Year: 2018, Issue: December

Reclamation of the effluent of a chlor-alkali industry by environmental chemicals in presence of a cyanobacterium.

Author:

N. H. H. Verma, A. Leelaveni and A. K. Panigrahi

Keyword:

Chlor-alkali industry, Mercury pollution, Effluent, Cyanobacterium, Detoxification, Phytoremediation

Maximum concentration mercury was recorded in the effluent channel of the chlor-alkali industry. A maximum of 2.65 mg l-1 was recorded, which is much more than the stipulated limit of 0.01 mg l-1, set by Pollution Control Board. Effluent and sediment samples showed significant variable levels of mercury concentration at different sites. Highest level of mercury in both water and sediment was obtained at the junction zone where effluent channel meets the river water. Out of 10 varieties of chemicals tried only selenium dioxide showed positive results and other chemicals showed negative results. Panchagavya a formulation prepared in the laboratory did not show any positive result. Rather panchagavya showed negative effects along with mercury. Toxicity testing indicated that the effluent (mercury contained) showed dichotomous behaviour, at lower concentrations stimulating effects were observed and at higher concentrations inhibitory effects were observed. The exposed alga accumulated 1.22±0.09 μg, 2.42±0.52 μg and 3.92±0.88 μg of Hg/50 ml culture after 15th days of exposure in 0.45% (X), 1.6% (Y) and 3.8% (Z) effluent concentration, respectively. After 15th days of recovery period, 68.5%, 23.97% and 19.89% of mercury removal / excretion was marked in X, Y & Z effluent concentrations, respectively. At lower concentration exposure, higher percent of mercury removal was marked, when compared to higher concentration exposure. The cyanobacterium, Westiellopsis prolifica, Janet could volatilize mercury from the medium as seen from the experiment designed by us in our laboratory. The exposed alga could volatilize 1.93 μg, 3.94 μg and 5.14 μg of mercury in X, Y and Z concentrations within a period of 15th days. The exposed alga could accumulate 1.26 μg, 2.62 μg and 3.94 μg of mercury within 15th days in X, Y and Z effluent concentrations. The exposed alga could remove 98.46%, 56.94% and 35.83% of total mercury present in the medium of 0.45% (X), 1.6% (Y) and 3.8% (Z) effluent concentration either by residual accumulation or by volatilization. In the entire process 0.93%, 2.86% and 1.82% of mercury was lost/unseen/not traceable in 0.45% (X), 1.6% (Y) and 3.8% (Z) concentrations, respectively. The pigment analysis and photosynthetic efficiency studies indicated the possible use of a chemical for reclamation. None of the chemicals indicated any promise except selenium dioxide where mercury had no effect and removal of mercury was a possibility.

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