The amount of food waste that is generated all over the world is enormous. As food wastes are rich in nutrients and organics, they serve as a potential source for the generation of many value-added commodities and energy. In most countries, food wastes are predominately dumped in open lands or incinerated, along with other combustible materials such as municipal solid wastes, for the possible extraction of energy. However, these two modes of food wastes disposal are encountering more and more environmental, technical, and economical challenges. More recently, it has been realized that food wastes can be transformed into energy and value-added products, such as horticultural biochars, using thermochemical technologies such as pyrolysis and gasification. In the current research work, three selected food items, carrots, cucumbers, and tomatoes, have been studied using thermogravimetric analysis. The biochar analysis involves one single food item (carrot), one binary mixture (carrot + cucumber), and one ternary blend of carrot, cucumber, and tomato. Two heating rates were used in order to perform kinetic modeling studies using the Arrhenius and Coats-Redfern models. Since the production of the pyrolysis gases—for energy and chemicals production—is of major economic significance regarding the overall process viability, the TGA syngas for a single component, binary component and tertiary component systems were analyzed by TGA coupled mass spectrometry. The results of the gas analysis indicate an increase in hydrogen generation due to blending the food wastes.

The continuing increase in population means an increasing demand for products and services, resulting in huge amounts of waste being discharged into the environment. Therefore, waste management requires the application of new and innovative solutions. One new approach involves converting waste into value-added chemicals and products for use directly or after further processing into higher value-added products. These processes include biological, thermochemical, and physiochemical methods. Furthermore, biosolids, including treated sewage sludge (SS), represent one of the major by-products of human activities, constituting a major environmental hazard and requiring the treatment of contaminated wastewater with associated health hazards. Sustainable solutions to manage and dispose of this type of waste are required. In this review, pyrolysis, a thermochemical conversion technology, is explored to convert biosolids to biochars. The review addresses previous studies, by providing a critical discussion on the present status of biosolids processing, the potential for energy recovery from the pyrolysis bio-oil and biogas, and finally some benefits of the production of biochars from biosolids.

In comparison to other methods, valorising food waste through pyrolysis appears to be the most promising because it is environmentally friendly, fast, and has a low infrastructure footprint. On the other hand, understanding the pyrolytic kinetic behaviour of feedstocks is critical to the design of pyrolysers. As a result, the pyrolytic degradation of some common kitchen vegetable waste, such as tomato, cucumber, carrot, and their blend, has been investigated in this study using a thermogravimetric analyser. The most prevalent model fitting method, Coats–Redfern, was used for the kinetic analysis, and the various mechanisms have been investigated. Some high-quality fitting mechanisms were identified and used to estimate the thermodynamic properties. As the generation of pyrolysis gases for chemical/energy production is important to the overall process applicability, TGA-coupled mass spectrometry was used to analyse the pyrogas for individual and blend samples. By comparing the devolatilization properties of the blend with single feedstocks, the presence of chemical interactions/synergistic effects between the vegetable samples in the blend was validated. The model, based on a first-order reaction mechanism, was found to be the best-fitting model for predicting the pyrolysis kinetics. The calculated thermodynamic properties (ΔH (enthalpy change $\approx$ E (activation energy))) demonstrated that pyrolysis of the chosen feedstocks is technically feasible. According to the TGA–MS analysis, blending had a considerable impact on the pyrogas, resulting in CO₂ composition reductions of 17.10%, 9.11%, and 16.79%, respectively, in the cases of tomato, cucumber, and carrot. Overall, this study demonstrates the viability of the pyrolysis of kitchen vegetable waste as a waste management alternative, as well as an effective and sustainable source of pyrogas.