Biological treatment of wastewater from a polymer coating process

Wastewater containing propylene glycol methyl ether from a powder and E-coating plant was treated biologically. The wastewater was circulated through a packed column at rates of 0.014, 0.028, and 0.042 m3/m2.s (14, 28, and 42 kg/m2.s) with an airflow in a countercurrent direction. Various air flowrates from 0.034 to 0.10 m3/m2.s (0.041-0.12 kg/m2.s) were used. The removal of the biological oxygen demand (BOD) of the wastewater did not change significantly with the air flowrate. After 4 days of treatment in the packed column the BOD was reduced by about 70% while a BOD reduction of 10% was observed with the wastewater in a stagnant tank. BOD removal with aeration in the packed column was about 40% higher than that without aeration. At the air flowrate of 0.068 m3/m2.s and the liquid flowrate of 0.028 m3/m2.s, BOD removal for the wastewater seeded with Polyseed® increased by about 25% compared with that of the unseeded wastewater. In order to minimize the power consumption, cyclic pumping of the liquid to the packed column with aeration was also tested. For the liquid-pumping cycle of 2-h on and 4-h off, BOD removal was about the same as that with a continuously pumping operation.