Management of tannery wastewaters: treatment of spent chrome tanning bath and vegetable tanning effluents

Abstract

In this work, a chain of treatment processes was proposed and described in order to reach better management of mineral and vegetable tannery wastewaters. First, chromium was precipitated from the spent chrome tanning bath by sodium hydroxide (NaOH) and then reformulated to form a complex of basic chromium sulfate which was tested successfully in mineral tanning process. On the other hand, the supernatant recovered after precipitation of chromium with NaOH was used to dilute vegetable tanning wastewaters characterized by a high concentration of polyphenols (about 2,574 mg/L). Diluted effluent was then treated by liming and tangential microfiltration using a ceramic membrane based on alumina with a nominal pore size of 100 nm and a average water permeability of 276 L/h m² bar. The tests revealed a very high efficiency of the combined processes dilution−liming−microfiltration. Treatment developed can work continuously and leads to a quasi-complete removal of polyphenolic compounds and turbidity from feed. The chemical oxygen demand (COD) of vegetable tanning effluent was reduced by 86−87%.