The isolation of a hydrolyzed polyacrylamide (HPAM)-degrading bacterium and its potential application for the treatment of HPAM-containing oilfield wastewater in a UASB reactor

Hydrolyzed polyacrylamides (HPAMs) contained in oilfield wastewater increase the difficulty of oil–water separation and the subsequent wastewater treatment. Besides, the residual HPAMs are detrimental to the nervous and reproductive systems of animals. Biodegradation of HPAMs is a potential solution, which can also increase the efficiency of oilfield wastewater treatment plants and lower their operating costs. This study shows that with the addition of an isolated HPAM-degrading bacterial strain (Clostridium bifermentans H5), the viscosity of HPAMs decreased as a result of (1) the biodegradation of their side chains, (2) the change of some functional groups, and (3) the hydrolysis of acylamide into carboxyl groups. The gas chromatograph mass spectrometer analysis showed that besides HPAM fragments with duplet bonds, epoxy, and carbonyl groups, most of the low-molecular-weight degradation products of HPAMs were normal derivatives of acrylamide oligomers. The addition of sodium lactate and sodium sulfate enhanced the removal efficiency of HPAMs. In a batch up-flow anaerobic sludge bed/blanket (UASB) reactor inoculated with pure cells of H5, the removal efficiency of HPAMs, with cane sugar as the carbon source, was competitive given its lower costs when compared with sodium lactate. The results of the polymerase chain reaction–denaturing gradient gel electrophoresis analysis showed that the strain H5 was predominant in the UASB reactor. In conclusion, strain H5 was feasible for the treatment of HPAM-containing wastewater in a UASB reactor.