Improving municipal solid waste co-composting performance using activated biochar, leonardite, and MgSO<sub>4</sub>-modified zeolite.

Abstract

In this research, the municipal solid waste (MSW) was co-composted with H₂SO₄-activated biochar (H₂SO₄-AB), NaOH-activated biochar (NaOH-AB), MgSO₄-modified zeolite (MgSO₄-zeolite), and leonardite. Several maturity and stability parameters were determined over the co-composting period. Results showed that activating biochar with NaOH or H₂SO₄ resulted in the formation of a mesh structure with irregularly sized cavities and deep pores, thereby modifying the biochar surface. All of the additives used in this study yielded higher microbial respiration and dehydrogenase activity during the thermophilic phase. Both NaOH-AB and H₂SO₄-AB amended composts exhibited higher respiration rates than that of leonardite and zeolite, averaging 24% greater than the control. However, the 10% leonardite amended compost created a higher degree of humification than the rest of the treatments in co-compost based on humic acid yield and the E₄/E₆ and E₃/E₅ ratios. Furthermore, the 5% NaOH-AB amended compost was identified as the superior treatment due to its longest thermophilic period (7 days) and the highest temperature (71.5 °C), germination index (130.9%), and total nitrogen content (1.37%). This treatment also resulted in the greatest decline in NH₄⁺ concentration and the lowest availability of Cu and Cd (p < 0.05). However, the 10% H₂SO₄-AB amended compost was noted as the superior treatment based on maximum organic matter content (36.8%) and C/N ratio (18.1), along with the lowest nitrate concentration (254.4 mg/kg) and the lowest available Zn, Fe, Mn, and Pb concentrations (p < 0.05). Therefore, acid and base-activated biochars are suggested as the most suitable additives for improving the quality of MSW-derived co-compost.