This study assessed sustainable solutions for organic waste management, focusing on biochar derived from kitchen waste. The characteristics and phytotoxicity effects of biochar produced from four different types of kitchen waste were investigated in view of potential agricultural applications. Analysis of the chemical and physical properties of the different biochar samples by X-ray fluorescence and Fourier transform infrared spectroscopy revealed a nutrient-rich composition with carbon, calcium, and potassium contents that ranged from 35 to 48%, from 1.6 to 24%, and from 1.5 to 28.5%, respectively. In phytotoxicity tests, the highest germination rate (45%) was observed with Coffee residue biochar obtained at 300 °C (application rate of 1%) and the longest shoot length (25 cm) with orange peel biochar obtained at 300 °C (application rate of 1%). Germination rate and shoot length were not significantly different between biochar-exposed soils and control soils (without biochar), indicating no toxic effect due to biochar addition. Washing biochar improved germination rates significantly (control: 98%; potato peel biochar: 92%; banana peel biochar: 83%). The longest shoot length (8.3 cm) was obtained with the washed potato peel biochar (pyrolysis temperature = 400 °C) extract. These findings suggest that biochar can be safely used as a soil amendment without harming the environment or hindering plant growth. The Tukey honestly significant difference (HSD) test results further emphasized the influence of different factors, such as pyrolysis temperature and feedstock type, in biochar applications.

The escalating threats of climate change, pollution, and a rapidly growing global population are putting immense pressure on water resources, highlighting the urgent need for innovative wastewater recycling solutions. This study explores the potential of biochar, derived from common kitchen waste as a sustainable and efficient adsorbent for copper removal from contaminated water. Seven factors were studied for their influence on the adsorption process, including heavy metal concentration (50–250 ppm), biochar dosage (0.5–2.5 g), contact time (30 min to 29 h), temperature (20–80 °C), pH (2.67–8.07), and the efficacy of activated versus non-activated biochar, with activation carried out using phosphoric acid, silver nitrate, and sulfuric acid. Biochar characterization using Raman spectroscopy, specific surface area by Brunauer–Emmett–Teller analysis (BET), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), Scanning Electron Microscopy—Energy Dispersive X-ray Spectroscopy (SEM-EDX), and zeta potential analysis revealed its robust adsorption capacity. Notably, silver nitrate-loaded biochar exhibited the highest adsorption capacity (24.44 mg/g) at 250 ppm of copper and the highest removal rate at about 99.3%, whereas phosphoric acid activation reduced this capacity to 5 mg/g due to structural damage. Importantly, biochar’s adsorption capacity was found to be pH-independent, simplifying operational requirements for treatment systems. Optimal conditions for maximum copper removal were determined to be 100 ppm of copper, a temperature of 60 °C, and a contact time of 30 min. The Langmuir isotherm model best described the adsorption process, indicating a monolayer adsorption with a maximum capacity of 23.25 mg/g. This comprehensive analysis underscores biochar’s potential as a cost-effective, efficient, and environmentally friendly solution for copper removal from wastewater.