Fertilizer and soil conditioner value of broiler manure biochars

Abstract

Pyrolysis is an option for enhancing the sustainable management of broiler manure surpluses by producing a concentrated, hygienic char product with a fertilizer and soil conditioner value. In this study, the impacts of pyrolysis conducted at 350, 400 and 450 °C on total nutrient and harmful element concentrations in biochars derived from peat-bedded broiler manure were examined. Emphasis was placed on the availability of phosphorus (P). In addition, the pore structures of these biochars were explored using X-ray microtomography and image analysis. During pyrolysis, 35-50%, 40-55% and 35-45% of the original carbon, nitrogen and sulfur contents, respectively, of the feedstock biomass were lost as volatiles. Mineral elements, including P, were concentrated in the biochar. Although water-extractable P was found to be converted to less labile forms due to charring, the concentration effect and notable increase in sodium bicarbonate-extractable P rendered broiler manure biochars richer in total labile P in comparison with feedstock manure (7.1, 10.0, 11.1 and 14.8 g labile P kg −1 in feedstock and biochars produced at 350, 400 and 450 °C, respectively). The pore volume of the micrometer-scale porosity of the broiler manure biochar was comparable to that found earlier in wood-based biochars. In comparison with wood-based biochars, the pore structure of broiler manure biochars was more versatile, and the pore size distribution was wider. Consequently, part of the porosity was too large to store plant-available water, which may reduce the potential of broiler manure biochars to improve soil water storage capacity.

Feasibility of Nitrogen-Enriched Chars as Circular Fertilizers

“…The wood-based chars tend to exhibit a higher specific surface area and total C content but a lower CEC and total and available element concentrations than manureand biosolids-based chars [12]. The elemental composition of the water extracts showed the activated charcoal (LG85) to be very poor in available elements, whereas the manurebased BR released K, P and S. Broiler manure is one of the nutrient richest manures and in our previous study [9] the peat bedded broiler manure feedstock was found to contain 24.9, 14.9 and 5.8 g K, P and S per kg dry mass (dm), respectively. The wood-based SA released some K, and the sewage-sludge-based chars mainly released Ca and S but also some N (Table 2, Sect.…”

“…The targeted process peak temperature was 450-500 °C, and the process was run until the gas formation ceased. Sphagnum peat bedded broiler manure was obtained from Biolan Oy (Eura, Finland), pre-dried at 37 °C and pyrolyzed in a batch-type laboratory-scale pyrolysis equipment [9]. Commercial activated charcoal (SORBOTECH LG85) intended for filtration use was acquired from a local distributor.…”

“…Agronomic benefits achievable by char amendments in soil comprise improved water holding ability, increased cation exchange capacity (CEC) and nutrient availability, and higher pH values [6,7]. The key properties of chars contributing to these possible positive impacts, namely porosity, surface activity and nutrient contents vary greatly depending on the process conditions and especially on the feedstock material [e.g., [8][9][10][11]. Chars derived from animal manures and biosolids are generally rich in nutrient elements due to the inherently high nutrient contents of the feedstock biomasses, whereas woodbased (lignocellulosic) chars typically contain relatively low amounts of nutrients but exhibit the greatest C contents [12].…”

“…However, scarcity of bioavailable nitrogen (N), is common to all charred materials due to gaseous losses of N compounds and the formation of recalcitrant N-ring structures during pyrolysis [13][14][15][16][17]. An increase in the maximum process temperature tends to increase volatilization of N and other volatile elements (e.g., C, and sulfur (S)), whereas non-volatile elements (e.g., phosphorus (P) and potassium (K)) remain enriched in the char fraction [9,18].…”

How clonal differences and within-tree heterogeneity affect pore properties of hybrid aspen wood and biochar?

“…While the pore properties are affected by choices in the pyrolysis process (e.g., temperature and duration), they are generally more controlled by choice of the feedstock [6,8,11,12]. Particularly wood-based biochars have been found to have desirable properties in terms of porosity, pore size distributions, and surface area [6][7][8], while biochar produced from substances such as manure, sludge, and agricultural residue has often reported to have less suitable pore properties [7,13]. Therefore, from the point of view of pore properties, wood feedstocks can be of particular interest when producing an applicable biochar amendment.…”