Soil Amendments and Biostimulants from the Hydrothermal Processing of Spent Coffee Grounds

Jackie Massaya,Christopher J Chuck,Ben Mills-Lamptey

doi:10.1007/s12649-022-01697-x

Jackie Massaya, Christopher J Chuck + Show 1 more

Open Access

https://doi.org/10.1007/s12649-022-01697-x

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Abstract

PurposeUse of spent coffee grounds (SCG) in horticulture has deleterious effects on plant health and yields, suggesting that processing of SCG is necessary prior to field application. To this end, two products of an SCG based biorefinery were investigated: primary chars from the hydrothermal carbonisation (HTC) of SCG and enzymatic protein hydrolysates.MethodsPrimary chars were produced under various HTC regimes from raw SCG, and alkaline pre-treated SCG. Primary chars were evaluated in germination toxicity tests and under soil stress conditions using Arabidopsis thaliana (Arabidopsis). Proteolytic enzymes were screened in production of SCG protein hydrolysates; biostimulant activity in the growth of Saccharomyces Cerevisiae, germination of Arabidopsis thaliana under normal and cold conditions and auxin-like activity was assessed.ResultsToxicity assays of primary chars with land cress (Barbarea verna L.) showed a maximum 35% increase in root length, relative to the control. In Arabidopsis growth trials, outstanding performances were recorded at 100 t/ha for primary chars produced from alkaline pre-treated SCG: rosette diameter and dry weight increased by 531 and 976%, respectively, relative to the control. SCG protein hydrolysate from Bacillus lichenformis proteolysis (glycine present at 47% of total) gave 140% increase in Arabidopsis seeds with expanded cotyledons, relative to the control. Auxin-like activity was also measured in the extracts.ConclusionCascade process design was used to valorise a major waste stream. Removal of phytotoxic components from SCG hydrochars enhanced plant growth, while biostimulant activity of SCG protein hydrolysates was observed.Graphical

Highlights

Treatment of soil with carbonaceous material such as biochar is a traditional strategy towards ameliorating soil quality
We demonstrate for the first time, that alkaline hydrolysis of the protein fraction, converting the rest of the biomass into a hydrochar by hydrothermal carbonisation (HTC), followed by a polar extraction to remove phytotoxic components, can produce higher value, high performance additives for horticulture
In line with the overall sustainability research arch, we explored the viability of spent coffee grounds as an amendment for peat-free media to support vegetative growth of Arabidopsis

Summary

Introduction

Treatment of soil with carbonaceous material such as biochar is a traditional strategy towards ameliorating soil quality. The slurry product from the hydrothermal carbonisation (HTC) of biomass under comparatively milder processing conditions (T = 180–260 °C) in up to 95% vol water, have been highlighted as suitable soil amendments. The volatile phase is attributed to the observed phytotoxicity of hydrochar, necessitating post-treatments such as composting and thermal processing prior to soil application [2,3,4]. As horticultural substrates, both hydrochars and biochars have been highlighted for improving the nutrient uptake, water holding capacity, N-retention, and crop productivity [5,6,7]. Production of hydrochars and biochars beneficially utilises waste streams from the agricultural, industrial, food-processing, and municipal sectors as well as promoting carbon sequestration [8, 9]

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