Municipal Sludge–Derived Biochar Enriched with Pseudomonas sp. Isolate RA-21 Enhances Soil Properties and Capsicum annuum Growth

Abstract

The growing world population has increased the demand for food to meet global needs, which contributed to the growth and vibrancy of the agricultural sector. There is an urgent need for soil treatment to restore healthy soil conditions due to extensive and unregulated agricultural activities that have degraded soil fertility, resulting in reduced crop yields. Sludge from a municipal wastewater treatment plant is potentially used in biochar production. Thus, the combination of biochar with plant growth-promoting bacteria offers an ecologically friendly alternative for improving soil health and agricultural output. ICP-MS and Brunauer–Emmett–Teller (BET) analysis were used to determine the quality of the developed biochar. An indigenous Pseudomonas sp. isolate, RA21, was mixed with biochar and used as a soil conditioner to promote chili plant growth. Plant height, leaf size, and stem diameter were measured to compare treated and untreated plants. ICP-MS analysis indicates that zinc and iron were the dominant metals present in all samples. BET analysis shows that approximately 70% of the biochar pore volume is composed of mesopores. The Fe and Zn nutrients in biochar serve as nutrient sources for plant uptake, while the high proportion of mesopores provides sites for bacterial colonization and enhances adsorption capacity. The application of a soil conditioner resulted in greater plant growth variables such as height, leaf size, and stem diameter when compared to the control group, and was equivalent to commercial fertiliser. Using soil conditioner resulted in more leaf area (651 cm²) in chilli plants compared to those treated with commercial fertiliser (629 cm²). Biochar, in particular, serves as a transporter for bacteria, allowing for optimal growth and activity while also providing nutrients that promote healthy plant development. The combination of sludge-derived biochar with the indigenous Pseudomonas sp. strain RA21 has shown encouraging results as a soil conditioner by increasing nutrient availability, allowing for the value-added use of municipal sludge within a circular economy framework.