Deciphering the microbial and chemical complexity of kraft paper industry sludge through metagenomic and toxicological evaluation

Abstract

The effluent from kraft paper mills is a significant cause of aquatic pollution owing to the discharge of substantial quantities of contaminated water. The study revealed that wastewater sludge discharged from kraft paper mill has different pollution parameters beyond their permissible limit i.e. phenol (350.21 μg/g), chlorophenol (437.507 μg/g), lignin (1197.512 μg/g), sodium (7164.371 μg/g), chloride (5641.087 μg/g), phosphate (610.621 μg/g), sulphate (5005.944 μg/g), heavy metals Ni (70,123 μg/g), Mn (22.903 μg/g), Cu (62.921 μg/g), Fe (182.256 μg/g), Pb (1.812 μg/g) and Cr (1.801 μg/g). GCMS analysis showed the presence of 3-Ethyltridecane (RT 37.57), 1,2-Pentanediol (RT 16.66), and (Z)-4-methyl-3-decen-2-ol (RT 42.25), 8-Methylnonanoic acid (RT 16.73), Octadecanoic acid ethenyl ester (RT 37.63), and 2-Octen-2-ol acetate (RT 42.35) in upstream and downstream sludge respectively. The detected pollutants are known for their toxicity and EDC properties which significantly cause adverse effect on aquatic organism. Metagenomic analysis showed Treponema & Azotobacter followed by Megasphaera & Prevotella and Pseudomonas & Azotobacter followed by Treponema & Georgenia in the upstream and downstream sludge respectively. Abundance of polymyxin resistance protein in sludge indicated a potential environmental threat. The toxicity test with Tubifex tubifex showed EC50 at 20 % concentration of both the sludge while mortality was noted at 80 % concentration of upstream sludge and 40 % concentration of downstream sludge. Seed germination test of Vigna radiata with sludge inhibited the germination at 20 % concentration of sludge of both site samples. The presented study provides important insights into contaminant features and bacterial communities in kraft paper mill waste contaminated environments.