Remediation of Boron-Contaminated Soil Using Biochar from Cocoa Pod Husk Waste Modification by Low-Pressure Cold Plasma

This study examines the effect of applying low-pressure cold plasma (LPCP)- modified biochar on boron-contaminated soil. Five treatments were tested: boron-contaminated soil (SB) as the control treatment, and contaminated soil amended with biochar, either untreated (SBNP) or plasma-treated LPCP for 10 (SBP10), 20 (SBP20), or 30 minutes (SBP30). Results indicated that LPCP treatment enhanced the fixed carbon content within the biochar structure and modified its surface characteristics, increasing biochar porosity. This increased porosity and surface reactivity, thereby improving boron adsorption and removal efficiency by up to 59.85% in the soil amended with biochar treated by LPCP for 30 minutes (SBP30). Soil quality parameters significantly improved (p ≤ .05) following LPCP-treated biochar application, including increased pH (from 4.6 to 5.6), cation exchange capacity (from 20.56 to 34.44 meq 100 g−1), available phosphorus (from 7.15 to 19.74 mg kg−1), and exchangeable cations such as K+, Ca2+, and Mg2+. Greenhouse gas measurements revealed slightly lower CO2 emissions for LPCP treatments than untreated biochar, while CH4 fluxes remained stable across treatments. A preliminary techno-economic analysis suggested that the energy consumption for LPCP treatment is minimal (0.025–0.075 kWh kg−1), with an estimated cost of US$ 0.0045–0.0135 per kg of biochar. These findings demonstrate that LPCP-modified biochar not only effectively removes boron from soil but also enhances soil quality and offers a sustainable, scalable solution for agricultural remediation, with a low economic impact when applied at field scale.