Biochars and hydrochars generated from organic waste streams such as forestry waste (Oak Wood), treated municipal waste, Digestate, Greenhouse waste (Paprika), Green waste and Pig manure have been characterized. In addition, model compounds; cellulose hemicellulose and lignin were also processed under identical conditions. Under standard conditions, the biochar yields ranged from 26% to 69% for biochar and 20% to 75% for hydrochar. Model compounds (lignin, cellulose and hemicellulose also had similar yields of 21% to 75%. Temperature was observed to have a great impact on biochar and hydrochar yields as they decrease with increasing temperature. Other process conditions such as time, doubling solid and additives such as acetic acid, 1%O2 and plastics also had similar impact on the yields of biochar and hydrochar. It also was observed that the biochemical components of the feedstock had no interaction, with each component decomposing separately.
The fate and levels of macro nutrients, micro nutrients and heavy metals were also determined with most metals within the quality standards of the International biochar initiative and the European biochar certificate. Waste biochars were observed to have more nutrients when compared to woody biochars. Both nutrient and metal concentrations in the biochars and hydrochars were affected by the type of feedstock, processing technique and processing temperature with the elements increasing with increase in temperature, while some of the nutrients and metals were partitioned in the aqueous phase using hydrothermal carbonization technique. Acetic and formic acids used as additives extracted more metals into the aqueous phase, but the results are comparable to the metals extracted with water.
Adsorbed organic hydrocarbons from the biochars and hydrochars were also determined. The Influence of processing conditions and feedstock composition on the nature and yields of extractable hydrocarbons, water extractable organic carbon (WEOC) and water extractable organic nitrogen is investigated. The nature of the hydrocarbons adsorbed onto the biochar and hydrochar has also been assessed using GC-MS, size exclusion chromatography and 1H NMR following exhaustive solvent extraction.
Levels of polycyclic aromatic hydrocarbons (PAH) have been determined using single ion monitoring (SIM) from the extracted tars. Additional insight into the chemical and structural nature of the tars has been investigated using 1H NMR, FTIR and size exclusion chromatography. The levels of PAH adsorbed onto biochar are dependent upon feedstock and processing conditions. The levels of PAH ranged from 1.43 µg/g to 3.37 µg/g for hydrochars at 250°C, 1.63 µg/g to 9.79 µg/g for biochars at 400°C and 2.12 µg/g to 6.50 µg/g for biochars at 600°C respectively and were dependent on biomass, pyrolysis temperature, and time. With increasing pyrolysis time and temperature, PAH concentrations generally increase. Total concentrations were below existing environmental quality standards for PAH in soils. Total PAH concentrations in the hydrochars are comparable to biochars and fall between and fall within the quality standards. The levels of non PAH extractable hydrocarbons are higher at the lower temperature processing and include oxygenated hydrocarbons and nitrogen heterocycles although size exclusion chromatography suggests the majority of these tars have a high molecular weight. Hydrochars contain higher levels of tar compared to biochars. 1H NMR indicates the tars contain higher levels of aliphatic hydrogen in methyl or methylene groups. Thermal desorption GC-MS indicates that lower molecular weight hydrocarbons are also present adsorbed on both pyrolysis and HTC chars. This is not observed following solvent extraction due to loss on evaporation. Toxicity tests of the oak and municipal solid waste chars was observed not to have a toxic effect on a pure culture of Pseudomonas aeruginosa, a common microorganism in the soil.
CORE (COnnecting REpositories)
CORE (COnnecting REpositories)