Solution developed to convert paper sludge, food and textile waste into bioethanol

A pioneering solution has been developed to convert cellulose fibre-rich waste from pulp and paper mill operations into ethanol using a specialised fermentation process. Ethanol is a versatile starting material that finds diverse application in the production of industrial chemicals, bio-based plastics and sustainable aviation fuel.

The solution by the Paper Manufacturers Association of South Africa (PAMSA), in collaboration with Stellenbosch University (SU), Sappi Southern Africa and Mpact. A demonstration plant, co-funded by the Department of Science and Innovation (DSI) and PAMSA, was shown to government officials, media and industry partners at Sappi Tugela mill in Mandini, KwaZulu-Natal, on 24 April 2024.

Paper sludge is a solid waste with a high moisture content. It comes from the production of paper using virgin wood fibre and/or recycled paper and collected from the paper mill wastewater treatment systems.

Driven by the vast potential of this feedstock, the research by SU has shown that paper sludge, as well as food and textile waste, does not require pre-treatment before hydrolysis-fermentation. This solution will help to reduce the amount of waste disposed to landfill and the associated greenhouse gas emissions and improve water reclamation for re-use, further contributing to the circular economic and industrial decarbonisation.

The solution holds substantial economic promise as waste-derived bioethanol commands premium prices in global markets, and furthermore the project has the potential to generate sustainable employment and upskilling opportunities and stimulate regional economic development.

The plant aims to demonstrate the commercial readiness of the fermentation technology under industrial conditions.

Given that the process had only been tested and proven under laboratory conditions, the Stellenbosch team designed and built a containerised demonstration plant housing a 1,000-litre bioreactor and key utilities with the specific aim of fermenting approximately 100kg paper sludge per day to ethanol.

The current demonstration plant has been deployed for a nine-month period at Sappi’s Tugela mill in northern KZN with a follow-up project planned at Mpact’s mill in Springs, Gauteng.

There is global recognition in local and international markets for the environmental benefits of waste-derived bioethanol due to attractive greenhouse gas (GHG) reduction credits from the avoided emissions through diversion from landfilling, as well as the benefits from fossil-fuel replacement.