Microbial mineralization of diisopropanolamine

Abstract

Diisopropanolamine (DIPA) is a "sweetening agent" used to remove hydrogen sulfide from sour natural gas, and it is a contaminant at some sour gas treatment facilities in western Canada. To investigate the biodegradation of this alkanolamine,14C-DIPA was used in anaerobic and aerobic mineralization studies. Between 3 and 78% of the radioactivity from this compound was released as14CO2in sediment-enrichment cultures incubated under nitrate-reducing conditions. Similarly, 12-78% of the label was converted to14CO2in sediment-enrichment cultures incubated under Mn(IV)-reducing conditions. These activities were observed at 8°C, a typical groundwater temperature in western Canada, and at 28°C. In contrast, DIPA-degrading activity was difficult to sustain under Fe(III)-reducing conditions, and <25% of the radioactive label from14C-DIPA was liberated as14CO2. Two mixed cultures and two isolates (both irregular, non-sporeforming, Gram-positive rods) were used to assess aerobic mineralization of14C-DIPA. The aerobic mixed cultures released 73 and 79% of the radioactive label as14CO2, whereas the pure cultures liberated only 39 and 47% as14CO2. Between one-third and one-half of the nitrogen from DIPA was found as ammonium-N in aerobic batch cultures. These results clearly demonstrate that DIPA is mineralized under a variety of incubation conditions.Key words: alkanolamine, biodegradation, diisopropanolamine, mineralization, natural gas.