Comparison of scales for faecal sludge gravimetric characterization in low-resource settings

Physical and chemical properties of faecal sludge (FS) samples must be routinely measured for FS characterization as well as for design treatment and monitoring purposes. Many of the parameters of interest for FS rely on gravimetric methods of measurement (e.g. total solids, total volatile solids, etc.). As such, they require the use of weighing scales of sufficient reliability, accuracy and precision. Laboratory-grade analytical scales can be difficult to use in remote areas because of their bulk and price point. This study aims to compare two relatively low-cost, off-the-shelf electronic scales to a laboratory-grade analytical (reference) scale. Three scales were compared using their bias, load eccentricity errors and sensitivity errors. The comparison showed that the low-cost scales exhibit a positive bias and are more prone to eccentricity errors than the reference scale. However, they perform well enough to warrant further investigation into whether they can be an acceptable alternative to laboratory scales in field or low-resource settings for faecal sludge characterization.