A large paper mill uses waste paper as raw material and produces 12000 tons of papermaking white water and intermediate wastewater per day. The wastewater contains a large amount of fine fibers, fillers, and adhesives, with high suspended solids concentration. The original air flotation system has low treatment efficiency, and the COD fluctuation in the biochemical stage is large, resulting in high discharge pressure and high water consumption per ton of paper. The combination process of “efficient shallow air flotation+anaerobic expanded granular sludge bed (EGSB)+aerobic MBBR+Fenton deep treatment” is adopted, and multiple disc filters are used to recover fibers. After the renovation, the fiber recovery rate reached over 90%, the COD stabilized from 3500mg/L to below 50mg/L, the drainage capacity per ton of paper decreased from 15 tons to 6 tons, the water reuse rate increased to 75%, the annual COD emissions were reduced by about 800 tons, and the annual efficiency of fiber recovery was about 2 million yuan.