Energy Recovery from Garden and Park Waste by Hydrothermal Carbonization with Process Water Recycling

Abstract

This study aims to obtain a carbonaceous material with suitable properties to be used as a solid biofuel by recycling process water from hydrothermal carbonization (HTC) of garden and park waste (GPW). The research is focused on maximizing mass yield and energy recovery as well as facilitating the treatment of the liquid fraction throughout reusing cycles of the liquid fraction. Process water recycling moderately improved the mass performance of the hydrochar, resulting in a higher energy recovery of almost 20 percentage points compared with that achieved (less than 79%) with conventional HTC (GPW + freshwater feed). An improvement in char fuel quality was observed, showing more suitable morphological, physical, and chemical characteristics, higher reactivity and combustion temperature, and lower probability of ash sintering. Successive process water reuse cycles allowed some increase in energy yield but, at the same time, degraded the quality of hydrochar as a biofuel. Process water composition showed an increase in chemical oxygen demand and total organic carbon, which almost doubled after three successive reuse cycles. The concentration of volatile fatty acids increased around 5-fold (up to 20 g L −1 ), with acetic acid accounting for 85% of the total. Subsequent anaerobic digestion of the process water removed up to 75% of the COD and yielded a biogas with high methane content (225−302 N mL CH 4 g −1 COD added ). Recycling of the process water significantly improved the total energy recovery (hydrochar + methane) to 90% after a single recycling, compared to 84% achieved with conventional HTC and subsequent anaerobic treatment of the resulting process water.

Cost Effective Photothermal Materials Selection for Direct Solar-Driven Evaporation

“…However, cost-effective methods exist, such as hydrothermal carbonization, which can be conducted at lower temperatures ranging from 150 to 190 °C. These processes can take as little as 20 to 40 min. , It is more promising that hydrothermal carbonization to produce biochar products from such garden and park wastes is being further developed to enhance its economic viability by maximizing heat recovery through the recycling of process water, as illustrated in Figure . Moreover, even handmade strategy treatments such as crochet, as shown in Figure , can be considered an economical approach to produce, for instance, a cost-effective handmade flowerlike light absorber (HFLA) with a superhydrophilic surface, especially after processes such as the dyeing of waste materials …”

“… Fundamental pathways of reaction in hydrothermal carbonization. Reproduced from Ipiales et al 50 Copyright 2024 American Chemical Society. …”