Anaerobic degradation of industrial carbon capture reclaimer MEA waste

Abstract

Global warming and its impacts are serious and challenging international problems (Vitousek, 1994). Increasing fossil fuel consumption results in rising atmospheric greenhouse gas levels which enhances global warming (Vitousek, 1994). To limit the global temperature increase, protocols to reduce CO2 emission worldwide promote CO2 capture and storage (CCS) (IPCC, 2007). The most established CCS technology involves post-combustion CO2 absorption using amine solvent and CO2 desorption for storage (Rochelle, 2009). Life cycle assessment has shown that CCS can be a good solution to achieve a significant reduction in greenhouse gas emissions (Singh et al., 2011). There are, however, environmental trade-offs to consider, such as increased human and environmental toxicity potential due to solvent and the degradation products emissions (Singh et al., 2011). Chapter 1 gives a general introduction of the global warming and the proposed CCS technology. The degradation products (amine waste) from CCS are recognized as hazardous waste (Council directive, 1991). It can pose threats to both humans and the environment, thus it is important to mitigate the threats in proper manners. Alternative waste treatment methods, including biological waste treatment, have been suggested for such waste (Abend et al., 1999). Anaerobic digestion (AD), that assimilates and degrades organics in a closed environment and produces renewable energy (CH4), is the focus in this research. The degradation potential of monoethanolamine (MEA) waste (MEAw) is explored in Chapter 2. The amine solvent degradation in CCS processes, the products generated and their potential impacts are also summarized. Possible degradation pathways of the waste constituents of the specific MEA waste collected from an industrial CCS system are also introduced. Researches of lab-scale AD of MEA waste with easily degradable co-digestion organics which resembles domestic wastewater are introduced in Chapter 3. Co-digestion feed provides minerals and easily accessible organics for organisms??development. A hybrid reactor system applying the concepts of a suspended sludge blanket and attached biofilm growth of the AD culture was employed with semi-continuous feeding. Mixed cultures from various sources were added initially to increase the diversity of AD culture. Experimental and theoretical analytical methods are also introduced in this chapter. A slow culture adaptation to the MEA waste content that is resilient to degradation was observed. Degradation results presented in Chapter 4 show a stable and robust method to treat MEA waste. The main process limitation identified is that the methanogenesis AD step becomes inhibited when the feed contains less than ~ half co-substrate. Ammonia, as a product of MEA waste degradation, can be the main inhibition factor and caused the toxicity effects for aquatic species. MEA waste organics are degraded by AD to an extent that most of the toxicity to aquatic life is removed. The expanded anaerobic digestion model No.1 (ADM1) model successfully captured the trends of AD digester performances and can be used as an effective tool to investigate and understand MEA waste degradation. Successful anaerobic degradation of CCS MEA waste contributes directly to the deployment of CCS technology, by ensuring safe disposing of generated waste substances. Researches of co-digestion of MEA waste with easily degradable and accessible organics, such as domestic wastewater, can potentially reduce the cost of applying AD of MEA waste in full scale. Studying the AD capability and limitations for MEA waste treatment also expanded the knowledge associated with biological industrial waste treatment. Investigation of lab-scale AD of MEAw in terms of bioreactor efficiency, organisms??cultivation and inhibition preventions enhanced knowledge accumulation and can promote the development of CO2 capture into a more efficient and environment friendly technology. This study recognized the importance of co-digestion substrates and the positive effects of long sludge retention on waste assimilation and degradation. Further study on identification of the specific inhibitory chemicals in AD of MEA waste, the degradability of identified CCS MEA degradation products and promotion of lab scale to pilot scale tests can be interesting research topics.