Removal of cadmium, chromium, lead and copper from urban sewage by Aspergillus Niger and Pseudomonas fluorescens

Aspergillus Niger and Pseudomonas fluorescens have the ability to absorb heavy metals during the stationary phase of growth. To improve the removal the efficiency of the oxidation ditch, we have introduced Aspergillus Niger and Pseudomonas fluorescens to the traditional Carrousel oxidation ditch process and the comparative experimental study were carried out when the Hydraulic Retention Time (HRT) was 36h. According to the HRT of the oxidation ditch in the criterion, six different HRTs of 12h, 16 h, 20 h, 24 h, 28 h, and 32 h were considered to study the degradation of cadmium (Cd), chromium (Cr), lead (Pb) and copper (Cu) by Aspergillus Niger or Pseudomonas fluorescens which was introduced to the oxidation ditch process, respectively. The results indicated that the removal efficiency of the four heavy metals by each of the two strains compared to the control group was improved significantly, and the removal increased with the increasing HRT. When the HRT was 20h, the removal of the four heavy metals by the Aspergillus Niger was found to be in the range of 52% to 91%, and the removal of Pseudomonas fluorescens reached more than 70%. Most of the heavy metals can be degraded at the HRT of 20h, and this time is exactly the conventional design parameter of oxidation ditch. It can be say that the removal efficiency of heavy metals can be significantly improved after introduced Aspergillus Niger and Pseudomonas fluorescens to the traditional Carrousel oxidation ditch process.