Stability of Fe–C micro-electrolysis and biological process in treating ultra-high concentration organic wastewater

•Combination processes can treat the high concentrated wastewater successfully.•The highly concentrated contaminants will severely strain microorganism growth.•The combined system exhibited high ability of resisting loading shock.

Three kinds of industrial wastewater were treated using combined Fe–C micro-electrolysis (FCME), hydrolysis acidification (HA), and bio-contact oxidation (BCO) processes. Two waste streams were characterized as ultra-high concentration of organic wastewater (UHCOW, more than 150,000 mg/L of CODcr). The other stream called clean water (CW), was a mixture of lower-concentration industrial wastewater and office block sewage. Efficiency and stability of the combined system were investigated in a pilot-scale experiment.The combined system can be operated normally under most suitable conditions, but its operation stability is poor. With increasing the ratio of UHCOW/CW, activated carbon in the FCME tank and carriers in the HA tank are fouled by oil droplets and lose certain functions gradually after 10 days of operation. As a result, CODcr removal efficiency decreased, particularly in the FCME tank. Moreover, the highly concentrated contaminants will severely restrict the growth of the microorganism in BCO tanks. The method of adding CW primarily functions in determining the system’s stability. At UHCOW/CW ratio of 1:10, the system showed higher stability after changing the manner of adding CW. Interestingly, the CODcr of the wastewater can still be reduced from more than 150,000 mg/L to ∼500 mg/L upon increasing the quantity or quality of the UHCOW by 30% in the shock test.