The economics of sugar mill waste management in the Australian Sugar Industry: Mill mud case study

Abstract

Sugar mills produce a range of by-products during the process of sugar extraction. Mill mud is one of the by-products that is produced in significant volume. Often mill mud is mixed with mill ash from the firing of bagasse, which together forms the bulk of mill waste available for disposal from raw sugar mills. The practice of spreading mill mud over nearby cane fields has been the primary means of disposing mill mud for many years. Mills generally promote the practice by offering freight subsidies to reduce the cost burden on growers who use this practice as a routine measure. The low level of nutrients and high moisture content makes mill mud a dilute source of nutrients, and supply of mill mud often exceeds the demand, leading to stockpiling of mill mud at most mills. Moreover, the continued application of mill mud and ash at high rates, without appropriate recognition of the soil condition and crop requirements, has raised a number of concerns in recent years. The risk of over-fertilization and heavy metal contamination of cane fields, and the concerns relating to offsite impacts from spillage to waterways, have raised questions about the indiscriminate use of mill mud in the industry. This study examines the issues relating to more responsible management of mill mud and reports on the cost-effectiveness of its application across a wider range of farms more distant from the mills as a means to minimise environmental risks.