Treatment of Leather and Fur Wastewater by a Rotating Biological Contactor

The operation of a leather and fur wastewater treatment plant has been stable for 8 years. The volumetric loading was 85 to 110 l/m^2.d, and the BOD loading and COD loading of the influent to the rotating biological contactor (RBC) were 15 to 20 g/m^2.d and 50 to 65 g/m^2.d respectively. Analyses have shown that the BOD₅, COD, suspended solids (SS), S²⁻, and Cr³⁺ removals were 87.8, 77.4, 84.8, 93.6, and 81.0%, respectively.

Several factors were considered in the design and performance of this leather and fur wastewater treatment plant. The pretreatment stage has a great influence on the operation of the RBC. The performance of the pre-aeration tank and primary clarifier regarding both BOD and COD removal approached 50%, therefore the organic loading of the RBC was reduced. However, shock flows of limewash waste from the workshop decreased the efficiency of the RBC. The high pH in the liquid film on the discs caused CaCO₃ to precipitate and settle as scale on the surfaces of the discs. As the pH increased, NH₃ stripping in the liquid film increased, and care had to be taken regarding proper room ventilation when the wastewater pH was high. Due to the high concentrations of organic matter and poorly biodegradable matter in the leather and fur wastewater, the rotational speed of the RBC must be increased compared with municipal wastewater treatment to ensure adequate aeration and to prevent blockages. In practice, the RBC linear velocities were between 25 to 30 m/min.