Biological pretreatment of tannery wastewater using a full-scale hydrolysis acidification system

To evaluate the performance of hydrolysis acidification (HA) system on the tannery wastewater treatment in a cold region, the effects of COD, SS, sulphides concentration and the low temperature on tannery wastewater treatment were investigated in a 5000 m3/d full-scale HA reactor. The results showed that the removal ratios of COD and SS were in the range of 20%-45% and 65%-82%, respectively. The average BOD/COD of the tannery wastewater was improved from 0.38 to 0.56, and the pH decreased from 8.4 to 7.6 after the HA treatment. The concentration of sludge and COD in the bottom of the HA reactor was significantly higher than those of the top region. The thickness sludge layer shortened the required hydraulic retention time and improved the SS removal efficiency. When the temperature of HA reactor dropped below 8 °C, the COD removal ratio decreased to less than 10%. However, the SS removal ratio was not obviously impacted. The results obtained from this study indicated that the HA system provided an effective biological pre-treatment of the tannery wastewater for organic loading reduction and biodegradability improvement, even in a cold season.