Activated sludge has been widely used in wastewater treatment throughout the world. However, the biggest disadvantage of this method is the by-production of excess sludge in a large amount, resulting in difficulties in operation and high costs for wastewater treatment. Technological innovations for wastewater treatment capable of reducing excess sludge have thus become research topics of interest in recent years. In our present research, we developed a new biological wastewater treatment process by repeated coupling of aerobes and anaerobes (rCAA) to reduce the excess sludge during the treatment of wastewater. During 460-day continuous running, COD (300–700 mg/L) and TOC (100–350 mg/L) were effectively removed, of which the removal rate was above 80 and 90%, respectively. SS in the effluent was 13 mg/L on average in the rCAA bioreactor without a settling tank. The on-site reduction of the excess sludge in the rCAA might be contributed by several mechanisms. The degradation of the grown aerobes after moving into the anaerobic regions was considered to be one of the most important factors. Besides, the repeatedly coupling of aerobes and anaerobes could also result in a complex microbial community with more metazoans and decoupling of the microbial anabolism and catabolism.

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