Characterization of fecal sludge as biomass feedstock in the southern Indian state of Tamil Nadu.

: Transformative sanitation technologies aim to treat fecal sludge (FS) by thermal processes and recover resources from it. There is a paucity of data describing the relevant properties of FS as viable feedstock for thermal treatment in major geographical target areas, such as India. : This study characterized FS collected from septic tanks in two cities located in the Indian southern state of Tamil Nadu. FS samples were obtained at the point of discharge from trucks in Tiruppur (n=85 samples) and Coimbatore (n=50 samples). Additionally, biosolids obtained from sewage treatment plants (STP) in the cities of Coimbatore and Madurai were characterized. Proximate and ultimate analysis as conducted by the fuel industry was carried out. The average higher heating value (HHV) across all FS samples in Tiruppur (13.4 MJ/kg) was much higher than the value for FS in Coimbatore (5.4 MJ/kg), which was partially attributed to the high ash content of 69% in the latter samples.  The HHV in the biosolids samples ranged between 10 and 12.2 MJ/Kg. The average total solids (TS) content for FS was 3.3% and 2.0% for Tiruppur and Coimbatore respectively, while the median TS content for the two cities was 2.3% and 1.2%. The heavy metal content of the ash was found to be below the thresholds for land disposal. This is one of the first studies that has systematically characterized fecal sludge in cities in India and determined its calorific content. We expect these data to serve as input data in the design of thermal processes for fecal sludge treatment.