Biochar produced from water hyacinth in different pyrolysis temperatures as potential P fertlizer

Prof. Deborah Dick1, Msc Luana Botezzini1, Doctor Alberto Wienievski2, Doctor Heike Knicker4, Doctor Daniel Hanke3, Ms Djennifer Neckel1

1Federal University Of Rio Grande  Do Sul, Porto Alegre, Brazil, 2Federal University of Sergipe, Aracaju, Brazil, 3Federal University of Pampa, Dom Pedrito, Brazil, 4IRNAS-CSIC, Seville, Spain

Water Hyacinth (WH) is a plague that occurs frequently in rivers and estuaries along the Brazilian Coast, hampering port activities and navigation. WH may contain a significant phosphorus (P) concentration, and that makes it a potential soil P fertilizer. Our work aimed to determine chemical and molecular composition of WH biochars (WHBC) produced in different temperatures in order to identify adequate conditions for soil conditioners production. WH samples from Sergipe (BR) were air-dried and submitted to pyrolysis (5 L N2 min-1) at 400 (WHB4), 500 (WHB5) and 600°C (WHB6). Contents of C and N were determined and bulk chemical composition was investigated by FTIR, 13C and 31P NMR CP/MAS spectroscopies. Extractable P forms were quantified by exchange resin method (Pexc) and by liquid 31P NMR spectroscopy after extraction with NaOH + EDTA solution. C content ranged from 37 to 40 %, while that of N decreased steadily up to 600°C, indicating a continuous N loss with temperature. C/N ratio ranged from 13 to 18, and these values are relatively low in comparison BC’s from other sources. With increasing temperature, proportion of O/N-alkyl C groups decreased from 15.8 to 6.4 % while that of aromatic C gradually increased reaching 66% in WHBC600. Up to 500°C, alkyl C increased from 31 to 38% and decreased to 20% at 600°C. It seems that heating up to 500°C, carbohydrates are consumed preferentially with a relative enrichment of alkyl and aromatic structures. Further temperature rise concentrates aromatic C at the expenses of alkyl C consume. Increasing pyrolysis temperature also caused a gradual change from P-mono/diester groups towards phosphate in the bulk sample and a decrease of Pexc (60 to 10 mg P kg-1). Our results show that 400ºC is the most suitable temperature to produce WHB to be used as soil P fertilizer.


Prof. Dr. Deborah Pinheiro Dick graduated in Chemistry at the Federal University of Rio Grande do Sul, Brazil, where she also got a Master degree in Soil Science (1986). In 1993 she obtained her Doctorate in Soil Science at the Technical University of Munich, Germany. In !986, Deborah started as Assistant Professor at the Federal University of Rio Grande do Sul and currently she is Senior Professor at the Physical-Chemistry Department of the same University. Her main research topics are 1) soil organic matter composition and interactions in subtropical and tropical soils under different soil uses (forest, pasture) and management (no-tillage and vegetation burning), 2) Use and obtaining of organic matter and humic fractions from biochar, composts and mineral coal for agronomic uses; 3) Organic matter interactions with pesticides and minerals in tropical and subtropical environments; accelerated degradation of pesticides in adapted soils from subtropical and tropical environments: Dissipation mechanisms of pesticides applied as slow release formulations; 4) Composting of agronomic wastes; fertilizer potential, green-house gases emission and effect of biochar. Since 2012, she is board member of the IHSS.

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