Table 3

Overview of characteristics of technologies that produce a solid fuel end product

TechnologyRequired input dryness (% ds)Output dryness (% ds)Energy input (kWh/tonne end product)Pathogens in end productRelative required land area for technologyCO2 equivalent (kg/MJ end product)a
Dried sludge (passive drying) 20b 90 NA ••• 0.00603
Dried sludge (energy required) 20b 90 79–101 (low-temperature solar drying)c 252–396 (conventional thermal drying)c •/•• NA
Conventional pelletizers with binders 70 70 36–57d • NA
Bioburn pelletizer 30–60 30–60 64e • 0.0088
LaDePa 20–30 80 507f  •• NA
Pyrolysis 70–90 100 297g  • 0.0502
HTC 20 100 392–533g  • NA
TechnologyRequired input dryness (% ds)Output dryness (% ds)Energy input (kWh/tonne end product)Pathogens in end productRelative required land area for technologyCO2 equivalent (kg/MJ end product)a
Dried sludge (passive drying) 20b 90 NA ••• 0.00603
Dried sludge (energy required) 20b 90 79–101 (low-temperature solar drying)c 252–396 (conventional thermal drying)c •/•• NA
Conventional pelletizers with binders 70 70 36–57d • NA
Bioburn pelletizer 30–60 30–60 64e • 0.0088
LaDePa 20–30 80 507f  •• NA
Pyrolysis 70–90 100 297g  • 0.0502
HTC 20 100 392–533g  • NA

The listed energy inputs are for pre-drying (from 20% ds to technology input) and the technology operation, and do not include additional energy needed for post-drying after processing. Plus signs (+) indicate the presence of pathogens in the end product. Dots indicate the amount of land area required for a technology, with (•) indicating small area and (•••) indicating large area.

aEgloff & Whett (2017).

bFor the purpose of this paper, calculations started at 20, but for these options, the starting point could be the dryness of the raw faecal sludge.

cBux et al. (2002) (based on wastewater sludge, adapted for drying from 20% ds to 90% ds).

dZhao et al. (2010) (based on wastewater sludge).

eGold (2017).

fNikiema et al. (2013).

gFakkaew et al. (2015a).

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