Ngodwana energy biomass power plant

Sappi Southern Africa holds a 30% stake in Ngodwana Energy, a 25 MW biomass energy plant at Ngodwana Mill. The plant, which came on stream in March 2022, uses biomass recovered from surrounding plantations and screened waste material from the mill production process. Up to 35 tonnes an hour of biomass is burned in a boiler to generate steam and drive a turbine to generate electricity which is fed into the national grid. Some questions have been raised about the environmental sustainability of the project, which we have answered here.

Q: The Public Partnership Agreement specifies that all the biomass utilised will be from ‘sustainable’ sources. What does this mean? 

A: This refers to ecological, economic and social sustainability, in line with Forest Stewardship Council™ (FSC™ N003159); and Programme for the Endorsement of Forest Certification™ (PEFC/01-44-43) principles. Sappi’s plantations are 100% certified to both these internationally recognised, independently verified accreditation systems. 

Q: Leaves are known to be high in nutrients. Won’t the process of biomass removal compromise soil fertility?

A: Harvesting procedures that utilise additional woody biomass (large branches, stem tops, non-utilisable wood such as broken trees or non-commercial species) while minimising nutrient removal by leaving nutrient-rich leaves and needles behind, are being used wherever practical. Sappi Forests has estimated that the harvest residue comprises 74% woody material (branches, broken stems and tops), 22% bark and 4% foliage, as seen below.

In addition, timber trees are not heavy feeders and in the case of eucalypts, are only harvested once every 10 to 12 years. This means that even with more intensive biomass removal, the nutrient export would still be much less compared to that of agricultural crops. Nutrient budgets comparing the balance between input and output fluxes provide useful information on long-term nutrient supply. Generally, deposition of nutrients, the large buffering capacity of the soils and the rate of resupply through weathering of parent material exceeds the rate of nutrient removal by plantation trees in South Africa.