Utilizing industrial wastewater sludge-derived biochar for enhancing strength and microstructure of soft soil- An infrastructure application of wastewater sludge

This study proposes a waste-to-value approach; specifically focusing on the utilization of industrial wastewater sludge (IWS) derived pyrolytic biochar (PBC) as an alternative to conventional carbon positive soil stabilizing materials. The IWS was subjected to thermogravimetric analysis (TGA) in N2 environment which suggested the pyrolysis temperature of 450 °C for the synthesis of PBC. Five different dosages of PBC by weight were mixed with the soft soil (SS) and unconfined compressive strength (UCS) values were examined across the various curing periods. Test results confirmed that UCS and stiffness values of soil-PBC matrix increased 4–5 and 5–6 times to that of virgin soil respectively. The PBC increased the cation exchange capacity (CEC), point of zero charge (pHpzc), alkalinity, and water holding capacity of the soil thereby assisted to initiate pozzolanic reactions. Various spectroscopic techniques were performed to investigate the strength development mechanism. Free oxide of calcium (CaO) in PBC disturbed the laminated structure of soil, reacted with oxides of silica (SiO2) and other silicates of aluminum thereby densifying the soil-PBC structure. Further, leaching test was performed on soil-PBC matrices to evaluate the environmental viability of the PBC. The statistical significance of the test results was confirmed using the Analysis of Variance (ANOVA) technique. Overall, this study concludes that PBC has the potential to serve as an environmentally friendly alternative to conventional soil stabilizing materials. [Display omitted] •IWS-derived biochar improved the UCS values of SS from 47 kPa to 235 kPa.•The highest UCS was achieved after 28 days of curing with 10% PBC dosages.•PBC increased the CEC of soil matrices from 17.2 cmolckg−1 to 24.7 cmolckg−1.•Heavy metal leaching from soil-biochar matrices was reduced.