Treatment of synthetic tannery wastewater in a continuous two-phase partitioning bioreactor: Biodegradation of the organic fraction and chromium separation

Abstract

A continuous two-phase partitioning bioreactor has been tested for treating a synthetic leather tannery wastewater with the objective of achieving effective removal of the organic load and complete chromium separation. The bioreactor was operated with 5.5 m of Hytrel 8206 polymeric tubing fed with a synthetic tannery wastewater consisting of 4-chlorophenol (concentration in the range of 1000–2500 mg L−1) and potassium dichromate (100 mg L−1 as Cr (VI)), and immersed in a 4 L bioreactor containing the microbial culture acclimatized to the compound. This configuration prevents the direct contact between the toxic wastewater and the microorganisms themselves, and provides the gradual organic substrate delivery through the tubing walls. Abiotic partition and mass transfer tests were performed to investigate the transport of dichromate and 4-chlorophenol across the tubing into the bulk phase of the bioreactor. No appreciable mass transfer of dichromate was detected. During biotic testing, the influent organic load in tubing has been varied in the range of 19–94 mg h−1 and the hydraulic retention time from 3 to 6 h. Achieved biological removal efficiencies were in the range of 89–95% for the highest applied loads. Process kinetics (which included consideration of both mass transfer and biological rates) were evaluated, and it was found that the increased load did not result in any decrease in 4-chlorophenol removal rate. This work has shown that the continuous two-phase partitioning bioreactor has significant potential in enhancing the biological treatment of tannery wastewater, which is a typical representative of industrial “hostile” wastewater.