Anaerobic degradation of carbon capture reclaimer MEA waste

Abstract

The anaerobic biodegradation of reclaimer MEA (monoethanolamine) waste (MEAw) with easily degradable co-substrates was investigated in a laboratory-scale bioreactor at room temperature during a 160 d experimental run. The reactor that was constructed with three phases to facilitate attached biofilm and suspended biomass retention for degradation of the complex and challenging MEAw performed well. A feed strategy of step-wise increasing organic loading rate (OLR) by either increasing feed MEAw concentration or the hydraulic loading rate was applied. The system performance was evaluated by chemical oxygen demand (COD) removal efficiency, methane yield, MEA removal, and the accumulation of ammonia and volatile fatty acid (VFA). The total COD removal efficiency initially was 93% when the feed was mainly easily degradable co-substrate. The total removal dropped to 75% at the end when MEAw constituted 60% of the feed COD. Ion chromatography results show that the MEA and some unidentified feed chemicals were almost completely consumed. The main products of MEAw degradation were ammonia, VFAs and biogas. The ammonia nitrogen concentration reached about 2.0 g/L, which may explain the observed inhibition of acetoclastic methanogenesis leading to acetate accumulation. Methane accounted for up to 80% of the biogas generated. The highest methane yield was 0.34 L/g-COD while the yield was 0.16 L/g-COD at the highest load. This study shows that more than 80% reclaimer MEAw COD degradation with a co-substrate can be maintained in a hybrid anaerobic bioreactor operated in a wide loading range.

Detoxifying CO2 Capture Reclaimer Waste by Anaerobic Digestion

“…The total ammonia nitrogen (TAN = NH 4 + + NH 3 ) concentration was 2.0 g N/L with a free ammonia, FAN, concentration of 68 mg N/L. Ammonia concentrations gradually increased during the 2 years of reactor operation prior to this test and degradation of MEAw was the main source of ammonia [9, 10]. …”

“…The co-substrate was used to provide necessary nutrients, minerals and easily degradable organics to maintain biomass that can tolerate exposure to toxic and inhibitory chemicals from the MEAw and to increase the relatively low carbon to nitrogen ratio in the MEAw that could otherwise inhibit microorganisms, especially methanogenesis [9, 10]. Properties and quantities of the co-substrate are shown in Table 1.…”

“…Effluents for the toxicity test were collected when steady state reactor performance was observed. The analytical methods, except the toxicity tests, are given in [9]. …”

“…According to EU regulations and directives [7], the waste is classified as hazardous waste in accordance with hazardous waste Directive 91/689/EEC [8]. Anaerobic digestion (AD) that combines assimilating and degrading organics and recovering energy (in the form of methane) is a promising amine waste treatment method investigated [9–11]. …”

“…A hybrid anaerobic reactor with an adapted culture that has been treating MEAw together with an easily degradable co-substrate since 2010 [9, 10] was employed and operated at steady state when effluent samples were collected for toxicity assessments. The freshwater toxicity of this treated waste (TW) was compared to toxicity of pure MEA and MEAw by using standard regulatory Organisation for Economic Co-operation and Development (OECD) bioassays [12] for the unicellular algae Pseudokirchneriella subcapitata , the freshwater crustacean Daphnia magna , and the embryos of the zebra fish Danio rerio .…”