Hydrochar, digestate, and process water impacts on a soil's microbial community, processes, and metal bioavailability

Abstract

Hydrothermal carbonization converts organic wastes into potentially soil-improving solids. The nutrient-rich process waters generated are prospective fertilizers. Two hydrochars were produced from maize (Zea mays L.) biogas digestate after 1 or 6 h of carbonization. Nutrient concentrations of the digestate, hydrochars, and process waters were determined. A 28-d incubation, in which digestate, hydrochars, or process waters were added to a sandy loam soil, assessed their effects on microbial biomass, community composition, respiration, and nitrification. The hydrochars became enriched in Fe and Zn but featured lower macronutrient concentrations than the feedstock. The application of process waters as fertilizers could be hindered by their electrical conductivity and nitrite levels. All amendments stimulated nitrification and C mineralization. The C losses of the latter add to losses during hydrochar production. Growth of microbial biomass was induced particularly by digestate, due to its high bioavailable fractions of C and nutrients. Fungal biomass thrived in hydrochar-amended soils, possibly due to a combination of their aromaticity and elevated micronutrient concentrations. A separate 56-d incubation tested the amendments' impact on metal bioavailability in an artificially contaminated substrate. In reducing concentrations of Cd, Zn and Cu, hydrochars were less effective than digestate, whose application likely led to increased complexation and sorption. However, application to the contaminated substrate of hydrochar permitted superior microbial biomass growth; its higher surface area and porosity may have provided an improved microbial habitat. Hydrochar application to soils may benefit the microbial biomass, but hydrothermal carbonization is not advantageous where the goal is C sequestration or increasing feedstock nutrient availability. INTRODUCTIONExcess nutrients can be delivered to soils and adjacent water bodies through indiscriminate application of organic wastes Abbreviations: DON, dissolved organic nitrogen; ICP-OES, inductively coupled plasma-optical emission spectrometer; MBC, microbial biomass carbon; MBSRR, microbial biomass specific respiration rate; PW, process water; qPCR, quantitative polymerase chain reactionThis is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made.

Olive Tree Physiology and Productivity Responses under No-Tillage or Digestate Amendment in an Acid Clay Soil

“…For instance, Adani, et al [41] observed a 50% increase in labile carbon loss as a result of a 75% increase in the compost dose. Nevertheless, the potential storage of freshly added C pools through digestate amendment strongly dependent on either the anaerobic biogas properties or the recipient soil characteristics [42][43][44][45]. We surmise that the pedogenetic features of the studied olive grove soil rich in fine-textured particles, poor in calcium carbonate, and with limited aeration produced soil fabric conditions suitable for physical protection and reduced mineralization of newly added organic pools, whatever their content of easily degradable organic substrates.…”

Preparation and Application of Carbon-Based Materials in the Production of Medium-Chain Carboxylic Acids by Anaerobic Digestion: A Review

“…Compared to pyrolysis, the temperature of hydrothermal carbonization is relatively lower than that of pyrolysis, and the yield of coke obtained is also higher than that of pyrolysis (the carbon yield of hydrothermal carbonization reaches 20-80%). It is a promising alternative thermal conversion technology [74]. During hydrothermal carbonization, wet organic raw materials are generated into liquid, solid, and gas phases at a temperature of 180-250 • C and a self-pressure of 2-10 Mpa.…”

Contrasted fate of zinc sulfide nanoparticles in soil revealed by a combination of X-ray absorption spectroscopy, diffusive gradient in thin films and isotope tracing

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