Tarbiat Modares University Journal of Agricultural Science and Technology 1680-7073 28 2 2026 03 01 Co-Composting of Municipal Solid Waste with Activated Biochar: A Promising Approach to Improve the Quality of Compost 449 462 16846 EN Kamal Khalkhal Department of Soil Science, Faculty of Agriculture, University of Tabriz, Tabriz, Islamic Republic of Iran. Adel Reyhanitabar Department of Soil Science, Faculty of Agriculture, University of Tabriz, Tabriz, Islamic Republic of Iran. Shahin Oustan Department of Soil Science, Faculty of Agriculture, University of Tabriz, Tabriz, Islamic Republic of Iran. Nasser Aliasgharzad Department of Soil Science, Faculty of Agriculture, University of Tabriz, Tabriz, Islamic Republic of Iran. Journal Article 1970 01 01 Biochar reduces composting problems and improves compost quality. However, Activated Biochar (AB) and its size are often overlooked.<span><span dir="RTL"> </span>This research aimed to evaluate the impact of co-composting of Municipal Solid Waste (MSW) with different-sized biochar and AB on the quality of the resulting co-compost.</span><span><span dir="RTL"> </span>The MSW were mixed thoroughly with different-sized (B<sub>2-4mm</sub>, B<sub>1-2mm </sub>and B<sub>0.5-1mm</sub>) and activated biochars (H<sub>2</sub>SO<sub>4</sub>-AB<sub>0.5-1mm </sub>and NaOH-AB<sub>0.5-1mm</sub>) and co-composted for 90 days until compost maturity. The results revealed that the activation of biochar with NaOH and H<sub>2</sub>SO<sub>4</sub> caused the appearance of a mesh structure on the biochar surface, leading to improved stability and maturity, enhanced biodegradation and humification indices. Specifically, NaOH-AB (5%, w/w) showed the highest temperature (71.5°C), germination index (130.9%), and total nitrogen content (1.37%) and the longest thermophilic period (7 days). The highest Organic Matter content (OM) (37.9%) and the lowest electrical conductivity (7.4 dS m<sup>-1</sup>) were recorded in B<sub>1-2mm </sub>(10%, w/w). Furthermore, the lowest nitrate concentration (254.4 mg kg<sup>-1</sup>) and the highest C/N ratio (18.1) were in H<sub>2</sub>SO<sub>4</sub>-AB (10%).</span><span><span dir="RTL"> </span>Principal Component Analysis (PCA) highlighted the critical role of the C/N ratio and OM content during the composting. The study recommends the addition of biochar to MSW to achieve an appropriate C/N ratio and prevent nitrogen loss. Overall, incorporating NaOH- and H<sub>2</sub>SO<sub>4</sub>-activated biochars was found to be a valuable strategy for the composting of municipal solid wastes. Our findings provide valuable insights into the potential of biochar in optimizing the composting process.</span> <br><br> Biochar activation C/N ratio Composting process Humification https://jast.modares.ac.ir/article_16846_2bed57b5e7da7db0be5cd65a00bf6405.pdf