Abstract
Forest management practices in boreal peatlands increase nutrient export and suspended solids to watercourses calling for development of new water protection methods. One potential solution could be adsorption-based purification of runoff water using biochar. The aim of this study was to determine the adsorption rate and capacity for Norway spruce and silver birch biochars to design a biochar-filled reactor for a ditch drain. In a 10-day laboratory experiment, biochar was stirred with runoff water from a clear-cut peatland forest, and changes in water pH, total nitrogen, nitrate nitrogen, ammonium nitrogen, phosphorus, and total organic carbon concentrations were measured. Based on the concentration changes, adsorption was quantified and adsorption model containing the adsorption rate and capacity was fitted to the data. Our results indicate that biochar effectively adsorbs both inorganic and organic nitrogen from runoff water. Birch biochar had higher adsorption capacity of nitrogen than spruce biochar. This study demonstrates that the adsorption of nitrogen compounds onto biochar surfaces increases with increasing initial concentrations. Thus, aquatic ecosystems exposed to high nutrient loads from fertile peatlands would particularly benefit from biochar-based water purification.
Highlights
Clear-cutting and ditch network maintenance in drained forested peatlands markedly increase export of nutrients and suspended solids to watercourses (Joensuu et al 2002; Nieminen 2004; Kaila et al 2015; Nieminen et al 2017a)
Our analysis revealed that kad and Qmax were different for experiments done in October and November, indicating that the initial concentration affects the adsorption
Our results indicated efficient adsorption of N onto biochar surfaces
Summary
Clear-cutting and ditch network maintenance (ditch cleaning) in drained forested peatlands markedly increase export of nutrients and suspended solids to watercourses (Joensuu et al 2002; Nieminen 2004; Kaila et al 2015; Nieminen et al 2017a). Recent studies indicate that old drained peatland forests may cause a longer term and much higher nutrient load than previously understood (Nieminen et al 2017b). The characteristics of activated carbon are well studied; the adsorption efficiency is based on the exceptionally high specific surface area and porosity. Pyrolysis produces energy in the form of biogas and bio-oil, and the remaining carbon-rich solid material is called biochar. Characteristics of biochar resemble those of activated carbon; it has porous structure, large specific surface area and high cation and
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