Long chain fatty acid(LCFA) degradation and microbial diversity in a two-phase anaerobic SBR(ASBR) and upflow anaerobic sludge blanket(UASB) reactor

Abstract

This study was focused on lipid biodegradation in anaerobic condition. LCFAs, the intermediate products in lipid biodegradation are known to inhibit microorganisms by its toxicity and floatation. To reduce LCFA inhibition, two-phase anaerobic system consisted of anaerobic SBR(ASBR) and upflow anaerobic sludge blanket(UASB) reactor was applied to synthetic dairy wastewater. Effect of protein and microorganisms related to lipid degradation were also investigated. During 153 days of continuous operation, two-phase system showed stable performance in lipid degradation. In ASBR performance, failure due to high organic loading (19.2 g COD/L/day) was observed. Except failure period, 13% of lipid removal efficiency and 10% of double bond removal efficiency were maintained. In UASB performance, COD, lipid and VFA removal efficiencies up to organic loading rate 6.5 g COD/L/day were more than 80%, 70%, 95%, respectively. Methane yield was 0.24~0.41 L/g COD. There was no operational problem like serious scum formation and sludge washout. In the batch test, protein degradation was conducted completely in four days. In contrast, lipid degradation was lowered as amount of protein was increased. 9% of Lipid removal efficiency and 12% of double bond removal efficiency were dropped when protein concentration was increased 0 to 4.0 g-casein/L. The degradation of casein in acidogenesis has contributed to ammonia, butyrate, valerate and $CO_2$ production. The mixed culture sampled in two-phase system contained a lot of bacteria in both of ASBR and UASB. Bacteria were separated according to degradation step, and it showed successful phase separation. Clostridium sp.-like bacteria were abundant in acidogenesis, no dominant species was found in methanogenesis. In archaea group, methanogens like methanosarcina and methanocaldococcus were found in methanogenesis. Methanogen found in acidogenesis was disappeared as organic loading rate was increased.