Household waste drying can bias moisture-based measurements

What the study found: Manual sorting of household waste can lead to moisture loss during exposure to indoor air, and this may bias waste characterization results. The study found that food waste lost about 2 mass-% of its initial water after 8 hours, while residual waste showed larger variability.
Why the authors say this matters: The authors conclude that these moisture losses can affect the accuracy of compositional results and can lead to overestimation of wet-basis performance indicators. The study suggests the resulting bias may be large enough to exceed uncertainty levels commonly accepted in waste characterization and related assessments.
What the researchers tested: The researchers examined food waste and residual waste, which they note contain most of the water in municipal household waste collection. Six food waste samples and six residual waste samples were repeatedly weighed over 6 to 8 hours under typical indoor sorting conditions, then oven-dried to determine total water content.
What worked and what didn't: Food waste samples lost about 2 mass-% of initial water after 8 hours. Residual waste losses were more variable, ranging from 1.6 to 5 mass-% and reaching up to 14 mass-% in some cases. The observed moisture losses corresponded to 9-13% higher estimates of lower heating values and biogas potential.
What to keep in mind: The authors note that the number of samples was limited, so the results should be treated as indicative rather than definitive. The reported losses apply to the indoor conditions described, about 20.6 °C and 55.4% relative humidity, and the authors suggest losses could be larger under warmer or more ventilated conditions.

Key points

• Manual sorting can cause waste samples to lose moisture while exposed to indoor air.
• Food waste lost about 2 mass-% of its initial water after 8 hours.
• Residual waste showed greater variation, with losses from 1.6 to 5 mass-% and up to 14 mass-% in some cases.
• The moisture losses corresponded to 9-13% higher estimates of lower heating values and biogas potential.
• The study was limited to 12 samples under about 20.6 °C and 55.4% relative humidity.