Zero Waste Scotland Examines Biostabilization of Residual Waste

The country of Scotland has placed a ban on the disposal of biodegradable municipal waste to landfill, which is expected to be implemented in December 2025.

A new report prepared for Zero Waste Scotland by Ricardo analyzed different mechanical biological treatment technologies (MBT) 

"Biological treatment of waste degrades complex organic compounds into simpler compounds," the study stated. "If the treated waste is then landfilled, it is more stable and will degrade less within the landfill and so will generate less landfill gas than it would without prior biological treatment. Landfill gas is a mixture that includes gases with global warming potential (GWP). The more organic material that is degraded in the MBT process, the more stable the waste becomes (biostabilization)."

While researchers did not compare treatment methods or provide suggestions to the country, they did focus on how selected EU countries such as Britain handled MBT methods. In addition, a carbon lifecycle assessment was performed.

The findings also took into consideration "the balance and interaction of technical, economic, policy and environmental factors that influence the implementation of biostabilization techniques in practice."

The biological waste disposal methods studied included in-vessel composting (IVC),  biological drying (Biodrying) and anaerobic digestion (AD).

"Of the above biological processes, IVC and dry-AD (a form of AD) followed by IVC can be designed and operated to allow various extents of biostability, including to meet the Scottish ban criteria," researchers stated. "Biodrying will not achieve a high level of biostability and wet-AD (another form of AD) output is not practicably amenable to the necessary subsequent IVC process required to achieve a high level of biostability."

The viability of each method in comparison to Scottish's biostabilization criteria varied. While anaerobic digestion did not meet the standards, the combination of dry AD and in-vessel composting would be feasible.

"Biodrying involves aeration of waste to commence the composting process to raise the waste’s temperature to drive off moisture," the report stated. "However, the composting process is cut-short once the waste has dried to the desired level and, unlike a full composting process, water is not added. A humus-like composted output is not produced in biodrying. Biodrying will not stabilize residual waste to the level necessary to allow its landfill in Scotland."

Case studies in France, Italy, Germany and Spain also provided a glimpse into viable waste diversion methods.\

"Some differences exist between waste policies in France, Germany, Italy, Spain and Scotland. However, at a high-level, waste reduction and diversion from landfill are common themes," the study noted.

While each country has its own standards for waste removal, the policies are specialized for each nation. France and Spain do not have criteria for the landfill of biodegradable municipal waste, while Germany and Italy do. Some areas of Spain have enacted policies that ban organic materials.

The drive to divert biological municipal waste from landfills was based on "….concerns that Scottish residual waste would be sent across the border to be landfilled in England, as some local authorities and commercial operators had not made sufficient progress towards complying with the ban," according to the study.