Carbon dynamics in biosolids destined for land application
Creators: name: Albuquerque, Nihal
Publisher: name: RMIT University
Year: 2024
Subjects: classificationCode: 4104
subject: Environmental management
classificationCode: 410404
subject: Environmental management
classificationCode: 410699
subject: Soil sciences not elsewhere classified

description: This thesis describes an investigation into the characteristics of biosolids produced in Victoria Australia and how their properties impact on their potential for incorporation into carbon sequestration programs. Biosolids are a by-product of the sewage treatment process, and as a result, contain nutrients and organic matter that can be utilised as fertiliser products in agricultural systems. To date, research has focussed on the nutrient potential of biosolids, but there is a growing interest in biosolids' carbon which has the potential to be sequestered in agricultural soils to offset water corporations' large carbon emission footprint. Organic waste streams were recently recognised in a CSIRO review of soil carbon sequestration potential in Australian soil as the most promising option to generate carbon credits in agricultural systems. In order to capitalise on this management approach, water corporations require quantitative information on the characteristics of the diverse range of biosolids products as well as their carbon sequestration dynamics. <br><br>The current project was designed after extensive industry consultation to address some inadequacies in reported information on biosolids, in particular, the lack of information on physicochemical properties of biosolids products. The primary aim of this project was to characterise the vast range of biosolids materials and how this impact on their potential for soil C sequestration.<br><br>An initial review of the literature showed inconsistency in the description and classification of biosolids, and the first stage of this project was to survey water corporations in Victoria. The survey identified 17 biosolids products which consisted of four distinct types and based on the analysis of these products, a new system of classification was proposed that better represent the diverse nature of the biosolids produced in Victoria. The new classification system will allow biosolids managers to identify similarities and differences between biosolids types.<br><br>During the characterisation studies, it was found that spectroscopic characterisation of biosolids using techniques such as MID-IR combined PLS could predict (C, N, Si, Al, clay, silt and sand). It was concluded that the use of MID-IR combined with PLS could be used as an alternative and cost-effective method to measure multiple analytes in biosolids. A methodology was subsequently developed for the specific use of MID-IR and PLS for the estimation of C in biosolids products. The results showed that MID-IR combined with PLS could give a reasonably accurate estimation of biosolids C. This methodology was then used to determine biosolids C in mineralisation studies.<br><br>Mineralisation studies were undertaken to provide information on the likely fate of these products when they are land applied. It was found that there was a significant difference in the mineralisation behaviour of the 4 types and this was concluded to be due to the ageing and maturation time.  It was also found that biosolids components that could be considered as contaminants or impurities such as heavy metals and clays have some impact on carbon mineralisation which further emphasises the need to undertake site-specific pre-application analysis to develop a sequestration program. It was beyond the scope of this present study to thoroughly investigate soil/biosolids interactions, but the mineralisation behaviour of all biosolids types provides information on the likely fate of these products when they are land applied. A preliminary investigation was undertaken on some historical land application sites to determine if there was any evidence of sequestration and also what factors were important. It was found that the application of biosolids could result in soil C sequestration, but this was dependent on site-specific factors such as soil type, application frequency and nutrients in the receiving soil. Suggestions for further work were made based on these observations and other findings from the project.<br><br>The study has provided essential information to water corporation managers to execute existing land application arrangements better and also to investigate the sequestration potential on suitable sites. This study has clearly shown the factors that affect biosolids C mineralisation, and it was determined that under the appropriate soil type and biosolids management, it is possible to sequester C in the Victoria region. However, more information on matching biosolids properties and receiving soils characteristics is required to enable water corporations to offset emissions in any soil C sequestration programs. This study has revealed the key factors that need to be considered and can serve as a guide to future research and development on this emerging biosolids management strategy.