Hydrochar, digestate, and process water impacts on a soil's microbial community, processes, and metal bioavailability
Author(s) -
Watson Conor,
Schlösser Charlotte,
Vögerl Jakob,
Wichern Florian
Publication year - 2021
Publication title -
soil science society of america journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.836
H-Index - 168
eISSN - 1435-0661
pISSN - 0361-5995
DOI - 10.1002/saj2.20239
Subject(s) - digestate , hydrothermal carbonization , environmental chemistry , chemistry , biomass (ecology) , mineralization (soil science) , soil water , environmental science , agronomy , anaerobic digestion , carbonization , adsorption , methane , organic chemistry , soil science , biology
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.