reduced fire risk [hot spots] and LFG migration.
- Remote real time data acquisition and control for improved regulatory compliance.
- Cost effective [automated] monitoring and reporting.
- Our advanced systems technology offers excellent rates of return, with many systems paying for themselves within the first year of operation.