Hydrothermal Carbonization of Fruit Wastes: A Promising Technique for Generating Hydrochar

TLDR

Hydrothermal carbonization converts wet biomass into value‑added products, and fruit waste from juice industries offers abundant moist feedstock for hydrochar production, with increased ash content above 225 °C attributed to higher porosity. The study investigates HTC of four fruit wastes—rotten apple, apple chip pomace, apple juice pomace, and grape pomace—to evaluate their conversion to hydrochar. HTC was performed at 190 °C, 225 °C, and 260 °C for 15 min on the selected wastes. HTC raised higher heating value and fixed carbon while lowering volatile matter and oxygen, increased ash content (except ACP) and mass yield for RA and GP, and TGA/SEM confirmed successful conversion to valuable hydrochar.

Abstract

Hydrothermal carbonization (HTC) is a useful method to convert wet biomass to value-added products. Fruit waste generated in juice industries is a huge source of moist feedstock for such conversion to produce hydrochar. This paper deals with four types of fruit wastes as feedstocks for HTC; namely, rotten apple (RA), apple chip pomace (ACP), apple juice pomace (AJP), and grape pomace (GP). The operating conditions for HTC processing were 190 °C, 225 °C, and 260 °C for 15 min. For all samples, higher heating value and fixed carbon increased, while volatile matter and oxygen content decreased after HTC. Except for ACP, the ash content of all samples increased after 225 °C. For RA, AJP, and GP, the possible explanation for increased ash content above 225 °C is that the hydrochar increases in porosity after 230 °C. It was observed that an increase in HTC temperature resulted in an increase in the mass yield for RA and GP, which is in contrast with increasing HTC temperature for lignocellulose biomass. Other characterization tests like thermogravimetric analysis (TGA) and scanning electron microscopy (SEM) also showed that the HTC process can be successfully used to convert fruit wastes into valuable products.