title: The effects of feedstock pre-treatment and pyrolysis temperature on the production of biochar from the green seaweed Ulva.
abstract: Green seaweeds from the genus Ulva are a promising feedstock for the production of biochar for carbon (C) sequestration and soil amelioration. Ulva can be cultivated in waste water from land-based aquaculture and Ulva blooms ("green tides") strand millions of tons of biomass on coastal areas of Europe and China each year. The conversion of Ulva into biochar could recycle C and nutrients from eutrophic water into agricultural production. We produce biochar from Ulva ohnoi, cultivated in waste water from an aquaculture facility, and characterize its suitability for C sequestration and soil amelioration through bio-chemical analyses and plant growth experiments. Two biomass pre-treatments (fresh water rinsing to reduce salt, and pelletisation to increase density) were crossed with four pyrolysis temperatures (300-750 °C). Biomass rinsing decreased the ash and increased the C content of the resulting biochar. However, biochar produced from un-rinsed biomass had a higher proportion of fixed C and a higher yield. C sequestration decreased with increasing pyrolysis temperatures due to the combination of lower yield and lower total C content of biochar produced at high temperatures. Biochar produced from un-rinsed biomass at 300 °C had the greatest gravimetric C sequestration (110-120 g stable C kg(-1) seaweed). Biochar produced from un-pelletised Ulva enhanced plant growth three-fold in low fertility soils when the temperature of pyrolysis was less than 450 °C. The reduced effectiveness of the high-temperature biochars (>450 °C) was due to a lower N and higher salt content. Soil ameliorated with biochar produced from pelletised biomass had suppressed plant germination and growth. The most effective biochar for C sequestration and soil amelioration was produced from un-rinsed and un-pelletised Ulva at 300 °C. The green tide that occurs annually along the Shandong coastline in China generates sufficient biomass (200,000 tons dry weight) to ameliorate 12,500 ha of soil, sequester 15,000 t C and recycle 5500 t N into agriculture. We provide clear parameters for biochar production to enable the beneficial use of this biomass.
authors.affiliation: MACRO - The Centre for Macroalgal Resources and Biotechnology, College of Marine and Environmental Sciences, James Cook University, Townsville, Australia. Electronic address: david.roberts1@jcu.edu.au.
authors.forename: David A
authors.initials: DA
authors.lastname: Roberts
authors.affiliation: MACRO - The Centre for Macroalgal Resources and Biotechnology, College of Marine and Environmental Sciences, James Cook University, Townsville, Australia.
authors.forename: Rocky
authors.initials: R
authors.lastname: de Nys
mesh_terms: D000383:Agriculture / Q000379:methods; D018533:Biomass; D057965:Carbon Sequestration; D002606:Charcoal; D002681:China; D005060:Europe; D005618:Fresh Water; D012624:Seaweed / Q000737:chemistry; D012987:Soil / Q000737:chemistry; D013696:Temperature; D044445:Ulva; D062065:Wastewater
chemical_list: D002606:Charcoal; D012987:Soil; D062065:Wastewater; C540010:biochar
keywords: Aquaculture; Biochar; Carbon sequestration; Green tide; Seaweed; Soil amelioration