Hydrochars from Biosolids and Urban Wastes as Substitute Materials for Peat

Abstract Peat is the most widely used substrate component and extensively used in greenhouse cultivation, landfill cover soils, urban parks and gardens, urban agriculture or green roofs, due to its excellent combination of physicochemical properties. The production of hydrochar by hydrothermal carbonization (a process at lower temperatures than pyrolysis and using wet conditions) could industrially reproduce the initial conditions of biomass humification and lead to materials with similar properties to those of peat. The objective of this work was to compare peat (PT, Control), a hydrochar prepared from biosolids (HSL), a hydrochar prepared from the organic fraction of urban wastes (HUW) and two mixtures (PT + HSL and PT + HUW) at a 50% volume rate for their potential use as substrates with multiple applications. Ryegrass was established at a rate of 40 g seeds cm −2 in the potting mixtures. Hydrophysical and biochemical properties (microbial biomass and the enzymes dehydrogenase, β‐glucosidase and phosphomonoesterase) were analyzed for PT, HSL, HUV and their combination (PT + HSL and PT + HUW). Treatments with biosolids hydrochar increased ryegrass production by 184% (HSL) and by 216% (PT + HSL) dry weight compared to the control (peat). Biochemical properties depended strongly on hydrochar type, while the hydrophysical properties of the hydrochars were similar to those of peat. Overall, our results found hydrochar–peat mixtures (PT + HSL and PT + HUW) to be suitable for the preparation of growing media. Copyright © 2017 John Wiley & Sons, Ltd.