Looking for lipases and lipolytic organisms in low-temperature anaerobic reactors treating domestic wastewater

Underestimation of Extracellular Lipid Contribution to Fouling in Anaerobic Membrane Bioreactors

“…It agreed with previous studies which showed that the SMP of anaerobic bioreactors contained massive amounts of microbe-produced lipids primarily identified as phospholipids, ceramides, and cardiolipins. , The high amount of colloidal lipids and soluble lipids could not only be originated from wastewater but also be generated from the digestion of cell wall/cell lysis by functional microorganisms and their metabolism ,− (Figure a). Of note, when compared to carbohydrates and proteins, lipids were poorly degraded in AnMBRs. , Moreover, aerobic conditions could increase the first-order degradation rate of lipids around 10 times as compared to anaerobic conditions . Therefore, it might be the reasons why there was a higher content of lipids in AnMBRs (31%) than that of AeMBRs which could only make up around 3% .…”

“…However, the results suggested that lipids in AnMBRs are more important as compared to those in AeMBRs, especially considering that there was a high concentration of lipids in the supernatant (colloidal lipids) (Figure a). This difference could mainly be attributed to the production of lipids during the anaerobic digestion of microbial cells and cell lysis ,− and the slow degradation rate of lipids under anaerobic conditions. ,, It could be another reason why there was more serious membrane fouling in AnMBRs compared to AeMBRs reported consistently in the literature . The proteins rather than lipids of mixed liquor were retarded by QQ, and it was attributed to the disruption of the metabolic processes of QS-regulated microorganisms (e.g., Anaerolineaceae ) in AnMBRs. ,, The lipids could be regulated by complex anaerobic microbial communities and interspecies interplay .…”

“…Specifically, the proportion of lipids was only around 1% in EPS and 3% in SMP of activated sludge in a full-scale AeMBR . The lipid fraction of the cake layer on membrane surfaces in AeMBRs was suggested to be insignificant as compared to other fouling constituents (e.g., proteins and carbohydrates). , In anaerobic bioreactors, extracellular lipids were mainly investigated as microbial metabolites, precursors of methane production, or inhibitors of methanogens. − However, the significance of lipid-related membrane fouling has rarely been studied and compared to that of typically recognized foulants such as proteins and carbohydrates in AnMBRs. Different from aerobic bioreactors, extracellular lipids and long-chain fatty acids (LCFAs) are produced by both prokaryotes and eukaryotes during the digestion of microbial cells and cell lysis in anaerobic bioreactors (e.g., hydrolysis of cells), ,− which could inevitably lead to the accumulation of lipids in AnMBRs. ,, For example, lipids were found to be the dominant organics of anaerobic sludge, which accounted for 21–44% in the mixed liquor .…”

“…Different from aerobic bioreactors, extracellular lipids and long-chain fatty acids (LCFAs) are produced by both prokaryotes and eukaryotes during the digestion of microbial cells and cell lysis in anaerobic bioreactors (e.g., hydrolysis of cells), ,− which could inevitably lead to the accumulation of lipids in AnMBRs. ,, For example, lipids were found to be the dominant organics of anaerobic sludge, which accounted for 21–44% in the mixed liquor . Furthermore, as compared to carbohydrates and proteins, lipids were found to be poorly degraded in AnMBRs, especially at low temperatures. , Considering the hydrophobic interactions between lipids and membranes and the high fouling nature of lipids (e.g., oils and wax), it is imperative to investigate the fate and quantities of lipids in AnMBRs treating DWW and their impact on membrane fouling.…”

“…27 Furthermore, as compared to carbohydrates and proteins, lipids were found to be poorly degraded in AnMBRs, especially at low temperatures. 17,28 Considering the hydrophobic interactions between lipids and membranes and the high fouling nature of lipids (e.g., oils and wax), 11 it is imperative to investigate the fate and quantities of lipids in AnMBRs treating DWW and their impact on membrane fouling. Noticeably, lipids with molecular weight (M w ) lower than 2 kDa (e.g., phospholipids, ceramides, and cardiolipins), which are considered as the metabolites of microorganisms and byproducts of the breakdown of microbial cells, have been detected in the SMPs in anaerobic bioreactors.…”