Biodegradation of low molecular weight polyacrylamide under aerobic and anaerobic conditions: effect of the molecular weight.

The biodegradation of polyacrylamide (PAM) includes the hydrolysis of amino groups and cleavage of the carbon chain; however, the effect of molecular weight on the biodegradation needs further investigations. In this study, biodegradation of low molecular weight PAM (1.6 × 10 Da) was evaluated in two aerobic (25 °C and 40 °C) and two anaerobic (35 °C and 55 °C) reactors over 100 days. The removal of the low molecular weight PAM (52.0-52.6%) through the hydrolysis of amino groups by anaerobic treatment (35 °C and 55 °C) was much higher than that of the high molecular weight (2.2 × 10 Da, 11.2-17.0%) observed under the same conditions. The molecular weight was reduced from 1.6 × 10 to 6.45-7.42 × 10 Da for the low molecular weight PAM, while the high molecular weight PAM declined from 2.2 × 10 to 3.76-5.87 × 10 Da. The results showed that the amino hydrolysis of low molecular weight PAM is easier than that of the high molecular weight one, while the cleavage of its carbon chain is still difficult. The molecular weights of PAM in the effluents from the two aerobic reactors (25 °C and 40 °C) were further reduced to 4.31 × 10 and 5.68 × 10 Da by the biofilm treatment, respectively. The results would be useful for the management of wastewater containing PAM.