Materials and methods
2.1. Sludge and properties
Three types of sludge were collected for this study: municipal
sludge, dyeing sludge, and leather-tanning sludge, from three
East China cities: Hangzhou, Jiangyin and Huzhou, respectively.
The physicochemical properties of the collected sludge samples are
provided in Table 1. The municipal sludge has the highest content
in water and volatile solid, but the lowest pH and sulfur content
among all the sludge samples. The dyeing sludge has the highest
pH, but the lowest volatile solid content. The leather-tanning sludge
has the lowest water content, but the highest sulfur content.