Extracting value from onion waste - Evaluation of pyrolysis to improve the sustainability of onion production and reduce costs on the journey to Net Zero

Onion growing and packing operations produce significant volumes of waste which is currently sent for composting and disposal, the costs of which are covered by each grower as part of their grading charges. This represents a major cost to the farming businesses and presents significant environmental and logistical challenges. Significant efforts have been made to reduce waste volumes and to find more cost-effective strategies for disposal, but this remains a major financial burden for the growers.

The current project aims to establish if pyrolysis (gasification) could offer a solution to the challenges faced by the onion industry. Experience from other areas indicates that this approach has potential for various biological waste streams, but there is no experience with onion waste and little experience with comparable waste streams.

The project will establish if pyrolysis can add value to the onion waste and/or reduce costs associated with waste disposal. The work will also evaluate seasonal changes in waste output to determine how this might affect commercial exploitation. Previous work suggests that pyrolysis efficiency is reduced in high moisture substrates and low-energy/cost moisture reduction strategies will be evaluated as part of the project.

Pyrolysis also has the potential to generate valuable outputs that can be exploited in both the farming and packing operations, such as biochar for soil improvement and energy for onion storage. All the potential benefits arising from the pyrolysis process will be quantified so that a full cost-benefit analysis of the process can be completed. This will be used by the business to provide them with confidence to invest in this technology.