Abstract
The ability of Aspergillus niger strain to reduce organic and mineral pollution as well as the toxicity of two tannery wastewaters, the unhairing effluent (UE) and the final effluent (FE), taken from a local Tunisian tannery and under nonsterile conditions, was studied. Raw effluents show alkaline pH ≥11; thus experiments were carried out at initial pH values and at pH adjusted to 6. Characterization of effluents also revealed high salt levels (EC > 17 mS/cm) and high organic matter content (25 g/L for the UE and 7.2 g/L for the FE) but a low biodegradability since BOD5 did not exceed 2.5 and 1.25 g/L for the UE and the FE, respectively. The results of the biological treatment showed that A. niger was able not only to grow at high pH and salinity values, but also to reduce organic and mineral pollutant load. After treatment, the COD reduction for the UE reached 90% and 70% at pH=6 and at initial pH (12.13), respectively. For the FE, the decrease of COD values reached 75% at pH=6 and 64% at initial pH (11.64). Monitoring of mineral pollution levels showed a reduction in chromium (Cr) concentrations reaching 70% for the FE. This was reflected by an increase of the biomass of A. niger from 9.25 g/L (control) to 9.84 g/L for the FE. To confirm the efficiency of the biological treatment using A. niger, phytotoxicity (tomato seeds) and microtoxicity (Escherichia coli and Bacillus subtilis) tests were carried out. Results of this monitoring showed an important decrease in the toxicity levels for both effluents.
Highlights
Environmental pollution is turning into a worldwide problem in which water pollution is a critical issue since water is used for different purposes [1]
Two effluents from a Tunisian tannery were used in this study: the unhairing effluent (UE) and the final effluent (FE)
According to the study made by UNEP [45], BOD5 and Chemical oxygen demand (COD) values in the tannery effluent are generally higher than the tolerance limits for inland surface water
Summary
Environmental pollution is turning into a worldwide problem in which water pollution is a critical issue since water is used for different purposes [1]. The management of water pollution is considered as one of the major challenges for environmentalists [2] This pollution is generally due to the quick rise of industrial activities which extremely increased the release of toxic wastes into water bodies along with ground water [3]. During the leather making process, 25 up to 80 m3 of wastewater are generated per ton of raw material [7] These wastewaters are highly turbid, colored, and foul-smelling [8]. The main odorous gases in tannery effluents are volatile organic compounds (VOCs), hydrogen sulfide (H2S), and ammonia (NH3) [12]. High concentrations of such organic and inorganic pollutants with low biodegradability represent a serious technological and environmental challenge [13]. Mendes et al [16] proved that even a short-term exposure of male and female C57Bl/6 J mice to tannery effluents led to a deficit of their olfactory response, to a low response to predators as well as a partial memory deficit in the task of inhibitory avoidance
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