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Recycling underutilized resources from food waste (FW) to agriculture through hydrothermal carbonization (HTC) has been proposed to promote a circular economy (CE) in food-energy-water (FEW) nexus. However, most HTC studies on FW were conducted at laboratory scale, and little is known on the efficacy and feasibility of field application of HTC products from FW, i.e. the aqueous phrase (AP) and solid hydrochar (HC), to support agriculture production. An integrated pilot-scale HTC system was established to investigate practical HTC reaction conditions treating FW. A peak temperature of 180 ◦C at a residence time of 60 min with 3 times AP recirculation were recommended as optimal HTC conditions to achieve efficient recovery of nutrients, and desirable AP and HC properties for agriculture application. Dilution of the raw AP and composting of the fresh HC are necessary as post-treatments to eliminate potential phytotoxicity. Applying properly diluted AP and the composted HC significantly improved plant growth and nutrient availability in both greenhouse and field trials, which were comparable to commercial chemical fertilizer and soil amendment. The HTC of FW followed with agricultural application of the products yielded net negative carbon emission of 􀀀 0.28 t CO2e t􀀀 1, which was much lower than the other alternatives of FW treatments. Economic profit could be potentially achieved by valorization of the AP as liquid fertilizer and HC as soil amendment. Our study provides solid evidences demonstrating the technical and economic feasibility of recycling FW to agriculture through HTC as a promising CE strategy to sustain the FEW nexus. 

The water retention capability of soil significantly impacts plant growth. A scarcity of water in agricultural soil may cause low crop productivity, potentially leading to critical food-deficit problems in arid areas with increasing populations such as central California. New ways to enhance the water retention capability of soil to enable farmers to utilize water more effectively are thus urgently needed. Research has shown that hydrochar, which is produced by hydrothermal carbonization (HTC), can potentially improve soil quality by enabling it to hold water for longer periods. This study therefore explored how the addition of hydrochar affects water retention capacity in the root zone using soil experiments. For the experiments, a column filled with sample sandy soil but without hydrochar, which was used as a control. Meanwhile, 8% weight of hydrochar were mixed with soil at the top of soil columns to investigate how the presence or absence of hydrochar affected: (1) the temporal variation of soil moisture vs depth; (2) the temporal variation in the water’s potential head vs. depth at different times; and (3) the distribution of soil moisture vs the water’s potential head. The results of these experiments can be utilized to show the agricultural benefit gained by soil amendment with a certain amount of hydrochar. 

The water retention capability of soil significantly impacts plant growth. A scarcity of water in agricultural soil may cause low crop productivity, potentially leading to critical food-deficit problems in arid areas with increasing populations such as central California. New ways to enhance the water retention capability of soil to enable farmers to utilize water more effectively are thus urgently needed. Research has shown that hydrochar, which is produced by hydrothermal carbonization (HTC), can potentially improve soil quality by enabling it to hold water for longer periods. This study therefore explored how the addition of hydrochar affects water retention capacity in the root zone using soil experiments. For the experiments, a column filled with sample sandy soil but without hydrochar, which was used as a control. Meanwhile, 8% weight of hydrochar were mixed with soil at the top of soil columns to investigate how the presence or absence of hydrochar affected: (1) the temporal variation of soil moisture vs depth; (2) the temporal variation in the water’s potential head vs. depth at different times; and (3) the distribution of soil moisture vs the water’s potential head. The results of these experiments can be utilized to show the agricultural benefit gained by soil amendment with a certain amount of hydrochar.