Document Type : Research Paper
Authors
1
Associate prof. of Wood Science and Technology University of Mohaghegh Ardabili, Faculty of Agriculture and Natural Resources, Ardabil, Iran.
2
1. M.Sc. graduated of Wood Science and Technology department of natural resources Faculty of agriculture and natural resources University of Mohaghegh Ardabili Ardabil Iran.
3
Assistant prof. of Wood Science and Technology department of natural resources Faculty of agriculture and natural resources University of Mohaghegh Ardabili Ardabil Iran.
4
M.Sc. Student of Wood Science and Technology department of natural resources Faculty of agriculture and natural resources University of Mohaghegh Ardabili Ardabil Iran.
10.22034/ijwp.2025.2063966.1712
Abstract
Problem definition and objectives: The growing demand for water and the resulting increase in wastewater generation in the pulp and paper industry particularly in soda and kraft pulping processes have led to the production of large volumes of black liquor with extremely high pollutant loads. These effluents are mainly composed of lignin, phenolic compounds, sulfur compounds, silica, and ash, which make their treatment and disposal both technically challenging and environmentally hazardous. Traditional treatment methods such as evaporation and incineration are economically unfeasible due to high energy demands, large capital investments, high operational costs, and relatively low efficiency. This study aims to investigate the potential of biological treatment of black liquor obtained from wheat straw soda and kraft pulping using free cells of Bacillus subtilis. The effectiveness of this method in reducing key pollution parameters including Biological Oxygen Demand (BOD), Chemical Oxygen Demand (COD), Total Suspended Solids (TSS), and Total Dissolved Solids (TDS) was evaluated.
Methodology: Black liquor was prepared under controlled laboratory conditions from soda and kraft pulping of wheat straw. Free cells of B. subtilis, obtained from the Iranian Industrial Microorganism Collection, were cultured in nutrient-rich media containing carbon and nitrogen sources, and added to diluted black liquor samples. The experiments were conducted at optimal conditions (pH = 7, 30°C, 80 rpm) over incubation periods of 0, 1, 3, 7, 11, and 14 days. Key parameters (BOD, COD, TSS, TDS) were measured in triplicate and statistical analysis was carried out using SPSS software.
Results: The results showed that B. subtilis significantly reduced pollution indicators, particularly in soda black liquor. After 14 days of treatment, COD reduction reached 51.04% in soda and 38.03% in kraft liquor. BOD was reduced by 67.54% in soda and 40.14% in kraft. TDS and TSS reduction rates were 45.88% and 22.43% in soda, and 49.32% and 17.32% in kraft, respectively. The most effective performance was observed within the first five days of treatment. Afterward, the rate of reduction decreased, likely due to nutrient depletion and increased environmental toxicity. The overall treatment efficiency was significantly lower in kraft liquor due to its higher lignin condensation and sulfur content.
Conclusion: Biological treatment of soda and kraft black liquor using B. subtilis free cells proved effective in reducing major pollutants such as BOD, COD, TSS, and TDS. This method can serve as a cost-effective, efficient, and environmentally friendly approach for the primary treatment of effluents from cellulosic industries. Moreover, it may improve the performance of downstream processes such as activated sludge systems and biogas production.
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