Microplastics extraction from pulp and paper industry wastewater sludges

There is a growing concern about environmental pollution caused by microplastics (MPs), which are plastic particles smaller than 5 mm. Their origins are diverse, stemming from both the breakdown of larger plastics and intentional use in various products and industrial processes. Wastewater treatment plants (WWTPs) play a significant role in the dispersion of MPs into the environment when effluent water and sludges are released into the environment. While MPs in municipal wastewater and sludges have been well studied, there exists limited, if any, knowledge regarding the existence of MPs in sludges originating from industrial wastewater treatment. Characterizing MPs is vital for understanding their environmental impact and devising effective pollution control policies. Analyzing MPs in sludge is challenging due to the organic-rich nature of the sample, requiring essential pre-treatment steps to remove organic and inorganic substances adhering to MPs. Standardized analysis methods are lacking, primarily due to variations in sample matrices and analytical instruments. This study focuses on optimizing the extraction protocol for primary sludge and bio-sludge generated by pulp and paper wastewater. The optimization process involves adjusting several variables in the extraction process, including digestion duration, reagents, temperature, and digestion stages. It was found that an extraction process, including sodium dodecyl sulfate (SDS) treatment, a sequence digestion of hydrogen peroxide-cellulase- hydrogen peroxide, at an incubation temperature of 45 °C, was effective in removing materials. A density extraction, with sodium polytungstate (SPT) solution of ρ = 1.8 g/mL, is included as a final stage of the extraction process, only to primary sludge. In conclusion, this study provides MPs extraction protocol for industrial wastewater sludge, with potential for further optimization.