Micro-aerobic granulation for actual coking wastewater treatment in an expanded granular sludge bed (EGSB) reactor: Intermittent oxygenation

To accomplish rapidly the micro-aerobic granulation process of digestion sludge for the treatment of actual coking wastewater and meanwhile achieve high COD, the EGSB reactor was employed with two operation stages. Stage I: Granular sludge was formed from digestion sludge using brewery wastewater as substrate in the anaerobic way (meanwhile adding little granules, which were 1/7 of the total biomass). Stage II: Granular sludge was acclimatized with the actual coking wastewater through intermittent micro-oxygenation way of 800-20000 ml·min^-1 18-12 times at 20-60 min intervals, 1 h each time. The experimental results showed that the granular sludge could quickly form in 10 d in the EGSB reactor seeded with digestion sludge and little loose granules. It took only about 6 months for the successful micro-aerobic acclimating of the granular sludge by the actual coking wastewater. With 631-1220 mg·L^-1 influent COD concentration, 1.0 L·h^-1 influent flow, 12h HRT, 20000ml.min^-1 air flow and 3g·L^-1 NaHCO₃ supplement, the micro-aerobic EGSB reactor could have 75% high COD removal efficiency. The actual coking wastewater was not restrain the granules at the primary stage (at least for more than 1 month), but at 4 months, the SMA reduced 62.9% compared with the parallel, before treating CWW. The supplement of some oxygen and NaHCO₃ was very important. Directly using the actual coking wastewater and through an intermittent oxygenation way was an effective acclimation approach.