Suitability of Different Agricultural and Urban Organic Wastes as Feedstocks for the Production of Biochar—Part 1: Physicochemical Characterisation

Abstract

Biochar is traditionally made from clean lignocellulosic or waste materials that create no competition for land use. In this paper, the suitability of alternative feedstocks of agricultural and urban origins are explored. A range of biochars was produced from holm oak and a selection of organic wastes, such as greenhouse wastes, greenwastes, a cellulosic urban waste, municipal press cake and pig manure. They were characterized and assessed for their potential agricultural use. The physicochemical properties of biochars were mainly driven by the characteristics of feedstocks and the pyrolysis temperature. The use of pre-treated lignocellulosic residues led to biochars with a high concentration of ash, macro and micronutrients, whereas raw lignocellulosic residues produced biochars with characteristics similar to traditional wood biochars. All biochars were found to be suitable for agricultural use according to the international standards for the use of biochars as soil amendments, with the exception of a biochar from urban origin, which presented high levels of Cr and Pb. The use of these biochars as soil amendments requires a thorough agronomical evaluation to assess their impact on soil biogeochemical cycles and plant growth.

Properties of Biochar from Anaerobically Digested Food Waste and Its Potential Use in Phosphorus Recovery and Soil Amendment

“…Thermochemical conversion of digestate results in the formation of a solid material known as biochar. This conversion happens in an oxygen-limited environment [13]. Several studies have reported on carbon sequestration and soil amelioration applications.…”

Suitability of Different Agricultural and Urban Organic Wastes as Feedstocks for the Production of Biochar—Part 2: Agronomical Evaluation as Soil Amendment

“…In addition, two commercial biochars, from holm oak feedstock by a large-scale slow pyrolyser (residence time of about 15 h) by Proininso Inc. (Málaga, Spain) were used: OC450 and OC650, produced at 450 • C and 650 • C, respectively. The main characteristics of the biochars are reported in this Special Issue [18].…”

“…Although their contents in some raw lignocellulosic biochars are rather low [18] (this Special Issue), biochars prepared from urban wastes (GW400, CM400, and PC400) and from manure (PM400) present high mineral contents, and may have agronomic relevance. The availability of these micronutrients in the biochar itself and after soil application was evaluated by the changes in the DTPA-extractable fraction.…”

“…In general, the addition of biochar did not increase the amount of DTPA extractable micronutrients in soil, with the only exception of the concentration of Mn ( Figure S3). Increasing biochar application rate to the soil did not affect DTPA-available content of micronutrients despite the great differences between mineral concentrations in the different biochars, especially in the case of biochars prepared from pre-treated organic wastes, such as CM400, PC400, GW400 and PM400, characterised by a high content in Fe, Cu, Mn and Zn [18] (this special issue).…”

“…Pyrolysis of organic wastes led to a concentration of the metals, originally present in the feedstocks, into the ash fraction of the biochars. Some of the biochars used in this study had a high concentration of metals [18] (this Special Issue). The concentration of potentially toxic metals in CM400, PM400, PC400, and GW400 are in some cases above the threshold for biochar of basic quality grade according to the European Biochar Certificate (EBC) [35].…”