Intermittent aeration in biological treatment of wastewater containing ethylene glycol using a packed column aerator

Simulated wastewater containing ethylene glycol with an initial biological oxygen demand (BOD5) of 230 mg.dm-3 was treated biologically using intermittent aeration. The wastewater was circulated at a rate of 28.4 kg.m-2.s-1 with a countercurrent air flow of 0.1 kg.m-2.s-1 through a packed column aerator. Various aeration cycles, such as: 0, 6, 8, 9, 12, 16, 18 and 24 hour aeration per day, were investigated. Optimum aeration cycle, which could save energy but still provide enough oxygen to decompose organic carbon aerobically, was found to be 16 hours of aeration per day. After 72 hours of treatment time, the BOD5 was reduced by about 87% with the optimum aeration cycle that yields about 33% energy saving compared with continuous aeration.;Based on the optimum aeration time of 16 hours per day, the effect of aeration frequency on the BOD5 removal was investigated. Five operational ratios of aeration time to non-aeration time of 1:0.5 (16 cycles per day), 2:1 (8 cycles per day), 4:2 (4 cycles per day), 8:4 (2 cycles per day) and 16:8 (1 cycle per day) were examined. The BOD5 removal rate for 16, 8, 4, 2 and 1 cycle per day were 91%, 90%, 87%, 82% and 78% respectively. On-line measurement of dissolved oxygen (DO) in water was also carried out. From the DO data, the specific oxygen uptake rate of the wastewater and the mass transfer coefficient of oxygen transfer from air to water in the packed column were determined to be 0.816 mg.L-1.h-1 and 6.10x10-7 m.s-1 respectively.