Predicting relative agronomic efficiency of phosphorus-rich organic residues.

Relative agronomic efficiency (RAE) of phosphorus (P) in nutrient-rich residues with different chemical characteristics must be known in order to optimize their use as fertilizers, to avoid underfertilization of crops or eutrophication of surface waters due to overfertilization. In this study, we determined the chemical characteristics and RAE of manures (cattle, pig, fox) and sewage sludges subjected to different treatments (anaerobic digestion, composting, lime stabilization, thermal hydrolyzation, pyrolyzation, hydrothermal carbonization (HTC)) by growing barley (Hordeum vulgare, var. Elmeri) to maturity in three independent growth trials. All manures had high RAE (up to 189% in pig slurry), while RAE was only 6-17% for digested and composted sewage sludges when precipitation with Fe used for P removal from wastewater. Pyrolyzation and HTC further depressed RAE to 1-6%. Alternative wastewater treatment processes are therefore needed to increase P recycling potential. For cattle and pig manures and anaerobically digested or composted sewage sludges, molar ratio of (Fe + Al)/P, varying from 0.08 to 2.69, was the best predictor of RAE (R2 = 0.99), with negative correlations with grain yield. Sources in which calcium was more influential for P solubility (fox manure and lime-stabilized sewage sludge) and pyrolyzed and HTC-treated residues did not follow this trend. Conventional extraction methods (2% formic acid, 2% citric acid, neutral ammonium citrate, water and 0.5 M NaHCO3) either underestimated or overestimated RAE of P-rich organic residues, depending on their chemical characteristics.

Quantitative characterization of pore structure of several biochars with 3D imaging.

Pore space characteristics of biochars may vary depending on the used raw material and processing technology. Pore structure has significant effects on the water retention properties of biochar amended soils. In this work, several biochars were characterized with three-dimensional imaging and image analysis. X-ray computed microtomography was used to image biochars at resolution of 1.14 µm and the obtained images were analysed for porosity, pore size distribution, specific surface area and structural anisotropy. In addition, random walk simulations were used to relate structural anisotropy to diffusive transport. Image analysis showed that considerable part of the biochar volume consist of pores in size range relevant to hydrological processes and storage of plant available water. Porosity and pore size distribution were found to depend on the biochar type and the structural anisotopy analysis showed that used raw material considerably affects the pore characteristics at micrometre scale. Therefore, attention should be paid to raw material selection and quality in applications requiring optimized pore structure.

Hydrothermal treatment followed by enzymatic hydrolysis and hydrothermal carbonization as means to valorise agro- and forest-based biomass residues.

The suitability of several abundant but underutilized agro and forest based biomass residues for hydrothermal treatment followed by enzymatic hydrolysis as well as for hydrothermal carbonization was studied. The selected approaches represent simple biotechnical and thermochemical treatment routes suitable for wet biomass. Based on the results, the hydrothermal pre-treatment followed by enzymatic hydrolysis seemed to be most suitable for processing of carbohydrate rich corn leaves, corn stover, wheat straw and willow. High content of thermally stable components (i.e. lignin) and low content of ash in the biomass were advantageous for hydrothermal carbonization of grape pomace, coffee cake, Scots pine bark and willow.

Hydrothermal carbonization of pulp mill streams.

The progress of the conversion, the yield, the structure and the morphology of the produced carbonaceous materials as a function of time were systematically studied with pyrolysis-GC/FID and FESEM microscope. The conversion of galactoglucomannan, bleached kraft pulp and TEMPO oxidized cellulose nanofibrils followed the reaction route of glucose being slower though with fibrous material, higher molar mass and viscosity. The conversion of kraft lignin was minor following completely different reaction route. Carbonaceous particles of different shape and size were produced with yields between 23% and 73% after 4h with being higher for lignin than carbohydrates. According to the results, potential pulp mill streams represent lignocellulosic resources for generation of carbonaceous materials.