Tannery effluents characterization and impacts on the marine environment
In this study, the pollution load and the impact of tannery wastewaters on the marine environment were assessed. The composition of the effluents from different fabrication steps varied considerably. Pre-tanning operations seem to be more polluting than other tanning operations, with the Chemical Oxygen Demand (COD) reaching 30 000 mg•L‐1. The analysis of the global effluent showed an important and variable pollution load versus time. The COD ranged from 700 to 3,400 mg•L‐1, and the suspended matter from 500 to 8,000 mg•L‐1 for an average pollution load of 114 and 358 kg•d‐1 respectively. Chromium concentrations ranged from 40 to 115 mg•L‐1, giving a daily load of 6.5 kg•d‐1. Sulfide concentrations varied from 65 to 160 mg•L‐1. The biodegradability index (DBO5/DCO: 0.1‐0.2) indicates that the effluent is not readily biodegradable. In order to assess the impact of the tannery wastewaters on the marine environment, the mussel Mytilus galloprovincialis and the algae Ulva lactuca and Corallina officinalis were selected as bioindicators. The results indicated high chromium contents in the species living near the point of discharge into the sea.