Innovative use of wastes for carbon capture

Abstract

Carbon capture, utilization and storage (CCUS) is an important emissions reductions technology that has gained much attention in the last decade, owing to its ability to contribute to guaranteed large scale negative emissions. Incineration bottom ash (IBA) is a by-product generated during the incineration of municipal solid waste (MSW) while seawater desalination brine is a by-product generated during the seawater desalination process. Both are considered as wastes and currently being disposed to the landfill (IBA) or to the sea (brine) without beneficial reuse or material recovery. Nevertheless, both waste materials are found to have chemical compositions that are potentially favourable for carbon capture and materials recovery. To contribute towards Singapore’s aim of being net-zero in carbon emission by 2050, this study aims to utilize these waste materials to determine whether a high yield of good quality products such as calcium carbonates can be generated through carbonation. In this study, carbonation of different types of wash water produced from applying different leachants was carried out. Wash water was mixed with seawater and brine to generate alkaline residues, which were subsequently added back into brine to determine its possible usage as an alkali source.

Carbonation results of different solutions throughout this study concluded that the P-alkalinity of a solution has a strong correlation to the yield of carbonates formed. Upon mixing wash water with seawater or brine, an alkaline residue was precipitated, and it has been established through this study that it can be used as an alkali source for carbonation, as a replacement for a base additive such as the commonly used NaOH. However, more research is required to optimize the design parameters of this process for more efficient carbonation. Analysis of used water generated during the experiments revealed that trace heavy metals such as Ba, Cu and Zn are present, along with high amounts of chlorides and sulfates, which may require further treatment before discharge. More research should be performed in the future to further reduce the concentration of metal ions, chlorides and sulfates in the used water to make it suitable for discharge by avoiding the negative environmental impacts associated. More research should also be performed to increase confidence in stakeholders, such as plant owners, such that they will be more agreeable to implementing CCUS technology once it is available commercially. At the same time, the negative environmental impacts of discharging the waste products formed into Singapore’s natural environment should also be assessed carefully and mitigated accordingly.