Aerobic and anoxic biodegradability of amines applied in CO2-capture

Abstract

Integrated and sustainable waste handling is becoming essential in large scale employment of amine-based post combustion CO2 capture and storage (CCS). We have previously proven the feasibility of biological nitrogen removal of amines in a moving bed biofilm reactor (MBBR) in pre-denitrification mode, thereby serving as a carbon source for denitrification. To evaluate novel solvents, it is essential to test their biodegradability under anoxic conditions. Generally, biodegradability is assessed by standardized aerobic tests, but no equivalent method is available for anoxic degradation. Therefore, a new anoxic batch screening test in syringes was used, measuring the headspace volume expansion due to produced N2 gas over time. Aerobic biodegradability was measured the conventional way by determining the biological oxygen demand (BOD). Nine different amine samples were tested, including monoethanolamine (MEA) and reclaimer waste. Comparison of biodegradability under aerobic fresh and sea water conditions showed generally improved biodegradation in fresh water. The anoxic screening identified subgroups of amines classified as a) easily degradable, b) slowly degradable and c) undegraded. The results show that BOD alone cannot be relied upon as the only parameter to describe biodegradability. Our anoxic biodegradability test provides essential information on potential carbon sources for denitrification in MBBR and describes the biodegradation kinetics involved.